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Year 13 Biology A Level > Neuronal Communication > Flashcards

Neuronal Communication Flashcards

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1
Q

What is the role of a neuron?

A

Transmit electrical impulses

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2
Q

Describe the structure and function of the cell body

A
  • Contains nucleus surrounded by cytoplasm
  • Lots of endoplasmic reticulum and mitochondria for production of neurotransmitters.
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3
Q

What is the function of the dendrites?

A

Responsible for transmitting electrical impulses towards cell body

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4
Q

Describe the structure and function of the axon

A
  • Single elongated nerve fibre
  • Transmit impulses away from cell body
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5
Q

What is the role of the myelin sheath?

A

Insulates the nerve.
Allows electrical impulses to travel faster.

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6
Q

What is the myelin sheath made of?

A

Schwann cells

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7
Q

Outline the pathway of most nervous responses

A

receptor → sensory neurone → relay neurone → motor neurone → effector

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8
Q

Describe the function of a sensory neurone

A

Transmit impulses from sensory receptor to relay neurone, motor neurone or brain

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9
Q

Describe the function of a relay neurone

A

Transmit impulses between sensory and motor neurones

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10
Q

Describe the function of a motor neurone

A

Transmit impulses from relay neurone to an effector (e.g. muscle, gland)

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11
Q

Outline differences between sensory and motor neurone

A

Sensory neurons have the cell body in the middle of neurone, but motor neurons have the cell body at end of neurone.

Sensory neurons have shorter axons, motor neurons have longer axons.

Sensory neurons have cell body in peripheral nervous system, but motor neurons have cell body in central nervous system.

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12
Q

What are sensory receptors?

A
  • Specialised cells
  • Detect changes in environment
  • Specific to a single type of stimulus
  • Often located in sense organs e.g. ear, eye
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13
Q

Define transducer

A

Something that converts one form of energy to another

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14
Q

How do sensory receptors act as a transducer?

A

Converts stimulus (e.g. chemical energy) into a nerve impulse (generator potential)

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15
Q

What does the Pacinian corpuscle detect?

A

Change in pressure

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16
Q

Where are Pacinian corpuscles located?

A

In the skin and in joints

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17
Q

Describe the structure of the Pacinian corpuscle

A
  • End of sensory neurone in centre
  • Surrounded by layers of connective tissue (lamellae)
  • Each layer separated by layer of gel
  • Stretch-mediated sodium ion channels in membrane of neurone
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18
Q

Explain how the Pacinian corpuscle converts mechanical pressure into a nerve impulse

A
  • Pacinian corpuscle found within skin detects pressure
  • Pressure changes shape of Pacinian corpuscle
  • Stretch-mediated sodium channels in neuronal membrane stretch
  • Channels widen
  • Sodium ions diffuse into membrane
  • Membrane is depolarised and generator potential created
  • Generator potential creates an action potential
  • Action potential transmitted along neurones to CNS
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19
Q

Define resting potential

A
  • Electrical potential of a neurone relative to its surroundings when not stimulated
    • 70mV
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20
Q

Describe and explain how the resting potential is established and how it is maintained

A
  • Sodium-potassium pump uses ATP
  • Actively transport 3 sodium ions out of cell and 2 potassium ions in
  • K+ ions also diffuse freely back out of cell
  • Voltage-gated Na+ channels closed
  • Membrane less permeable to Na+ so fewer Na+ diffuse back in
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21
Q

Define action potential

A

Depolarisation and repolarisation of a neurone

22
Q

How is an action potential generated?

A
  • Due to facilitated diffusion across the membrane
  • Through voltage gated ion channels
23
Q

Define nerve impulse

A

Action potentials which are propagated along axons of neurones

24
Q

What is depolarisation?

A
  • Entry of sodium ions into axon through voltage-gated sodium ion channel
  • Inside of neurone now has net positive charge
  • Potential across membrane reversed (to +40mV)
25
Q

What is repolarisation?

A
  • Voltage-gated potassium ion channels open
  • Positively charged potassium ions diffuse down concentration gradient out of neurone
  • Voltage-gated sodium ion channels close
  • Inside of neurone has net negative charge again
  • Hyperpolarisation occurs, then resting potential restored
26
Q

What is the threshold potential?

A
  • Potential difference value that must be reached before sodium ion channels open
  • -50mV
27
Q

What is hyperpolarisation?

A
  • When potential difference is lower than resting potential
  • Known as ‘refractory period’
  • -80mV
28
Q

What is the purpose of the refractory period?

A
  • Prevents axon being immediately depolarised again after an action potential
  • Stops action potential travelling backwards
29
Q

Explain how an impulse passes along the axon of a neurone

A
  • Resting potential is -70 mV
  • Na+/K+ pumps maintain and re-establish the resting potential by active transport
  • When at the resting potential:
  • More sodium ions outside than inside, more potassium ions inside than outside
  • Nerve impulse is an action potential that stimulates a wave of depolarisation along axon
  • If -50 mV is reached (threshold potential) sodium ion channels open
  • Sodium ions diffuse in causing depolarisation (+40mV)
  • Potassium ion channels then open
  • Potassium ions diffuse out causing repolarisation
30
Q

Explain why depolarisation is an example of positive feedback

A
  • Na+ entering neurone at receptor causes inside of neurone to become more positive
  • This causes some voltage-gated sodium ion channels to open and Na+ to diffuse in
  • Influx of Na+ ions causes more sodium ion channels to open and depolarisation occurs
31
Q

How does potassium move across the membrane of a neurone during repolarisation?

