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A - Biology > Topic 6B - Nervous co-ordination ARN * > Flashcards

Topic 6B - Nervous co-ordination ARN * Flashcards

neurones synaptic transmission muscle contraction

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1
Q

what are charges like when a neurone is in its resting state?

A

the outside of the membrane is positively charged compared to the inside, there are more positive ions outside
the membrane is polarised

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2
Q

what does it mean if the neurone membrane is polarised?

A

there’s a difference in charge (potential difference) across it

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3
Q

what is the resting potential?

A

the voltage across the membrane when it’s at rest

-70mV

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4
Q

how is the resting potential of a neurone created and maintained?

A

Na+/K+ pumps move 3 Na+ out for 2 K+ in
there is an open K+ channel which allows K+ to diffuse out of the membrane
this creates an electrochemical gradient, outside more positive than inside

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5
Q

how does the sodium potassium ion pump work?

A

they use active transport to move 3 Na+ out of the neurone for 2 K+ in
using ATP

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6
Q

how does the ‘leaky’ potassium ion channel work?

A

allow facilitated diffusion of K+ out of the neurone, down their concentration gradient

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7
Q

what are the steps of an action potential?

A 
stimulus
depolarisation
repolarisation
hyperpolarisation
resting potential
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8
Q

what does a stimulus do to cause an action potential?

A

excites neurone cell membrane, causing voltage gated Na+ channels to open
increasing permeability to Na+
Na+ diffuse into neurone down electrochemical gradient
inside of neurone less negative

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9
Q

what is depolarisation?

A

if potential difference reaches threshold (-55mV)
more voltage gated Na+ channels open
more Na+ diffuse rapidly into neurone

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10
Q

what is repolarisation?

A

when potential difference reaches +30mV Na+ channels close and K+ channels open
membrane more permeable to K+ so they diffuse out down concentration gradient.
returns membrane back to resting potential

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11
Q

what is hyperpolarisation?

A

K+ channels are slow to close so there’s a slight overshoot where too many K+ diffuse out of neurone
potential difference becomes more negative than resting potential

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12
Q

how is resting potential restored from hyperpolarisation?

A

ion channels are reset

Na+/K+ pump returns membrane to its resting potential

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13
Q

what is the refractory period?

A

Na+ channels closed during repolarisation
K+ channels closed during hyperpolarisation
another action potential can’t occur during this time because ion channels are recovering

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14
Q

what is a wave of depolarisation?

A

when an action potential happens, some Na+ that enter the neurone diffuse sideways, causing Na+ channels in the next region to open

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15
Q

what direction does the wave of depolarisation move in?

A

away from the parts of the membrane in the refractory period because they can’t have another action potential

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16
Q

why is the refractory period essential?

A

time delay between 1 action potential and next so:
action potentials don’t overlap, but pass along as discrete impulses
limit the frequency at which nerve impulses can be transmitted
action potentials are unidirectional

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17
Q

what is the all or nothing nature of action potentials?

A

once threshold is reached, an action potential will always fire wit the same change in voltage
if threshold isn’t reached, there’s no action potential

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18
Q

how is the size of a stimulus quantified if action potentials are all the same?

A

a bigger stimulus won’t cause a bigger action potential

it will cause them to fire more frequently

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19
Q

what does it mean if a neurone is myelinated?

A

it has a myelin sheath

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20
Q

what is a myelin sheath?

A

an electrical insulator

in the peripheral nervous system it is made of Schwann cells

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21
Q

what is between the schwann cells on a neurone?

A

tiny patches of bare membrane called nodes of ranvier

Na+ channels are concentrated at the nodes

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22
Q

what happens at the nodes of ranvier?

A

in a myelinated neurone, depolarisation only happens at the nodes of ranvier

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23
Q

what is saltatory conduction?

A

the neurone’s cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node
this is very fast

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24
Q

how do myelinated sheaths affect the speed of conduction of action potentials?

A

in non-myelinated neurones the impulse travels as a wave along the whole length of the axon membrane this is slower than saltatory conduction

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25
Q

what 3 factors affect the speed of conduction of action potentials?

A

myelination
axon diameter
temperature

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26
Q

how does axon diameter affect the speed of conduction of action potentials?

A

action potentials are conducted quicker along axons with bigger diameters

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27
Q

why are action potentials conducted quicker along axons with bigger diameters?

