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biology a1 & a2 > 6B: Nervous coordination > Flashcards

6B: Nervous coordination Flashcards

- Nerve impulses - Synaptic transmission - Cholinergic vs neuromuscular - Skeletal muscles: structure & contraction

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1
Q

Describe and explain the polarisation of a neuron at resting potential

A

The inside of the neuron is more negative than the outside. This is because there are more + ions outside the neuron than inside

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2
Q

What is the resting potential of neurons?

A

-65mv

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3
Q

Describe how resting potential is maintained in neurons

3 steps

A
  1. Sodium potassium pump actively transports N+ ions out of cell and K+ ions into cell (ATP required)
  2. There’s a higher conc. of Na+ outside of the cell than inside, so it should diffuse into the cell
    - But, most of the leakage channel proteins for Na+ are closed, preventing it from diffusing in
  3. Higher conc. of K+ inside the cell than outside, so it should diffuse out
    - Most of the leakage channel proteins for K+ are open, allowing it to diffuse out
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4
Q

How many Na+ ions does the sodium potassium pump actively transport? In or out of the cell?

A

3 sodium ions out of the cell

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5
Q

How many K+ ions does the sodium potassium pump actively transport? In or out of the cell?

A

2 potassium ions into the cell

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6
Q

Why is the membrane impermeable to sodium ions during resting potential?

A

The membrane is largely impermeable to sodium ions, because most sodium leakage channels are closed, preventing sodium ions from diffusing into the cell.

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7
Q

Describe how a stimulus results in depolarisation of a neuron

A
  • A stimulus causes some voltage gated Na+ ion channels to open
  • Allows Na+ ions to diffuse into cell
  • Makes the inside of the cell less negative (depolarisation)
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8
Q

What is depolarisation of a neuron?

A

When the inside becomes less negative

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9
Q

Describe how depolarisation of a neuron results in an action potential

A
  • If enough voltage gated Na+ channels open, enough Na+ ions enter the cell and the cell reaches threshold
  • Allows even more voltage gated Na+ channels to open and the action potential occurs
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10
Q

What is the threshold of a neuron?

A

-55mv

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11
Q

When the neuron reaches action potential, what is the voltage of the membrane?

A

The membrane reaches +40mv

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12
Q

Describe repolarisation

A

The voltage gated Na+ close and voltage gated K+ channels open
- Allows K+ to diffuse out of the cell and causes the membrane to become more negative (repolarises)

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13
Q

Describe hyperpolarisation

A

Slightly more potassium ions leave than sodium ions entered, causing the membrane to become too negative

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14
Q

Describe how the resting potential is restored

A

The voltage gated potassium ions channels shut and the sodium potassium pump restores the resting potential.

The axon is depolarised.

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15
Q

Describe the refractory period

A

The period of time after an action potential has occurred during which it is impossible for there to be another action potential. During this time the voltage gated sodium channels are closed and cannot be opened.

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16
Q

What is the importance of the refractory period?

A
  • Ensures action potentials are only propagated in one direction
  • Produces discrete impulses (can distinguish between two different action potentials)
  • Limits the number of actions potentials
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17
Q

Describe the ‘All or Nothing Principle’ in neurons

A
  • Action potentials will only occur once the threshold stimulus is reached
  • Once the threshold is reached the action potential occurs and all action potentials are the same size
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18
Q

What are 3 factors that affect rate of impulse transmission between neurons

A
  • Myelin sheath
  • Diameter of axon
  • Temperature
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19
Q

Describe how the myelin sheath affects the rate of impulse transmission

A

Neurons that are myelinated transmit impulses faster than neurons that are not myelinated.

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20
Q

Describe a myelinated neuron

A

Myelinated neurons have their axons and dendrites covered with an insulating myelin sheath. It is made up from the membrane of Schwann cells that wrap around the axons and dendrites.

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21
Q

Describe how and why the diameter of the axon affects the rate of impulse transmission

A

The larger the diameter of the axon, the faster the impulse is transmitted as there is less leakage of ions from a large axon.

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22
Q

Describe how and why temperature affects the rate of impulse transmission

A

Temperature - The higher the temperature the greater the rate of diffusion of ions and so the faster the impulse is transmitted.

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23
Q

Describe the nodes of ranvier.

A

Gaps formed between the myelin sheath where the axons are left uncovered.
Only place where voltage gated Na+ & K+ channels are found

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24
Q

What is saltatory conduction?

A

In neurons that are covered in a myelin sheath, action potential can only flow through the nodes of ranvier.
= the action potential jumps from one node to the next

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25
Q

how do the nodes of ranvier allow electrical impulses to travel?

A

Because the myelin sheath is largely composed of an insulating fatty substance, the nodes of ranvier allow the generation of a fast electrical impulse along the axon.

