19 - Cranial Nerves V Flashcards
CN VIII
Vestibulocochlear nerve
Function of CN VIII cochlear nerve
Hearing (SSA)
Ganglion of CN VIII cochlear nerve
Spiral (cochlear) ganglion
Spiral (cochlear) ganglion of cochlear nerve
Spiral (cochlear) ganglion
a. contains bipolar sensory neurons (1st order neurons of the auditory pathway)
b. sensory
c. no synapses
Auditory pathway of cochlear nerve
- First order neurons
- Second order neurons
- Third order neurons
- Nuclei of the lateral lemniscus
- Inferior colliculus
- Medial geniculate nucleus (MGN)
- Auditory cortex
- Descending auditory projections
- Sound attenuation reflex
Auditory first order neurons
a. cell bodies: in cochlear ganglion
b. peripheral processes terminate in receptor hair cells of the organ of Corti
c. central processes (form root of cochlear nerve) enter pons, bifurcate and synapse in the dorsal cochlear nucleus and ventral cochlear nucleus
d. carry information from ipsilateral ear
Auditory second order neurons
a. are housed in the dorsal and ventral cochlear nuclei
b. axons from the ventral cochlear nucleus, form the ventral acoustic stria (trapezoid body), which terminates in a nucleus of the trapezoid body and the superior olivary nucleus. Others ascend in the lateral lemniscus (LL) to terminate in the nucleus of the LL and the inferior colliculus
c. axons from the dorsal cochlear nucleus form the dorsal acoustic stria, ascend in the LL to terminate in the inferior colliculus
d. carry information from the ipsilateral ear
Auditory third order neurons
From here on, each auditory pathway relays input from both ears…
a. are housed in the superior olivary nuclei which are involved in the localization of sound
b. carry information from both ears
Lateral lemniscus
Lateral lemniscus → inferior colliculus
a. is the main pathway of the auditory system
b. carries auditory information from both ears
Nuclei of the lateral lemniscus
Nuclei of the lateral lemniscus
a. process input from both ears
Inferior colliculus
Inferior colliculus
a. is a relay nucleus for hearing in the midbrain
b. processes input from the lateral lemniscus
c. projects to the medial geniculate nucleus (MGN)
Medial geniculate nucleus (MGN)
Medial geniculate nucleus (MGN)
a. is a relay nucleus for hearing in the thalamus
b. processes sound intensity and frequency
c. gives rise to the auditory radiation which projects to the primary auditory cortex
Auditory cortex - two areas
1 - Primary auditory cortex
2 - Secondary cortical areas
Primary auditory cortex
Primary auditory cortex
i. Brodmann’s areas 41 and 42
ii. transverse temporal gyri of Heschl
iii. role in localization of sound
iv. role in detection of alterations in pattern of sound
Secondary cortical areas of auditory cortex
Secondary cortical areas
i. multiple, difficult to locate
ii. interpretation of sound, voices, language, music
Descending auditory projections
Olivocochlear bundle
i. modulates the transmission of auditory input to the CNS
Last step in auditory pathway
Sound attenuation reflex
Two types of deafness
- Conduction deafness
- Sensorineural deafness
Sensorineural deafness
Sensorineural deafness
- cochlea
- cochlear nerve
- central auditory pathways
Other portion of CN VIII
Vestibular nerve
Function of CN VIII vestibular nerve
Equilibrium (balance) (SSA)
Ganglion of CN VIII vestibular nerve
Vestibular (Scarpa’s) ganglion
a. contains bipolar sensory neurons (1st order neurons of the vestibular pathway)
b. sensory
c. no synapses
CN VIII Vestibular Pathway
- First order neurons
- Second order neurons
- Third order neurons
- Afferents (input) to the vestibular nuclei
- Efferents (output) from the vestibular nuclei
First order neurons
First order neurons
a. cell bodies: in vestibular ganglion
b. peripheral processes terminate in receptor hair cells of the maculae of the utricle and saccule and the cristae of the semicircular canal ampullae
c. central processes (form root of vestibular nerve) enter pons, bifurcate and synapse in the vestibular nuclei. Some central processes pass into the inferior cerebellar peduncle to end in the ipsilateral flocculonodular lobe of the cerebellum