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AQA Biology > 6.2 Nervous Coordination > Flashcards

6.2 Nervous Coordination Flashcards

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1
Q

Describe the general structure of a motor neuron.

A

Cell body containing organelles and high proportion of RER
Dendrons branching into dendrites which carry impulses towards cell body
Axon a long unbranched fibre carrying nerve impulses away from cell body

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2
Q

Describe the additional features of a myelinated motor neuron.

A

Schwann cells wrap around the axon
Myelin sheath made from myelin rich membranes of Schwann cells
Nodes of Ranvier very short gaps between Schwann cells where there is no myelin sheath

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3
Q

Name 3 processes Schwann cells are involved with.

A

Electrical insulation
Phagocytosis
Nerve regeneration

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4
Q

How does an action potential pass along an unmyelinated neuron?

A

Stimulus leads to influx of Na+ ions that depolarises first section of membrane
Local electrical currents cause sodium voltage gated channels further along membrane to open while section behind repolarises
Sequential wave of depolarisation

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5
Q

How does an action potential pass along a myelinated neuron?

A

Saltatory conduction
The impulse “jumps” between nodes of Ranvier
Depolarisation cannot occur where mylein sheath acts as electrical insulator

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6
Q

Why is conduction quicker in myelinated axons?

A

Impulse doesn’t travel along whole length of axon

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7
Q

What is resting potential?

A

Potential difference across neuron membrane when not stimulated

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8
Q

Whats the range of resting potential?

A

-50mV to -90mV

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9
Q

What is the average resting potential in humans?

A

-70mV

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10
Q

How is resting potential established?

A

Membrane is more permeable to K+ than Na+
Sodium potassium pump actively transports 3Na+ out of cell & 2K+ into cell
Establishes electrochemical gradient as intracellular environment more negative than extracellular

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11
Q

Name the stages in generating an action potential.

A

Depolarisation
Repolarisation
Hyperpolarisation
Return to resting potential

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12
Q

What happens during depolarisation?

A

Stimulus causes Na+ ions to move into cell down electrochemical gradient by facilitated diffusion
Potential difference across membrane becomes more positive
If membrane reaches threshold potential, voltage gated Na+ channels open
Significant influx of Na+ ions reverses potential difference to +40mV

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13
Q

What is threshold potential?

A

-50mV

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14
Q

What happens during repolarisation?

A

Voltage gated Na+ channels close and voltage gated K+ channels open
Facilitated diffusion of K+ ions out of cell down electrochemical gradient
Potential difference across memrbane becomes more negative

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15
Q

What happens during hyperpolarisation?

A

“Overshoot” when K+ ions diffuse out, potential difference more negative than resting potential
Refractory period - no stimulus large enough to raise membrane potential to threshold
Voltage gated K+ channels close and sodium potassium pump reestablishes resting potential

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16
Q

Explain the importance of the refractory period.

A

No action potential can be generated in hyperpolarised sections of membrane to:

Ensure unidirectional impulse
Ensure discrete impulses
Limit frequency of impulse transmission

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17
Q

What is meant by the “all or nothing” principle?

A

Any stimulus that causes the membrane to reach threshold potential will generate an action potential
All action potentials have same magnitude

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18
Q

Name the factors that affect the speed of conductance.

A

Myelin sheath
Axon diameter
Temperature

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19
Q

How does myelin sheath affect speed of conductance?

A

Myelin sheath = faster

Provides insulation to axons

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20
Q

How does axon diameter affect the speed of conductance?

A

Greater diameter = faster

Less resistance to flow of ions (for depolarisation and repolarisation)
Less “leakage” of ions (easier to maintain membrane potential)

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21
Q

How does temperature affect speed of conductance?

A

Higher temperature = faster

Faster rate of diffusion (for depolarisation and repolarisation)
Faster rate of respiration (enzyme controlled) so more ATP for active transport to reestablish resting potential

Temperature too high = membrane proteins denature

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22
Q

Suggest an appropriate statistical test to determine whether a factor has a significant effect on the speed of conductance.

A

Student t-test
Compares the means of continuous data

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23
Q

Suggest appropriate units for the maximum frequency of impulse conduction.

A

Hz

24
Q

How can an organism detect the strength of a stimulus?

A

Larger stimulus raises membrane to threshold potential more quickly after hyperpolarisation
Greater frequency of impulses

25
Q

What is the function of a synapse?

A

To transmit impulses between neurons & neurons/effectors

26
Q

Why are synapses needed?

A

Electrical impulses cannot travel over junctions between neurons

27
Q

Describe the structure of a synapse.

A

Presynaptic neuron
Synaptic cleft
Postsynaptic neuron

28
Q

Describe the presynaptic neuron.

