AP - Muscles, Contraction/Relaxation

Question 1

What are the three types of muscle tissue?

Answer 1

1. cardiac
2. smooth
3. skeletal

Question 2

what are the 4 main characteristics of muscle fibers?

Answer 2

1. extensibility
2. elasticity
3. excitability
4. contractibility

Question 3

what are the 4 major functions of muscle?

Answer 3

1. produce movement
2. maintain body position vs gravity
3. wrap around joints and stabilize
4. helps to produce/generate heat

Question 4

the epimysium is a connective tissue wrapping that _____________

Answer 4

separates muscle from over tissues and organs by covering each muscle

Question 5

the perimysium is a connective tissue perimysium that _____________

Answer 5

surrounds fascicles and helps provide resistance of a muscle to tensile forces

Question 6

the endomysium is a connective tissue wrapping that _____________

Answer 6

surrounds each myofiber

Question 7

walk me through the composition of muscles (fascicles vs myofibers vs myofibrils vs myofilmaments)

Answer 7

the smallest component of muscles are the myofilaments - actin and myosin which do the actual contracting

myofibrils are composed of myofilaments

myofibers are composed of myofibrils

fascicles are bundles of myofibers

Question 8

explain sarcomeres

Answer 8

sarcomeres are the smallest functional unit of muscle

composed of actin and myosin filaments (acTHIN - thin filament)

they undergo contraction via the sliding filament theory

Question 9

what is the sarcoplasmic reticulum and why is it important?

Answer 9

it is a specialized muscle organelle which stores, releases, and retreives Ca2+ ions

it is important as it is needed to help propagate the action potential into the muscle cell

Question 10

what are the key characteristics of skeletal muscle?

Answer 10

striated, long cylindrical shape

multinucleated, and attaches to bone and skin

voluntary contraction

Question 11

what are the key characteristics of cardiac muscle?

Answer 11

branched, striated, one nucleus per fiber, intercalated discs at the end of each fiber

involuntary contraction

Question 12

what are the key characteristics of smooth muscles?

Answer 12

spindle shaped, one nucleus per fiber

involuntary contraction

Question 13

walk me through the sliding filament theory and the excitation-contraction coupling

Answer 13

Mechanism for muscle contraction

1. AP from neuromuscular junction
2. depolarization of the myocyte membrane (motor end plate) ➔ Na+ enters muscle cell allowing the propagation of the AP along the sarcolemma
3. opens the sarcoplasmic reticulum
4. Ca2+ released in the muscle cell
5. binds to troponin (which is bound to actin)
6. allows for conformational change and tropomyosin can shift and actin becomes free to bind to myosin
7. myosin head binds with ATP and ATP hydrolyzes into ADP-P
8. myosin - ADP - P forms a cross bridge w/ actin
9. powerstroke where actin is slide over myosin and ADP - P are released
10. new ATP binds and allows for the myosin head to break cross bridge and reset for new powerstroke

*crossbridging and powerstrokes continue so long as there is Ca2+ bound to troponin

Question 14

what is the sarcolemma?

Answer 14

the plasma membrane surrounding the myofiber

Question 15

what are regulators of muscle contraction?

Answer 15

troponins and tropomyosin - blocks myosin and actin interaction

ATP - needed to dissociate
ADP-P - needed for cross bridge formation and powerstroke

Ca - needed for action potential/depolarization