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biology y13 > Neurones and Nervous Coordination > Flashcards

Neurones and Nervous Coordination Flashcards

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1
Q

Neurones

A
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2
Q

What are neurones?

A

Neurones (nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to the other.

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3
Q

Neurones

A
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4
Q

What is a neurone?

A

Neurones (nerve cells) are specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another

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5
Q

What are the three neurones?

A
  • sensory
  • relay
  • motor
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6
Q

What is the sensory neurone connected to?

A

the sensory receptor

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7
Q

What is the role of the Sensory neurone?

A

Nervous/ electrical Impulses are generated in response to a stimulus and passes to relay or motor neurone

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8
Q

Draw and label a sensory neurone

A
  • cell body - in the middle of the neurone
  • longer dendrites
  • dendron (comes before the cell body)
  • Axon (after cell body)
  • nodes of ranvier
  • myelin sheath
  • Schwaan cell
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9
Q

What is the role of a motor neurone?

A

transmits signals from the CNS to effectors

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10
Q

Draw and label a motor neurone

A
  • short dendrites
  • one long axon extending away from the cell body
  • nodes of ranvier
  • Myelin sheath
  • Schwaan cell
  • Axon terminal
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11
Q

What is the role of a relay neurone?

A

also known as an intermediate neurone, transmits signals from sensory to motor neurone

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12
Q

Draw a label a motor neurone

A
  • cell body
  • small axons
  • small dendrites
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13
Q

What is the role of the Cell body?

A

Contains all the usual cell organelles, including a nucleus, mitochondria and lot’s of ER, which is involved in the synthesis of neurotransmitter molecules and proteins

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14
Q

What are dendrons and dendrites?

A

these are extensions of the cell body which subdivide into smaller branched fibres called dendrites, that carry nerve impulses towards the body

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15
Q

What is an axon?

A

an axon is a single long fibre that carries nerve impulses away from the cell body

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16
Q

What are Schwaan cells?

A

schwaan cells surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis and play a part in nerve regeneration. Schwaan cells wrap themselves around the axon many times, so that thin layers of their membrane build up around it

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17
Q

What is the myelin Sheath?

A

The myelin sheath, forms a covering over the axon and is made up of membranes of schwaan cells. These membranes are rich in a lipid known as myelin. Neurones with a myelin sheath are called myelinated neurones

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18
Q

What are nodes of ranvier?

A

Constrictions between adjacent Schwaan cells where there is no myelin sheath. The constrictions are 2-3μm long and occur every 1-3mm in humans

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19
Q

What is a nerve impulse?

A

a wave of self-propagating wave of electrical activity that travels along the axon membrane. It is temporary reversal of electrical difference across the axon membrane

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20
Q

What is the reversal between?

A

The resting potential and the action potential.

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21
Q

The Resting Potential

A
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22
Q

What is the resting potential?

A

When a neurone is in it’s resting state the outside of the neurone is more positively charged than the inside of the neurone. this is because there are more positive ions outside of the cell than inside.

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23
Q

When the outside is more positive than the inside of the cell, the membrane is..?

A

Polarised - there’s a difference in charge (called the potential difference or voltage) across the membrane.

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24
Q

What is the Voltage of the membrane when it’s at it’s resting potential?

A

The voltage across the membrane when it is at rest is called the resting potential - It’s about -70mV (milivolts)

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25
Q

How is a resting potential of -70mV maintained?

A
  • the phospholipid bilayer of the axon plasma membrane prevents sodium and potassium ions diffusing across it
  • sodium-potassium pump actively transports 3 Na+ out of the axon, 2K+ into the axon
  • potassium ion channels allow facilitated diffusion of K+ out of the neurone, down their concentration gradient
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26
Q

How is a resting potential of -70mV produced?

