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24 Cards in this Set
- Front
- Back
What's in the retina?
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rods (light); cones (light & color)
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Where does the optic nerve go?
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optic nerve goes from the retina to the optic chiasm
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Where does the optic tract go?
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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
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What is the Optic Radiation?
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aka geniculocalcarine tract; fibers from the lateral geniculate to the Primary Visual Cortex in the Occipital Lobe
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Where do the optic nerves from each eye unite?
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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 |
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What happens when there are lesions to the optic nerve?
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lesions of optic nerve --> blindness of ipsilateral eye.
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In what case would you have total blindness of the right or left eye?
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total blindness of one eye: if the lesion is on the ipsilateral optic nerve. (Usually due to trauma)
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How would you get Bitemporal Hemianopsia?
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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. |
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How would you get Right (or left) nasal hemianopsia?
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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.
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How would you get Right homonymous hemianopsia?
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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).
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Is the Vestibulocochlear nerve, CN VIII, aka Acoustic, sensory or motor or both?
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CN VIII = sensory. Also somatic & affarent.
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What are the two special sensations from the Acoustic nerve?
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Vestibular, from semicircular canals, and auditory from cochlea
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Where are the cell bodies for the auditory pathway?
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cell bodies in spiral ganglion, in the modiolus (central bony core)
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What kind of cells are the auditory neurons?
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bipolar cells with a periphera process (dendrites) going out to stereocilia & central process (axons) going towards brain
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How many neurons can supply each hair cell?
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Up to 8 neurons can supply each hair cell, but each neuron only goes to one hair cell. Hair cells don't share neurons.
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How can the auditory pathway be described?
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There is tonotopic arrangement; it is a frequency-dependent sensory system.
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Where does CN VIII go after the cochlea?
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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.
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Describe the sequence of incoming nerves in the brainstem.
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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 |
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From the dorsal cochlear nucleus, where do the fibers go?
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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 |
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What is the lateral lemniscus?
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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) |
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From the ventral cochlear nucleus, where do fibers go?
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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)
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What happens when lesions of CN VIII destroy receptors in the cochlea?
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lesions destroying receptors incochlea --> total deafness in that ear
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What happens when lesions of CN VIII destroy elements along auditory pathway?
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lesions along aud pathway --> impaired hearing in contralateral ear (not total deafness)
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What happens when lesions of the CN VIII are in the Gyrus of Heschl?
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lesions in G of H --> auditory agnosia, not total deafness; just hear sound but do not know what it means
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