A

less resistance to flow of ions than in cytoplasm of smaller axon
less resistance = depolarisation reaches other parts of neurone cell membrane quicker
smaller SA: vol, fewer ions leak through K+ channels, membrane potential maintained better

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28
Q

how does temperature affect the speed of conduction of action potentials?

A

temperature increases = speed of conduction increases
ions diffuse faster
ATP gives energy to Na+/K+ carrier
until 40*C when proteins denature

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29
Q

what is a synapse?

A

the junction between a neurone and another neurone

or between a neurone and an effector cell

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30
Q

what is the synaptic cleft?

A

the tiny gap between the cells at a synapse

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31
Q

what is the presynaptic neurone?

A

the neurone before the synapse

it has a synaptic knob containing synaptic vesicles filled with chemicals called neurotransmitters

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32
Q

what happens when an action potential reaches the end of a neurone?

A 
Ca2+ channels open
Ca2+ diffuses synaptic knob
vesicles fuse to the presynaptic membrane
neurotransmitter released into synaptic cleft
they diffuse across
bind to specific receptors/ Na+ channels
Na+ diffuse in
depolarisation
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33
Q

what happens when neurotransmitters bind to receptors on the postsynaptic neurone?

A

they might trigger an action potential, cause a muscle contraction or cause a hormone to be secreted

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34
Q

how do synapses make sure impulses are unidirectional?

A

neurotransmitter only released from presynaptic neurone

receptors are only on the postsynaptic membranes

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35
Q

how is a response stopped from repeating at the synapse?

A

neurotransmitters are removed from the cleft so the response doesn;t keep happening
taken back into presynaptic neurone or broken down by enzymes

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36
Q

what is a common neurotransmitter?

A

acetylcholine (ACh)

used at cholinergic synapses

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37
Q

what happens when an action potential arrives at the synaptic knob in a cholinergic synapse?

A

AP arrives at synaptic knob
voltage-gated Ca2+ channels in neurone open
Ca2+ diffuse into synaptic knob

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38
Q

what do the calcium ions do at the cholinergic synapse?

A

influx of Ca2+ causes synaptic vesicles to fuse to membrane

vesicles release ACh into cleft in exocytosis

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39
Q

what does the acetylcholine do once is has been released into the cholinergic synapse cleft?

A

ACh diffuses across cleft and binds to specific cholinergic receptors on postsynaptic neurone
Na+ channels open
influx of Na+ causes depolarisation
AP generated if threshold reached

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40
Q

what happens after the postsynaptic neurone has generated an action potential at the cholinergic synapse?

A

ACh removed from synaptic cleft so response doesn’t keep happening
its broken down by an enzyme called acetylcholinesterase and the products are reabsorbed by presynaptic neurone to make more ACh

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41
Q

what are excitatory neurotransmitters?

A

they depolarise the postsynaptic membrane, making it fire an action potential if threshold is reached
e.g. acetylcholine at cholinergic synapses in the CNS

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42
Q

what are inhibitory neurotransmitters?

A

they hyperpolarise the postsynaptic membrane, preventing it from firing an action potential
e.g. ACh at cholinergic synapses in the heart open K+ channels

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43
Q

what is summation?

A

where the effect of neurotransmitter released from many neurones is added together

44
Q

what are the 2 types of summation?

A

spatial summation

temporal summation

45
Q

what is spatial summation?

A

many neurones connect to 1 neurone
small amount of neurotransmitter released from each altogether can reach threshold in postsynaptic neurone to trigger/ inhibit an action potential

46
Q

what is temporal summation?

A

2 or more nerve impulses arrive in quick succession from the same presynaptic neurone
an action potential is more likely because more neurotransmitter is released into synaptic cleft

47
Q

what is a neuromuscular junction?

A

a synapse between a motor neurone and a muscle cell

48
Q

what neurotransmitter do neuromuscular junctions use?

A

ACh, which binds to nicotinic cholinergic receptors

49
Q

how do neuromuscular junctions work differently to a cholinergic synapse between 2 neurones?

A

postsynaptic membrane has lots of folds that form clefts. these clefts store AChE
postsynaptic membrane has more receptors than other synapses
ACh always excitatory at neuromuscular junction

50
Q

how can drugs affect synaptic transmission?

A 
agonists 
antagonists
inhibit breakdown of neurotransmitters
stimulate release of neurotransmitter
inhibit release of neurotransmitter
51
Q

what are agonists?

A

drugs that are the same shape as neurotransmitters so they mimic their action at receptors
more receptors are activated

52
Q

what are antagonists?

