L10. Properties and Process of Muscle Contraction

Question 1

Skeletal muscle?

Answer 1

• Core and limb muscles
• Movement of our skeleton, posture, thermoregulation
• Somatic nervous system (voluntary)

Question 2

Layers of muscle?

Answer 2

Muscle –> muscle fascicle –> muscle cell/fibre –> myofibrils –> myofilaments

Question 3

Myofibre?

Answer 3

Muscle cell

Question 4

Sarcolemma?

Answer 4

(Barrier) surrounds each myofibre, cell membrane, keeps it all together

Question 5

Sarcomere?

Answer 5

(Functional unit) comprised of myofilaments thin and thick contractile unit - stripes, striated muscle

Thin - actin, troponin-tropomyosin complex
Thick - myosin, myosin head

Question 6

Transverse tubules?

Answer 6

(t-tubules, regulatory unit) are extensions of the sarcolemma that dive deep into the muscle - sarcoplasmic reticulum

Question 7

Development of skeletal muscle?

Answer 7

Muscle precursor cells (myoblasts) fuse together to form large multi-nucleated cells
Each muscle fibre has hundreds to thousands of nuclei
Fibres are approximately 20-40um in diameter, but may be many cm long

Question 8

Neuromuscular junction?

Answer 8

Communication between nerve and skeletal muscle

Question 8

Excitation-contraction coupling?

Answer 8

A) Excitation = motorneuron excites the muscle fibre –> electrical-chemical-electrical transmission –> release of Ca2+ from the internal store

B) Contraction = Ca2+ binds to actin myofilament –> cross bridge cycling - sliding of the myofilaments –> shortens sarcomeres - muscle produces force/tension

C) Relaxation = re-uptake of Ca2+ in the internal store –> cross bridge de-attachment –> return to the resting state

Question 9

Excitation of the sarcoplasmic reticulum? A) - B)

Answer 9

*after excitation at the NMJ
1. Action potential propagates along the sarcolemma of the myofibre
2. The sarcolemma dives into the myofibre –> t-tubule
3. The membrane of the t-tubule is within close proximity to the membrane of the sarcoplasmic reticulum (SR), the internal Ca2+ store
4. When the action potential arrives at the t-tubule, it initiates Ca2+ release from the SR
5. Ca2+ in the sarcoplasm diffuses to the myofilaments

• This initiates cross bridge cycling –> the sarcomere shortens –> muscle contraction
• Z-lines move closer together, actin-myosin slide into each other sliding filaments - sarcomere shortens

Question 10

Botulinum toxin?

Answer 10

Reduces release of ACh at nerve terminals neuromuscular transmission is blocked - no muscle contraction

Question 11

Ca2+ re-uptake in sarcoplasmic reticulum?

Answer 11

1. Ca2+ in the sarcoplasm diffuses away from the myofilaments and the Ca2+ is taken back up into the sarcoplasmic reticulum (SR)
   This consumes ATP (energy)
2. This terminates cross bridge cycling - sarcomere lengthens - muscle relaxation

Question 12

Neuronal skeletal muscle interaction?

Answer 12

Muscles fibres should contract near simultaneously along their entire length

Question 13

Types of contractions?

Answer 13

Isotonic contraction = length changes to develop tension
Shortens = concentric contraction
Lengthens = eccentric contraction

Isometric contraction = remains the same length while developing tension

Question 14

During cross bridge cycling the sarcomere shortens BECAUSE during cross bridge cycling the myosin and actin filaments slide into each other

A. Both statements are correct and causally related
B. Both statements are correct and NOT causally related
C. Only the first statement is correct and the second statement is incorrect
D. Only the second statement is correct and the first statement is incorrect
E. Both statements are incorrect

Answer 14

A