L3 Striated Muscle Physiology

Question 0

How contraction works:

Answer 0

Using ATP, myosin walks along actin filaments.
Actin has tropomyosin and 2 troponins on in (including troponin-C). Troponin-C binds Ca and disengages from actin, exposing the myosin binding site on actin. Then contraction can begin

Question 1

From macro to micro:

Answer 1

Skeletal muscle -> Fascicle -> muscle fiber/myofibril -> thick&thin filaments
many filaments make a muscle fiber, and many muscle fibers are within a fascicle, and many fascicles are within a muscle

Layering of connective tissue:
endomysium around myofibrils-> perimysium around fascicles -> epimysium around entire muscle

Question 2

E-C coupling:

Answer 2

1. AP comes down the axon
2. Ach NT released and received on post-synaptic muscle cell by Ach-gated cation (Na) channel
3. Na is brought into the cell and carries the AP into the T tubule.
4. Depolarization activates DHPR (voltage gated), which causes a conformational change in RyR.
5. RyR is a Ca-gate and pumps Ca from the SR into the muscle cell.
6. Ca in the muscle initiates muscle contraction.
7. Ca is pumped back into the SR lumen by SERCA.

Then, Ca binds troponin-C, tropomyosin/troponin move away and myosin binds via sliding filament model

Question 3

Length-Tension Diagram

Answer 3

Shows that maximal tension is not at too short or too long but in between
drop in tension could be due to filaments being stretched away from each other so they can’t grip, or due to overlapping of the filaments

Question 4

Sarcomere length:

Answer 4

2.65 micrometers

Question 5

Force-Velocity curve

Answer 5

Indicates that velocity is greatest when force is smallest, ie when the object lifted or whatever is very light and easy to move

Maximal power is at an intermediate load

Question 6

Isometric vs. Isotonic contractions

Answer 6

Isometric - same length - muscle held at a length

Isotonic - same force but muscle moves
(Concentric = muscle shortens)
(Eccentric = muscle lengthens while flexing, ie walking down a hill - exercises increase strength)

Question 7

Skeletal vs. Cardiac E-C coupling

Answer 7

Skeletal: see previous notecard; uses DHPR and RyR

Cardiac: Ca induced Ca release from SR
^????

Question 8

Muscle Fiber types

Answer 8

Type I: SLOW, endurance, posture, lots of mito, oxidative phosphorylation

Type II: FAST, fatigue easily, make lactate, less mito, glycolysis

most muscles have both types intermixed