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Spinal Cord: Anatomy

The spinal cord is the major conduction pathway connecting the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification to the body; it is part of the CNS. The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions, though because the spinal cord is shorter than the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy, these regions do not line up with their corresponding vertebral levels. In cross section, the spinal cord is divided into an H-shaped area of gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome (consisting of ascending and descending tracts of myelinated Myelinated Internuclear Ophthalmoplegia axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology). Like the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification, the spinal cord is surrounded by 3 layers of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology, collectively known as the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy; these layers are the dura mater Dura mater The outermost of the three meninges, a fibrous membrane of connective tissue that covers the brain and the spinal cord. Meninges: Anatomy, arachnoid mater Arachnoid mater A delicate membrane enveloping the brain and spinal cord. It lies between the pia mater and the dura mater. It is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid. Meninges: Anatomy, and pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy. The spinal cord is supplied by 1 anterior and 2 posterior spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology.

Last updated: Jun 13, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Development

Summary of neurulation Neurulation An early embryonic developmental process of chordates that is characterized by morphogenic movements of ectoderm resulting in the formation of the neural plate; the neural crest; and the neural tube. Improper closure of the neural groove results in congenital neural tube defects. Gastrulation and Neurulation

Neurulation Neurulation An early embryonic developmental process of chordates that is characterized by morphogenic movements of ectoderm resulting in the formation of the neural plate; the neural crest; and the neural tube. Improper closure of the neural groove results in congenital neural tube defects. Gastrulation and Neurulation is the process by which ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation in the trilaminar embryo Embryo The entity of a developing mammal, generally from the cleavage of a zygote to the end of embryonic differentiation of basic structures. For the human embryo, this represents the first two months of intrauterine development preceding the stages of the fetus. Fertilization and First Week develops into the neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation. This process occurs as the cells destined to become the spinal cord progress through the following structures:

  • Neural plate Neural plate The region in the dorsal ectoderm of a chordate embryo that gives rise to the future central nervous system. Tissue in the neural plate is called the neuroectoderm, often used as a synonym of neural plate. Gastrulation and Neurulation: a thickening of the ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation along the midline
  • Neural groove Neural groove Gastrulation and Neurulation: a depression forms in the center of the neural plate Neural plate The region in the dorsal ectoderm of a chordate embryo that gives rise to the future central nervous system. Tissue in the neural plate is called the neuroectoderm, often used as a synonym of neural plate. Gastrulation and Neurulation
  • Neural folds Neural folds Gastrulation and Neurulation
    • Consists of cells forming the lateral walls around the neural groove Neural groove Gastrulation and Neurulation
    • Some of these cells differentiate into neural crest Neural crest The two longitudinal ridges along the primitive streak appearing near the end of gastrulation during development of nervous system (neurulation). The ridges are formed by folding of neural plate. Between the ridges is a neural groove which deepens as the fold become elevated. When the folds meet at midline, the groove becomes a closed tube, the neural tube. Hirschsprung Disease cells, which form a number of different peripheral nervous structures, including:
      • Dorsal root ganglia
      • Sympathetic root ganglia
      • Adrenal medulla Adrenal Medulla The inner portion of the adrenal gland. Derived from ectoderm, adrenal medulla consists mainly of chromaffin cells that produces and stores a number of neurotransmitters, mainly adrenaline (epinephrine) and norepinephrine. The activity of the adrenal medulla is regulated by the sympathetic nervous system. Adrenal Glands: Anatomy (part of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. Nervous System: Anatomy, Structure, and Classification)
      • Enteric nerve plexuses
  • Neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation
    • The lateral edges of the neural groove Neural groove Gastrulation and Neurulation meet together in the midline, forming a tube.
    • This tube is pulled below the outer layer of ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation.
    • Neural crest Neural crest The two longitudinal ridges along the primitive streak appearing near the end of gastrulation during development of nervous system (neurulation). The ridges are formed by folding of neural plate. Between the ridges is a neural groove which deepens as the fold become elevated. When the folds meet at midline, the groove becomes a closed tube, the neural tube. Hirschsprung Disease cells separate and are located between the neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation and the ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation.
    • Cranial portion of the neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation: enlarges to become the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
    • Caudal portion of the neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation: remains tubular, becomes the spinal cord
    • Development requires folate Folate Folate and vitamin B12 are 2 of the most clinically important water-soluble vitamins. Deficiencies can present with megaloblastic anemia, GI symptoms, neuropsychiatric symptoms, and adverse pregnancy complications, including neural tube defects. Folate and Vitamin B12; folate deficiency Folate deficiency A nutritional condition produced by a deficiency of folic acid in the diet. Many plant and animal tissues contain folic acid, abundant in green leafy vegetables, yeast, liver, and mushrooms but destroyed by long-term cooking. Alcohol interferes with its intermediate metabolism and absorption. Folic acid deficiency may develop in long-term anticonvulsant therapy or with use of oral contraceptives. This deficiency causes anemia, macrocytic anemia, and megaloblastic anemia. It is indistinguishable from vitamin B12 deficiency in peripheral blood and bone marrow findings, but the neurologic lesions seen in B12 deficiency do not occur. Megaloblastic Anemia neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defects

Differentiation of the spinal cord

The neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation differentiates into 3 layers. 

