5.1.3 neuronal communication NOT ON MOCK Flashcards Preview

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1

what features are common to all sensory receptors

- act as an energy transducers which establish a generator potential

-respond to specific stimuli

2

describe the basic structure of a pacinian corpuscle

single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule

stretch-mediated Na+ channels on plasma membrane

capillary runs along base layer of tissue

3

what stimulus does a pacinian corpuscle respond to? how?

1. pressure deforms membrane, causing stretch-mediated Na+ ion channels to open

2. if influx of Na+ raises membrane to threshold potential, a generator potential is produced

3. action potential moves along sensory neuron

4

describe the features of all neurons

cell body: contains organelles and high proportion of RER

dendrons: branch into dendrimer which carry impulses towards the cell body

axon: long, un- branched fibre carries nerve impulses away from cell body

5

describe the structure and function of a sensory neuron

usually unipolar, transmits impulses from receptors to CNS

dendrites are at the top they look like branches, long axon and the cell body is in the middle of the axon and have axon terminals

6

describe the structure and function of a relay neuron

usually bipolar
transmits impulses between neurons

have highly branched dendrites, cell body and highly branches axon terminals

7

describe the structure and function of a motor neuron

usually multipolar
transmits impulses from relay neurons in the CNS to effectors

dendrites at the top, cell body at the end of axon and have axon terminals

8

describe the additional features of a myelinated neuron

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

9

name 3 processes schwann cells are involved in

electrical insulation

phagocytosis

nerve regeneration

10

explain why myelinated axons conduct impulses faster than un myelinated axons

saltatory conduction : impulse jumps from one node of rangier to another. depolarisation cannot occur where myelin sheath acts as electrical insulator

so impulse does not travel along whole axon length

11

where are myelinated and non-myelinated neurons found in the body

myelinated: most neurons in central and peripheral nervous systems eg those involved in spinal reflex

non-myelinated: group c nerve fibres involved in transmitting secondary pain

12

what is resting potential

potential difference (voltage) across neuron membrane when not stimulated

usually about -70 mV in humans

13

how is resting potential established

1. membrane is more permeable to K+ than Na+

2. sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell

establishes electrochemical gradient : cell contents more negative than extra cellular environment

14

name the states in generating an action potential

depolarisation
repolarisation
hyperpolarisation
return to resting potential

15

what happens during depolarisation

1. stimulus -> facilitated diffusion of Na+ into cell electrochemical gradient

2. potential difference across membrane becomes more positive

3. if membrane reaches threshold potential (-50mV), voltage gated Na+ channels open. (positive feedback mechanism)

4. significant influx of Na+ ions reverses potential difference to +40mV

16

what happens during repolarisation

1. voltage gated Na+ channels close and voltage gated K+ channels open

2. facilitated diffusion of K+ ions out of cell down their electrochemical gradient

3. potential difference across membrane becomes more negative

17

what happens during hyperpolarisation

1. “overshoot” when K+ ions diffuse out = potential difference becomes more negative than resting potential

2. refractory period: no stimulus is large enough to raise membrane potential to threshold

3. voltage gated K+ channels close and sodium-potassium pump re establishes resting potential

18

explain the importance of the refractory period

no action potential can be generated in hyperpolarised sections of membrane

- ensures unidirectional impulse

-ensures discrete impulses

- limits frequency of impulse transmission; large stimuli have higher frequency

19

why is the frequency of impulse transmission significant

enables organism to distinguish size of stimulus although all action potentials have same magnitude

larger stimuli result in higher frequency of transmission since they overcome hyperpolarisation more quickly

20

what is the function of synapses

electrical impulse cannot cross junction

neurotransmitters send impulses between neurons / from neurons to effectors for excitatory or inhibitory response

summation of sub threshold impulses

new impulses can be initiated in several different neurons for multiple simultaneous responses

21

describe the structure of a synapse

presynaptic neuron ends in synaptic knob: contains lots of mitochondria, endoplasmic reticulum and vesicles of neurotransmitter

synaptic cleft: 20-30 nm gap between neurons

postsynaptic neuron : has complimentary receptors to neurotransmitter (ligand-gated Na+ channels)

22

what happens in the presynaptic neuron when an action potential is transmitted between neurons

1. wave of depolarisation travels down presynaptic neuron, causing voltage gated Ca2+ channels to open

2. vesicles move towards and fuse with presynaptic membrane

3.ecocytosis of neurotransmitter into synaptic cleft

23

how do neurotransmitters cross the synaptic cleft

simple diffusion

24

what happens in the postsynaptic neuron when an action potential is transmitted between neurones

1. neurotransmitter binds to specific receptor on postsynaptic membrane

2. ligand-gated Na+ channels open

3. id influx of Na+ ions raises membrane to threshold potential, action potential is generated

25

what happens in an inhibitory synapse

1. neurotransmitter binds to and opens CL- channels on postsynaptic membrane and triggers k+ channels to open

2. Cl- moves in and K+ moves out via facilitated diffusion

3. potential difference becomes more negative: hyper polarisation so no action potential is generated

