Lesson 3 - Synaptic Transmission

Question 1

How does synaptic transmission happen?

Answer 1

• When a neuron is in resting state, the inside of the cell is negative
• When it is activated by a stimulus, the inside becomes positive for a split second, and this creates an action potential and this allows an impulse to travel down the axon.
• The impulse reaches the axon terminal and it needs to be transferred from the pre synaptic neuron to the post synaptic neuron across the synapse
• Synaptic vesicles in the axon terminals contain chemical messengers known as neurotransmitters and those assist the transfer of the action potential
• When the action potential reaches the vesicles, they release their contents through exocytosis
• They diffuse across the synaptic cleft and they bind to receptors on the dendrites on the post synaptic neuron, which activate the neuron
• The effect of the neurotransmitter stops when it re-uptake occurs

Question 2

Excitatory and Inhibitory neurotransmitters

Answer 2

All neurotransmitters can be both, except for GABA which is inhibitory

• When an excitatory neurotransmitter binds to a post synaptic receptor, this causes an excitatory post synaptic potential (EPSP) and the cell is more likely to fire
• When an inhibitory neurotransmitter binds to a post synaptic receptor it creates an inhibitory post synaptic potential (IPSP) and it is less likely to fire
• A neuron can receive both types of neurotransmitters at the same time. The net result of the totals of both types (summation) dictates whether it will fire or not

Question 3

How can the strength of an EPSP be increased?

Answer 3

Spatial summation - large numbers of EPSP’s generated from many different synapses on the same post synaptic neuron

Temporal summation - large numbers of EPSP’s generated from the same synapse by a series of fast action potentials