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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

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
what 3 factors affect the speed of conduction of action potentials?
myelination axon diameter temperature
26
how does axon diameter affect the speed of conduction of action potentials?
action potentials are conducted quicker along axons with bigger diameters
27
why are action potentials conducted quicker along axons with bigger diameters?
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
28
how does temperature affect the speed of conduction of action potentials?
temperature increases = speed of conduction increases ions diffuse faster ATP gives energy to Na+/K+ carrier until 40*C when proteins denature
29
what is a synapse?
the junction between a neurone and another neurone | or between a neurone and an effector cell
30
what is the synaptic cleft?
the tiny gap between the cells at a synapse
31
what is the presynaptic neurone?
the neurone before the synapse | it has a synaptic knob containing synaptic vesicles filled with chemicals called neurotransmitters
32
what happens when an action potential reaches the end of a neurone?
``` 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 ```
33
what happens when neurotransmitters bind to receptors on the postsynaptic neurone?
they might trigger an action potential, cause a muscle contraction or cause a hormone to be secreted
34
how do synapses make sure impulses are unidirectional?
neurotransmitter only released from presynaptic neurone | receptors are only on the postsynaptic membranes
35
how is a response stopped from repeating at the synapse?
neurotransmitters are removed from the cleft so the response doesn;t keep happening taken back into presynaptic neurone or broken down by enzymes
36
what is a common neurotransmitter?
acetylcholine (ACh) | used at cholinergic synapses
37
what happens when an action potential arrives at the synaptic knob in a cholinergic synapse?
AP arrives at synaptic knob voltage-gated Ca2+ channels in neurone open Ca2+ diffuse into synaptic knob
38
what do the calcium ions do at the cholinergic synapse?
influx of Ca2+ causes synaptic vesicles to fuse to membrane | vesicles release ACh into cleft in exocytosis
39
what does the acetylcholine do once is has been released into the cholinergic synapse cleft?
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
40
what happens after the postsynaptic neurone has generated an action potential at the cholinergic synapse?
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
41
what are excitatory neurotransmitters?
they depolarise the postsynaptic membrane, making it fire an action potential if threshold is reached e.g. acetylcholine at cholinergic synapses in the CNS
42
what are inhibitory neurotransmitters?
they hyperpolarise the postsynaptic membrane, preventing it from firing an action potential e.g. ACh at cholinergic synapses in the heart open K+ channels
43
what is summation?
where the effect of neurotransmitter released from many neurones is added together
44
what are the 2 types of summation?
spatial summation | temporal summation
45
what is spatial summation?
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
what is temporal summation?
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
what is a neuromuscular junction?
a synapse between a motor neurone and a muscle cell
48
what neurotransmitter do neuromuscular junctions use?
ACh, which binds to nicotinic cholinergic receptors
49
how do neuromuscular junctions work differently to a cholinergic synapse between 2 neurones?
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
how can drugs affect synaptic transmission?
``` agonists antagonists inhibit breakdown of neurotransmitters stimulate release of neurotransmitter inhibit release of neurotransmitter ```
51
what are agonists?
drugs that are the same shape as neurotransmitters so they mimic their action at receptors more receptors are activated
52
what are antagonists?
drugs that block receptors so they can't be activated by neurotransmitters fewer receptors can be activated
53
what do drugs that inhibit breakdown of neurotransmitters do?
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
what affect do drugs that stimulate the release of neurotransmitter from presynaptic neurone have?
more receptors are activated
55
what do drugs that inhibit release of neurotransmitter do?
fewer receptors are activated
56
what is skeletal muscle?
the type of muscle used to move | attached to bones by tendons
57
what do ligaments do?
they attach bones to other bones to hold them together
58
how do we move?
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
what are antagonistic pairs?
muscles that work together to move a bone agonist - contracting muscle antagonist - relaxing muscle
60
what is skeletal muscle made up of?
large bundles of long cells called muscle fibres
61
what is the cell membrane of a muscle fibre cell called?
sarcolemma
62
what is the cytoplasm of a muscle fibre cell called?
sarcoplasm
63
what are the holes in the muscle fibre made from the sarcolemma folding inwards called?
transverse tubules | T tubules
64
what do T tubules do?
they help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
65
what is the sarcoplasmic reticulum?
a network of internal membranes that run through the sarcoplasm
66
what does the sarcoplasmic reticulum do?
it stores and releases calcium ions that are needed for muscle contraction
67
why do muscle fibres contain lots of mitochondria?
to provide the ATP that's needed for muscle contraction
68
what are some properties of muscle fibres?
they have lots of mitochondria they are multinucleate they contain myofibrils
69
what does multinucleate mean?
they contain many nuclei
70
what are myofibrils?
long, cylindrical organelles | made up of proteins and are highly specialised for contraction
71
what do myofibrils contain?
thick and thin myofilaments
72
what are thick myofilaments made of?
myosin
73
what are thin myofilaments made of?
actin
74
what does a myofibril look like under a microscope?
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
what are myofibrils made up of?
many short units called sarcomeres
76
what does a sarcomere contain?
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
what happens when sarcomeres contract?
myosin filaments pull actin inwards
78
what do myosin filaments have?
globular heads that are hinged so they can move back and forth
79
what does each myosin head have?
a binding site for actin | a binding site for ATP
80
what does actin have that allows myosin to move along it?
actin-myosin binding sites | tropomyosin is another protein wrapped around actin which has to move out of these binding sites
81
what does tropomyosin do in resting muscle?
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
what happens when an action potential from a motor neurone stimulates a muscle cell?
it depolarises the sarcolemma, depolarisation spreads down the T-tubules o the sarcoplasmic reticulum
83
what happens when the sarcoplasmic reticulum is depolarised?
it releases stored calcium ions into sarcoplasm
84
what do calcium ions do to tropomyosin?
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
what does calcium do in the sarcomere?
bind to tropomyosin | activate ATP hydrolase
86
what do myosin heads do in a muscle contraction?
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
what happens when a muscle stops being stimulated?
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
how is ATP generated for muscle contractions?
aerobic respiration anaerobic respiration ATP-Phosphocreatine system
89
how does aerobic respiration provide ATP for muscle contractions?
most ATP is generated via oxidative phosphorylation in the cell's mitochondria only works when oxygen is present
90
how does anaerobic respiration provide ATP for muscle contractions?
ATP made rapidly by glycolysis | lactate can quickly build up in muscles and cause muscle fatigue
91
how does PCr system provide ATP for muscle contractions?
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
what does alactic mean?
doesn't form any lactate
93
what 2 types of muscle fibre are skeletal muscles made up of
slow twitch | fast twitch
94
what are the properties of slow twitch muscle fibres?
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
what are the properties of fast twitch muscle fibres?
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
what is the nervous system?
``` 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
what is the hormonal system?
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
what is a nerve impulse?
a self propagating wave of electrical activity that travels along an axon membrane
99
how is a generator potential produced?
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
what happens in a nerve impulse?
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
what does the synaptic knob contain?
vesicles containing neurotransmitter (ACh) voltage gated Ca2+ channel proteins smooth ER - store Ca2+ mitochondria
102
what is the purpose of synapses?
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
what is epilepsy?
an inability to regulate action potentials in brain neurones to prevent over excitation
104
how do inhibitory neurones work?
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
what purpose does ATP have in muscular contractions?
providing energy for: breaking actin-myosin cross-bridges re-cocking myosin heads for the power stroke
106
what purpose do calcium ions have in muscular contractions?
activating ATPase | altering tropomyosin tertiary structure to expose myosin binding sites of actin filaments
107
what happens in muscle relaxation?
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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