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Human Physiology > 3,4 Vision > Flashcards

3,4 Vision Flashcards

1
Q

Define sensation ?

A

process initated by stimuli acting on sensory receptors

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2
Q

What are receptors ?

A

respond to stimuli by generating AP which propagat ealong thenerves to the spinal cord and brain .

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3
Q

What are senses ?

A

means by which the brain recieves sensory information about environment and body ;divided into 2 basic groups

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4
Q

Define general sense ?

A

include the somatic (touch,pain) and visceral senses (info about internal organs )

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5
Q

Define special senses ?

A

smell
taste
sight
balance
hearing

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6
Q

What does a sensation require ?

A
  1. stimulas
  2. receptor
  3. AP propagation to the CNS
  4. translation and processing of AP in CNS
  5. person is aware of stimulas/sensation (perception)
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7
Q

What are the accessory structures of the eye ?

A

eyebrows
eyelids
eyelashes
conjuctivia(thin transparent mucas membrane)
Lacrimal apparatus ( where tears are made )
Extrinsic eye muscles (6 attached to each eye)

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8
Q

What is the blink reflex ?

A

eyelids rapidly close and open –>protect eye,keep it lubricated

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9
Q

What are the 2 parts of conjuctivia ?

A
  1. Palpebral conjuctivia :covers the inner surface of eyelids
  2. Ocular/bulbar conjuctivia :covers the anterior surface of the eye (not over the cornea)
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10
Q

What is conjuctivitus ?

A

inflammation of the conjuctiva
causes are: bacterial or viral infection,allergens,physical irritants
comman agents :streptococcus pneumonia ,S sureus

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11
Q

What is the tunic ?

A

1 of the enveloping layers of a part a covering membrane

3 layers aka tunics

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12
Q

Where is the fibrous tunic (outer layer) located ?

A

consists of sclera and cornea

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13
Q

What is sclera made of and its function ?

A

firm outer white layer
dense collagenous connective tissue with eleastic fibres
maintains eyeball shape and protects its internal structures provides attachmnts point for muscles

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14
Q

What is the cornea made of and its function ?

A

avscular transparent window
connective tissue matrix ;epithelial tissue on either side
is part of the eyes focusing system :as light passes through the cornea –>bends or refracts

central part of cornea recieves oxygen from air
contact lenses must be permeable so air can reach cornea

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15
Q

What is the middle tunic ?

A

Vascular tunic consists of the choroid ,cillary body and iris

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16
Q
A
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17
Q

What is the choroid ?

A

the layer beneath the sclera
thin pigmented layer highly vascular

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18
Q

What is the cilliary body ?

A

continuos with the choroid ,+iris makes up the anterior region of vascualr tunic
attached to lens by zonular fiber
Cilliary muscles-act as sphincter=contraction alters shape of lens -focussing

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19
Q

What is the iris ?

A

coloured part of the eye
smooth muscle of iris determines pupil diameter/size thus controling much light enters the eyes
sphincter muscle-parasympathetic-decrease size
dilator pupillae- muscle contracts

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20
Q

What is the inner layer ?

A

nervous tunic
consists :retina
fovea centralis
optic disc

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21
Q

Function of retina ?

A

sensory region,retina layers
1. pigmented retina /epithelium:outer pigmented layer of choroid helps seperate sensory cells and reduce light scattering
Sensory retina :inner ,neural layer
1. Photoreceptors :rods & cones both sensitive to light
2. contains other neurons
bipolar,horizontal,amacrine
Final 2 layers contain retinal output :ganglion cells

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22
Q

Who processes light first ?

A

deepest layer of neurons processes first
PHOTORECEPTORS
only cells in retina that can convert light into nerve impuses .(AP)

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23
Q

What is seen when looking at an opthalmoscopic view of retina?

