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AQA A Level Biology GRICE/HALL 12 > ✅15 - Nervous Coordination And Muscles > Flashcards

✅15 - Nervous Coordination And Muscles Flashcards

1
Q

How does the nervous system control actions?

A

It uses nerve cells to pass electrical impulses along their length and stimulate target cells by secreting neurotransmitters.

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2
Q

What is the main benefit of control via the nervous system?

A

The response is very quick, reflex action

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3
Q

What is the main potential drawback of control via the nervous system?

A

The response is short lived and restricted to one part of the body.

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4
Q

How does the hormonal system have control over the body?

A

It produces hormones which are transported in the blood plasma to their target cells, which have specific receptors on the cell surface membrane, sensitive to hormone concentration.

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5
Q

What are the main parts of a nerve cell?

A

A cell body
Dendrons
An axon
Schwann cells//myelin sheath

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6
Q

What does the cell body contain?

A

It contains all the usual cell organelles, including a nucleus and large amounts of rough endoplasmic reticulum, associated with the productions of proteins and neurotransmitters.

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7
Q

What are the dendrons?

A

Extensions of the cell body which subdivide into smaller branched fibres called dendrites that carry nerve impulses towards the cell body.

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8
Q

What is the axon?

A

A single long fibre that carries nerve impulses away from the cell body

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9
Q

What do the Schwann cells do?

A

The surround the axon, protecting it and providing electrical insulation. They also carry out phagocytosis and play a part in nerve regeneration. They wrap around the axon many times so the layers build up.

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10
Q

What is the structure and function of the myelin sheath?

A

Covers the axon and is made up of the membranes of the Schwann cells. Membranes are rich in the lipid myelin.

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11
Q

What is the structure and function of the nodes of Ranvier?

A

Constrictions between adjacent Schwann cells where there is no myelin sheath. 2-3 micro metres long and occurs every 1-3mm in humans.

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12
Q

Describe the structure and function of Sensory neurones:

A

Transmit nerve impulses from a receptor to an intermediate or motor neurone. One dendron that is often very long, carries nerve impulse towards cell body and one axon carries away from ell body

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13
Q

What is the structure and function of motor neurones?

A

Transmit nerve impulses from an intermediate or ready neurone to an effector, such as a gland or muscle. Motor neurones have a long axon and many short dendrites.

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14
Q

What is the structure and function of intermediate neurones?

A

Transmit impulses between neurones. For example from sensory to motor neurones. Have numerous short processes.

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15
Q

What can a nerve impulse be described as?

A

A sell propagating wave of electrical activity that travels along the axon membrane

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16
Q

What are the two states of the axon?

A

Resting potential and action potential

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17
Q

How is the movement of ions across the axon membrane controlled?

A

Phospholipid bilayer prevents Na+ and K+ diffusing across it
Gated ion channels only allow ions through at certain times or under certain conditions, some all the time
Some carrier proteins actively transport ions in and out of the axon, sodium-potassium pump

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18
Q

What does the control of ion movement result in?

A

The inside of the axon being negatively charged relative to the outside - RESTIG POTENTIAL, usually around 65mV

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19
Q

How is the potential difference between the axon and outside established?

A

Na+ actively transported OUT of axon by pump
K+ actively transported IN to axon by pump
Active transport of Na+ greater, so 3 Na+ move out for every 2 K+ in
More Na+ in tissue fluid outside, creates electrochemical gradient
Sodium ions begin to diffuse back in naturally, Potassium diffuse out
Most K+ gates are open while most Na+ gates are closed

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20
Q

How is an action potential created?

A

When a stimulus of a sufficient size is detected by a receptor, energy causes a temporary reversal of charge either side of this part of the axon membrane, from -65mV to 40mV

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21
Q

When an action potential is caused, the axon membrane is…

A

…depolarised

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22
Q

How does depolarisation occur?

A

Channels in the axon membrane change shape and hence open or close depending on the voltage across the membrane (voltage gated channels) at a perticular point on the axon membrane

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23
Q

Describe the process of creating an action potential:

A

Energy from stimulus causes Na+ channels to open, Na+ diffuse in and reverse potential difference
As Na+ diffuse in, more channels open, greater influx
Once action potential of 40mV established, Na+ voltage gates close and K+ open
K+ voltage gated channels open and reverse electrochemical gradient, more K+ in and repolarisation started
Outward diffusion of K+ causes temporary overshoot with inside of axon being more negative and K+ channels close

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24
Q

What are action potentials caused by?

