Neuromuscular transmission and Excitation-Contraction coupling

Question 1

neuromuscular junction

Answer 1

the junction midpoint between the nerve fiber terminal and the muscle fiber is neuromuscular junction

Question 2

motor end plate

Answer 2

the nerve fibers make BRANCHING NERVE TERMINALS that invaginate into the muscle fiber but stays outside of the plasma membrane, the entire structure is called motor end plate

Question 3

synaptic trough/ gutter

Answer 3

the invaginated membrane is called as synaptic trough or gutter

Question 4

synaptic space/cleft

Answer 4

the space between the terminal and muscle fiber is known as synaptic space/cleft

Question 5

wideness of synaptic cleft

Answer 5

20-30 meters wide

Question 6

what subneural clefts and its function

Answer 6

the area beneath the gutter has many small folds of the muscle membrane which are subneural clefts and it increase the area of for the synaptic transmitter to act

Question 7

acetylcholine is synthesized in?

Answer 7

cytoplasm of terminal

Question 8

synaptic vesicle?

Answer 8

the acetylcholine is synthezied in the cytosol of terminal and absorbed by the synaptic vesicle, about 300,000 vesicles are present on single terminal end plate.

Question 9

acetylcholinesterase

Answer 9

is in enzyme that hydrolases acetylcholine into acetate and choline

Question 10

when the nerve impulse reaches the nerumuscular junction how many acetylcholine vesicles are released

Answer 10

125

Question 11

dense bars

Answer 11

the inside of neural membrane have linear dense bars, and each have protein particle on its sides that penetrate through neural membrane

Question 12

what are the protein particles that are present on the sides of dense bars

Answer 12

voltage gated calcium channels

Question 13

the function of these voltage gated calcium channels

Answer 13

when an action potential spreads over the nerve terminal, it opens these channels which allow the calcium ions to move into the terminal from the synaptic space

Question 14

what does the calcium ions inside the nerve terminal do ?

Answer 14

the calcium ions activate the CA+2 calmodulin dependent protein kinase, that phosphorylates the protein synapisn that anchors the acetylcholine vesicles to the cytoskeleton of presynaptic terminal

Question 15

active zone

Answer 15

the anchoring of acetylcholine vesicles to cytoskeleton actually frees up the acethylcholine vesicles from the cytoskeleton and allows them to move to the ACTIVE ZONE of pre synaptic neural membrane ADJACENT TO DENSE BARS where the vesicles dock themselves and release the acetylcholine into the synaptic space by EXOCYTOSIS

Question 16

in association with acetylcholine opening ions channel on postsynaptic membrane what is present on muscle fiber membrane

Answer 16

it contains acetylcholine receptors and voltage gated sodium channels

Question 17

mouth of suneural clefts has ?

Answer 17

acetylcholine gated ion channels which are right below the dense bars

Question 18

describe fetal acetylcholine receptor?

Answer 18

it is composed of five protein subunits which are two alpha and one each of beta delta and gamma

Question 19

whats the diff b/w fetal and adult acetylcholine receptor

Answer 19

the subunit gamma is substituted by EPSILON in adults

Question 20

the protein channel in acetylcholine receptors are opened how?

Answer 20

when two acetylcholine comes and attaches themselevs to each alpha subunit the channels goes under conformational change and opens the before constricted channel

Question 21

size the of acetylcholine gated ion channel and what ions does it allow (the quantity ) and what ions it doesn’t allow

Answer 21

the size is 0.65 nanometer and it allows sodium, potassium and calcium to pass through in the amount of 15k to 30k sodium ions in 1 millisecond and it doesn’t allow chloride ions to pass because chloride is negatively charged and so is the inner walls of the gated ion channel

Question 22

why far more NA ions move towards the outside than any other ions through the acetylcholine gated channels

Answer 22

for 2 reasons, firstly there are only two positively charged ions present in higher concentrations, one is sodium ion on the outside and potassium ion to the inside
secondly, the negative potential inside the muscle membrane is -80 to-90 which pulls the +NA ions to the inside and restricts the efflux of +K ions to the outside

Question 23

end plate potential

Answer 23

the action of movement of sodium ions through the acetylcholine gated ion channels to the inside crates a positive potential inside the muscle membrane which is called end plate polarization

Question 24

curare

Answer 24

is a poison that blocks the gating action of acetylcholine on the acetylcholine channels by competing with acetylcholine receptors

Question 25

botulinum

Answer 25

a bacteria that decreases the amount of acetylcholine released from the nerve terminal

Question 26

fatigue of neuromuscular junction

Answer 26

stimulations of nerve fiber at rates greater than 100 times per second for several minutes that diminishes the number of acetylcholine vesicles so that causes the impulse to not to reach to the muscle fiber

Question 27

drugs that stimulate the muscle fiber through acetylcholine like action

Answer 27

methacholine, carbachol, nicotine

Question 28

drugs that stimulate the muscle fiber by inactivating acetylcholinesterase

Answer 28

neostigmine, physostigmine, and diisopropyl flurophopsphate

Question 29

drugs that block transmission at neuromuscular junction

Answer 29

curariform drugs such as D-tubocurarine

Question 30

myasthenia gravis

Answer 30

an autoimmune disease in which antibodies kill their on acetylcholine receptors, at post synaptic neuromuscular junction the voltage gated Na channels doesn’t open so depolarization doesn’t take place
it causes of muscles weakness and inability of neuromuscular junction to send signals from nerve fiber to muscle fiber
people die due to respiratory failure

Question 31

what drug is given for myasthenia gravis

Answer 31

neostigmine

Question 32

difference of muscle action potential in skeletal muscles and neurons

Answer 32

1. the action potential is -80 to -90 which is 10-20 millivolts more negative in skeletal muscles
2. the duration of action potential is 1-5 milliseconds five times as long as neurons
3. the velocity of conduction is 1-5m/sec which is 1/13th as long as the nerve terminals conducting it towards the skeletal muscle

Question 33

how action potential is transmitted to skeletal muscles?

Answer 33

through t-tubules that extend from one end to the other end of the fiber

Question 34

when the action potential is reached to the T tubule the boltage change is sense by?

Answer 34

dihydropyridine receptors linked to calcium release channels

Question 35

the ca binding protein inside the reticulum is ?

Answer 35

calsequestrin