Histogenesis of the Nervous System
- Histogenesis means the embryologic development of tissues from early cell layers into mature tissue types.
- Neuroepithelium is early embryonic epithelial tissue that gives rise to major nervous-system structures.
- Neural plate is a thickened area of neuroepithelium that forms early in nervous-system development.
- Neural groove forms when the neural plate bends inward.
- Invagination means inward folding, and it helps convert the neural plate into the neural groove.
- Neural tube forms when the edges of the neural groove fuse.
- Cranial end means the head end of the developing neural tube.
- Cranial neural tube develops into the brain.
- Caudal neural tube develops into the spinal cord.
- Neural crest cells are embryonic cells that separate from the edges of the neural plate before the neural tube closes.
- Migration means movement of cells from their original location to new body regions during development.
- Neural crest migration is important because neural crest cells form many peripheral nervous-system and head-region structures.
- Cranial sensory ganglia contain sensory neuron cell bodies associated with cranial nerves.
- Spinal sensory ganglia contain sensory neuron cell bodies associated with spinal nerves.
- Neural crest cells form sensory neurons of cranial and spinal sensory ganglia.
- Neural crest cells form many sensory neurons of the peripheral nervous system.
- Schwann cells come from neural crest cells and support peripheral axons.
- Autonomic ganglia are peripheral ganglia involved in involuntary motor control.
- Postganglionic neurons are autonomic neurons whose cell bodies lie in autonomic ganglia and whose axons go to target organs.
- Associated glia are supporting cells that develop along with peripheral autonomic neurons.
- Mesenchymal cells are embryonic connective-tissue-forming cells.
- Ectomesenchymal cells are neural-crest-derived mesenchymal cells, especially important in the head and anterior neck.
- Neural crest cells form most mesenchymal and ectomesenchymal cells of the head and anterior neck.
- Melanocytes are pigment-producing cells in the skin and oral mucosa.
- Oral mucosa is the moist epithelial lining of the mouth.
- Odontoblasts are tooth-forming cells that produce dentin.
- Dentin is the hard mineralized tissue beneath tooth enamel.
- Arachnoid mater is the middle meningeal covering of the brain and spinal cord.
- Pia mater is the delicate inner meningeal covering that closely follows the brain and spinal cord surface.
- Rostral means toward the head or front part of the nervous system.
- Mesencephalon means the embryologic midbrain.
- Neural crest cells form arachnoid and pia mater cells rostral to the mesencephalon.
- Chromaffin cells are hormone-releasing cells of the adrenal medulla.
- Adrenal medulla is the inner part of the adrenal gland, and it releases catecholamine hormones during stress.
- Congenital malformation means an abnormal structure present at birth.
- Abnormal central nervous system (CNS) histogenesis can cause congenital malformations.
- Spina bifida is defective closure of the spinal column during development.
- Meninges are the protective membranes around the brain and spinal cord.
- Severe spina bifida can allow the spinal cord and meninges to protrude through unfused vertebral areas.
- Viscera are internal organs, especially organs in the thorax and abdomen.
- Severe spina bifida at the extreme end can be associated with defective development of thoracic and abdominal viscera.
- Anencephaly is failure of anterior neuropore closure with a poorly formed brain and absent cranial vault.
- Anterior neuropore is the head-end opening of the neural tube before closure is complete.
- Cranial vault is the bony skull covering that normally protects the brain.
- Anencephaly is usually incompatible with life because the brain and skull do not develop adequately.
- Hirschsprung disease is congenital megacolon caused by failure of neural crest cells to migrate into the gut wall.
- Congenital megacolon means abnormal dilation of the colon present from birth.
- Auerbach plexus is a nerve plexus in the gut wall that helps control intestinal movement.
- Parasympathetic innervation to the colon is reduced in Hirschsprung disease because the distal colon lacks Auerbach plexus neurons.
- Motor function of the affected colon is lost, so stool cannot move normally through that segment.
- Colonic dilation occurs in Hirschsprung disease because material backs up behind the nonfunctioning segment.
- Neuroglial tumors are tumors derived from supporting cells of the central nervous system.
- Intracranial tumors are tumors located inside the skull.
- Central nervous system (CNS) tumors rarely arise from neurons and more often arise from neuroglial cells.
- Astrocytes, oligodendrocytes, and ependymocytes are neuroglial cells that can give rise to central nervous system tumors.
- Oligodendroglioma is a tumor associated with oligodendrocyte-lineage cells and can be relatively benign.
- Malignant astrocytoma is an aggressive tumor associated with astrocyte-lineage cells and can be fatal.
- Acquired immunodeficiency syndrome (AIDS) is advanced disease caused by human immunodeficiency virus infection.
- Human immunodeficiency virus type 1 (HIV-1) can affect the brain environment.
- Microglia are immune-like supporting cells in the central nervous system.
- AIDS-affected brains can contain large microglial populations.
- Cytokines are signaling proteins that immune and support cells use to communicate.
- Neuron-toxic cytokines can injure neurons even when microglia do not directly attack the neurons.
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