A

Diffusion

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25
What are resting potentials maintained by?
Active transport
26
Does the size of the action potential change from one end of the axon to the other?
No
27
How is an action potential passed along the axon?
As one region of the axon produces an action potential and becomes depolarised, it acts as a stimulus for the depolarisation of the next region of the axon
28
What is saltatory conduction?
Localised currents arise between adjacent nodes of Ranvier and the action potentials ‘jump’ between nodes
29
Does an action potential move faster along a myelinated or unmyelinted axon?
Myelinated - because the events of depolarisation don’t have to take place all the way down the neurone, saltatory conduction occurs instead
30
What are the factors affecting the speed at which action potentials travel?
The myelin sheath Diameter of the axon Temperature
31
How does the myelin sheath affect the speed at which an action potential travels?
The myelin sheath increases speed at which the action potential travels because it allows saltatory conduction
32
How does the diameter of the axon affect the speed at which an action potential travels?
The greater the diameter, the faster the speed of conductance due to less leakage from a large axon (meaning membrane potentials are easier to maintain)
33
How does temperature affect the speed at which an action potential travels?
Temperature affects the rate of diffusion of ions and therefore the higher the temperature, the faster the nerve impulse. Respiration is controlled by enzymes, functioning more rapidly at high temperatures, so the higher the temperature, the more ATP and the more active transport.
34
What is the all or nothing principal?
There is a certain level of stimulus, called the threshold value, which triggers an action potential. Any stimulus below threshold will not create AP, any stimulus above will.
35
How is the size of an impulse perceived by an organism?
- By the number of impulses passing in a given time. Larger stimuli generate more impulses - By having different neurones with different threshold values, as the brain interprets the number and type of neurones the pass impulses as a result of a given stimulus and thereby determines its size.
36
What is the refractory period?
Once an action potential has been created in any region of an axon, there is a period afterwards when inward movement of sodium ions is prevented because voltage gated channels close. During this time, it is impossible for further AP.
37
What are the purposes of the refractory period?
- Ensures that APs are propagated in one direction only - It produces discrete impulses - It limits the number of action potentials
38
How does a refractory period ensure that action potentials only propagate in one direction?
APs can only pass from an active region to a resting region, as APs cannot propagate to a region that is refractory, so can only move in the direction away from the region in the refractory period.
39
How does a refractory period ensure that discrete impulses are produced?
Due to the refractory period, a new action potential cannot be formed immediately behind the first one, ensuring they are separated
40
How does a refractory period ensure that the number of actin potentials are limited?
As action potentials are separated from one another, this limits the number of APs that can pass along an axon in a given time, limiting the strength of the stimulus.
41
What is the synaptic cleft?
The gap separating two neurones
42
What is the presynaptic neurone?
The neurone releasing the neurotransmitter
43
What is the synaptic knob?
The portion at the end of the presynaptic neurone that is swollen.
44
What are synaptic vesicles?
Pockets storing neurotransmitters
45
Why are there many mitochondria and smooth ER in the synaptic knob?
They are required for producing neurotransmitters
46
What is unidirectionality?
Synapses can only pass information in one direction
47
What is spatial summation?
A number of presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone, triggering an AP
48
What is temporal summation?
A single presynaptic neurone releases neurotransmitter many times over a very short period. If the concentration exceed threshold value, an AP is triggered
49
What are inhibitory synapses?
Synapses that make it less likely that a new AP will be created on the postsynaptic neurone
50
How do inhibitory synapses operate?
- Presynaptic neurone releases neurotransmitter that binds to chloride ion protein channels, causing them to open - Cl- move into postsynaptic neurone by facilitate diffusion - Binding of neurotransmitter causes opening of K+ protein channels, K+ move out of neurone into synapse - Combined effect of Cl- moving in and K+ moving out makes inside more negative and outside more positive - Membrane potential increases to up to -80mV with -65mV resting potential - Hyperpolaristion - makes it less likely that a new AP will be created because larger influx of Na+ needed to produce one
51
What are the functions of synapses?
- Allow a single impulse along one neurone to initiate new impulses in a number of different neurones at a synapse, allowing a single stimulus to create a number of simultaneous responses - Allow a number of impulses to be combined at a synapse, allowing nerve impulses from receptors reacting to different stimuli to contribute to a single response
52
How are neurotransmitters recycled?
Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid which diffuse back across the synaptic cleft into the presynaptic neurone
53
How is recycling neurotransmitters beneficial?
It prevents it from continuously generating new action potentials in the postsynaptic neurone, so leads to the discrete transfer of information across synapses.
54
How do muscles respond to nervous stimulation?
They contract, so bring about movement
55
