Biopsychology - Neurons and synaptic transmission

Question 1

What is a neuron?

Answer 1

Cells that are specialised to carry neural information throughout the body

Question 2

Three types of neuron

Answer 2

Sensory, motor , relay

Question 3

What are neurons typically made up of ?

Answer 3

A cell body, dendrites and an axon

Question 4

What is the function of dendrites?

Answer 4

At one end of the neuron they receive signals from neurons and sensory receptors

Question 5

What are dendrites connected to - what is the function?

Answer 5

Dendrites are connected to the cell body, the control centre of the neuron

Question 6

Where does the impulse go from the cell body?

Answer 6

The impulse is carried along the axon, where it terminates at the axon terminal.

Question 7

What is the myelin sheath? Function?

Answer 7

An insulating layer that forms around the axon. Allows the nerve impulse to transmit more rapidly along the axon. If the myelin sheath is damaged , impulses slow down.

Question 8

Length of a neuron?

Answer 8

The length of a neuron can vary from a few millimeters up to one metre

Question 9

Function of sensory neurons?

Answer 9

Carry nerve impulses from sensory receptors to the spinal cord and brain.

Question 10

Where are sensory neurons found?

Answer 10

Eyes, ears, tongue, skin. Sensory neurons convert information from these sensory receptors into neural impulses. When the neural impulse reaches the brain they are translated into sensations e.g heat, pain.

Question 11

Why do some sensory neurons terminate at the spinal cord?

Answer 11

This allows reflex actions to occur quickly without the delay of sending impulses to the brain.

Question 12

Where can relay neurons be found?

Answer 12

They lie somewhere between the sensory input and the motor input. Wholly within the brain and spinal cord

Question 13

Function of relay neurons?

Answer 13

Allows sensory and motor neurons to communicate with each other

Question 14

What are motor neurons?

Answer 14

Neurons which conduct signals from the CNS to effector organs such as muscles.

Question 15

Motor neuron cell bodies may be in the ___ but they have long ______ which form part of the ____.

Answer 15

CNS , axons, PNS

Question 16

How do motor neurons create movement in the body?

Answer 16

Motor neurons form synapses with muscles and control their contractions. When stimulated, the motor neuron releases neurotransmitters that bind to receptors on the muscle and triggers a response which leads to muscle movement. When the axon of a motor neuron fires, the muscle with which it has formed a synapse with contracts.

Question 17

What does the strength of a muscle depend on?

Answer 17

Depends on the rate of firing of the axons on the motor neurons that control it. Muscles relaxation is caused by inhibition of the motor neuron.

Question 18

KT = Synaptic transmission

Answer 18

Refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron (presynaptic neuron) to another (postsynaptic neuron).

Question 19

What is action potential?

Answer 19

Information that has arrived at the axon travels down its length in the form of an electrical signal which is known as an action potential.

Question 20

What must an action potential cross in order to be transferred to another neuron or tissue?

Answer 20

It must cross a gap between the presynaptic and postsynaptic neuron which is called the Synapse.

Question 21

What does the synapse include?

Answer 21

The end of the presynaptic neuron, the membrane of the postsynaptic neuron and the gap in between.

Question 22

What is the gap between the pre- and postsynaptic cell membranes known as?

Answer 22

The synaptic gap

Question 23

What is at the end of the axon of the nerve cell?

Answer 23

Sacs known as synaptic vesicles

Question 24

What do vesicles contain? What is their role in synaptic transmission?

Answer 24

Chemical messengers that assist in the transfer of the impulse (neurotransmitters). As the action potential reaches the synaptic vesicles, it causes them to release their contents through a process called exocytosis.

Question 25

Where does the neurotransmitter go once it has been released from the vesicles?

Answer 25

Diffuses across the gap where it binds to specialised receptors on the surface of the cell that recognise it and are activated by that particular neurotransmitter. Once they have been activated , the receptor molecules produce either excitatory or inhibitory effects on the postsynaptic neuron.

Question 26

Explain ‘re-uptake’

Answer 26

The neurotransmitter is taken up again by the presynaptic neuron where it is stored and made available for later release.

Question 27

What does the speed of reuptake determine?

Answer 27

How quickly the presynaptic neuron takes back the neurotransmitter from the synaptic cleft determines how prolonged its effects will be. The quicker re-uptake is, the shorter the effects on the postsynaptic neuron.

Question 28

Neurotransmitters can be turned ___ after they have stimulated the postsynaptic neuron.

Answer 28

‘off’ This takes place through the action of enzymes produced by the body, which makes the neurotransmitters ineffective.

Question 29

How can neurotransmitters be classified?

Answer 29

As either excitatory or inhibitory

Question 30

What are excitatory neurotransmitters?

Answer 30

The nervous system’s ‘on’ switches. These increase the likelihood that an excitatory signal is sent to the postsynaptic cell, which is then more likely to fire.

Question 31

Examples of excitatory neurotransmitters?

Answer 31

Noradrenaline, acetylcholine

Question 32

What are inhibitory neurotransmitters?

Answer 32

The nervous system’s ‘off switches’ in that they decrease the likelihood of that neuron firing .

Question 33

What are inhibitory neurotransmitters responsible for?

Answer 33

Calming the mind and body, inducing sleep, and filtering out unnecessary excitatory signals.

Question 34

What does an excitatory neurotransmitter binding with a postsynaptic receptor cause?

Answer 34

Causes an electrical change in the membrane of that cell, resulting in an excitatory post-synaptic potential (EPSP) meaning that the postsynaptic cell is more likely to fire.

Question 35

What does an inhibitory neurotransmitter binding with a postsynaptic receptor cause?

Answer 35

Results in an inhibitory postsynaptic potential (IPSP), making it less likely that the cell will fire.

Question 36

How is the likelihood of the cell firing determined?

Answer 36

By adding up the excitatory and the inhibitory synaptic input. The net result of summation determines whether or not the cell fires.

Question 37

What two ways can EPSP be increased?

Answer 37

Spatial summation - a large number of EPSPs are generated at many different synapses on the same postsynaptic neuron at the same time .

Temporal summation - a large number of of EPSPs are generated at the same synapses by a series of high frequency action potentials on the presynaptic neuron.

Question 38

What is the rate at which a particular cell fires is determined by?

Answer 38

By what goes on in the synapses.
If excitatory synapses are more active, the cell fires at a high rate. If inhibitory synapses are more active, the cell fires at a much lower rate, if at all.