Neuromuscular Junction Lecture Flashcards
What is the neuromuscular junction?
It is the site of regulation of skeletal muscle by the nervous system
How many neuromuscular junctions are generally on a skeletal muscle cell?
Just one
Give me the sequence of events from an action potential in a motor neuron to an action potential in the sarcomolemma of a muscle cell.
- AP travels along the motor neuron axon
- AP invades the presynaptic terminal
- Ca++ influx occurs in the presynaptic terminal
- Vesicles carrying ACh are released into the synaptic cleft
- ACh diffuses across the cleft
- ACh binds to its receptors in the postsynaptic membrane
- Na+ and K+ channels open and there is an influx of Na+ and an efflux of K+ across the motor endplate
- An endplate potential is generated
- Voltage gated Na+ channels in the sarcolemma open and an action potential is initiated in the sarcolemma.
T/F the end plate potential is an all or none amplitude?
False- they are graded, don’t propagate, and can undergo summation
When do end plate potentials occur?
After an action potential in a motor neuron
What are mini endplate potentials? (MEPPs)
They are spontaneous end plate potentials that are really small- 1-2 mV
If acetylcholinesterase wasn’t present in the motor endplate membrane and the basal lamina of the muscle cell, what would happen?
Well, the muscle would undergo continuous contraction. AChesterase serves to break down the ACh in the synaptic cleft so that stimulation occurs only at the proper time
Pharmacology- what does curare do to the NMJ?
It binds to ACh receptors so that ACh can’t bind. No action potentials can occur
Pharmacology- what does Botulinum toxin do to the NMJ?
This blocks ACh release
Pharmacology- what do organophosphates do to the NMJ?
These block the action of AChEsterase so that it won’t be hydrolyzed
How is skeletal muscle organized, from smallest component to largest?
Protein–> filaments–>sarcomere–>myofibril–>muscle fiber (cell)–>fascicle–> whole muscle
Each strand tropomyosin is composed of what?
a dimer of tropomyosin
Tropomyosin sits where?
In the grooves of the actin filaments
Troponin has how many subunits? What is each responsible for?
3
TnC- calcium binding
TnI- inhibitory role
TnT- tropomyosin binding - anchors the whole molecule
Tell me about the myosin filament/molecules.
Well, the myosin filament is thick and has many cross bridges on it. The head of the cross bridge has two parts due to two heavy chains. There is a head and neck and tail region of the filament. There are two heavy chains and two pairs of light chains. The actin and ATP binding sites are on the heavy chains, but the light chains modulate the activity thereafter.
