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AS and A level > Biology A2 Chapter 15 - Nervous Coordination and Muscles > Flashcards

Biology A2 Chapter 15 - Nervous Coordination and Muscles Flashcards

1
Q

What are the two main forms of coordination in animals as a whole?

A

The nervous system and the hormonal system

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2
Q

What is the function of the nervous system?

A

To use nerve cells to pass electrical impulses along their length and then stimulate the target cell by secreting chemicals (neurotransmitters) directly onto them

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3
Q

Define the term neurotransmitter

A

One of a number of chemicals that are involved in communication between adjacent neurones or between nerve cells and muscles

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4
Q

What is an example of nervous coordination?

A

A reflex action, such as the withdrawal of the hand from an unpleasant stimulus

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5
Q

What is the function of the hormonal system?

A

To produce chemicals (hormones) that are transported in the blood plasma to their target cells

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6
Q

Why are hormonal responses long lasting and widespread?

A

The target cells have specific receptors on their cell surface membranes and the change in concentration of hormones stimulates them. This results in a slower, less specific form of communication

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7
Q

What is an example of hormonal coordination?

A

The control of blood glucose concentration

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8
Q

What are neurones/nerve cells?

A

Specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another

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9
Q

What are the six components of a mammalian motor neurone?

A

Cell body, dendrons, axon, Schwann cells, myelin sheath, nodes of Ranvier

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10
Q

What is the function of the cell body in a motor neurone?

A

Contains all of the usual cell organelles, including a nucleus and large amount of RER. This is associated with the production of proteins and neurotransmitters

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11
Q

What is the function of dendrons in a motor neurone?

A

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

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12
Q

What is the function of the axon in a motor neurone?

A

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

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13
Q

What is the function of Schwann cells in a motor neurone?

A

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

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14
Q

What is the function of the myelin sheath in a motor neurone?

A

Forms a covering to the axon and is made up of membranes of Schwann cells. These membranes are rich in a lipid known as myelin

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15
Q

What is a neurone with a myelin sheath known as?

A

A myelinated neurone

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16
Q

What is the function of the nodes of Ranvier in a motor neurone?

A

Constrictions (gaps) between adjacent Schwann cells where there is no myelin sheath which allow nervous impulses to ‘jump’ from node to node

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17
Q

What do sensory neurones do?

A

Transmit nerve impulses from a receptor to an intermediate or motor neurone

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18
Q

What do motor neurones do?

A

Transmit nerve impulses from an intermediate or relay neurone to an effector, such as a gland or a muscle

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19
Q

What do intermediate or relay neurones do?

A

Transmit impulses between neurones, for example, from sensory to motor neurones

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20
Q

How is the movement sodium and potassium ions across the axon controlled (3 ways)?

A
  • The phospholipid bilayer of the axon membrane prevents ions from diffusing across
  • Channel proteins span the bilayer which allow facilitated diffusion at specific times
  • The sodium potassium pump
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21
Q

What is the resting potential of the axon in humans?

A

-65mV

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22
Q

Why can the axon be described as polarised at resting potential?

A

The inside of the axon is negatively charged relative to the outside

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23
Q

Describe the events that occur to create a difference in charge between the inside and outside of the axon

A
  1. Sodium ions are actively transported out of the axon by the sodium-potassium pumps
  2. Potassium ions are actively transported into the axon by the sodium-potassium pumps
  3. The active transport of sodium ions is more than the potassium, so 3 sodium ions move out for every 2 potassium in
  4. Although both ions are positive, outward movement of sodium is greater than the inward movement of potassium, creating an electrochemical gradient
  5. The sodium ions begin to diffuse back into the axon while the potassium ions begin to diffuse out
  6. However, most of the gates in the channels that allow potassium ions through are open, whilst sodium ones are closed
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24
Q