  • Layers:
    • Ependymal zone: 
      • Made up of neuroepithelial cells 
      • Ultimately lines the spinal canal Spinal Canal The cavity within the spinal column through which the spinal cord passes. Spinal Cord Injuries and produces CSF
    • Mantle zone: 
      • Made up of neuroblast cells 
      • Ultimately becomes the gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy
    • Marginal layer: 
      • Made up of neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology
      • Ultimately becomes the white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome
  • Cells move outward as they mature: ependymal → mantle → marginal zone Marginal zone MALT Lymphoma
  • Mantle zone differentiation: some areas begin thickening → ultimately become the “horns” of the spinal cord:

Gross Anatomy

General structure

  • Cylinder of nerve tissue 
  • Located within the vertebral canal
  • Extends from the foramen magnum in the occipital bone Occipital bone Part of the back and base of the cranium that encloses the foramen magnum. Skull: Anatomy to the level of the L1 vertebra 
  • Size (adults):
    • Length: 42–45 cm 
    • Width: approximately 1.8 cm 
  • Divided into 4 regions:
    • Cervical
    • Thoracic
    • Lumbar
    • Sacral 
  • Divided into 31 segments:
    • Cord gives rise to 31 pairs of spinal nerves that exit through the intervertebral foramina.
    • A single segment is the area supplying a pair of spinal nerves.
  • Conus medullaris Conus Medullaris Spinal Cord Injuries
    • Tapered end of the spinal cord
    • Filum terminale: thin strand of connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology running in the center of the cauda equina Cauda Equina The lower part of the spinal cord consisting of the lumbar, sacral, and coccygeal nerve roots. Spinal Cord Injuries ( extension Extension Examination of the Upper Limbs of the pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy)
  • Cauda equina Cauda Equina The lower part of the spinal cord consisting of the lumbar, sacral, and coccygeal nerve roots. Spinal Cord Injuries
    • Bundle of nerve roots extending off the end of the conus medullaris Conus Medullaris Spinal Cord Injuries
    • Innervates the pelvic organs and lower limbs
    • Named for its resemblance to a horse’s tail
  • Grooves: the spinal cord has 2 longitudinal grooves in the cord running its entire length:
  • Enlargements: the spinal cord is enlarged in 2 regions:
    • Cervical enlargement: extends from C4 through T1
    • Lumbosacral enlargement: extends from T11 through S1 S1 Heart Sounds
  • Spinal nerves:
    • Each nerve consists of:
      • Pair (left and right) of ventral/ motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology spinal nerve roots 
      • Pair (left and right) of dorsal/ sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology spinal nerve roots 
    • The ventral and dorsal roots combine with each other laterally to form a spinal nerve.
    • The spinal nerve passes through the intervertebral foramen Intervertebral Foramen Spinal Stenosis as it exits the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy.
Cross-sectional view of an individual spinal segment

Cross-sectional view of an individual spinal segment

Image by Lecturio.

Cross-sectional anatomy

When viewed in cross section, the spinal cord is divided into gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy and white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome.

Gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy: 

  • H- or butterfly-shaped area in the center of the cord
  • Consists of the neuronal cell bodies 
  • Site of synaptic connections between neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology
  • Dorsal horns (posterior):
  • Ventral horns (anterior):
    • Gives rise to the ventral roots at the ventrolateral surface of the cord
    • Consists of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology:
      • Neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology that innervate proximal muscles are medial
      • Neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology that innervate distal muscles are lateral
  • Lateral horns (anterolateral):
    • Also called the intermediolateral columns
    • Found only in the thoracic and lumbar regions
    • Contains neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology of the sympathetic nervous system Nervous system The nervous system is a small and complex system that consists of an intricate network of neural cells (or neurons) and even more glial cells (for support and insulation). It is divided according to its anatomical components as well as its functional characteristics. The brain and spinal cord are referred to as the central nervous system, and the branches of nerves from these structures are referred to as the peripheral nervous system. Nervous System: Anatomy, Structure, and Classification
    • Send out axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology via the ventral roots
  • Gray commissure:
    • Central area where the right and left halves cross over
    • Contains the central canal (collapsed in most areas in the adult)

White matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome:

  • Area surrounding the gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy
  • Consists of myelinated Myelinated Internuclear Ophthalmoplegia neuronal axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology 
  • Composed of bundles of axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology called tracts
  • Organized into: 
    • Columns (funiculi):
      • Dorsal (posterior) column
      • Lateral column
      • Ventral (anterior) column
    • Columns are subdivided into fasciculi or tracts.

