Muscle Structure & Function

Question 1

Mesoderm

Answer 1

Bone, cartilage, connective tissue, and muscles

Question 2

Cells in mesoderm to myoblast

Answer 2

PAX7 - marker of skeletal muscle lineage retained in satellite cells
MYOD & MYF5 - early mesodermal cells to myoblast lineage
Myogenin - terminal myoblast differentiation

Question 3

Myoblast to mature myofiber

Answer 3

Myoblast start fusing together
Myotube - multinucleate tube
Myofiber - tube matures & nuclei go to nuclear peripheral positioning

Question 4

Epimysium

Answer 4

Covers myofibers
Outer covering of muscle
Protects from external forces

Question 5

Perimysium

Answer 5

Connects to tendon
Thick bands of ECM that surround fascicles

Question 6

Endomysium

Answer 6

Connects fibers together - move at the same time
Thin layer of ECM that surrounds individual fibers

Question 7

Physiological cross sectional area (PCSA)

Answer 7

Largest determinant of force generating capacity
Directly proportional to the number of myofibers
(Muscle volume/fiber length)*cosX

Question 8

Path of contractile stimulus from motor neuron action potential to cross bridge cycling

Answer 8

AP (from brain) travel to terminal axons of motor neurons
ACh is released at neuromuscular junction
ACh bings to ACh receptors in sarcolemma that propagates the AP
AP enters myofiber through T-tubules
AP activate DHPR on T-tubule
DHPR activation opens RYR in SR
Calcium released from SR through open RYRs
Calcium binds to actin and initiates contraction

Question 9

Longitudinal force transmission

Answer 9

Shortening muscle
Sliding filament theory within fiber

Question 10

Lateral force transmission

Answer 10

Increases uniformity of sarcomere length and muscle shortening
Outside fiber
Transmits force laterally between fibers

Question 11

Main types of fiber types

Answer 11

Slow
Intermediate
Fast