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Biology A-level > 6B Nervous Coordination > Flashcards

6B Nervous Coordination Flashcards

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1
Q

What is the charge like in a neuron at resting state?

A

Outside of membrane is positively charged to inside the membrane (membrane is polarised)

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2
Q

What is the resting potential across the neurons membrane?

A

-70mV

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3
Q

How is the resting potential maintained in a neuron?

A
  • Sodium potassium pump

- Potassium ion channels

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4
Q

What does the sodium potassium pump do?

A
  • Pumps 3 Na+ out of the neuron

- Pumps 2 K+ into the neuron

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5
Q

Is the neuron membrane permeable to Sodium and Potassium?

A

No Sodium

Yes Potassium

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6
Q

How do Potassium ions diffuse through the membrane?

A

Diffuse out of neuron through Potassium ion channels

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7
Q

What is created when sodium moves out of the cell?

A

Sodium ion electrochemical gradient

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8
Q

What are the stages when a cell membrane is stimulated?

A

1) Stimulus
2) Depolarisation
3) Repolarisation
4) Hyperpolarization
5) Resting potential

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9
Q

What happens when there is a stimulus?

A
  • Excites cell membrane causing sodium channels to open

- Sodium ions diffuse into cell making is less negative

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10
Q

What happens during depolarisation?

A
  • Occurs after stimulus
  • If threshold of -55mv is reached more sodium channels open
  • Rapid diffusion into membrane
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11
Q

What happens during repolarization?

A
  • Occurs at potential difference of about +30 mv
  • Sodium ion channels close and potassium ion channels open
  • K+ ions diffuse out of cell so PD goes back to resting potential
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12
Q

What happens during hyperpolarization?

A
  • After repolarization K+ channels slow to close so there is a ‘overshoot’
  • PD becomes more negative (less than -70 mv)
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13
Q

What happens after hyperpolarization?

A
  • Ion channels are reset

- Sodium potassium pump returns membrane to resting potential

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14
Q

Where does the action potential move to?

A

Move along the neuron like a wave or depolarization

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15
Q

When an action potential happens how do some of the sodium ions diffuse?

A

They diffuse sideways

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16
Q

Why do sodium ions diffuse sideways during an action potnential?

A

It causes sodium ion channels in next region to open (wave of depolarisation)

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17
Q

What occurs after an action potential?

A

The refractory period

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18
Q

What is the refractory period?

A

Where sodium and potassium ion channels are recovering and can’t be opened

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19
Q

What is the purpose of the refractory period?

A
  • Means action potentials don’t overlap
  • action potentials are unidirectional (one directional)
  • Limits the frequency at which nerve pulses can be transmitted
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20
Q

What is an action potentials all or nothing nature?

A

If the threshold inst met an action potential wont fire

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21
Q

Does the size of the stimulus affect the size of the action potential?

A

No, but it will cause it to become more frequent

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22
Q

What are the 3 factors that affect the speed of an action potentials?

A
  • Myelination
  • Axon diameter
  • Temperature
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23
Q

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

A
  • A larger diameter means action potential are conducted quicker
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24
Q

Why does having a larger diameter increase action potentials speed of conduction?

A

Less resistance to flow of ions - therefore depolarization reaches other parts of cell membrane quicker

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25
Q

How does temperature affect action potentials speed of conduction?

A

Speed of conduction increases with the temperature

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26
Q

Why does temperature increase action potentials speed of conduction?

A

Because ions diffuse faster (up to 40 degrees where they start to denature)

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27
Q

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

A

It increases it

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28
Q

What structure do myelinated neurons have?

A
  • Myelinated sheath (electrical insulator)
  • Sheath made up of Schwann cells
  • Between Schwann cells are nodes of Ranvier
  • Sodium ions are concentrated at the nodes
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29
Q

Why is conduction of action potential faster in myelinated neurons?

A
  • Depolarization occurs at nodes of ranvier
  • Neuron’s cytoplasm conducts electrical charge to depolarise the next node, makes impulses jump from node to node (which is faster)
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30
Q

What are nodes of Ranvenir?

A

Gaps in between the myelin sheath

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31
Q

Why does the myelin sheath cause impulses to move faster?

A

The myelin sheath is an electrical insulator

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32
Q

What is Saltatory conduction?

A

Where the neuron’s cytoplasm conducts electrical charge to depolarise the next node, makes impulses jump from node to node

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33
Q

Why do impulses travel more quickly along mylenated neurons than non-myelenated neurons?

A

Non-mylenated –> impulses have to travel as a wave the whole way length of the axon membrane

Slower process than saltatory conduction

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34
Q

Can there be multiple types of neurotransmitters?

A

Yes

They can be excitatory, inhibatory or both

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35
Q

How do excitatory neurotransmitters act and what does this cause?

A

They depolarise the postsynaptic membrane

Causes it to fire an action potential if the threshold is reached

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36
Q

What is a synapse?

