Synapses
What is a synapse?
A junction where the axon of neuron #1 (pre-synaptic neuron) makes contact and communicates with the cell body of neuron #2 (post-synaptic neuron)
What is acetylcholine?
Acetylcholine is a neurotransmitter
The main molecule that binds to the acetylcholine receptors in MG
AChR antibodies
What is repetitive use?
"It’s like repeating something and then repeating it again and then you repeat it again and again and again!!!!!" - Sinjon (2025), running for Academic Rep.
What is the main mechanism of synaptic transmission?
Chemical synapse
What does it do when activated in motor neurons?
causes muscle movement
The most common cause of MG.
Large thymus gland in adulthood.
What is fatiguability?
A tendency to feel tired or lose strength, or a susceptibility to fatigue
How do ions flow from the presynaptic neuron to the postsynaptic neuron in electrical synaptic transmission?
Gap junction
What is the speed of effect of muscarinic receptors?
The protein complex that destroys the synaptic folds.
The membrane attack complex (MAC).
Why does rest help in myasthenia gravis?
Rest allows your body to replenish it’s ACh stores in the NMJ
What is required for the ion channels to open in the postsynaptic neuron in chemical synapse?
Neurotransmitters bind to specific receptors on the postsynaptic neuron
What is the length of effect of muscarinic vs nicotinic receptors?
Muscarinic: long-lasting
Nicotinic: short-lived
Which of the following is reduced in the muscle membrane of a neuromuscular junction of someone who has MG?
a) acetylcholine receptors
b) acetylcholine
c) voltage gated sodium channels
a) acetylcholine receptors AND
c) voltage gated sodium channels
Why do people with MG feel stronger in the morning?
The acetylcholine reserves are replenished in the NMJ allowing them to release adequate ACh to cause muscle contraction.
What is required for exocytosis of the presynaptic neuron in chemical synapse?
Voltage gated Ca2+ channels open and Ca2+ enters axon terminal
What type of receptor is a muscarinic receptor and what type is a nicotinic receptor?
(effect on ion channels accepted for 300 points)
Muscarinic receptors are metabotropic (indirectly affect ion channels)
Nicotinic receptors are ionotropic (directly opens ion channels)
The specific potentials affected by MG.
1. Mini End Plate Potential (MEPP) AND
2. End Plate Potential (EPP)
Why does repetitive use cause muscle weakness?
With repeated muscle use:
The nerves keeps releasing acetylcholine (ACh)
→ But because there are fewer ACh receptors (due to MG), each subsequent signal has less of an excitatory effect!
→ Eventually, the depletion of the ACh stores in the NMJ result in muscle weakness