L3 - Synaptic Transmission

Question 1

Synaptic transmission

Answer 1

• refers to the process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (synapse) that separates them
• Definition: a nerve impulse passes across the synaptic cleft from one neuron (the presynaptic neuron) to another (the postsynaptic neuron)

Question 2

Pre-synaptic neuron

Answer 2

• neuron transferring the action potential

Question 3

Post-synaptic neuron

Answer 3

• neuron receiving the action potential

Question 4

electric transmission

Answer 4

• neuron is in resting state the inside of the cell is negatively charged (nothing happening) compared to the outside.
• Neurons must transmit information within the neuron and from one neuron to the next
• When activated by a stimulus, 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 5

What happens when reached end of neuron?

Answer 5

• reaches axon terminal & needs to be transferred to another neuron by crossing the gap between the pre-synaptic neuron & the post-synaptic neuron
• This area is called the synapse and includes the end of the pre-synaptic neuron, the membrane of the post-synaptic neuron and the gap in between
• The physical gap between the pre-synaptic neuron and postsynaptic neuron is called the synaptic cleft.
• On the axon terminal are a number of sacs known as synaptic vesicles which contain chemical messengers, known as neurotransmitters, which assist in the transfer of the action potential
• As the action potential reaches the vesicles, it causes them to release their contents through a process called exocytocis.

Question 6

What happens when neurotransmitter is released?

Answer 6

• it diffuses across the synaptic gap where it binds to specialised receptors on the surface of the dendrites of the post-synaptic neuron that recognise it and are activated by that particular neurotransmitter
• The whole process of synaptic transmission takes only a fraction of a second, with the effects terminated at most synapses by a process called re-uptake
• The neurotransmitter is taken up again by the pre- synaptic neuron where it is stored for later release
• The quicker the neurotransmitter is taken back the shorter the effects

Question 7

How can neurotransmitters be classified?

Answer 7

• excitatory or inhibitory in their action
• Inhibitory neurotransmitters are generally responsible for calming the mind and body, inducing sleep and filtering out unnecessary excitatory signals - includes adrenaline & dopamine
• Excitatory neurotransmitters are likely to increase your chances to activate or carry out a behaviour (e.g to be aggressive) - serotonin & GABA
• all neurotransmitters can be excitatory or inhibitory except for GABA (just inhibitory)

Question 8

Excitatory neurotransmitter

Answer 8

An excitatory neurotransmitter binding to a post-synaptic receptor causes an electrical charge in the membrane of the post-synaptic neuron resulting in an excitatory post-synaptic potential (EPSP), meaning that the post-synaptic cell is more likely to fire

Question 9

inhibitory neurotransmitter

Answer 9

An inhibitory neurotransmitter binding to a post-synaptic receptor results in an inhibitory post-synaptic potential (IPSP), making it less likely that the neuron will fire.

Question 10

Summation

Answer 10

• A nerve cell can receive both EPSP’s and IPSP’s at the same time
• The likelihood that the cell will fire is determined by adding up the excitatory and the inhibitory synaptic input - The net result, known as summation, determines whether or not the cell will fire

Question 11

How to increase strength of EPSP

Answer 11

In two ways:
1) spatial summation - a large number of EPSPs are generated at many different synapses on the same post-synaptic neuron at the same time
2) temporal summation - a large number of EPSPs are generated at the same synapse by a series of high-frequency action potentials by a pre-synaptic neuron
- The rate at which a particular cell fires is determined by what goes on in the synapse.
- 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 it fires at all.