Muscle

Question 1

Outline smooth muscle

Answer 1

• Medium sized with small fibres
• Single nucleus
• Multi unit: pilomotor
  Single unit: intestines
  Mixed unit: blood vessel
• Often found in involuntary movement such as the GI tract

Question 2

Outline skeletal muscle

Answer 2

• Used in voluntary movement to walk and move
• Large, multinucleate cells, each activated individually
• Controls strength of contraction

Question 3

How are skeletal muscle contractions regulated?

Answer 3

1) Different nerves innervating different fibres

2) Frequency of stimulation

Question 4

What is seen under a light microscope when looking at skeletal muscle?

Answer 4

Striations caused by actin and myosin.
Light areas: actin
Dark areas: myosin
Grey areas: smooth ER which is filled with calcium

Question 5

What is isometric contraction?

Answer 5

Muscle is at the same length but tension is produced to support weight

Question 6

What is isotonic contraction?

Answer 6

Muscle tension is the same but the length changes so we can move our limbs

Question 7

Explain skeletal muscle contraction and tropomysins role

Answer 7

1) Myosin binds to ATP and hydrolyses it to ADP and Pi
2) Mysosin binds to actin
3) Myosin changes shape and actin is pulled forwards
4) ADP is released, ATP binds and myosin separates from actin
Tropomysin complexes cover actin which prevents myosin from binding, it can only bind when calcium is released from the sacroplasmic reticulum

Question 8

Explain smooth muscle contraction

Answer 8

Protein blocks myosin rather than actin, Ca2+ binds to calmodulin, which binds to MLC, which changes the shape of myosin so it can bind to actin.

Question 9

Outline the sacroplasmic reticulum

Answer 9

It is full of calcium which is released when the muscle is depolarised, causing contraction. Each bundle of myofibrils is surrounded by SR. The plasma membrane on the outside of the muscle fibre is called the sarcolemma.
It goes into the muscle as transverse tubules.

Question 10

What is the triad structure?

Answer 10

How calcium gets into the cell:
TTubules sit between the sacroplasmic reticulum at terminal cisternase
Sarcolemma is depolarised by AP –> AP travels down TT deep into muscles –> bundles of SR have proteins sticking out of them which are Ca2+ release channels –> Ca2+ releases into actin and myosin fibres.

Question 11

Outline energetics

Answer 11

ATP is hydrolysied to ADP and Pi –> ADP is converted back into ATP creatine using CP –> increase of ADP triggers glycogen breakdown to create more ATP which is used for:

1) Contraction
2) Creatine phosphoyrlation