Skeletal Muscle Anatomy
What are the contractile proteins in skeletal muscle?
actin and myosin
During contraction, calcium binds to ________, causing _________ to move, revealing the ________ binding sites on ______.
During contraction, calcium binds to troponin, causing tropomyosin to move, revealing the myosin binding sites on actin.
Explain the creatine phosphate energy pathway (equation)
Creatine phosphate + ADP --creatine kinase--> creatine + ATP
Describe a motor unit and give 2 characteristics of motor units.
One motor neuron and all of the muscle fibers it is attached to.
- Motor units consist of all the same muscle fiber type.
- All muscle fibers in a motor unit contract simultaneously.
- Large motor units are good for gross motor function, while small motor units are good for fine motor function.
What are the 2 sources of calcium for smooth muscle contraction?
Extracellular fluid and sarcoplasmic reticulum
List the levels of organization of skeletal muscle from outermost/largest to innermost/smallest (including connective tissue layers) (hint: 8 items)
Epimysium, skeletal muscle, perimysium, fascicle, endomysium, muscle fiber, myofibrils, myofilaments
During depolarization, ______________ channels open. During repolarization, _____________ channels open.
Depolarization: voltage-gated Na+ channels
Repolarization: voltage-gated K+ channels
________ muscle fibers will have the greatest glycogen stores, while _________ muscle fibers will have the greatest myoglobin stores.
Fast glycolytic (type IIb/x); slow oxidative (type I)
Describe 4 factors that contribute to increased muscle tension
Wave summation, increased recruitment of motor units, large muscle fibers (hypertrophy), sarcomeres stretched 80-120% of resting length
other factors: hyperplasia, maximal stimulus
What structure on an autonomic nerve fiber contains the neurotransmitters that signal smooth muscle to contract?
Varicosities
Distance between consecutive A bands
How does muscle relaxation occur? (2 ways)
ACh is degraded in the synaptic cleft, Ca2+ is actively pumped back into the SR
For each type of muscle fiber, give: 1) the primary energy pathway utilized for ATP synthesis, 2) rate of fatigue, and 3) example of an activity that fiber is best suited for
Type I: 1) aerobic respiration, 2) slow, 3) marathon
Type IIa: 1) mix of aerobic and anaerobic pathways, 2) intermediate, 3) sprint event
Type IIb: 1) glycolysis, 2) fast, 3) 1 rep max powerlift
During the upwards motion of a bicep curl (hand moving toward shoulder), which type(s) of muscle contraction are happening?
During a plank hold, which type(s) of muscle contraction are happening?
(isometric, isotonic, concentric, eccentric)
Bicep curl: Isotonic, concentric
Plank hold: Isometric
MLCK phosphorylates the myosin head to allow the cross bridge cycle to begin.
What type of channels are found at the motor end plate, and how do they work? (what chemical binds, direction of ion flow)
Ligand-gated Na+/K+ channels
ACh binds to receptor on channel, causes channel to open, Na+ flows into the muscle fiber and K+ flows out.
List the 3 phases of a muscle twitch, and explain what is happening in each phase
Latent period: cross bridges are forming, no muscle tension measured
Contraction period: cross bridges are active, tension is generated
Relaxation period: cross bridges detach, tension decreases, Ca2+ pumped back into SR
After glycolysis, in the absence of oxygen, ____(a)_____ is converted to ____(b)_____. During oxygen debt, what is happens to (b)?
(a) = pyruvate, (b) = lactic acid
During oxygen debt, lactic acid is converted back to pyruvate.
Which type of muscle fiber is recruited first, and why?
Type I (slow oxidative) fibers are recruited first because they are the smallest in size and are fatigue-resistant
How does an action potential travel to every cell in single-unit smooth muscle?
Through gap junctions.
Draw the neuromuscular junction, label as much as possible (come up to the board)
answer on slideshow
In the cross-bridge cycle, the binding of ATP to myosin causes _____________, while hydrolysis of ATP on myosin causes _____________.
Cross-bridge detachment; cross-bridge attachment and power stroke
Muscle fatigue is not due to ___________, but instead is caused by: (5 factors)
Not due to: a major lack of ATP
Caused by: ionic imbalances, increased Pi levels, decreased ATP, increased Mg2+, decreased glycogen
Aerobic training will primarily cause changes within which muscle fiber type? Give 3 adaptations that occur in skeletal muscle due to aerobic training.
Increased mitochondria, increased myoglobin, angiogenesis
How does single-unit smooth muscle differ from multi-unit smooth muscle? Give an example of each.
Single-unit: Autonomic nerve innervates one cell, connected electrically via gap junctions, all cells function together. Ex. Digestive tract
Multi-unit: Autonomic nerve innervates every cell, cells contract individually. Ex. Eyes (pupil dilation/constriction)