The neural tube
• The neural tube gives rise to the CNS
(including the brain & spinal cord).
• The brain stem & spinal cord have:
1. An alar plate that gives rise to the sensory
2. A basal plate that gives rise to sensory
• The neural tube gives rise to 3 primary
vesicles, which develop into 5 secondary
The neural crest
• Gives rise to the peripheral nervous system (peripheral
nerves & sensory & autonomic ganglia).
1. Pseudounipolar ganglion cells of the spinal & cranial nerves
2. Schwan cells (which elaborate the myelin sheath).
3. Multipolar ganglion cells of the autonomic ganglia.
4. Leptomeninges (the pia-arachnoid).
5. Chromaffin cells of the suprarenal medulla.
7. Odontoblasts (which elaborate predentine).
8. Aortopulmonary septum of the heart.
9. Parafollicular cells (calcitonin producing C cells).
10.Skeletal & connective tissue component of the pharyngeal
• The anterior neuropore:
• The closure of the anterior neuropore gives rise to
the lamina terminalis.
Failure of closure of the
anterior neuropore gives
rise to anencephaly
Failure of closure of the
posterior neuropore gives
rise to spina bifida
N Site Supply
Somatic motorSomatic motor 3, 4, 6
Lie medially Striate muscles
5, 7, 9
develop in the
Visceral motorVisceral motor 3, 7, 9
•Head & neck.
N Site Supply
Lie lateral to the
Chemo & baro
7 & 9 Taste receptors
5 Initially develop
(in the skin,
muscles & joints of
8 Lie most lateral
Ganglia and nuclei
• Aggregation of cell bodies in a peripheral
• Aggregation of cell bodies inside the CNS.
• Ganglia are peripheral and nuclei are central.
• Basal ganglia is a misnomer (basal nuclei).
Motor, parasympathetic & sensory
Motor nuclei contain the cell bodies of lower
contain the cell bodies of the pre-
ganglionic para-symathetic fibers
Sensory nuclei (somatic or visceral) contain the
cell bodies of the secondary
Parasympathetic & sensory ganglia
Sensory ganglia contain cell bodies of the
peripheral sensory (somatic or visceral) nerve.
• It also contain somatic motor fibers which pass
Autonomic ganglia contain the cell bodies of the
postganglionic parasympathetic fibers.
• It also contains visceral sensory fibers which pass
Autonomic ganglia (ganglia with synapses).
Sensory ganglia (ganglia without synapses).
Functional Classification of CN
• Spinal Nerve classification
– General Efferent or Afferent: serve general motor, sensory.
• Cranial Nerves classification
– Receptor type:
• General - just like spinal nerves
• Special –Use special receptors and neurons to serve additional
– Signal type
• Efferent – Sensory
• Afferent - Motor
– Voluntary or reflexive?
• Somatic. Innervate somatic muscles (muscles that arise from the
soma in the embryological stage – voluntary muscle control)
• Visceral. Innervate visceral structures.
Types of nerve fibers within cranial nerves
Direction of impulse:
• motor (efferent) or
• sensory (afferent).
The mode of control:
• voluntary or
The embryological origin of the structure innervated:
• Somatic (somite, body wall) or
• Visceral (gut tube, internal organs).
The distribution in the body:
• General (widespread) or
• Special (restricted to the head and neck).
General Somatic Efferent GSE Muscles from somites (skeletal, extraocular,
General Visceral Efferent GVE Smooth muscles of visceral Organs
Special Visceral Efferent SVE Muscles of face, palate, mouth, pharynx and
larynx (excludes eye & tongue muscles).
Special Visceral Afferent SVA visceral sensation of taste from tongue
Olfaction from Nose
General Visceral Afferent GVA sensory innervation from visceral organs
General Somatic Afferent GSA Sensory innervation from muscles, skin,
ligament and joints
Special Somatic Afferent SSA special sensations of vision from retina and
audition and equilibrium from inner ear
Somatic motor fibers – oculomotor, trochlear and abducens nuclei:
Extrinsic ocular muscles are derived from pre-otic somites.
Motor fibers innervating them, therefore, are somatic motor fibres and nuclei
are somatic motor nuclei.
Upper motor neuron input to nuclei of each side is bilateral.
Nuclei also receive fibers from medial longitudinal fasciculus for control of eye
periaqueductal grey matter of midbrain, near midline, immediately ventral to
aqueduct of Sylvius. Axons pass ventrally to emerge in the interpeduncular
in periaqueductal grey matter of midbrain, below oculomotor nuclei. Axons pass
dorsally, decussating within midbrain dorsal to aqueduct.
in pons, related to VII motor nucleus
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