Neuroanatomy 5

Question 1

how many turns in the cochlea?

Answer 1

2.5 turn spiral

3 tubes turning together

Question 2

where is the organ of corti?

Answer 2

long ribbon of tissue between scala media and scala tympani on top of the basilar membrane
function = receptor for hearing includes inner and outer hair cells

Question 3

organization of the cochlea?

Answer 3

tonotopically organised
base = high pitched sounds
tip = low pitched sounds

Question 4

how sound travel to brain?

Answer 4

tectorial membrane vibrates on the stereocilia (hair cells) of the organ of corti which create APs which travel through the spiral ganglion where bipolar neurons are stimulated and carry the AP from organ of corti to the cochlear nuclei in the pons via vestibulocochlear nerve

Question 5

how do sound signals travel?

Answer 5

synapse at dorsal and ventral cochlear nuclei either side of the inferior cerebellar peduncle
superior to the nuclei, some fibres are crossed and some are not, therefore input above the level of the nuclei is bilateral
2nd order neurons then travel and synapse on the superior olivary nucleus
3rd order neurons travel and synapse on the inferior colliculus
4th order neurons travel and synapse at the thalamus at the medial geniculate body
5th order neurons then travel to specific area of the brain

Question 6

how is sound localised?

Answer 6

to do with timing of perception of sound - difference in time taken for sound to reach right vs left ear
superior olivary nucleus and nucleus of lateral lemniscus (band of white matter carrying auditory information up the brainstem) are involved

Question 7

where are auditory areas of the brain found?

Answer 7

upper, posterior part of temporal lobe
- just underneath lateral fissure
primary auditory complex = most superior
auditory association cortex (surrounds primary and extends backwards)

Question 8

how is the primary auditory cortex organized?

Answer 8

tonotopically
high frequencies = more posteromedial
low frequencies = more anterolateral

Question 9

what is aphasia?

Answer 9

inability to use language

• cant interpret incoming language (Wernicke’s/sensory/receptive aphasia - damage to Wernicke’s area)
• cant generate outgoing language (motor/expressive aphasia - due to damage in brocas area)

Question 10

association areas?

Answer 10

present adjacent to primary cortex areas

• important for making sense of incoming information
• larger than primary areas

Question 11

maintenance of equilibrium (balance) uses information from where?

Answer 11

vision
proprioception
vestibular apparatus (labyrinth)

Question 12

course of vestibular signalling?

Answer 12

signals to vestibular ganglion
cell bodies then project into the brainstem and synapse on vestibular nuclei
cell axons then project upwards to nuclei of oculomotor, trochlear and abducens nerves, thalamus, cerebellum and spinal cord

Question 13

where in the brain does vestibular information converge?

Answer 13

posterior to the area of postcentral gyrus representing hand and mouth
area rostral to primary auditory complex
posterior insular cortex

Question 14

layers of retina?

Answer 14

ganglions
amacrine cells
bipolar cells
horizontal cells
mullers cells
rods
cones
lamina vitrea
choroid

Question 15

how does light travel through the retina?

Answer 15

goes all the way through the layers to the photoreceptive cells (rods and cones) at the back
then travels back up (being partly processed by some cells on the way up) back to the ganglion
fibres of the ganglia converge to form the optic nerve and travel to the brain

Question 16

path of optic nerve?

Answer 16

optic tract > optic chiasm > lateral geniculate nucleus (bump on the back of the thalamus) > project back to the occipital lobe either side of the calcarine sulcus (this section called optic radiation)

Question 17

the optic tracts carry visual information from which visual fields?

Answer 17

right optic tract = left visual field
left optic tract = right visual field
this revered visual field representation persists until the visual cortex

Question 18

where else is visual information projected to?

Answer 18

superior colliculi

• for aiming the eyes, reflexes etc
• therefore people can be visually blind but still aim eyes correctly and maintain eye reflexes if these fibres are still intact

Question 19

where are the visual areas of the brain?

Answer 19

primary visual cortex = over calcarine sulcus at very back centre of occipital lobe
visual association cortex either side of this

Question 20

describe organisation between the macula and the visual cortex?

Answer 20

visual information received by the macula is projected to the posterior pole of the visual cortex and occupies a huge amount of space in the cortex relative to the size of the visual field perceived by the macula
this gives great acuity in centre of visual field

Question 21

what is Meyers loop?

Answer 21

fibres containing information from upper visual field (lower retina) has to take a large detour round the lateral ventricle on the way to the visual cortex

Question 22

types of eye movements?

Answer 22

tracking movements - controlled by the visual cortex, much smoother
movements of command - from frontal eye fields (motor cortex), jumpy movements

Question 23

describe the pupillary light reflex?

Answer 23

light activates optic nerve which synapses at the Edinger Westphal nucleus
oculomotor nerve travels from nucleus and synapses at ciliary ganglion which constricts pupillary constrictor muscle of iris
pupillary constriction is parasympathetic

Question 24

visual fields defects?

Answer 24

optic nerve = complete blindness in one eye
optic chiasm = bitemporal hemianopia
optic tract = homonymous hemianopia
optic radiation = homonymous hemianopia
occipital cortex = macular sparing,

Question 25

where is the primary gustatory area?

Answer 25

sits just above the lateral fissure

Question 26

what are the 3 types of fibres in white matter of the cerebral hemispheres?

Answer 26

association fibres - connect cortical sites in same hemispheres
commissural fibres - connect one hemisphere to other
projection fibres - connect hemispheres to deeper structures including thalamus, corpus striatum, brainstem and spinal cord