5.1.3 - neuronal communication

Question 1

stimulus

Answer 1

changes in the internal and external environment

Question 2

neurones

Answer 2

transmit electrical impulses rapidly around the body so that the organism can respond to changes in its internal and external environment

Question 3

cell body of a neurone

Answer 3

contains the nucleus surrounded by the cytoplasm
lots of ER and mitochondria

Question 4

dendrons

Answer 4

short extensions which come from the cell body - responsible for transmitting electrical impulses towards the cell body

Question 5

axons

Answer 5

singular elongated nerve fibres that transmit impulses away from the cell body - can be very long

Question 6

sensory neurones

Answer 6

transmit impulses from a sensory receptor cell to other neurones
one dendron and one axon

Question 7

relay neurone

Answer 7

transmit impulses between neurones - lots of axons and dendrons

Question 8

motor neurones

Answer 8

transmit impulses from a relay/sensory neurone to an effector.
one axon and many short dendrons

Question 9

myelin sheath

Answer 9

covers axons of some neurones, made up of many layers of plasma membrane and acts as an insulating layer

Question 10

advantages of a myelienated neurone

Answer 10

faster transmission

Question 11

features of all sensory receptors

Answer 11

• specific to a single type of stimulus
• act as a transducer - convert a stimulus into a nerve impulse

Question 12

pacinian corpuscle

Answer 12

specific sensory receptors that detect mechanical pressure
most abundent in the fingers and soles of the feet

Question 13

structure of a Pacinian corpuscle

Answer 13

neurone ending surrounded by many layers of connective tissue. each layer of tissue is separated by a layer of gel.

Question 14

steps of how the Pacinian corpuscle converts mechanical pressure into a nervous impulse

Answer 14

1. resting potential
2. pressure is applied and the corpuscle changes shape - causing membrane to stretch
3. sodium channels widen, sodium ions can diffuse in
4. influx of + sodium ion causes depolarisation
5. action potential
6. action potential transmitted along sensory neurone

Question 15

resting potential

Answer 15

when a neurone is not transmitting an impulse - the outside of the membrane is more positively charged than inside, so it is polarised

Question 16

resting potential ion movement

Answer 16

• sodium potassium pump - ACTIVE TRANSPORT - 3Na+ pumped out, 2K+ pumped in
• sodium ion channels are CLOSED so cannot diffuse back in
• potassium channels are OPEN so can diffuse back out

= more positive outside the membrane

Question 17

action potential ion movement

Answer 17

• sodium channels OPEN - Na+ can diffuse in
• the mmore that diffuse in, the more that open - positive feedback causing influx of na+ ions
• potassium ion channels CLOSED

= DEPOLARISATION

Question 18

repolarisation

Answer 18

the neurone returning back to the resting potential.

Question 19

hyperpolarisation

Answer 19

initially lots of potassium ions diffusing out of the axon, resulting in the inside of the axon becoming more negative than in its normal resting stage

Question 20

propagation of an action potential - non myelinated neurone

Answer 20

first region is depolarised, then this acts as a stimulus for the depolarisation of the next region of the membrane, this process continues due to a localised current of sodium ions

Question 21

refractory period

Answer 21

short period of time after an action potential when the axon cannot be excited again.

Question 22

why is the refractory period important?

Answer 22

prevents the propagation of an action potential backwards along the axon as well as forwards - makes sure action potentials are unidirectional

Question 23

difference between action potentials in mylenated axons and non

Answer 23

much faster as can only take place at the nodes so will ‘jump’ from one node to another

Question 24

other factors that affect the speed at which action potentials travel

Answer 24

• axon diameter - the bigger the diameter, the faster the impulse (less resistence to the flow of ions in the cytoplasm)
• temperature - the higher the temp, the faster the nerve impulse (ions diffuse faster)

Question 25

all or nothing principle

Answer 25

if the threshold value is reached, the action potential will always be created no matter how large the stimulus is, the same sized action potential will always be triggered.

Question 26

synaptic cleft

Answer 26

the gap which separates the axon of one neurone from the dendrite of the next neruone

Question 27

synaptic knob

Answer 27

the swollen end of the presynaptic neurone - contains lots of mitochondria and large amounts of ER

Question 28

excitatory neurotransmitters

Answer 28

result in the depolarisation of the post synaptic neurone e.g acetylcholine

Question 29

inhibitory neurotransmitters

Answer 29

neurotransmitters that result in the hyperpolarisation of the postsynaptic membrane e.g GABA

Question 30

synaptic transmission steps

Answer 30

- action potential enters presynaptic neurone - depolarisation of the presynaptic membrane so calcium ion channels open - calcium ion influx - synaptic vesicle fuses with membrane, releasing neurotransmitter into synaptic cleft - neurotransmitter diffuses across synaptic cleft and binds to recptors on post synaptic neurone - sodium ion channels open, causing influx of sodium into postsynaptic neurone - triggers an action. potential

Question 31

how are the neurotransmitters removed after the action potential?

Answer 31

neurotransmitter is broken down by the enzyme, releasing it from the receptors, and the products are taken back to the presynaptic knob acetylcholine is hydrolysed by acetylcholinesterase to form choline and ethanoic acid

Question 32

why are the neurotransmitters removed?

Answer 32

so that the stimulus is not maintained and anoother stimulus can arrive and affect the synapse

Question 33

role of the synapse in the nervous system

Answer 33

- ensure impulses are unidirectional - allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses

Question 34

how do synapses result in undirectional movement

Answer 34

receptors are only present in the postsynaptic membrane

Question 35

summation

Answer 35

if the amount of neurotransmitter builds up sufficiently to reach the threshold, this will trigger an action potential

Question 36

spatial summation

Answer 36

occurs when a number of presynaptic neurones connect to one postsynaptic neurone - each release neurotransmitter which builds up to a high enough level to trigger an action potential

Question 37

temporal summation

Answer 37

occurs when a single presynaptic neurone releases neurotransmitter as a result of action pontial several times over a short period.