Development of the Nervous System and Face

Neurulation and Neural Crest Migration

The development of 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 is a specific part of gastrulation Gastrulation Both gastrulation and neurulation are critical events that occur during the 3rd week of embryonic development. Gastrulation is the process by which the bilaminar disc differentiates into a trilaminar disc, made up of the 3 primary germ layers: the ectoderm, mesoderm, and endoderm. Gastrulation and Neurulation, called 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, that creates the cells of the 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.

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

Day 16 after fertilization Fertilization To undergo fertilization, the sperm enters the uterus, travels towards the ampulla of the fallopian tube, and encounters the oocyte. The zona pellucida (the outer layer of the oocyte) deteriorates along with the zygote, which travels towards the uterus and eventually forms a blastocyst, allowing for implantation to occur. Fertilization and First Week → embryonal cells belong to 1 of 3 germ cell layers:

• Ectoderm Ectoderm The outer of the three germ layers of an embryo. Gastrulation and Neurulation:
  • Differentiates into the neuroectoderm, creating 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
  • Cell replication in 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 gives rise to 2 ridges (neural crests).
  • The depression between the crests is known as the neural fold.
• Mesoderm Mesoderm The middle germ layer of an embryo derived from three paired mesenchymal aggregates along the neural tube. Gastrulation and Neurulation:
  • Differentiates and transforms in a tube structure called the notochord Notochord A cartilaginous rod of mesodermal cells at the dorsal midline of all chordate embryos. In lower vertebrates, notochord is the backbone of support. In the higher vertebrates, notochord is a transient structure, and segments of the vertebral column will develop around it. Notochord is also a source of midline signals that pattern surrounding tissues including the neural tube development. Gastrulation and Neurulation.
  • The notochord Notochord A cartilaginous rod of mesodermal cells at the dorsal midline of all chordate embryos. In lower vertebrates, notochord is the backbone of support. In the higher vertebrates, notochord is a transient structure, and segments of the vertebral column will develop around it. Notochord is also a source of midline signals that pattern surrounding tissues including the neural tube development. Gastrulation and Neurulation signals the neural fold to enlarge on either side of the neural groove Neural groove Gastrulation and Neurulation, creating 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.
• Endoderm Endoderm The inner of the three germ layers of an embryo. Gastrulation and Neurulation: will give rise to the lining of the GI and respiratory systems

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 cell migration

Neuroectoderm cells migrate in waves from the neural crests to create peripheral 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 structures:

• The 1st wave of migration creates:
  • Sympathetic ganglia
  • Parasympathetic ganglia
  • Chromaffin cells Chromaffin cells Cells that store epinephrine secretory vesicles. During times of stress, the nervous system signals the vesicles to secrete their hormonal content. Their name derives from their ability to stain a brownish color with chromic salts. Characteristically, they are located in the adrenal medulla and paraganglia of the sympathetic nervous system. Adrenal Hormones (sympathetic ganglia migrated into the 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)
• The 2nd wave of migration creates:
  • Posterior root ganglia
  • Schwann cells
  • Satellite cells Satellite Cells The non-neuronal cells that surround the neuronal cell bodies of the ganglia. They are distinguished from the perineuronal satellite oligodendrocytes (oligodendroglia) found in the central nervous system. Nervous System: Histology
• The 3rd wave of migration creates:
  • Melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions
• Neural crest cells Neural crest cells Gastrulation and Neurulation in the head and neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess also form different structures:
  • Make up secondary ganglia of cranial nerves Cranial nerves There are 12 pairs of cranial nerves (CNs), which run from the brain to various parts of the head, neck, and trunk. The CNs can be sensory or motor or both. The CNs are named and numbered in Roman numerals according to their location, from the front to the back of the brain. The 12 Cranial Nerves: Overview and Functions 5, 7, 9, and 10
  • Migrate into the pharyngeal arches Pharyngeal arches The branchial arches, also known as pharyngeal or visceral arches, are embryonic structures seen in the development of vertebrates that serve as precursors for many structures of the face, neck, and head. These arches are composed of a central core of mesoderm, which is covered externally by ectoderm and internally by endoderm. Branchial Apparatus and Aortic Arches of the head, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, and face to create mesenchyme, which contributes to 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 and 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