A

A junction between a neurone and the next cell or between a neurone & an effector cell

e.g. a muscle or glad cell

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37
Q

What is the synaptic cleft?

A

The tiny gap between the cells at a synapse

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38
Q

What is the presynaptic neurone like?

A

It has a swelling called a synaptic knob - this contains synaptic vesicles filled with chemicals called neurotransmitters

39
Q

What happens when an action potential reaches the end of the presynaptic neuron?

A

It causes neurotransmitters to be released into the synaptic cleft

They diffuse into across the postsynaptic membrane & bind to specific receptors

40
Q

What happens when neurotransmitters bind to receptors?

A

They might trigger an action potential (in a neurone), cause muscle contraction (in a muscle cell), or cause a hormone to be secreted (from a glad cell)

41
Q

Why can impulses only travel in one direction?

A

The receptors are only on the postsynaptic membranes, synapses make sure impulses are unidurectional

42
Q

Why are neurotransmitters removed from the synaptic cleft?

A

So the response doesn’t keep happening

e.g. they’re taken back into the presynaptic neurone or they’re broken down by enzymes

43
Q

Give some examples of different neurotransmitters

A

Acetlycholine & noradrenaline

44
Q

What are synapses that use acetylcholine called?

A

They are called cholinergic synapses

45
Q

Where does acetylcholine transmit nerve impulses?

A

Across a cholinergic synapse

46
Q

How is a nerve impulse transmitted across a cholinergic synapse?

A

1 - Action potential (AP) arrives at synaptic knob of the presynaptic neurone

2 - AP stimulates voltage-gates calcium ion channels in presynaptic neurone to open

3 - Ca2+ ions diffuse into the synaptic knob

4 - Influx of Ca2+ ions into the synaptic knob causes synaptic vesicles to move to the presynaptic membrane. They then fuse with presynaptic membrane

5 - Vesicles release the NT acetylcholine (ACh) into synaptic cleft - this is called exocytosis

6 - ACh diffuses across the synapticcleft & binds to specific cholinergic receptors on the postsynaptic membrane

7 - Causes Na2+ ion channels in postsynaptic neurone to open

8 - Influx of sodium ions into postsynaptic membrane causes depolarisation. An AP on postsynaptic membrane is generated if threashold is reached

9 - ACh removed from synaptic cleft so response doesn’t keep happening - broken down by enzyme called acetylcholinesterase (AChE) & products are re-absorbed by presynaptic neurone & used to make more ACh

47
Q

Give an example of an excitatory NT

A

Acetylcholine, it’s found at cholinergic synapses in the CNS

It binds to cholinergic receptors to cause an action potential in the postsynaptic membrane & and at neuromuscular junctions

48
Q

What do inhibitory neurotransmitters do?

A

They hyperpolarise the postsynaptic membrane (makes potential difference more -ive), preventing it from firing an action potential

49
Q

Give an example of an inhibitory NT

A

Acetylcholine is inhibitory at cholinergic synapses in the heart

When it binds to receptors here, it can cause potassium ion channels to open on the postsynaptic membrane, hyperpolarising it

50
Q

What are the two types of summation?

A
  • Spatial summation

- Temporal summation

51
Q

What is summation?

A

Is where the effect of NT released from many neurones (or one neurone that’s stimulated a lot in a short period of time) is added together

52
Q

What is spatial summation?

A

Where many neurones summate at one neurone

53
Q

What happens in spatial summation?

A

1 - Sometimes many neurones connect to one neurone

2 - The small amount of NT released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone & trigger an action potential

3 - If some neurones release inhibitory NT then the total effect of all the NTs might be no AP

54
Q

What is temporal summation?

A

Is where two or more nerve impulses arrive in quick succession from the same presynaptic neurone

Makes an AP more likely because more NT is released into the synaptic cleft

55
Q

What are skeletal muscles like?

A

They are the type of muscle you use to move - also called voluntary muscles

They are attached to bones by tendons

56
Q

How do muscles work in antagonistic pairs?

A

Pairs of skeletal muscles contract & relax to move bones at a joint

The bones of the skeleton are INCOMPRESSIBLE (rigid) so act as a lever - give the muscles something to pull against

57
Q

What are antagonistic pairs?

A

Muscles that work together to move a bone

58
Q

What does the agonist muscle do?

A

It is the contracting muscle

59
Q

What does the antagonist muscle do?

A

It is the relaxing muscle

60
Q

What is skeletal muscle made up of?

A

Long muscle fibres

61
Q

How are muscles stimulated to contract?

A

By neurones - they act as effectors to the stimulus

62
Q

What is the sarcolemma?

A

The cell membrane of muscle fibre cells

63
Q

What are the folds in the sarcolemma called?

A

Transverse (T) tubules

64
Q

What are T tubules?

A

Where bits of the sarcolemma fold inwards across the muscle fibre into the sarcoplasm to create folds

65
Q

What do T tubules do?

