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Nervous System

Nervous system develops from ectoderm (neuroectoderm). Nervous system develops from neural tube which in turn develops by process of neurulation, i.e. formation of neural plate and in folding into neural tube. Structures formed from neural tube are:-
  1. From cranial part (enlarged cephalic part)
    Gives rise to brain. Developmental parts are:
    1. Forebrain (prosencephalon)
      1. Telencephalon: Cerebral hemisphere and lateral ventricle.
      2. Diencephalon: Optic cup and stalk (gives rise to retina, pituitary, thalamus, hypothalamus, Epithalamus, pineal gland, and third ventricle.
    2. Midbrain (mesencephalon)
      1. Cerebral aqueduct.
    3. Hindbrain (rhombencephalon)
      1. Metencephalon: Cerebellum, pons
      2. Myelencephalon: Medulla oblongata
  2. From caudal part
    Gives rise to spinal cord.
Layers in wall of neural tube
The wall of neural tube at first has a single layer of cells. The cells multiply and form three layers: (i) ependymal, (ii) mantle and (iii) marginal. Neurons develop in mantle layer. The mantle layer divides into ventral part (basal lamina or basal plate) and dorsal part (alar lamina or alar plate). This division of mental layer is of considerable functional importance. The basal lamina (basal plate) develops into structures which are motor in function (e.g. motor or efferent nuclei) and the alar lamina (alar plate) into those that are sensory (e.g. sensory or afferent nuclei).
  From alar lamina From basal lamina
MIDBRAIN Colliculi
Substantia nigra
Red nucleus
Mesencephalic nu. Of trigeminal n.
Oculomotor nu.
Edinger Westphal nu.
Trochlear nu
PONS Pontine nuclei
Vestibular nu.
Main sensory nu. Of trigeminal n.
Nu. Of spinal tract of trigeminal n.
Nu. Of tractus solitarius
Motor nu. Trigeminal n.
Motor nu. Of facial n.
Nucleus of abducent n.
Sup. Salivatory nu.
Lacrimatory nu.
MEDULLA Inf. Olivary nu.
Nu. Of spinal tract of trigeminal n.
Nu. Of tractus solitarius
Part of dorsal nu. of vagus n.
Part of dorsal nucleus of vagus n.
Inf. Salivatory nu.
Nu. Ambiguous
Hypoglossal nu.

  • In spinal cord the alar lamina forms the posterior grey column, and the basal lamina forms the ventral grey column. The marginal layer becomes white matter.
  • Cerebellum is derived from alar lamina of the metencephalon

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