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Biology - Module 5 > Neuronal Communication > Flashcards

Neuronal Communication Flashcards

1
Q

What is a nerve

A

Bundle of neurones

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2
Q

State 4 features of a neurone

A

Cell body

Dendron

Dendrites

Axon

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3
Q

Describe cell body

A

Has nucleus surrounded by cytoplasm

Large numbers of ER + mitochondria = involved in production of neurotransmitters

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4
Q

Describe dendron

A

Short extension from cell body

Transmit electrical impulses TOWARDS cell body

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5
Q

Describe dendrite

A

Smaller branches extended from dendron

Transmit electrical impulses TOWARDS cell body

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6
Q

Describe axon

A

Singular elongated nerve fibres

Transmit impulses away from cell body

Can be very long

Fibre is cylindrical + has narrow region of cytoplasm surrounded by plasma membrane

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7
Q

Describe sensory neuron

A

Transmit impulses form sensory receptor cells to relay neurone or motor neurone or brain

1 dendron – carries impulse to cell body

1 axon – carries away from cell body

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8
Q

Relay neurone

A

Transmit between neurones

Many short axons + dendrons

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9
Q

describe a motor neurone

A

Transmit from relay neurones or sensory neurone to effector

1 long axon

Many short dendrites

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10
Q

draw a sensory relay + motor neurone

label
- dendron
- dendrites
- axon
- cell body
- myelin sheath

A
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11
Q

what is myelin sheath

A

protective covering that surrounds and insulates axons in the nervous system.

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12
Q

how is myelin sheath produced

A

Schwann cells

produce these layers of membrane by growing around the axon many times

Each time they grow around – a double layer of phospholipid bilayer is laid

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13
Q

what is the purpose of myelin sheath

A

enhance the speed and efficiency of nerve signal transmission.

as an electrical insulator - preventing the loss of electrical signals + allowing the nerve impulses to travel more rapidly along the axon.

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14
Q

what are nodes of ranvier and what is its function

A

small gaps or nodes that exist between adjacent myelin sheath segments

essential for the saltatory conduction of nerve impulses

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15
Q

whats the size of nodes of ranvier

A

2-3 micrometres

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16
Q

what do sensory actors act as

A

transducer – convert energy

convert stimulus into nerve impulse called generator potential

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17
Q

examples of sensory receptors

A

photoreceptors - light

chemoreceptors - chemicals

mechanoreceptors - mechanical strain

baroreceptors - blood pressures

osmoreceptors - body fluids

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18
Q

what do olfactory cells detect

A

Presence of volatile chemicals

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19
Q

what do taste buds detect

A

Presence of soluble chemicals

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20
Q

what does the cochlea detect

A

Vibrations in air / sound waves

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21
Q

what does the pacinian receptor detect

A

mechanical pressure

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22
Q

where are pacinian receptors found

A

feet / fingers / external genitalia / joints

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23
Q

what does a pacinian corpuscle consist of

A

consists of a single sensory neurone, surrounded by layers of connective tissue which are each separated by a gel = lamella

gel between the layers contains Na+

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24
Q

what channels are in the membrane of pacinian corpuscle

A

stretch-mediated sodium ion channels

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25
Q

describe how an action potential is formed in the pacinian corpuscle

A

Resting state – stretch mediated ion sodium channels too narrow for Na+ to pass through

at resting potential

When pressure applied = corpuscle changes shape + membrane stretches

Sodium ion channels widen + Na+ diffuse in

Influx of positive sodium ions depolarises cell – generator potential

Creates action potential

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26
Q

describe how an action potential is created in a photoreceptor cell

A

In dark – membrane of rod cells depolarised at their resting state

This is because – rod cells actively transport sodium ions out of cell which flow back in

This depolarisation – triggers release of neurotransmitters = inhibit bipolar neuron = no action potential sent to brain

In light – light causes rhodopsin to break into retinal and opsin

Causes sodium ion channels to close

Still sodium actively transported out but no come back in

Charge difference across membrane

Inside is more negative – cell is hyperpolarised

Stops releasing neurotransmitters

No more inhibition of bipolar neuron

Now can send impulse

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27
Q

what does the term resting potential mean

A

in a resting axon inside of the axon always has a more negative electrical potential compared to the outside of the axon

