What happens when the propagation of the action potential reaches the presynaptic terminal?
- Action potential opens voltage-gated Ca2+ channels at presynaptic terminal
- Ca2+ influx → vesicle exocytosis to release neurotransmitters
What happens after neurotransmitters are released into the synaptic cleft?
- NT binds to receptors on post-synaptic membrane
- Receptors modulate post-synaptic activity
What happens after the neurotransmitter is detected at the post synaptic terminal?
Neurotransmitter Reuptake - Neurotransmitter dissociates from receptor and can be:
→ Metabolised by enzymes in synaptic cleft
→ Recycled by transporter proteins
What is autocrine signalling?
Cell secretes an autocrine agent (hormone) or chemical messenger that binds to autocrine receptors on the same cell
What is paracrine signalling?
Cell produces a signal to cause changes to nearby cells
What is a axodendritic synapse?
connection to neuronal dendrite
What is a axosomatic synapse?
connection to neuronal soma
What is a axoaxonic synapse?
connection to neuronal axon
What is a neuromuscular junction?
specialised structure incorporating the axon terminal & muscle membrane allowing unidirectional chemical communication between peripheral nerve & muscle
What kind of cell signalling happens at the NMJ?
Paracrine signalling
What is the purpose of the NMJ?
Place of paracrine signalling from the nervous system, determines whether the muscle contracts or relaxes!
What neurotransmitter is used at the NMJ?
Acetyl choline
What receptors are at the post synaptic terminal of the NMJ?
nicotinic ACh receptors (nAChR) on the sarcolemma → changes the end-plate potential
What happens after Ach binds to the receptors at the post synaptic terminal of the NMJ?
- Miniature end-plate potential causes release of ACh in vesicles into the post-synaptic cell
- This causes ion channels to open and allows sodium and other cations to flow across the membrane into the muscle cell
- The flow of sodium ions across the membrane into and potassium ions out of the muscle cell generates an action potential which travels to the myofibril and results in muscle contraction
What is sarcoma?
- skeletal muscle membrane
- contains nACh receptors
- T-tubules are continuous with the sarcolemma + closely connected to the sarcoplasmic reticulum; action potential travels through these tubules
What is the sarcoplasmic reticulum?
- surrounds myofibrils (contractile units of muscle)
- involved in Ca2+ storage + release following depolarisation of sarcolemma
Name 3 disorders of the NMJ?
- Botulism
- Myasthenia Gravis (MG)
- Lambert-Eaton myastenic syndrome (LEMS)
What is botulism?
- Botulinum toxin (BTx): causes irreversible disruption of stimulation-induced ACh release from the
presynaptic nerve terminal
What is myasthenia gravis?
- Autoimmune disorder where antibodies are directed against ACh receptor
- Causes fatiguing weakness (i.e. becomes more pronounced with repetitive use)
What is lambert-eaton myastenic syndrome?
- Autoimmune disorder where antibodies are directed against voltage-gated Na+ channels