In terms of ions and charge, describe what happens during an action potential

A
  1. At resting potential some potassium voltage gated channels are open but sodium ones are closed
  2. The energy of the stimulus causes some sodium gates to open and sodium ions to diffuse into the axon through these channels along their electrochemical gradient, triggering a reversal in the potential difference across the membrane
  3. As sodium ions diffuse into the axon, more channels open, causing an influx of sodium ions
  4. Once +40mV is established the sodium ion channels close and potassium channels open
  5. With some potassium channels open, the gradient that was preventing outward movement of potassium ions is reversed, causing more channels to open. More diffuse out
  6. The outward diffusion of potassium ions cause an overshoot of the electrical gradient, with the inside being more negative than usual. The potassium channels close and the sodium-potassium pump causes sodium ions to be pumped out and potassium ions to be pumped in, -re-establishing -65mV
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25
Q

What are the four stages that occur when an action potential takes place (in order)?

A

Resting potential, depolarisation, hyperpolarisation, repolarisation

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26
Q

Describe how a nerve impulse is propagated in an unmyelinated axon

A
  1. A stimulus causes a sudden influx of sodium ions and so a reversal in the charge of the axon membrane
  2. The localised electrical currents established by this cause the opening of sodium ion channels further along the axon. Behind this new region of depolarisation, the sodium channels close and potassium channels open. So, once initiated, the depolarisation moves along the membrane
  3. The action potential is propagated in the same way along the axon. The outward movement of the potassium ions has continued to the extent that the axon membrane behind the action potential has returned to its original charged state
  4. Repolarisation of the axon allows sodium ions to be actively transported out, returning the axon to its resting potential and prepared for another stimulus
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27
Q

Why does an action potential pass along the axon of a myelinated neurone faster than an unmylinated one of the same diameter?

A

Action potentials occur at node of Ranvier in myelinated neurones and they ‘jump’ from node to node. In an unmyelinated neurone, the events of depolarisation have to take place all the way along the axon and not just at nodes

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28
Q

What is saltatory conduction?

A

When an action potential ‘jumps’ from node to node

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29
Q

What are the 3 factors that affect the speed of an action potential and why?

A
  1. The myelin sheath - saltatory conduction increases the speed of an action potential
  2. Diameter of the axon - greater = faster as less leakage of ions from a larger axon
  3. Temperature - affects rate of diffusion so higher = faster. Energy for active transport comes from respiration which is controlled by enzymes and these work faster at higher temperatures until a certain point.
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30
Q

What is the threshold value?

A

A certain level of stimulus which triggers an action potential. Anything below will fail to generate an action potential

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31
Q

How is strength of a stimulus detected as it is not by the size of action potentials?

A
  • The number of impulses passing in a given time. The larger the stimulus, the more impulses
  • 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 its size
32
Q

What are the 3 purposes of the refractory period?

A
  • Ensures that action potentials are propagated in one direction only as they can only pass from an active region to a resting region
  • Produces discrete impulses as a new action potential cannot be formed immediately behind the first
  • Limits the number of action potentials as they are separated from one another
33
Q

What is the refractory period?

A

Once an action potential has been created, there is a period afterwards when the sodium voltage gated channels are closed, preventing them from moving in. During this time it is impossible for another action potential to be generated and is known as the refractory period

34
Q

What is a synapse?

A

The point where one neurone communicates with another or with an effector

35
Q

What are different neurones separated by?

A

The synaptic cleft

36
Q

What is the presynaptic neurone?

A

The neurone that releases the neurotransmitter

37
Q

What is the synaptic knob?

A

Where the axon of the presynaptic neurone ends, the swollen portion is known as the synaptic knob

38
Q

Why does the synaptic knob have many mitochondria and endoplasmic reticulum?

A

To manufacture the neurotransmitter which takes place in the axon

39
Q

Where is the neurotransmitter stored?

A

Synaptic vesicles

40
Q

What is the function of the postsynaptic neurone?

A

It possesses specific receptor proteins on its membrane to receive the neurotransmitter

41
Q

What is spacial summation?

A

A number of different presynaptic neurones together release enough neurotransmitter to trigger a new action potential in the postsynaptic neurone

42
Q

What is temporal summation?