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26
Q

Describe the (9) stages of the passage of impulses along cholinergic synapses

A
  1. AP arrives at presynaptic membrane
  2. Causes gated Ca2+ channels to open & Ca2+ ions enter the synaptic knob by facilitated diffusion
  3. The influx of Ca2+ causes synaptic vesicles to fuse with the presynaptic mem
  4. Acetylcholine is released into the synaptic cleft & diffuses across
  5. Acetylcholine binds to receptors on Na+ protein channels causing them to open
  6. Na+ ions diffuse into the postsynaptic neuron
  7. AP is generated in postsynaptic neuron
  8. Acetylcholinesterase hydrolyses acetylcholine into ethanoic acid (acetyl) and choline which diffuse back across the cleft to the presynaptic membrane
  9. ATP released from the mitochondria is used to recombine choline and ethanoic acid to acetylcholine
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27
Q

What does acetylcholinesterase hydrolyse acetylcholine into?

A

Ethanoic acid (acetyl) and choline

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28
Q

By which process does acetylcholine diffuse across the synaptic cleft?

A

Diffusion

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29
Q

What is acetylcholine?

A

A neurotransmitter

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30
Q

What is the gap between the cells at a synapse called?

A

The synaptic cleft

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31
Q

What type of synapse does ACh transmit across?

A

A cholinergic synapse

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32
Q

Describe the effect excitatory neurotransmitters have on postsynaptic membranes

A

Excitatory neurotransmitters depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached.

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33
Q

Describe the effect inhibitory neurotransmitters have on postsynaptic membranes

A

Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane (making the potential difference more negative) preventing it from firing an action potential

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34
Q

What is summation?

A

Where the effect of neurotransmitter released from many neurons (or one) is added together.

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35
Q

Describe spatial summation

A

When many neurons connect to one neuron. Neurotransmitters released from each one are added together to reach threshold in the postsynaptic neuron and trigger and action potential

36
Q

Describe temporal summation

A

Where 2 or more nerve impulses arrive in quick succession from the same presynaptic neuron.
= makes AP more likely because more neurotransmitter is released from the synaptic cleft

37
Q

What is a schwann cell?

A

Cells that wrap around some neurons and have membrane rich in the lipid myelin

38
Q

What is a myelin sheath?

A

An insulating layer of myelin around some neurons

39
Q

Explain why synaptic transmission is

unidirectional.

A

Only presynaptic neuron contains vesicles of neurotransmitter & only postsynaptic membrane has complementary receptors.
So impulse always travels presynaptic → postsynaptic

40
Q

Name the 4 stages in generating an action potential

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
  4. Return to resting potential
41
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to and opens Clchannels on postsynaptic membrane & triggers K+ channels to open.
  2. Cl- moves in & K+ moves out via facilitated
    diffusion.
  3. p.d. becomes more negative: hyperpolarisation
  4. AP less likely to be reached
42
Q

Describe the structure of a

neuromuscular junction

A

Synaptic cleft between a presynaptic

neuron and a skeletal muscle cell.

43
Q

Name 4 differences between a cholinergic synapse and a neuromuscular junction.

A
  1. Postsynaptic cell:
    - cholinergic synapses with another neuron
    - neuromuscular synapses with a muscle cell
  2. AP:
    - In cholinergic a new AP is produced
    - neuromuscular is the end of the neural pathway
  3. Type of response:
    - Cholinergic: inhibitory/excitatory
    - Neuromuscular: always excitatory
  4. Neurons involved:
    - cholinergic: motor, relay or sensory
    - neuromuscular: always motor
44
Q

How might drugs increase synaptic transmission?

A
  • Inhibit Acetylcholine

- Mimic shape of neurotransmitter

45
Q

How might drugs decrease synaptic

transmission?

A
  • Inhibit release of neurotransmitter.
  • Decrease permeability of postsynaptic
    membrane to ions.
  • Hyperpolarise postsynaptic
    membrane.
46
Q

Describe the structure of a skeletal muscle

A

Muscle –> lots of muscle fibres –> Myofibril –> Myofilament

47
Q

What is the cell membrane of a muscle cell called?

A

Sarcolemma

48
Q

What are transverse (T) tubules?

A

Inversions of the sarcolemma (bits of the membrane fold inwards across the muscle fiber and stick to the sarcoplasm)

49
Q

What is the cytoplasm of a muscle cell called?

A

Sarcoplasm

50
Q

What is the function of T tubules in muscle fibres?

A

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

51
Q

What is the sarcoplasmic reticulum and what is its function?

A

A network of internal membranes that runs through the sarcoplasm. It stores and releases Ca2+ ions that are needed for muscle contraction

52
Q

Why do muscle fibres have a lot of mitochondria?

A

To produce ATP that’s needed for muscle contraction

53
Q

Why are muscle fibres ‘multinucleated’?

A

Because they contain many nuclei

54
Q

What are muscle fibres made up of ?

A

Myofibrils

55
Q

What are myofibrils made up of?

A

Protein filaments called myofilaments

56
Q

What is the name of the thin myofilament?

