Neuronal communication

Question 1

what is a transducer

Answer 1

something that coverts energy from one form to another

Question 2

how do sensory receptors act as transducers

Answer 2

they convert a stimulus into a nervous impulse

Question 3

type of sensory receptors

Answer 3

mechanoreceptors e.g pacinial corpuscle on skin detect pressure and movement

chemoreceptors e.g olfactory receptors in nice detect chemicals (smell)

photoreceptors e.g come cells in eye detect light

thermoreceptors e.g end bulbs of krause on tongue detect heat

Question 4

how is a action potential generated in pacinial corpuscle

Answer 4

when pressure is applied the membrane surround the neurone stretches causing gaps between the phospholipids.
this opens sodium ions channels so sodium ions diffuse into the neurone down a electrochemical gradient
the influx of sodium ions changes the potential of the membrane causing it be be depolarised
this results in an action potential that passes along the sensory neurone

Question 5

structure of sensory neurone

Answer 5

one dendron which carries impulses to the cell body
cell body in the middle
one axon which carries impulse away from the cell body

connects sensory receptors to relay neurones , motor neurone or the brain

Question 6

structure of replay neurone

Answer 6

short axon and dendron
contains dendrites
transmutes impulse between neurones

Question 7

structure of motor neurone

Answer 7

no dendron
cell body at end
dendrites directly connected to the cell body
long axon

transports impulse from relay or sensory neurone to an effector

Question 8

structure and function of myelin sheath

Answer 8

produced by schwann cells
between schwann cells there are node of ranvier
acts as an insulating layer allowing it to conduct electrical impulses at a faster rate

Question 9

saltatory conduction

Answer 9

membrane is only depolarised at the nodes of ranvier
creating a longer localised circuit
increases the rate of impulse transmission

Question 10

describe resting potential

Answer 10

3 Na+ pumped out 2 K+ pumped in by active transport by the sodium potassium pump

sodium ions channels are closed but potassium ions channels are open so some K+ diffuse out of the axon

this creates a resting potential across the membrane of -70mV

Question 11

describe action potential DEPOLARISATION

Answer 11

depolarisation
energy from a stimulus triggers some sodium voltage gated ion channels to open
makes the membrane more permeable to Na+ so it diffuses into the axon down an electrochemical gradient
this makes inside less negative
change in charge causes more sodium ion channels to open allowing more sodium ions to diffuse into the axon - positive feedback
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Question 12

describe action potential REPOLARISATION

Answer 12

when pd reaches +40mV voltage gated Na+ channels close and voltage gated K+ channels open making membrane more permeable to K+

K+ diffuses out of the axon down their electrochemical gradient reducing the charge inside axon

Question 13

describe action potential hyper polarisation

Answer 13

initially lots of K+ diffuse out making inside more negative then normal resting state

the voltage gated K+ channels close and sodium potassium pump causes Na+ to diffuse out and K+ in and the axon restores its resting potential

Question 14

refractory period

Answer 14

short period after action potential where the axon cannot be exited again

prevents propagation of action potential backwarda

Question 15

all or nothing principle

Answer 15

if threshold is not reached no action potential is generated

the size of the stimulus doesn’t affect size of action potential but frequency of it

Question 16

3 factors that affect speed of action potential

Answer 16

1. axon diameter- bigger diameter then the faster the impulse travels due to less resistance
2. temperature - higher temps faster transmission
3. myelination

Question 17

temporal summation

Answer 17

a single pre synaptic neurone releasing neurotransmitter several times over a short period to build up in the synapse until the quantity is sufficient to trigger an action potential

Question 18

spartina summation

Answer 18

allowes convergence
impulses from more then one neurone to be passed to a single neurone

Question 19

role of synapses

Answer 19

allows nuerones to communicate/ cell signalling

ensures transmission in one direction

alllows convergence
allows divergence

Question 20

why do synapse allow one direction flow

Answer 20

vesicles contains neurotransmitter are only found in the presynaptic neurone

receptors in the sodium voltage channel’s can only be found on the postsynaptic membrane

calcium channels only found on the presynaptic neurone

Question 21

excitatory neurotransmitter

Answer 21

truly in the depolarisation of the post synaptic neurone

if threshold is reach in postsynaptic membrane action potential is triggered

Question 22

inhibitory neurone

Answer 22

these results in the hyper polarisation of post synaptic membrane preventing an action potential being triggered

GABA is an example

Question 23

transmission across cholinergic synapse

Answer 23

1. the arrival of an action potential at the end of the presynaptic neurone causes calcium ion channels to open and calcium ions enter the synaptic knob
2. the influx of calcium ions into the presynaptic neurone causes synaptic vesicles to fuse to the presynaptic membrane releasing acetylcholine into the synaptic cleft
3. acetylcholine molecules fuse with receptors sites on the sodium ion channels in the postsynaptic membrane. this causes sodium ion channels to open allowing sodium ions to diffuse in rapidly along a concentration gradient
4. influx of sodium ions generates a new action potential in postsynaptic neurone
5. Acetylcholinesterase hydrolyse acetylcholine into choline and ethanoic acid which diffuse back across the synaptic cleft into the presynaptic neurone. break down of acetylcholine prevent continuously generating new action potentials in the postsynaptic neurone
6. ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine. this is stored in synaptic vesicles for future use. sodium ion channels close in absence of acetylcholine in receptors sites