Skeletal Muscle

Structure of skeletal muscle

Striated

In what way are muscles excitable tissues

Membrane potential is linked to activation of that cell’s function (contraction)

What percentage of an adult’s body weight is skeletal muscle (& smooth muscle)

Skeletal muscle = 40%
Heart & Smooth muscle = 10%

Under what 3 headings are muscles classified

Location & function of skeletal muscle

What controls shivering vs non shivering thermogenesis

Shivering - muscle

Non shivering - brown fat

Name a muscular dystropy

Duchenne Muscular dystrophy

Name a Neuromuscular disorder of skeletal muscle

Myasthenia gravis

name a muscular atrophy

Sarcopenia / Cachexia

what is defective in Type II Diabetes

Insulin stimulated glucose uptake into skeletal muscle is defective

Label

1. Periosteum

2. Tendon

3. Fascia

4. Epimysium

5. Perimysium

6. Fasciculus

7. Endomysium

8. Muscle Fibre

9. Sarcolemma

10. Sarcoplasm

11. Filaments

12. Myofibrils

13. Nuclei

Sarcolemma

Plasma membranes

Unique feature of skeletal muscle

Multinucleated

Name of light & dark bands

Light = I bands

Dark = A bands

What are myofibrils

Thick (myosin) & thin (actin) myofilaments that run the length of the muscle fibre

3 types of muscle proteins

Contractile

Regulatory

Structural

Name 2 contractile muscle proteins

Myosin & actin

Name 2 regulatory muscle proteins

Troponin
Tropomyosin

Name 5 regulatory muscle proteins

Titin

Nebulin

Alpha-actin

Myom

Which muscle protein is the largest

Titin

Which muscle protein has the largest gene

Dystrophin

Identify

Thick filament with myosin molecule

Identify

Portion of a thin filament

1 and 3 are the same

1. Z line

2. One sarcomere

3. Z line

4. I band

5. A band

6. H zone

7. M line

8. Thick & thin filaments overlap

One myosin filament is surrounded by how many actin filaments in 3D arrangement

6

What do sarcomeres do when a muscle contracts

Sarcomeres shorten

What do A and I bands do when a muscle contracts

A bands do not alter in size (they reflect the myosin filament length within a sarcomere).
I bands decrease in size (they reflect actin filament that has no overlapping myosin filaments on adjacent ends of two sarcomeres)

Do thin filaments slide towards to / away from the H zone

Towards

What are thick myofilaments composed of

Composed of the protein myosin

(Each protein has two globular heads with actin-binding sites and ATP-binding sites)

What are thin myofilaments composed of

Composed of the protein actin with proteins called tropomyosin and troponin

Role of tropomyosin and troponin

prevent myosin binding at rest

What are formed between myosin & actin during sliding

Cross bridges

Role of myosin head when muscle is stimulated

The myosin head serves as a myosin ATPase enzyme, splitting ATP into ADP + Pi.
This allows the head to bind to actin when the muscle is stimulated due to electrical & chemical events

Cross bridge cycle

How do myosin heads on myosin filaments move

like oars knifing through water, but do not move synchronously

What percentage of crossbridges make contact with actin to form the protein complex actomyosin

50%

How is contraction regulated

Tropomyosin physically blocks cross bridges

How does troponin complex regulate contraction

Troponin I inhibits binding of myosin.
Troponin T binds to tropomyosin.
Troponin C binds to calcium.

When is Ca2+ released inside the muscle fibre

When muscle cells are stimulated, Ca2+ is released inside the muscle fibre

What happens when some Ca2+ attaches to troponin C

Conformational change in troponin and tropomyosin occurs

Myosin is allowed access to form cross bridges

What 2 things are required for muscle contraction

ATP & Calcium