Spinal meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy

The meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy are the fibrous Fibrous Fibrocystic Change membranes that encase the spinal cord (and brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification). The 3 layers and 2 defined spaces between/around the layers are (from outside to inside):

  • Dura mater Dura mater The outermost of the three meninges, a fibrous membrane of connective tissue that covers the brain and the spinal cord. Meninges: Anatomy:
    • Outermost membrane of the spinal cord
    • Forms a long tubular sheath around the spinal cord within the vertebral canal called the dural sheath
    • Composed mainly of tough fibrous Fibrous Fibrocystic Change tissue, with some elastic Elastic Connective Tissue: Histology fibers
    • Epidural space Epidural space Space between the dura mater and the walls of the vertebral canal. Epidural Hemorrhage
      • The space outside the dura mater Dura mater The outermost of the three meninges, a fibrous membrane of connective tissue that covers the brain and the spinal cord. Meninges: Anatomy, between dura mater Dura mater The outermost of the three meninges, a fibrous membrane of connective tissue that covers the brain and the spinal cord. Meninges: Anatomy and periosteum Periosteum Thin outer membrane that surrounds a bone. It contains connective tissue, capillaries, nerves, and a number of cell types. Bones: Structure and Types of the vertebral bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types 
      • Occupied by small vessels and adipose and loose connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue: Histology
  • Arachnoid mater Arachnoid mater A delicate membrane enveloping the brain and spinal cord. It lies between the pia mater and the dura mater. It is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid. Meninges: Anatomy:
    • Delicate, avascular Avascular Corneal Abrasions, Erosion, and Ulcers membrane 
    • Composed of simple squamous epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology
    • Adheres to the dura mater Dura mater The outermost of the three meninges, a fibrous membrane of connective tissue that covers the brain and the spinal cord. Meninges: Anatomy
    • Subarachnoid space Subarachnoid space The space between the arachnoid membrane and pia mater, filled with cerebrospinal fluid. It contains large blood vessels that supply the brain and spinal cord. Subarachnoid Hemorrhage:
      • Space between the arachnoid mater Arachnoid mater A delicate membrane enveloping the brain and spinal cord. It lies between the pia mater and the dura mater. It is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid. Meninges: Anatomy and pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy
      • Contains: CSF and a web of collagenous and elastic Elastic Connective Tissue: Histology tissue (connecting the pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy and arachnoid mater Arachnoid mater A delicate membrane enveloping the brain and spinal cord. It lies between the pia mater and the dura mater. It is separated from the pia mater by the subarachnoid cavity which is filled with cerebrospinal fluid. Meninges: Anatomy)
  • Pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy:
    • Innermost membrane, in direct contact with the spinal cord
    • Thin and transparent
    • Closely follows all the surface features of the spinal cord
    • Directly covers the roots of the spinal nerves and the spinal blood vessels
    • Inferior to the conus medullaris Conus Medullaris Spinal Cord Injuries, the pia mater Pia mater The innermost layer of the three meninges covering the brain and spinal cord. It is the fine vascular membrane that lies under the arachnoid and the dura mater. Meninges: Anatomy continues as the filum terminale.
Layers of the back and spinal cord

Layers of the back and spinal cord

Image by Lecturio.

Spinal Cord Segments

Overview

  • The spinal cord is divided into 31 segments, each corresponding to a pair of spinal nerves.
  • The spinal cord is shorter than the bony vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy; therefore, the spinal cord segments do not all match up with their similarly named vertebral level.
Cross sectional view of the 31 spinal segments and their relationship to the bony vertebral column

Cross-sectional view of the 31 spinal segments and their relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship to the bony vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy

Image by Lecturio.

Cervical cord segments Cervical Cord Segments The segment of the spinal cord within the cervical vertebrae. Spinal Cord Injuries

  • 8 segments: C1–C8
  • Cervical cord segments Cervical Cord Segments The segment of the spinal cord within the cervical vertebrae. Spinal Cord Injuries C1–C7 give rise to nerve roots that exit above their corresponding vertebrae.
  • C8 nerve root emerges between C7 and T1.
  • C1–C8 cord segments lie within the C1–C7 region of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy.
  • Cervical spinal segments and nerves innervate:
    • Diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm: Anatomy (C3–C5)
    • Upper limb sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology and motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology structures

Thoracic cord segments Thoracic Cord Segments Spinal Cord Injuries

  • 12 segments: T1–T12
  • Thoracic cord segments Thoracic Cord Segments Spinal Cord Injuries give rise to nerve roots that exit below their corresponding vertebrae.
  • T1–T12 cord segments lie within the T1–T8 region of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy.
  • Thoracic spinal segments and nerves innervate:
    • Intercostal nerves
    • Thoracic and abdominal wall Abdominal wall The outer margins of the abdomen, extending from the osteocartilaginous thoracic cage to the pelvis. Though its major part is muscular, the abdominal wall consists of at least seven layers: the skin, subcutaneous fat, deep fascia; abdominal muscles, transversalis fascia, extraperitoneal fat, and the parietal peritoneum. Surgical Anatomy of the Abdomen muscles and dermatomes
    • Sympathetic innervation of the thoracic, abdominal, and pelvic viscera