A
  1. sodium-potassium pump actively transports 3 Na+ out of the axon/neurone and 2K+ into the axon
  2. There is a high concentration of sodium ions outside (tissue fluid surrounding axon), and a high concentration of potassium ions inside the axon
  3. The outside of the membrane is relatively more positively charged than the inside, which establishes and electrochemical gradient. The membrane is said to be polarised, meaning it has an electrochemical gradient or voltage (potential difference) across it.
  4. There are also voltage-gated sodium and potassium ions imbedded within the membrane. More Voltage-gated sodium channels are closed and more Voltage gated potassium ion channels are open

5.some sodium ions diffuse naturally back into the axon but more potassium ion channels are open

  1. Therefore, High rate of K+ by facilitated diffusion, out of the axon down a concentration gradient
  2. Outward diffusion of K+ makes the inside of the membrane more negative compared to the outside.
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27
Q

Action Potential

A
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28
Q

What triggers an action potential to occur?

A

when a neurone is stimulated, Voltage-gated sodium ion channels in the cell membrane open, if the stimulus is big enough, it will cause a change/reversal in potential difference. The membrane is said to be depolarised

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29
Q

How is an action potential generated?

A
  1. At the resting potential, some Potassium voltage-gated channels are permanently open but sodium voltage-gated channels are closed
  2. The energy of a stimulus excites the neurones cell membrane, causing Voltage-gated sodium ion channels to open. the membrane becomes more permeable to sodium ions, so sodium ions diffuse down into the axon down the sodium ion electrochemical gradient. this makes the inside of the axon less negative, being positively charged.
  3. Thus triggers a reversal in potential difference across the membrane, causing depolarisation of the cell membrane
  4. if the potential difference reaches the threshold value around -55mV, more sodium ion channels open, so more sodium ions diffuse into the neurone.
  5. Once an action potential of around +40mV has been established, the voltage gates on the sodium ion channels close and voltage gated potassium ion channels open, the membrane is more permeable to potassium ions
  6. with these channels now open, the electrochemical gradient that was now preventing further outward movement of K+ is now reversed, causing more K+ to diffuse out of the neurone, starting to repolarise the axon
  7. Hyperpolarisation - the outward diffusion of these potassium ions causes a temporary overshoot of the electrochemical gradient, with the inside of the axon being more negatively charged to outside (than the resting potential)
  8. voltage-gated potassium ion channels now close and the activities of the sodium-potassium pump, causes sodium ions to be pumped out of the membrane and potassium ions into the axon.
  9. The resting potential of -65mV is restablished, and the axon is said to be repolarised.
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30
Q

Briefly describe the passage of an axon potential down an unmyelinated neurone. (intro)

A
  • Once an action potential has been created, an action potential rapidly moves along the axon
  • The size of the axon potential remains the same from one end of the axon to the other
  • nothing physically moves from one side to the other
  • when one region of an axon produces an axon potential, and becomes depolarised, it acts as a stimulus for the next region of the axon
  • therefore, action potentials are generated across the axon membrane in this manner
  • the action potential is thus a travelling wave of depolarisation
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31
Q

Describe fully how an action potential is propagated along an unmyelinated neurone?

A
  1. at this point, the neurone is at rest. so conc. of Na+ = high compared to inside, whereas K+ = high inside compared to outside. However more positive ions on outside. so membrane = polarised.
  2. A stimulus causes a sudden influx of sodium ions hence a reversal of charge on the axon membrane. This is the action potential and the membrane is depolarised
  3. the localised electrical currents established by the influx of sodium ions cause the opening of Sodium voltage-gated channels a little further along the axon. The resulting influx of sodium ions in this region causes depolarisation.
  4. Behind this region of depolarisation, the sodium-voltage gated channels close and potassium ion channels open. potassium ions begin to leave the axon down their electrochemical gradient. So once initiated, the depolarisation moves along the membrane.
  5. the action potential is propagated in the same way further along the axon. the outward movement of potassium ions has continued to the extent that the axon membrane behind the action potential has returned to it’s original charge (+ outside, - outside). The membrane has been repolarised. so has returned to it’s resting potential. ready for a new stimulus
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32
Q

state the difference between the propagation of an action potential down an myelinated and unmyelinated neurone?