A

Macula lutea :’yellow’ spot found near centre of posterior retina in its centre is a pit ,fovea centralis
^ greatest visual acuity -photoreceptors are tightly packed :only cones
Optic Disc medial to macular :white spot
central retinal activity and vein enters ,exits respectively
Ganglion cell axon exits the eye ->form optic nerve
BLIND SPOT:no photoreceptors

24
Q

How many chambers are in the eye ?

A

3
anterior & smaller posterior chamber filled with aqueous humour ;located between cornea & iris
maintaining intraocular pressure
large vitreous chamber-filled with vitreous humour (jelly like) surrounded by retina ;its rate of production is much slower

25
Q

What is problem that can arise with pressure of the eye ?

think mum

A

Glaucoma
abnormal increase in the intraocular pressure so image formation is disrupted ;not clear image

26
Q

How is the introcular pressure maintained ?

balance between

A
  1. Aqueous humour forms by filtration from the capillaries in cilliary proces
  2. aqeous humour flows from the posterior chamber through the pupil into the anterior chamber some also flows through the vitreous humour
  3. Aqueous humour is reabsorbed into the venous blood by the sclera venous sinus

if there is an ibstruction in drainage =glaucoma

27
Q

What are the different types of glaucoma ?

A

Open angle glaucoma :outflow of aqeous humour is obstructed at trabecular meshwork or at canal of Schlemm (drainage issue)
Closed angle glaucoma :aqeous humour encounters resistance to fow through the pupil ;iris is displaced towards the cornea

usually 1st symptom is loss pf peripheral

28
Q

How does image formation form ?

A

light enters the eye via the cornea and pupil and is focussed onto the retina by the lens (light must also pass the humours :liquid medium

29
Q

What is refraction ?

A

bending of light occurs when light enters a medium of different density
greatest refraction occurs at cornea (convex)

30
Q

How are clear images focussed on the retina ?

A

When light strikes a convex surface the light rays converge ;eventually reach a poijnt at which they cross ->focal point
focussing :causing light rays to converge

image on retina is inverted –>upside down and reversed

31
Q

What is emmetropia ?

A

normal resting condition of lens
lens are flattened /oval shape nearly parallel rays from a distant object are focussed on retina

32
Q

What is accomodation ?

A

process of changing that shape of the lens so that image of a nearby object is brought into focus on retina
contraction of ciliary muscles
reduced tension of zonular->lens thicken :more spherical->greater refraction of light

33
Q

What is vision chart ?

A

eye test to read letters as letters decrease in size
if there is a defect detected -corrective lenses is prescribed
Myopia (short sighted)
Hyperropia/hypermetropia(far-sightedness)
Presbyopia and astigmatism

34
Q

Other ways to correct vision ?

A

Refractive and laser eye surgery
1. PRK: series of radiating corneal cuts–>flattens cornea
2. LASIK:thin portion of cornea etched away –>cornea less convex;laser reshapes underlying tissue
3. SMILE: femtosecond laser used to create a lenticule (lens shaped from tissue) within cornea ,which is then removed –>alters crneal shape

35
Q

What is the function of rods ?

A

function in low light ;used in night vision (scotopic vision)
non colour vision
monochromatic -1 pigment rhodopsin
high sensitivitty
low visual acuity (many rods converge to 1 ganglion cell)
more rods for every 1 cone
mostly in peripheral retina

36
Q

What is the function of cones ?

A

used during the day when ambient light levels are high
photopic vision–>responsible for high acuity and 3 colour vision
low sensitivity
high acuity(1 cone for 1 ganglion cell)
less numerous
motly in central retina -FOVEA

37
Q

How are the photoreceptors distributed ?

A

modest visual acuity
at periphery visual field :where rods predominate
convergance increases and thus visual acuity falls
rods have a high degree of convergence

visula field: area of space that can be seen at any instant of time

38
Q

What is the cause of macular degeneration ?

A

eading cause of blindness in adults over the age of 55:
age-related macular degeneration (AMD) is the most common type.

