Vestibulocochlear (Cn Viii), Accessory (Cn Xi), And Hypoglossal (Cn Xii) Nerves

Front 1

vestibulocochlear nerve

Back 1

- actually consists of two nerves supplying the inner ear with sensory fibers
- the two nerves exit the inner ear through the internal auditory meatus and enter the brainstem at the jcn of b/w the pons and medulla (cerebellopontine angle), where the vestibulocholear nerve is closely associated with the facial nerve (CN VII)

Front 2

Vesticbular nerve of the vestibulocochlear nerve

Back 2

special sensory nerve sensing equilibrium (balance); stim by changes in position, changes in the rate of movement or both
- cell bodies of bipolar neurons are located in the vestibular ganglion
- peripheral processes extend to the hair cells of the cristae of the three otic ampullae and thoes of the utricular and saccular maculae. Hair cells are specialized ciliated cells that detect movement of fluid in the inner ear. Three semicircular ducts, arranged at right angles to each other, detect angluar movement of the head in space. The saccule and utricle detect the position of the head relative to gravity
- central processes transverse internal acoustic meatus, becoming the cochlear part of hte vestibulocochlear nerve and synapse on secondary sensory gaglion in the vestibular nuclear complex located on the floor of the 4th ventricle
- central projections are complex
1. cerebellum (movement coordination and balance)
2. motor nuclei of III, IV, VI - eye movements in response to head position
3. dorsal motor nucleus of X (naseua, vomiting, and cardiopulmonary response)

clinican consideration: loss of vestibular portion of CN VIII = vertigo (loss of balance) dizziness, abnormal eye movements (nystagmus), and even nausea and vomiting

clinical consideration: balance disorders

Front 3

cochlear nerve of the vestibulocochlear nerve

Back 3

- special sensory nerve responsibe for hearing through stim of hair cells within the organ of corti, the major receptor for auditory stimuli
- cell bodies of bipolar neurons are located in spiral ganglion of modiolus of the cochlea
- short peripheral processes extend to the hair cells of the organ of corti, a major receptor for auditory stimuli
- central processes tranverse the internal acoustic meatus, becomeing the vestibular part of the vestibulocochlear nerve, and synapse on secondary sensory neurons in either the dorsal cochlear nucleus (high frequency sound) or the ventral cochlear nucleus (low frequency sound)
- central projections are complex
1. motor nuclei of CNs V, VII to the tensor veli tympani and stapedius
2. motor nuclei of CNs III, IV, VI to eye movements respond to sound
3. motor nuclei of CNs XI - head movement in response to sound

clinical consideration: loss of the cochlear portion of CN VIII causes unilateral hearing loss, tinnitus, damage often caused by skull fractures or infections

clinical consideration: loss of CN VII and CN VIII nerve - acoustic neuroma at the cerebellopontine angle or within the internal acoustic meatus