What are the three types of muscle?
Cardiac muscle Smooth muscle Skeletal muscle
56
What are myofibrils?
Tiny muscle fibres
57
What is sarcoplasm?
The cytoplasm shared by many muscle fibres
58
Where is most of the sarcoplasm found?
Around the circumference of the fibre
59
What is the structure of a muscle?
Muscle fibres bundled together along with capillaries and nerves. The bundles are then bundled together again to form the whole muscle
60
What is actin?
A thin filament, consisting of two strands twisted around one another
61
What is myosin?
A thicker filament consisting of long rod-shaped tails with bulbous heads that project to the side.
62
Why do myofibrils appear striped?
Due to their alternating light coloured (isotropic) and dark coloured (anisotropic) bands
63
Why do anisotropic bands appear darker?
Because thick and thin filaments overlap
64
What is the H zone?
The light coloured centre of each A band
65
What is the Z line?
The dark line in the centre of an I band
66
What is a sarcomere?
The distance between adjacent Z-lines
67
What happens to the sarcomere when a muscle contracts?
It shortens and the pattern of dark and light bands changes
68
What are the two types of muscle fibre?
Slow twitch and fast twitch
69
What are slow-twitch fibres?
Contract more slowly and provide less powerful contractions but over a longer period. Adapted to endurance work and more common in muscles that contract constantly. Adapted for aerobic respiration.
70
How are slow twitch fibres adapted?
- A large store of myoglobin (oxygen storing molecule) - Rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration - Numerous mitochondria to produce ATP
71
What are fast-twitch fibres?
Contract more rapidly and produce powerful contractions for a short period. Adapted to intense exercise and are more common in muscles which need short bursts of intense activity.
72
How are fast twitch fibres adapted?
- Thicker and more numerous myosin filaments - A high concentration of glycogen - A high concentration of enzymes involved in anaerobic respiration, provides ATP rapidly - A store of phosphocreatine, a molecule that can rapidly generate ATP from ADP in anaerobic conditions.
73
What is a neuromuscular junction?
Where a motor neurone meets a skeletal muscle fibre
74
Why are there many neuromuscular junctions along a muscle?
Because contraction of a muscle needs to be rapid and powerful
75
What happens at a neuromuscular junction?
When a nerve impulse is received, synaptic vesicles fuse with presynaptic membrane and release acetylcholine. It diffuses into postsynaptic membrane and alters its permeability to Na+ which enter rapidly, depolarising the membrane.
76
What are the similarities between the synapse and neuromuscular junction?
- Both have neurotransmitter transported by diffusion - Both have receptors, tat on binding with the neurotransmitter, cause an influx of Na+ - Both use a sodium-potassium pump to repolarise axon - Both use enzymes to break down neurotransmitter
77
How are skeletal muscles arranged?
In antagonistic pairs
78
What is the sliding filament mechanism?
The process of the actin and myosin filaments sliding past one another
79
How does the sarcomere change when a muscle contracts?
- I-band becomes narrower - Z-lines move closer together, shortening sarcomere - H-zone becomes narrower
80
What does change about the sarcomere when a muscle contracts?
The A-band remains the same width, as it is determined by the length of the myosin filaments
81
What is the structure of myosin?
Made up of two types of protein: - a fibrous protein arranged into a filament made up of several hundred molecules (the tail) - A globular protein form into two bulbous structures at one end (the head)
82
What is the structure of actin?
A globular protein whose molecules are arranged into long chains that are twisted around one another to form a helical strand
83
What is the structure of tropomyosin?
Forms long thin threads that are wound around actin filaments
84
How are actin and myosin connected?
The myosin filaments form cross bridges with the actin filaments by attaching themselves to binding sites
85
How does myosin move actin?
When attached, the filaments flex in unison, pulling the actin along. Then, they detach and using ATP as a source of energy, return to their original angle and reattach further along the actin repeatedly.
86
How does muscle stimulation occur?
An action potential reaches many neuromuscular junction simultaneously, casuing Ca2+ protein channels to open and diffuse into synaptic knob. Ca2+ casue synaptic vesicles to fuse with presynaptic membrane and release acetylcholine into cleft Acetylcholine diffuses across synaptic cleft and binds with receptors in muscle cell, causing depolarisation
87
Describe the process of muscle contraction:
- AP travels into fibre through T tubules - Tubules in contact with ER of muscle, that has low Ca2+ concentration - AP opens Ca2+ channels on ER and Ca2+ diffuse in - Ca2+ cause tropomyosin that were blocking actin binding sites to move away - ADP attached to myosin head allow myosin to form cross bridge - Myosin heads pull actin filaments - ATP attaches to head, detaching it from actin - Ca2+ activate ATPase, hydrolyses ATP to ADP, providing energy - Myosin pulls actin along again - Myosin joined tail to tail, so move actin in opposite directions - This shortens distance between Z lines as actin moved towards each other, shortens muscle
88
Describe the process of muscle relaxation:
- When nervous system ceases, Ca2+ actively transported back to ER using energy form ATP - Absorption of Ca2+ allows tropomyosin to block actin filament again - Myosin heads now unable to bind with actin, muscle relaxes
89
What is ATP needed for in muscle contraction?
- Movement of myosin heads | - Reabsorption of Ca2+ by active transport

AQA A Level Biology GRICE/HALL 12 (22 decks)

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