A

action potentials move faster along myelinated neurones compared to unmyelinated neurones

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33
Q

describe the role of the myelin sheath during the propagation of an action potential?

A

the myelin sheath is an insulating layer of fatty material secreted by schwaan cells. Na+ and K+ ions cannot pass through this thin layer, so prevents the movement of ions into and out of the axon, preventing depolarisation. (so action potentials)

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34
Q

Describe fully how an action potential is propagated along a myelinated neurone?

A
  • action potentials move down the neurone via saltatory conduction
  • the myelin sheath is an insulating layer of fatty material secreted by schwaan cells. Na+ and K+ ions cannot pass through this thin layer, so prevents the movement of ions into and out of the axon, preventing depolarisation. (so action potentials)
  • depolarisation only occurs at the nodes of Ranvier
  • and action potentials can jump from node to node due to localised electrical circuits between adjacent nodes
  • this process in known as saltatory conduction
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35
Q

What is the nerve impulse?

A

the transmission of an action potential along the axon of a neurone.

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36
Q

What are the factors affecting the speed at which an action potentials travels?

A
  • the myelin sheath
  • diameter of the axon
  • temperature
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37
Q

Describe how the myelin sheath affects the transmission of an action potential?

A

the myelin sheath acts as an electrical insulator, preventing an action potential from forming in the part of the axon covered by myelin. it jumps from one node of Ranvier to the other (saltatory conduction). This increases the speed of conduction from 30m s-1 in an unmyelinated neurone to 90 ms-1 in a similar myelinated one.

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38
Q

Describe how the diameter of the axon affects the speed at which an action potential travels along a neurone?

A

the greater the diameter of the axon, the faster the speed of conductance. this is due to less leakage of ions from a large axon. (leakage makes membrane harder to maintain)

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39
Q

Describe how the temperature affects the speed of an action potential down an axon?

A

Temperature affects the rate of diffusion of ions and therefore the higher the temperature, the faster the nerve impulse. The energy for active transport comes from respiration. Respiration, like sodium-potassium pump is controlled by enzymes. enzymes function more rapidly at higher temperatures and above a certain temperature, they are denatured and impulses fail to be conducted at all

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40
Q

What type of animals is this crucial for?

A

in cold-blooded animals (ectotherms), whose body temperature varies in accordance to the environment

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41
Q

What is the All or Nothing principle?

A
  • nerve impulses are described as all or nothing responses.
  • there is a certain level of stimulus. called the threshold value (-55mV) , which triggers an action potential
  • below the threshold value no action potential is generated
  • Any stimulus above the threshold value above the threshold will succeed in generating an action potential and so a nerve impulse will travel
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42
Q

Explain the use of this?

A

this is important, s it makes sure animals only respond to large enough stimuli rather than responding to every slight change in the environment, which would overwhelm them.

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43
Q

In which two ways can an organism perceive the size of a stimulus?

A
  • By the number of impulses passing in a given time. the larger the stimulus, more impulses generated in a given time
  • by having different neurones with different threshold values. the brain interprets the number and type of neurones that pass impulses, as a result of a given stimulus and thereby determines it’s size
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44
Q

What is the refractory period?

A

once an action potential has been generated, the membrane enters a refractory period when it can’t be stimulated, because sodium voltage-gated ion channels are closed and can;t be opened

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45
Q

what are the three purpose of the refractory period?

A
  • it ensures that action potentials are only propagated in one direction only– this stops the action potential from spreading out in two directions, which would prevent a response
  • it produced discrete impulses - meaning that an action potential cannot be generated immediately after another one to make sure each is separate from another
  • it limits the number of action potentials - As action potentials are separate from one another. This is important to prevent over reaction to a stimulus and therefore overwhelming the senses
46
Q

Structure and function of Synapses

A
47
Q

What is a synapse?

A

a synapse is a junction between two neurones
OR the point where one neurone communicates with another neurone or effector

48
Q

Draw and label the different parts of the synapse?

A
49
Q

What is the synaptic cleft?

