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Biology A Level > Nervous System > Flashcards

Nervous System Flashcards

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1
Q

Features of a reflex arc

A
  • immediate
  • specific
  • involuntary
  • innate
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2
Q

What is a stimulus

A

A change in the environment that can be detected and may provoke a response

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3
Q

What is a receptor

A

A cell that is sensitive to a stimulus

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4
Q

What is a sensory neurone?

A

A nerve cell that carries an electrical impulse from a receptor to the central nervous system

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5
Q

What is a synapse

A

A gap between two neurones

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6
Q

What is a relay neurone

A

A nerve cell that acts as a coordinator between sensory and motor neurones

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7
Q

What is a motor neurone

A

A nerve cell that carries electrical impulses from the central nervous system and the effector

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8
Q

What is effector

A

An organ or a cell that carries out a response to an electrical impulse

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9
Q

What is a response

A

A hormone is released by a gland or a muscle contracts as a result of an electrical impulse

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10
Q

What is a coordinator

A

Formulates a suitable response to a stimulus

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11
Q

What are the two parts of the nervous system?

A
  • Central nervous system

- Peripheral nervous system

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12
Q

What is the peripheral system made up of ?

A
  • Somatic (conscious control)

- autonomic system (unconscious control)

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13
Q

What is the autonomic system made up of?

A
  • Sympathetic (speeding up)

- parasympathetic (slowing down).

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14
Q

What is heart rate controlled by?

A

The sympathetic and parasympathetic nervous system

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15
Q

What receptors detect CO2 in the blood?

A

Chemoreceptors

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16
Q

Where are the receptors that detect CO2 in the blood?

A

They are in the carotid arteries (which carry blood to the brain), and the aortic arch

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17
Q

What does the sympathetic nervous system do?

A

It increases heart rate and stroke volume by releasing noradrenaline to the SAN

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18
Q

What does the parasympathetic nervous system do?

A

It decreases heart rate, blood pressure and stroke volume by releasing acetylcholine on to the SAN

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19
Q

Describe the reflex to increase heart rate

A
  • Normal heart rate due to normal conc of CO2 in blood
  • Exercise or fight or flight raises CO2
  • Chemoreceptors detect rise in CO2, and send an impulse along the sensory neurone to the medulla (acts as a relay neurone).
  • An impulse is sent along the sympathetic (motor) neurone
  • neurotransmitter noradrenaline is released to the SAN, causing an increase in heart rate and stroke volume.
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20
Q

Describe the reflex to decrease heart rate

A
  • Normal heart rate due to normal conc of CO2 in blood
  • CO2 levels decrease
  • Chemoreceptors detect drop in CO2, and send an impulse along the sensory neurone to the medulla (acts as a relay neurone).
  • An impulse is sent along the parasympathetic (motor) neurone
  • neurotransmitter acetylcholine is released to the SAN, causing a decree in heart rate and stroke volume.
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21
Q

Describe how changing heart rate is similar to a reflex

A

Stimulus (change in blood CO2) -> Receptor (chemoreceptors) -> Coordinators (Medulla) -> Effector (SAN in heart) -> Response (increase in heart rate + stroke volume).

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22
Q

What is a reflex?

A

An automatic response to a stimulus, requiring no conscious thought.

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23
Q

What is the Sinoatrial node?

A

The SAN is a small mass of specialised muscle cells in the right atrium. It initiates the cardiac cycle, spontaneously generating action potentials that cause atria to contract. It sets the basic heart rate, which can be influenced by hormones and impulses

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24
Q

What is the bundle of His

A

A tract of conducting (Purkyne) fibres that distribute the action potentials over the ventricles causing ventricular contraction

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25
Q

What can increase heart rate?

A
  • Increased physical activity
  • decrease in blood pressure
  • secretion of noradrenaline
  • imcrease in H+ or CO2 in blood
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26
Q

Why can heart rate decrease?

