neuronal communication

Question 1

what do sensory receptors do?

Answer 1

convert stimuli from the environment into nerve impulses

Question 2

what does it mean to be a transducer?

Answer 2

transfer energy from one form into another

Question 3

what is a parcinian corpuscle?

Answer 3

these are sensory receptors which detect pressure on the skin and convert it into a nerve impulse the end of a sesnory impulse is within the centre of the corpuscles surrounded by connective tissue which has layers separated by a gel

Question 4

How does the parcinian corpuscle produce a nerve impulse?

Answer 4

the receptors detect a change in pressure which causes stretch mediated channels within the parcinian corpuscle to open. at resting state the channels are too narrow fro sodium ions to pass through but when they stretch there is room for sodium ions to diffuse into the neurone and depolarise it which creates a nerve impulse

Question 5

what is the cell body within a neurone?

Answer 5

contains the nucleus and cytoplasm as well as lots of endoplasmic reticulum and mitochondria which are important in the production of neurotransmitters

Question 6

what are dendrons?

Answer 6

these are short extensions which divide into dendrites and transmit electrical impulses towards the cell body

Question 7

what are axons?

Answer 7

these are long nerve fibres that transmit impulses away from the cell body

Question 8

what are sensory neurone?

Answer 8

sensory neurons transmit information from receptors to the CNS, they have 1 dendron and 1 axon

Question 9

what are motor neurones?

Answer 9

these transmit information from the CNS to effectors and have on long exon and many short dendrites

Question 10

what are relay neurones?

Answer 10

these connect motor and sensory neurone, they have many short axons and dendrons

Question 11

what is the point of a myelin sheath?

Answer 11

axons of some neurones are covered in a myelin sheath made of schwann cells which insulates the axon and allows it to conduct impulses faster. there are small gaps between the myelin sheath called the nodes of ranvier where impulses jump from one node to the next in salutatory conduction

Question 12

when does an action potential occur?

Answer 12

when the potential difference across an axon it temporarily reverses and the potential difference changes to +40 mv and is depolarised

Question 13

summarise how an action potential is produced

Answer 13

when the receptors react to stimuli some sodium voltage gated ion channels open making the membrane more permeable to sodium ions. these diffuse into the axon which makes the neurone less negative. eventually the potential difference will reach +40mv and voltage gated sodium channels close and voltage gated potassium ion channels open. this makes the membrane more permeable to potassium ions so these diffuse out of the axon down the electrochemical gradient which reduces the charge inside the neurone so it becomes more negative. initially lots of potassium ions leave which result sin hyperpoarization so the channels close and the neurone returns to resting state and is depolarised.

Question 14

what is the refractory period?

Answer 14

this is when the voltage gated sodium chain;es remain closes so that the axon cannot from a new action potential to ensure that the action potential does not propagate backwards

Question 15

how does axon diameter affect the speed at which an action potential is propagated?

Answer 15

a large diameter allows faster transmission as there is less resistance to the flow of ions in the cytoplasm

Question 16

how does temperature affect the speed at which an action potential is propagated?

Answer 16

at higher temperatures there is faster transmission as ions diffuse faster at higher temperatures up until 40 degrees where they may become denatured

Question 17

What is the all or nothing principle?

Answer 17

if the threshold value of a stimuli (+40mv) it will always trigger an action potential. the size affects the number of potentials triggered not how big

Question 18

summarise action potentials at a synapse

Answer 18

ana action potential reaches the synaptic bulb
this causes the voltage gated calcium ion channels to open
calcium ions diffuse into the synaptic bulb
calcium ions cause vesicles to fuse with the presynaptic membrane
acetylcholine is released into the synaptic cleft via exocytosis
acetylcholine diffuses across the synaptic cleft
these molecules bind to receptors on sodium ion channels on the post synaptic membrane
sodium ion channels open
diffuse across post synaptic membrane into post synaptic neurone
an excitatory post synaptic potential is created

Question 19

what is summation?

Answer 19

the build up of neurotransmitters from several impulses which will allow the threshold potential to be reached

Question 20

what is spatial summation?

Answer 20

several pre synaptic neurones connect to one post sy attic neurone and neurptrasnmiiters from all neurones combine to trigger an action potential

Question 21

what is temporal summation?

Answer 21

a single press optic neurone releases neurotransmitters as a result of several action potentials over a short period.

Question 22

what is habituation?

Answer 22

if action potentials keep arriving at they synapse it may run out of vesicles containing neurotransmitters. so the nervous system no longer reacts to the stimulus.

Question 23

what are ISPS

Answer 23

Some pre synaptic neurones can produce an inhibitory post synaptic potential which prevents an action potential being triggered in the post synaptic neurone.