Anatomy of the Auditory and Visual Pathways Flashcards
Where are the organs of hearing and balance located?
In the inner ear within the temporal bone
What nerve is responsible for hearing?
Cochlear nerve = CN VIII
What does the organ of Corti contain?
Outer and inner hair cells
What does the spiral ganglion contain?
Bipolar neurons stimulated by hair cells and carrying APs from organ of Corti to cochlear nuclei of pons
Why is input above the cochlear nuclei essentially bilateral?
Some fibres are crossed and some are not
What are the superior olivary nucleus and nucleus of the lateral lemniscus important in?
Sound location and as relays for stapedial and tensor tympani reflexes
Where is the auditory cortex located?
Medial geniculate nucleus of the thalamus
What is Wernicke’s area known as?
Auditory association cortex
What kind of organisation is present in the auditory cortex?
Tonotopic organisation
Where do fibres carrying low frequency sound information end?
In the anterolateral part of the auditory cortex
Where do fibres carrying high frequency sound information end?
In the posteromedial part of the auditory cortex
What is aphasia?
Inability to use language
What are the potential mechanisms for aphasia?
Damage to Broca’s area or to Wernicke’s area
What are some features of aphasia caused by damage to Broca’s area?
Also termed motor or expressive aphasia
Have difficulty in producing language
Do not usually have difficulty comprehending language
What are some signs of expressive aphasia?
Often use few words
Only say most important word in a sentence
What are some features of aphasia caused by damage to Wernicke’s area?
Also known as sensory or receptive aphasia
Have difficulty comprehending language
Can say words out of order or meaningless words
What does maintenance of balance require?
Uses info from vision, proprioception and the vestibular apparatus
What nerve is responsible for balance?
Vestibular nerve = CN VIII
What are the connections of the vestibular nuclei?
Thalamus, cerebellum and spinal cord
Nuclei of CNs III, IV and VI
How is vestibular info projected onto the cerebral cortex?
Bilaterally = less well defined than for other senses
What are the areas that vestibular info has been found to converge?
Area of parietal cortex just posterior to area of postcentral gyrus that represents hand and mouth
Area just rostral to primary auditory cortex
Posterior insular cortex
Is there an agreed region of the brain responsible for vestibular stimulation?
No
What causes objects to be projected onto the retina reversed and upside down?
The lens
Where would something present in the temporal visual field of the right eye be projected onto?
The nasal part of the right retina
Where does each optic tract look?
At the contralateral visual field
What makes up the visual pathway?
Optic tract, lateral geniculate nucleus, optic radiation, visual cortex
Where is the lateral geniculate nucleus located?
In the visual cortex of the thalamus
Where is the primary visual cortex located?
Posterior pole of the occipital lobe
Where is the lower visual field projected?
To the gyrus superior to the calcarine sulcus
Where is the superior visual field projected?
To the gyrus inferior to the calcarine sulcus
Where does the macula project?
Posterior pole of the visual cortex = occupies a much greater proportion of cortex relative to the size of the visual field it covers
What do the fibres of the geniculocalcarine tract form initially?
Part of the internal capsule
What happens to fibres of the geniculocalcarine tract that are carrying visual info from the upper half of the visual field?
First loop anteriorly around the temporal part of the lateral ventricle in Meyer’s loop = ends below the calcarine sulcus
How does the visual cortex relate to eye movements?
Provides movements in response to visual stimuli
What movements does the frontal eye field control?
Movements of command = movements that are independent of moving visual stimuli
What are some characteristics of different eye movements?
Tracking movements tend to be smooth
Movements of command tend to be jumpy (saccadic)
What happens in the pupillary light reflex?
Direct light reflex = pupil of eye light is shone into constricts
Consensual light reflex = other pupil constricts
How do pretectal fibres project into the Edinger-Westphal nucleus?
Bilaterally
What does the accommodation reflex require?
Input to oculomotor and Edinger-Westphal nucleus from the visual cortex
What is an hemianopia?
Blindness for half the field of vision in one or both eyes
What is a homonymous visual defect?
Vision lost in same visual field in both eyes
What is a heteronymous visual defect?
Vision lost on different visual fields in each eye?
What is a dominant hemisphere?
Hemisphere that take the lead in a higher function, despite both hemispheres receiving similar inputs
What functions is dominance high for?
Language functions
For truly right handed people, what hemisphere is usually dominant for language?
The left hemisphere
How are fibres in the white matter classified?
By origin and destination
What are association fibres of white matter?
Connect cortical sites lying in the same hemisphere
What are commissural fibres of white matter?
Connect one hemisphere to the other = usually connecting areas of similar function
What are projection fibres of white matter?
Connect hemispheres to deeper structures including the thalamus, corpus striatum, brainstem and spinal cord
