Vision and hearing Flashcards
2 layers of the retina
Pigmented layer
Neural layer
What is contained within the neural layer of the retina
Rods + cones
Horizontal cells
Bipolar/connecting cells
Axons of ganglionic cells to optic nerve
Function of pigmented retina layer
Contains melanin to absorb some light and reduce refraction within eye
Anchors photoreceptive cells
Function of horizontal cells
Dampen amount of impulses to ganglion cells
Causes of retinopathies
Hypertension
Diabetes
What causes amaurosis fugax
TIA affecting central retinal or ophthalmic arteries
Consequence of lesion at optic nerve
Lose nasal and temporal fibres of ipsilateral side so causes ipsilateral monocular blindness
Causes of optic nerve lesion
Children: retinoblastoma, optic nerve glioma
Middle aged: optic sheath meningioma
Describe pathway of nasal fibres
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
Describe pathway of temporal fibres
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
Consequence of lesion at optic chiasm
Bitemporal hemianopia
Lose both nasal fibres so lose vision in both temporal fields
Consequence of lesion at optic tract
Contralateral homonomous hemianopia
Lose ipsilateral temporal fibre and contralateral nasal fibre
Therefore you lose ipsilateral nasal field and contralateral temporal field of vision
Causes of lesion at optic chiasm
Pituitary adenoma
Anterior communicating artery aneurysm
Causes of lesion at optic tract
Stroke
Neoplasm
Trauma
What lesion would causes a left lower quadratic anopsia
Right superior optic radiation lesion
Where are the superior and inferior optic radiations
Superior in parietal lobe
Inferior in temporal lobe
Blood supply to the macula and its significance to visual field defects
Posterior and middle cerebral artery
Stroke affecting posterior cerebral artery will damage most of the occipital lobe however the macula will be spared
Describe frequency and magnitude of sound
Frequency - cycles per second in hertz
Magnitude - intensity of sound in decibels (more APs and more axons recruited)
Components of the inner ear
Bony labyrinth containing perilymph
Membranous labyrinth containing endolymph
Organ of Corti
Where are hair cells
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)
Describe inner and outer hair cells
Inner: move in response to movement of endolymph. They sense sound.
Outer: move in response to movement of basilar membrane. They amplify sound.
What does the basilar membrane separate
Endolymph and perilymph
Where do hair cells conduct signals to
Spiral ganglion afferents which go to cochlear division of CNVIII
Composition of endolymph
High K+
Low Na+
How is sound transducers to electrical impulses
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
Where is the auditory cortex
Broadmans area in temporal lobe
How to assess hearing loss
Otoscope
Audiograms - frequency vs sensitivity
Oteoacoustic emissions - amplifier function
Causes of conductive hearing loss
Otosclerosis Otitis media Glue ear Blockage Ruptured tympanic membrane
Causes of sensorineural hearing loss
Hair cell death/damage - gentamicin, loop diuretics, excessive noise
Acoustic neuroma
Auditory neuropathy
Treatment for hearing loss
Hearing aids
Cochlear implants to stimulate primary neurones
Cochlear nucleus implants to stimulate secondary neurones
