Neurons and Synaptic Transmission

Question 1

Define the term ‘Synaptic Transmission’

Answer 1

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

Question 2

Define motor neurons

Answer 2

Form synapses with muscles, controlling their contractions.

Question 3

Define relay neurons

Answer 3

The most common types of neurons found in the CNS that allow sensory and motor neurons to communicate with one another.

Question 4

Define sensory neurons

Answer 4

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

Question 5

Define the synapse

Answer 5

The conjunction of the end of the axon of one neuron and the dendrite or cell body of another.

Question 6

Define neurotransmitters

Answer 6

Chemical substances vital for the working of the nervous system by transmitting nerve impulses across a synapse.

Question 7

Describe motor neurons in a bit more detail

Answer 7

Located in the CNS, but project their axons outside it.
They directly or indirectly control muscles.
Form synapses with muscles controlling their contractions.
When stimulated, motor neurons release neurotransmitters that bind onto the receptor sites of muscles and trigger a response that leads to muscle movement.

Question 8

What does the strength of a muscle contraction depend on?

Answer 8

Depends on the rate of firing of the axons of motor neurons.

Question 9

What is muscle relaxation caused by?

Answer 9

By inhibition of motor neuron.

Question 10

Step by step, describe the process of synaptic transmission.

Answer 10

Once an action potential arrives at terminal button at the end of an axon it has to be transferred to another neuron/tissue.
Has to cross the synapse I.E the area between the pre and post- synaptic neuron.
Synaptic vesicles = located in the end of an axon that hold neurotransmitters i.e chemical transmitters that will help transfer the nerve impulse.
Via exocytosis, vesicles release their contents and released neurotransmitter diffuses across synaptic gap and binds to receptor molecules on the surface of the postsynaptic neuron. Once activated, either excitatory or inhibitory effects are produced.

Question 11

What happens to access neurotransmitters?

Answer 11

Either turned off by body by production of enzymes, or taken back up by re-uptake process.

Question 12

How long does process of synaptic transmission last?

Answer 12

Fraction of a second

Question 13

What determines the duration of the effects of the neurotransmitter? And give example.

Answer 13

How quickly its taken back up, so the faster its taken back up the shorter the effects. Some antidepressant drugs prolong action of neurotransmitter by inhibiting re-uptake process leaving neurotransmitters in synapse for longer.

Question 14

What 2 types of neurotransmitters are there?

Answer 14

Excitatory and inhibitory

Question 15

Explain excitatory neurotransmitters

Answer 15

Are neurons like acetylcholine and noradrenaline, which are the on switches of the nervous system and increase the likelihood of an excitatory signal being sent to postysynaptic neuron, which then makes it more likely to fire.

Question 16

Explain inhibitory neurotransmitters

Answer 16

Are neurons like Serotonin or GABA that are the nervous systems off switches that decrease the likelihood of the neuron firing. responsible for calming mind, inducing sleep and filtering out unnecessary signals.

Question 17

Describe the process of and Excitatory or inhibitory neurotransmitters

Answer 17

Excitatory binds to postsynaptic casuing an electrical change, resulting in an excitatory post synaptic potential. So cell = more likely to fire.

Inhibitory binds to postsynaptic creating electrical change of inhibitory post synaptic action potential making cell less likely to fire.

Question 18

Can a cell receive both EPSPs and IPSPs? And what happens in that case?

Answer 18

Yes. In that case the likelihood of cell firing will be determined from the total excitatory and inhibitory synaptic input. The net result determines if/ if not the cell fires. If excitatory synapses more active the cell fires and at a faster rate, but if inhibitory then it doesnt.

Question 19

Explain the 2 ways the strength of an EPSP can be increased.

Answer 19

Spatial summation - large no. of EPSPs generated at many different synapses on same PSN at same time.
Temporal summation - large no. of EPSPs generated at same synapse by series of high frequency action potentials on presynaptic neuron.