A

A single presynaptic neurone releases the neurotransmitter many times over a short period. If the concentration of neurotransmitter exceeds the threshold value of the postsynaptic neurone then an action potential is triggered

43
Q

What are inhibitory synapses?

A

Synapses that make it less likely for a new action potential to be created on the post synaptic neurone

44
Q

How do inhibitory synapses operate?

A
  • The presynaptic neurone releases a type of neurotransmitter that binds to the chloride ion protein channels on the postsynaptic neurone
  • The neurotransmitter causes the chloride ion channels to open
  • Chloride ions move into the postsynaptic neurone by facilitated diffusion
  • The binding of the neurotransmitter causes the opening of nearby potassium protein channels
  • Potassium ions move out of the postsynaptic neurone into the synapse
  • The combined effect of negatively charged chloride ions moving in and positively charged potassium ions moving out makes the inside of the postsynaptic membrane more negative
  • The membrane potential increases to -80mV
  • This is hyperpolarisation and makes it less likely that a new action potential will be created as a larger influx of sodium ions is needed to produce one
45
Q

What are excitatory synapses?

A

Synapses that produce new action potentials by causing the neurotransmitter to bind with the receptor proteins which leads to a new action potential on the postsynaptic neurone

46
Q

What is a cholinergic synapse?

A

One in which the neurotransmitter is acetylcholine

47
Q

What is acetylcholine made up of?

A

Acetyl (ethanoic acid) and choline

48
Q

Where are cholinergic synapses most commonly found?

A

In vertebrates where they occur in the CNS and at neuromuscular junctions

49
Q

What is the 6 step process of transmission across a synapse? Use acetylcholine as an example

A
  1. The arrival of an action potential at the end of the presynaptic neurone causes calcium ion protein channels to open and calcium ions to enter the synaptic knob by facilitated diffusion
  2. This influx of calcium ions cases synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft
  3. These diffuse across the cleft quickly due to a short pathway and then bind to the receptor sites on sodium ion channel proteins in the membrane of the postsynaptic neurone. This causes the sodium ion protein channels to open, allowing sodium ions to diffuse in rapidly along a concentration gradient
  4. The influx of sodium ions generates a new action potential in the postsynaptic neurone
  5. Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid which diffuse back across the synaptic cleft into the presynaptic neurone (recycling). The rapid breakdown prevents it from continuously generating a new action potential and leads to discrete impulses
  6. ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine. This is stored in synaptic vesicles for future use. Sodium ion protein channels close in the absence of acetylcholine in their receptor sites
50
Q

What are muscles?

A

Effector organs that respond to nervous stimulation by contracting and so bring about movement

51
Q

Where is smooth muscle found?

A

In the walls of blood vessels and the gut

52
Q

What is cardiac muscle?

A

A type of muscle found only in the heart and contracts continuously throughout life with no stimulation by nerve impulses

53
Q

What is smooth muscle?

A

Muscle where the contraction is not under conscious control

54
Q

What is skeletal muscle?

A

The muscle that makes up the bulk of the body and which works under conscious control

55
Q

What is the sarcoplasm?

A

The cytoplasm of muscles

56
Q

What are the two main types of protein filament which make up myofibrils, and how do they differ?

A
  • Actin - thinner and two strands twisted around each other
    -Myosin - thinker and long rod shaped tails with bulbous heads that are projected out to the side
57
Q

What are slow twitch muscle fibres?

A

Contract slower than fast twitch and provide less powerful contractions but over a long period of time

58
Q

How are slow twitch muscle fibres adapted?

A

-Adapted for aerobic respiration as found in muscles which must contract continuously, such as the calf muscles to keep the body in an upright position
- A large store of myoglobin (stores oxygen)
- Rich supply of blood vessles
- Numerous mitochondria to produce ATP

59
Q

What are fast twitch muscle fibres?

A

Contract rapidly and produce powerful contractions which last short periods of time

60
Q

How are fast twitch muscle fibres adapted to their role?