A

this is a small gap between the two neurones, which is approximately 20-30nm wide

50
Q

What is a neurotransmitter?

A

a neurotransmitter is a chemical released from vesicles in the presynaptic neurone

51
Q

what is the presynaptic neurone?

A

the neurone that releases the neurotransmitter

52
Q

What is the synaptic knob?

A

the axon of the pre-synaptic neurone ends in a swollen portion called the synaptic knob

53
Q

What is also present in the synaptic knob in abundance?

A

Mitochondria - (ATP needed)

54
Q

Describe how information is transferred between two synapses.

A
  1. An action potential arrives at the synaptic knob. Depolarisation of the synaptic knob leads to the opening of voltage gated calcium ion channels. Ca2+ diffuse into the synaptic knob
  2. Influx of Ca2+ stimulates vesicles containing neurotransmitter to move towards and fuse with the pre-synaptic membrane. The neurotransmitter is released into the synaptic cleft
  3. The neurotransmitter diffuses across the synaptic cleft, down a concentration gradient to the post-synaptic membrane and binds to receptors on the surface of the post-synaptic membrane - as the neurotransmitter is complimentary in shape to receptor
  4. This causes Na+ channels on the post-synaptic membrane to open, Na+ diffuse into the post-synaptic neurone. If enough Na+ diffuse in, above the threshold (-55mV), then the post-synaptic membranes becomes depolarised and can trigger an action potential.
  5. Neurotransmitter is then degraded and released from the receptor, Na+ channels and the post-synaptic neurone can re-establish resting potential. The neurotransmitter is transported back into the pre-synaptic neurone where it is recycled.
55
Q

What is some features of the synapse?

A
  • unidirectionality
  • summation
  • excitatory and inhibitory
56
Q

What is meant by unidirectionality?

A

synapses can only pass information in one direction only - from the pre-synaptic neurone to the post-synaptic neurone.

57
Q

Why do impulses only travel in one direction?

A

Vesicles are only found in the pre-synaptic neurone, so neurotransmitters are only released fro the pre-synaptic membrane. Receptors are also only found on the post-synaptic neurone, so neurotransmitters can only bind to to the receptors on that side.

58
Q

Why do Neurotransmitter need to be hydrolysed/broken down?

A

If the neurotransmitter remains attached to the receptors on the post-synaptic membrane, this means that constant action potentials will be generated and still carry out responses even when the stimulus is no longer present.

59
Q

Neurotransmitters can have two types of effects on the synapse, what are they?

A

Neurotransmitter can have either an EXCITATORY or INHIBITORY effect on the synapse (or BOTH)

60
Q

What is an Excitatory neurotransmitter?

A

An excitatory neurotransmitter leads to depolarisation of the post-synaptic neurone, making it fire an action potential

61
Q

What is an example of a Excitatory neurotransmitter?

A

Acetylcholine at a Cholinergic Synapse

62
Q

What is a Cholinergic Synapse?

A

A type of synapse where the neurotransmitter is Acetylcholine and can be broken down into acetyl and choline

63
Q

Describe how information is passed across a Cholinergic Synapse?

A
  1. An action potential arrives at the synaptic knob. Depolarisation of the synaptic knob leads to the opening of voltage gated calcium ion channels. Ca2+ diffuse into the synaptic knob
  2. Influx of Ca2+ stimulates vesicles containing acetylcholine to move towards and fuse with the pre-synaptic membrane. Acetylcholine is released into the synaptic cleft by exocytosis
  3. Acetylcholine molecules diffuse across the synaptic cleft, down a concentration gradient (very quickly because the diffusion pathway is short) to the post-synaptic membrane and binds to (cholinergic) receptors on the surface of the post-synaptic membrane - as the neurotransmitter is complimentary in shape to receptor
  4. This causes Na+ channels on the post-synaptic membrane to open, Na+ diffuse along a concentration gradient into the post-synaptic neurone. If enough Na+ diffuse in, above the threshold (-55mV), then the post-synaptic membranes becomes depolarised and can trigger an action potential.
  5. Acetylcholine is then hydrolysed by acetylcholinesterase into acetyl and choline, which diffuses back via the synaptic cleft into the pre-synaptic neurone. (recycled)
  6. ATP is released by the mitochondria and is used to re-synthesise acetylcholine and is stored in vesicles for future use. ATP is also used to actively transport calcium ions out of the presynaptic membrane
  7. Na+ channels close and the post-synaptic neurone can re-establish resting potential.
64
Q

Describe the importance of breaking down Acetylcholine at the post-synaptic membrane?

