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2B > CGP Nervous Communication > Flashcards

CGP Nervous Communication Flashcards

1
Q

What is a receptor?

A

A receptor is a cell or protein on a cell surface membrane that detects stimuli.

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2
Q

What is an effector?

A

A cell that brings about a response to a stimulus, to produce an effect.

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3
Q

How do receptors and effectors communicate to produce a response?

A

Via the nervous or hormonal system, or both.

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4
Q

The nervous system is made up of 3 main types of receptors. What are they?

A

Sensory neurones, relay neurones and motor neurones

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5
Q

What do sensory neurones do?

A

Sensory neurones transmit electrical impulses from receptors to the CNS (the brain and spinal cord).

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6
Q

What do relay neurones do?

A

Relay neurones transmit electrical impulses between sensory and motor neurones.

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7
Q

What do motor neurones do?

A

Transmit electrical impulses from the CNS to effectors.

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8
Q

What happens when an electrical impulse reaches the end of a neurone?

A

An electrical impulse reaches the end of a neurone, then neurotransmitters pass the info onto the next neurone, which then sends an electrical impulse.

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9
Q

Outline the stages in the nervous system, from stimulus to response.

A

Stimulus –> receptor –> CNS –> effector –> response

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10
Q

Their nervous system is split into..?

A

The central nervous system and the peripheral nervous system.

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11
Q

Outline the CNS.

A

Made up of brain abs spinal cord.

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12
Q

Outline the peripheral nervous system.

A

PNS made up of the neurones that connect the CNS to the rest of the body.

Split into: somatic and autonomic system.

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13
Q

What is the somatic nervous system?

A

The somatic movie system controls conscious activities, eg running.

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14
Q

What is the autonomic nervous system?

A

The autonomic nervous system controls unconscious activities eg digestion.

It’s split into two divisions that have opposite effects on the body: sympathetic and parasympathetic system.

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15
Q

What is the sympathetic nervous system?

A

The sympathetic nervous system gets the body ready for action - the FoF system.

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16
Q

What is the parasympathetic system?

A

The parasympathetic nervous system calms the body down, resting.

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17
Q

What is a reflex?

A

Where the body responds to a stimulus without making a conscious decision to respond.

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18
Q

How are reflexes so fast?

A

Because you don’t have to spend time deciding how to respond, so info travels really fast from receptor to effector.

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19
Q

What is a reflex arc?

A

The pathway of neurones linking receptors to effectors in a reflex.

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20
Q

Explain this reflex: hand withdrawal response to heat.

A
  1. Thermoreceptor in the skin detect the heat stimulus.
  2. The sensory neurone carries impulse to relay neurone.
  3. Relay neurone connected to motor neurone.
  4. Motor neurone sends impulses to the effector.
  5. Your muscle contracts to withdraw your hand and stop it being damaged.
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21
Q

How is a nervous response localised?

A

Because the electrical impulse reaches the end of the neurone, and neurotransmitters are secreted directly onto target cells (e.g. muscle cells) - so the nervous response is localised.

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22
Q

How are nervous responses short lived?

A

Neurotransmitters are quickly removed once they’ve done their job, so it’s short lived.

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23
Q

How are nervous responses so quick?

A

Electrical responses are really fast - so the response is rapid, allowing animals to react quickly to stimuli.

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24
Q

Are receptors specific or unspecific?

A

Specific - they only detect one type of stimulus (eg light, pressure)

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25
Q

In terms of the nervous system, what is ‘potential difference’?

A

When a nervous system receptor is in its resting state (not being stimulated) there’s a difference in charge between the inside and outside of a cell - this is generated by ion pumps and ion channels.
This means that there’s a voltage across the membrane: potential difference.

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26
Q

What is resting potential?

A

When the potential difference in a cell is at rest.

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27
Q

What is generator potential?

A

When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference.

Basically, this change in potential difference due to a stimulus is called the generator potential.

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28
Q

What affects the size of a generator potential?

A

A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference - so a bigger generator potential is produced.

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29
Q

What happens if a generator potential is big enough?

A

It triggers an action potential - an electrical impulse along a neurone.
This action potential is only triggered if the generator pit dial reaches threshold level.

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30
Q

Action potentials are all one size, so how is the strength of the stimulus measured?

A

By the frequency if action potentials (the number triggered in a certain time period).

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31
Q

What happens if a stimulus is too weak?

A

The generator potential won’t reach threshold, so there’s no action potential.