Mnemonics

• To quickly recall that each Schwann cell Schwann Cell Neuroglial cells of the peripheral nervous system which form the insulating myelin sheaths of peripheral axons. Nervous System: Histology myelinates only 1 axon of the peripheral nervous system Peripheral nervous system The nervous system outside of the brain and spinal cord. The peripheral nervous system has autonomic and somatic divisions. The autonomic nervous system includes the enteric, parasympathetic, and sympathetic subdivisions. The somatic nervous system includes the cranial and spinal nerves and their ganglia and the peripheral sensory receptors. Nervous System: Anatomy, Structure, and Classification, remember: “Schwone” = 1 axon.
• To quickly recall where oligodendrocyte Oligodendrocyte A class of large neuroglial (macroglial) cells in the central nervous system. Oligodendroglia may be called interfascicular, perivascular, or perineuronal (not the same as satellite cells, perineuronal of ganglia) according to their location. They form the insulating myelin sheath of axons in the central nervous system. Nervous System: Histology and Schwann cells are located, remember: COPS: CNS = Oligodendrocyte; PNS = Schwann cells.

Neural Tube

Primary vesicles Vesicles Female Genitourinary Examination

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 develops 3 bulges (primary 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 vesicles Vesicles Female Genitourinary Examination) at the cranial end:

1. Prosencephalon (forebrain) splits, giving rise to:
   • The telencephalon, which becomes 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. This portion of the neural canal becomes the lateral ventricles and 3rd ventricle.
   • The diencephalon, which becomes 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, hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus, and pineal gland Pineal gland A light-sensitive neuroendocrine organ attached to the roof of the third ventricle of the brain. The pineal gland secretes melatonin, other biogenic amines and neuropeptides. Hormones: Overview and Types
2. Mesencephalon ( midbrain Midbrain The middle of the three primitive cerebral vesicles of the embryonic brain. Without further subdivision, midbrain develops into a short, constricted portion connecting the pons and the diencephalon. Midbrain contains two major parts, the dorsal tectum mesencephali and the ventral tegmentum mesencephali, housing components of auditory, visual, and other sensorimotor systems. Brain Stem: Anatomy): also contains the cerebral aqueduct Cerebral aqueduct Narrow channel in the mesencephalon that connects the third and fourth cerebral ventricles. Ventricular System: Anatomy
3. Rhombencephalon (hindbrain) splits to become:
   • The metencephalon, which becomes the pons Pons The front part of the hindbrain (rhombencephalon) that lies between the medulla and the midbrain (mesencephalon) ventral to the cerebellum. It is composed of two parts, the dorsal and the ventral. The pons serves as a relay station for neural pathways between the cerebellum to the cerebrum. Brain Stem: Anatomy and 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
   • The myelencephalon, which becomes 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
   • The remnant of the neural canal present around the metencephalon and myelencephalon, which becomes the 4th ventricle

Cerebrospinal fluid Cerebrospinal Fluid A watery fluid that is continuously produced in the choroid plexus and circulates around the surface of the brain; spinal cord; and in the cerebral ventricles. Ventricular System: Anatomy (CSF) circulatory system

• Ependymal cells Ependymal Cells The macroglial cells of ependyma. They are characterized by bipolar cell body shape and processes that contact basal lamina around blood vessels and/or the pia mater and the cerebral ventricles. Muller cells of the retina are included based on similar microenvironmental contacts and morphology. Nervous System: Histology:
  • Line the central canal and the core 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
  • In lateral, 3rd, and 4th ventricles, ependymal cells Ependymal Cells The macroglial cells of ependyma. They are characterized by bipolar cell body shape and processes that contact basal lamina around blood vessels and/or the pia mater and the cerebral ventricles. Muller cells of the retina are included based on similar microenvironmental contacts and morphology. Nervous System: Histology become the choroid plexus Choroid plexus A villous structure of tangled masses of blood vessels contained within the third, lateral, and fourth ventricles of the brain. It regulates part of the production and composition of cerebrospinal fluid. Ventricular System: Anatomy.
• Choroid plexus Choroid plexus A villous structure of tangled masses of blood vessels contained within the third, lateral, and fourth ventricles of the brain. It regulates part of the production and composition of cerebrospinal fluid. Ventricular System: Anatomy: filters blood and releases CSF into the ventricular system Ventricular System The ventricular system is an extension of the subarachnoid space into the brain consisting of a series of interconnecting spaces and channels. Four chambers are filled with cerebrospinal fluid (CSF): the paired lateral ventricles, the unpaired 3rd ventricle, and the unpaired 4th ventricle. Ventricular System: Anatomy

