Spinal Cord

The spinal cord is the major conduction pathway connecting the brain 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, 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 (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Like the brain, 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, 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; these layers are the dura mater, arachnoid mater, and pia mater. 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.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Development

Summary of neurulation

Neurulation is the process by which ectoderm in the trilaminar embryo develops into the neural tube. This process occurs as the cells destined to become the spinal cord progress through the following structures:

  • Neural plate: a thickening of the ectoderm along the midline
  • Neural groove: a depression forms in the center of the neural plate
  • Neural folds: 
    • Consists of cells forming the lateral walls around the neural groove
    • Some of these cells differentiate into neural crest cells, which form a number of different peripheral nervous structures, including:
      • Dorsal root ganglia
      • Sympathetic root ganglia
      • Adrenal medulla (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. General Structure of the Nervous System)
      • Enteric nerve plexuses
  • Neural tube: 
    • The lateral edges of the neural groove meet together in the midline, forming a tube.
    • This tube is pulled below the outer layer of ectoderm.
    • Neural crest cells separate and are located between the neural tube and the ectoderm.
    • Cranial portion of the neural tube: enlarges to become the brain
    • Caudal portion of the neural tube: 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 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 deficiency → neural tube defects Neural tube defects 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

Differentiation of the spinal cord

The neural tube differentiates into 3 layers. 

  • Layers:
    • Ependymal zone: 
      • Made up of neuroepithelial cells 
      • Ultimately lines the spinal canal and produces CSF
    • Mantle zone: 
      • Made up of neuroblast cells 
      • Ultimately becomes the gray matter
    • Marginal layer: 
      • Made up of neurons
      • Ultimately becomes the white matter
  • Cells move outward as they mature: ependymal → mantle → marginal zone
  • Mantle zone differentiation: some areas begin thickening → ultimately become the “horns” of the spinal cord:
    • Basal plate:
      • Forms on the anterior/ventral side of the spinal cord
      • Ultimately becomes the motor neurons of the anterior and lateral horns 
    • Alar plate: 
      • Forms on the posterior/dorsal side of the spinal cord
      • Ultimately becomes the sensory neurons of the posterior horn

Gross Anatomy

General structure

  • Cylinder of nerve tissue 
  • Located within the vertebral canal
  • Extends from the foramen magnum in the occipital 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. Structure of Bones 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: 
    • 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 running in the center of the cauda equina (extension of the pia mater)
  • Cauda equina: 
    • Bundle of nerve roots extending off the end of the conus medullaris
    • 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:
    • Ventral median fissure
    • Dorsal median sulcus
  • Enlargements: the spinal cord is enlarged in 2 regions:
    • Cervical enlargement: extends from C4 through T1
    • Lumbosacral enlargement: extends from T11 through S1
  • Spinal nerves:
    • Each nerve consists of:
      • Pair (left and right) of ventral/motor spinal nerve roots 
      • Pair (left and right) of dorsal/sensory 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 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.
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 and white matter.

Gray matter: 

  • H- or butterfly-shaped area in the center of the cord
  • Consists of the neuronal cell bodies 
  • Site of synaptic connections between neurons
  • Dorsal horns (posterior):
    • Gives rise to the dorsal roots at the dorsolateral surface of the cord
    • Consists of sensory neurons
  • Ventral horns (anterior):
    • Gives rise to the ventral roots at the ventrolateral surface of the cord
    • Consists of motor neurons:
      • Neurons that innervate proximal muscles are medial
      • Neurons that innervate distal muscles are lateral
  • Lateral horns (anterolateral):
    • Also called the intermediolateral columns
    • Found only in the thoracic and lumbar regions
    • Contains neurons 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. General Structure of the Nervous System
    • Send out axons 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:

  • Area surrounding the gray matter
  • Consists of myelinated neuronal axons 
  • Composed of bundles of axons 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

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 are the fibrous membranes that encase the spinal cord (and brain). The 3 layers and 2 defined spaces between/around the layers are (from outside to inside):