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32
Q

Outline how the pacinian corpuscle works.

A
  1. Pressure is detected, stimulating the PC.
  2. This distorts the stretch mediated ion channels.
  3. The channels open and sodium ions diffuse into the cell, creating generator potential.
  4. If generator potential reaches threshold it triggers an action potential.
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33
Q

The human eye has two types of photoreceptors…

A

Rods and cones.

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34
Q

Where are rods found?

A

Concentrated at the peripheral parts of the retina (edges)

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35
Q

Where are cones found?

A

Concentrated at the fovea.

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36
Q

Which shows only black and white: rods or cones?

A

Rods.

There are 3 types of cones: red-sensitive, green-sensitive and blue-sensitive.

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37
Q

Outline rod cells.

A
  • very sensitive to light. (They fire action potentials in dim light). This is because many rods join one neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential.
  • low visual acuity. Because many rods join the same neurone, which means light from two points can’t be told apart.
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38
Q

Outline cone cells.

A
  • less sensitive to light (only fire action potentials in bright light). This is because one joins one neurone, so it takes more light to reach threshold and trigger an action potential.
  • high visual acuity. Because cones are close together and one cone joins one neurone. When light from 2 points hits 2 cones, 2 action potentials (one from each cone) go to the brain, so you can distinguish 2 point that are close together as separate points.
39
Q

The cardiac cycle is myogenic. What does that mean?

A

It can contract and relax without receiving signals from nerves.

40
Q

Outline the heartbeat cycle.

A
  1. The SAN (in right atrium) sends out regular waves of electrical activity to the atrial walls.
  2. This causes left and right atrium to contract at same time.
  3. A band of non-conducting collagen tissue prevents waves of activity from being passed directly from the atria to ventricles.
  4. Instead, these waves of electrical activity are transferred from the SAN to the AVN.
  5. The AVN then passes the waves of electrical activity into the bundle of His. (But there’s a slight delay before the AVN reacts to make sure the atria have emptied before the ventricles contract.
  6. The Purkyne tissue (muscle fibres in bundle of His) carries the waves of electrical activity into muscular walls of right and left ventricles, causing them to contract simultaneously, from bottom up.
41
Q

Where does the heart beat cycle start?

A

The SAN, in the wall of the right atrium.

42
Q

What does the SAN do?

A

The SAN is like a pacemaker - it sets the rhythm of the heart by sending out regular waves of electrical activity to the atrial walls.

43
Q

In the heart beat cycle, why is there a slight delay before the AVN responds?

A

There’s a slight delay before the AVN reacts to make sure the atria have emptied before the ventricles contract.

44
Q

In the heart beat cycle, what is the bundle of His?

A

The bundle of His is a group of muscle fibres which are responsible for conducting the waves of electrical activity between the ventricles and to the apex (bottom of ❤️).

45
Q

In the heart beat cycle, what is the ‘Purkyne tissue’?

A

A division of the bundle of His.

The Purkyne tissue are finer muscle fibres in the right and left ventricle walls.

46
Q

In the heart beat cycle, what is the job of the Purkyne tissue?

A

The Purkyne tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously from the bottom up.

47
Q

Heart rate is controlled by…

A

The medulla oblongata.

48
Q

Outline a neurone at its resting state.

A

At a neurone’s resting state, the OUTSIDE is POSITIVELY charged compared to the inside (because there’s more positive ions outside the cell than in it).

So, the membrane is polarised - there’s a difference in charge (a potential difference) across it.

49
Q

In a neurone, how is the resting potential created and maintained?

A

By the sodium-potassium pumps.

  • the SP pumps move S ions OUT of the neurone, but the membrane isn’t permeable to S ions, so thy can’t move back in. This creates a S ion electrochemical gradient, bc there are more positive S ions outside the cell than inside.
  • the SP pump moves P ions IN to the neurone, but the membrane is permeable to P ions, so they diffuse back out the P ion channels.

This makes the outside of the cell positive charged compared to inside.

50
Q

Outline the change in potential difference during an action potential.

