6.1.3 The Process of Synaptic Transmission

Synaptic transmission

Structure of a synapse

Process of synaptic transmission

1. An action potential arrives at the pre-synaptic terminal, causing synaptic vesicles to travel towards the pre-synaptic membrane
2. Synaptic vesicles and the pre-synaptic membrane fuse, causing neurotransmitters to be released into the synaptic cleft

1. Neurotransmitters diffuse across the synaptic cleft, towards the post-synaptic terminal and bind to receptors on the post-synaptic membrane
2. When the neurotransmitters bind to the receptors, it will either produce an excitatory post-synaptic potential, or an inhibitory post-synaptic potential
3. Neurotransmitters are released back into the synaptic cleft and removed through the process of re-uptake

Neurotransmitters can only travel in one direction because:

• Synaptic vesicles containing neurotransmitters are only found on the pre-synaptic membrane
• Receptor cells that neurotransmitters bind to are only found on the post-synaptic membrane
• Neurotransmitters diffusing across the synaptic cleft mean they can only travel from a high to low concentration, so from the pre-synaptic neuron to the post-synaptic neuron

Neurotransmitters

Chemical messengers found in neurons

Excitatory and inhibitory neurotransmitters:

Excitatory neurotransmitters:

• Cause positively charged particles to enter the post-synaptic neuron
• Make nerve impulses more likely to occur
• Create excitatory post-synaptic potentials (EPSP's)

Inhibitory neurotransmitters:

• Cause negatively charged particles to enter the post-synaptic neuron
• Make a nerve impulse less likely to occur
• Create inhibitory post-synaptic potentials (IPSP's) Summation: For a nerve impulse to occur the net effect needs to be excitatory, so there needs to be more excitatory neurotransmitters released than inhibitory neurotransmitters, if the net effect is inhibitory a nerve impulse won't occur

Types of neurotransmitters:

Acetylcholine: Used to control our muscles. (Excitatory)

Adrenaline: Triggers the body's fight or flight response (Excitatory)

GABA: Used in the brain. (Inhibitory)

Serotonin: Controls our response to mood. (Inhibitory)

Dopamine: Controls our response to reward. (Inhibitory)