Physiology of skeletal ms
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Striated Muscle: definition and type
The contractile apparatus is highly organized into sarcomere structures giving a “striated” appearance under the microscope.
–Skeletal Muscle performs mechanical work via the skeleton under voluntary neural control.
–Cardiac Muscle performs mechanical work in the heart under its own pacing control modulated by the autonomic nervous system.
•The contractile apparatus is loosely organized without a defined banding pattern.
–Smooth muscle performs mechanical work in many target organ systems and is modulated by neurotransmitters, metabolic, local and hormonal factors.
Equilibrium of Forces
insufficient because in order to hold up 10kg ball, the bicep has to produce 70kg force
The lever system of the arm amplifies...
the velocity and range of movement.
General Features of Skeletal Muscle
•Muscle cells (fibers) are multinucleated, striated and organized in parallel bundles.
- •Diameters range from 10 mm - 100 mm;
- lengths range from 1 mm - 20 cm.
- •Individual muscle fibers are activated by motor neurons from the central nervous system (spinal cord) at neuromuscular
- junctions leading to muscle action potentials and voluntary contraction.
organization of skeletal ms
muscle --> ms fiber --> myofibril
what is in ECM of skeletal ms?
collagen, intermediate filament and dystrophin
the basic repeating contractile units in striated muscle: both skeletal and cardiac
What are the contractile proteins found in sarcomere?
myosin, tropomyosin, troponin and actin
Shorten Sarcomeres & Muscle Fibers involves ...
Sliding of Thin Filaments past Thick Filaments
the molecular motor that generates force and movement in muscle via the Crossbridge
Excitation Contraction Coupling
- is the sequence of events that link the depolarization of the surface membrane
- with tension development by the contractile machinery
EC couple in skeletal vs cardiac: difference
the sources of these action potentials and calcium pools
Calcium Regulates Contraction:
what is needed to keep myosin crossbridges cycling along actin filament?
sufficient ATP and proximity to an available actin binding site.
- •Striated muscle contraction is regulated by calcium via the thin filament proteins,
- troponin and tropomyosin.
how does Ca2+ regulate crossbridging of myosin with actin?
by covering and uncovering the binding site of myosin on actin
Release & Uptake of Calcium: unique mechanism that applies only to
DHP -ryanodine receptor and its opening from AP propagating on T-tubule
ATP-depending Ca2+ channel on SR
True or false:
Events at the Neuromuscular Junction: cell to cell connection
What happens between the action potential and contraction?
Latent period, which is the time it take for Ca2+ to move around and start acting
what helps transmit AP accross ms in the muscle bundle?
Sarcoplasmic Reticulum / Transverse Tubules / Myofibrils
which receptor triggers Calcium Release from the SR?
what is the difference between heart's DHP receptor vs. ms?
in the muscle, DHP receptor is physically opened by AP whereas heart DHP receptor is opened upon Ca2+
Skeletal EC Coupling: Sequence of Events
•Action potential generated at the neuromuscular junction is propagated along the sarcolemma.
•Signal transduction across the T-SR junction.
–Via DHP / Ryanodine Receptor complex signaling mechanism.
•Calcium release from the SR.
•Calcium binding to TnC.
•Crossbridge cycling and contraction.
- resequestration by longitudinal SR.
100% of the calcium that binds to TnC in skeletal muscle is derived from...
SR not extracellular space.
True or False
calcium that binds to TnC in skeletal muscle is come from extracellular space and SR
force vs. time at a constant length.
length vs. time at a constant force
force, length & time all change
Isotonic Twitches with different load (light, intermediate and heavy): velocity
Light > intermediate > heavy
when load becomes too heavy, ms is lengthened and contract at the same time
land from a jump produce (force? and type of contraction)
Tetanic force is larger than twitch force because...
the calcium is released faster than its re-uptake --> more available Ca2+ within the ms to activate contraction
Muscle length and force: Length-Tension curve
there is a normal working range where maximal tension is obtained
inc in length inc in force. up to a point then the force dec in the presence of inc in ms length
cardiac vs skeletal ms: which one has longer working range?
source of energy in skeletal ms. which one is the most important source or give instant energy to ms?
creatinine, glucolysis and oxidative phosphorylation
Creatinine is the most important
how does ms fatigue happen?
deplete ATP or intracellular [Ca2+]
Types of skeletal ms:
- Fast glycolytic
Fiber type: rate of fatigue
Slow-oxidative > fast-oxidative > fast glycolytic
Fiber type: Diameter
Fast-glycolytic > Fast-oxidative > Slow-oxidative
Fiber type: myoglobin type
- Red: Fast and slow-oxidative
- White: fast-glycolytic (fewer mitochondria and myoglobin)
Differences in the Development of Fatigue in the Three Skeletal Muscle Fiber Types
Slow-oxidative fiber > Fast-oxidative fiber > Fast glycolytic fiber
Force in skeletal ms is modulated by. Compared with cardiac modulation?
recruiting or derecruiting motor units in skeletal muscle.
change in Ca2+ concentration in cardiac ms.
Motor unit in skeletal vs cardiac ms
- Skeletal: single or multiple unit
- Cardiac: no motor unit
Factors determining ms tension
- 1. tension developed by each fiber
- a. AP frequency
- b. Fiber length
- c. Fiber diameter
- d. Fatigue
- 2. number of active fibers
- a. # of fiber per motor unit
- b. # of active motor unit
“Aerobic exercise” improves
endurance via increased mitochondria & oxidative fibers.
“Strength training” improves
short-term power via increased glycolytic fibers & diameter.
exercise ms leads to
hypertrophy & alters ATP production capacity
True or False
exercise will increase # of ms fiber
When does skeletal muscle become fatigue, energetically?
•Skeletal muscle can fatigue when ATP generation can’t meet the metabolic demand of the muscle.
True or False
The rate of ATP production and use is not related to fiber type
Skeletal muscle force is modulated by...
recruting or de-recruiting motor units
True or false:
Motor units contains many different types of muscle
True or False
In motor units, fiber type and metabolic efficient is fixed and constant since birth
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