Neuroanatomy -- Optic Cn Ii (Vis) & Acoustic Cn Viii (Aud)

Front 1

What's in the retina?

Back 1

rods (light); cones (light & color)

Front 2

Where does the optic nerve go?

Back 2

optic nerve goes from the retina to the optic chiasm

Front 3

Where does the optic tract go?

Back 3

from the optic chiasm to the lateral geniculates; some fibers go from lateral geniculates to superior colliculi but most from LG will form Optic Radiation aka geniculocalcarine tract

Front 4

What is the Optic Radiation?

Back 4

aka geniculocalcarine tract; fibers from the lateral geniculate to the Primary Visual Cortex in the Occipital Lobe

Front 5

Where do the optic nerves from each eye unite?

Back 5

optic nerves unite and cross over at the OPTIC CHIASM.

There is PARTIAL decussation; fibers from nasal half (inner) of retina cross; fibers from temporal half (outer) do not cross

Front 6

What happens when there are lesions to the optic nerve?

Back 6

lesions of optic nerve --> blindness of ipsilateral eye.

Front 7

In what case would you have total blindness of the right or left eye?

Back 7

total blindness of one eye: if the lesion is on the ipsilateral optic nerve. (Usually due to trauma)

Front 8

How would you get Bitemporal Hemianopsia?

Back 8

Bitemporal Hemianopsia = lesion is right at the optic chiasm where decussation happens. "tunnel vision" -- do not have vision on either temporal half.

Usually due to chiasmal lesions such as pituitary tumors.

Front 9

How would you get Right (or left) nasal hemianopsia?

Back 9

Right nasal hemianopsia = blindness in R nasal visual field. Lesion is on the part of the optic nerve on the ipsilateral side that will not decussate at optic chiasm.

Front 10

How would you get Right homonymous hemianopsia?

Back 10

Right homonymous hemianopsia = two right halves blind. (L nasal and R temporal). Occurs when there is a lesion in the LEFT (contra to blind side) optic tract (after optic chiasm).

Front 11

Is the Vestibulocochlear nerve, CN VIII, aka Acoustic, sensory or motor or both?

Back 11

CN VIII = sensory. Also somatic & affarent.

Front 12

What are the two special sensations from the Acoustic nerve?

Back 12

Vestibular, from semicircular canals, and auditory from cochlea

Front 13

Where are the cell bodies for the auditory pathway?

Back 13

cell bodies in spiral ganglion, in the modiolus (central bony core)

Front 14

What kind of cells are the auditory neurons?

Back 14

bipolar cells with a periphera process (dendrites) going out to stereocilia & central process (axons) going towards brain

Front 15

How many neurons can supply each hair cell?

Back 15

Up to 8 neurons can supply each hair cell, but each neuron only goes to one hair cell. Hair cells don't share neurons.

Front 16

How can the auditory pathway be described?

Back 16

There is tonotopic arrangement; it is a frequency-dependent sensory system.

Front 17

Where does CN VIII go after the cochlea?

Back 17

The medulla: there are dorsal and ventral cochelar nuclei (each with a dorsal and ventral PART) of the CN VIII in the medulla. This is where the first set of synapses occur. There is an orderly (tonotopic) sequence of incoming nerves.

Front 18

Describe the sequence of incoming nerves in the brainstem.

Back 18

Fibers from apex of cochlea (low tones) terminate in VTRL part of DORSAL Cochlear N and in the (entire) VENTRAL Cochelar N.

Fibers from basal end of cochlea (high tones) terminate only in the DRSL part of the DORSAL Cochlear N

Front 19

From the dorsal cochlear nucleus, where do the fibers go?

Back 19

half of fibers cross midline and ascend contralaterally -- do NOT go to superior Olivary n ucleus, but rather ascend via lateral lemniscus

remaining half ascend ipsilaterally via the superior olivary complex

Front 20

What is the lateral lemniscus?

Back 20

lateral lemniscus is a very important tract to which all fibers will eventually project -- on both sides

ascends through brainstem

primary termination/synapse is at inferior colliculus (then to medial geniculate)

a few fibers cross over at MG before asending to Gyrus of Heschl contralaterally (MGB is FINAL synapse before Heschl)

Front 21

From the ventral cochlear nucleus, where do fibers go?

Back 21

Large group of fibers from Ventral C Nuclei, both ipsilaterally & contralaterally, synapse at Superior Olivary Nucleus/Complex THEN ascend via lateral lemniscus (--> eventually to inferior colliculus)

Front 22

What happens when lesions of CN VIII destroy receptors in the cochlea?

Back 22

lesions destroying receptors incochlea --> total deafness in that ear

Front 23

What happens when lesions of CN VIII destroy elements along auditory pathway?

Back 23

lesions along aud pathway --> impaired hearing in contralateral ear (not total deafness)

Front 24

What happens when lesions of the CN VIII are in the Gyrus of Heschl?

Back 24

lesions in G of H --> auditory agnosia, not total deafness; just hear sound but do not know what it means