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AQA A Level Biology 2018 > Nervous Coordination > Flashcards

Nervous Coordination Flashcards

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1
Q

What is skeletal muscle?

A

The muscle you use to move - they are attached to bones by tendons.

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2
Q

What stitches bones to other bones?

A

Ligaments.

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3
Q

Muscles that work together to move a bone are called…

A

Antagonistic pairs

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4
Q

Contracting muscle is called…

A

Agonist

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5
Q

Relaxing muscle is called…

A

Antagonist

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6
Q

Skeletal muscle structure

A

Made up of large bundles of long cells called muscle fibres

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7
Q

What is the cell membrane of muscle fibre cels called?

A

Sarcolemma

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8
Q

What do the Sarcolemma do?

A

Food onwards across the muscle fibre forming transverse tubules which help to spread electrical impulses throughout the sarcoplasm.

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9
Q

What runs through the sarcoplasm?

A

A network of internal membranes called the sarcoplasmic reticulum.

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10
Q

What does the sarcoplasmic reticulum do?

A

Stores and releases calcium ions that are needed for muscle contraction.

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11
Q

Muscle fibre features: (3)

A
  • lots of mitochondria for energy
  • contain many nuclei
  • have lots of myofibrils (long, cylindrical organelles) specialised for contraction
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12
Q

Myofibrils contain:

A

Thick and thin myofilaments that move past eachother.

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13
Q

Thick myofilaments

A

Myosin

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14
Q

Thin myofilaments

A

Actin

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15
Q

Dark bands contain…

A

Thick myosin filaments - called A bands

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16
Q

Light bands contain…

A

Thin actin filaments - I bands

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17
Q

Myofibril is made up of …

A

Sarcomeres (small units)

Marked with a Z line

Middle marked with the M line

Around the M line is the H zone

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18
Q

How do muscles contract?

A

Myosin and actin filaments slide over one another to make the sarcomeres contract.

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19
Q

What happens when the sarcomeres contract?

A

A bands stay the same length

I hands get shorter

H zones get shorter

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20
Q

Myosin filaments structure:

A

Globular hinged heads that can move back and forth

Has a binding site for actin and ATP

Tropomyosin found between actin filaments - helps myofilaments move past eachother.

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21
Q

What’s going in a resting muscle?

A

The actin myosin binding site is blocked by tropomyosin.

Can’t slide past eachother because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments.

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22
Q

Muscle contraction is triggered by…

A

An influx of calcium ions

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23
Q

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

A

It depolarises the sarcolemma and the depolarisation spreads down the T-Tubules to the sarcoplasmic reticulum causing them to release stored calcium ions into the sarcoplasm.

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24
Q

What do the calcium ions do when released?

A

They bind to a protein attached to tropomyosin causing the protein to change shape - this pulls the tropomyosin out the actin-myosin binding site.

Exposes it = allows myosin head to bind.

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25
Q

What is the bond formed when a myosin head binds to an actin filaments?

A

Actin-myosin cross bridge.

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26
Q

Calcium ions activate…

A

The enzyme ATP hydrolyse which breaks down ATP to provide energy for contraction.

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27
Q

The energy released from ATP causes…

A

The myosin head to bend which pulls the actin filaments along in a kind of rowing action.

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28
Q

How does the actin-myosin cross bridge break?

A

Another ATP molecule provides the energy so the myosin head detaches and re attaches to a different binding site further along the actin - new bond formed and repeated.

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29
Q

What happens when many cross bridges are formed?

A

They form and break quick pulling the actin filaments along which shortens the sarcomeres causing the muscle to contract.

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30
Q

What happens when the muscle stops being stimulated?

A

Calcium ions leave their binding sites and are moved to sarcoplasmic reticulum via active transport.

Caused tropomyosin molecules to move back so they block binding sites again - no myosin heads attached = no contraction and sarcomere is lengthened as actin filaments slide back to their relaxed position.

31
Q

How is ATP generated?

A

Oxidative phosphorylation in Aerobic Respiration.

Anaerobic respiration - glycolysis produces pyruvate which is converted to lactate.

ATP-Phosphocreatine System - adding a phosphate taken from PCR - this is stored inside cells and generates ATP very quickly.

32
Q

Skeletal music have two types of muscle fibres:

A

Slow twitch

Fast twitch

33
Q

Slow twitch muscle fibres: (3)

A
  • contract slowly as they are used for posture etc
  • can work for a long time without getting tired
  • rich in myoglobin so they are red
34
Q

Fast twitch muscle fibres: (3)

A
  • contract very quickly as used for fast movement.
  • get tired very quickly.
  • not much myoglobin so they’re whitish.
35
Q

Neurone’s resting state:

A

Voltage of about -70

36
Q

The resting potential is created and maintained by…

A

The sodium potassium pumps and potassium ion channels

37
Q

Why is a sodium electrochemical gradient created?

A

Because the sodium pump moves sodium ions out of the neurone but the membrane isn’t permeable to sodium ions so they can’t move back in.

38
Q

What happens when cell membranes become stimulated?

3

A
  • stimulus excites neurone causing sodium channels to open so move sodium diffuse in = less negative.
  • depolarisation = If the potential difference reaches threshold, more sodium open and more diffuse in.
  • at potential difference of +30, sodium channels close and potassium channels close = more permeable membrane so potassium diffuse out so membrane gets back to resting potential.
39
Q

What happens after repolarisation? (2)

A

4) potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone - potential difference becomes more negative.
5) ion channels are reset and the sodium potassium pump returns to its resting potential.

40
Q

What happens when some of the sodium ions diffuse sideways?

A

Sodium ion channels in the nd t region of the neurone to open and sodium ions diffuse into that part - causes a wave of depolarisation.