A
  • prevents it from continuously generating a new action potential
  • leads to discrete transfer of information across synapses
65
Q

Why is there large amounts of mitochondria in the pre-synaptic knob?

A

ATP is needed to re-synthesise acetylcholine and to actively transport calcium ions out of the pre-synaptic membrane

66
Q

What is an Inhibitory Synapse?

A

Some synapses make it less likely for a new action potential to be created on the post-synaptic membrane.
OR
A synapse where inhibitory neurotransmitters are released from the pre-synaptic membrane following an action potential

67
Q

Describe the effect of inhibitory neurotransmitters?

A

Inhibitory neurotransmitters HYPERPOLARISE the post-synaptic membrane (make the potential difference more negative), preventing it from firing an action potential.

68
Q

Give an example of a neurotransmitter which has an Inhibitory effect n the synapse?

A

GABA - when it binds to it’s receptor it causes K+ channels to open on the post-synaptic membrane, hyperpolarising the neurone

69
Q

Describe how an Inhibitory synapse works?

A
  1. the pre-synaptic neurone releases inhibitory neurotransmitter (GABA) which binds to Chloride ion channels on the post-synaptic membrane
  2. this causes Chloride ion channels to open
  3. Chloride ion channels move into the post-synaptic membrane by facilitated diffusion
  4. The binding of GABA causes the opening of nearby potassium K+ ion channels to open
  5. potassium ion K+ move out of the post-synaptic neurone into the synapse
  6. The combined effect of negatively charged chloride ions moving in and positively charged potassium ions moving out is to make the inside of the post-synaptic membrane more negative and the outside more positive (Hyperpolarisation)
  7. the membrane potential increases to as much as -80mV compared with the usual -65mV at resting potential (hyperpolarisation)
  8. Hyperpolarisation and reduces the chance of a new action potential occurring, and so a larger influx of Sodium ions Na+ is needed to reach threshold for an action potential
70
Q

What is Summation?

A

summation is the rapid build-up of neurotransmitters in the synapse to help generate an action potential. (spatial or temporal)

or in other words (the total sum of lot’s of smaller impulses triggers an action potential)

71
Q

Why is summation needed?

A

This is needed because some action potential (low-frequency AP) do not result in sufficient concentrations of neurotransmitter being released to bind to the post-synaptic membrane to generate a new action potential. But they can do in summation

72
Q

What is spatial summation?

A

where a number of of different pre-synaptic neurones together release enough neurotransmitter to exceed the threshold value of the post-synaptic neurone. Together they therefore trigger an action potential

73
Q

What is Temporal Summation?

A

Where a single presynaptic neurone releases neurotransmitter many times over a short period. If the concentrations of neurotransmitter exceeds the threshold value of the postsynaptic neurone, then a new action potential is triggered.

74
Q

What is convergence and divergence?

A

Divergence: Allow a single action potential along one neurone to be transmitted to several different neurones

Convergence: effect of stimuli at different receptors can interact (single response)

75
Q

Effect of Drugs at the synapse

A
76
Q

Some drugs are the same shape as the neurotransmitter, so mimic their action at receptors, what are these types of drugs called?

A

Agonists

77
Q

Some drugs block receptors so they can’t be activated by receptors, what are they called?

A

Antagonists

78
Q

Describe the effect of Curare a known antagonists on the synapse of neuromuscular junction?

A
  • Curare blocks the effect of acetylcholine by blocking receptors
  • muscle cells can not be stimulated
  • results in muscle being paralysed
79
Q

Some drugs inhibit the enzyme that breaks down neurotransmitter. This means there is more neurotransmitter bound to receptors and are there for longer. Describe what these drugs may lead to in the synapse of Neuromuscular junction?

A
  • preventing breakdown of acetylcholine in the synaptic cleft = more action potentials
  • this can lead to a loss of muscle control
80
Q

Give example of a drug which prevents neurotransmitter being released. And what does this do?

A
  • e.g Opioids
  • Block calcium ion channels
  • less receptors activated
  • less neurotransmitter released
  • no action potential
81
Q

Neuromuscular Junction

A
82
Q

What is the Neuromuscular Junction?

A

This is the synapse that occurs between a motor neurone and a muscle.

83
Q

Describe Synaptic Transmission at he Neuromuscular Junction?

A
  • when an impulse travelling along the axon of a motor neurone arrives at the presynaptic membrane, the action potential causes calcium ions to diffuse into the presynaptic neurone
  • This stimulates vesicles containing neurotransmitter acetylcholine to fuse with the presynaptic membrane
  • The acetylcholine that is releases diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma (surface membrane of the muscle fibre)
  • this stimulates sodium ion channels in the sarcolemma top open, allowing sodium ions to diffuse in
  • This depolarises the sarcolemma, generating an action potential that passes along the sarcolemma and down the t-tubules towards the centre of the muscle fibre
  • These action potentials cause voltage-gates calcium ion channel proteins in the membranes of the sarcoplasmic reticulum to open
  • Calcium ions diffuse out of the sarcoplasmic reticulum and into the sarcoplasm surrounding the myofibrils
  • this causes the muscles to contract via the sliding filament theory.
84
Q

Compare the Cholinergic Synapse to the Neuromuscular junction.

A
  • FINISH OFF CARD
85
Q

TYPES OF MUSCLES/ MUSCLE STRUCTURE

A
86
Q

What is a muscle?

A

Muscles are effector glands made up of contractile tissue, they contract in response to nervous impulses

87
Q

What are the different types of muscle?

A

Skeletal muscle, Cardiac muscle, Heart muscle

88
Q

What is the cardiac muscle?
Describe the type of contraction, control, speed of fatigue, distribution in the body and overall function of the cardiac muscle?

A
  • Also known as the heart muscle
  • contraction is rapid and powerful
  • Involuntary control - Myogenic
  • Resistant to fatigue
  • Found in the heart (cells)
  • Overall function - Pump blood
89
Q

What is the Smooth muscle?
Describe the type of contraction, control, speed of fatigue, distribution in the body and overall function of the smooth muscle?

A
  • Also known as the unstriated muscle
  • contraction is slow and less powerful
  • Control is voluntary (by the ANS)
  • Speed of fatigue is slow
  • Found in internal organs such as the stomach, oesophagus, uterus, veins, arteries
    Overall function is PERISTASIS - responsible for often slow and rhythmic squeezing
90
Q

What is the Skeletal muscle?
Describe the type of contraction, control, speed of fatigue, distribution in the body and overall function of the Skeletal muscle?

A
  • Also known as the striated muscle
  • Contraction is rapid and powerful
  • Control is voluntary
  • Rapidly fatigues
  • Attached to the skeleton by tendons
  • Responsible for locomotion and posture
91
Q

What are Antagonistic Pairs?

A

Muscles that work together to to move a bone are called antagonistic pairs.

They pull in opposite directions. One muscle contracts, the other relaxes.

The contracting muscle is called the agonist and the relaxing muscle is called the antagonist

92
Q

Describe the structure of the skeletal muscle

A

Muscles are made up of muscle fibres called myofibrils. Myofibrils are made up of fused cells that share the same nuclei and cytoplasm, Known as the Sarcoplasm, and there is a high number of mitocodria.

93
Q

In the sarcoplasm, what organelles is there?

A

There is a large concentration of mitochondria and endoplasmic reticulum (sarcoplasmic reticulum0

94
Q

Importance of Myofibrils?

