Lab 10 - Cranial Nerve Nuclei and Brain Stem Circulation

Cranial Nerve V-Trigeminal Nerve

Components of the Trigeminal Nerve include

Cranial Nerve V-Trigeminal NerveThe trigeminal motor nucleus provides motor innervation to the muscles of mastication, the tensor tympani and the tensor veli palatini. Damage to the trigeminal motor neurons results in paralysis of the masticatory muscles. The force of bite is reduced in power, and the jaw deviates toward the injured side on opening the mouth. With bilateral damage, the lower jaw droops, but the mouth can be closed by means of the facial muscles. However, chewing is impossible and swallowing is difficult.

Among the inputs to the trigeminal motor nucleus are the collaterals from the mesencephalic trigeminal nucleus for reflex control of jaw muscles. Additional inputs from the other sensory trigeminal nuclei provide reflex control of jaw muscles to superficial stimuli, especially from the lingual and oral mucus membranes.

The corticofugal input to the trigeminal motor nucleus is both direct and indirect via the reticular formation and bilateral with a slight contralateral dominance. Central or upper motor neuron lesions lead to little disturbances unless they are bilateral, as in pseudobulbar palsy. In this disease, cerebral vascular disorders produce areas of necrosis, which interrupt the corticobulbar fibers. Volitional movements of the jaw are impaired and the jaw jerk reflex is usually increased.

The somatosensory components of the trigeminal nerve (facial skin, eyes, oral and nasal cavities and dura) and those of the vagus (outer ear canal, pinna, and dura), glossopharyngeal (outer ear canal, ear drum, and middle ear cavity) and facial (pinna) nerves end in the spinal trigeminal nucleus (crude touch, pain and temperature) and main sensory trigeminal nucleus(discriminative touch). The axons of the mesencephalic trigeminal nucleus travel in the trigeminal nerve to innervate and provide proprioceptive information from the jaw muscles and joints.

Cranial Nerve (V) Exam: