13. visual function and effect of ageing

bipolar cells

bipolar cells

cells in the retina which transmit impulses from photoreceptor cells to ganglion cells

blind spot

point at the back of the eye where optic nerve exits

cone cell

photoreceptor cell in retina that is responsible for colour vision

fovea

centre area of the macula that contains only cone cells

ganglion cells

cells in retina that transmit impulses from bipolar cells to brain

generator potential

depolarisation of receptor plasma membrane which reaches threshold and initiates action potential

infraction

tissue death caused by lack of blood supply

iodopsins

Photoreceptor proteins in cone cells

Macula

area of retina with most cone cells

rhodopsin

Photoreceptor protein in rod cells

rod cells

light sensitive photoreceptor cell in retina that functions in low light

transducers

sensory receptors that convert light to electrical energy

sclera

tough white outer layer containing collagen that protects the eye

choroid layer

layer behind retina which absorbs light, rich blood supply

retina

innermost layer containing photoreceptor cells

fovea centralis

area of retina with high concentration of cone cells for best visual acuity

optic nerve

bundle of neurones carrying impulses from eye to brain

blind spot

point where optic nerve exits and there is no photoreceptor cells

conjunctiva

protective layer at at front of eye kept moist by film of fluid

iris

coloured tissue at front of eye which controls light entering pupil by smooth muscle

pupil

black hole in centre which lets light in

cornea

clear part of sclera at front that covers iris and pupil which helps focus light

lens

stacks of long, narrow, transparent cells which focus light

ciliary body

muscle which holds lens and alters its shape

suspensory ligament

inelastic ligaments that attach ciliary muscle to lens

vitreous humour

gelatinous fluid within eye which exerts pressure outwards to maintain eye shape

aqueous humour

watery fluid in front of lens which helps maintain shape

conjunctivitis

inflammation or infection of a part of the eye where the blood vessels become dilated or haemorrhage appearing pink or red

dim light

more light let in, radial muscles contract, circular muscles relax, sympathetic nervous system

bright light

reduces light entering, radial muscle relax, circular muscle contract, parasympathetic nervous system

refracting surfaces of eye

cornea, front and back of lens

distant object

circular ciliary muscles relax, suspensory ligaments taut, lens pulled thin, less refraction of light

near object

circular ciliary muscles contact, suspensory ligaments slackened, lens bulge, more refraction of light m

myopia

elongated eyeball, light from distance focus in front of retina, treated with concave lens, laser eye surgery, or lens implant

types of cone cells

cells sensitive to red, blue or green

rod cell

longer photoreceptor cell

order of retina cells

optic nerve axons, ganglion cells, bipolar cells, photoreceptor cells, pigment epithelium

retinal

absorbs a photon of light and is converted to trans-isomer from cis-isomer. activates opsin

opsin

protein in rhodopsin with retinal

bleaching

when rhodopsin spits due to retinal changing isomers, reversed by re synthesis with ATP

ATP produced for re synthesis of rhodopsin

many mitochondria in inner segment of rod cells

vitamin A

vitamin needed to to re synthesise retinal into rhodopsin

iodopsin

photosynthesis pigment in cone cells which eolith absorbs red, green, or blue light

s cone

short wave light blue light - 420nm

m cone

medium wavelength green light - 543nm

l cone

long wavelength red light - 564nm

bipolar cells

synapse with many rod cells or single cone cell, and ganglion cell on other

summate

when many rod cells combine to depolarise bipolar neurone

glutamate

inhibitory neurotransmitter which causes the adjacent bipolar neurone to become hyper polarised

glutamate

causes ganglion neurone to become depolarised creating generator potential

visual acuity, colour vision, pupil response

3 aspects of eye tests

every 2 years

routine eye test carried out

snellen chart

letters chart, big to small, viewed at 6m, one eye covered

20/20 visual acuity

ability to ready letters 1cm high at 6m

near vision test

reading card with different size blocks of text at 30cm

presbyopia

near vision loss. lens is less flexible as older (40+) so less able to focus near objects

colour blindness

absence of one or more types of cone, recessive sex linked condition affecting makes more

protanopia

absence of red cone cells

deuteranopia

absence of defect in green cone cells

Ishihara colour vision test

individuals with colour blindness don’t see numbers, different colour combinations

Farnsworth-munsell 100 hue test

caps sorted into hue order, red, green, blue and yellow

optical coherence tomography

OCT, non invasive, beam of near infra red light, detects reflected light, scattered removed with interferometry, 3d image of retina, map and measure thickness

neurones die

loss of synaptic connections at about age 20

brain volume and mass

brain decrease by 10% at 90, frontal lobe and hippocampus effected most

thinner cortex

thins from age 20, due to loss of synaptic connections

white matter

decreases with age, leading to reduced speed of cognitive processing like memory, attention, action, problem solving, and decision making

ventricles

enlargement with age, more significant with dementia

neurotransmitters

effects memory due to less synthesis of receptor proteins and…

onset of dementia

age related memory loss is temper lapses of memory however severe disruptive loss indicates…

slow age related memory loss

regular exercise, manage stress, crosswords

worsen age related memory loss

smoking and alcohol

effect of ageing on reaction times

simple involuntary reflex, different ages, unpaired t test

presbycusis

age related hearing los, gradual from 18 years, loss of sensitive share cells in cochlea and neurone in auditory nerve

high frequencies

frequencies most effected by age related hearing loss

range of normal speech

autograph carried out between 250 and 8000Hz

normal hearing level

up to 25dB

glaucoma

tunnel vision, optic nerve damage, increased eye pressure as aqueous humour doesn’t drain, eye drops, laser, medication, or surgery

chronic open angle

drainage channels slowly come blocked, reduced visual field

acute closed angle

less common, rapid onset, pressure in eye pushes edge of iris against cornea blocking drainage channels

age related macular degeneration

ARMD, loss of central vision due to degeneration of macula, dry- debris from pigments not broken down, retina detaches, wet- blood vessels grow, laser treatment, strong glasses

cateracts

clouding of lens and loss of elasticity, blurred vision, worse in low light, denaturation and aggregation of lens proteins, age related, stronger glasses and brighter lights, replacement lens

alzheimers

degenerative disease of nerve system effecting frontal and temporal lobes

early Alzheimers

• minor memory loss eg names and location of objects

• suffers aware of memory loss

• long term memory intact

mid-stage Alzheimers

• personality changes, physical problems

• dependant on others for care

• no longer aware of memory loss

• impaired long term memory

late stage Alzheimers

• deterioration of personality

• loss of control over body functions

• total dependency on others

• speech severely effected

• inability to swallow and lead to death

multifactorial

disease with many factors contributing to it eg Alzheimers, effected by age and family history

abnormal break down of protein

B amyloid proteins are produced from myelin sheath which accumulate and form plaques around neurones causing them to degenerate and less neurotransmitter produced.

tau proteins

proteins which normally stabilise microtubules in cytoskeleton, defective ones aggregates forming neurofibrillary tangles in neurones. microtubules disintegrates and transport system collapse, less neurotransmitter, nerve dies

cholinergic

reduction in acetylcholine levels, most treatments based on this

amyloid

location of even for protein precursor on chromosome 21, links it to down syndrome. maybe derrivative called ADDLs that cause damage

tau

abnormalities in proteins cause neurofibrillary tangles interfering with microtubules and intracellular transport in neurones

acetylcholine inhibitors

use to prevent breakdown of acetylcholine to treat Alzheimers

carers activities

help with eating, washing, dressing, going to toilet

carers difficulties

financial cost, ability to work, distress, patients legal maters