Lecture 6 - Neuromuscular Junction

Question 1

What structures are found in the synaptic end plate?

Answer 1

• many mitochondria
• synaptic versicles
• dense bars
• synaptic gutter
• synaptic cleft
• sarcolemma
• presynaptic membrane

Question 2

What are dense bars and what role do they play in the motor end plate?

Answer 2

Structures anchored to the presynaptic membrane that associate with synaptic vesicles.

It is unknown what their function is.

Question 3

What are synaptic gutters?

Answer 3

Groove/furrow in the sarcolemma where the axon terminal makes contact.

They contain subneural clefts which are throughs that increase surface area.

Question 4

What is the synaptic cleft?

Answer 4

A 20-30nm gap between the presynaptic membrane and sarcolemma.

Question 5

What is special about the sarcolemma at the motor end plate?

Answer 5

It contains acetylcholine-gated ion channels and acetylcholinesterase.

Question 6

What is the structure of the acetylcholine gated ion channel?

Answer 6

5 subunits; 2 alpha, 1 beta, 1 gamma, and 1 delta

There is an Ach binding site on each alpha subunit. Two Ach are required to bind to open the channel

Question 8

What are synaptic vesicles?

Answer 8

Vesicles containing a neurotransmitter (in this case Ach) which is release via exocytosis.

Question 9

Where are the vesicles formed and what should be noted about them?

Answer 9

The Golgi apparatus which is found in the cell body.

They are brought to the axon terminus by axonal transport.

They do not contain acetylcholine at this time.

Question 10

Where is acetylcholine synthesized?

Answer 10

In the cytoplasm of the axon terminus.

Question 11

Binding of ______________ acetylcholine molecules to acetylcholine receptors causes ______________ to cross the sarcolemma creating an ______________ which initiates an ______________.

Answer 11

Two; sodium ions; end plate potential; action potential

Question 12

The action potential along the sarcolemma travels down ______________, where voltage gated ______________ are activated which then activates ______________ on the sarcoplasmic reticulum. This causes calcium to be released at the boundary of the ______________.

Answer 12

the T tubules; dihydropyridine (DHP) channels; ryanodine-sensitive channels; A band and I band

Question 13

What 4 things occur at the synapse at the end of an action potential to prepare it for the next action potential?

Answer 13

• formation of new synaptic vesicles from axon terminal
• degradation of acetylcholine into choline and acetate
• reuptake of choline
• delusional of acetylcholine

Question 14

What is meant by excitation-contraction coupling?

Answer 14

Conversion of an action potential into mechanical energy but the sliding filament mechanism.

Question 15

What affect do metacholine, carbachol, and nicotine have on the neuromuscular junction?

Answer 15

Same affect as acetylcholine other than they are not broken down and therefore cause spasm.

Question 16

What effect does neostigmine, physostigmine, and diisopropyl flurophosphates have on the neuromuscular junction?

Answer 16

They deactivate acetylcholinesterase causing build up of acetylcholine resulting in spasm.

Question 17

What affect does curare have on the neuromuscular junction?

Answer 17

Prevents passage of impulse from nerve ending resulting in muscle relaxation.

Question 18

What is myasthenia gravis? Which drug can be used to treat this and how does it work?

Answer 18

An autoimmune disease which attacks acetylcholine receptors resulting in end plate potentials that are too weak to open voltage-gated channels.
Can be treated with neostigmine which inactivates acetylcholinesterase.