Synaptic Transmission

• Information is passed down the axon of the neuron as an electrical impulse known as action potential.
• Once the action potential reaches the end of the axon it needs to be transferred to another neuron or tissue.
• The electrical impulse must cross over a gap between the pre-synaptic neuron and post-synaptic neuron, which is known as the synaptic gap.
• At the end of the neuron, in the axon terminal, are the synaptic vesicles which contains chemical messengers, known as neurotransmitters.
• When an electrical impulse (action potential) reaches the synaptic vesicles, it releases neurotransmitter.
• Neurotransmitters carry signals across the synaptic gap. They bind to receptor sites on the post-synaptic cell that then become activated.
• Once receptors have been activated, they either produce excitatory or inhibitory effects on the post-synaptic cell.
• Some neurotransmitters are excitatory and some are inhibitory.
• Excitatory neurotransmitters (e.g. noradrenaline) make the post-synaptic cell more likely to fire.
• Inhibitory neurotransmitters (e.g. GABA) make cells less likely to fire.
• A synapse is a small gap between two neurons, where nerve impulses are relayed by a neurotransmitter from the axon of a presynaptic (sending) neuron to the dendrite of a postsynaptic (receiving) neuron.
• A synapse is referred to as the synaptic cleft or synaptic gap.
• During synaptic transmission, the action potential (an electrical impulse) triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters (chemicals).
• Neurotransmitters diffuse across the synaptic cleft (the gap) and bind to specialised receptor sites on the post-synaptic neuron.
• Neurons essentially communicate with each other through synapses.
• Synapses can be either chemical or electrical and are essential to the functioning of neural activity.
• Synapses play a vital role in a variety of cognitive functions, including learning and memory formation.
• When an action potential arrives at the pre-synaptic terminal, it activates voltage-gated calcium channels (Ca² +) in the neuron’s membrane. Ca² + are highly concentrated on the outside of the neuron and will rush into the neuron when activated.
• Ca² + allows the synaptic vesicles to fuse with the pre-synaptic terminal’s membrane, enabling it to release neurotransmitters into the synaptic cleft.
• When receptors are activated, there is an opening or closing of ion channels, which are membrane proteins that provide a passageway through which charged ions can cross.
• Depolarising is making the inside of the cell more positive.
• Hyperpolarisation makes the inside of the cell more negative, less likely to fire.
• Dopamine and serotonin are common neurotransmitters found in the brain.
• Neurotransmitters are made in the pituitary gland in the brain.
• For a synapse to function effectively, it must be shut off once the signal is sent.
• Signal termination allows the post-synaptic neuron to return to its resting potential state, ready for new signals.
• When neurotransmitters get released into the synaptic cleft, not all of them are able to attach to the receptors of the next neuron.
• Re-uptake is when neurotransmitters get reabsorbed back into the pre-synaptic neuron from which they came from.
• Imbalances in the way serotonin is transmitted between neurons through too much reuptake has implications for contributing to mood disorders like depression.
• SSRIs are antidepressants that prevent the reuptake of serotonin back into the pre-synaptic neuron.
• Neurons communicate with other in groups called neural networks.
• Action potential can only travel in one direction (from pre-synaptic to post-synaptic).
• Neurotransmitters have their own specialised functions.
• Serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire.
• Adrenaline causes excitation of the post-synaptic neuron, increasing the positive charge, making it more likely to fire.
• Whether a post-synaptic neuron fires is decided by the process of summation.
• Summation is the addition of positive and negative post-synaptic potentials. A neuron can receive both positive and negative potentials simultaneously. These are summed and if the net effect on the post-synaptic neuron is inhibitory, the neuron will be less likely to fire, and if the net effect is excitatory, the neuron will be more likely to fire.
• Synaptic transmission.