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BDS1 BAMS: Nervous System > Neurons > Flashcards

Neurons Flashcards

1
Q

What are neurons?

A

Nerve cells present in the nervous system

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2
Q

What are neurons specialised for?

A

Communication

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3
Q

What do neurons synapse with

A
  • Other neurons
  • Muscles
  • Glands
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4
Q

What is the axon hillock?

A

Where the cell body and axon join

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5
Q

Where does input converge on neurons?

A

Dendrites

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6
Q

Which type of neurons have lots of dendrites?

A

Purkinje cells

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7
Q

Why does a resting membrane exist across the membrane of all cells?

A
  • Due to the distribution of +ve and -ve charges on each side of the membrane
  • In the range of 20 to 90 mV; inside negative relative to outside
  • Approximately equal numbers of +ve and -ve charges on each side of the membrane but they are not evenly distributed
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8
Q

Is [Na+] higher in the ICF or ECF?

A

ECF = 145 mM

15mM in ICF

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9
Q

Is [K+] higher in the ICF or ECF?

A

ICF = 150 mM

4 mM in ECF

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10
Q

Is [Cl-] higher n the ICF or ECF?

A

ECF = 110 mM

10 mM in ICF

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11
Q

What does the resting membrane potential arise from?

A

The RMP arises from the separation of charges on either side of the membrane

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12
Q

What determines the resting membrane potential (RMP)?

A
  • Diffusion of K+ from cell interior through K+ channels

- The Na+K+ ATPase moves unequal amounts of Na+ and K+ (3 Na+ out for 3 K+ in) pumps ions against their conc. gradient

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13
Q

What effect would applying an electric current have to the membrane potential of a cell?

A

Would alter the membrane potential

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14
Q

Which direction does a hyper-polarising current move the MP?

A

A hyper polarising current moves the MP further from 0

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15
Q

Which direction does a depolarising current move the MP?

A

A depolarising current moves the MP nearer to 0

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16
Q

When a current is applied to a cell membrane, the responses are ‘graded’. What does this mean?

A

The amplitude depends on the size of the stimulus

17
Q

What happens to a cell when the MP is moved to around -55 mV?

A

A large depolarisation occurs

18
Q

Describe how an action potential is generated

A
  • Stimulus applied
  • Depolarisation occurs
  • Threshold reached ~ -55mV
  • This opens voltage-gated Na+ channels. Na+ flows in
  • MP moves overshoots 0
  • When membrane potential reaches +35 mV, Na+ channels shut and voltage-gated K+ channels open
  • K+ leaves the cell, making the MP more negative (repolarisation)
  • After a small overshoot, MP returns to original ‘resting’ level
19
Q

Why is an action potential described as an ‘all or nothing’ event?

A

Amplitude is independent of stimulus

20
Q

How do anaesthetics work?

A

Block Na+ channels -> stops nerve conduction

21
Q

What is the refractory period?

A
  • After an action potential is initiated, the neuron cannot generate another action potential until the first one has ended
  • Period of unexcitability
  • It is due to inactivation of voltage-gated sodium channels
22
Q

What causes the refractory period?

A

Inactivation of voltage-gated Na+ channels

23
Q

How is an action potential propagated along an axon?

A
  • An AP in one part of axon depolarises adjacent ‘resting’ parts of the axon
  • The AP is regenerated further along the axon
  • APs travel along axon as waves of depolarisation
24
Q

During action potential propagation, why does the action potential not travel back on itself?

A
  • Because of the refractory period

- Refractory period allows the body to maintain uni-directionality of the action potential

25
Q

What effect does an increase in axon diameter have on the speed in action potential propagation?

A

Increases the speed of AP propagation

26
Q

What is the diameter of a giant squid axon?

A

1mm

27
Q

What is the maximum conduction velocity of a giant squid axon?

A

35m/s

28
Q

What have vertebrates evolved as a means of increasing AP conduction speed whilst decreasing axon diameter?

A

Myelination

29
Q

What is myelination and what is its purpose?

A

Wrapping a layer of myelin round an axon

Increases AP conduction speed

30
Q

What is the maximum speed of conduction in human axons?

A

120 m/s

31
Q

What is myelin?

A

A fatty layer

32
Q

How is myelination achieved?

A

By wrapping the membranes of ‘glial’ cells round the axon

33
Q

Which substance is used to insulate the axon and, resultantly, increases AP conduction?

A

Myelin

34
Q

What are nodes of Ranvier?

A
  • Gaps between myelin sheaths

- Axon membrane is exposed to the ECF at the nodes of Ranvier and ions flow can occur

35
Q

What is saltatory conduction?

A

The AP ‘jumps’ from one node of Ranvier to the next. This increases the conduction velocity of APs.

BDS1 BAMS: Nervous System (4 decks)

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