skeletal muscle structure

Question 1

skeletal muscle structure

Answer 1

filaments together form a myofibril. filaments together form a muscle fiber. the fiber is surrounded by sarcolemma [has nuclei]. the area between the myofibrils is the sarcoplasm. muscle fibers together form the fascicle. HAS STRIATIONS

Question 2

myofibrils

Answer 2

where the main contractions occur. inside the myofibrils there is myosin [thick] and actin [thin]

Question 3

sarcomere

Answer 3

when an AP has occured, myosin filaments will use ATP to move along the actin filaments. actin moves closer to the centre- decreases the size of the I band, decreases length of sarcomere.

Question 4

1) M line
2) Z line
3) A band
4) I band

Answer 4

1) line of myosin
2) line of actin
3) length of the thick filament [myosin]
4) length between A bands [thin filament [actin]]

Question 5

dystrophin

Answer 5

part of protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the membrane

Question 6

Duchenne Dystrophy

Answer 6

mutation in the gene for the protein dystrophin

Question 7

endomysium

Answer 7

loose CT with some delicate and some strong fibers, surround each muscle fiber, connects to the basement membrane

Question 8

perimysium

Answer 8

mixed CT, some loose some dense, separating groups of nerve fibers into fascicles. main venue for nerves ad supporting blood vessels

Question 9

fascicle

Answer 9

bundle of nerve fibers held together by perimysia

Question 10

epimysium

Answer 10

relatively loose CT between fascia and muscle body

Question 11

fascia

Answer 11

dense layer of CT covering the body

Question 12

different skeletal muscle shapes

Answer 12

the fibrous nature of skeletal muscle allows a wide range of muscle architectures

Question 13

skeletal muscle contraction

Answer 13

1) AP generated is propagated along the sarcolemma and down the T tubules
2) AP triggers Ca++ release from terminal cisternae of SR
3) Ca++ bind to troponin, which changes shape, removing the blocking action of tropomysin, actin active sites exposed
4) contraction: myosin cross bridges alternately attach to actin and detach, pulling the actin filaments towards the center of the sarcomere; release of energy of ATP hydrolysis powers the cycling process
5) removal of Ca++ by active transport into the SR after the AP ends
6) tropomyosin blockage restored blocking actin active site; contraction ends and muscle fiber relaxes

Question 14

motor unit

Answer 14

a motor neuron plus the muscle fibers it innervates

Question 15

Golgi Tendon Organ

Answer 15

• a negative feedback mechanism
• function is to protect muscle and connective tissue from injury
• allows brain to monitor the load a muscle is bearing, to ensure the tendons associated with the muscle are not damaged.
• when a muscle is contracted the Golgi Tendon Organ is activated, if the GTO senses too much load being exerted by the muscle, it triggers a reflexive release of chemicals into the muscle causing it to relax

Question 16

what types of fibers are darker?

Answer 16

type 1 fibers are darker as they have more mitochondria.

2A are the lightest

Question 17

motor unit recruitment

Answer 17

progression activation of additional motor units to accomplish an increase in contractile strength in a muscle. the higher the recruitment the stronger the muscle contraction will be. the small [type 1 fiber] motor units are recruited first.if more force is needed, larger type 2 motor units are recruited next, with type IIX usually last.

Question 18

satellite cells

Answer 18

• muscle stem cells and are helped by Fibro/adipogenic progenitors [FAPs]
• when the muscle is damaged, satellite cells and FAPs become activated and expand rapidly
• FAPs secrete trophic factors, which stimulate satellite cells to regenerate the muscle fibres