Neuromuscular Junction (exam 1)

Question 1

What are anchored to the presynaptic membrane and associated with the synaptic vesicles with they are tethered to by short filaments

Answer 1

Dense Bars

Question 2

In order for acetylcholine-gated ion channels to open, how many Ach molecules are necessary to attach to its alpha subunits

Answer 2

2

Question 3

The vesicles for acetylcholine are transported to the axon terminal from where

Answer 3

The golgi apparatus

Question 4

What drugs are used to inactive acetylcholinesterase

Answer 4

Neostigmine, physostigmine, and diisoproyl fluorophophates

Question 5

What drugs are not broken down by acetylcholinesterase

Answer 5

Methacholine, carbachol, and nicotine

Question 6

What drugs have the same effect on muscle fibers as acetylcholine but are not broken down by acetylcholinesterase

Answer 6

Methacholine, carbachol, and nicotine

Question 7

What drugs cause muscle spasms

Answer 7

methacholine, carbachol, nicotine, Neostigmine, physostigmine, and diisopropyl fluorophosphates

Question 8

What effect does Curare have on muscle contractions

Answer 8

It prevents passage of impulses from nerve endings into muscles

Question 9

How many mitochondria do a single axon terminal have

Answer 9

Many

Question 10

How are acetylcholine vesicles release

Answer 10

calcium influx triggers exocytosis

Question 11

What are dense bars

Answer 11

Anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered to by short filaments

Question 12

what is the synaptic gutter (trough)

Answer 12

groove or furrow into the surface of the sarcolemma in which the axon terminal makes contact with the sarcolemma

Question 13

What are sub neural clefts

Answer 13

They are clefts or troughs that are in the bottom of the synaptic trough

Question 14

about how wide are synaptic clefts

Answer 14

about 20-30nm wide

Question 15

How many subunits does an acetylcholine-gated ion channel have and what are they

Answer 15

5 subunits,

2 alpha, 1 beta, 1 gamma, and 1 delta

Question 16

When does the tubular channel of acetylcholine-gated ion channels open

Answer 16

when tow acetylcholine molecules attach to the alpha subunits

Question 17

What is the function of acetylcholinesterase

Answer 17

It breaks down Acetylcholine to acetate and choline

Question 18

what is a local potential

Answer 18

potential that is established by the opening of a ligand-gated channel if hits threshold it can depolarize surrounding membranes

Question 19

where are the 40nm vesicles for Ach formed

Answer 19

in the Golgi apparatus

Question 20

how are golgi vesicles transported

Answer 20

by axonal transport

Question 21

where is Ach synthesized

Answer 21

in the cytosol of the nerve axon terminal

Question 22

when the AP arrives at the terminus of the axon what happens next

Answer 22

Voltage gated calcium channels open and calcium ions enter the axon terminus

Question 23

What is the purpose of calcium ions in the nerve terminal

Answer 23

It draws synaptic vesicles closer to the neurolemma for exocytosis

Question 24

about how many vesicle fuse to the neuronal membrane and empty their contents into the synaptic cleft

Answer 24

About 125 vesicles

Question 25

How many Ach molecules bind to the ligand-gated channel on the sarcolemma. and where do they bind

Answer 25

2. one to each alpha subunit

Question 26

After the ligand-gated channels are open what happens

Answer 26

both potassium and sodium pass through the channel but sodium is more permeable

Question 27

What does the large amount of sodium influx caused by the opening of the ligand gated channels cause

Answer 27

It leads to a local potential or end-plate potential (50-75mV). This leads to AP on the sarcolemma

Question 28

what activates the Ryanodine-sensitive calcium ion channels

Answer 28

conformational change caused by the activation of the DHP (dihydropyridine channels) on the T-tubules

Question 29

What affect does increase calcium have on Ryanodine receptors

Answer 29

It initially activates them thus leading to positive feedback and more release of calcium but at a certain point the concentration makes them close.

Question 30

what do calcium ions bind to in muscles

Answer 30

Troponin

Question 31

Where do T-tubules run in skeletal muscles

Answer 31

on both sides of the SR at the boundaries of the A-I bands

Question 32

How is acetylcholine removed form the synaptic cleft

Answer 32

Acetylcholinesterase

Question 33

What is acetylcholine degraded to by acetylcholinesterase

Answer 33

choline and acetate

Question 34

After degradation the reuptake of choline occurs where. and why

Answer 34

Choline is reabsorbed at the axone terminal end. it is recycled because it is expensive

Question 35

What is meant by excitation-contraction (electro-mechanical) coupling?

Answer 35

the coupling of AP with a mechanical motion such as contraction

Question 36

After an AP what is formed at the axon terminal and why

Answer 36

Clathrin coated pits. to be refilled as new synaptic vesicles

Question 37

Calcium concentration increases by how much after SR releases calcium

Answer 37

0.1micromol/liter to 10micromol/liter. about 100x

Question 38

what is Myasthenia Gravis

Answer 38

Autoimmune disease
antibodies attack acetylcholine receptors on the sarcolemma
end plate potential are too weak to initiate opening of the voltage-gated sodium channels (can’t initiate AP)

Question 39

Give an example of a drug that can be used to treat myasthenia Gravis

Answer 39

drugs that decrease the activity (inactivate) Acetylcholinesterase
Example in class Neostigmine
-other examples would be physostigmine and diisopropyl fluorophosphates