Lumbar, sacral, and coccygeal cord segments

  • 5 lumbar segments:
    • Named L1–L5
    • Lie within the T9–T11 region of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
  • 5 sacral segments:
    • Named S1 S1 Heart Sounds–S5
    • Lie within the T12–L1 region of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
  • 1 coccygeal segment:
    • Named C0
    • Lies within the L1 region of the vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy
    • Arises from the conus medullaris Conus Medullaris Spinal Cord Injuries
  • Innervate lower limb sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology and motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology structures

Spinal Tracts

Functions

In general, the major functions of the spinal cord include:

  • Conduction of nerve signals:
    • Afferent Afferent Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology/ sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology input from the periphery → brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
    • Efferent Efferent Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology/ motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology/visceral signals from the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification → periphery
  • Modulates reflexes

Overview of spinal tracts

  • Ascending tracts: 
    • Carry sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology information up the cord to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification
    • Pathway consists of 3 types of neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology:
      • 1st-order neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology: detect the stimulus and transmit it to the spinal cord
      • 2nd-order neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology: carry the signal up the spinal cord to the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification stem
      • 3rd-order neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology: carry the signal to the sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology region of the cerebral cortex Cerebral cortex The cerebral cortex is the largest and most developed part of the human brain and CNS. Occupying the upper part of the cranial cavity, the cerebral cortex has 4 lobes and is divided into 2 hemispheres that are joined centrally by the corpus callosum. Cerebral Cortex: Anatomy
  • Descending tracts: 
    • Carry motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology and visceral impulses down the cord
    • Pathway consists of 2 types of neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology:
      • Upper motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology (UMNs): soma in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification, synapses with the lower motor neuron Lower Motor Neuron Motor Neuron Lesions
      • Lower motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology (LMNs): carries the signal to the muscle or target organ
  • Decussation: refers to neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology crossing over Crossing over The reciprocal exchange of segments at corresponding positions along pairs of homologous chromosomes by symmetrical breakage and crosswise rejoining forming cross-over sites (holliday junctions) that are resolved during chromosome segregation. Crossing-over typically occurs during meiosis but it may also occur in the absence of meiosis, for example, with bacterial chromosomes, organelle chromosomes, or somatic cell nuclear chromosomes. Basic Terms of Genetics the midline (from right to left or vice versa) within the spinal cord or brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification stem
  • Naming conventions: 
    • Tracts are named by combining 2 locations: origin (1st) → termination (2nd)
    • For example, the corticospinal tract originates in the cortex and travels down through the spinal cord.
  • Autonomic fibers: 
    • Located in the lateral aspect of the spinal cord
    • Do not exist in well-defined tracts
    • Synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission with cell bodies in the intermediolateral columns of gray matter Gray matter Region of central nervous system that appears darker in color than the other type, white matter. It is composed of neuronal cell bodies; neuropil; glial cells and capillaries but few myelinated nerve fibers. Cerebral Cortex: Anatomy
    • Sympathetic fibers: exit T1–L2
    • Parasympathetic fibers: exit S2 S2 Heart Sounds S4 S4 Heart Sounds 
Major ascending and descending tracts of the spinal cord

Major ascending (blue) and descending (red) tracts of the spinal cord:
The letters C, T, L, and S denote where the fibers associated with each region are located.

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Major ascending spinal tracts

Dorsal columns Dorsal Columns Posterior Cord Syndrome: 

  • Ascending sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology tracts in the posterior portion of the cord
  • No decussation 
  • Fibers end in the ipsilateral medulla oblongata Medulla Oblongata The lower portion of the brain stem. It is inferior to the pons and anterior to the cerebellum. Medulla oblongata serves as a relay station between the brain and the spinal cord, and contains centers for regulating respiratory, vasomotor, cardiac, and reflex activities. Brain Stem: Anatomy thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy somatosensory cortex Somatosensory cortex Area of the parietal lobe concerned with receiving sensations such as movement, pain, pressure, position, temperature, touch, and vibration. It lies posterior to the central sulcus. Cerebral Cortex: Anatomy
  • Decussates within the medulla
  • Divided into:
  • Transmit sensations of:
    • Proprioception Proprioception Sensory functions that transduce stimuli received by proprioceptive receptors in joints, tendons, muscles, and the inner ear into neural impulses to be transmitted to the central nervous system. Proprioception provides sense of stationary positions and movements of one’s body parts, and is important in maintaining kinesthesia and postural balance. Neurological Examination (conscious)
    • Vibration Vibration A continuing periodic change in displacement with respect to a fixed reference. Neurological Examination 
    • Fine touch
    • Visceral pain Visceral pain Pain originating from internal organs (viscera) associated with autonomic phenomena (pallor; sweating; nausea; and vomiting). It often becomes a referred pain. Pain: Types and Pathways
Locations of the 1st-, 2nd-, and 3rd-order sensory neurons in the dorsal columns

