Neurones and Synaptic Transmission

Question 1

How many neurones are in the human nervous system? How many of those are located in the brain?

Answer 1

100 billion

80%

Question 2

What is the purpose of a neurone? What does this provide the nervous system?

Answer 2

Transmit signals electrically and chemically which provides nervous system its primary means of communication

Question 3

Name the three types of neurones

Answer 3

Sensory
Relay
Motor

Question 4

Describe the function of a sensory neurone and its structure

Answer 4

Carry messages from PNS to CNS

Long dendrites and short axons

Question 5

Describe the function of a relay neurone and its structure

Answer 5

Connect sensory neurons to motor or other relay neurones

Short dendrites and short axons

Question 6

Describe the function of a motor neurone and its structure

Answer 6

Connect CNS to effectors

Short dendrites and long axons

Question 7

How does the size of neurones vary?

Answer 7

Less than a mm to a metre

Question 8

Name the seven basic structures of a neurone

Answer 8

Cell body
Nucleus
Dendrites
Axon
Myelin sheath
Nodes of Ranvier
Terminal buttons

Question 9

Describe the structure of dendrites and their function

Answer 9

Branch like structures that protrude from the cell body Carry nerve impulses from neighbouring neurones towards cell body

Question 10

Describe the function of an axon

Answer 10

Carries impulses away from cell body down neurone

Question 11

What is the myelin sheath and two of their functions?

Answer 11

Fatty layer that covers the axon

Protection and speeds up electrical transmission of impulse

Question 12

What are the nodes of Ranvier and their function?

Answer 12

Gaps in the myelin sheath

To speed up transmission by forcing it to ‘jump’ across gaps along the axon

Question 13

Where are terminal buttons on a neurone and what is their function?

Answer 13

End of an axon

Communicate with next neurone in chain across a gap (synapse)

Question 14

Describe the process of firing a neuron (3)

Answer 14

When a neuron is in a resting state the inside of the nerve cell is negatively charged compared to the outside
When neuron activated by a stimulus, inside of cell becomes positively charged for a split second causing an action potential to occur
Creates an electrical impulse than travels down the axon towards end of neuron

Question 15

Define neurotransmitter

Answer 15

Brain chemicals 
released from synaptic vesicles 
relay signals 
across synapse 
from one neuron to another

Question 16

Define synaptic transmission

Answer 16

Process by which neighbouring neurons communicate with each other by sending chemical messages across the synapse

Question 17

Describe the process of electrical transmission (6)

Answer 17

Electrical impulse reaches presynaptic terminal
Triggers release of neurotransmitters from the synaptic vesicles
Neurotransmitter crosses the synapse
Taken up by postsynaptic receptor site on next neuron
Chemical message converted back to electrical impulse
Process of electrical transmission can begin

Question 18

How do the type of signals vary depending on where they are happening in the neuron?

Answer 18

Inside = electrical
Between = chemically

Question 19

What two effects can neurotransmitters have?

Answer 19

Excitatory and inhibitory

Question 20

Describe the excitatory effect of a neurotransmitter

Answer 20

Binds with postsynaptic receptor
causes electrical change in the membrane of that cell
results in excitatory post-synaptic potentional postsynaptic cell is more likely to fire

Question 21

Describe the inhibitory effect of a neurotransmitter

Answer 21

Binds with postsynaptic receptor causes
electrical change in the membrane of that cell
results in inhibitory post-synaptic potential
postsynaptic cell is more less to fire

Question 22

Describe the effect of summation

Answer 22

Excitatory and inhibitory influences summed
Must reach a certain threshold for the action potential for the post synaptic neuron to be triggered
If net effect of neurotransmitter is inhibitory then post synaptic neuron is less likely to fire, excitatory net effect, more likely to

Question 23

Describe the reflex arc

Answer 23

E.g. Knee-jerk reflex
Stimulus detected by sense organs in PNS
Conveys message along a sensory neuron
Message reaches CNS where it connects with a relay neuron
Transfers message to motor neuron
Carries message to effector which brings about the response