STRUCTURE OF NEURONS

Question 1

Three types of neuron

Answer 1

> Sensory Neurons
Relay Neurons
Motor Neurons

Question 2

Sensory Neuron

Answer 2

> carry messages from the PNS to the CNS. They have long dendrites and short axons. Located in the PNS in clusters called ganglias.

Question 3

Relay Neuron

Answer 3

Connect sensory neurons to motor or other relay neurons. They have short dendrites and short axons. Of all neurons, 97% are relay neurons and most are in the brain and visual system.

Question 4

Motor neurons

Answer 4

Connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons. Cell bodies may be in the CNS but long axons form part of PNS.

Question 5

What are neurons?

Answer 5

> 100 billion nerve cells in the human nervous system, 80% are located in the brain.
By transmitting signals electrically and chemically, they provide the nervous system with its primary means of communication.

Question 6

What is the structure of a neuron?

Answer 6

Cell body (soma)
Dendrites
Axon
Terminal buttons

Question 7

Cell body

Answer 7

> Includes a nucleus which contains the genetic material of the cell

Question 8

Dendrites

Answer 8

Branchlike structures that protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body.

Question 9

Axon

Answer 9

Carries the electrical impulse away from the cell body down the length of the neuron
>It is covered in a fatty layer of myelin sheath that protects the axon
>Gaps in the axon called nodes of Ranvier speed up the transmission of the impulse

Question 10

Terminal Buttons

Answer 10

> At the end of the axon

>Communicate with the next neuron in the chain across a gap called the synpase.

Question 11

Electrical transmission

Answer 11

> the firing of a neuron.
When a neuron is in a resting state, the inside of the cell is negatively charged compared to the outside.
When a neuron is activated, the inside of the cell becomes positively charged for a split second causing an action potential to occur.
This creates an electrical impulse that travels down the axon towards the end of the neuron

Question 12

Synapse

Answer 12

Each neuron is separated from the next by an extremely tiny gap called the synapse

Question 13

Chemical Transmission

Answer 13

> Signals WITHIN neurons are transmitted electrically but signals BETWEEN neurons are transmitted chemically across the synpase
When the electrical impulse reaches the end of the neuron (presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
Once a neurotransmitter crosses the gap, it’s taken up by a postsynaptic receptor site on the next neuron, so the impulse only ever travels in one direction.
Chemical message is converted back into an electrical impulse and the process of electrical transmission begins.

Question 14

Neurotransmitters

Answer 14

> Chemicals that diffuse across the synapse to the next neuron in the chain.
Many neurotransmitters have been identified, Each has its own specific molecular structure that fits perfectly into a postsynaptic receptor site, like a lock and key.
Each has specific functions. ie. serotonin affects mood and social behaviour (among other things) which is why it has been impacted as a cause of depression.

Question 15

Excitation and Inhibition

Answer 15

> Neurotransmitters generally have either an excitatory or inhibitory effect on the neighbouring neuron.
examples,
Adrenaline, generally excitatory, increasing the positive charge of the postsynaptic neuron, making it more likely the postsynaptic neuron will fire.
Serotonin, generally inhibitory, increasing the negative charge of the postsynaptic neuron, making it less likely the postsynaptic neuron will fire.
Dopamine, ununusal neurotransmitter as it is equally likely to have an excitatory or inhibitory effects on the postsynaptic neuron.

Question 16

Summation

Answer 16

> Excitatory and inhibitory influences are summed and must reach a certain threshold in order for the action potential of the postsynaptic neuron to be triggered.
If the net effect of the neurotransmitters is inhibitory then the postsynaptic neuron is less likely to fire (ie. no electrical signal is transmitted). It is more likely to fire if the net effect is excitatory.