Diagram depicting the locations of the 1st-, 2nd-, and 3rd-order sensory neurons Sensory neurons Neurons which conduct nerve impulses to the central nervous system. Autonomic Nervous System: Anatomy in the dorsal columns Dorsal Columns Posterior Cord Syndrome
VPL = ventral posterolateral nucleus Nucleus Within a eukaryotic cell, a membrane-limited body which contains chromosomes and one or more nucleoli (cell nucleolus). The nuclear membrane consists of a double unit-type membrane which is perforated by a number of pores; the outermost membrane is continuous with the endoplasmic reticulum. A cell may contain more than one nucleus. The Cell: Organelles of the thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy

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Spinothalamic tracts Spinothalamic tracts A bundle of nerve fibers connecting each posterior horn of the spinal cord to the opposite side of the thalamus, carrying information about pain, temperature, and touch. It is one of two major routes by which afferent spinal nerve fibers carrying sensations of somaesthesia are transmitted to the thalamus. Central Cord Syndrome: 

  • Ascending sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology tracts in the anterolateral portion of the cord
  • Decussate upon entering the spinal cord 
  • Fibers end in the contralateral thalamus Thalamus The thalamus is a large, ovoid structure in the dorsal part of the diencephalon that is located between the cerebral cortex and midbrain. It consists of several interconnected nuclei of grey matter separated by the laminae of white matter. The thalamus is the main conductor of information that passes between the cerebral cortex and the periphery, spinal cord, or brain stem. Thalamus: Anatomy.
  • Transmit sensations of:
    • Pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways
    • Temperature
    • Gross touch
    • Pressure
    • Itch and tickle
Locations of the 1st-, 2nd-, and 3rd-order sensory neurons in the spinothalamic tracts

Diagram depicting the locations of the 1st-, 2nd-, and 3rd-order sensory neurons Sensory neurons Neurons which conduct nerve impulses to the central nervous system. Autonomic Nervous System: Anatomy in the spinothalamic tracts Spinothalamic tracts A bundle of nerve fibers connecting each posterior horn of the spinal cord to the opposite side of the thalamus, carrying information about pain, temperature, and touch. It is one of two major routes by which afferent spinal nerve fibers carrying sensations of somaesthesia are transmitted to the thalamus. Central Cord Syndrome

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Spinocerebellar tracts:

  • Ascending sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology tracts in the lateral portion of the cord
  • Have dorsal and ventral components
  • Decussation:
    • Dorsal fibers: no decussation
    • Ventral fibers: decussate upon entering the spinal cord; decussate again in the brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification stem
  • All fibers end in the ipsilateral cerebellum Cerebellum The cerebellum, Latin for “little brain,” is located in the posterior cranial fossa, dorsal to the pons and midbrain, and its principal role is in the coordination of movements. The cerebellum consists of 3 lobes on either side of its 2 hemispheres and is connected in the middle by the vermis. Cerebellum: Anatomy.
  • Transmits: proprioception Proprioception Sensory functions that transduce stimuli received by proprioceptive receptors in joints, tendons, muscles, and the inner ear into neural impulses to be transmitted to the central nervous system. Proprioception provides sense of stationary positions and movements of one’s body parts, and is important in maintaining kinesthesia and postural balance. Neurological Examination ( unconscious Unconscious Those forces and content of the mind which are not ordinarily available to conscious awareness or to immediate recall. Psychotherapy)

Descending spinal tracts

Corticospinal tracts Corticospinal Tracts Central Cord Syndrome ( CSTs CSTs Central Cord Syndrome): 

  • Descending motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology tracts in the anteromedial portion of spinal cord
  • Previously called “pyramidal tracts”
  • Have lateral and ventral/anterior components
  • Decussation:
    • Lateral CST (90%): decussate in the medulla oblongata Medulla Oblongata The lower portion of the brain stem. It is inferior to the pons and anterior to the cerebellum. Medulla oblongata serves as a relay station between the brain and the spinal cord, and contains centers for regulating respiratory, vasomotor, cardiac, and reflex activities. Brain Stem: Anatomy
    • Ventral/anterior CST (10%): decussate just before exiting the spinal cord
  • Control limb (lateral CST) and axial Axial Computed Tomography (CT) (anterior CST) movements on the contralateral side
Pathway of the corticospinal tract

Diagram showcasing the pathway of the corticospinal tract
UMN = upper motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology neuron
LMN = lower motor neuron Lower Motor Neuron Motor Neuron Lesions

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Extrapyramidal tracts:

