Section 6:Nervous coordination and muscles

Question 1

What are the two main features of the synapse?

Answer 1

Undirectionality and summation

Question 2

Three points

What is meant by undirectionality and why it occurs?

Postsynaptic and presynaptic

Answer 2

Passes impulses from presynaptic membrane to postsynaptic membrane. This is because:
* Synaptic vesicles containing neurotransmitter only produced in presynaptic neurone
* Receptor protiens for neurotransmitter only in postsynaptic membrane
* Channel proteins for neurotransmitter for Na+ only on postsynaptic membrane

Question 3

What is meant by summation?

Answer 3

Impulses arriving don’t always result in impulses being generated in the postsynaptic neurone~must be enough transmitter released to reach and exceed the threshold to cause an action potential

Question 4

What are the two types of summation?

Answer 4

Spatial and temporal

Question 5

Describe spatial summation

Answer 5

No. of presynaptic neurones form synapses with one postsynaptic neurone~each neurone releases transmitter,exceeds threshold + initatiates action potential and causes depolorisation

Question 6

Describe temporal summation

Answer 6

No. of action potentials have to arrive at the same presynaptic neurone before there wiill enough transmitter released to exceed threshold + initiate an action potential

Question 7

Describe the difference between low and high frequency action potential for temporal summation

Answer 7

• Low-frequency~neurotransmitters broken down rapidly=Conc is below threshold to trigger an action potnetial
• High-frequency~neurotransmitter release in a short time=Conc is above threshold to trigger an action potential

Question 8

What are the two types of syanpses?

Answer 8

Excitatory and inhibitory

Question 9

Describe the role/function of an excitatory syanspe

Answer 9

Impulse passed from presynaptic neurone to a postsynaptic neurone~new action potential is created in postsynaptic neurone=action potential is passed from presynaptic neurone to postsynaptic neurone

Excitatory neurotransmitter is acetylecholine

Question 10

Describe the basic role/function fo an inhibitory synapse

Answer 10

Impulses can be stopped/slowed at synapses by neurotransmitters~makes it less likely that an action potential is created

Inhibitory neurotransmitter is GABA

Question 11

Four points

Describe what happens at an inhibitory synapse

Answer 11

1. Presynaptic neurone releases neurotransmitter that binds to Cl- channels on postsynaptic membrane~open channels,Cl- flow into postsynaptic neurone via FD
2. Neurotransmitter causes K+ channels to open=K+ move out of neurone into the synapse via SD
3. Combined effect of Cl- diffusing in and K+ diffusing out~inside of postsynaptic membrane becomes more negative than resting (hyperpolorised)
4. Less likely a new action potential with be created as a larger influx of Na+ will be needed

Question 12

Explain how the release of acetylcholine reduces the membrane potential of the postsynaptic membrane

Answer 12

Acetylcholine binds to receptor site of Ca2+ channels causing them to open
Ca2+ diffuses in which causes the membrane to depolorise

Question 13

Explain how a lower temperature leads to slower nerve impulse conduction

Answer 13

Decrease in temeprature,decreases KE=Decreasing the rate of diffusion of Na+ ions
Takes longer for depolorisation to occur and to trigger an action potential

Question 14

Give a basic description of each

Give three factors that affect the speed of nerve impulse conduction

Answer 14

1. Axon diameter~greater diameter,greater rate of transmission
2. Temperature~speeds up rate of diffusion via increased KE
3. Myelinated sheath~insulates the axon via saltatory conduction

Question 15

Threshold

What does the ‘all or nothing’ principle mean?

Answer 15

Action potential can only be generated if the stimulus recahes and exceeds a certain theshold
An axon cannot send a mild or strong response

Question 16

Two factors

What affects the perception of the size of an action potential?

Answer 16

1. Number of impulses sent
2. Having different neurones with different theshold values

Question 17

Describe how the strength of impulses affect action potential

Answer 17

• Increased strengths of stimuli will give increased frequency of action potential
• Size of action potentials remain the same

Question 18

How is it caused

What is a refractory period?

Answer 18

A brief period of time between the triggering of an impulse and when it is available for another
Voltage gated Na+ channels closeprvent inward movement of Na+

Question 19

Three points

What are the consequences of a refractory period?

Answer 19

1. Impulses can only travel in one direction
2. Produces discreat impulses
3. Limits the number of action potentials