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EDEXCEL BIOLOGY > Topic 8: Grey Matter > Flashcards

Topic 8: Grey Matter Flashcards

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1
Q

What does the CNS consist of? (5)

A
  • brain
  • spinal cord
  • optic nerve
  • relay neurons
  • protected by bones and meninges
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2
Q

What is the role of the CNS?

A

Integrate information and initiate responses

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3
Q

What does the PNS consist of? (2)

A
  • sensory nerves

- motor nerves

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4
Q

What is the role of the PNS?

A

Connects CNS to limbs and organs

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5
Q

Describe the structure of a motor neuron (3)

A
  • cell body in CNS
  • axon extends out of CNS
  • Schwann cells (myelin)
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6
Q

Describe the structure of a sensory neuron (4)

A
  • cell body and dendrons outside CNS
  • axon extends into CNS
  • cell body found in dorsal root ganglia
  • myelinated
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7
Q

Describe the structure of a relay neuron (2)

A
  • found in CNS

- not myelinated

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8
Q

What is the role of Schwann cells? (2)

A
  • protect neuron from damage

- speed up transmission of nerve impulses

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9
Q

What is a nerve and what is its role? (2)

A
  • bundle of nerve fibres (axons/dendrons) in PNS

- blood vessels to supply glucose and oxygen to neurons

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10
Q

What is a reflex?

A

Immediate, involuntary response to a stimulus

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11
Q

What is the pathway in the reflex arc?

A
  1. Stimulus
  2. Receptor
  3. Sensory neuron
  4. Relay neuron
  5. Motor neuron
  6. Effector
  7. Response
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12
Q

How is a reflex arc different to normal neural pathways?

A
  • sensory neurons synapse with relay in spinal cord rather than passing to brain
  • brain receives sensory input and analysis happens after response
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13
Q

What happens to a pupil in dim light?

A
  • radial muscles contract
  • circular muscles relax
  • pupil dilates (sympathetic)
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14
Q

What happens to a pupil in bright light?

A
  • radial muscle relaxes
  • circular muscles contract
  • pupil constricts (parasympathetic)
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15
Q

How is an AP propagated along an axon?

A

Membrane at site of AP has opp charge to adjacent resting membrane.
+ve ions attracted to -ve area, creating a local electric current.
Resting membrane depolarised, generated AP as channels open

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16
Q

What are the factors affecting speed of impulse conduction?

A
  1. Diameter of axon: larger axon, higher speed of prop
  2. Myelination: conduct nerve impulses faster
  3. Temperature: higher increases speed of prop because higher rate of diffusion
  4. Concentration of Na+ in tissue fluid: more Na+, faster conduction
17
Q

What is meant by saltatory conduction?

A

Impulse jumps from node of Ranvier to other node because Ap’s can’t form where myelin is present. This speeds up propagation

18
Q

What is an action potential?

A

Rapid reversal of potential difference across neuron membrane from -70 to +40 to -70

19
Q

What is a nerve impulse?

A

AP propagated in one direction along an axon as a wave of depolarisation

20
Q

Describe what happens at resting potential (4)

A
  1. Na+/K+ pump creates conc. gradient: 3Na+ out, 2K+ in
  2. K+ diffuse out through channel along conc gradient. Na+ channel closed
  3. Positive charge builds up outside cell
  4. K+ conc gradient and electrical gradient counteract so no net movement of K+
21
Q

What happens when the membrane is depolarised?

A

Stimulus changes shaped of V-gate Na+ channels so they open and diffuse into axon along electrochemical gradient (-70 to +40)

22
Q

What happens when the membrane is repolarised?

A

V-gated Na+ close and K+ channels open. K+ diffuse out of axon due to electrochemical gradient (+40 to -70)

23
Q

What happens when the membrane is hyperpolarised?

A

K+ channels are open so membrane is more permeable so K+ continues to diffuse out (-90)

24
Q

How does the membrane return to resting potential?

A

V-gated K+ close but non V-gated still open so K+ diffuses into axon

25
Q

What is a refractory period?

A

The time after an AP when membrane cannot react to a new stimulus

26
Q

Why is a refractory period needed?

A
  • limit to frequency of impulses

- ensure nerve impulses are only in 1 direction

27
Q

What is the threshold to generate an action potential?

A

-55 to -50mV or it doesn’t happen at all

28
Q

Why do some stimuli not cause an AP?

A

Only a small number ot V-gated Na+ channels open so depolarisation doesn’t reach -55 to -50mV

29
Q

How can a stronger stimulus affect action potential?

A
  • does not trigger higher AP as size is always the same
  • frequence of AP increased as more neurons conduct impulse
  • electrical activity increased

EDEXCEL BIOLOGY (14 decks)

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