Neurons

Question 1

Types of neurons

Answer 1

1. Motor neurons
2. Sensory neurons
3. Relay neurons

Question 2

Sensory neuron

Answer 2

Function-
* carries messages from sense organs (e.g. eyes) to the brain to be turned into meaningful information / carries messages from PNS to CNS
Structure-
* long dendrites and short axon
* cell body
* myelin sheath
* receptor cell
located in PNS- ganglias

Question 3

Motor neuron

Answer 3

Function-
* carries nerve impulses from the brain/ spinal cord (CNS) to muscles or glands
Stucture-
* short dendrites and long axon
* cell body
* pre-synaptic terminal
located in the CNS

Question 4

Relay neuron

Answer 4

Function-
* connect sensory neurons to motor neurons
Structure-
* short dendrites and short axons
* large cell body
* myelin sheath
* node of ranvier
found within brain and visual system

Question 5

Cell body

Answer 5

contains nucleus (chromosomes)

Question 6

Dendrites

Answer 6

• extend from cell body
• carry electrical impulses from other neurons towards the cell body

Question 7

Axon

Answer 7

• extension of the neuron
• carries impulses away from cell body
• covered in myelin-sheath

Question 8

Myelin sheath

Answer 8

• covers axon
• fatty substance
• protects the axon and increases speed of electrical transmission of the impulse

Question 9

Nodes of Ranvier

Answer 9

• breaks of between 0.2 - 2mm in myelin sheath
• speed up transmission of the impulseby forcing it to jump acroos the gaps along the axon

Question 10

Axon terminal

Answer 10

• at the end of axon
• communicates with next neuron across synapse

Question 11

Neuron ‘at rest’

Answer 11

• neuron is not sending a signal
• inside of neuron is negative to outside
• negatively charged

Question 12

Action potential

Answer 12

• neuron is activated by stimulus, and becomes positively charged (for some time)
• it increases the electrical impulse that travels through the axon to the end of the neuron

Question 13

Synapse

Answer 13

• neurons dont make direct contact but impulse travels through gap
• signal crosses gap to continue journey to/from CNS
• neurotransmitters (chemicals) diffuse across the gap
• signals within neurons are transmitted electrically
• signals between neurons, across synapse, transmitted chemically

Question 14

How does synaptic transmission work?

Answer 14

1. Nerve impulse reaches axon terminal (presynaptic terminal)
2. Here, it triggers the release of neurotransmitters
3. Neurotransmitters cross the synaptic gap and they are taken up by postsynaptic receptors on the dendrites of the next neuron
4. A chemical messgae is converted back into an electrical impulse and whole process begins again in this other neuron
   * Direction of travel for neurotransmitters can only be one way because they are released from the presynaptic neuron terminal and received by the post synaptic

Question 15

Inhibitory effect

Answer 15

some neurotransmitters act by making the neuron more negatively charged
* neuron is less likely to fire
* e.g. depression has been linked to low levels of serotonin

Question 16

Excitatory effect

Answer 16

some neurotransmitters increase the positive charge
* neuron is more likely to fire
* e.g. adrenaline during fight or flight
* e.g. dopamine - caffeine encourages dopamine to be released encouraging a person to feel more alert and able to focus for a short period of time

Question 17

Process of summation

Answer 17

the action potential of the post synaptic neuron is only triggered if the sum of exitatory and inhibitory signals at one time reaches the threshold
* the right amount of neurons must be required for firing neurons