The Neuromuscular Junction Flashcards
Where is the neuromuscular junction?
- Between a motor neurone and a muscle cell.
- At the neurovascular hilum / nerve entry point of a muscle.
What triggers fusion of vesicles with the presynaptic membrane?
Ca2+ influx into presynaptic terminal.
What is the name of the Ca2+ sensor?
Synaptotagmin
What is another term for ligand-gated ion channels?
Ionotropic channels
Give examples of excitatory ionotropic receptors.
Glutamate Receptors:
- AMPA Receptors
- NMDA Receptors
- Kainate Receptors
ACh Nicotinic Receptors
What do excitatory receptors cause at the postsynaptic membrane?
Na+ influx
Excitatory postsynaptic potential (EPSP)
What are the specialised features of the postsynaptic membrane?
Junctional folds:
- Allow for high density of nACh receptors - the receptors of the NMJ.
- Allow for high density of voltage gated of Na+ channels.
What are quanta?
Packaged vesicles containing neurotransmitters released into a synapse.
What is the major amino acid excitatory neurotransmitter?
Glutamate
What is the major amino acid inhibitory neurotransmitter?
GABA
Are nicotinic ACh receptors excitatory, inhibitory or both?
All nicotinic AChRs are excitatory.
Are muscarinic ACh receptors excitatory, inhibitory or both?
Muscarinic AChRs can be either excitatory or inhibitory.
List 4 monoamine neurotransmitters
1 - Adrenaline.
2 - Noradrenaline.
3 - Dopamine.
4 - Serotonin.
What is another term for G-protein coupled receptor?
Metabotropic
What are the two receptor signalling mechanisms?
Ionotropic and metabotropic.
What do inhibitory receptors cause at the postsynaptic membrane?
Cl- influx
Inhibitory post synaptic potential (IPSP)
Give 2 examples of inhibitory ionotropic receptors.
GABA(a) Receptors
Glycine Receptors
What is the end plate potential?
The end plate potential initiates an action potential in the muscle. These are 2 different electrical events.
EPP decays as it moves away from the end-plate.
What is an end plate?
The postsynaptic terminals of the NMJ. So called for large, saucer-like appearance.
How does the voltage of an EPP differ from that of most other synaptic potentials?
What causes this?
What is the advantage of this?
- An EPP is much larger than most other synaptic potentials.
- This is because there are many NAChRs at the NMJ, triggering the opening of many Na+ channels.
- This ensures that the threshold for AP generation in the muscle is easily passed.
What is the function of T tubules?
They allow for transmission of AP deep into the muscle fibre (to individual myofibrils)
What are the levels of organisation of a muscle?
Sarcomere < Myofilament < Myofibril < Myocyte (Fibre) < Fascicle < Muscle
When very frequent action potentials are summated, what happens to muscle contraction?
Contraction is sustained.
What is ACh hydrolysed by in the synaptic cleft?
Acetylcholinesterase (AChE)
Name a symptom of myesthenia gravis.
Muscle weakness during sustained activity.
What is the cause of myesthenia gravis?
Autoimmune disease of nAChR that causes a reduced number of nAChRs at the NMJ.
What is a treatment of myesthenia gravis?
AChE inhibitors, e.g. neostigmine.
This will prolong the signal.
