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Thursday, October 09, 2008

Which is the Nucleus of Masseteric Reflex - Nucleus of Mesencephalic Tract of Spinal Nerve

Question 15
Which is the Nucleus of Masseteric Reflex
a.       Chief Sensory Nucleus
b.      Nucleus of Spinal Tract of Trigeminal Nerve
c.       Nucleus of Mesencephalic Tract of Spinal Nerve
d.      Dorsal Vagal Nucleus
Answer
c. Nucleus of Mesencephalic Tract of Spinal Nerve
Reference
Gray’s Anatomy 38th Edition Page 1237
QTDF
Gray
Quality
Thinker
Status
New
Discussion
Ä     The trigeminal, the largest cranial nerve, is the sensory supply to the face, the greater part of the scalp, the teeth, the oral and nasal cavities, the dura mater and the cerebral blood vessels. It gives the motor supply to the masticatory muscles, and the anterior belly of digastric and mylohyoid, and contains proprioceptive nerve fibres from the masticatory and probably the extraocular and facial muscles
Expanation
a.       Chief Sensory Nucleus is concerned with Tactile sensation.
b.      Nucleus of Spinal Tract of Trigeminal Nerve is concerned with Pain and Temperature Sensation.
c.       Nucleus of Mesencephalic Tract of Spinal Nerve is concerned with proprioception
d.      Dorsal Vagal Nucleus is a General Visceral Efferent Nucleus which innervates glands of the head, the sphincter pupillae and ciliary muscles, and the thoracic and abdominal viscera.
Comments
Ä     Masseter is supplied by a branch of the anterior trunk of the mandibular nerve.
Tips
Other ascending fibres enter the mesencephalic nucleus, a column of unipolar cells, whose peripheral branches may convey proprioceptive impulses from the masticatory muscles; it is also stated that similar impulses reach it from the teeth and from the facial and ocular muscles. Its neurons are unique in being the only primary sensory neurons with somata in the CNS. It is the relay for the only supraspinal monosynaptic reflex, namely the 'jaw-jerk'. If, however, the primary proprioceptive neurons of extraocular muscles are in fact situated in their motor nerves or in the trigeminal ganglion, some mesencephalic trigeminal neurons may be 'secondary' in status. Small multipolar cells, possibly interneurons, occur near the unipolar neurons.

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