Flexion Flexion Examination of the Upper Limbs 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

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 develops a series of bends in the sagittal Sagittal Computed Tomography (CT) plane:

• At 3-vesicle stage:
  • Cervical flexure: between spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy and rhombencephalon
  • Cephalic flexure: between prosencephalon and mesencephalon
• As 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 develops further: pontine flexure (between myelencephalon and metencephalon)

Development of the Spinal Cord and Brainstem

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 the cephalic 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 becomes 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 rest becomes the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy.

• Proliferation of neuroepithelial cells
  • As they push outward, intermediate and marginal zones are created.
  • Marginal zone Marginal zone MALT Lymphoma: comes in contact with sclerotomal mesenchyme that will form 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
  • Intermediate and marginal zones fill the space inside the neural canal.
  • The cells in the marginal and intermediate zones will differentiate into 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. 
• The neuroepithelial tissue of the 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 has a regional specialization:
  • Alar plate ( sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology):
    • Axons Axons Nerve fibers that are capable of rapidly conducting impulses away from the neuron cell body. Nervous System: Histology extend 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.
    • 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 in dorsal root ganglia (originally from neural crest cells Neural crest cells Gastrulation and Neurulation) extend to the 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 and back to the Alar plate.
  • Basal plate ( 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 innervate  myotome Myotome Development of the Limbs.
  • Sulcus limitans: separates alar plate from the basal plate
• Top and bottom 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 are closed by the roof plate and floor plate.
• Central canal at the core of 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: lined by ependymal cells Ependymal Cells The macroglial cells of ependyma. They are characterized by bipolar cell body shape and processes that contact basal lamina around blood vessels and/or the pia mater and the cerebral ventricles. Muller cells of the retina are included based on similar microenvironmental contacts and morphology. Nervous System: Histology
• The spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy fills the bony 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 the fetus develops.
  • Week 8: Spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy extends along the entire length 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.
  • Inferior end reaches:
    • L3 level at birth
    • L1 level in adulthood
  • Spinal nerve roots that exit below L1–L3 create the cauda equina Cauda Equina The lower part of the spinal cord consisting of the lumbar, sacral, and coccygeal nerve roots. Spinal Cord Injuries
  • Conus medullaris Conus Medullaris Spinal Cord Injuries: tapered end of the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy
  • Filum terminale Filum terminale Spinal Cord: Anatomy: connects conus medullaris Conus Medullaris Spinal Cord Injuries to the coccygeal vertebra

Brainstem

The brainstem resembles the spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy in embryological organization. The basal plate gives rise to motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology nuclei, while the alar plate gives rise to sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology nuclei.

• Caudal medulla
  • Sensory Sensory Neurons which conduct nerve impulses to the central nervous system. Nervous System: Histology nuclei are dorsal.
  • Motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology nuclei are ventral.
• Cranial medulla
  • Roof plate is more opened up (“open book” appearance).
  • The basal plate is more medially located.
  • The alar plate is more laterally located.
  • Some sensory neurons Sensory neurons Neurons which conduct nerve impulses to the central nervous system. Autonomic Nervous System: Anatomy migrate anteriorly to form the olivary 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 later in development.
• Pons Pons The front part of the hindbrain (rhombencephalon) that lies between the medulla and the midbrain (mesencephalon) ventral to the cerebellum. It is composed of two parts, the dorsal and the ventral. The pons serves as a relay station for neural pathways between the cerebellum to the cerebrum. Brain Stem: Anatomy
  • Alar plate migrates to take a spot anterior to the basal plate and gives rise to the pontine nuclei.
  • Basal plate is now more posterior, but still gives rise to all the motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology nuclei.
  • 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 develops directly posterior to the pons Pons The front part of the hindbrain (rhombencephalon) that lies between the medulla and the midbrain (mesencephalon) ventral to the cerebellum. It is composed of two parts, the dorsal and the ventral. The pons serves as a relay station for neural pathways between the cerebellum to the cerebrum. Brain Stem: Anatomy from neuroepithelial cells.