A
  • decreased physical activity
  • Increase in blood pressure
  • reuptake and metabolism of noradrenaline
  • decrease in H+ or CO2 in blood
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27
Q

What kind of receptor detects changes in blood pressure?

A

Baroreceptors

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28
Q

Where are baroreceptors located?

A

In the aorta, carotid arteries and vena cava

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29
Q

What is the name of the nerve for parasympathetic output from the brain to the heart?

A

The vagus nerve

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30
Q

What is the name of the nerve for sympathetic output from the brain to the heart?

A

The Cardiac nerve

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31
Q

What is the resting membrane potential?

A

In a neurone’s resting state the outside of the membrane is positively charged compared to the inside. This is because there are more positive ions outside the cells, meaning the membrane is polarised.

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32
Q

How is the resting potential created and maintained?

A

It is created and maintained by the sodium potassium pumps, which move three Na+ out for every two K+ ions moved in, but requires ATP. This creates a sodium ion electrochemical gradient because there are more Na+ out than in. The inside of the axon is negative relative to the outside.

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33
Q

What does the grey matter in the spinal cord contain?

A

Non-myelinated relay neurones

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34
Q

What does the white matter in the spine contain?

A

Myelinated neurones running up and down the cord

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35
Q

What is the myelin sheath?

A

An insulating lipid which speeds up impulses

36
Q

Describe the stages of an action potential?

A

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

37
Q

What is the stimulus stage of action potentials?

A

The stimulus excited the neurone fell membrane, causing sodium ion channels to open. Sodium ions diffuse into the neurone down the ion electrochemical gradient. This part of the membrane is depolarised

38
Q

What is the depolarisation stage of action potentials?

A

If the potential difference reaches the threshold (around -55mV) then

  • Na+ ion channel proteins open and Na+ diffuses in
  • K+ ion channel closes and the Na+/K+ pump is not working
39
Q

What is the repolarisation stage of action potential?

A

At a potential difference of around 40mV the Na+

  • Na+ ion channel closes
  • K+ ion channel opens and K+ diffuses out
  • Na+/K+ pump is active
40
Q

What is the hyperpolarisation stage of action potential?

A

The K+ channels are slow to close so there’s a slight “overshoot” where too many potassium ions diffuse out of the neurone. The voltage becomes more negative than the resting potential

41
Q

Describe saltatory conduction

A

An action potential starts at the node of ranvier, which jumps to the next node, and so on. This allows the impulse to travel much more rapidly as it doesn’t have to generate an action potential along the entire length.

42
Q

What three factors affect the speed of impulse?

A
  • Myelination and Saltatory conduction
  • Axon diameter
  • Temperature.
43
Q

How does axon diameter affect the speed of impulse?

A

With a wider diameter, there is less leakage of ions and therefore action potentials can be generated faster, as the threshold potential (of -55) is reached faster.

44
Q

How does temperature increase the speed of conductance?

A
  • The ions diffuse faster

- The enzymes involved in respiration work faster. Therefore there is more ATP for active transport in the Na+/K+ pump.

45
Q

Why is there a refractory period for action potentials?

A
  • It ensures that discrete impulses are produced, meaning that each is separate from each other.
  • It ensures that action potentials travel in one direction.
  • It limits the number of impulse transmission, which prevents overreaction to a stimulus and overwhelming the senses
46
Q

What do transducers do?

A

They convert energy in stimulus into an action potential/impulse

47
Q

What do pacinian corpuscles do?

A

They detect changes in pressure exerted on the skin

48
Q

Describe a pacinian corpuscle

A

It consists of a series of membranes containing a gel, with a naked axon (unmyelinated) which is attached to a sensory neurone

49
Q

Describe how a pacinian corpuscle detects a stimulus

A

When pressure is applied the naked axon is distorted and causes an impulse to travel along the sensory neurone. This happens as this distortion causes the stretch-mediated sodium ion channels to open

50
Q

What are the two types of light receptors, and where are they found?

A

Rod and cone cells, and on the retina of the eye.

