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A-Level AQA Biology > Nervous coordination > Flashcards

Nervous coordination Flashcards

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1
Q

Describe the general structure of a motor neuron.

Cell body: Contains
Dendrons: branch
Axon: long

Dendron - towards
Axon: away

A

Cell body: contains organelles & high proportion of RER.

Dendrons: branch into denrites which carry impulses towards cell body.

Axon: a single long unbranched fibre that carriers nerve impulses away from cell body.

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2
Q

Describe the additional features of a myelinated motor neuron.

Wrap

made from

short between

A
  • Schwann cell: wrap around the axon many times.
  • Myelin sheath: made from myelin-rich membranes of schwann cells.
  • Nodes of Ranveir: very short gaps between neighbouring Schwann cells where there is no myelin sheath,
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3
Q

Name 3 processes Schwann cells are involved in.

A
  • Electrical insulation
  • Phagocytosis
  • Nerve regeneration.
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4
Q

How does an action potential pass along an unmyelinated neuron?

  1. points
A
  1. Stimulus leads to influx of Na ions. First setion of membrane depolarises.
  2. Local electrical currents cause sodium voltage-gated channels
    further along membrane to open. Meanwhile, the section behind begins to repolarise.
  3. Sequential wave of depolarisation
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5
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axon

what happens to impulse

what cannot occur

what does this mean for the impulse

A

Saltatory conduction: Impulse “jumps’ from one node of Ranivier to another.

why?: Depolaristion cannot occur where myelin sheath acts as electrical insulator.

meaning: So impulse does not travel along whole axon length.

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6
Q

What is resting potential?

A

Potential difference (voltage) across neuron membrane when not stimulated (-50 to -90mV< usually about -70 mV in humans).

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7
Q

How is resting potential established?

adaptation of membrane

what comes in and out

cell contents are more..

A
  1. Membrane is more permeable to K⁺ than Na⁺.
  2. Sodium-potassium pump activetly transports 2Na⁺ out of cell & 2K⁺ into cell.
  3. Establishes electrochemical graident: cell contents more negative than extracelluary enviroment
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8
Q

Name the stages in generating an action potential.

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
  4. Return to resting potential.
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9
Q

What happens during depolarisation?

A
  1. Stimulus → facillitated diffusion of Na⁺ ions into cell down electrochemical gradient.
  2. p.d. across membrane becomes more postive.
  3. If membrane reaches theshold potential (-50mV), voltage-gated Na⁺ Channels open.
  4. Significantly influx of Na⁺ ions reverses p.d. to +40mV.
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10
Q

What happens during repolarisation?

A
  1. Voltage-gated Na⁺ channels close and voltage-gated K+ channels open.
  2. Facillitated diffusion of K⁺ ions our of ccell down their electrochemical graident.
  3. p.d. across membrane become more negative.
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11
Q

What happens during hyperpolarisation?

A
  1. ‘Overshoot” when K⁺ ions diffuse out = p.d becomes more negative than resting potential.
  2. Refractory period: no stimulus is large enough to raise membrane potential to threshold.
  3. Voltage-gated K⁺ channels close & sodium-potassium pump re-establishes resting potential.
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12
Q

Explain the important of the refractory period.

A

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

  • Ensures unidirectional impulse
  • Ensures discrete impulses
  • Limits frequency of impulse transmission
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13
Q

What is the ‘all or nothing” principle?

A

Any stimulus that causes the membrane to reach threshold potenital will generate an action potential

All action potential have same magnitude.

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14
Q

Name the factors that affect the speed of conductance.

A
  • Myelin sheath
  • Axon diameter
  • Temperature
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15
Q

How does axon diameter affect the speed of conductance?

A

Greater diameter = faster

  • Les resistance to flow of ions (depoloraisation & repolarisation).
  • Less ‘leakage’ of ions (easier to maintain membrane potential).
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16
Q

How does temperature affect speed of conductance?

A

Higher temperature = faster

  • Faster rate of diffusion (depolarisation & repolarisation)>
  • Faster rate of respiration (enzyme-controlled_ = more ATP for active transport to re-establish resting potential.

Temperature too high = membrane potential denature.

