Nervous system

Question 1

At a resting potential is the outside more positive or negative than the inside

Answer 1

Positive

Question 2

What does polarised mean

Answer 2

There is a difference in charge

Question 3

What is the voltage at a resting potential

Answer 3

-70mV

Question 4

How is a resting potential maintained

Answer 4

The Na/K pump
Na moved out
Membrane imperméable to Na so they can’t move back in
Creates Na electrochemical gradient (more Na outside than in)
K move in
Membrane permeable to k
K moves back out (by channel proteins)

Question 5

What ratio does the Na/K pump move ions

Answer 5

Na:K
3:2

Question 6

Give the 5 stages of an action potential

Answer 6

Stimulus 
Depolarisation 
Repolarisation 
Hyper polarisation 
Resting potential

Question 7

Explain how a stimulus starts the action potential

Answer 7

Excites neurone plasma membrane 
Na channels open 
More permeable to Na
Na diffuse into neurone down electrochemical gradient 
Inside is less negative

Question 8

Explain depolarisation

Answer 8

Potential difference reached threshold potential
More Na channels open
Na diffusés more rapidly into the neurone
Less negative

Question 9

Explain repolarisation

Answer 9

Na channels close
K channels open
More permeable to k
K move out down conc grad

Question 10

Explain hyperpolarisation

Answer 10

K channels are slow to close
Overshoot of how many k diffuse out of neurone
More negative than resting potential

Question 11

Explain resting potential after an ap

Answer 11

Ion channels are rests

Na/k pump returns membrane to -70mV

Question 12

What is the refractory period

Answer 12

After ap
Ion channels are recovering and can’t open
No action potential can happen

Question 13

How do ap move along neurone

Answer 13

Na ions diffuse sideways
Na channels in the next region open
Na diffuse into the next part
Wave of depolarisation away from areas in refractory period

Question 14

What are the effects of the refractory period

Answer 14

Ap don’t overlap = they are discrète Impulses
The frequency is limited
Unidirectional

Question 15

Why do ap have “all or nothing” nature

Answer 15

If threshold reached the ap will always fire at the same voltage no matter the stimulus size. If the threshold isn’t reached then no ap

Question 16

What is the effect of a bigger stimulus

Answer 16

More frequent ap

Question 17

What is a myelin sheath

Answer 17

Electrical insulator

Question 18

What makes the myelin sheath

Answer 18

Schwann cell

Question 19

What structure is between the Schwann cells

Answer 19

Nodes of ranvier

Question 20

Where are Na channels concentrated

Answer 20

Nodes of ranvier

Question 21

Where does depolarisation happen at a myelinated neurone

Answer 21

At nodes of ranvier

Question 22

Explain saltatory conduction

Answer 22

The neurone cytoplasm conducts enough electrical charge to depolarise the next node of ranvier. So depolarisation jumps from node to node

Question 23

What is the benefit of salutatory conduction

Answer 23

Very fast

Question 24

Explain the conduction in non myelinated neurones

Answer 24

The impulse travels along the whole length of the axon membrane so is slower

Question 25

What are dendrites

Answer 25

Extensions of cell body that connect to other neurones

Question 26

How does axon diameter effect speed of depolarisation

Answer 26

Big diameter = fast rate of depolarisation | Because there’s less resistance to flow of ions

Question 27

How does temp effect speed of depolarisation

Answer 27

Temp increases = depolarisation rate increases Because ions diffuse faster Until 40 = channel proteins denature and speed decreases

Question 28

What is a synapse

Answer 28

Junction between 2 neurones or a neurone and effector cell

Question 29

Why are synapses uni directional

Answer 29

Receptors are only on the post synaptic membrane

Question 30

How does the synapse stop the the impulse continually happening

Answer 30

Neurotransmitters are removed from cleft by enzymes or réabsorbed by presynaptic knob

Question 31

What structure does the presynamptic knob have

Answer 31

Synaptic vesicles

Question 32

What do synaptic vesicles store/release

Answer 32

Neurotransmitters

Question 33

What is the neurotransmitter at a cholinergic synapse

Answer 33

Acetylcholine

Question 34

How is a nerve impulse transmitted across a cholinergic synapse

Answer 34

1. Ap arrives at presynaptic knob 2. Voltage gated ça ion channels open in presynaptic neurone 3. Ça diffuse into synaptic knob 4. Synaptic vesicles move to presynaptic membrane and fuse 5. Vesicles release ACh into synaptic cleft 6. ACh binds to cholinergic receptors on the post synaptic membrane 7. Na channels open on post synaptic neurone 8. Post syn. Neurone is depolarised 9. Ap fired when threshold reached

Question 35

How is ACh removed from synaptic cleft

Answer 35

Broken down by enzyme: acetylcholineesterase | Products reabsorbed by presynaptic neurone

Question 36

What are excitatory neurotransmitters

Answer 36

Cause the post synaptic membrane to be depolarised | Causing an ap when threshold reached

Question 37

Give an example of an excitatory neurotransmitter

Answer 37

Acetylcholine

Question 38

What is an inhibitory neurotransmitter

Answer 38

They hyperpolarise the post synaptic membrane | Preventing the ap being fired

Question 39

How does acetylcholine act as a inhibitory neurotransmitter at the heart

Answer 39

It binds to receptors Causes k channels to open Hyper polarising the post synaptic membrane

Question 40

What happens to the amount of neurotransmitter with a weak stimulus

Answer 40

Small amount released from presynaptic neurone

Question 41

What is summation

Answer 41

The effect of neurotransmitters released from many neurones is added together

Question 42

What is spatial summation

Answer 42

Many neurones connect to 1 neurone The small amount of neurotransmitter released from each neurone is added together to reach the threshold Or if inhibitory = to stop the the ap

Question 43

What is temporal summation

Answer 43

2+ impulses arrive in quick succession from the same presynaptic neurone More neurotransmitter released More likely to cause ap

Question 44

Where is a neuromuscular junction

Answer 44

Synapse Between motor neurone and muscle cell

Question 45

What neurotransmitter is used at neuromuscular junctions

Answer 45

Acetylcholine

Question 46

What does the neurotransmitter bind to at neuromuscular junctions

Answer 46

Nicotinic cholinergenic receptors

Question 47

What are the differences between cholinergenic synapses and neuromuscular junctions

Answer 47

1. At neuromuscular junctions the post syn. Membrane has lots of folds which form clefts. The clefts store acetylcholinesterase 2. Neuromuscular junctions have more receptors 3. Neuromuscular junctions always have excitatory ACh

Question 48

What are agonist drugs

Answer 48

Drugs that have the same shape as neurotransmitters and mimic their action at receptors. So more receptors are activated

Question 49

Give an example of an agonist drug

Answer 49

Nicotine | Binds to nicotinic receptors in the brain

Question 50

What are antagonist drugs

Answer 50

Block receptors so can’t be activated by neurotransmitters | So fewer receptors are activated

Question 51

What drug blocks nictotinic cholinergenic receptors

Answer 51

Curare

Question 52

What is the affect of nicotinic cholinergenic receptors being blocked

Answer 52

Muscle paralysis

Question 53

What is the effect of drugs that stop the enzyme for the neurotransmitter

Answer 53

More neurotransmitter in the syn cleft More can bind to receptors on post syn membrane More there for longer More frequent ap

Question 54

What is the effect of nerve gases

Answer 54

Loss of muscle control

Question 55

What is the affect of amphétamines on synapses

Answer 55

Release more neurotransmitter from pre syn membrane | More receptors activated

Question 56

What is the effect of alcohol on synapses

Answer 56

Inhibit the release of neurotransmitters | Fewer receptors activated