Vestibulocochlear Flashcards
In the cochlea what are the cilia embedded in?
The tectorial membrane
What happens when a sound wave causes upward movement of the basilar membrane?
There’s upward and inward bending of hair cell against the tectorial membrane bending all the cilia in the direction of the kinocilium➡️ this opens sodium channels and Depolarizes the hair cells ➡️ which causes an AP generation in the peripheral process the first order neuron in the auditory pathway
What happens with downward movement of the basilar membrane?
The hairs bend in the opposite direction of the kinocilium and it hyperpolarizes the cell turning it off
What is the DRG of the ear?
The spiral ganglion. It is a bipolar cell who’s axon receives input from the hair cells and projects to the dorsal and ventral cochlear nuclei.
*This is the cochlear nerve portion of cranial nerve VIII
Where are the second order neurons for hearing?
In the dorsal and ventral cochlear nuclei in the base of the pons
Where do axons from the cochlear nuclear neurons project?
They project bilaterally to either the ipsilateral or contralateral superior olivary nucleus. Or directly to the lateral lemniscus. Eventually all axons go to the inferior colliculus where the third or fourth order neuron projects to the MGN (medial geniculate nucleus) where a fourth or fifth order neuron will project to the primary auditory cortex
Where is the primary auditory cortex?
The superior temporal gyrus
What happens to a lesion of the cochlear nerve prior to or including cochlear nuclei? This also applies to unilateral damage to an auditory apparatus
unilateral loss of hearing or deafness on the ipsilateral side
What happens to a lesion above the cochlear nuclei?
Some hearing loss bilaterally but worse on the contralateral side
What makes up the vestibular apparatus?
The semicircular Canal’s and the otolith organs (saccule and utricle)
What is the difference between the semicircular Canal hair cell and the otolith hair cell?
Semicircular Canal’s are filled with endolymph which moves cilia when the head moves. The otolith hair cells cilia project into a gelatinous substance called the otolythic membrane. This membrane contains calcium crystals called otoconia that are aligned with gravity and only respond when the head is maintained in a rotated or tilted position.
What are otoconia and what do they do?
They are calcium crystals within the otolithic membrane that act pull and hold the cilia in a bent position as long as the head is tilted.
Explain what happens to endolymph and cilia when the head is turned to the left
On turning head to the left➡️ endolymph turns to the right➡️ bending the cilia of the hair cells in the left horizontal duct to the right in the direction of their kinocilium ➡️depolarizing the hair cells➡️ while the fluid bends cilia in the right horizontal duct to the left in the direction opposite their kinocilium ➡️hyperpolarizing the hair cells.
There is increased firing from the left and decreased firing from the right telling the brain that it’s movement of head to the left.
What direction do the hair cells bend to depolarize and hyperpolarize?
Bending towards the Kinocilium Depolarizes the hair cell. Bending the cilia away from the kinocilium hyperpolarizes the hair cell.
What happens with a unilateral lesion to the frontal eye field?
You lose the ability to voluntarily rotate your eyes. The contralateral frontal eye field controls voluntary movement of eyes to the same side. If the right side is lesioned then the intact left I will take over and push both eyes to the right. If it also involves area four, which is nearby, you have hemiplegia and the eyes will look away from the hemiplegia. The eyes point to the side of the lesion.