17
Q

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

A

Student’s t-test (comparing means of continous data.)

18
Q

Suggest appropriate units for the maximum frequency of imoulse conduction.

A

Hz.

19
Q

How can an organism detect the strength of a stimulus?

A

Larger stimulus raises membrane to theshold potential more quickly after hyperpolarisation = greater frequency of impulses.

20
Q

What is the function of synapses>

A

Electrical impulse cannot travel over junction between neurons.

  • Neurotransmitters send impulses between neurons/ from neurons to effectors.
  • New impulses can be intitated in several different neurons for multiple simultaneous responses.
21
Q

Describe the structure of a synapse.

A

Presynaptic neuron ends in a synaptic knob: contain lots of mitochondria, endoplasmic reticulum & vesciles of neurotransmitter.

Synaptic clef: 20-30 nm gap between neurons.

Postsynaptic neuron: has complemntary receptors to neurotransmitter (ligand-gated Na⁺ channels).

22
Q

Outline what happens in the presynaptic neuron when an action potential is transmitted from one neuron to another.

A
  1. Wave of depolarisation travels down presynaptic neuron, causing voltage-gated Ca²⁺ channels to open.
  2. Vesciles move towards & ruse with presynaptic membrane.
  3. Exocytosis of neurotransmitter into synaptic cleft.
23
Q

How do neurotransmitters cross the synaptic cleft?

A

Via simple diffusion

24
Q

Outline what happens in the postsynaptic neuron when an action potential is transmitted from one neuron to another.

A
  1. Neurotransmitter binds to specific receptor on postynaptic membrane.
  2. Ligand-gated Na⁺ channels open.
  3. If influx of Na⁺ ions raises membrane to threshold potential, action is generated.
25
Q

Explain why synaptic transmission is unidirectional.

A

Only presynaptic neuron contain vesicles of neurotransmitter & only postynaptic membrane has complementary receptors.

so impulse always travels presynaptic → postsynaptic.

26
Q

Define summation and name the 2 types.

A

Neurotransmitter from several sub-theshold impulses accumulates to generate action potential:

  • Temportal summation
  • Spatial summation

NB no summation at neuromuscular junctions.

27
Q

What is the difference between temportant and spatial summation>

A

Temportal: one presynaptic neuron releases neurotransmitter several times in quick succession.

Spatial: multiplse presynaptic neurons release neurotransmitter.

28
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmittery,

Exicitaroy or inhibitiory. Located at:

  • Motor end plate (muscle contraction).
  • Preganglionic neurons (exicitation).
  • Parasympathetic postganglionic neurons (inhibitation e.g. of heart of breathing rate).
29
Q

What happens to acetylcholune from the synaptic cleft?

A
  1. Hydrolysis into acetyl choline by acetylcholinesterase (AChE).
  2. Acetyle & choline diffuse back into presynaptic membrane.
  3. ATP is used to reform acetylecholine for storage in vesicles.
30
Q

Explain the importance of AChE.

A
  • Prevents overstimulation of skeletal musles cells.

- Enables acetyl and choline to be recyled.

31
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to and open Cl⁻ channels on postynaptic membrane & triggers K+ channels to open.
  2. Cl⁻ moves in & K+ out via facilitated diffusion.
  3. p.d. becomes more negative: hyperpolarisation.
32
Q

Describe the structure of a neuromuscular junction.

A

Synaptic cleft between a presynaptic neuron and skeletal muscle cell.

33
Q

Contrast a cholinergic synapse and a neuromuscular junctio.

A

Refer to PMT table

Difference (1)
Postsynaptic cell
AChE location
Action potential
Response
Neurons involved

Cholinergic (2)
Refer to PMT table

Neuromuscular (3)
Refer to PMT table

34
Q

How might drugs increase synaptic transmission?

A
  • Inhibit AChE

- Mimic shape of neurotransmitter.

35
Q

How might drugs decrease synaptic transmission?

A
  • Inhibit release of neurotransmitter.
  • Decrease peremabiity of postsynaptic membrane to ions
  • Hyperpolarise postsynaptic membrane.

A-Level AQA Biology (77 decks)

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