A

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

66
Q

What is the sarcoplasm?

A

They cytoplasm of muscle fibre cells

67
Q

What is the sarcoplasmic reticulum and what does it do?

A

A network of internal membranes that run through the sarcoplasm

It stores & releases calcium ions that are needed for muscle contraction

68
Q

Why do muscle fibres have lots of mitochondria?

A

They provide the ATP that’s needed for muscle contraction

69
Q

What does muscle cells being multinucleate mean?

A

They contain many nuclei

70
Q

What are muscle fibres made up of?

A

Myofibrils - long, cylindrical organelles, made up of proteins specialised for contraction

71
Q

What are the two types of filaments contained in myofibrils?

A
  • Thick mysoin filaments

- Thin actin filaments

72
Q

What are thick myofilaments made up of?

A

The protein myosin

73
Q

What are thin actin filaments made up of?

A

The protien actin

74
Q

What protien is contained in the dark bands (muscles)?

A

The thick myosin filaments & some overlapping actin filaments - these are called the A band

75
Q

What protien is contained in the light bands (muscles)?

A

Thin actin filaments only - these are called I bands

76
Q

What makes up a myofibril?

A

Many short units called sarcomeres

77
Q

What is the Z-line?

A

The end of each sarcomere (short unit fo the myofibril)

78
Q

What is the M-line?

A

The middle of each sarcomere is the M-line

The M-line is in the middle of the myosin filament

79
Q

What is the H-zone?

A

It contains ONLY myosin filaments

Around the M-line is the H-zone

80
Q

What is the A-band?

A

It contains BOTH thick myosin filaments and thin actin filaments

81
Q

What is the I-band?

A

Contains only thin actin filaments

82
Q

What theory is used to explain muscle contraction?

A

The sliding filament theory

83
Q

How does the sliding filament theory work?

A
  • Myosin & actin filaments slide over one another to make sarcomeres contract - myofilaments themselves don’t contract
  • Simultaneuos contraction of lots of sarcomeres means myofibrils & muscle fibres contract
  • Sarcomeres retun to their original length & muscle relaxes
84
Q

What happens to each band when the sarcomere contracts (shortens)?

A
  • A-bands stay the same length
  • I-band gets shorter
  • H-zone get shorter
85
Q

What are myosin filaments like?

A

They have globular heads & binding sites

86
Q

What are the globular heads on myosin filaments like?

A

They’re hinged, so they can move back and forth

87
Q

What do each myosin head have?

A

A binding site for actin & a binding site for ATP

Actin filaments have binding sites for myosin heads, called actin-myosin binding sites

88
Q

Where is tropomyosin found?

A

It is found between actin filaments

89
Q

What does tropomyosin do?

A

It is a protein that helps myofilaments move past each other

It blocks the bindign sites in resting muscles for the myosin head

90
Q

Why can’t myofilaments slide in a resting (unstimulated) muscle?

A

In a resting muscle, the actin-myosin binding site is blocked by tropomyosin

The myosin heads can’t bind to the actin-myosin binding site on the actin filaments

91
Q

What is muscle contraction triggered by?

A

An influx of calcuim ions

92
Q

What is the process of a triggering a muscle to contract? (long version)

A

1 - When an AP from motor neurone stimulates a muscle cell, it depolarises sarcolemma - depolarisation spreads down T-tubules to the sarcoplasmic reticulum

2 - Causes sarcoplasic reticulum to release stored calcium ions (Ca2+) into the sarcoplasm

3 - Ca2+ ions bind to protein attached to tropomyosin, causes protein to change shape - pulls attached tropomyosin out of actin-myosin binding site on actin filament

4 - Exposes binding site - allows myosin head to bind

5 - Bond formed when mysoing head binds to actin filament –> called actin-myosin cross bridge

6 - Ca2+ ions activate enzyme ATP hydrolase - hydrolyses ATP to provide energy for muscle contraction

7 - Energy released from ATP causes myosin head to bend, pulls acting filament along

8 - Another ATP molecule provides energy to break actin-myosin cross bridge - so myosin head detaches from actin filament once moved

9 - Myosin head reattaches to different binding site further along actin filament - new actin-myosin cross bridge formed & cycle repeats

Cycle will cont. as long as Ca2+ ions are present

93
Q

How do myosin heads work together to pull the actin filament at the same time?

A

Many cross bridges form & break very rapidly, pulling the actin filament along - shortens the sarcomere, causes muscle to contract

94
Q

Describe the sliding filament theory of muscle contraction

A
  • Ca2+ ions cause tropomyosin to move away froma ctin binding sites, allowing myosin head to attach & form a cross-bridge
  • Myosin head changes angle, pulling actin filament along & releasing ADP
  • ATP attaches to myosin head, allowing it to detach
  • ATP hydrolysed, allowing myosin head to return to original position

Biology A-level (20 decks)

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