39
Q

How do photoreceptors absorp light ?

A

photopigment consist of membrane-bound proteins called opsins bound to chromophore molecule :retinal
retinol enzymatically transformed into 11 -cis retinal
Photopigments convert light into change in membrane potential

40
Q

What is night blindness ?

A

nyctalopia :rod fucntion is seriously affected
if from malnutrition most comman cause is prolonged vitamin A deficiency
take deficiency

41
Q

What is retinis pigmentosa ?

A

inherited,degenerative retinal diseases ;result in rod and then cone degeneration –>loss of periphereal ;night blindness
mutations in > 50 genes can rsult in this :,many forms

42
Q

What are cones responsible for ?

A

high acuity
colour vision
3 types of cones ;each photopigment sensitivew to light of particular wavelengths
red or L cones:long wavelength
green/M cones:medium
Blue/s cones:short

43
Q

What is colour perception ?

A

ability to discriminate between diff colours
depends on relative outposts of all 3 cones in response to incoming light and by higher-order processing

44
Q

How does colour blindness happen ?

A

Several types of defects in colour
vision that result from mutations
in the cone pigments.
* Most common form of colour
blindness (red-green blindness)
affects mainly men: 1 in 12.

45
Q

What is the mechanism for phototransduction ?

A
  1. Retinal ansorbs light and changes shape ,visual pigment activates
  2. Visual pigemnt activates transducin (G protein )
  3. Transducin activates phosphodiesterase (PDE)
  4. PDE converts cGMP causing cGMP levels to fall
  5. As cGMP levels fall -,cGMP-gated cation channels close resultingin hyperpolarisation
46
Q

How do the cGMP gated ion channels work ?

in the dark

A

dark -levels of cGMP are high
cGMP binds to interna, surface of cGMP gated cation channels so
channels open
cations enter
cell depolarises :membrane potential of dark-adapted photoreceptors is about -35-40mV so
increaseof neurotranmitters release

47
Q

How do cGMP channels work ?

in the light

A

levels of cGMP in photoreceptors are low
PDE break down cGMP
channels close
call hyperpolarises memebrane potential of light-adapted photoreceptors is about 70 mV
decrease neurotransmitter release

48
Q

What are ON bipolar cells ?

A

activated in the light so they depolarise
because glutamte binds to metabtropic glut\amte receptor :mGluR6

49
Q

What are OFF bipolar cells ?

A

inhibited in the light
in the dark tonic releases of glutamate excites these cells
because glutamate binds to an ionotropic glutamate receptor
iGlur:binding causes opening of ion channels

50
Q

How does retinal processaing of signals work ?

A

horizontal cells synapse with photoreceptors and bipolar cells to mediate lateral inhibition –>enhances stimulas location and contrast
amacrine cells modulatye information between bipolar and ganglion cells
centre:direct phtoreceptor input
surround: input from horizontal cells (mediate lateral inhibiton )

51
Q

What is receptive field ?

A

sensory range/space over which a receptor a receptor can respond ;it is the area of the retina ehen stimulated with light changes a cells membrane potential (Vm)

52
Q

What are the retinal ganglion cells receptive fields ?

A

Due to diff inputs fro bipolar cells pathways discussed
each ganglion cells receptive field has an inner core that responds differently than its surrounding area

53
Q

On-centre off-surround of the receptive field ?

A

ganglion cells discharge is higher when light shone on cenrtre of receptive field

54
Q

Off-centre on surround of receptive field ?

A

ganglion cells discharge is decreased when light shone on centre of receptive field (increase if on surround)
uniform light across field –>ganglion cells respond weakly

55
Q

How does visual pathway work ?

A

binocular vision
each cerebral hemisphere receive input from both eyes
-Have ipsilateral (same side)
contralateral (opposite) projection
central portion of the visual field allows for binocular vision
-3D representation of objects
important for depth perception

Human Physiology (11 decks)

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