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Human Systems and Anatomy > Neurons and Electrical Impulses in the Nervous System > Flashcards

Neurons and Electrical Impulses in the Nervous System Flashcards

1
Q

what are neurons

A

nerve cells present in the nervous system that are specialised for communication. they connect with each other and with other excitable cells like muscles and glands. there are various types and their structure is related to their function

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2
Q

what are the different elements to the classical neuron

A

dendrites, axons and axon terminals

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3
Q

where are inputs received on neurons

A

the dendrites

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4
Q

where are the outputs produced on neurons

A

axon terminals

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5
Q

what are the different types of neuron

A
  • purkinje cell
  • spinal interneuron
  • sensory neuron
  • pyramidal neuron
  • motor neuron
  • bipolar cell
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6
Q

where are purkinje cell neurons found

A

the cerebellum

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7
Q

where are spinal interneurons found

A

the spine

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8
Q

where are pyramidal cells found

A

cerebral cortex

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9
Q

where are motor neurons found

A

spinal cord

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10
Q

where are bipolar cells found

A

retina

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11
Q

what is the membrane potential

A

potential difference that exists across the membrane of all cells

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12
Q

what does resting membrane potential arise from

A

the separation of charges on either side of the membrane

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13
Q

what is resting membrane potential determined by

A

diffusion of potassium ions from the cell interior through the potassium channels. the sodium potassium pump also contributes by moving unequal amounts of sodium and potassium

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14
Q

how can membrane potential be altered

A

by applying an electric current to the cell ie a stimulus. the hyperpolarising current moves the membrane potential further from 0, and a depolarising current moves the membrane potential closer to 0. the membrane potential then returns to the original resting level, and these responses are graded. the amplitude will depend on the size of the stimulus

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15
Q

what value does the membrane potential have to reach in order to have depolarisation

A

-55mV

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16
Q

what is action potential amplitude independent of

A

stimulus intensity

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17
Q

what is action potential

A

a large change in membrane potential, where the membrane potential overshoots zero and reverses polarisation

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18
Q

describe the process of generating action potential

A
  • stimulus applied
  • depolarisation
  • membrane potential moves toward 0 mV
  • membrane potential reaches threshold (-55mV) for opening of voltage gated sodium ion channels
  • membrane potential moves rapidly toward 0 mV
  • start of the action potential
  • upstroke of the action potential is due to entry of sodium ions
  • sodium ions diffuse inward through voltage gated channels
  • when the membrane potential reaches about +35mV the sodium channels shut and the potassium channels open
  • potassium channels are also voltage gated
  • potassium leave the cell and this makes membrane potential more negative
  • after overshoot, the membrane potential returns to original resting level
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19
Q

give a summary of action potential

A
  • all or none
  • independent of stimulus
  • at the threshold, the voltage gated sodium channels open and sodium diffuse in which leads to depolarisation
  • at the peak the sodium channels close and the voltage gated potassium channels open. potassium ions diffuse out and there is repolarisation
  • resting membrane potential
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20
Q

how do local anaesthetics work

A

they stop nerve conduction by blocking the sodium channels

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21
Q

what is the refractory period

A

after action potential is intiated, the neuron cannot generate another action potential until the first one has ended. this period of inexcitability is known as the refractory period, and happens due to the inactivation of voltage gated sodium channels. the action potentials cannot add together, so they are all or none events

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22
Q

how is action potential propagated across the neuron

A

action potential in one section of axon depolarises adjacent resting parts of the axon, so the action potential is regenerated further along the axon, and the action potentials travel along the axon as waves of depolarisation

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23
Q

what does the speed of action potential propagation increase with

A

the axon diameter

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24
Q

do large axons conduct impulses faster or slower than smaller ones

A

faster

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25
Q

in what size of axon is rapid conduction achieved

A

very large

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26
Q

why did vertebrates evolve a means of increasing action potential conduction speed

A

their speed of action potential propagation is too slow to enable the fast postural reflexes present in vertebrates

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27
Q

what is myelination

A

wrapping a layer of myelin round an axon

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28
Q

what does myelination do

A

it increases the action potential conduction speed

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29
Q

what is myelination of axons

A

myelin is a fatty layer formed by wrapping the membranes of glial cells round the axon, which insulates the axon and improves conduction

