Flashcards in Synaptic Transmission And Neuromuscular Junction (session 5) Deck (26):
How is a signal passed from nerve to muscle?
Neuromuscular junction (synapse between nerve and skeletal muscle fibre)
Which voltage-gated channels are present in the nerve terminal?
What happens at the nerve terminal? (4)
2. Opens voltage-gated Ca2+ channels
3. Ca2+ entry
4. Release of neurotransmitter
Why can the internal concentration of Ca2+ be increased significantly at the nerve terminal?
Because the concentration of Ca2+ inside is so low
Complete the sentence:
Increasing the frequency of AP _________ the amount of nerve terminal Ca2+ entry
The alpha subunit of voltage-gated Ca2+ channels is very similar to which other voltage-gated channel?
What is a pore forming subunit necessary for?
A functional channel
What do other associated subunits do in channels?
Fine-tune the properties and enable correct regulation of channel activity
True or false: voltage-gated Ca2+ channels activate quicker than voltage-gated Na+ channels
What does acetylcholine esterase do?
Breaks down ACh
What type of acetylcholine receptors are on the postsynaptic membrane?
Describe the process of transmitter release (5)
1. Ca2+ entry through Ca2+ channels
2. Ca2+ binds to synaptotagmin
3. Vesicle brought close to membrane
4. Snare complex make fusion pore
5. Transmitter released through this pore
What is reverse potential?
No net flow of charge when the channel is open-halfway between K+ and Na+ equilibrium potential
What happens at the synaptic cleft when two ACh molecules bind to the receptor?
Leads to a conformational change and the pore opens
What is excitation contraction coupling?
Muscle AP initiated adjacent to the end-plate and propagates along the muscle fibre.
The AP initiates contraction of the skeletal muscle fibre.
Give an example of a competitive nicotinic ACh receptor blocker
Give an example of a depolarising nicotinic ACh receptor blocker
How can the block by d-tubocurarine be overcome?
By increasing the concentration of ACh
What is a potential problem of using succinylcholine during operations?
Sometimes the anaesthetic doesn't work but the neuromuscular blocker does work so the patient is left paralysed but can still feel pain
Name an autoimmune disease targeting nACh receptors
What happens in myasthenia gravis?
Patients suffer profound weakness
Weakness increases with exercise
What causes myasthenia gravis?
Antibodies directed against nACh receptor on postsynaptic membrane of skeletal muscle. Antibodies lead to loss of functional nAChR by complement mediated lysis and receptor degradation. Endplate potentials are reduced in amplitude, leading to muscle weakness and fatigue
Complete the sentence:
ACh binds to _________ ACh receptors on the muscle end-plate , causing a depolarisation called the ___-_____ _________
Why does the muscle fibre contract when an AP is initiated there?
Due to excitation-contraction coupling
What is the difference between nicotinic and muscarinic receptors?
Nicotinic receptors are ligand-gated
Muscarinic receptors are in the parasympathetic nervous system so there is no intrinsic ion channel involved