A

Myofibrils collectively line up to maximise strength. So myofibrils are arranged in order to give maximum strength for contraction. If muscle was made up of individual cells joined end to end, it would not be able to perform the function of contraction efficiently.

95
Q

Which two key types of protein is myofibrils made up of?

A
  • Actin - which is thinner is a globular protein and consists of two strands twisted around one another to form a helical strand. Tropomyosin forms a thin thread around Actin (specifically the Binding sites)
  • Myosin - which is thicker Fibrous protein made up of several hundred molecules with a globular head
96
Q

Why do myofibrils appear striped under a microscope, and why do these light and dark bands change?

A

-Myofibrils appear striped due to their alternating light-coloured and dark-coloured bands.
-The light bands are called the I bands (isotropic bands). They appear lighter because the thick and thin filaments do not overlap in this region.
-The dark bands are called A bands (anisotropic bands). They appear darker because the thick and think filament overlap in this area.
- At the centre of each A band is a lighter-coloured region called the H-zone
- At the centre of each I band is a line called the Z-line. The distance between the adjacent Z-lines is called the sarcomere.
- when a muscle contracts, these sarcomeres shorten and the pattern of light and ark bands changes

97
Q

Evidence for the Sliding Filament theory?

A
  • If the sliding Filament theory is correct. Then there will be more overlap of Actin and Myosin in a contracted muscle than in a relaxed one.
  • When a muscle contracts the following changes are observed
  • The I band becomes narrower
  • The Z-lines move closer together, or in other words, the sarcomere shortens.
  • The A band remains the same width, (as the width of this band is determined by the length of myosin filaments
  • (myosin filaments have not become shorter)
98
Q

What is another important protein found in muscle?

A

Tropomyosin, which forms a fibrous strand over the actin filament

99
Q

What is the Sliding Filament Theory?

A

Muscle contraction is explained by the sliding Filament theory. This is where myosin and Actin filaments slide over one another to make the sarcomeres contract- the myofilaments themselves don’t contract

100
Q

What is the sarcomere?

A

The membrane of the muscle

101
Q

What is Myosin, describe it’s appearance?

A

Myosin filaments have a globular head that are cross-bridge, so they can move back and forth. Each myosin head has a binding site for actin and a binding site for

102
Q

Describe the positions of Actin and Myosin in resting muscles?

A

-in a resting muscle, the actin-myosin binding site is blocked by tropomyosin
-This prevents Actin-myosin cross bridges being formed, as myosin heads can not bind to the actin filaments

103
Q

What are Actin filaments?

A

Actin filaments have binding sites for myosin heads, called actin-myosin binding sites. Another protein called tropomyosin is found between actin filaments. It helps myofilaments move past each other.

104
Q

Describe the process of muscle contraction, using the sliding Filament Theory?

A
  • An action potential reaches many neuromuscular junctions simultaneously, causing calcium ion protein channels to open and calcium ion protein channels to open and calcium ions to diffuse into the synaptic knob
  • The calcium ions cause the synaptic vesicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
  • acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle cell-surface membrane (sarcolemma), causing it to depolarise
    MUSCLE CONTRACTION
  • The action potential/depolarisation travels deep into the muscle fibre through a system of t-tubules that are extensions of the cell-surface membrane to the sarcoplasm and to the sarcoplasmic reticulum
  • This causes the sarcoplasmic reticulum to release stored Ca2+ ions into the sarcoplasm down a conc gradient
  • the calcium ions cause (bind to) the tropomyosin molecules, causing them to change shape. The tropomyosin molecules that were blocking the (actin-myosin) binding sites on the actin filament to pull away.
  • ADP molecules attached to the myosin heads mean they are in a state to bind to the actin filament and form a actin-myosin cross-bridge
  • Once attached to the actin filament binding site, the myosin heads change their angle , pulling the actin filament along as they do so and releasing a molecule of ADP
  • An ATP molecule attaches to each myosin head, causing it to become detached from the actin filament
  • The calcium ions then activate the enzyme ATPase which hydrolyses the ATP to ADP. The hydrolysis of ATP to ADP provides the energy for the myosin head to return to it’s original position
  • The myosin head, once more with an attached ADP molecule then reattaches itself further along the actin filament pulling in a kind of rowing action and the cycle is repeated until the muscle contraction is completed and as long as the conc. of the calcium ions in the myofibrils remains high
  • then ATP is used to cause active transport to move calcium ions out of the muscle fibre causing relaxation of the muscle.
105
Q

Describe what occurs during muscle relaxation?

