Muscle Physiology Flashcards
Function of Nebulin?
stabilizes thin filament in certain types of muscle
Filament polarity?
- polarity of proteins (actin/myosin) switches when you cross from one side of the sarcomere to the other side
- produces force in a certain direction
- length of filaments is fixed to slide past each other during contraction
What helps pull muscle sarcomere back to original length?
agonist/antagonist pairs pull muscle back
-biceps/triceps
Sarcomere length tension relationship, passive?
- if muscle is relaxed and it is passively stretched out to increase sarcomere length, the sarcomere increases its force to resist stretch (like rubber band)
- not interaction between actin/myosin
- greater length= greater force
Sarcomere length tension relationship, active?
- does useful work
- subtract passive work from total
- due to actin/myosin interaction
- there is an optimal length where actin/myosin interaction is greatest and force is greatest
Sarcomere length is too long, tension relationship?
- actin and myosin are stretched beyond overlap
- no interaction
- force goes to 0, no contraction
Force of contraction is proportional to what?
number of myosin heads interacting with actin
Plateau region, length-tension relationship?
- bare zone
- any change in length has little effect on the number of myosin heads that can interact with actin (.2 microns)
- amount of overlap changes but the number of heads remains constant
- result of the change of polarity at halfway point of sarcomere
Sarcomere length is too short, tension relationship?
- opposing sides start to interfere and overlap each other
- tension decreases with decreasing sarcomere length until they crash into Z disk
- thick and thin filaments are compressed, cannot function properly
What is the bare zone?
- center without myosin heads
- area where polarity flips
Frank Starling law of heart?
- greater the volume of blood entering heart during diastole, the greater the volume of blood ejected during systole and greater the force
- there is a balance between venous return and systolic delivery
Passive tension, skeletal vs heart muscle?
- skeletal- passive starts where active tension peaks
- cardiac- passive starts before active muscle peaks
- results in resting state of cardiac muscle shorter than skeletal muscle
Length tension relationship, Cardiac vs skeletal muscle?
- Cardiac
- trades mechanical efficiency for self regulation
- shorter optimal sarcomere length, stretched as blood fills heart
- the stretching moves cardiac sarcomeres to a more optimal length for greater interactions and contraction
- if heart is stretched too much, loses its ability to pump (CHF)
- resting tension starts to rise earlier - skeletal
- operates at maximal mechanical efficiency
- generates most force at resting length
- dip in total tension
How does Myosin detach from actin?
- need ATP
- stays attached if no ATP, Rigor Mortis
T/F
Each myosin head cycles independent of the others.
True
Steps of sarcomere filament sliding?
- Calcium influx, cross bridge binds to actin
- cross bridge moves
- ATP binds myosin, causing cross bridge to detach
- Hydrolysis of ATP, energizes cross bridge
Force velocity relationship?
- the heavier the load, the slower the velocity of muscle contraction
- if the load is less than isometric force, you can contract
- the lower the load, the faster the contraction
- as load increases, velocity of concentric contraction decreases, once the load reaches max force that can be supported, the velocity of eccentric contraction increases
Slow oxidative (type 1) muscle fibers characteristics?
- slow contraction velocity
- oxidative phosphorylation primary source of ATP
- many mitochondria
- high Myoglobin content (red fibers)
- slow rate of fatigue
- low glycogen and glycolytic enzymes
- made for endurance
Fast Oxidative Glycolytic (type 2a) muscle fibers?
combination of slow and fast twitch fibers
Fast Glycolytic (type 2b, 2x) muscle fibers?
- fast contraction velocity
- Glycolysis primary source of ATP
- few mitochondria
- high glycogen and glycolytic enzymes
- fast rate of fatigue
- low Myoglobin content (white muscle)
- made for short burst exercise
Muscle triad?
- junctional SR
- T tubule
- junctional SR
- skeletal muscle has a lot of triads, cardiac muscle has few
Excitation-contraction coupling in skeletal muscle?
- mechanical coupling
- depolarization of T-tubule membrane causes conformational change to voltage sensitive protein
- releases calcium from SR
Excitation-contraction coupling in cardiac muscle?
- depolarization of T-tubule membrane causes conformational change of voltage sensitive protein to release calcium from extracellular space
- Calcium binds to receptor on SR membrane
- Channel opens in SR to release more calcium
- After a certain amount of time, the channel closes
- positive feedback
- difficult to tetanize cardiac muscle
How does calcium get sequestered back into SR?
-ATPase pump brings calcium against its electrochemical gradient back into the SR
Control of contraction in skeletal muscle?
- Troponin C- binds calcium
- Troponin I- turns off the switch, when calcium is no longer bound (inhibitory peptide)
- Troponin T- glues complex to Tropomyosin
- when calcium binds, Tropomyosin is removed, exposing the myosin binding site on Actin (regulation step)
Neural control of contraction, one twitch?
- action potential at motor end plate (1 msec)
- calcium in cytoplasm peaks (5 msec)
- tension of muscle peaks (25 msec)
- sarcomere active for 60 msec
Fused tetanus?
- multiple twitches close in time together
- calcium levels remain high in cell
- sustained contraction
Excitation contraction coupling in smooth muscle?
calcium phosphorylates the myosin regulatory light chain to activate it
Effect of epinephrine on smooth muscle?
- relaxation (depends on particular smooth muscle)
- relaxes bronchioles
- activates arterioles
Latch bridge in smooth muscle?
- only in smooth muscle
- ATP turns system on as a regulatory mechanism
- Myosin is dephosphorylated and dissociates from Actin very slowly, forming a latch bridge
- smooth muscle can hold contraction without using more ATP, and very little ATP is needed to create another movement
- efficient system
