Skeletal Muscles

Question 1

Skeletal muscle is the ?

Answer 1

Largest body organ

Question 2

Human body comprises of over 600 muscles responsible for ?

Answer 2

• Movement
• Posture
• Active transport
• Heat generation

Question 3

Note on The muscle fibre

Answer 3

*Also known as the skeletal muscle cell

• It is multi nucleated (with more than 100 nuclei located at its periphery )

*Postmitotic (cannot undergo cell division )

*Comprises 75% water , 20% of protein and 5% other substances.

Question 4

What is Sarcolemma ?

Answer 4

Sarcolemma is the plasma membrane of the muscle cell.

Question 5

Note on The Sarcoplasm ?
(5)

Answer 5

• The Sarcoplasm is the cytoplasm of the skeletal muscle cell / muscle fibre
• Contains all the cell organelles and the intracellular fluid .
• Contain vital energy store (such as muscle glycogen and triglycerides)
• contain myglobin responsible for storing oxygen
• The largest component of the sarcoplasm is the myoglobin

Question 6

Note on The myofibrils ?

Answer 6

• They are rod like structures that traverse the length of the muscle fibre..
• They are contractile apparatus of the muscle fibre…
• Contains contractile.proteins “Actin and myosin”…
• Actin and myosin takes 60% of the 85% of the total muscle proteins
• Actin filaments contains a myosin binding site where muscle contraction is initiated..

*In relaxed muscle, tropomyosin protein covers the binding site and prevents binding with actin.

*Tropomyosin is held in place by the regulatory protein troponin.

*Myofibril is divided into sarcomere.

Question 7

Continuation of
The myofibrils ( diagram interpretation)

Answer 7

*A band predominantly Myosin

• I band predominantly Actin

*There is H Zone at the center of the A band

• The H Zone is bisected by the M line
• M line comprises M protein and myomesin , which attach one thick filament to another
• Each sarcomere is separate by a Z line comprising nebuline

Question 8

Note on Sarcoplasmic reticulum?

Answer 8

• A membranous network of channels that surrounds the myofibril..
• Runs parallel to the myofibril and serves as a reservoir of calcium.
• The SR also contains a protein pump that is known as the Sarcoendoplamic Reticulum Ca2+ ATPase (SERCA).

Question 9

Neuromuscular junction?

Answer 9

The point of communication between the neuron and the muscle fibre.

Question 10

Note on Neuromuscular junction?

Answer 10

• The skeletal muscle are adequately innervated by the alpha motor neurons.
• A single alpha neurones and all the muscle fibres it supplies is referred to as a motor unit.

Question 11

Muscle contraction
(Stage 1- 6 )

Stage 1

Answer 11

• Nerve impulse arrives at the axon terminal and triggers the release of Ach.

Question 12

Stage 2

Answer 12

Ach diffuses through the synaptic cleft and binds to its receptor at the motor end plate and triggers muscle action potential..

Question 13

Stage 3

Answer 13

Acetycholinesterase in the synaptic cleft destroys Ach,

prevents the rise of another Action potential unless More Ach are released from motor neurons

Question 14

Stage 4

Answer 14

Muscle action potential travelling along the transverse tube opens calcium ions release channels in the sarcoplasmic reticulum (SR) membrane

Which allows calcium ions to flood into the sarcoplasm.

Question 15

Stage 5

Answer 15

Calcium ions binds to troponin on the thin filament, exposing the binding sites for myosin.

Question 16

Stage 6

Answer 16

Contraction: power strokes uses ATP, myosin heads bind to actin , swivels and release

Thin filaments are pulled towards the center of sarcomere .

Question 17

Stage 7-9
Relaxation

Stage 7

Answer 17

Calcium release channels in SR close and calcium active transport pumps use ATP to restore low level of Calcium in sarcoplasm.

Question 18

Stage 8

Answer 18

Troponin- tropomyosin complex slides back into position where it blocks the myosin binding sites on actin.

Question 19

Stage 9

Answer 19

Muscle relaxes