A
  • calcium ions are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP
  • This reabsorption of calcium ions allows tropomyosin to block the actin-myosin binding site
  • Myosin heads are now unable to bind to the actin-myosin binding sites
  • Therefore contraction ceases
106
Q

What is ATP require for? - MSA

A
  • Attachment/cross-bridges between acting and myosin (ADP allows for binding)
    -‘Power stroke’/ movement of myosin heads (pulling of action)
  • Attachment of myosin heads
  • Myosin heads move back to their original positions/ ‘recover stroke’
  • Active transport of calcium ions back into the sarcoplasmic reticulum during muscle relaxation.
107
Q

During situations of Fight or flight, there is a great demand for ATP, at a faster rate at which the blood can supply oxygen, How does the muscle cell obtain more ATP?

A

Three main ways:
- Most ATP is generated via oxidative phosphorylation, however it’s more suitable for low-energy exercise
- therefore, a means of rapidly generating ATP anaerobically is also required
- This is achieved by using a chemical called PHOSPHOCREATINE (phosphorylating ADP)

108
Q

Describe how phosphocreatine supply more ATP and oxygen to muscle cells during the Situations of danger?

A
  • phosphocreatine cannot supply energy directly to the muscle , so instead it regenerates ATP, which can supply.
  • Phosphocreatine is stored in muscles and acts as a reserve supply of phosphate, which is available immediately to combine with ADP and so reform ATP.
    -The phosphocreatine store is replenished using phosphate from ATP when the muscle is relaxed.
109
Q

What are the two type of muscle twitch fibres?

A
  • Slow twitch fibres
  • Fast Twitch fibres
110
Q

SLOW TWITCH FIBRES: - Finish off using Powerpoint
-Function:
-Where are they found:
-Length of contraction
- Blood supply
-Type of respiration
-Number of mitochondria
-Size of calcium ion stores in the endoplasmic reticulum
-Amount of phosphocreatine
-Stores of Glycogen
-Speed of ATP hydrolysis

A

Function: Contract slowly and can work for a long time without getting tired. This makes them good for endurance activities
Found: Are found in muscles you use for posture, such as muscles in the back and calves (must contract continually to keep body in an upright position)
Contraction: Constantly contracting - long time
Blood supply: Good blood supply - more capillaries
Type of respiration - Aerobic respiration
-Number of mitochondria - Lots/numerous of mitochondria
-Calcium store: Small stores
-Phosphocreatine =
-Glycogen Stores = small amounts
- Speed of ATP hydrolysis - Slow rate

111
Q

FAST TWITCH FIBRES: - Finish off using Powerpoint
-Function:
-Where are they found:
-Length of contraction
- Blood supply
-Type of respiration
-Number of mitochondria
-Size of calcium ion stores in the endoplasmic reticulum
-Amount of phosphocreatine
-Stores of Glycogen
-Speed of ATP hydrolysis

A

-Function = Contract very quickly over a short period of time
-Where are they found = Are found in muscles you use for fast movement , such as legs arms, eyes
-Length of contraction = Short, Rapid
- Blood supply = Less capillaries = low blood supply
-Type of respiration = Anaerobic respiration
-Number of mitochondria = Few
-Size of calcium ion stores in the endoplasmic reticulum - Large stores
-Amount of phosphocreatine =
-Stores of Glycogen = High amounts
-Speed of ATP hydrolysis = Faster rate

112
Q

DONE!!

A

biology y13 (13 decks)

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