A

drugs that block receptors so they can’t be activated by neurotransmitters
fewer receptors can be activated

53
Q

what do drugs that inhibit breakdown of neurotransmitters do?

A

drugs that inhibit the enzyme that breaks down neurotransmitters
means there are more neurotransmitters in the synaptic cleft to bind to receptors and they’re there for longer

54
Q

what affect do drugs that stimulate the release of neurotransmitter from presynaptic neurone have?

A

more receptors are activated

55
Q

what do drugs that inhibit release of neurotransmitter do?

A

fewer receptors are activated

56
Q

what is skeletal muscle?

A

the type of muscle used to move

attached to bones by tendons

57
Q

what do ligaments do?

A

they attach bones to other bones to hold them together

58
Q

how do we move?

A

pairs of skeletal muscles contract and relax to move bones at a joint
bones are incompressible so act as levers, giving the muscle something to pull against

59
Q

what are antagonistic pairs?

A

muscles that work together to move a bone
agonist - contracting muscle
antagonist - relaxing muscle

60
Q

what is skeletal muscle made up of?

A

large bundles of long cells called muscle fibres

61
Q

what is the cell membrane of a muscle fibre cell called?

A

sarcolemma

62
Q

what is the cytoplasm of a muscle fibre cell called?

A

sarcoplasm

63
Q

what are the holes in the muscle fibre made from the sarcolemma folding inwards called?

A

transverse tubules

T tubules

64
Q

what do T tubules do?

A

they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre

65
Q

what is the sarcoplasmic reticulum?

A

a network of internal membranes that run through the sarcoplasm

66
Q

what does the sarcoplasmic reticulum do?

A

it stores and releases calcium ions that are needed for muscle contraction

67
Q

why do muscle fibres contain lots of mitochondria?

A

to provide the ATP that’s needed for muscle contraction

68
Q

what are some properties of muscle fibres?

A

they have lots of mitochondria
they are multinucleate
they contain myofibrils

69
Q

what does multinucleate mean?

A

they contain many nuclei

70
Q

what are myofibrils?

A

long, cylindrical organelles

made up of proteins and are highly specialised for contraction

71
Q

what do myofibrils contain?

A

thick and thin myofilaments

72
Q

what are thick myofilaments made of?

A

myosin

73
Q

what are thin myofilaments made of?

A

actin

74
Q

what does a myofibril look like under a microscope?

A

it looks stripy
it is dark where the myofibrils over lap - A-band
it is light in places where there is only 1 myofibril
I-bands = only thin actin filaments
H-zone = only myosin

75
Q

what are myofibrils made up of?

A

many short units called sarcomeres

76
Q

what does a sarcomere contain?

A

the ends are marked with a Z-line with actin attached

in the middle there is an M-line which is the middle of the myosin filaments

77
Q

what happens when sarcomeres contract?

A

myosin filaments pull actin inwards

78
Q

what do myosin filaments have?

A

globular heads that are hinged so they can move back and forth

79
Q

what does each myosin head have?

A

a binding site for actin

a binding site for ATP

80
Q

what does actin have that allows myosin to move along it?

A

actin-myosin binding sites

tropomyosin is another protein wrapped around actin which has to move out of these binding sites

81
Q

what does tropomyosin do in resting muscle?

A

the actin-myosin binding site is blocked by tropomyosin
myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments

82
Q

what happens when an action potential from a motor neurone stimulates a muscle cell?

A

it depolarises the sarcolemma, depolarisation spreads down the T-tubules o the sarcoplasmic reticulum

83
Q

what happens when the sarcoplasmic reticulum is depolarised?

A

it releases stored calcium ions into sarcoplasm

84
Q

what do calcium ions do to tropomyosin?

A

Ca2+ bind to protein attached to tropomyosin, causing it to change shape, pulling tropomyosin out of actin-myosin binding site
meaning an actin-myosin cross bridge can be formed

85
Q

what does calcium do in the sarcomere?

A

bind to tropomyosin

activate ATP hydrolase

86
Q

what do myosin heads do in a muscle contraction?

A

when myosin binds to tropomyosin it changes shape and releases ADP, causing myosin head to swivel, pulling actin inwards - power stroke
ATP binds to myosin breaking cross bridge
ATP hydrolysed by ATPase region of myosin head, causing it to recock ready for next power stroke

87
Q

what happens when a muscle stops being stimulated?

