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Thursday, October 09, 2008

All of the following are Somatic Efferent except

Question 14
All of the following are Somatic Efferent except
a.       Facial nerve
b.      III Nerve
c.       IV Nerve
d.      VI Nerve
a) Facial nerve
Gray’s Anatomy 38th Edition Pages 238, 241
Gray / Neuroanatomy Books
  • General somatic efferent neurons exit ventrally in a similar manner to those of the spinal cord, comprising the oculomotor, trochlear, abducens and hypoglossal nerves. Thus nerves III, IV, VI and XII parallel the organization of the somatic motor neurons in the spinal cord.
Self Explanatory
  • The second motor component, special branchial efferent, comprises the accessory nerve and the motor parts of the trigeminal, facial, glossopharyngeal and vagus nerves, whose nerve exit points lie more dorsally than the somatic motor system.
  • The cranial nerves also contain a third class of efferent neurons, the general visceral efferent neurons (parasympathetic preganglionic) travelling in nerves III, VII, IX and X, which leave the hindbrain via the same exit points as the special branchial efferent fibres.
  • The most rostral sensory ganglion, the trigeminal (V) comprises both neural crest and placode-derived neurons that mediate general somatic afferent functions. In the case of more caudal cranial nerves (VII, IX and X) the same applies, but the two cell populations form separate ganglia in the case of each nerve. Analogous with the trigeminal, the proximal series of ganglia is neural crest derived (forming the proximal ganglion of VII, the superior ganglion of IX and the jugular ganglion of X) while the distal series derives from placodal cells (forming the geniculate ganglion of VII, the petrosal ganglion of IX and the nodose ganglion of X). These ganglia contain neurons that mediate special, general visceral and somatic afferent functions. The VIIth nerve has a vestibular ganglion containing both crest and placodal cells and an acoustic ganglion from placodal neurons only; it conveys special somatic afferents.
  • Both neurons and supporting cells of the cranial autonomic ganglia in the head and the trunk originate from neural crest cells
Types of Functional Components in a Nerve
Fibres and Sensation Carried
Sensory or Afferent
General Visceral Afferent
·        Pain arising from Viscera
·        Dorsal Nucleus of Vagus
Special Visceral Afferent
·        Taste
·        Nucleus Tractus Solitarius
·        Nucleus of Dorsal Visceral Gray
General Somatic Afferent
·        Exteroceptive impulses – cutaneous sensations of pan, touch and temperature -
·        Proprioceptive impulses arising in muscles, tendon and joints conveying information regarding movement and position of joint
·        Chief Sensory Nucleus (Tactile)
·        Nucleus of Spinal Tract of Trigeminal Nerve (Pain Temp)
·        Nucleus of Mesencephalic Tract of Spinal Nerve (Proprioception)
Special Somatic Afferent
·        Vision
·        Hearing
·        Equilibrium
·        Nucleus of the Vestibulocochlear nerver
Motor of Efferent
General Visceral Efferent
·        General visceral efferent neurons
·        Parasympathetic preganglionic (III, VII, IX and X)
·        innervate glands of the head,
·        the sphincter pupillae and ciliary muscles,
·        and the thoracic and abdominal viscera.
·        Smooth muscle
·        Cardiac Muscle
·        Glands
·        Dorsal Vagal Nucleus
·        Superior Salivatory Nucleus
·        Inf Salivatory Nucleus
·        Lacrimatory Nucleus
·        Edinger Westpal Nucleus
Special Visceral Efferent
·        (accessory nerve and the motor parts of the V, VII, IX, X nerves)
·        Also called as Branchial Efferent.
·        Striated muscles developing within the pharyngeal (branchial) arches
·        Mucles of Mastication, face, larynx
·        Nucleus Ambigus
General Somatic Efferent
·        Supply striated muscle now known to be derived from the cranial (occipital) somites and prechordal mesenchyme.
·        Muscles of Body wall and Limbs
·        Eye and Tongue
·        Oculomotor Nucleus (III)
·        Trochlear Nucleus (IV)
·        Abducent Nucleus (VI)
·        Hypoglossal Nucleus (XII)

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