U3 Lecture 19

Question 1

Structural organization of skeletal muscle

Answer 1

• Muscles covered by epimysium are made of groups called fasicles covered by perimysium which is made of groups called individual muscle fibers surrounded by endomysium

Question 2

What level of organization is each layer of skeletal muscle?

Answer 2

1. organ level : muscle
2. Tissue level : fasicles
3. Cellular level : muscle fibers
4. Chemical level : myofibrils

Question 3

What are muscle cells called?

Answer 3

Fibers

Question 4

Why are muscle fibers multinucleated?

Answer 4

The develop from the fusion of myoblasts

Question 5

Define hypertrophy

Answer 5

the growth of muscles due to an increase in muscle cell size

Question 6

Define hyperplasia

Answer 6

growth of muscle due to an increase in muscle cell number

Question 7

How do muscles develop and grow?

Answer 7

• after birth, growth of muscle fibers happens by hypertrophy (not hyperplasia) bc muscle fibers cannot undergo mitosis

Question 8

What type of cells are able to undergo mitosis and aid in muscle regeneration?

Answer 8

Satellite cells

Question 9

What are the 3 C’s of skeletal muscle physiology?

Answer 9

1. Conduction
2. Control
3. Contraction

Question 10

Define conduction

Answer 10

Conduction of electrical signals

• It results from EXCITATION of a muscle fiber
• occurs @ sarcolemma

Question 11

Define sarcolemma

Answer 11

the plasma membrane of skeletal muscle fibers

• forms transverse tubules (T-Tubules) that run through the muscle fiber

Question 12

Define control

Answer 12

Control of muscle contraction

• regulates activities of smooth ER in skeletal muscle fiber (= sarcoplasmic reticulum SR)

Question 13

What does the SR do in muscle fibers?

Answer 13

SR stores Ca2+

Surrounds myofibrils

E-C coupling releases Ca2+ from the SR to start contractions

The SR stops contractions later by recovering more Ca2+

Question 14

Define contraction

Answer 14

Contraction of muscle

• carried out by the cross bridge cycle
• results from the shortening of organelles called myofibrils in the cytoplasm of skeletal muscle fibers

Question 15

What is myofibril made of?

Answer 15

Sarcomeres composed of actin and myosin

Question 16

What causes striations on muscle fibers?

Answer 16

The alignment of sarcomeres

Question 17

Structure of sarcomeres

Answer 17

Z disc, I band, Zone of overlap, H zone, M line, thin filament (actin) and thick filament (myosin)

Question 18

What increases in a sarcomere during contraction?

Answer 18

Zone of overlap

Question 19

What stays the same in a sarcomere during contraction?

Answer 19

A band

Question 20

What are the contractile proteins in muscle?

Answer 20

Actin and myosin

Question 21

What are the regulatory proteins in muscle?

Answer 21

Troponin and tropomyosin

Question 22

What are the structural proteins in muscle?

Answer 22

Titin, dystrophin, alpha-actin, myomesin, and nebulin

Question 23

Define actin

Answer 23

• found in thin filaments
• has myosin binding sites for crossbridge formation with myosin
• actin is the “red” circles on models in class

Question 24

Define myosin

Answer 24

• in thick filament

- myosin heads connect to myosin binding sites on actin

Question 25

Define tropomyosin

Answer 25

• in thin filaments
• covers the myosin binding sites on actin when its relaxed
• its the band that actin and troponin is attached to

Question 26

Define troponin

Answer 26

• in thin filaments
• holds tropomyosin in place when relaxed
• during contraction, Ca2+ binds to it and causes tropomyosin to move away from myosin binding sites on actin
• other colored balls on thin filament

Question 27

Define titin

Answer 27

• spans half of sarcomere length (z disc to M line)
• stabilizes the position of thick filament, eleasticity and extensibility, lets sarcomere return to length after contraction
• spring by z disc extends to m line

Question 28

Define Dystrophin

Answer 28

• cytoskeletal protein that links the thin filament to the sarcolemma
• attached to the extracellular proteins in the connective tissues surrounding the muscle fibers
• helps transmit tension from the sarcomeres to tendons

Question 29

Define nebulin

Answer 29

• spans the length of the thin filament (little protein line in middle of actin line)
• anchors thin filament to Z disc

Question 30

Define alpha-actinin

Answer 30

• protein in Z disc

- binds to actin molecules of the thin filament and to titin

Question 31

Define myomesin

Answer 31

• protein in M line (“paper chains”)

- binds to titin and thick filaments at m line

Question 32

Define sliding filament model of muscle contraction

Answer 32

Actin and myosin filaments slide over each other to shorten the length of muscle fibers

Question 33

Steps of sliding filament model

Answer 33

1. myosin heads bind to actin to form cross bridge
2. conformational change (energized by ATP hydrolysis) causes thin filaments to slide along thick filaments
3. Myosin head group releases, forms new cross bridge, sliding cycle repeats