26

ppq: outline the ways in which the STRUCTURES of a sensory neurone and a motor neurone are similar

they both have
dendrites
an axon
a cell body with a nucleus
myelin sheath covered with schwann cells

27

ppq: the table below lists a number of statements about the functions of neurones. indicate whether each statement refers to:

sensory neurone only (s), motor neurone only (m), sensory and motor neurones (B)

have a resting potential of approximately -70mV
transmit nerve impulses from the CNS
connect to other neurones via synapses
connect to effectors

have a resting potential of approximately -70mV = B

transmit nerve impulses from the CNS = M

connect to other neurones via synapses = B

connect to effectors = M

28

ppq: fever is accompanied by sweating , explain the effect that this sweating will have on the body

evaporation will have a cooling effect , reduce body temperature

heat taken from the body is needed for evaporation

water has a high latent heat of vaporisation

29

ppq: suggest why shivering occurs during fever

as the new normal body temp is higher the body is using shivering to raise the temperature of the internal environment

30

ppq: explain why it is not a good idea to give alcohol to someone with hypothermia

vasodilation results in more blood nearer to the skin surface

body will love even more heat

organs will not be able to maintain function

31

ppq: why is the pacinian corpuscle described as a transducer

it converts energy (mechanical) into another form of energy (electrical)

32

ppq: deformation of the plasma membrane of the top of the neurone causes the membrane to become more permeable to Na+ suggest why

deformation of membrane will allow more Na+ through because the increased pressure causes sodium ion channels to open

33

ppq: the generation of an action potential follows the “all or nothing” law
explain what this means

if the, stimulus is not strong enough / threshold value is not reached then an action potential is not generated

34

ppq: describe how info about the strength and intensity of a stimulus is communicated to the brain

it is represented by the frequency of the action potential

a higher frequency of action potentials shows a strong stimulus

35

ppq: suggest an explanation for the fact that action potentials are not generated constantly whilst wearing clothes

action potentials not generated because sodium ion channels remain open / resting potential not re-established

36

ppq: outline the roles of synapses in the nervous system

they allow neurones to communicate for cell signalling

ensure transmission between neurones is in one direction only

allows convergence (impulses from more than one neurone to be passed to a single neurone)

allows divergence (impulses from a single neurone to be passed to more than one neurone)

37

ppq: name one chemical that transfers a nerve impulse from one neurone to another

acetylcholine

38

ppq: suggest the part of the neurone where the plasma membrane has TRPA1 receptors

post synaptic membrane ; TRPA1 prevents attachment of neurotransmitter to its receptor

39

ppq: name the gap between two adjacent schwann cells along the length of the neurone

nodes of ranvier

40

ppq: explain the difference in the speed of conduction of an action potential along the length of a myelinated neurone and a non-myelinated neurone

in myelinated neurones conduction is faster , depolarisation can only occur where voltage gated na+ channels present and myelinated neurones have longer sections with no voltage gated Na+ channels present .

41

ppq: name the process by which the acetylcholine is secreted

exocytosis

42

ppq: name the part of a neurone from which acetylcholine is secreted

synaptic knob / bulb

43

ppq: botulinum toxin is a protease that is produced by the bacterium

if this toxin is present in the body the toxin enters the neurones

suggest the effects that botulinum toxin may have once it has entered a neurone

vesicle cannot fuse with cell membrane and acetylcholine not secreted

protease hydrolyses protein so the protein can’t bind to the complex

44

ppq: describe and explain how the resting potential is established and how it is maintained in a sensory neurone

pumping: sodium-potassium pump uses atp and pumps actively moves Na+ ions out of cell and K+ in

passive: diffusing: k+ diffuse back out of the cell, membrane less permeable to Na+ so fewer Na+ diffuse back in. voltage gated channels closed

45

ppq: what term is used to refer to the value of -50 mV

threshold potential

46

ppq: comment on the relationship between the strength of a stimulus and the resulting action potential

only stimuli that reach threshold value (-50mV) produce an action potential

47

ppq: state the name given to the gap between 2 neurones at this junction

synaptic gap

(also allow synapse)

48

ppq: outline how the 1st neurone communicated with the 2nd neurone across the gap

neurotransmitter / acetylcholine released from pre-synaptic membrane

diffuses across synaptic cleft

attaches to receptors on post synaptic membrane of second cell

neurotransmitter / acetylcholine broken down in cleft

49

ppq: outline the importance of the junctions between neurones in the functioning of the nervous system

ensures movement of action potential in one direction only

integration : one neurone can connect to many neurones

allows summation

filters out low level/ background stimuli

50

ppq: give the most suitable word for the increase in the diameter of the lumen of an arteriole to allow more blood to flow through

vasodilation

51

When an impulse is not passing along a neurone, a resting potential of____mV is established.

When the neurone is stimulated, it causes ___ of
the cell surface membrane.