A
  1. A stimulus excites the neurone cell membrane, causing the S ion channels to open. The membrane becomes more permeable to S, so ions diffuse into the neurone down the S ion electrochemical gradient. This makes the inside of the neurone less negative.
  2. If the potential difference reaches threshold, more S ion channels open - so more S ions diffuse readily into the neurone: depolarisation.
  3. When the potential difference increases again, the S ions channels close, whilst P ion channels open. The membrane is now more permeable to P so P ions diffuse out of the neurone, back down the P ion conc gradient. This is repolarisation and gets the membrane back to its resting potential.
  4. Hyperpolarisation - P ion channels are slow to close so there is a slight overshoot where too many P ions diffuse out of the neurone. The potential difference becomes more -ve than the resting potential.
  5. Resting potential - the S-P pump returns the membrane to its resting potential and maintains it until the membrane is excited by another stimulus.
51
Q

Define refractory period?

A

After an action potential, the channels are still recovering and can’t be made to open. So the refractory period acts as a time delay between one action potential and the next.

52
Q

The refractory period results in…

A
  • action potentials that don’t overlap, but pass as discrete (separate) impulses.
  • action potentials that are unidirectional
  • there’s a limit to the frequency at which the nerve impulses can be transmitted.
53
Q

What does it mean; the ‘all or nothing’ nature of action potentials?

A

Once threshold is reached, an action potential will always fire with the same change in voltage, no matter how big the stimulus.

However if the threshold isn’t reached, an action potential won’t fire.

54
Q

Outline the wave of depolarisation.

A
  1. When an action potential happens, some sodium ions that enter the neurone diffuse sideways.
  2. This causes S ion channels in the next region of the neurone to open, and S ions to diffuse into that part.
  3. This causes a wave of depolarisation to travel along the neurone.
55
Q

What affects the speed of the conduction of action potentials?

A
  • myleination
  • axon diameter
  • temperature
56
Q

Outline myleination as a factor affecting the speed of conduction of action potentials.

A

In a myelinated neurone, depolarisation only occurs at the nodes of Ranvier.

The neurone’s cytoplasm conducts enough electrical charge to depolarise the next move, so the impulse jumps from node to node.

This is saltatory conduction.

57
Q

What happens in a non-myelinated neurone?

A

In a non-myelinated neurone, the impulse travels as a wave along the whole length of the axon membrane (so you get depolarisation along the whole length of membrane).

This is therefore slower than saltatory conduction.

58
Q

What are nodes of Ranvier?

A

Between Schwann cells, they are tiny patches of bare membrane. Sodium channels are concentrated here.

59
Q

Outline ‘axon diameter’ as a factor affecting the speed of conduction of an action potential.

A

Action potentials are conducted quicker along axons with bigger diameters because there’s less resistance to the dole of ions than in the cytoplasm of a smaller axon.

With less resistance, depolarisation reaches other parts of the neurone cell membrane quicker.

60
Q

Outline ‘temperature’ as a factor affecting the speed of conduction of an action potential.

A

The speed of conduction increases as the temperature increases, because ions diffuse faster.

However, the speed only increases to about 40*C, after that proteins begin to denature.

61
Q

The myelin sheath is an ________ __________.

A

Electrical insulator.

62
Q

What is a synapse?

A

The JUNCTION between a neurone and another neurone. Or between a neurone and an effector cell.

63
Q

What is a synaptic cleft?

A

The tiny gap between cells at a synapse.

64
Q

Where are neurotransmitters stored?

A

The presynaptic neurone has a swelling - a presynaptic knob. This contains synaptic vesicles filled with neurotransmitters.

65
Q

What is the reason for impulses being unidirectional?

A

Receptors are only on the post synaptic membrane, so can only travel in one direction.

66
Q

Once an impulse has occurred, and neurotransmitters are in the synaptic cleft, how is another impulse prevented?

A

Neurotransmitters are removed from the cleft so the response doesn’t keep happening.

Eg they’re broken down by enzymes, or taken back to the presynaptic neurone

67
Q

Outline the nerve impulse across a cholinergic synapse.

A
  1. Action potential arrives at the synaptic knob of pre neurone.
  2. The action potential stimulates the calcium ion channels in pre neurone to open.
  3. Calcium ions diffuse into synaptic knob.
  4. This influx of C ions into synaptic knob causes the vesicles to fuse with pre membrane.
  5. The vesicles then release acetylcholine (ACh) into the synaptic cleft (aka exocytosis).
  6. ACh diffuses across synaptic cleft and binds to specific cholinergic receptors on post neurone.
  7. This causes S ion channels in post neurone to open.
  8. This influx of S ions into post neurone causes depolarisation. An action potential in the post membrane is generated if threshold is reached.
  9. ACh is removed from the synaptic cleft so the response doesn’t keep happening. It’s broken down by an enzyme into acetylcholinease and the products are reabsorbed by the pre neurone and used to make more ACh.
68
Q

What are the different types of neurotransmitters?

