Trigeminal Reflexes

A. Introduction (Table 10-1)

1. The corneal reflex is a consensual disynaptic reflex.

Table 10-1.

The Trigeminal Reflexes

Reflex

Afferent Limb

Efferent Limb

Corneal reflex

Ophthalmic nerve (CN V-l)

Facial nerve (CN VII)

Jaw jerk

Mandibular nerve (CN V-3)*

Mandibular nerve (CN V-3)

Tearing (lacrimal) reflex

Ophthalmic nerve (CN V-l

Facial nerve (CN VII)

Oculocardiac reflex

Ophthalmic nerve (CN V-l)

Vagal nerve (CN X)

*The cell bodies are found in the mesencephalic nucleus of CN V. CN - cranial nerve.

*The cell bodies are found in the mesencephalic nucleus of CN V. CN - cranial nerve.

2. The jaw jerk reflex is a monosynaptic myotatic reflex (Figure 10-3).

3. The tearing (lacrimal) reflex

4. The oculocardiac reflex occurs when pressure on the globe results in bradycardia.

B. Clinical correlation. Trigeminal neuralgia (tic douloureux) is characterized by recurrent paroxysms of sharp, stabbing pain in one or more branches of the trigeminal nerve on one side of the face. It usually occurs in people older than 50 years of age, and it is more common in women than in men. Carbamazepine is the drug of choice for idiopathic trigeminal neuralgia.

Jaw Reflex

Figure 10-3. The jaw jerk (masseter) reflex. The afferent limb is V-3, and the efferent limb is the motor root that accompanies V-3. First-order sensory neurons are located in the mesencephalic nucleus. The jaw jerk reflex, like all muscle stretch reflexes, is a monosynaptic myotactic reflex. Hyperreflexia indicates an upper motor neuron lesion. CN = cranial nerve.

Figure 10-3. The jaw jerk (masseter) reflex. The afferent limb is V-3, and the efferent limb is the motor root that accompanies V-3. First-order sensory neurons are located in the mesencephalic nucleus. The jaw jerk reflex, like all muscle stretch reflexes, is a monosynaptic myotactic reflex. Hyperreflexia indicates an upper motor neuron lesion. CN = cranial nerve.

Cavernous sinus

Pituitary gland (hypophysis)

Optic chiasm

Internal carotid artery

Anterior clinoid process

CN III

Infundibulum

Ophthalmic Artery Infundibulum

CN VI and postganglionic sympathetics

Figure 10-4. The contents of the cavernous sinus. The wall of the cavernous sinus contains the ophthalmic cranial nerve (CN) V-l and maxillary (CN V-2) divisions of the trigeminal nerve (CN V) and the trochlear (CN IV) and oculomotor (CN III) nerves. The siphon of the internal carotid artery and the abducent nerve (CN VI), along with postganglionic sympathetic fibers, lies within the cavernous sinus.

Cavernous sinus

Pituitary gland (hypophysis)

Optic chiasm

Internal carotid artery

Anterior clinoid process

CN III

CN VI and postganglionic sympathetics

Infundibulum

Figure 10-4. The contents of the cavernous sinus. The wall of the cavernous sinus contains the ophthalmic cranial nerve (CN) V-l and maxillary (CN V-2) divisions of the trigeminal nerve (CN V) and the trochlear (CN IV) and oculomotor (CN III) nerves. The siphon of the internal carotid artery and the abducent nerve (CN VI), along with postganglionic sympathetic fibers, lies within the cavernous sinus.

V. THE CAVERNOUS SINUS (Figure 10-4) contains the following structures:

A. Internal carotid artery (siphon)

C. Postganglionic sympathetic fibers en route to the orbit

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