51
Q

Describe rod cells

A
  • Give black and white vision
  • Work in low light intensity, meaning it is more sensitive
  • Low acuity - low resolution
52
Q

Describe cone cells

A
  • Give colour vision
  • Work in high light intensity, meaning that they are less sensitive
  • High acuity - high resolution
53
Q

Describe how rod cells detect a stimulus

A

On the outer segment they are packed with Rhodopsin. Rhodopsin bleaches under low light sensitivity, changing it into another isomer with a different shape. This results in a generator potential being produced.

54
Q

Describe how cone cells detect a stimulus

A

Iodopsin breaks down in high light intensity. There are three types of cone cells, that each break down in either red, blue or green light. This results in a generator potential. The generator potential is transmitted to the ganglion cell which results in an action potential. ATP is needed to resynthesise iodopsin.

55
Q

Describe how an impulse is transmitted along a synapse.

A

1) an action potential travels down the presynaptic neurone, depolarising it
2) this depolarisation opens voltage gated Ca2+ ion channels, allowing ions to diffuse in
3) this release of ions triggers vesicles to release neurotransmitters through exocytosis
4) neurotransmitters diffuse across the cleft, and bind to stereospecific receptors in the post synaptic neurone
5) this binding changes the shape of the chemically gated ion channels, allowing Na+ to diffuse in (Results in depolarisation)
6) Enzymes degrade neurotransmitters, removing them so that their effect is short-lived
7) molecules are resynthesised and reincorporated into synaptic vesicles after being reabsorbed.

56
Q

Where are Catecholamines released from in a synapse (and give an example of one)

A

Catecholamines such as adrenaline are released from adrenergic nerve endings

57
Q

Where is acetylcholine released from?

A

Cholinergic nerve endings

58
Q

What causes excitatory post-synaptic potentials, and what do they do?

A

When the neurotransmitter binding to the receptors opens chemically gated ion channels, making depolarisation more likely.

59
Q

What causes inhibitory post-synaptic potentials, and what do they do?

A

When the neurotransmitters binding to the receptors keeps chemically gated ion channels closed, promoting hyperpolarisation and making depolarisation more likely.

60
Q

Give examples of enzymes that break down neurotransmitters

A 
Monoamine oxidase (degrades Catecholamines)
Acetylcholine esterase (degrades acetylcholine)
61
Q

What are the two types of drugs?

A

Agonists and Antagonists

62
Q

What do agonists do, and how do they do this?

A

Agonistic drugs increase the usual effect of a neurotransmitter, by either

  • Mimicking it’s action at the synapse
  • preventing breakdown of the neurotransmitter
  • Increasing neurotransmitter production
63
Q

What do antagonists do, and how?

A

Antagonistic drugs decrease the usual effect of neurotransmitters, and they do this by :

  • Blocking receptor sites
  • Increasing neurotransmitter removal
  • Decreasing neurotransmitter production
64
Q

What is the cell membrane of the muscle fibre called?

A

Sarcolemma

65
Q

What does muscle contain (in terms of proteins)

A

The thin fibre Actin (which consists of triopsin and tropomyosin) and myosin (the thick fibre)

66
Q

Describe the structure of an entire muscle

A

Sarcomeres make up single muscle fibres. Multiple muscle fibres bundle together to form fascicles. Multiple fascicles bundle together to form skeletal muscle tissue, which is then enclosed in a connective tissue

67
Q

Between which two points is the sarcomere?

A

Between two Z-lines

68
Q

What is attached to the Z-line?

A

Actin is attached to the Z-line

69
Q

What is the I-band and where is it located?

A

The I-band is located where there is only actin (the thinner filament) and is attached to the Z-line. More light can pass through as it is thinner, making it lighter.

70
Q

What is the H-band and where is it located?

A

Attached to the M-line, it is a darker band due to Myosin’s thickness, meaning less light passes through.

71
Q

What is the A-band?

A

The darkest area of the sarcomere, that contains the overlap of both myosin and actin, meaning the least light can pass through.