A

Excitatory or inhibitory.

69
Q

Outline excitatory neurotransmitters

A

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

70
Q

Outline inhibitory neurotransmitters.

A

Inhibitory neurotransmitters hyper polarise the post neurone (make the potential difference more -ve), preventing it from firing an action potential.

71
Q

What is summation?

A

Where the effect of neurotransmitter released from many neurones is added together. There are two types: spatial or temporal summation.

72
Q

What is spatial summation?

A

Many neurones connect to one neurone.
The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the post neurone and trigger an action potential.

If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters might be no action potential.

73
Q

What is temporal summation.

A

Where 2 or more nerve impulses arrive in quick succession from the same pre neurone. This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.

74
Q

What is a neuromuscular junction?

A

A synapse between a motor neurone and a muscle cell.

75
Q

In what was are neuromuscular junctions different to cholinergic synapses?

A
  • on the NJ, the post neurone has lots of folds that form clefts. These clefts store the enzyme that breaks down ACh.
  • on the NJ, the post membrane has more receptors than other synapses.
  • on the NJ, ACh is always excitatory. So when a motor neurone fires an action potential, it normally triggers a response in a muscle cell. This isn’t always the case for a synapse between 2 neurones.
76
Q

Drugs affect synaptic transmission. In what ways?

A
  • some drugs are the same shape as neurotransmitters
  • some block receptors; so can’t be activated by neurotransmitters
  • some drugs inhibit the enzymes that break down neurotransmitters
  • some drugs stimulate the release of neurotransmitters
  • dine drugs inhibit the release of neurotransmitters.
77
Q

What are skeletal muscles?

A

Skeletal muscle is the type of muscle you use to move.

Skeletal are attached to bones by tendons.

78
Q

Muscles act is ___________ pairs.

A

Antagonistic

79
Q

Regarding antagonistic pairs of muscles, what is the relaxing / contracting muscle?

A

The contracting muscle is the agonist.

The relaxing muscle is the antagonist.

80
Q

Myofibrils contain…

A

Bundles of thick and thin myofilamenfs that move past each other to make muscles contract:

  • thick myofilaments (made of myosin)
  • thin myofilaments (made if actin)
81
Q

What are dark bands?

A

dArk bands contain the thick myosin filaments, and some overlapping thin actin filaments - A bands.

82
Q

What are light bands?

A

Light bands contain thin actin filaments only - there are called I - bands.

83
Q

What is a myofibril?

A

Made up of many short units - sarcomeres

84
Q

What are Z lines?

A

The ends of each sarcomere are marked with a Z line.

85
Q

What are M lines?

A

In the middle of each sarcomere is an M line.

86
Q

What is a H zone?

A

Around the M line is the H zone. This contains myosin filaments.

87
Q

Outline the sliding filament theory.

A

Myosin and actin filaments slide over one another to make the sarcomeres contract.

This simultaneous contraction of lots of sarcomeres means that the myofibrils and muscle fibres contract.

Sarcomeres return to their original length as the muscle relaxes.

88
Q

How are myosin filaments adapted to their function?

A

Myosin filaments have globular heads that are hinged, so can move back and forth.

Each myosin has a binding site for actin and one for ATP.

89
Q

How are actin filaments adapted to their function?

A

Actin filaments have binding sites for myosin heads: actin-myosin binding heads.

90
Q

What does tropomyosin do?

A

Tropomyosin is found between actin filaments. It helps myofilaments move past each other.

91
Q

At points, why can’t myofilaments slide past each other thus contracting?

A

Because in a resting muscle, the actin myosin binding site is blocked by tropomyosin.

So myofilaments can’t slide past each other because the myosin heads can’t bind to the actin myosin binding site on the actin filament.

92
Q

Skeletal muscles are made of?

A

Slow and fast twitch muscle fibres.

93
Q

Outline slow twitch muscle fibres.

A
  • muscles that contract slowly.
  • energy is released slowly through aerobic respiration.
  • red in colour as they’re rich in myoglobin.
  • can work for long time without getting tired.
94
Q

Outline fast twitch muscle fibres.

A
  • muscle fibres that contract very quickly.
  • energy is released through anaerobic respiration using glycogen.
  • white in colour as they don’t have myoglobin.
  • get tired quickly.
  • muscles you use for fast movement.

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