A
  • Thicker and more numerous myosin filaments
  • High concentration of glycogen
  • High concentration of enzymes involved in anaerobic respiration which provides ATP rapidly
  • Store of phosphocreatine which can rapidly generate ATP from ADP in anaerobic conditions so can provide energy
61
Q

What is a neuromuscular junction?

A

The point where a motor neurone meets a skeletal muscle fibre

62
Q

What ensures that muscle contractions are rapid and powerful?

A

There are many neuromuscular junctions along the muscle and so all the fibres can be simultaneously stimulated by action potentials rather than the wave of contraction travelling along the muscle which would take longer

63
Q

What is a motor unit?

A

When all muscle fibres supplied by a single motor neurone act together as a single functional unit

64
Q

What happens when a neuromuscular junction receives a nerve impulse?

A

The synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine which diffuses across the synaptic cleft to the postsynaptic membrane, altering its permeability to sodium ions which enter rapidly, depolarising the membrane

65
Q

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

A
  • Both have neurotransmitters that are transported by diffusion
  • Both have receptors that, once bound to the neurotransmitter, cause an influx of sodium ions
  • Both use the sodium-potassium pump to repolarise the axon
  • Both use enzymes to breakdown the neurotransmitter
66
Q

When a muscle contracts, what changes occur to the sacromere?

A
  • I band becomes narrower
  • Z lines move closer together (sacromere shortens)
  • H zone becomes narrower
  • A band remains the same as myosin has not changed length
67
Q

What is the structure of myosin?

A

A fibrous protein made arranged into a filament made up of hundreds of molecules (the tail) and a globular protein formed into 2 bulbous structures at one end (the head)

68
Q

What is the structure of actin?

A

A globular protein whose molecules are arranged into long chains that are twisted around each other to form a helical strand

69
Q

What is the structure of tropomyosin?

A

Long thin threads that are wound around the actin filaments

70
Q

What is the sliding filament mechanism?

A

The theory that actin and myosin filaments slide past one another during muscle contraction

71
Q

What is the process of muscle stimulation?

A
  • An action potential reaches many neuromuscular junctions simultaneously, causing 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, causing it to depolarise
72
Q

What is the very long process of muscle contraction? Good luck….

A
  1. The action potential travels deep into the fibre through a system of tubules that are extensions of the cell surface membrane and branch throughout the sarcoplasm
  2. The tubules are in contact with the sarcoplasmic reticulum which has actively transported calcium ions from the cytoplasm of the muscle, leading to low calcium ion concentration in the cytoplasm
  3. The action potential opens the calcium ion protein channels on the ER and calcium ions diffuse into the muscle cytoplasm
  4. The calcium ions cause the tropomyosin molecules that were blocking the binding sites on the actin filament to pull away
  5. ADP molecules attached to the myosin heads mean they are in a state to bind to the actin filament and form a cross bridge
  6. Once attached, the myosin heads change their angle, pulling the actin filament along and releasing a molecule of ADP
  7. An ATP molecule attaches to each myosin head, causing it to become detached from the actin filament
  8. The calcium ions activate ATPase which forms ADP and this hydrolysis provides the energy for the myosin heads to return to their original position
  9. The myosin head reattaches itself further along the actin filament and the cycle is repeated as long as the concentration of calcium ions in the myofibril remains high
73
Q

What is the process of muscle relaxation?

A
  • When nervous stimulation ceases, calcium ions are actively transported back into the ER using energy from the hydrolysis of ATP
  • The reabsorption of the calcium ions allows the tropomyosin to block the actin filament again
  • Myosin heads are now unable to bind to actin filaments and concentration ceases, so the muscle relaxes
  • In this state force from antagonistic muscles can pull actin filaments out from between myosin
74
Q

What is the energy for muscle contraction needed for?

A

The movement of myosin heads and the reabsorption of calcium ions into the ER by active transport

75
Q

What is phosphocreatine and how is it replenished?

A

A chemical which cannot supply energy directly to the muscle so instead regenerates ATP which can. It can act as a reserve supply of phosphate and is stored in the muscle. It is replenished using phosphate from ATP when the muscle is relaxed

AS and A level (30 decks)

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