72
Q

During contraction, how does each band change in shape?

A

The I-band and H-band shortern/shrink. The A-band stays the same length.

73
Q

Describe muscle relaxation at rest according to sliding filament theory.

A

At rest, the actin-myosin binding site is blocked by tropomyosin, meaning myocfilaments can’t slide past each other because the myosin heads can’t bind to the actin filaments.

74
Q

Describe the arrival of an action potential during muscle contraction according to sliding filament theory.

A

When an action potential stimulates a muscle cell, it depolarises the sarcolemma. Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum, causing the release of Ca2+ ions into the sarcoplasm, which binds to troponin, causing a conformational shape change, pulling the tropomyosin out of the actin binding site, exposing it, allowing the myosin head to form an actin-myosin cross bridge.

75
Q

Describe the movement of the actin filament during muscle contraction according to sliding filament theory?

A

Calcium ions activate ATP hydrolyse, which hydrolyses ATP to provide the energy needed for muscle contraction. The energy released from ATP causes the myosin head to bend, which pulls the actin filament along.

76
Q

Describe the breaking of the cross bridge during muscle contraction according to sliding filament theory.

A

Another ATP molecule provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after it’s moved. The myosin head then returns to its starting position, and attaches to a different binding site further along the actin filament.

77
Q

What is a motor unit?

A

A group of muscle fibres controlled by 1 motor neurone

78
Q

What does the strength of a muscle contraction correlate to?

A

It correlates to the number of motor units activated

79
Q

What is the neuromuscular junction?

A

Where the axon terminal joins the sarcolemma, at the motor end plate.

80
Q

Describe all the steps in how an action potential results in the formation of myosin cross bridges.

A

1) An action potential travels down the motor neurone, causing voltage gated Ca2+ channels to open. These Ca2+ ions cause vesicles to release acetylcholine through exocytosis, and these neurotransmitters diffuse across the junction.
2) When enough acetylcholine bind to the nicotinic receptors, depolarisation occurs, and spreads across the sarcolemma. This travels down into the muscle cell through ivanginations in the sarcolemma called T-tubules.
3) This action potential stimulates the release of Ca2+ ions into the myofibrils from the sarcoplasmic reticulum. Ca2+ binds to troponin, causing a conformational shape change, exposing the binding sites on actin, allowing the formation of myosin cross bridges.

81
Q

What does phosphocreatine do?

A

Phosphocreatine (which is stored in muscles) assists respiration by providing phosphates to regenerate ATP from ADP.

82
Q

Describe the structure of a slow-twitch fibre.

A

Contains a large store of myoglobin, a rich blood and many mitochondria

83
Q

Describe the structure of a fast-twitch muscle fibre.

A

Thicker and more myosin filaments, large stores of glycogen, a large store of phosphocreatine, high concentration of enzymes involved in anaerobic respiration.

84
Q

Describe the general properties of slow-twitch muscle fibres.

A

Contract slower and can respire aerobically for longer periods of time due to the rich blood supply and myoglobin oxygen store. These muscles are adapted for endurance work.

85
Q

Describe the general properties of fast-twitch muscle fibres.

A

Contract faster to provide short bursts of powerful contraction. These are adapted for intense exercise such as weight lifting.

86
Q

Describe why rod cells provide a lower visual acuity.

A

Multiple rod cells synapse with a single bipolar cell
Multiple bipolar cells synapse with a single ganglion cell
Approximately 100 rod cells are synaptically connected to a single ganglion cell
The brain is not able to interpret which impulses are sent by specific rods
If multiple rod cells connected to the same bipolar cell detect light, only one impulse from the bipolar cell is sent
Therefore, the brain receives a general, not specific, understanding of the fields of vision that are light or dark

87
Q

Describe why cone cells provide a higher visual acuity.

A

A single cone cell synapses with a single bipolar cell
A single bipolar cell synapses with a single ganglion cell
If two cones are stimulated to send an impulse the brain is able to interpret these as two different spots of light

Biology A Level (23 decks)

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