  • Dura mater:
    • 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 tissue, with some elastic fibers
    • Epidural space: 
      • The space outside the dura mater, between dura mater and periosteum 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. Structure of Bones 
      • 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
  • Arachnoid mater:
    • Delicate, avascular 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
    • Adheres to the dura mater
    • Subarachnoid space:
      • Space between the arachnoid mater and pia mater
      • Contains: CSF and a web of collagenous and elastic tissue (connecting the pia mater and arachnoid mater)
  • Pia mater:
    • 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, the pia mater 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; 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 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

Image by Lecturio.

Cervical cord segments

  • 8 segments: C1–C8
  • Cervical cord segments 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.
  • 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 (C3–C5)
    • Upper limb sensory and motor structures

Thoracic cord segments

  • 12 segments: T1–T12
  • Thoracic cord segments 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.
  • Thoracic spinal segments and nerves innervate:
    • Intercostal nerves
    • Thoracic and abdominal wall 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
  • 5 sacral segments:
    • Named S1–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
  • 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
    • Arises from the conus medullaris
  • Innervate lower limb sensory and motor structures

Spinal Tracts

Functions

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

  • Conduction of nerve signals:
    • Afferent/sensory input from the periphery → brain
    • Efferent/motor/visceral signals from the brain → periphery
  • Modulates reflexes

Overview of spinal tracts

  • Ascending tracts: 
    • Carry sensory information up the cord to the brain
    • Pathway consists of 3 types of neurons:
      • 1st-order neurons: detect the stimulus and transmit it to the spinal cord
      • 2nd-order neurons: carry the signal up the spinal cord to the brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain Stem
      • 3rd-order neurons: carry the signal to the sensory 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
  • Descending tracts: 
    • Carry motor and visceral impulses down the cord
    • Pathway consists of 2 types of neurons:
      • Upper motor neurons (UMNs): soma in the brain, synapses with the lower motor neuron
      • Lower motor neurons (LMNs): carries the signal to the muscle or target organ
  • Decussation: refers to neurons crossing over the midline (from right to left or vice versa) within the spinal cord or brain stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain 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
    • Sympathetic fibers: exit T1–L2
    • Parasympathetic fibers: exit S2–S4 
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.

Image by Lecturio.

Major ascending spinal tracts

Dorsal columns: 

  • Ascending sensory tracts in the posterior portion of the cord
  • No decussation 
  • Fibers end in the ipsilateral medulla oblongata → 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 → somatosensory cortex
  • Decussates within the medulla
  • Divided into:
    • Fasciculus gracilis (lower limbs)
    • Fasciculus cuneatus (upper limbs)
  • Transmit sensations of:
    • Proprioception (conscious)
    • Vibration 
    • Fine touch
    • Visceral pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
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 in the dorsal columns
VPL = ventral posterolateral nucleus 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

Image by Lecturio.

Spinothalamic tracts: 

  • Ascending sensory 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.
  • Transmit sensations of:
    • Pain
    • 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 in the spinothalamic tracts

Image by Lecturio.

Spinocerebellar tracts:

  • Ascending sensory 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 stem Brain Stem The brain stem is a stalk-like structure that connects the cerebrum with the spinal cord and consists of the midbrain, pons, and medulla oblongata. It also plays a critical role in the control of cardiovascular and respiratory function, consciousness, and the sleep-wake cycle. Brain 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.
  • Transmits: proprioception (unconscious)

Descending spinal tracts

Corticospinal tracts (CSTs): 

  • Descending motor 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
    • Ventral/anterior CST (10%): decussate just before exiting the spinal cord
  • Control limb (lateral CST) and axial (anterior CST) movements on the contralateral side
Pathway of the corticospinal tract

Diagram showcasing the pathway of the corticospinal tract
UMN = upper motor neuron
LMN = lower motor neuron

Image by Lecturio.

