Neuronal Communication

Question 1

what features are common to all sensory receptors

Answer 1

act as energy transducers which establish generator potential
respond to specific stimuli

Question 2

describe the basic structure of a pacinian corpuscle

Answer 2

single nerve fibre surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule
stretch mediated sodium channels on membrane
capillary runs along base layer of tissue

Question 3

what stimulus do a pacinian corpuscle respond to and how

Answer 3

pressure deforms membrane causing channels to open
influx of sodium raises membrane to threshold potential, a generator potential is produced
action potential moves along sensory neurone

Question 4

describe the features of all neurones

Answer 4

cell body-contains organelles
dendrons-branch into dendrites which carry impulses towards cell body
axon-long unbranched fibre carries nerve impulses away from cell body

Question 5

describe the structure and function of a sensory neurone

Answer 5

cell body in the middle of axon
transmits impulses from receptors to CNS

Question 6

describe the structure and function of a relay neurone

Answer 6

transmits impulses between neurones

Question 7

describe the structure and function of a motor neurone

Answer 7

cell body at the end of axon
transmits impulses from relay neurones in CNS to efefctor

Question 8

describe the additional features of a myelinated neurone

Answer 8

schwann cells-wrap around axon
myelin sheath-made of myelin rich membranes of schwann cells
nodes of ranvier- very short gaps between neighbouring schwann cells where there is no myelin sheath

Question 9

name 3 processes schwann cells are involved in

Answer 9

phagocytosis
nerve regeneration
electrical insulation

Question 10

explain why myelinated neurones conduct impulses faster

Answer 10

saltatory conduction-impulse jumps from one node to another
depolarisation cannot occur where myelin acts as electrical insulator
nerve impulse does not travel whole length of axon

Question 11

where are myelinated and non myelinated neurones found

Answer 11

myelinated-most neurones in central and peripheral nervous systems non-myelinated-group C nerve fibres involved in transmitting secondary pain

Question 12

what is resting potential

Answer 12

potential difference across neurone membrane is about -70mV

Question 13

how is resting potential established

Answer 13

membrane is more permeable to potassium than sodium
sodium potassium pump actively transports 3 sodium out of cell and 2 potassium into cell
establishes electrochemical gradient

Question 14

name the stages in generating an action potential

Answer 14

depolarisation
Repolarisation
hyperpolarisation

Question 15

what happens during depolarisation

Answer 15

stimulus –>facilitated diffusion of sodium into cell down electrochemical gradient
potential difference across membrane becomes more positive
if membrane reaches threshold potential (-50) sodium voltage gated channels open
influx of sodium ions reverses potential difference to +40

Question 16

what happens during repolarisation

Answer 16

sodium voltage gated channels close and potassium voltage gated channels open
Facilitated diffusion of potassium ions out of cell down electrochemical gradient
potential difference becomes more negative

Question 17

what happens during hyperpolarisation

Answer 17

potassium ions diffuse out so potential difference becomes more negative than resting potential
refractory period:no stimulus large enough to raise membrane to threshold
voltage gated potassium channels close and sodium potassium pump restablishes resting potential

Question 18

explain the importance of the refractory period

Answer 18

no action potential can be generated in hyperpolarised sections of membrane
ensures unidirectional impulses
discrete impulses

Question 19

why is the frequency of impulse transmission significant

Answer 19

organism can distinguish size of stimulus

Question 20

what is the function of synapses

Answer 20

electrical impulse cannot pass junction
neurotransmitters send impulses between neurones
summation of sub threshold impulses

Question 21

describe the structure of a synapse

Answer 21

presynaptic neurone ends in synaptic cleft
contains lots of mitochondria, RER and vesicles of neurotransmitter
postsynaptic neurone has complementary receptors to neurotransmitter

Question 22

what happens in the presynaptic neurone when an action potential is transmitted

Answer 22

wave of depolarisation travels down presynaptic neurone causing calcium voltage gated channels to open
vesicles move and fuse with presynaptic membrane
exocytosis of vesicle

Question 23

what happens in the post synaptic neurone when an action potential is transmitted

Answer 23

neurotransmitter binds to specific receptor on post synaptic membrane sodium gated channels open
influx of sodium ions raises membrane to threshold potential-action potential generated

Question 24

what happens in an inhibitory synapse

Answer 24

neurotransmitter binds to opens chloride channels on post synaptic membrane-triggers potassium channels to open
chloride moves in and potassium moves out
potential difference becomes more negative

Question 25

what is the difference between temporal and spatial summation

Answer 25

temporal- one presynaptic neurone releases neurotransmitter several times in quick succession
spatial- multiple presynaptic neurones release neurotransmitter

Question 26

what are cholinergenic synapses

Answer 26

use acetylcholine as primary neurotransmitter

Question 27

what happens to acetyl choline from synaptic cleft

Answer 27

hydrolysis into acetyl and choline by acetylcholinesterase
acetyl and choline diffuse back into presynaptic membrane
ATP used to reform acetylcholine for storage in vesicles