This will not generate an action potential unless it is large enough to exceed the___ ___

a neurone will either conduct an action potential or not this is describe as the ___ - ___ -___ law.

action potentials all have the same ___. the only way in which the intensity of a stimulus can be interpreted is by the ___ of the action potential

When an impulse is not passing along a neurone, a resting potential of -70 mV is established.

When the neurone is stimulated, it causes DEPOLARISATION of the cell surface membrane.

This will not generate an action potential unless it is large enough to exceed the THRESHOLD POTENTIAL

a neurone will either conduct an action potential or not this is describe as the ALL-OR-NOTHING law.

action potentials all have the same SIZE the only way in which the intensity of a stimulus can be interpreted is by the FREQUENCY of the action potential

52

ppq: describe the function of structure a ( schwann cell)

schwann cells produces myelin

which insulates

prevents movements of ions into and out of the neurone

53

ppq: name the process by which acetylcholine leaves the neurone

exocytosis

54

ppq: name the process by which acetylcholine travels across the synaptic cleft

diffusion

55

ppq: a feature of synapses is that they allow transmission in only one direction

state how this is achieved

only the presynaptic neurone produces acetylcholine

only the presynaptic membrane has calcium ion channels

postsynaptic membrane has acetylcholine receptors

acetylcholine broken down at postsynaptic membrane

56

ppq: explain how the presence of atropine (a toxin similar shaped to acetylcholine that prevents the initiation of an action potential in the post synaptic neurone) in the synapse will prevent the initiation of an action potential

atropine bind to acetylcholine receptor on postsynaptic membrane

this prevents acetylcholine binding / blocks the receptor

ion gates do not open

Na+ cannot enter, k+ cannot leave nerve cell

no depolarisation so does not reach threshold potential

57

ppq: tetradotoxin is poisonous to humans because it blocks gated sodium channels in cell membranes, preventing action potentials

suggest why tetradotoxin is not toxic to the puffer fish

the channel is different

58

ppq: describe the structure of the feature labelled a (myelin sheath)

myelin sheath

schwann cells wrapped around axon

except at nodes of ranvier

59

ppq: suggest why an increase in temperature results in an increase in the speed of conduction

increased kinetic energy so ions diffuse acros membrane into neurone more quickly

60

ppq: as the temperature continues to increase, it reaches a point at which the conduction of the impulse ceases. suggest why

ion channels / pumps no longer function

fluidity of membrane disrupted

synaptic enzymes denatured

61

ppq: outline the events following the arrival of an action potential at the synaptic knob until the acetylcholine has been released into the synapse

calcium channels open

Calcium ions diffuse into acetylcholine in vesicles

synaptic vesicles move towards presynaptic membrane

vesicles fuse with membrane

release acetylcholine by exocytosis into synaptic cleft

62

Specialised cells that are able to detect stimuli can be found both within and at the surface of
an animal's body. These specialised cells can be found singly or in groups and are known as
sensory ____

Each cell is specialised to respond to a particular type of stimulus. Some specialised cells in
the retina of the eye respond to the______
and wavelength of light.

Groups of specialised cells in the nose and on the tongue detect____ stimuli and this results in the ability to smell and taste.

When specialised cells receive an appropriate stimulue which is above the threshold____
the cells are able to convert this energy into a nerve ____

Specialised cells that are able to detect stimuli can be found both within and at the surface of
an animal's body. These specialised cells can be found singly or in groups and are known as
sensory RECEPTORS

Each cell is specialised to respond to a particular type of stimulus. Some specialised cells in
the retina of the eye respond to the INTENSITY and wavelength of light.

Groups of specialised cells in the nose and on the tongue detect CHEMICAL stimuli and this results in the ability to smell and taste.

When specialised cells receive an appropriate stimulue which is above the threshold POTENTIAL
the cells are able to convert this energy into a nerve IMPULSE

63

ppq: state one way in which the structure of a motor neurone differs from that of a sensory neurone

the motor neurone - Structure

the cell body is at (one) end of the , neurone / cell
or
the cell body is in , brain / spinal cord / CNS
or
dendrites connected (directly) to cell body
or
long(er) axon
or
no dendron
or

64

state one way in which the function of a motor neurone differs from that of a sensory neurone

the motor neurone - function
carries , impulse(s) / action potential (s),
from, brain / spinal cord / CNS / relay neurone
or
carries , impulse(s) / action potential(s),
to, effector / muscle / gland ;

65

define summation and the two types

neuro transmitter from several sub-threshold impulses accumulate to generate action potentials

- temporal summation
-spatial summation

66

what is the difference between temporal and spatial summation

temporal: ONE presynaptic neurone releases neurotransmitter several times in quick succession

spatial: multiple presynaptic neurons release neurotransmitter

67

what are cholinergic synapses

use acetylcholine as primary neurotransmitter. excitatory or inhibitory
located at
motor end plate (muscle contraction)
preganglionic neurons (excitation)
parasympathetic postganglionic neurons (inhibition eg breathing rate)

68

what happens to acetylcholine from the synaptic cleft

hydrolysis into acetyl and choline but AchE

acetyl and choline diffuse back into presynaptic membrane

atp is used to reform acetylcholine for storage in vesicles