A

Ends in synaptic knob
Contains many mitochondria, endoplasmic reticulum and vesicles of neurotransmitter

29
Q

What is a synaptic cleft?

A

20-30nm gap between neurons

30
Q

Describe the postsynaptic neuron.

A

Receptors on membrane complementary to neurotransmitter
(ligand-gated Na+ channels)

31
Q

Outline the events in the presynaptic neuron when an action potential is transmitted.

A

Wave of depolarisation travels down presynaptic neuron causing voltage-gated Ca²⁺ channels open
Vesicles move towards and fuse with presynaptic membrane
Exocytosis of neurotransmitter into synaptic cleft

32
Q

How do neurotransmitters cross the synaptic cleft?

A

Simple diffusion

33
Q

Outline the events in the postsynaptic neuron when an action potential is transmitted.

A

Neurotransmitter binds to specific receptor on postsynaptic membrane
Ligand-gated Na⁺ channels open
If influx of Na⁺ ions raises membrane to threshold potential, actional potential is generated

34
Q

Why is synaptic transmission is unidirectional?

A

Only presynaptic neuron contains vesicles of neurotransmitter
Only postsynapticc membrane has complementary receptors

35
Q

Define summation.

A

Neurotransmitter from several sub-threshold impulses accumulates to generate action potential

36
Q

Where can summation not happen?

A

Neuromuscular junctions

37
Q

Name the two types of summation.

A

Temporal summation
Spatial summation

38
Q

What is temporal summation?

A

One presynaptic neuron releases neurotransmitter several times in quick succession

39
Q

What is spatial summation?

A

Multiple presynaptic neurons release neurotransmitter

40
Q

What is specific about cholinergic synapses?

A

Inhibitory or Excitatory
Use acetylcholine as primary neurotransmitter

41
Q

Where are cholinergic synapses located?

A

Motor end plate (muscle contraction)
Preganglionic neurons (excitation)
Parasympathetic postganglionic neurons (inhibition)

42
Q

What happens to acetylcholine from the synaptic cleft?

A

Hydrolysed by acetylcholinesterase into acetyl and choline
Acetyl and choline diffuse back into presynaptic membrane
ATP is used to reform acetylcholine for storage in vesicles

43
Q

Explain the importance of acetylcholinesterase.

A

Prevent overstimuation of skeletal muscle cells
Enables acetyl and choline to be recycled

44
Q

Describe the events in an inhibitory synapse.

A

Neurotransmitter binds to and opens Cl⁻ channels on postsynaptic membrane & triggers K⁺ channels to open
Cl⁻ moves in & K⁺ moves out by facilitated diffusion
Potential difference becomes more negative - hyperpolarisation

45
Q

Describe the structure of a neuromuscular junction.

A

Synaptic cleft between presynaptic neuron and skeletal muscle cell

46
Q

Compare the postsynaptic cell in a cholinergic synapse and neuromuscular junction.

A

CS: another neuron
NJ: skeletal muscle cell

47
Q

Compare the AChE location in a cholinergic synapse and neuromuscular junction.

A

CS: synaptic cleft
NJ: postsynaptic membrane

48
Q

Compare the action potential in a cholinergic synapse and neuromuscular junction.

A

CS: new action potential produced
NJ: end of neural pathway

49
Q

Compare the response in a cholinergic synapse and neuromuscular junction.

A

CS: excitatory or inhibitory
NJ: excitatory only

50
Q

Compare the neurons involved in a cholinergic synapse and neuromuscular junction.

A

CS: motor/sensory/relay
NJ: motor only

51
Q

How could drugs increase synaptic transmission?

A

Inhibit AChE
Mimic shape of neurotransmitter

52
Q

How would inhibition of AChE increase synaptic transmission?

A

Neurotransmitter will remain in synaptic cleft
Continuous stimulation of postsynaptic neurone to generate electrical impulse

53
Q

How would mimicing the shape of neurotransmitter increase synaptic transmission?

A

Able to bind to receptors
Won’t be broken down
Continuous stimulation of postsynaptic neurone to generate electrical impulse

54
Q

How could drugs decrease synaptic transmission?

A

Inhibit release of neurotransmitter
Decrease permeability of postsynaptic membrane to ions
Hyperpolarise postsynaptic membrane

55
Q

How would inhibiting the release of neurotransmitter decrease synaptic transmission?

A

Nothing will bind to receptor
No stimulation of postsynaptic neurone to generate electrical impulse

56
Q

How would decreasing the permeability of postsynaptic membrane to ions decrease synaptic transmission?

A

Won’t be enough Na⁺ ions to raise membrane to threshold potential Actional potential can’t be generated

57
Q

How would hyperpolarisation of the postsynaptic membrane decrease synaptic transmission?

A

Postsynaptic membrane potential more negative than threshold
Actional potential can’t be generated

AQA Biology (43 decks)

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