paper 2: Nervous Coordination

Question 1

what is one nerve cell called

Answer 1

neurone

Question 2

draw a labelled diagram illustrating the structure of a myelinated motor neurone

Answer 2

Question 3

explain how the resting potential of a neurone is achieved

Answer 3

• the sodium potassium pump actively transports sodium ions out of the neurone and potassium ions into the neurone
• membrane is more permeable to potassium ions than sodium ions
• there is a higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone
• the membrane is polarised, there is more positive charge outside the cell than inside creating a resting potential

Question 4

give the step-by-step stages for how an action potential is achieved

Answer 4

1. when the neurone is stimulated the voltge gated sodium ion channels open
2. Na+ ions diffuse into the axom down thier electrochemical gradient causing depolarisation
3. more voltage gated sodium ion channels open and if threshold is rezched the neurone depolarises to about +40mV
4. the sodium ion channels then close prevent Na+ ions entering the axon and potasium ion channels open
5. K+ ions diffuses out down its electrochemical gradient. the neurone become more negative
6. too many K+ ions diffuse out causing the neurone to become too negative. This is hyperpolarisation
7. potassium ion channels close and the sodium potassium pump returns the neurone back to the resting potential

Question 5

sketch a graph showing the changes in voltage accros a membrane during an action potential

Answer 5

Question 6

complete this table:

Answer 6

Question 7

explain what the refractory period is

Answer 7

• the time during which no new action potentials can be generated

Question 8

explain 3 functions of refactory period

Answer 8

• so action potentials move in one direction
• produces discrete impulses
• limits maximum frequency of action potentials

Question 9

explain what is meant by the all or nothing principle

Answer 9

• an action potential is an all or nothing response. it is always the same size
• if threshold is reached you get an ection potential, if not reached ther eis no action potential

Question 10

how does the brain determine the strenght of a stimulus

Answer 10

• the stronger the stimulus the greater the frequency of action potentials

Question 11

how does the brain determine the strength of the stimulus

Answer 11

the stronger the stimulus, the greater the frequency of action potentials

Question 12

describe how an action potential spreads along a non-myelinated neurone

Answer 12

1. an action potential occurs at a section of axon membrane
2. the membrane adjacently in front of the action potential detects the depolarisation and adjacent voltage gated Na+ channels open, also forming an action potential
3. the action potential moves foreward. The refractory period behind the action potential prevents the impulse being conducted backwards

Question 13

describe how an action potential spreads along the myelinated axon by saltatory conduction

Answer 13

1. the myelin insulates the axon ( preventing ion movements )
2. depolarisations only take place at the nodes of Ranvier
3. action potentials ‘jump’ bfrom node to node. this is known as saltatory conduction
4. therefore there are less depolarisations along the whole length of the axon membrane

Question 14

what are the 3 ways you can speed up the conduction of action potentials

Answer 14

1. myelination allows saltatory conduction
2. a higher temperature increases the kinetic energy of ions so they diffuse faster through the membrane
3. a greater diameter reduces resistance to ion flow

Question 15

draw a labelled diagram showing the structure of a cholinergic synapse

Answer 15

A= pre-synaptic neuronw
B = post synaptic neurone
1. mitochondria
2. synaptic vessel full of neurotransmitter
3. calcium channel
4. synaptic cleft
5. neurotransmitter receptor
6. calcium channel
7. fused vesicle releasing neurotransmitter
8. neurotransmitter re-uptake pump

Question 16

give the sequence of events in transmission across a cholinergic synapse

Answer 16

1. an action potential depolarises the pre-synaptic membrane, voltage gated Ca2+ channels open and calcium ions diffuse in
2. calcium ions cause synaptic vesicles to fuse with the presynaptic membrane and release ACh into the synaptic cleft
3. ACh diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane
4. sodium ion channels open and sodium ions diffuse into the postsynaptic neurone, depolarising the postsynaptic membrane, causing an action potential
5. acetylcholinesterase hydrolyses the acetylcholine. the sodium ion channels close and no more action potentials are generated

Question 17

why is summation used

Answer 17

• increase neurotransmitter in the synaptic cleft to increase depolarisation of postsynaptic membrane so threshold is reached

Question 18

what is spatial summation

Answer 18

more than one pre-synaptic neurone connected to one postsynaptic neurone

Question 19

what is temporal summation

Answer 19

several action potentials arrive in short time from one presynaptic provide enough neurotransmitter to reach threshold in postsynaptic neurone

Question 20

synapses have unidirectionality, what is this?

Answer 20

action potentials travel in one dircetion across the synapse from pre-synaptic neurone to post-synaptic neurone

Question 21

explain why synaptic trnasmission is unidirectional

Answer 21

• neurotransmitter is only released from the presynaptic neurone
• receptors are only on the postsynaptic membrane

Question 22

explain how a synapse can be inhibitory

Answer 22

• calcium ions hyperpolarise the post synaptic neurone so it becomes more negative
• this means more sodium ions are needed to reach threshold for an action potential
• so without sodium ions, action potential is less likely to be reached

Question 23

describe step-by-step how the action potential crosses the neuromuscular junction

Answer 23

1. nerve impulse depolarises the pre-synaptic membrane and calium ion channels open
2. calcium ions diffuse into the presynaptic neurone causing synaptic vesicles to fuse with the presynaptic membrane
3. ACh is released into the synaptic cleft and diffuse across
4. ACh binds to receptors on the muscle fibre membrane
5. sodium ion channels open and sodium ions diffuse into the muscle fibre
6. causing depolarisation of muscle fibre membrane

Question 24

what are the similarities and differences between a neuromuscular junction and a cholinergic synapse

Answer 24

similaries:
1. both used acetylcholine as the neurotransmitter

differences:
1. cholinergic synapse connect neurone to neurone wherease neuromuscular junction connects meruone to muscle fibre
2. cholinergic synapse has less ACh receptors on the post synaptic membrane whereas a neuromuscular junction has more ACh receptors on the muscle fibre
3. cholinergic synapse can be excitatory or inhibitory whereas neuromuscular junction can only be excitatory
4. cholinergic synapse has no clefts in the post synaptic membrane whereas the neuromuscular junction contains clefts in muscle fibre membranes which store acetylcholinerase