Mechanisms of Muscle Contractions Flashcards
Speed of contraction in smooth vs cardiac and skeletal muscle
Smooth- slow. Cardiac/skeletal- fast.
Ringer experiment: Increase and decrease Ca in heart cells
Increase calcium: larger contractions. Remove calcium: smaller contractions.
A Band
Delineates extent of thick filaments
I band
Area that does not contain thick filaments. Contains Z line.
Z line
Scaffolding proteins that anchor thin filaments.
Titin
Anchors thick filaments to Z lines.
Thin filaments composed of?
Actin, troponin, tropomyosin
Sliding filament theory
Myosin pulls along actin filaments towards Z lines.
Role of Calcium in Muscle Contraction in skeletal/cardiac muscle
Binds to troponin C, which moves tropomyosin to expose myosin binding sites.
What happens when ACh binds to AChR?
Na influx through skeletal muscle
Difference between calcium in skeletal muscle/cardiac muscle
In heart, both Ca influx and release from SR is needed for contraction. Skeletal muscle does not require calcium influx.
Difference between cardiac/skeletal muscle and their contractions
Heart has 1 contraction per action potential, skeletal muscle has many.
Structure of Smooth Muscle
No troponin, so myosin must be phosphorylated to interact with actin using MLCK.
How is calcium released from SR in smooth muscle?
Via IP3 receptors.
Can smooth muscle contraction occur without action potentials?
Yes, via IP3 receptors. Can contract with or without them.
How do smooth muscles contract?
Release of Ca from reticulum binds to calmodulin, activating MLCK, which phosphorylates myosin, causing contraction.
MLCK
Myosin Light Chain Kinase, phosphorylates myosin light chains. Inhibited by cAMP.
B adrenergic stimulation effect on smooth muscle
Relaxation, due to activation of AC, then cAMP. Inhibits MLCK
A adrenergic stimulation effect of smooth muscle
Contraction, due to production of IP3, causes Ca release.
NO affect on smooth muscle
Relaxation, activation of GC, cGMP inhibits MLCK.