  • Reticulospinal tract, which is involved in:
    • Controlling limb muscles related to posture and balance 
    • Pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways signaling
  • Vestibulospinal tract: receives impulses to maintain balance and posture (impulses are based on input received from the inner ear Inner ear The essential part of the hearing organ consists of two labyrinthine compartments: the bony labyrinthine and the membranous labyrinth. Ear: Anatomy)
  • Tectospinal tract: involved in reflex movements of the head

Dermatomes

  • Dermatome Dermatome Spinal Disk Herniation: the sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology region of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions innervated by a single spinal nerve 
  • Cervical dermatomes: 
    • Head (C2–C3)
    • Neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess (C3–C4) 
    • Upper extremities (C5–C8) 
  • Thoracic dermatomes:
    • Inner arms (T1)
    • Chest wall Chest wall The chest wall consists of skin, fat, muscles, bones, and cartilage. The bony structure of the chest wall is composed of the ribs, sternum, and thoracic vertebrae. The chest wall serves as armor for the vital intrathoracic organs and provides the stability necessary for the movement of the shoulders and arms. Chest Wall: Anatomy (T1–T7) 
    • Abdomen (T8–T12) 
    • Back (T1–T12) 
    • T4 T4 The major hormone derived from the thyroid gland. Thyroxine is synthesized via the iodination of tyrosines (monoiodotyrosine) and the coupling of iodotyrosines (diiodotyrosine) in the thyroglobulin. Thyroxine is released from thyroglobulin by proteolysis and secreted into the blood. Thyroxine is peripherally deiodinated to form triiodothyronine which exerts a broad spectrum of stimulatory effects on cell metabolism. Thyroid Hormones: nipple Nipple The conic organs which usually give outlet to milk from the mammary glands. Examination of the Breast
    • T7: xiphoid
    • T10: umbilicus
  • Lumbar dermatomes:
    • Anterior and medial lower extremities
    • L1: hips
    • L4: knees
  • Sacral dermatomes:
    • Genitalia and anal region 
    • Posterior and lateral lower extremities
Dermatomes

Dermatomes

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Vasculature

Arterial blood supply

The spinal cord is supplied by 3 longitudinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology, including 1 anterior and 2 posterior spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology.

  • The spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology arise from the vertebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology and travel downward.
  • Anterior spinal artery Anterior Spinal Artery Anterior Cord Syndrome
    • Supplies the anterior ⅔ of the cord
    • Located just anterior to the ventral median fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes
    • Sulcal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology branch off the anterior spinal artery Anterior Spinal Artery Anterior Cord Syndrome → enter the spinal cord through the fissure Fissure A crack or split that extends into the dermis Generalized and Localized Rashes
  • Posterior spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
    • Paired vessels (right and left) are located around 11:00 and 1:00 when viewing the spinal cord in cross section with the posterior aspect at the top.
    • Each supplies ½ of the posterior ⅓ of the cord.
  • Segmental medullary and radicular arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology:
    • Arise from the aorta Aorta The main trunk of the systemic arteries. Mediastinum and Great Vessels: Anatomy, cervical, deep cervical, vertebral, intercostal, and lumbar arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
    • Run along the nerve roots
    • Join with the anterior and posterior spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology, providing collateral blood supply (especially to lower regions of the cord)
    • Great ventral radicular artery (Adamkiewicz artery): 

Venous drainage

The spinal cord is drained via spinal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology:

  • 3 anterior and 3 posterior spinal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology 
  • Run longitudinally along the cord
  • Have multiple communications between one another
  • Similar distribution to the spinal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries: Histology
  • Join the internal vertebral (epidural) venous plexuses in the epidural space Epidural space Space between the dura mater and the walls of the vertebral canal. Epidural Hemorrhage

