L9: Skeletal Muscle Neurophysiology I

Question 1

What is a sarcomere?

Answer 1

A sarcomere is an individual contractile unit in skeletal muscle, with the Z band as its boundaries and the M line as its middle line.

Question 2

Which is the thin and which is the thick filament? What are their jobs?

Answer 2

• thick filament = myosin, which has heads that do the pulling.
• thin filament = actin, which is pulled on.

Question 3

What is an active zone?

Answer 3

Where vesicles of ACh are kept and released from -> keeps ACh where it is useful and needed, rather than just anywhere in terminal

Question 4

What is the sarcolemma?

Answer 4

= membrane around muscle fibre

Question 5

Describe what ACh does at the NMJ

Answer 5

ACh diffuses across narrow gap and down into junctional folds (inceases surface area do lots of room for receptors)
- then interacts with receptors on the sarcolemma, depolarising the fibre and propagating an AP

Question 6

Which enzyme makes ACh? Where?

Answer 6

choline acetyltransferase (ChAT) in the cytoplasm of axon terminal

Question 7

What enzyme breaks ACh down? Where/when?

Answer 7

Acetylcholinesterase (AChE) - breaks ACh down in synapse before reuptake –> important for signal termination

Question 8

How does choline get back into the cell?

Answer 8

Choline transporter: coupled with Na+ gradient into the cell so choline transported back in, then combined with acetyl CoA