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Biology > Nervous Coordination > Flashcards

Nervous Coordination Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Describe the general structure of a motor neuron

A

Cell body: contains organelles & high proportion of RER
Dendrons: branch into dendrites which carry impulses towards cell body
Axon: long, unbranched fibre carries 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 axon many times
  • myelin sheath: made from myelin-rich membranes of schwann cells
  • nodes of ranvier: 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 AP pass along an unmyelinated neuron?

A
  1. Stimulus leads to influx of Na+ ions - first section of membrane depolarises
  2. Local electrical currents cause sodium vgc further along membrane to open - meanwhile section begins to repolarise
  3. Sequential wave of depolarisation
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5
Q

Explain why myelinated axons conduct impulses faster than unmyelinated axons

A

Saltatory conduction: impulse ‘jumps’ from one node of ranvier to another - depolarisation cannot occur where myelin sheath acts as electrical insulator
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 (approx -70 mV)

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7
Q

How is resting potential established?

A
  1. Membrane is more permeable to K+ than Na+
  2. Sodium-potassium pump actively transports 3Na+ out of cell & 2K+ into cell

Establishes electrochemical gradient: cell contents more negative than extracellular environment

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8
Q

Name the 4 stages in generating an AP

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—> faciliated diffusion of Na+ ions into cell down electrochemical gradient
  2. p.d. across membrane becomes more positive
  3. If membrane reaches threshold potential (-50mV) voltage-gated Na+ channels open
  4. Significant influx of Na+ ions reverses p.d. to +40mV
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10
Q

What happens during repolarisation?

A
  1. Na+ vgc close and K+ vgc open
  2. Facilitated diffusion of K+ ions out of cell down their electrochemical gradient
  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. K+ vgc close & sodium-potassium pump re-establishes resting potential
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12
Q

Explain the importance of the refractory period

A

No AP 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 potential will generate an AP
All AP 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

  • less resistance to flow of ions (depolarisation & repolarisation)
  • less ‘leakage’ of ions (easier to maintain membrane potential)
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16
Q

How does temperature affect the speed of conductance?

A
  • 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 proteins denature

17
Q

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

A

Student’s t-test

18
Q

Suggest appropriate units for the maximum frequency of impulse conduction

A

Hz

19
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

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 initiated in several different neurons for multiple simultaneous responses
21
Q

Describe the structure of a synapse

A

Presynaptic neuron ends in synaptic knob: contains lots of mitochondria, endoplasmic reticulum & vesicles of neurotransmitter

Synaptic cleft: 20-30 nm gap between neurons

Postsynaptic neuron: has complementary receptor to neurotransmitter (ligand-gated Na+ channels)

22
Q

Outline what happens in the presynaptic neuron when an AP is transmitted from one neuron to another

A
  1. Wave of depolarisation travels down presynaptic neuron, causing Ca2+ vgc to open
  2. Vesicles move towards & fuse 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 AP is transmitted from one neuron to another

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

Explain why synaptic transmission is unidirectional

A

Only presynaptic neuron contains vesicles of neurotransmitter & only postsynaptic membrane has complementary receptors

So impulse always travels presynaptic —> postsynaptic

26
Q

Define summation and name the 2 types

A

Neurotransmitter from several sub-threshold impulses accumulates to generate AP

  • temporal summation
  • spatial summation

No summation at neuromuscular junctions

27
Q

What is the difference between temporal and spatial summation?

A

Temporal: one presynaptic neuron releases neurotransmitter several times in quick succession
Spatial: multiple presynaptic neurons release neurotransmitter

28
Q

What are cholinergic synapses?

A

Use acetylcholine as primary neurotransmitter - excitatory or inhibitory found at:

  • motor end plate (muscle contraction)
  • preganglionic neurons (excitation)
  • parasympathetic postganglionic neurons (inhibition)
29
Q

What happens to acetylcholine from the synaptic cleft?

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

Explain the importance of AChE

A
  • prevents overstimulation of skeletal muscle cells

- enables acetyl and choline to be recycled

31
Q

What happens in an inhibitory synapse?

A
  1. Neurotransmitter binds to and opens Cl- channels on postsynaptic membrane & triggers K+ channels to open
  2. Cl- moves in & K+ moves 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 a skeletal muscle cell

33
Q

How might drugs increase synaptic transmission?

A
  • inhibit AChE

- mimic shape of neurotransmitter

34
Q

How might drugs decrease synaptic transmission?

A
  • inhibit release of neurotransmitter
  • decrease permeability of postsynaptic membrane to ions
  • hyperpolarise postsynaptic membrane

Biology (39 decks)

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