A

Actin

57
Q

What is the name of the thick myofilament?

A

Myosin

58
Q

Describe the A band of a sarcomere

A

A band = darkest band as it contains myosin filaments and overlapping actin filaments

59
Q

Describe the I band of a sarcomere

A

I band = lightest band as it contains only actin

60
Q

A myofibril is made up of many short units called _______.

A

A myofibril is made up of many short units called sarcomere.

61
Q

What marks the end of each sarcomere?

A

The Z line/ disc

62
Q

Describe the M line of the sarcomere

A

M line = the middle of the myosin filaments

63
Q

Describe the H-zone of the sarcomere

A

H zone = around the M line, contains only myosin filaments

64
Q

Describe sliding filament theory

A
  • Myosin and actin filaments over one another to make the sarcomeres contract
  • The simultaneous contraction of lots of sarcomeres means myofibrils and and muscle fibres contract
  • Sarcomeres return to their original length as the muscle relaxes
65
Q

Where is tropomyosin found in the sarcomere?

A

Tropomyosin forms long thin threads that are wound around actin filaments.

66
Q

Describe what happens to each band when a skeletal muscle contracts.

  • I band
  • H band
  • A band
  • Sarcomere as a whole
A
  • I band gets shorter
  • H band gets shorter
  • A band does not change
  • The sarcomere gets shorter
67
Q

Why does the I band appear light under the electron microscope?

A

Because it contains only the thin filament actin

68
Q

What is a motor unit

A

All the muscle fibres supplied by a single motor neurone

69
Q

Describe how the arrival of an action potential at the motor neuron leads to an influx of Ca2+ ions into the sarcoplasm

A
  • AP occurs in the muscle fibre
  • T-Tubules carry the wave of excitation to the sarcoplasmic reticulum
  • Activates Ca2+ channels in the sarcoplasmic reticulum and allows Ca2+ ions to diffuse into the sarcoplasm
70
Q

What 2 binding sites does each myosin head have?

A

A binding site for actin, and a binding site for ATP

71
Q

What type of pairs do muscles act in?

A

Muscles act in antagonistic pairs against an incompressible skeleton

72
Q

What does tropomyosin help to happen?

A

It helps myofilaments move past each other

73
Q

In a resting (unstimulated) muscle what binding site does tropomyosin block?

A

the actin-myosin binding site

74
Q

What effect does tropomyosin blocking the actin-myosin binding site have?

A

Myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on actin filaments

75
Q

What happens when an AP from the motor neuron stimulates the muscle cell?

A

It depolarises the sarcolemma, this spreads down the T-tubules to the sarcoplasmic reticulum (which release Ca2+ ions)

76
Q

What do the Ca2+ ions bind to, and what is the effect on tropomyosin?

A

Ca2+ ions bind to the protein attached to tropomyosin, causing the protein to change shape.
= Pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament (exposing the binding site so myosin head binds)

77
Q

What is the bond between the myosin head and actin filament called?

A

An actin-myosin cross bridge

78
Q

What enzyme do Ca2+ ions activate (and what effect does this have on ATP)

A

Ca2+ ions activate the enzyme ATP hydrolase which hydrolyses ATP into ADP +Pi to provide energy needed for muscle contraction

79
Q

How does the myosin head use the energy released from ATP hydrolysis?

A

The energy released from ATP causes the myosin head to bend, which pulls the actin filament along

80
Q

Why does the myosin head need a second ATP molecule?

A

To provide energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after its moved

81
Q

What happens to the Ca2+ ions when the muscle stops being stimulated?

A

Ca2+ ions leave their binding sites and are moved by active transport back to the sarcoplasmic reticulum (this needs ATP too)

82
Q

Describe the role of ATP in muscle contraction.

A

ATP: causes actin-myosin cross bridge to break which allows the myosin head to attach to a new actin binding site. ATP hydrolysis provides the energy for the myosin head to pull the actin filament.

83
Q

What is produced when a muscle contracts?

A

A force

84
Q

Name 6 features of slow twitch muscle fibres

A
  1. Contract slowly
  2. Less powerful contractions but over a longer period
  3. Adapted for aerobic respiration
  4. Large store of myoglobin (red colour)
  5. Rich supply of blood vessels
  6. Numerous mitochondria to produce ATP
85
Q

Name 7 features of fast twitch muscle fibres

A
  1. Contract more rapidly
  2. More powerful contractions but for a short period of time
  3. Adapted for anaerobic respiration
  4. Thicker and more numerous myosin filaments
  5. High concs. of glycogen
  6. Lots of enzymes involved in anaerobic respiration
  7. A store of phosphocreatine
86
Q

Why do fast twitch fibres contain a store of phosphocreatine?

A

Because it can rapidly generate ATP from ADP in anaerobic conditions by providing a phosphate group

87
Q

Which is darker in colour, fast or slow twitch muscle fibres?

A

Slow-twitch fibres are darker because they have more blood vessels

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