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28
Q

what is the normal resting potential

A

-70 mV

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29
Q

what are the two causes of the resting potential

A

active transport of sodium ions and potassium ions

Differential membrane permeability

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30
Q

how is a resting potential established

A

Sodium-potassium pumps in membranes – carrier proteins

Use ATP to pump 3 sodium ions out for every 2 potassium ions in

Larger conc of positive charge on outside

Establishes electrochemical gradient

Now more Na+ on outside and more K+ on inside

K+ channels open and Na+ channels closed

K+ diffuse out of cell

More +ve on outside

Channels are less soluble to Na than K

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31
Q

what is a nerve impulse

A

action potential that starts at one end of a neurone + is propagated along axon to other end of neurone

32
Q

state the 5 stages of how an action potential is generated

A

stimulus

depolarisation

repolarisation

hyperpolarisation

restoration

33
Q

describe how an action potential is generated

A

Stimulus triggers sodium ion channels in membrane to open

allows sodium ions to diffuse down electrochemical gradient into cell

Voltage-gated sodium channels in the axon membrane open

(Negative protein attracted to positive inner cell)

Sodium ions come into axon down electrochemical gradient - sudden influx

(Positively charged sodium attracted to negative inside axon + conc gradient)

More sodium ions in = inside less negative= depolarisation

Change in charge causes more channels to open = more sodium

Positive feedback

Reach +40mV

Positive protein repelled by positive inside cell and blocks channel for sodium channel

No more sodium coming in

Negative protein on potassium channel attracted to positive inside cell =opens channel

Potassium ions diffuse out – down conc gradient

Returns potential difference back to normal = -70mv

Negative feedback

Potassium ion channels = slow to close and as a result

too many potassium ions diffuse out of the neurone

short period of hyperpolarisation

briefly more negative

once closed – sodium-potassium pumps restore resting potential

34
Q

describe the stimulus stage in generating an action potential

A

Stimulus triggers sodium ion channels in membrane to open

allowing sodium ions to diffuse down electrochemical gradient into cell

35
Q

describe the depolarisation stage in generating an action potential

A

Voltage-gated sodium channels in the axon membrane open

(Negative protein attracted to positive inner cell)

Sodium ions come into axon down electrochemical gradient // sudden influx

(Greater conc of sodium on outside)
(Positively charged sodium attracted to negative inside axon)

More sodium ions in = inside less negative= depolarisation

Change in charge causes more channels to open = more sodium

Reach +40mV

36
Q

describe the repolarisation stage in generating an action potential

A

Now +40 mV

Positive protein repelled by positive inside cell and blocks channel for sodium channel

No more sodium coming in

Negative protein on potassium channel attracted to positive inside cell =opens channel

Potassium ions diffuse out – down conc gradient

Returns potential difference back to normal = -70mv

37
Q

describe the hyperpolorisation stage in generating an action potential

A

Potassium ion channels = slow to close and as a result

too many potassium ions diffuse out of the neurone = short period of hyperpolarisation

briefly more negative

38
Q

describe the restoration stage in generating an action potential

A

once closed – sodium-potassium pumps restore resting potential

39
Q

what voltage is the cell depolarised

A

+40mV

40
Q

what type of process is depolorisation

A

positive feedback

41
Q

what type of process is repolorisation

A

negative feedback

42
Q

draw out an action potential graph + label all the stages

A
43
Q

how are action potentials transmitted along an axon

A

when action potential happens in one = stimulate action potential in adjacent part of neurone

happens because sodium ions that diffuse into the neurone diffuse sideways causes voltage-gated ion channels in the next portion to open

sodium ion channels open there too = more positive inside

the wave moves away from part of neurone that just fired action potential

that neurone will be in refractory period / cannot be stimulated because sodium ion channels remain closed

44
Q

what is the refractory period

A

period of time when both sodium ion channels are closed ( repolarisation)

and potassium ion channels are closed
( hyperpolarisation).

45
Q

whats the significance of a refractory period

A

Ensure discrete event – stopping them from merging together

Ensure new action potentials are generated ahead – only in one direction

46
Q

state the factors that affect speed of conduction

A

Myelination

The diameter of the axon

Temperature

47
Q

how does myelin sheath affect speed of conductioj

A

increases speed as it allows for saltatory conduction

48
Q

what is saltatory conduction

A

In myelinated segments depolarisation cant occur = myelin sheath stops diffusion of Na + / K+

Action potentials can only occur – nodes of Ranvier (small uninsulated sections of axon)

nerve impulses jump from one section to the next – saltatory conduction

49
Q

how does axon diameter effect speed of conduction

A

Impulse will be quicker along thicker axons

Thicker axons – axon membrane with greater surface area – greater rate of diffusion

Less resistance to flow of ions in cytoplasm

50
Q

how does temperature effect speed of conduction

A

Higher temp = faster nerve impulse

Ions diffuse faster but only up to 40 degrees = proteins denature

51
Q

what is the all or nothing principle

A

If stimulus is strong enough to increase cell potential above threshold potential – stimulate action potential

if not - no action potential

52
Q

what do difference strengths of stimulus result in

A

different frequencies that action potentials are being fired

the bigger the stimulus = more often an action potential will occur along the neurone.