Development of the Cerebral Cortex

The cortex develops from the telencephalon.

• The neural canal at this level develops into the left and right ventricles.
• Interventricular foramen Interventricular foramen Ventricular System: Anatomy: connects lateral ventricles Lateral ventricles Cavity in each of the cerebral hemispheres derived from the cavity of the embryonic neural tube. They are separated from each other by the septum pellucidum, and each communicates with the third ventricle by the foramen of monro, through which also the choroid plexuses (choroid plexus) of the lateral ventricles become continuous with that of the third ventricle. Ventricular System: Anatomy to the 3rd ventricle
• The development of lobes of 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 occurs from the ventricles outward:
  • Neuron precursor cells near the ventricles replicate rapidly.
  • Glial cells Glial Cells The non-neuronal cells of the nervous system. They not only provide physical support, but also respond to injury, regulate the ionic and chemical composition of the extracellular milieu, participate in the blood-brain barrier and blood-retinal barrier, form the myelin insulation of nervous pathways, guide neuronal migration during development, and exchange metabolites with neurons. Neuroglia have high-affinity transmitter uptake systems, voltage-dependent and transmitter-gated ion channels, and can release transmitters, but their role in signaling (as in many other functions) is unclear. Nervous System: Histology extend radial processes to provide a pathway for the 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.
  • Neuroepithelial cells migrate laterally, passing through subventricular zone → intermediate zone → cortical plate → marginal zone Marginal zone MALT Lymphoma
  • Different kinds 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 stop at different points, giving rise to specialized layers.
• 6 months: Distinctive lobes start to appear.
• Corpus callosum:
  • Becomes more defined as 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 from 1 cortex migrate to the other
  • Nervous structure that allows 1 side of 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 communicate with another side
• Gyri and sulci are not evident until near term.
• 9 months: 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 looks like a smaller version of the adult 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.

Development of the Face

• End of the 4th week: 1st facial structures are visible.
  • Centrally: stomodeum (early mouth)
  • Inferiorly: mandibular prominence
  • Laterally: 2 maxillary prominences
  • Superiorly: frontonasal prominence with nasal placodes
• 5th week: Nasal placodes deepen into nasal pits surrounded by nasal prominences.
• 6th and 7th weeks:
  • Mandibular prominences fuse → jaw Jaw The jaw is made up of the mandible, which comprises the lower jaw, and the maxilla, which comprises the upper jaw. The mandible articulates with the temporal bone via the temporomandibular joint (TMJ). The 4 muscles of mastication produce the movements of the TMJ to ensure the efficient chewing of food. Jaw and Temporomandibular Joint: Anatomy formed
  • Eyes are visible on the lateral side of the face (as frontonasal prominence narrows, eyes move medially).
  • Nasolacrimal groove forms: junction between frontonasal prominence and maxillary prominence, future nasolacrimal duct Nasolacrimal Duct Nasolacrimal duct. Dacryocystitis
  • Medial nasal prominences:
    • Grow together and fuse at the midline → stretch inferiorly
    • Fuse with maxillary prominence → form the upper lip Upper Lip Melasma
  • Medial and lateral nasal prominences: fuse with the maxillary prominence → form cheek and upper lip Upper Lip Melasma
  • Frontonasal prominence → becomes the forehead Forehead The part of the face above the eyes. Melasma, nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose and Nasal Cavity: Anatomy, and philtrum
• Maxillary prominence → cheek
• Mandibular prominence → mandible Mandible The largest and strongest bone of the face constituting the lower jaw. It supports the lower teeth. Jaw and Temporomandibular Joint: Anatomy and area anterior to the ear