30
Q

what are nodes of ranvier

A

the intervals that interrupt the sheaths of myelin around axons in myelination

31
Q

what is saltatory conduction

A

the action potential jumps along the axon from node to node

32
Q

what do chemical synapses occur between

A
  • neurons and neurons
  • neurons and muscle cells
  • neurons and gland cells
33
Q

what do cells communicate via

A

synaptic vesicles

34
Q

what are the events at a chemical synapse

A
  • action potential depolarises presynaptic ending
  • an influx of calcium into the presynaptic ending
  • vesicles migrate toward the plasma membrane
  • release of transmitter into the cleft
  • transmitter binds to receptors on post synaptic cells
  • leads to changes in post synaptic cells
  • inactivation of the transmitter
35
Q

what are some general methods of inactivation of transmitter

A
  • reuptake into the presynaptic cell
  • enzyme destruction
36
Q

what are some neurotransmitter examples

A

amino acid derivatives - acetylcholine, dopamine, glutamate, glycine, noradrenaline, serotonin and GABA.
peptides - substance P, VIP, enkephalins, endorphins

37
Q

what is VIP

A

vasoactive intestinal polypeptide

38
Q

what is GABA

A

gamma amino butyric acid

39
Q

what do the effects of transmitters on cells depend on

A

the type of receptor and second messengers in the post synaptic cell

40
Q

what happens to the activity of a cell if it is depolarised

A

increased activity known as excitory

41
Q

what happens to the activity of a cell if it is hyperpolarised

A

decreased activity known as inhibitory

42
Q

what occurs at an excitatory synapse

A

transmitter causes depolarisation, there is excitatory post synaptic potential which brings the membrane potential nearer to the firing threshold

43
Q

what occurs at an inhibitory synapse

A

transmitter causes hyperpolarisation. there is inhibitory post synaptic potential which takes the membrane potential further from the firing threshold

44
Q

what can neurons receive inputs from

A

many other neurons

45
Q

can single post synaptic potentials have an effect on the membrane potential of the post synaptic cell

A

no they are too small

46
Q

why is it necessary for excitatory post synaptic potentials to add together or summate

A

the post synaptic potentials are very small and have little effect on the membrane potential of the post synaptic cell

47
Q

when will a post synaptic cell fire

A

if it receives sufficient excitation to drive the membrane potential beyond threshold. this occurs when it receives many excitatory inputs and few inhibitory inputs within a short time period

48
Q

what is convergence

A

when each neuron receives many inputs from other cells

49
Q

what is divergence

A

when each neuron synapses many other cells

50
Q

is the neuron more likely to fire if the excitatory inputs predominate

A

yes

51
Q

what is a neuromuscular junction

A

a synapse between a motor nerve and a muscle fibre. it is also referred to as a motor end plate, and the area of contact is greater than in a nerve nerve synapse. one action potential in the nerve leads to muscle contraction.

52
Q

what is the transmitter at a neuromuscular junction

A

acetylcholine

53
Q

what is acetylcholine broken down by

A

the enzyme acetyl cholinesterase

54
Q

what are the events at neuromuscular junctions

A
  • the action potential depolarises the motor nerve ending
  • an influx of calcium ions into the nerve ending
  • vesicles migrate toward the plasma membrane
  • release of acetylcholine into the cleft, which then diffuses into the cleft and binds to receptors on post synaptic cells.
  • choline and acetate are taken up by the neuron
55
Q

can drugs affect synaptic activity

A

yes

56
Q

how can drugs affect synaptic activity

A
  • synthesis or storage of transmitter
  • release of transmitter
  • action of transmitter on receptor
  • second messenger system
  • inactivation of transmitter
57
Q

how does botox paralyse facial muscles

A

prevents the release of neurotransmitter from motor nerves

58
Q

how does the drug beta blocker affect synaptic activity

A

it blocks beta adrenergic receptors and therefore blocks the release of adrenaline

59
Q

how does black widow spider venom affect synaptic activity

A

causes neurons to release excessive signalling molecules

60
Q

what does the drug curare do

A

paralyse muscles

61
Q

how does nicotine affect synaptic activity

A

increases communication between reward related neurons

62
Q

how does physostigmine affect synaptic activity

A

interferes with the metabolism of the neurotransmitter acetylcholine

63
Q

what is the axon hillock

A

the start of the axon

64
Q

what do ligand gated channels respond to

A

ligands, such as neurotransmitters

65
Q

what does an influx of positive charge into the cell cause

A

an excitatory post synaptic potential, which leads to depolarisation

66
Q

what does an influx of negative charge into the cell cause

A

inhibitory post synaptic potential, which leads to repolarisation

67
Q

what can multiple excitatory post synaptic potentials lead to

A

pushing the membrane potential to a particar threshold value, and this value will depend on the tissue type

68
Q

what is resting membrane potential charge

A

negative

69
Q

why is myelinated axons a faster way for signals to cross

A

due to saltitory conduction

70
Q

what is the soma

A

the cell body

71
Q

why is there a refractory period

A

to stop action potentials occuring too closely to each other, or going in the opposite direction back down the axon

72
Q
A

Human Systems and Anatomy (57 decks)

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