NMJ AND EPP

Question 1

What is a NMJ?

Answer 1

This is between a motor neurone and a muscle cell

Question 2

What is the name of the area on the pre synaptic membrane where vesicles with NT line up

Answer 2

Active zone

Question 3

Explain the concentration gradient of calcium ions inside vs outside the cell

Answer 3

Concentration of calcium ions greater outside the cell compared to inside. When voltage gated calcium ion channels are stimulated and opened Ca2+ travels into the presynaptic terminal down its concentration gradient

Question 4

Explain how NTs are released in NMJ

Answer 4

• stimulus results in depolarisation
• voltage-gated Na+ channels open, Na+ in
• voltage-gated Ca2+ channels open
• Ca2+ ions influx into presynaptic terminal
• Vesicles fuse with Pre synaptic membrane - exocytosis
• EACh released and diffuse across synaptic cleft
• Bind to receptors on post synaptic membrane on a muscle cell

Question 5

Which NT is released in NMJ

Answer 5

Acetylcholine

Question 6

What type of receptor is found on the motor end plate (post SM)

Answer 6

Nicotinic acetylcholine receptor which is an ionotropic receptor - ligand-gated or inotropic

Question 7

Give 3 features of the nicotinic Acetyl choline receptor

Answer 7

• Transmembrane spanning
• Has 5 subunits
• Needs 2 acetyl choline molecules to bind before it undergoes a conformational change and released the NT

Question 8

The NMJ is a specialised synapse, give a specialised feature of the presynaptic membrane

Answer 8

It has MULTIPLE QUANTA RELEASE. This means that there are lots of vesicles that dump NT (300) at the same time and this means that there is lots of NT for the post synaptic membrane.

Question 9

Give 3 specialised features of the post synaptic membrane

Answer 9

• Junctional folds
• High density of Nicotinic acetylcholine receptors
• High density of voltage gated Na+ channels

Question 10

What are junctional folds?

Answer 10

Deep invaginations or grooves of the sarcolemma that provide a large surface area for additional ACh receptors.

Question 11

What is generated when Na+ channels open up at the motor end plate?

Answer 11

End Plate Potential (EPP)

Question 12

What is the EPP

Answer 12

The binding of ACh to the nicotinic acetylcholine receptors causes Na+ channels to open and Na+ ions travel into the motor end plate. This generates an EPP which occurs before an action potential and is needed in order for an action potential can be generated. EPP initiates an action potential.

Question 13

What is the equilibrium potential for Na+ and K+

Answer 13

• Na+ = +60mV
• K+ = -90mV

Question 14

What is the RMP of a muscle cell?

Answer 14

• 90mV

Question 15

Why don’t K+ ions want to move out of the cell?

Answer 15

The RMP and the equilibrium potential of K+ are the same and so K+ wants to stay in that environment. This results in the influx of Na+ being greater than the efflux of K+

Question 16

What drives the influx of Na+ into the cell?

Answer 16

The cell is negatively charged and Na+ is positively charged. The opposite charges attract and create an electrical force. The concentration of Na+ is greater outside the cell compared to inside and this creates a chemical force which drives Na+ into the cell

Question 17

When does the EPP decay and why?

Answer 17

When it moves further away from the motor end plate because nicotinic acetylcholine receptors are not found away from the synapse