muscles Flashcards
What muscle type is limited by its ability to diffuse O2 and nutrients?
Skeletal muscle (big!)
What is the covalent action of ATP in skeletal muscle?
Hydrolysis of ATP by myosin energizes the cross-bridges, providing the energy for force generation
What is the allosteric action of ATP in the skeletal muscle?
Binding of ATP to myosin dissociates cross bridges bound to actin, allowing the bridges to repeat their cycle of activity.
Where does the calcium for cross bridge formation come from?
Intra-organelle (SR) calcium!
How does Ca get back into the sarcoplasmic reticulum?
ATP is require to provide the energy for the calcium pump in the SR
The body uses which form of contraction to create movement?
Unfused tetany
What causes a muscle to fail to sustain tension/fatigue?
- depletion of metabolic substrates
- depletion of neuromuscular transmitter
- psychological inability to drive nerve impulse
What metabolic substrate becomes less available to the muscles over periods of prolonged exercise?
muscle glycogen
what is the functional unit of muscular contraction?
motor unit
what is the definition of the motor unit?
the motor neuron and all the muscle fibers that it innervates
what are the contractile properties of muscle fibers?
speed
strength
endurance
what does the speed of contraction depend on?
the form of myosin ATPase (fast or slow)
what does the strength of contraction depend on?
the number and SIZE of muscle fibers innervated
what does endurance of contraction depend on?
the metabolic enzymes present (oxidative or glycolytic)
what is summation?
the increase in muscle tension from successive action potentials occurring during the phase of mechanical activity
what is a maintained contraction in response to repetitive stimuli?
tetanus
what is unfused tetanus?
low stimulation frequencies–tension oscillates as the muscle fiber partially relaxes between stimuli
what is produced at higher stimulation frequencies?
fused tetany
what are 3 ways a muscle fiber can form ATP?
- phosphorylation of ADP by creatine phosphate
- oxidative phosphorylation of ADP in the mitochondria
- phosphorylation of ADP by the glycolytic pathway in the cytosol
what are 3 types of skeletal muscle fiber?
- slow-oxidative fibers (SO)
- fast-oxidative-glycolytic fibers (FOG)
- fast-glycolytic fibers (FG)
how do type I or slow oxidative fibers work?
by combining LOW myosin-ATPase activity with high oxidative capacity
how do type IIa or fast oxidative glycolytic fibers work?
by combining HIGH myosin-ATPase activity with high oxidative capacity and intermediate glycolytic capacity
how do type IIb or fast glycolytic fibers work?
by combining HIGH myosin-ATPase activity with high glycolytic activity
what is the order of motor unit activation?
SO–>FOG–>FG
always start by activating fibers LEAST susceptible to fatigue, and those MOST fatigable for LAST
what are 3 characteristics of cardiac muscle?
- moderate SR with T-tubules
- dispersed mitochondria
- centrally located nuclei
which type of fiber gets its calcium from SR and EC?
cardiac muscle!
true or false: cardiac muscle has fused and unfused tetany?
FALSE - no tetany!
true or false: skeletal muscle has NO calcium channels in its plasma membrane?
TRUE
what type of Ca channels are in the plasma membrane of a cardiac muscle cell?
L-type
cardiac muscle has a LONG or SHORT refractory period?
LONG
skeletal muscle has a LONG or SHORT refractory period?
SHORT
true or false: smooth muscle lacks troponin
TRUE - which means tropomysin never covers actin binding sites (its not the regulatory step like striated muscle)
