Neuromuscular junction

Question 1

Characteristic of sarcolemma

Answer 1

2 alpha, 1 beta, 1 gamma and 1 delta proteins
Tubular channels closed until 2 acetylcholine molecules attach to its alpha subunits
Acetylcholinesterase

Question 2

Transmission of an action potential at the axon terminal

Answer 2

Vesicles formed in the golgi and carried by axonal transport to terminus
Vesicles filled with acetylcholine synthesized in the cytosol of the nerve
Action potential at the terminus opens voltage gated calcium channels
Vesicles fuse to the neuronal membrane and empty their contents into the synaptic cleft

Question 3

Transmission of an action potential at the post synaptic membrane

Answer 3

2 acetycholine molecules bind to each ligand gated channels
Na+,K+ passed through channels (Na+ more permeable)
Entry of Na+ caused end plate potential
End potential strong enough causes action potential on sarcolemma

Question 4

Transmission of an action potential through muscle

Answer 4

Action potential continues down T tubules and activates DHP channels
DHP channels activate ryanodine receptors
Ryanodine sensitive Ca2+ release channels on the SR
Ryanodine receptors also activated by Ca2+ released in cytosol
Ca2+ bind to troponin
High concentration of Ca2+ promotes ryanodine channels closure

Question 5

How is acetylcholine renew in the axon terminal?

Answer 5

After each action potential clathrin pits appear in the axon terminal
Pits are refilled as new synaptic vesicles
Resupply acetylcholine without waiting for new vesicles from the Golgi
Acetylcholine removed from synaptic cleft

Question 6

Steps of removal of acetylcholine from synaptic cleft

Answer 6

Degradation into choline and acetate by acetylcholinesterase
Reuptake of choline by axon end terminal
Diffusion of acetylcholine away from site

Question 7

What is Excitation contraction coupling?

Answer 7

Also knows as electro-mechanical coupling

It is the transformation of an electrical impulse into a mechanical action

Question 8

Mechanism of mechanical coupling

Answer 8

Action potential causes release of calcium ions

Calcium ions is reabsorbed by the calcium ion pump (SERCA)

Question 9

Drugs that affect transmission

Answer 9

Methacholine, carbachol and nicotine
Neostigmine, physostigmine and diisopropyl fluorophosphates
Curare

Question 10

Effects of methacholine,carbachol and nicotine

Answer 10

Same effect on muscle as acetylcholine
Not broken down by acetylcholinesterase—> bound to ligand gated
Cause muscle spasms

Question 11

Effects of Neostigmine, Physostigmine and diisopropyl fluorophosphates

Answer 11

Inactivate acetylcholinesterase—>bound to ligand gated

Cause muscle spasms

Question 12

Effects of Curare

Answer 12

Prevents passage of impulses from nerve ending to muscle

Question 13

Pathophysiology of myasthenia gravis

Answer 13

Autoimmune disease
Antibodies attack acetylcholine receptors
End plate potentials too weak to initiate opening of voltage gated sodiums channels
Neostigmine can be used to inactivate acetylcholinesterase

Question 14

Characteristics of a single axon terminal

Answer 14

Many mitochondria 
Synaptic vesicles with acetylcholine
Dense bars
Synaptic gutter
Synaptic cleft 
Sarcolemma of the skeletal muscle
End plate potential