Clinical Relevance

The following are pathological conditions that can arise as a result of errors in the development of 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, spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. 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). Spinal Cord: Anatomy, and face:

• Hydrocephalus Hydrocephalus Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial. Subarachnoid Hemorrhage: blockage of the ventricular system Ventricular System The ventricular system is an extension of the subarachnoid space into the brain consisting of a series of interconnecting spaces and channels. Four chambers are filled with cerebrospinal fluid (CSF): the paired lateral ventricles, the unpaired 3rd ventricle, and the unpaired 4th ventricle. Ventricular System: Anatomy that causes swelling Swelling Inflammation and pressure exerted on 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. In adults, the skull Skull 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 is already developed, so accumulated fluid presses on 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. In neonates, as bones have not yet completely ossified, the head circumference Head Circumference Physical Examination of the Newborn increases. May be caused congenitally by cerebral aqueduct Cerebral aqueduct Narrow channel in the mesencephalon that connects the third and fourth cerebral ventricles. Ventricular System: Anatomy stenosis Stenosis Hypoplastic Left Heart Syndrome (HLHS).
• Posterior fossa malformations (Arnold-Chiari malformations (CM)): Chiari I malformation is a congenital Congenital Chorioretinitis disorder associated with ectopic cerebellar tonsils Tonsils Tonsillitis located inferior to the foramen magnum. Children are usually asymptomatic. Chiari II malformation is caused by herniation Herniation Omphalocele of the cerebellar tonsils Tonsils Tonsillitis, as well as vermis, through the foramen magnum. Chiari II leads to non-communicating hydrocephalus Hydrocephalus Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, intracranial. Subarachnoid Hemorrhage.
• Frontonasal dysplasia ( cleft lip Cleft lip The embryological development of craniofacial structures is an intricate sequential process involving tissue growth and directed cell apoptosis. Disruption of any step in this process may result in the formation of a cleft lip alone or in combination with a cleft palate. As the most common craniofacial malformation of the newborn, the diagnosis of a cleft is clinical and usually apparent at birth. Cleft Lip and Cleft Palate and cleft palate Palate The palate is the structure that forms the roof of the mouth and floor of the nasal cavity. This structure is divided into soft and hard palates. Palate: Anatomy): Sonic hedgehog overactivity causes accumulation of excessive tissue in the frontonasal prominence area, resulting in a broad nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose and Nasal Cavity: Anatomy and widely separated eyes ( hypertelorism Hypertelorism Abnormal increase in the interorbital distance due to overdevelopment of the lesser wings of the sphenoid. DiGeorge Syndrome). This disorder may also cause cleft nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose and Nasal Cavity: Anatomy and midline cleft lip Cleft lip The embryological development of craniofacial structures is an intricate sequential process involving tissue growth and directed cell apoptosis. Disruption of any step in this process may result in the formation of a cleft lip alone or in combination with a cleft palate. As the most common craniofacial malformation of the newborn, the diagnosis of a cleft is clinical and usually apparent at birth. Cleft Lip and Cleft Palate due to the failure to fuse medial nasal prominences.
• Holoprosencephaly: a disorder caused by decreased activity of the sonic hedgehog gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics, resulting in narrowing of the face. More severe cases involve failure of the right and left cerebral cortexes to fully separate, as well as cyclopia. 
• 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: 1 of the most common congenital Congenital Chorioretinitis CNS malformations. The defects develop between the 3rd and 4th week of gestation and are often caused by folic acid deficiency Folic Acid 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 B 12 deficiency in peripheral blood and bone marrow findings, but the neurologic lesions seen in B 12 deficiency do not occur. Megaloblastic Anemia. The deficiency results in improper closure 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 in the 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, mainly at the caudal or cranial ends, giving rise to anencephaly Anencephaly A malformation of the nervous system caused by failure of the anterior neuropore to close. Infants are born with intact spinal cords, cerebellums, and brainstems, but lack formation of neural structures above this level. The skull is only partially formed but the eyes are usually normal. This condition may be associated with folate deficiency. Affected infants are only capable of primitive (brain stem) reflexes and usually do not survive for more than two weeks. Neural Tube Defects.