Vision and hearing

Question 1

2 layers of the retina

Answer 1

Pigmented layer

Neural layer

Question 2

What is contained within the neural layer of the retina

Answer 2

Rods + cones
Horizontal cells
Bipolar/connecting cells
Axons of ganglionic cells to optic nerve

Question 3

Function of pigmented retina layer

Answer 3

Contains melanin to absorb some light and reduce refraction within eye
Anchors photoreceptive cells

Question 4

Function of horizontal cells

Answer 4

Dampen amount of impulses to ganglion cells

Question 5

Causes of retinopathies

Answer 5

Hypertension

Diabetes

Question 6

What causes amaurosis fugax

Answer 6

TIA affecting central retinal or ophthalmic arteries

Question 7

Consequence of lesion at optic nerve

Answer 7

Lose nasal and temporal fibres of ipsilateral side so causes ipsilateral monocular blindness

Question 8

Causes of optic nerve lesion

Answer 8

Children: retinoblastoma, optic nerve glioma

Middle aged: optic sheath meningioma

Question 9

Describe pathway of nasal fibres

Answer 9

Represent temporal field of vision
Start medially from eye and cross over at the optic chiasm
Enter lateral geniculate nucleus of thalamus
Split into a superior and inferior
Enter primary visual cortex of occipital lobe

Question 10

Describe pathway of temporal fibres

Answer 10

Represent nasal field of vision
Start laterally from eye and remain ipsilateral
Enter lateral geniculate nucleus in thalamus
Split into superior and inferior
Enter primary visual cortex in occipital lobe

Question 11

Consequence of lesion at optic chiasm

Answer 11

Bitemporal hemianopia

Lose both nasal fibres so lose vision in both temporal fields

Question 12

Consequence of lesion at optic tract

Answer 12

Contralateral homonomous hemianopia
Lose ipsilateral temporal fibre and contralateral nasal fibre
Therefore you lose ipsilateral nasal field and contralateral temporal field of vision

Question 13

Causes of lesion at optic chiasm

Answer 13

Pituitary adenoma

Anterior communicating artery aneurysm

Question 14

Causes of lesion at optic tract

Answer 14

Stroke
Neoplasm
Trauma

Question 15

What lesion would causes a left lower quadratic anopsia

Answer 15

Right superior optic radiation lesion

Question 16

Where are the superior and inferior optic radiations

Answer 16

Superior in parietal lobe

Inferior in temporal lobe

Question 17

Blood supply to the macula and its significance to visual field defects

Answer 17

Posterior and middle cerebral artery

Stroke affecting posterior cerebral artery will damage most of the occipital lobe however the macula will be spared

Question 18

Describe frequency and magnitude of sound

Answer 18

Frequency - cycles per second in hertz

Magnitude - intensity of sound in decibels (more APs and more axons recruited)

Question 19

Components of the inner ear

Answer 19

Bony labyrinth containing perilymph
Membranous labyrinth containing endolymph
Organ of Corti

Question 20

Where are hair cells

Answer 20

Found in the organ of Corti which is the sensory area of the cochlear duct (part of membranous labyrinth)

OHC attach to the tectorial membrane (runs along length of organ of Corti)

Question 21

Describe inner and outer hair cells

Answer 21

Inner: move in response to movement of endolymph. They sense sound.
Outer: move in response to movement of basilar membrane. They amplify sound.

Question 22

What does the basilar membrane separate

Answer 22

Endolymph and perilymph

Question 23

Where do hair cells conduct signals to

Answer 23

Spiral ganglion afferents which go to cochlear division of CNVIII

Question 24

Composition of endolymph

Answer 24

High K+

Low Na+

Question 25

How is sound transducers to electrical impulses

Answer 25

Movement of endolymph bends stereocilia causing K+ influx into hair cell and depolarisation
This causes Ca+ influx leading to release of neurotransmitter to spiral ganglion afferents

Question 26

Where is the auditory cortex

Answer 26

Broadmans area in temporal lobe

Question 27

How to assess hearing loss

Answer 27

Otoscope
Audiograms - frequency vs sensitivity
Oteoacoustic emissions - amplifier function

Question 28

Causes of conductive hearing loss

Answer 28

Otosclerosis 
Otitis media 
Glue ear
Blockage
Ruptured tympanic membrane

Question 29

Causes of sensorineural hearing loss

Answer 29

Hair cell death/damage - gentamicin, loop diuretics, excessive noise
Acoustic neuroma
Auditory neuropathy

Question 30

Treatment for hearing loss

Answer 30

Hearing aids
Cochlear implants to stimulate primary neurones
Cochlear nucleus implants to stimulate secondary neurones