Chemical synapses can occur between neurones and what 3 types of cell?
- Neurones
- Muscle cells
- Gland cells
What happens at a chemical synapse?
- AP depolarises presynaptic ending
- Influx of Ca2+ into presynaptic ending
- Vesicles migrate towards plasma membrane
- Release of transmitter into cleft (exocytosis)
- Transmitter diffuses in cleft
- Transmitter binds to receptors on post-synaptic cell
- —> changes in post-synaptic cell
- Inactivation of transmitter which can be by:
- Reuptake into presynaptic cell
- Enzymatic destruction
What are some AA derivative Transmitters?
- Acetylcholine
- Noradrenaline
- Dopamine
What is an excitatory synapse?
- Cell polarised so increased activity
What is an inhibitory synapse?
- Cell hyperpolarised so decreased activity
What is summation of action potentials?
- Postsynaptic potentials are very small
- Single ones have little effect on the MP of the post-synaptic cell
- Necessary for EPSPs to add together
- This can happen in several ways
- EPSPs and IPSPs can also summate, but they tend to cancel each other
- A post synaptic cell will ‘fire’ only if it receives sufficient excitation to drive the MP beyond threshold
- This occurs when it receives many excitatory inputs (and few inhibitory inputs) within a short period of time
What is the convergence of neuronal connections?
Each neuron receives many inputs from other cells
What is the divergence of neuronal connections?
Each neurone then synapses with many other cells
What is the neuromuscular junction?
The synapse between a motor nerve and a muscle fibre which is also referred to as a motor end plate
What is the difference between a nerve-muscle synapse and a nerve-nerve synapse?
Area of ‘contact’ is greater than in a nerve-nerve synapse
What is the neurotransmitter at a neuromuscular junction and what enzyme breaks this down?
Acetylcholine which is broken down by acetyl cholinesterase
What are the action of events at the neuromuscular junction?
- AP depolarises motor nerve ending
- Influx of Ca2+ into nerve ending
- Vesicles migrate towards plasma membrane
- Release of ACh into cleft (exocytosis)
- ACh diffuses in cleft
- ACh binds to receptors on post-synaptic cell
- Action potential in muscle cell –> contraction
- Transmitter (ACh) broken down by acetyl cholinesterase
- Choline and acetate taken up by neuron
How might drugs affect synaptic activity by either enhancement or suppression?
- Synthesis, storage of neurotransmitter
- Release of neurotransmitter
- Action of neurotransmitter on receptor
- Second messenger system
- Inactivation of neurotransmitter
What does botulinum toxin do?
Used to paralyse face muscles to remove wrinkles
- Relaxes muscles by paralysing them - not permanent
- It prevents the release of transmitter from motor nerves