A

Facilitated diffusion

32
Q

Explain what is meant by the ‘All-or-Nothing’ principle

A
  • If the threshold value is not reached
  • Then an action potential is not generated
  • All action potentials generated are the same size
33
Q

How is information about the strength and intensity of a stimulus communicated to the brain?

A
  • Represented by the frequency of the action potentials
  • High frequency of action potentials shows a strong stimulus
34
Q

Explain how the myelin sheath results in faster transmission of action potentials

A
  • Schwann cells produce myelin
  • Myelin sheath provides electrical insulation
  • Prevents movement of ions into and out of neurone
  • Speeds up conduction of action potential
  • Local circuits set up between nodes of Ranvier
  • Action potentials only occur at nodes of Ranvier
  • Impulse jumps from node to node by saltatory conduction
35
Q

Why is transmission of action potentials along the axon slower in the absence of saltatory conduction?

A
  • No nodes of Ranvier
  • Shorter local circuits
  • Whole axon needs to be depolarised
36
Q

Explain the difference in the speed of conduction of an action potential along the length of a
myelinated neurone and a non-myelinated neurone

A

Conduction faster in myelinated neurone because:
- Depolarisation can only occur where voltage-gated Na+ channels present
- Myelinated neurones have longer sections with no Na+ channels present
- Ion movement can only take place at the nodes of Ranvier
- Longer local circuits set up
- Saltatory conduction occurs

37
Q

Apart from myelination, name two other factors that speed up the rate of action potential
transmission

A

Axon diameter
- The bigger the diameter, the faster the transmission
- Less resistance to flow of ions in cytoplasm

Temperature
- The higher the temperature, the faster the transmission
- Ions diffuse faster at higher temperatures
- If temperature too high, protein channels denture and transmission reduces

38
Q

What is a synapse?

A

Junction between neurones or between neurones and effector cells

39
Q

Explain how an electrical impulse passes across a synapse

A
  • Pre-synaptic neurones are depolarised by action potential arriving
  • Depolarisation causes calcium ion channels to open
  • Calcium ions enter pre-synaptic knob
  • Causes vesicles containing neurotransmitter to fuse with pre-synaptic membrane
  • Neurotransmitter released into synaptic cleft by exocytosis
  • Neurotransmitter diffuses across the synapse
  • Neurotransmitter binds to receptors on post-synaptic membrane
  • Causes sodium ion channels in post-synaptic membrane to open
  • Sodium ions enter post-synaptic membrane
  • Threshold potential reached causing depolarisation to occur
40
Q

What is the most common neurotransmitter?

A

Acetylcholine

41
Q

Define cholinergic synapse

A

A synapse where acetylcholine is the neurotransmitter used

42
Q

Explain how acetylcholine is recycled at a cholinergic synapse

A
  • Pre-synaptic membrane releases acetylcholine
  • Acetylcholine diffuses across the synapse
  • Acetylcholine binds to receptors on post-synaptic membrane
  • Acetylcholinesterase hydrolyses acetylcholine into ethanoic acid and choline
  • Ethanoic acid and choline diffuse back across synapse
  • Endocytosed back into vesicles in pre-synaptic knob
  • Acetylcholine reformed
  • Requires ATP
43
Q

Outline the difference between excitatory and inhibitory neurotransmitter

A

Excitatory
- Results in depolarisation of post-synaptic membrane
- Triggers action potential
- e.g. acetylcholine

Inhibitory
- Results in hyperpolarisation of post-synaptic membrane
- Prevents action potential being triggered
- e.g. gamma-aminobutyric acid (GABA)

44
Q

Define summation

A
  • Build up of neurotransmitter
  • To levels required to reach threshold value and trigger action potential
45
Q

Describe spatial summation

A
  • Many pre-synaptic neurones connected to one post-synaptic neurone
  • Each pre-synaptic neurone releases neurotransmitter into the synapse
  • Neurotransmitter reaches high enough levels to trigger action potential in post-synaptic neurone
46
Q

Describe temporal summation

A
  • One pre-synaptic neurone connected to one post-synaptic neurone
  • Neurotransmitter released whenever action potential arrives at pre-synaptic knob
  • If many action potentials arrive in a short period, required quantity of neurotransmitter
    released
  • Triggers action potential in post-synaptic neurone
47
Q

Outline the roles of synapses in the nervous system

A
  • Allows cell signalling between neurones
  • Ensures transmission between neurones in one direction only
  • Allows impulses from more than one neurone to be passed to a single neurone
  • Ensures only stimulation that is strong enough will be passed on
  • Prevents over-stimulation
  • Allows many low level stimuli to be amplified
  • Presence of inhibitory and stimulatory synapses allows impulses to follow specific path
48
Q

Explain how synapses ensure impulses are transmitted in one direction only

A
  • Neurotransmitter receptors only present on post-synaptic membrane
  • So can only cause depolarisation of this membrane resulting in action potential
49
Q

Explain how a drug similar in shape to acetylcholine (ACh) would prevent the initiation of an action
potential

A
  • Drug competes for ACh receptor on post-synaptic membrane
  • Prevents ACh binding by blocking binding site on receptor
  • Sodium ion channels remain closed
  • Na+ cannot enter neurone
  • Insufficient depolarisation of post-synaptic membrane
  • So does not reach threshold value
50
Q

Explain the potential effects of a chemical that inhibits acetylcholinesterase

A
  • Inhibition of acetylcholinesterase reduces rate of ACh breakdown at receptors
  • ACh remains bound to receptors causing constant depolarisation of postsynaptic neurone
  • Causes constant firing of action potentials
  • Results in intense muscle spasm

Year 13 Biology A Level (14 decks)

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