Lesson 3 Synaptic Transmission

Question 1

How long does synaptic transmission take

Answer 1

Only a fraction of a second

Question 2

What is synaptic transmission

Answer 2

Neurons transmit electrical impulses, known as action potentials, between the pre-synaptic neuron (the neuron transferring the action potential) and the post-synaptic neuron (the neuron receiving the action potential).

When the action potential reaches the pre-synaptic terminal it triggers the release of neurotransmitters (chemical messengers) from sacs on the presynaptic membrane known as vesicles in a process called exocytosis. The released neurotransmitter will diffuse across the synaptic cleft (physical gap between the pre-synaptic membrane and post-synaptic membrane) where it binds to specialised post-synaptic receptor sites.

Synaptic transmission takes only a fraction of a second, with the effects terminated by a process called re-uptake. The neurotransmitter is taken back by the vesicles on the pre-synaptic neuron where they are stored for later release. The quicker the neurotransmitter is taken back the shorter the effects.

Question 3

What are the different types of neurotransmitters

Answer 3

Excitatory or inhibitory (most can be both but GABA is purely inhibitory)

Question 4

Neurotransmitters

Answer 4

Neurotransmitters can be excitatory or inhibitory (most can be both but GABA is purely inhibitory). Excitatory neurotransmitters causes an electrical charge in the membrane of the post-synaptic neuron resulting in an excitatory postsynaptic potential (EPSP), meaning that the post-synaptic neuron is more likely to fire an impulse Inhibitory neurotransmitters cause an inhibitory postsynaptic potential (IPSP), making it less likely that the neuron will fire an impulse.

A neuron can receive both EPSPs and IPSPs at the same time. The likelihood that the neuron will fire an impulse is determined by adding up the excitatory and the inhibitory synaptic input. The net result of this calculation, known as summation, determines whether or not the neuron will fire an impulse. If the net effect is inhibitory the neuron will not fire, and if the net effect is excitatory, the neuron will fire

Question 5

Direction of Synaptic Transmission

Answer 5

Information can only travel in ONE direction at a synapse. The vesicles containing neurotransmitters are ONLY present on the pre-synaptic membrane. The receptors for the neurotransmitters are ONLY present on the post-synaptic membrane. It is the binding of the neurotransmitter to the receptor which enables the information to be transmitted to the next neuron. Diffusion of the neurotransmitters mean they can only go from high to low concentration, so can only travel from the pre-synaptic membrane to the postsynaptic membrane.

Question 6

Medication

Answer 6

Psychoactive drugs (medication that affects brain function to alter perception, mood or behaviour), such as SSRIs, work by affecting (increasing or inhibiting) the transmission of neurotransmitters across the synapse.

Some pain medications mimic the effects of inhibitory neurotransmitters. Stimulation of postsynaptic receptors by an inhibitory neurotransmitter results in inhibition of the postsynaptic membrane. When an inhibitory neurotransmitter binds to the post-synaptic receptors it makes the postsynaptic neuron less likely to fire. Due to summation, if inhibitory neurotransmitters are higher than excitatory neurotransmitters they can inhibit an action potential from occurring. Therefore, pain medications would decrease the overall activity and reducing brain activity may lead to less pain