53
Q

what is a synaptic cleft

A

gap between axon of one neurone and dendrite of next

54
Q

how large is a synaptic cleft

A

20-30nm across

55
Q

what is the presynaptic neurone

A

neurone which impulse has travelled along + has vesicles containing neurotransmitters

56
Q

what is the postsynaptic neurone

A

neurone that receives neurotransmitter

57
Q

what is a synaptic knob

A

swollen end of presynaptic neurone

– has mitochondria + a lot of ER to make neurotransmitters

58
Q

what are synaptic vesicles

A

vesicles that contain neurotransmitters in

fuse with presynaptic membrane + release into cleft

59
Q

where are neurotransmitter receptors found

A

on postsynaptic membrane

60
Q

2 types of neurotransmitter

A

excitatory

inhibitory

61
Q

function of excitatory neurotransmitter + example

A

Result in depolarisation of the postsynaptic neurone

Opens sodium ion channels = action potential

acetylcholine

62
Q

function of inhibitory neurotransmitter + example

A

Result in hyperpolarisation of postsynaptic neurone

Opens potassium ion channels – no action potential

GABA

63
Q

what is a cholinergic synapse

A

Uses Ach – acetylcholine neurotransmitter

64
Q

where are cholinergic synapses found

A

Common in CNS of vertebras + at neuromuscular junctions = where motor neurone + muscle cell meets

65
Q

describe how an action potential is transmitted across a cholinergic synapse

A

Action potential at the presynaptic membrane causes depolarisation of membrane

Stimulates voltage-gated calcium channels to open

Ca 2+ diffuse down electrochemical gradient

(from tissue fluid surrounding the neurones into the synaptic knob)

Stimulates Ach containing vesicles to fuse with presynaptic membrane (snare proteins shorten)

releases Ach molecules into synaptic cleft by exocytosis

Diffuse across + bind with choline receptors in post synaptic membrane

Sodium ion channels to open

Diffuse into the cytoplasm of postsynaptic neuron

Causes depolarisation – re starting electrical impulse once threshold is reached

Ach broken down + recycled

ATP released by mitochondria recombines choline + ethanoic acid

66
Q

what enzyme catalyses the break down of Ach

A

acetylcholinesterase

67
Q

what does acetylcholinesterase do

A

hydrolyses Ach into choline and ethanoic acid (acetyl)

68
Q

whats the significance of breaking down Ach

A

Prevents sodium channels staying open

Stops permanent depolarisation of post synaptic membrane

69
Q

why are synapses important

A

Unidirectionality

Allow impulse from one neurone to be transmitted to a number of neurones at multiple synapses = single stimulus creating a lot of responses

Number of neurones may feed into same synapses – stimuli from different receptors

70
Q

what ensures unidirectionality across a synapse

A

Neurotransmitter from one side + receptors from another

71
Q

how can a single impulse be insufficient to generate an action potential

A

Only small amount of acetylcholine is released into the synaptic cleft

small number of the gated ion channels are opened in the axon membrane

insufficient number of sodium ions pass through the membranes

threshold potential is not reached

small amount of acetylcholine attached to receptors is broken down rapidly by acetylcholinesterase

72
Q

what is summation

A

process by which postsynaptic potentials are combined to determine whether an action potential is generated in the postsynaptic neurone

73
Q

whats the benefits of summation

A

avoids nervous system being overwhelmed

synapses act as barrier = slows down rate = as only allowed to pass on if has input from other neurones

74
Q

what is temporal summation

A

multiple impulses arrive within quick succession

impulses can be ‘added’ together to generate an action potential

75
Q

describe how temporal summation work

A

many action potentials arrive in quick succession

effects cumulate together

large amount of acetylcholine is released into the synaptic cleft

large number of the gated sodium ion channels open

sufficient number of sodium ions pass through the membrane

76
Q

what is spatial summation

A

Multiple impulses arriving simultaneously at different synaptic knobs stimulating the same cell body

Biology - Module 5 (8 decks)

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