Anatomy and Physiology of the NMJ Flashcards
What is the NMJ?
Location in which signals transmitted from MOTOR NEURON to a MUSCLE FIBER
Components of the NMJ: motor neuron
Made up of cell body, dentrites and nucleus
What allows for faster impulse conduction
MYELIN-Covered Axon
Each axonal process has a ____________ That innervates
prejunctional motor nerve ending;
One muscle fiber
What is the synaptic cleft
Connect prejunctional motor nerve ending to Postjunctional muscle fiber
What neurotransmitters are release from the motor nerve ending to attach to receptors on the postjunctional muscle fiber?
Acetycholine
Mainly Ach receptors on POST JUNCTIONAL membrane
Nicotinic
When an action potential travels along the axon what happens?
Depolarizes, Ach released and diffuse across synaptic cleft -> Once Ach bind to acetylcholine receptors in causes an action potential in the MUSCLE FIBER
–> MUSCLE MOVEMENT.
Acetylcholine involved in transmission in both
Parasympathetic and Sympathetic Systems
Ach receptors classified as (2)
Nicotinic
Muscarinic
At NMJ, ACh binds to
NICOTINIC
Nicotinic receptors has 5 subunits
2 alpha
1 beta
1 Gamma
1 Delta
What is the only binding site/place where Ach can bind?
ALPHA
What must ACH occupy to cause a CONFORMATIONAL CHANGE? which lead to
BOTH alpha subunits.; Action potential
ACh is broken down into_______and ______by_____enzymes via ______(process)
Acetate and Choline
Acetylcholinesterase; HYDROLYSIS
Where are the enzyme acetylcholinesterase located?
ADJACENT TO acetylcholine receptors
The choline undergoes________ and together with ________, Ach is synthesized an stored
REUPTAKE
Acetyl-CoA
Receptors usually suppressed in burns and sepsis
EXTRAJUNCTIONAL receptors
What is important to know about EXTRAJUNCTIONAL RECEPTORS?
when activated, they tend to stay open for a longer period of time which CAN lead to HYPERKALEMIA
Up-regulation of Neuromuscular Receptors
The number of nAChRs INCREASE which develops on the postjunctional membrane
Cause by a DECREASED stimulation of the neuromuscular junction over time
Upregulation of receptors is associated with HYPERSENSITIVITY to _________ such as ________
and DESCREASED SENSITIVITY to _____ such as
Agonist; Succinylcholine
Non-Depolarizing NMBAs
Upregulation can lead to
lethal potassium release from cells after SCh administration
What determines the number ACh release into the cleft?
The extent of calcium influx into the presynaptic neuron determines the number of ACh quanta released into the cleft and is a function of the duration of nerve depolarization.
What percentage of the ACh is released into the cleft? What happens to the rest of the ACh? 2 fates
Only approximately 50% of the ACh released into the cleft reaches the postsynaptic receptors;
the rest is either hydrolyzed by acetylcholinesterases (AChEs) contained within the cleft or diffuses out of the cleft.