41
Q

Why do the wave move away from the parts of the membrane in the recractory period?

A

Because these parts can’t fire an action potential.

42
Q

What happens to the ions during the refractory period?

A

Ion channels are recovering and can’t be opened - acts as a time delay between one action potential to the end.

43
Q

What does the time delay mean:

A

Action potentials don’t overlap

Limit to the frequency at which the nerve impulses can be transmitted

Action potentials are undirectional

44
Q

What happens once the threshold is reached?

A

An action potential will always fire with the same change violate - no matter how big the stimulus is.

45
Q

3 factors which affect the speed of conduction of action potentials:

A
  • myelination
  • axon diameter
  • temperature
46
Q

How does temp affect the speed of conduction of action potentials?

A

Increases as temp increases because ions diffuse faster - only increases up to about 40degrees though befotr proteins denature.

47
Q

How does axon diameter affect the conduction of an action potential?

Why is less resistance good?

A

Conducted quicker along axons with bigger diameters because there’s less resistance to the flow of ions than in cytoplasm of a smaller axon -

less resistance means depolarisation reaches other parts of the cell membrane quicker.

48
Q

Some neurones are myelinated

Meaning?

A

They have a myelin sheath which is an electrical insulator - made up of a cell called a Schwann cell.

49
Q

What is present between the Schwann cells?

A

Don’t patches of bare membrane called the nodes of Ranvier - sodium ion channels are concentrated here.

50
Q

How does myelination affect the conduction of an action potential?

What is this known as?

A

If it is myelinated

Depolarisation happens at the nodes - cytoplasm conducts enough to depolarise next node - impulse jumps from node to node

This is known as Saltatory Conduction

51
Q

What happens in a non-myelinated neurone which makes it different?

A

The impulse travels as a wave along the whole length of the axon membrane so you get depolarisation along the whole length of the membrane - this is slower.

52
Q

What is a synapse?

A

A synapse is the junction between 2 neurones.

53
Q

Tiny gap between cells at a synapse:

A
  • synaptic cleft
54
Q

What is the presynaptic neurone?

What does it have?

A

The one before the synapse

Has a synaptic knob containing synaptic vesicles filled with chemicals called neurotransmitters.

55
Q

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

A

It causes neurotransmitters to be released into the synaptic cleft -

they diffuse across to the postsynaptic membrane and bind to specific receptors.

56
Q

What happens when neurotransmitters bind to receptors?

A

They might trigger an action potential causing muscle contraction or gland release.

57
Q

Why do synapses only make impulses that can only travel in one direction?

A

Because the receptors are only on the postsynaptic membranes.

58
Q

What happens to stop the response from keep happening?

A

Neurotransmitters aré removed from the cleft.

59
Q

1) 2)

A nerve impulse transmitting across a chloinergic synapse:

A
  • action potentials arrives at the synaptic knob of a presynaptic neurone - calcium ion channels open so calcium ions diffuse into the synaptic knob.
  • this causes the synaptic vesicles to move to the presynaptic membrane = vesicles releases neurotransmitter ACh into the synaptic cleft (exocytosis)
60
Q

Final steps to a nerve impulse transmitted across a cholinergic synapse:

A

ACH diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane - sodium channels open.

Sodium ions causes depolarisation = action potentials generatied id threshold reaches

Ach is removed so response doesn’t keep happening - broken down by ACHE.

61
Q

What do agonists do?

A

Some drugs are same shape as neurotransmitters so they mimic their action at receptors - more receptors are activated.

62
Q

What do anatagonists do?

A

Drugs block receptors so they can’t be activated by neurotransmitters - fewer receptors are activated.

63
Q

How do some drugs work as inhibitory?

A

Some drugs inhibit the enzyme that breaks down neurotransmitters so there are more neurotransmitters in the synaptic cleft to bind to receptors and they are there for longer.

Some inhibit the release of neurotransmitters so fewer receptors are activated.

64
Q

How do some drugs work as stimulators?

A

They stimulate the release of neurotransmitters from the presynaptic neurone so more receptors are activated.

65
Q

3 types of neurotransmitters:

A

Excitatory

Inhibitory

Or both

66
Q

What do excitatory neurotransmitters do?

A

They depolarise the postsynaptic membrane making it fire an action potential of threshold is reached.

67
Q

What do inhibitory neurotransmitters do?

A

They hyperpolarise the postsynaptic membrane preventing it from firing an action potential.

68
Q

2 types of stimulation:

A

Spatial summation

Temporal summation

69
Q

What is temporal summation?

A

Where two or more nerve impulses arrive in quick succession from the same presynatpic neurone

  • makes an action potential more likely because more neurotransmitter is released into synaptic cleft.
70
Q

What is spatial summation?

UNLESS

A

When many neurones connect to one neurone - the small amount of neurotransmitter releases from each can be enough to reach threshold and trigger an action potential.

UNLESS the neurones release an inhibitory neurotransmitter.

71
Q

What is a neuromuscular junction?

A

A synapse between a motor neurone and a muscle cell.

72
Q

What neurotransmitters do neuromuscular junctions use?

A

Acetylcholine - which binds to cholinergic receptors called nicotinic cholinergic receptors.

73
Q

How do neuromuscular junctions work?

A

In basically the same way as the cholinergic synapses.

BUT

74
Q

What are the differences between a neuromuscular junction and cholinergic synapse?

A
  • postsynaptic membrane has more receptors.
  • the postsynaptic membranes has lots of folds that form clefts - they store the enzyme that breaks down ACH.
  • ach is always excitatory at neuromuscular junction - not always the case for 2 synapses.

AQA A Level Biology 2018 (17 decks)

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