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biology A2-1 > the eye and muscle > Flashcards

the eye and muscle Flashcards

1
Q

conjunctiva

A

thin transparent membrane covering cornea
protects cornea from damage

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2
Q

sclera

A

tough opaque connective tissue covering the eye
protects against damage
site of attachment to muscle

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3
Q

cornea

A

front transparent part of scelera
most REFRACTION of light occurs here

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4
Q

aqueous humor

A

transparent watery fluid between cornea and lens
maintains shape of front part of eye

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5
Q

iris

A

muscular layer that contains both circular and radial muscle
contains pigment that absorbs light
adjusts size of pupil to control amount of light entering eye

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6
Q

pupil

A

gap within the iris
area through which light reaches the lens and enters the center of the eye

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7
Q

ciliary body

A

contains a muscular ring of muscle around the eyes.
adjusts to shape of lens to focus light rays

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8
Q

suspensory ligament

A

ligaments that connect ciliary body to the lens and hold it in place
transfers tension in the walls of the eyeball ball to make the lens thinner
important when focusing on distant objects

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9
Q

lens

A

transparent biconcave structure
refracts light and focuses light rays on retina

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10
Q

vitreous humour

A

transparent jelly like material between lens and back of eye
maintains shape of rear part of eye and supports lens

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11
Q

retina

A

innermost layer of the eyeball containing light sensitive receptor cells
when stimulated rods and cones initiate impulses in associated neurones

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12
Q

fovea

A

region in the center of the retina that is particularly rich in cones and DOES NOT contain rods
part of the eye that give the clearest daylight colour vision

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13
Q

choroid

A

a layer of pigmented cells between retina and sclera
contains blood vessels that supply retina
prevent reflection of light through eye

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14
Q

optic nerve

A

bundle of sensory nerve fibres that leave the retina
transmit impulses from retina to brain

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15
Q

blind spot

A

part of the retina where the sensory neurones that unite form the optic nerve
contains no light sensitive cells and so is not sensitive to light

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16
Q

how does the eye focus on distant objects

A

less refraction light arrives parallel
ciliary muscle relaxes
suspensory ligament is taut
lens pulled thin

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17
Q

how does eye focus on close objects

A

more refraction light rays diverge
ciliary muscles contract
suspensory ligament slack
lens is fat

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18
Q

what happens to eye in low light intensity

A

radial muscle contracts
circular muscle relaxes which makes pupil larger to allow more light to enter (maximum stimulation of photoreceptor cells)

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19
Q

what happens to the eye in bright light

A

circular muscle contracts
radial relaxes to make pupil smaller preventing damage to photoreceptor cells in retina

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20
Q

what are rod and cone cells and where are they located

A

specialised photoreceptor cells- light energy brings about a change in levels of polarisation of membrane
they convert light stimulus to a nerve impulse in their associated neurones
they are located in the retina

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21
Q

describe how rod cells are adapted for their function

A

-contain a light sensitive pigment called rhodopsin
-which is packed into an array of membranes in the outer part of rod cell
-Rhodopsin is formed from a protein called opsin, combined with a light absorbing compound called retinal which is derrived from vitamin A
when stimulated by light rhodopsin breaks down into those components.
they are adapted for vision in low light intensity
thy have high sensitivity as rhodopsin will break down readily in low light levels
provide monochromatic vision

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22
Q

how are cone cells adapted for their function

A

contains pigment iodopsin
this is less readily broken down
provides coloured vision
iodopsin exists in 3 forms red blue and green (aka trichromatic theory of colour vision)

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23
Q

how is rhodopsin resynthesised in rods

A

using the apt in mitochondria to resynthesise opsin and retinal

24
Q

how are rod cells adapted in low light intensity

A

they have high sensitivity as rhodopsin will break down readily in low light levels so requires only a small amount of light to do so

