Muscle Contraction Flashcards
What does each muscle fiber contain?
Myofibrils
What two myofibrils make up a muscle fiber?
Actin and myosin
What myofibril is a globular protein consisting of two alpha-helical twisted strands?
Actin
Which myofibril is made up of a heavy chain pair of alpha-helical tails and two light chain pairs of “heads”?
Myosin
Which component of myosin has an actin binding site that binds and hydrolyzes ATP?
The “Heads” (Light chains)
What is the basic contractile unit of a muscle fiber?
Sarcomere
Which myofibril is covered in tropomyosin?
Actin
What does tropomyosin function to do?
Covers Actin-myosin binding site at rest, moves from that site at AP
Which myofibril is associated with troponin?
Actin
What does troponin function to do?
Release Ca2+ for binding to tropomyosin allowing it move for Cross-Bridge cycling
What structure is the middle of the sarcomere?
M line
What structure is surrounding each side of the M line until actin site?
Bare zone (no overlap)
What structure is on each side of the actin?
Z disks
What makes up the I band of a sarcomere?
Actin lines
What makes up the A band of a sarcomere?
Actin and myosin lines
What actin-binding protein anchors the myofibrillar array to the CM?
Dystrophin
What large protein extends from the M line to Z disks, partly passing through the myosin?
Titin
What protein extends from one end of actin to the other, setting the length?
Nebulin
What protein anchors actin to Z disk?
Alpha Actinin
What structure does a contraction reach the muscle fiber via?
Transverse tubules
Through what structure does the contraction get to the SR from the Transverse Tubules?
Dihydropyridine receptors
What structure is the storage and release site of Ca2+ for E-C Coupling?
SR
What structure on the SR does Ca2+ flow through to get to muscle?
Ryanodine Receptors
What substance pumps calcium back to the SR?
Ca2+ ATPase (SERCA)
Summarize the mechanism of Excitation-contraction coupling of Skeletal Muscle. (seven steps)
- AP -> T-tubules for depolarization from the surface to interior of muscle fiber. 2. Depolarization of t-tubule causes dihydropyridine receptors to open Ryanodine receptors for Ca@+ release. 3. Ca2+ is releases from SR to muscle fiber. 4. Ca2+ binds to troponin, 5. That bind causes tropmyosin to unbind and move to allow for actin-myosin cross bridge. 6. Myosin and actin bind. ATP binds to myosin head. ATP is hydrolyzed to ADP+P providing the energy to walk along the actin filament. ADP is releases and myosin is returned to OG state and continue walking until Ca2+ unbinds to troponin. 7. Relaxation occurs when Ca2+ unbinds and is reaccumulated in SR by SERCA. Tropomyosin returns to binding sites to stop cross bridge cycling for relaxation.
Summarize the mechanism of Smooth Muscle E-C Coupling. (6 steps)
- depolarization opens Ca2+ channels in SR. Influx increases concentration and if threshold is reached, AP can occur and further depolarization occurs opening Ca2+ channels. 2. Neurotransmitters open Ca2+ channels = influx. 3. Ca2+ binds to calmodulin which binds to and activate myosin-light-chain kinase. 4. MLCK phosphorylates myosin light chain increasing ATPase for cross bridge coupling. 5. Calponin and caldesmon inhibit/excite myosin ATPase. 6. When [Ca2+] decreases to low enough levels, relaxation occurs by either hyperpolarization, direct inhibition of Ca2+ channels, or decreased release of Ca2+ from SR.
What is a sustained contraction of muscle twitch due to insufficient tome for SR to accumulate Ca2+?
Tetanus
What is the relationship between the length and tension of a muscle?
A full length, there is zero tension. As length decreases, produces overlap, producing tension
What is the relationship between force and velocity of a muscle contraction?
At initial length, as contraction occurs, velocity slows. (An isometric contraction initially @ 3 lengths has 0 velocity until added force.
What type of muscle fiber has rapid cross bridge cycling and rapid rate of shortening?
Fast twitch (Type II)
What type of muscle Fibers have slow cross bridge cycling and slow rate of shortening?
Slow Twitch (Type I)
What type of fibers withstand better fatigue?
Slow twitch (Type I) due to oxidative nature vs glycolytic nature of Type II
True/False: Fibers can be different within a given motor unit.
False, thy are all the same.
What is the relationship between control and size of fibers?
Small fibers have better control over large fibers
What is the relationship between reaction and size of fibers?
Small fibers are rapid reacting while large fibers are slower reacting
Hypertrophy (increase in size) does what to the stimulation of a muscle?
Increase force but not speed
Hyperplasia (increase in # of fibers) does what to the stimulation of a muscle?
Increase force but no change in velocity
Lengthening a fiber has what effect on the stimulation of a muscle?
No change in force but increase speed of contraction
Atrophy (decrease in size) does what to the stimulation of a muscle?
Decreases load, decreasing size, decreasing force
