Neuronal Communication

Question 1

What is the role of the nervous system?

Answer 1

Detecting stimuli in the internal and external environment, then processing the information and triggering an appropriate response

Question 2

What is the role of neurones?

Answer 2

To transmit electrical impulses around the body

Question 3

Sensory neurone

Answer 3

Transmit impulses from a sensory receptor to a relay neurone, motor neurone or the brain
One dendron and one axon

Question 4

Relay neurones

Answer 4

Transmit impulses between neurones
Many short axons and dendrons

Question 5

Motor neurones

Answer 5

Transmit impulses from a relay or sensory neurone to an effector cell
One long axon and many short dendrites

Question 6

What is the myelin sheath?

Answer 6

Electrical insulation of the neurone to help conduct electrical impulses at a much faster speed
Schwaan cells produce layers of plasma membrane by growing around the axon many times
Nodes of Ranvier are small gaps between adjacent Schwaan cells

Question 7

What are the features of a sensory receptor?

Answer 7

Are specific to a type of stimulus
Act as a transducer- convert a stimulus into a nerve impulse

Question 8

What is the pacinian corpuscle?

Answer 8

Sensory receptors that detect mechanical pressure
In its normal state, the stretch mediated sodium ion channels are closed (resting potential as the membrane is polarised)
Pressure applied causes the corpuscle to change shape and stretch the sodium ion channels
Sodium ions can diffuse into the neurone down an electrochemical gradient
The membrane becomes depolarised
This causes a generator potential, which in turn causes an action potential

Question 9

Describe resting potential

Answer 9

3 sodium ions are pumped out for every 2 potassium ions that are pumped in by the sodium- potassium pump using active transport
Voltage gated sodium ion channels are closed so they cannot diffuse back into the cell, however potassium ion channels are open so they can diffuse back out of the cell
This makes the inside of the cell negative relative to the outside at -70mV

Question 10

Describe how an action potential is generated

Answer 10

1) At a resting potential the membrane is at -70mv
2) A stimulus causes voltage gated sodium channels to open, an influx of sodium ions down the electrochemical gradient
3) When the threshold potential (-55mV) is reached, more voltage gated sodium ion channels open- positive feedback
4) Depolarisation occurs at +40mV and voltage gated sodium ion channels close, voltage gated potassium ion channels open
5) Potassium ions diffuse out of the cell- repolarisation occurs
6) Due to an overshoot of potassium ions hyperpolarisation occurs (-90mV)
7) The sodium potassium pump restores the membrane to resting potential

Question 11

What is the refractory period and why is it important?

Answer 11

After an action potential has been generated, there is a short period of time where the axon cannot be excited again
Prevents the action potential going backwards along the axon (only unidirectional)
Prevents action potentials from overlapping

Question 12

What is saltatory conduction

Answer 12

Depolarisation of the axon membrane can only occur at the nodes of Ranvier
Action potentials jump from one node to another- much faster than a wave of depolarisation across the whole length of the axon
It is also more energy efficient (repolarisation required ATP for the sodium potassium pump)

Question 13

What factors affect the speed of transmission

Answer 13

Myelination
Axon diameter
Temperature

Question 14

What is the all or nothing principle?

Answer 14

No matter how large the stimulus is, the size of the action potential generated will always be the same but the frequency will increase
If the threshold is not reached, no action potential will be generated

Question 15

What are the two types of neurotransmitter?

Answer 15

Excitatory- cause depolarisation of the postsynaptic neurone
Threshold reached= action potential generated
Inhibitory- cause hyperpolarisation of the postsynaptic neurone and prevents an action potential from being triggered

Question 16

Describe how a synapse works

Answer 16

1) Arrival of an action potential in the presynaptic neurone causes voltage gated calcium ion channels to open
2) Calcium ions diffuse into the presynaptic knob which cause synaptic vesicles to fuse with the presynaptic membrane
3) Neurotransmitter is released into the synaptic cleft by exocytosis
4) Neurotransmitter diffuses across the cleft and fuses with the receptors on sodium ion channels in the membrane of the post synaptic membrane
5) Sodium ion channels open and there is an influx of sodium ions into the neurone which causes a new action potential to be generated
6) An enzyme hydrolyses the neurotransmitter and it diffuses back into the presynaptic cleft
7) ATP is used to rejoin the elements and is stored for future use

Question 17

What are the two types of summation?

Answer 17

Spatial summation- more than one presynaptic neurone releases neurotransmitter to trigger an action potential in one post synaptic neurone
Temporal summation- a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period of time

Question 18

What are the effects of drugs on synapses?

Answer 18

Mimicking the shape of the neurotransmitter so it can bind to receptors on the post synaptic membrane and trigger action potentials
Inhibiting the enzyme responsible for breaking down the neurotransmitter
Blocking receptors so neurotransmitter can no longer bind