25
what happens to the rods in bright light
virtually all the rhodopsin is broken down (bleached) and it takes time for it to be resynthesised this is why if we move from a well lit room to a dark room our vision is initially poor but gradually improves (aka dark adaptation)
26
what happens when rhodopsin is broken down
it changes the membrane potential of the rid cell and creates a generator potential if a threshold level is reached this can cause adjacent linking neurone to become depolarised to the extent that it will conduct an action potential
27
what is a generator potential
the degree of depolarisation a stimulated receptor can produce
28
how do we see pure red light
it will only stimulate and ‘break down’ the red iodopsin red cones will fire impulses to the brain
29
how do we see orange light
orange light will stimulate red and green cones (more red) so the brain will interpret this as orange
30
how are rods and cones arranged in retina
rods and cones form a layer immediately inside choroid a layer of bipolar neurones lie immediately inside photosensitive cells and beyond is a layer of sensitive ganglion cells
31
what are ganglion cells
sensory cells it is the axons of the ganglion cells that group together to make up optic nerve that carries impulse from retina to brain
32
what is high visual acuity
the ability of cones and rods to provide highly precise colour vision of high resolution
33
compare and contrast rods v cones
rods - cones + -stimulated in low light intensity +stimulated in high light intensity -retinal convergence +no summation - high sensitivity +low sensitivity -low visual acuity +high visual acuity
34
what is retinal convergence
a number of rods synapse with common bipolar neurones (and a number of bipolar cells synapse with common ganglion cells) this allows generator potential from individual rods to combine together (summation) and reach the threshold required for producing an action potential in bipolar neurones
35
why do rods have low visual acuity
the light energy reaching any one rod is not enough to stimulate the bipolar cells sufficiently
36
why does arrangement of photosensitive cells in the retina seem less effective
light rays must pass through layers of neurones before reaching the light sensitive cells as it is ‘inverted’
37
describe the distribution of rods and cones in the retina (eg. left eye)
more rods at the rhs of retina compared to the left this allows peripheral vision on the lhs the distribution explains the phenomena such as blind spots and why we can distinguish shapes but not colour at the periphery ie why light rays are focused on the edge of the retina
38
what is binocular vision/ stereoscopic vision
if the two eyes create a single image it allows accurate judgement of distance (stereoscopic vision ability to form 3D images is also possible)
39
why is skeletal muscles described as voluntary muscle but cardiac and smooth are described as involuntary
skeletal muscle is voluntary as it is under conscious control cardiac muscle is myogenic and smooth muscle is involuntary as they are automatic reflex reactions
40
what is the differ between muscle fibres and myofibrils
myofibrils are highly specialised contractile units that make up the bulk of muscle fibres muscle fibres are large structures that bunch together and contain organelles and are particularly rich in mitochondria
41
what causes light and dark bands in skeletal muscles
thicker myosin filaments form denser or darker striations and thinner actin filaments form less dense or lighter regions
42
describe the structure of a myofibril
myofibril consists largely of two types of proteins (myosin and actin) myosin form thick filaments around 15nm in diameter and actin forms thin filaments around 7nm in diameter myosin filaments lie in the center region of each contractile unit and our linked together by a thin disc (m line) that runs perpendicular to the orientation of myosin filaments. the actin filaments slot between the outer edges of the myosin filaments and they are also held together by a thin disc(z line) a section of myofibrils between two z lines (basic contractile units) is called a sarcomere
43
describe the structure of muscle fibres
each fibre is surrounded by a cell surface membrane called the sarcolemma each fibre is multinucleate with each nuclei typically arranged inside the sarcolemma each fibre is effectively a specialised cell and contains cell organelles found in any cell but is particularly rich in mitochondria at intervals the sarcolemma fold deeply inwards to form t tubules the cytoplasm of the cell are the sarcoplasm the bulk of the muscle fibre is filled with highly specialised myofibrils
44
what determines strength of muscle contraction
hoe long the muscle is stimulated for but also how many muscle fibres are actually stimulated and contracting
45
what is the m line
a thin disc that runs perpendicular to the orientation of myosin filaments
46
what is the z line
a thin disc that runs perpendicular to the orientation of actin filaments and holds then together
47
what is a sarcomere
a section of myofibrils between two z lines (ie basic contractile units)
48
what is the A band
the part of the myofibril that contains myosin it includes the areas where the thinner actin penetrates between myosin filaments ANISOTROPIC band
49
what is the i band
part of the myofibril containing actin only ISOTOPIC band
50
what is the H zone
zone in the middle of the A band that contains myosin only
51
describe the A band
DARK
52
how does parts change in muscle CONTRACTION
sarcomere shortens, H zone shortens, I band shortens
53
describe skeletal muscles
-striated multinucleate fibres -attached to the bone throughout the body -voluntary control
54
describe smooth muscle
-discrete multinucleate cells are SPINDLE shaped (non striated) -lining gut and blood vessels, iris and ciliary body in the eye -involuntary or automatic reflex action
55
describe cardiac muscle
-striated but branched with intercalated discs between cells -uninucleate -wall of heart -myogenic and involuntary control
56
what are the similarities and differences between cardiac and skeletal muscles
-both striated but cardiac are branched -skeletal is voluntary, cardiac is myogenic -skeletal is multinucleate, cardiac is uninucleate -cardiac is attached at walls of heart, skeletal is attached to bone throughout body
57
what are similarities and differences between smooth and skeletal muscles
-smooth is uninucleate and spindle shape, skeletal is multinucleate and striated -smooth line the gut and blood vessels and are in the iris and ciliary body, skeletal is attached to bone throughout body -smooth involuntary control, skeletal voluntary control

biology A2-1 (4 decks)

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