Extrapyramidal tracts:

  • Reticulospinal tract, which is involved in:
    • Controlling limb muscles related to posture and balance 
    • Pain signaling
  • Vestibulospinal tract: receives impulses to maintain balance and posture (impulses are based on input received from the inner ear)
  • Tectospinal tract: involved in reflex movements of the head

Dermatomes

  • Dermatome: the sensory 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. Structure and Function of the Skin innervated by a single spinal nerve 
    • Named according to the innervating spinal nerve (e.g., the C4 dermatome)
    • Considerable overlap between adjacent dermatomes → lesions of a single nerve root cause a decrease but not a complete loss of sensation in a given dermatome
  • Cervical dermatomes: 
    • Head (C2–C3)
    • Neck (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 (T1–T7) 
    • Abdomen (T8–T12) 
    • Back (T1–T12) 
    • T4: nipple
    • 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

Image by Lecturio.

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, 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.

  • 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 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 and travel downward.
  • Anterior spinal artery: 
    • Supplies the anterior ⅔ of the cord
    • Located just anterior to the ventral median fissure
    • 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 branch off the anterior spinal artery → enter the spinal cord through the fissure
  • 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
    • 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:
    • Arise from the aorta, 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
    • 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, providing collateral blood supply (especially to lower regions of the cord)
    • Great ventral radicular artery (Adamkiewicz artery): 
      • Most common/consistent radicular artery
      • If present, enters the spinal cord around T5–L1 (usually T9–T12)
      • Supplies the anterior spinal 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:

  • 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 
  • 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
  • Join the internal vertebral (epidural) venous plexuses in the epidural space

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 (CCS): neurologic syndrome caused by an injury to the center of the spinal cord, affecting the spinothalamic tracts (sensory) and medial aspect of the CSTs (motor). 
  • 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. Clinical manifestations are loss of motor and sensory 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, the CSTs (motor), and descending autonomic tracts to the bladder. Clinical symptoms include gait ataxia, paresthesias with loss of position and vibration 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 of the spinal cord, leading to ipsilateral loss of motor 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 Amyotrophic lateral sclerosis 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 ( 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, is a sporadic or inherited neurodegenerative disease of both UMNs and LMNs. Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis 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 is the most common progressive motor neuron disease in the United States. The diagnosis is made clinically, and management is supportive, progressing to end-of-life care. 
  • Multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis: chronic inflammatory autoimmune disease leading to demyelination of the central 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. General Structure of the Nervous System (CNS). Multiple sclerosis Multiple Sclerosis Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease that leads to demyelination of the nerves in the CNS. Young women are more predominantly affected by this most common demyelinating condition. Multiple Sclerosis 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, motor functions, sensation, and autonomic function. The diagnosis is made via MRI imaging of the entire CNS (brain and spine) as well as CSF examination. 

Neural tube defects

  • Neural tube defects (NTDs): caused by the failure of the neural tube to close properly during embryologic development, potentially resulting in protrusion of neural tissue. These defects may involve the spinal cord and/or cranium 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 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). Prenatal diagnosis by ultrasonography and maternal α-fetoprotein level is common. Management of an open NTD is mainly surgical. 
  • Specific types of NTDs related to the spinal cord:
    • Meningocele: 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 protrude
    • Meningomyelocele: 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 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 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. General Structure of the Nervous System (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 Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts: Injection of opioid medications into the epidural or subarachnoid space can provide effective anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts for childbirth and surgical procedures in the lower abdomen (e.g., cesarean section). Epidural anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts involves placement of a catheter in the epidural space, allowing for continuous infusion of medication. Spinal anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. Anesthesiology: History and Basic Concepts is a single injection of opioid into the subarachnoid space; the effects are much shorter, though anesthesia Anesthesia Anesthesiology is the field of medicine that focuses on interventions that bring a state of anesthesia upon an individual. General anesthesia is characterized by a reversible loss of consciousness along with analgesia, amnesia, and muscle relaxation. 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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