Lecture 05 Neuromuscular Junction

Question 0

What is a motor end plate

Answer 0

The junction between a motor neuron and a skeletal muscle fiber

Question 1

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

Answer 1

Dense bars

Question 2

What are three things axon terminals have?

Answer 2

Many mitochondria, synaptic vesicles with acetylcholine and dense bars

Question 3

How many acetylcholine molecules are in one synaptic vesicle?

Answer 3

300,000

Question 4

What is a synaptic gutter or trough

Answer 4

A groove in the surface of a sarcolemma in which the axon terminal makes close contact with the sarcolemma

Question 5

What are subneural clefts?

Answer 5

Smaller clefts than synaptic gutters that are in the bottom of the synaptic gutter

Question 6

How wide are synaptic clefts?

Answer 6

20-30nm wide.

Question 7

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

Answer 7

2

Question 8

What is the first thing that happens after Ach binds to the ligand gated channels on the sarcolemma?

Answer 8

An end-plate potential is created on the muscle fiber

Question 9

What are the characteristics of the acetylcholine-gated ion channels of the skeletal muscle?

Answer 9

It has a mw of 275,000. Has 2 alpha proteins and a beta, gamma and delta protein. They are a tubular channel that remains closed until two Ach attach.

Question 10

What is the function of acetylcholinesterase

Answer 10

Break down Ach to acytal groups and choline

Question 11

What type of potential is end plate potential?

Answer 11

local. involves ligand-gated channels

Question 12

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

Answer 12

Golgi

Question 13

How are the vesicles for Ach carried to the axon terminus where they are filled?

Answer 13

By axonal transport

Question 14

Where is Ach synthesized?

Answer 14

Cytosol of the nerve axon terminal

Question 15

Once activated, the Ach ligand-gated channel allows for the passage of what ions?

Answer 15

Sodium and potassium

Question 16

What else activates ryanodine receptors?

Answer 16

Activated by the calcium released into the cytosol, thus allowing more calcium ion to be released

Question 17

What promotes ryanodine channels to close?

Answer 17

High cytosolic calcium ion concentrations

Question 18

What two things are reused after each action potential?

Answer 18

Vesicles - clathrin coated pits appear and separate from the plasmalemma. Refilled as new synaptic vesicles
Choline-Acetylchoinesterase degrades Ach into choline and acetate. Choline is reuptaked by axon end terminal

Question 19

What are two ways acetylcholine is removed from the synamptic cleft?

Answer 19

Diffusion away from the site or acetylcholinesterase breaking down Ach

Question 20

What is excitation-contraction coupling?

Answer 20

Action potential down the T-tubules is the excitation

The contraction that occurs once the Ca is released.

Question 21

What can be used to inactivate acetylchoninesterase?

Answer 21

Neostigmine, physostigmine and diisopropyl flurophosphates

Question 22

What has the same effect on muscle fibers as acetylcholine but are not broken down by acetylcholinesterase? What symptom do they cause?

Answer 22

Methacholine, carbachol, and nicotine. They cause spasm

Question 23

What does curare do to neuromuscular junctions?

Answer 23

Prevents passage of impulses from nerve ending into muscle

Question 24

What is myasthenia gravis? What does it do?

Answer 24

Autoimmune disease. Causes antibodies to attach acetylcholine receptors. This causes end plate potentials to be too weak to initiate action potential.

Question 25

What is used as treatment for myasthenia gravis and why?

Answer 25

Neostigmine, because it can be used to inactivate acetylcholinesterase and therefore allows Ach to stay around longer in the synaptic cleft to open up more receptor channels and create an action potential. Helpful for early disease development.