Anatomy of Auditory and Visual Pathways Flashcards
How many turns is the cochlea?
2.5
Long strings….
Low tone
think ‘L for L’
Short strings…
High tone
What cranial nerve is responsible for hearing?
CN VIII
Vestibulocochlea
Name the auditory ossicles of the middle ear.
Malleus
Incus
Stapes
Where are inner and outer hair cells found?
Organ of Corti
Describe the spiral ganglion.
Bipolar neurones stimulated by hair cells and carrying AP’s from Organ of Corti to cochlear nuclei in the pons
Input above what level of the spinal cord is bilateral? Why?
Input superior to the cochlear nuclei
Here, some fibres are crossed and some are not
What are the SUPERIOR OLIVARY NUCLEUS + NUCLEUS OF LATERAL LEMISCUS important for?
Important in sound localisation
Important as relays for stapedial and tensor tympany reflexes
Where is the primary auditory cortex located?
Laterally, just inferior to the lateral fissure
Where is tonotopic organisation present?
Auditory cortex
Where do fibres carrying information regarding low frequency sound end?
In the anterolateral part of the auditory cortex
Where do fibres carrying information regarding high frequency sound end?
In the posteromedial part of the auditory cortex
What is aphasia?
The inability to use language
Describe how a person may be affected by damage to Broca’s area.
Difficulty in producing language, often using few words and only saying the most important words in a sentence.
Do not usually have difficulty comprehending language.
Termed: Broca’s, motor or expressive aphasia
Describe how a person with damage to Wernicke’s area may present.
Difficulty comprehending language.
Can manifest defects ranging from words out of order to meaningless words.
Termed: Wernicke’s, sensory or receptive aphasia.
What does the maintenance of equilibrium use information from?
Vision.
Proprioception.
Vestibular apparatus (Labyrinth).
What CN is responsible for balance?
CN VIII - vestibular
What cranial nerves receive significant input from vestibular nuclei?
III, IV, VI
Describe what the projection of vestibular information onto the cerebral cortex is like.
Bilateral
Less well defined than for other senses
What do areas upon which vestibular information has been found to converge include?
An area of parietal cortex, just posterior to the area of the postcentral gyrus that represents the hand and mouth.
An area just rostral to the primary auditory cortex.
Posterior insular cortex
THERE IS NO REGION OF THE BRAIN THAT IS ACTIVATED JUST BY VESTIBULAR STIMULATION. What does this mean?
There is no primary vestibular cortex
Name the 3 ‘coats’ surrounding the eye?
Corneoclearal - OUTER
Choroid - MIDDLE
Retina - INNER
Because of the LENS, what happens to objects that are projected onto the retina?
They are UPSIDE down and REVERSED
Something that’s in the temporal visual field of the right eye is projected onto the nasal part of the right retina
TRUE
What does the optic tract ‘look’ at?
The contralateral visual field
After the optic chiasm, outline the pathway through which visual information flows
- Optic tract
- Lateral geniculate nucleus (of thalamus)
- Optic radiation
- Visual cortex
After the optic chiasm, all structures deal with information from?
The contralateral visual field
Where does the superior colliculi receive input from?
Visual cortex
Frontal eye fields
Spinal cord
What does the superior colliculi provide output to?
Nuclei of CN III, CN IV and CN VI
Motor nucleus of CN VII
Spinal cord
Where is the lower visual field projected?
To the gyrus superior to the calcarine sulcus
Where is the upper visual field projected to?
To the gyrus inferior to the calcarine sulcus
Where does the macular project to?
To the posterior pole of the visual cortex
Centre of vision….
Posterior
Lateral of vision….
Anterior
The macula occupies a much greater proportion of the cortex, relative to the size of the visual field it covers
TRUE
The right hemisphere receives information from the right visual lobe
FALSE
From the left visual lobe
What does the visual area above the calcarine sulcus receive retinal projections from?
The upper right retinal quadrant
What does the visual area below the calcarine sulcus receive retinal projections from?
The LOWER RIGHT retinal quadrant. (makes sense because receives info from the upper visual field which is interpreted by the lower part of the retina!!!)
What do fibres of the GENIOCALCARINE TRACT initially form?
Part of the internal capsule
What do the fibres of the geniocalcarine tract which carry information from the UPPER HALF of the visual field first do?
Loop ANTERIORLY around the TEMPORAL part of the LATERAL VENRICLE in Meyer’s loop, ending below the calcarine sulcus.
What both have roles in eye movement?
The visual cortex and the frontal eye fields
In general, the visual cortex provides for movements in response to what?
Visual stimuli e.g tracking a moving object
What do frontal eye fields control?
‘Movements of command’ - movements that are independent of a moving stimuli
Describe the pupillary light reflex.
Shine light into right eye:
Right pupil constricts = direct light reflex
Left pupil constricts = consensual light reflex
Where do perceptual fibres project BILATERALLY to?
The Edinger-Westphal nucleus
What does the accommodation reflex require?
Input to oculomotor and Edinger-Westphal nucleus from the visual cortex
What is the accommodation reflex?
Convergence of gaze, contraction of ciliarly muscles, pupillary constriction
If vision is lost in the same visual field in both eyes, what is this known as?
Homonymous
If vision is lost in different visual fields in each eye, what is it known as?
Heteronymous
What do association fibres do?
Connect cortical sites lying in the same hemispheres
What do commissural fibres do?
Connect one hemisphere to the other (usually areas of similar function)
What do projection fibres do?
Connect hemispheres to deeper structures, including thalamus, corpus striatum, brain stem and spinal cord