A

Ca2+ leave binding sites and are moved by active transport back into sarcoplasmic reticulum
tropomyosin moves back into actin-myosin binding sites
actin filaments slide back to relaxed position

88
Q

how is ATP generated for muscle contractions?

A

aerobic respiration
anaerobic respiration
ATP-Phosphocreatine system

89
Q

how does aerobic respiration provide ATP for muscle contractions?

A

most ATP is generated via oxidative phosphorylation in the cell’s mitochondria
only works when oxygen is present

90
Q

how does anaerobic respiration provide ATP for muscle contractions?

A

ATP made rapidly by glycolysis

lactate can quickly build up in muscles and cause muscle fatigue

91
Q

how does PCr system provide ATP for muscle contractions?

A

ATP made by phosphorylating ADP adding phosphate group from PCr
PCr stored inside cells and system generates ATP very quickly
PCr runs out after a few seconds
system is anaerobic and alactic

92
Q

what does alactic mean?

A

doesn’t form any lactate

93
Q

what 2 types of muscle fibre are skeletal muscles made up of

A

slow twitch

fast twitch

94
Q

what are the properties of slow twitch muscle fibres?

A

contract slowly
less powerful contractions
used for posture
good for endurance
work for a long time without getting tired
slow release energy from aerobic respiration, lots of mitochondria and blood vessels
red - lots of myoglobin

95
Q

what are the properties of fast twitch muscle fibres?

A

more powerful, rapid contractions
intense activities
thicker and more myosin filaments
high glycogen conc. to hydrolyse into glucose for anaerobic respiration
high conc. of enzymes for anaerobic respiration
phosphocreatine stores - rapid ATP synthase in anaerobic conditions

96
Q

what is the nervous system?

A 
communication via nerve impulses
transmission by neurones
rapid transmission
impulse sent to specific body parts
response is localised, rapid, short lived
effect is temporary and reversible
97
Q

what is the hormonal system?

A

communication via hormones
transmission through blood
slower transmission
hormones travel around whole body, only target cells respond
response is widespread, slow, long lasting
effect may be permanent and irreversible

98
Q

what is a nerve impulse?

A

a self propagating wave of electrical activity that travels along an axon membrane

99
Q

how is a generator potential produced?

A

stretch mediated sodium ion channel opened
sodium ions diffuse into axon
depolarisation (generator potential) occurs in this region of the axon
this depolarisation propagates across the neurone via a series of action potentials

100
Q

what happens in a nerve impulse?

A

generator potential causes voltage gated Na+ channel proteins to open
Na+ diffuse into axon - depolarisation
if threshold reached, more Na+ channels open
action potential reached at +40mV
voltage gated Na+ channels close, K+ channels open
K+ diffuse out of axon - repolarisation
overshot of K+ - hyperpolarisation
voltage gated K+ channels close and Na+?K+ pump re-establishes resting potential - repolarisation

101
Q

what does the synaptic knob contain?

A

vesicles containing neurotransmitter (ACh)
voltage gated Ca2+ channel proteins
smooth ER - store Ca2+
mitochondria

102
Q

what is the purpose of synapses?

A

make sure action potentials unidirectional
single stimulus can initiate multiple responses - relay neurones have multiple axons
increase sensitivity to stimuli by spatial summation
allow weak stimuli to be filtered out - temporal summation

103
Q

what is epilepsy?

A

an inability to regulate action potentials in brain neurones to prevent over excitation

104
Q

how do inhibitory neurones work?

A

AP arrives at synaptic knob
Ca2+ channel proteins open and Ca2+ diffuses in
vesicles fuse to membrane and release inhibitory neurotransmitter
they diffuse across cleft and bind to K+ and Cl- channels in postsynaptic membrane
loss of K+ and gain of Cl- via diffusion results in more negative resting potential
making it more difficult to reach threshold, and preventing APs

105
Q

what purpose does ATP have in muscular contractions?

A

providing energy for:
breaking actin-myosin cross-bridges
re-cocking myosin heads for the power stroke

106
Q

what purpose do calcium ions have in muscular contractions?

A

activating ATPase

altering tropomyosin tertiary structure to expose myosin binding sites of actin filaments

107
Q

what happens in muscle relaxation?

A

nervous stimulation ceases
Ca2+ is actively transported back into the sarcoplasmic reticulum
energy from ATP used to do this
tropomyosin blocks myosin binding sites on actin filaments
myosin can’t bind so contraction ceases
antagonistic muscle can pull actin and myosin filaments apart

A - Biology (21 decks)

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