Lecture 4

Question 0

Briefly describe the structure of skeletal muscle

Answer 0

It is striated muscle composed if overlapping myosin filaments

Question 1

What are the contractile elements of muscle?

Answer 1

The myofibrils

Question 2

What is the name of the band which is mainly composed of thick filaments?

Answer 2

The Amisotropic band

Question 3

What is the name of the band which is mainly composed of thin filaments?

Answer 3

The isotropic band

Question 4

Describe the structure of the thick filaments

Answer 4

They are made up of large numbers of myosin ii molecules

They have globular hexagonal heads which have an alkali light chain and regulatory light chain attached.

Question 5

What us the function of the alkali light chain on thick filaments?

Answer 5

They stabilise the head structure of the thick filament

Question 6

What is the function of the regulatory light chain?

Answer 6

It regulates the myosin activity

Question 7

Briefly describe the structure of the thin filaments

Answer 7

It is made up of two intertwining chains of actin molecules, with troponin complexes attaches at intervals.

Question 8

What is the troponin complex made up of?

Answer 8

TnT
TnC
Tnl

Question 9

Outline the cross bridge cycle

Answer 9

1. ATP binds to the myosin head causing dissociation of the actin myosin complex
2. ATP is hydrolysed, causing myosin heads to return to resting position
3. Cross-bridge forms and myosin binds to the new position on actin
4. P is released, the power stroke occurs due to change in conformation of myosin head. Filaments slide past one another
5. ADP is released

Question 10

How does Ca2+ regulate the cross bridge cycle?

Answer 10

When it is present the tropomyosin shifts so it no longer sterically hinders the myosin binding site

Question 11

What is the transverse tubule system?

Answer 11

A deep invagination of the sarcolemma which creates a pathway through which the action potential can propagate rapidly to the centre of the cell.

Question 12

What is the sarcoplasmic reticulum?

Answer 12

Modified endoplasmic reticulum which is a calcium store

Question 13

Outline the process of excitation coupling

Answer 13

1. Membrane depolarisation opens the l-type calcium channel
2. Mechanical coupling between the l-type calcium channel and the calcium release channel causes the calcium channel to open
3. Calcium exits the sarcoplasmic reticulum via the calcium release channel and activates troponin C, leading to muscle contraction
4. Calcium entering the cell via l-type calcium channels also can activate the calcium release channels

Question 14

What factors determine the force of contraction?

Answer 14

Frequency of action potentials
Number of motor units activated
Active length of muscle