Clinical Relevance

Spinal cord syndromes

  • Central cord syndrome Central Cord Syndrome Central cord syndrome (CCS) is a neurological syndrome caused by an injury to the center of the spinal cord, affecting the spinothalamic tracts ((STTs) sensory) and medial aspect of the corticospinal tracts ((CSTs) motor), most often due to trauma in patients with cervical spondylosis. Central Cord Syndrome: neurologic syndrome caused by an injury to the center of the spinal cord, affecting the spinothalamic tracts Spinothalamic tracts A bundle of nerve fibers connecting each posterior horn of the spinal cord to the opposite side of the thalamus, carrying information about pain, temperature, and touch. It is one of two major routes by which afferent spinal nerve fibers carrying sensations of somaesthesia are transmitted to the thalamus. Central Cord Syndrome ( sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology) and medial aspect of the CSTs CSTs Central Cord Syndrome ( motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology). 
  • Anterior cord syndrome Anterior cord syndrome Anterior cord syndrome (ACS) is an incomplete cord syndrome predominantly affecting the anterior (ventral) …” of the spinal cord while sparing the dorsal columns. Anterior cord syndrome can be caused by occlusion of the anterior spinal artery or by trauma, which results in disc herniation and bone fragments disrupting the spinal cord. Anterior Cord Syndrome: incomplete cord syndrome resulting from injury to the anterior (ventral) ⅔ of the spinal cord and sparing the dorsal columns Dorsal Columns Posterior Cord Syndrome. Clinical manifestations are loss of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology and sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology function below the level of injury. 
  • Posterior cord syndrome Posterior cord syndrome Posterior cord syndrome (PCS) is an incomplete spinal cord syndrome affecting the dorsal columns, the corticospinal tracts (CSTs), and descending autonomic tracts to the bladder. Posterior cord syndrome is rare but has a diverse range of etiologies, including demyelinating disorders, degenerative spinal conditions, neoplastic causes, vascular abnormalities, and hereditary neurodegenerative disorders. Posterior Cord Syndrome: incomplete spinal cord syndrome affecting the dorsal columns Dorsal Columns Posterior Cord Syndrome, the CSTs CSTs Central Cord Syndrome ( motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology), and descending autonomic tracts to the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess. Clinical symptoms include gait Gait Manner or style of walking. Neurological Examination ataxia Ataxia Impairment of the ability to perform smoothly coordinated voluntary movements. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Ataxia may result from impaired sensory or motor function. Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases; cerebral cortex diseases; thalamic diseases; basal ganglia diseases; injury to the red nucleus; and other conditions. Ataxia-telangiectasia, paresthesias Paresthesias Subjective cutaneous sensations (e.g., cold, warmth, tingling, pressure, etc.) that are experienced spontaneously in the absence of stimulation. Posterior Cord Syndrome with loss of position and vibration Vibration A continuing periodic change in displacement with respect to a fixed reference. Neurological Examination sense, and urinary incontinence Urinary incontinence Urinary incontinence (UI) is involuntary loss of bladder control or unintentional voiding, which represents a hygienic or social problem to the patient. Urinary incontinence is a symptom, a sign, and a disorder. The 5 types of UI include stress, urge, mixed, overflow, and functional. Urinary Incontinence.
  • Brown-Séquard syndrome Brown-Séquard syndrome Brown-Séquard syndrome (BSS) is a rare neurologic injury that causes hemisection of the spinal cord, resulting in weakness and paralysis of one side of the body and sensory loss on the opposite side. Brown-Séquard Syndrome: rare neurologic injury that results in hemisection Hemisection Brown-Séquard Syndrome of the spinal cord, leading to ipsilateral loss of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology function and dorsal column sensations, and contralateral loss of spinothalamic sensations 1–2 levels below the level of cord damage.

Degenerative conditions

  • Amyotrophic lateral sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor ( ALS ALS Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). ALS is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of Caucasian ethnicity. Amyotrophic Lateral Sclerosis): also known as Lou Gehrig’s disease Lou Gehrig’s disease Amyotrophic lateral sclerosis (ALSs), also known as Lou Gehrig’s disease, is a sporadic or inherited neurodegenerative disease of upper motor neurons (UMNs) and lower motor neurons (LMNs). Als is the most common progressive motor neuron disease in North America, primarily affecting men and individuals of caucasian ethnicity. Amyotrophic Lateral Sclerosis, is a sporadic Sporadic Selective IgA Deficiency or inherited neurodegenerative disease of both UMNs and LMNs. Amyotrophic lateral sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor is the most common progressive motor neuron disease Motor neuron disease Diseases characterized by a selective degeneration of the motor neurons of the spinal cord, brainstem, or motor cortex. Clinical subtypes are distinguished by the major site of degeneration. In amyotrophic lateral sclerosis there is involvement of upper, lower, and brainstem motor neurons. In progressive muscular atrophy and related syndromes the motor neurons in the spinal cord are primarily affected. With progressive bulbar palsy, the initial degeneration occurs in the brainstem. In primary lateral sclerosis, the cortical neurons are affected in isolation. Amyotrophic Lateral Sclerosis in the United States. The diagnosis is made clinically, and management is supportive, progressing to end-of-life care. 
  • Multiple sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor: chronic inflammatory autoimmune disease leading to demyelination Demyelination Multiple Sclerosis of the central nervous system Central nervous system The main information-processing organs of the nervous system, consisting of the brain, spinal cord, and meninges. Nervous System: Anatomy, Structure, and Classification (CNS). Multiple sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor is the most common demyelinating condition, with young women affected more predominantly. The clinical presentation varies widely depending on the site of lesions but typically involves neurologic symptoms affecting vision Vision Ophthalmic Exam, motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology functions, sensation, and autonomic function. The diagnosis is made via MRI imaging of the entire CNS ( brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification and spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy) as well as CSF examination. 

Neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defects

  • Neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation defects ( NTDs NTDs Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed ntd) to very severe malformations of the spine or brain (open ntd). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects): caused by the failure of the neural tube Neural tube A tube of ectodermal tissue in an embryo that will give rise to the central nervous system, including the spinal cord and the brain. Lumen within the neural tube is called neural canal which gives rise to the central canal of the spinal cord and the ventricles of the brain. Gastrulation and Neurulation to close properly during embryologic development, potentially resulting in protrusion of neural tissue. These defects may involve the spinal cord and/or cranium Cranium The skull (cranium) is the skeletal structure of the head supporting the face and forming a protective cavity for the brain. The skull consists of 22 bones divided into the viscerocranium (facial skeleton) and the neurocranium. Skull: Anatomy and may be open (involving the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy and/or neural tissue) or closed (involving the bony vertebral column Vertebral column The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy). Prenatal diagnosis by ultrasonography and maternal α-fetoprotein level is common. Management of an open NTD is mainly surgical. 
  • Specific types of NTDs NTDs Neural tube defects (NTDs) are the 2nd-most common type of congenital birth defects. Neural tube defects can range from asymptomatic (closed ntd) to very severe malformations of the spine or brain (open ntd). Neural tube defects are caused by the failure of the neural tube to close properly during the 3rd and 4th week of embryological development. Neural Tube Defects related to the spinal cord:
    • Meningocele Meningocele A congenital or acquired protrusion of the meninges, unaccompanied by neural tissue, through a bony defect in the skull or vertebral column. Neural Tube Defects: only the meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy protrude
    • Meningomyelocele Meningomyelocele Congenital, or rarely acquired, herniation of meningeal and spinal cord tissue through a bony defect in the vertebral column. The majority of these defects occur in the lumbosacral region. Clinical features include paraplegia, loss of sensation in the lower body, and incontinence. This condition may be associated with the arnold-chiari malformation and hydrocephalus. Neural Tube Defects: both meninges Meninges The brain and the spinal cord are enveloped by 3 overlapping layers of connective tissue called the meninges. The layers are, from the most external layer to the most internal layer, the dura mater, arachnoid mater, and pia mater. Between these layers are 3 potential spaces called the epidural, subdural, and subarachnoid spaces. Meninges: Anatomy and spinal cord protrude (most common NTD)

Procedures

  • Lumbar spinal puncture: withdrawal of CSF from the lumbar cistern, below the level of the spinal cord. Lumbar spinal puncture is an important diagnostic tool for evaluating a variety of central nervous system Central nervous system The main information-processing organs of the nervous system, consisting of the brain, spinal cord, and meninges. Nervous System: Anatomy, Structure, and Classification (CNS) disorders. Many diseases of the CNS may alter the cells in the CSF or change the concentration of its chemical constituents, aiding diagnosis.
  • Epidural and spinal anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts: Injection of opioid Opioid Compounds with activity like opiate alkaloids, acting at opioid receptors. Properties include induction of analgesia or narcosis. Constipation medications into the epidural or subarachnoid space Subarachnoid space The space between the arachnoid membrane and pia mater, filled with cerebrospinal fluid. It contains large blood vessels that supply the brain and spinal cord. Subarachnoid Hemorrhage can provide effective anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts for childbirth and surgical procedures in the lower abdomen (e.g., cesarean section). Epidural anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts involves placement of a catheter in the epidural space Epidural space Space between the dura mater and the walls of the vertebral canal. Epidural Hemorrhage, allowing for continuous infusion of medication. Spinal anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts is a single injection of opioid Opioid Compounds with activity like opiate alkaloids, acting at opioid receptors. Properties include induction of analgesia or narcosis. Constipation into the subarachnoid space Subarachnoid space The space between the arachnoid membrane and pia mater, filled with cerebrospinal fluid. It contains large blood vessels that supply the brain and spinal cord. Subarachnoid Hemorrhage; the effects are much shorter, though anesthesia Anesthesia A state characterized by loss of feeling or sensation. This depression of nerve function is usually the result of pharmacologic action and is induced to allow performance of surgery or other painful procedures. Anesthesiology: History and Basic Concepts is superior to that achieved via an epidural catheter. 

References

  1. Blumenfeld, H. (2010). Neuroanatomy through clinical cases, 2nd ed. Chapter 8 of Spinal Nerve Roots, Sinauer Associates, pp. 320–327.
  2. Drake, R. L., Vogl, W. A., Mitchell, A. W. M. (2020). Gray’s anatomy for students, 4th ed., Chapter 9, Part V of Spinal cord. Elsevier, pp. e34–e48.
  3. Moore, K. L., Dalley, A. F., Agur, A. M. R. (2014). Clinically Oriented Anatomy, 7th ed. Chapter 4 of Back, Lippincott Williams & Wilkins, pp. 496–505.
  4. Lee, J., Muzio, M. R. (2020). Neuroanatomy, extrapyramidal system. StatPearls. Retrieved October 26, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK554542/
  5. Khan, Y. (2021). Neuroanatomy, spinal Cord. StatPearls. Retrieved October 26, 2021, from https://www.statpearls.com/ArticleLibrary/viewarticle/29308#
  6. Eisen, A. (2020). Anatomy and localization of spinal cord disorders. UpToDate. Retrieved October 26, 2021, from https://www.uptodate.com/contents/anatomy-and-localization-of-spinal-cord-disorders 

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