Upgrade to remove ads
Only $35.99/year

Muscle Physiology Questions

Terms in this set (36)

How would skeletal muscle activation occur if someone wanted to lift a book? The first step is
Excitation of the CNS (upper motor neuron)
The immediate trigger for the release of acetylcholine from the somatic (lower) α-motorneuron into the synaptic cleft is
Increase [Ca++i] in the neuronal terminal
The motor endplate region of the neuromuscular junction contains
Both acetylcholine receptors and regenerative sodium channels.
The graded potential (end plate potential, EPP) at the neuromuscular junction
Depolarizes the endplate membrane below threshold for an action potential.
A major function of the T-tubule system is
Maintain ion concentration differences across the cell membrane.
The major source of calcium for skeletal muscle contraction is
Sarcoplasmic Reticulum (No Ca coming across sarcolemma to trigger Ca release from SR)
Crossbridge powerstroke occurs when
Pi and ADP are released by the myosin head (esp. release of Pi! )
The rate at which calcium is sequestered by SERCA in the sarcoplasmic reticulum of skeletal muscle during a twitch is directly related to the
Rate of relaxation
Rate of tension development (force generation)- determined by
Myosin ATPase activity (also Na/K pump, SERCA)
skeletal muscle contraction ends when
CNS quits sending signals
Acetylcholine is degraded in the synaptic cleft.
Calcium uptake into the SR is greater than release from the SR.
Diffusion of calcium from troponin C.
During Crossbridge cycling- Pi & ADP fall off myosin head- leads to
Powerstroke (myosin head 90--> 45 deg)
ATP binds (to myosin ATPase site) -->
myosin lets go of actin
Myosin ATPase hydrolyzes ATP -->
Recocks myosin head (back to 90 deg)
A patient places her, palm to palm, and pushes. If the muscles of one hand are all fast twitch (Type IIB) and the muscles of the other hand are all slow twitch (Type I), what must happen to maintain her hands in a steady position?
More slow motor units must be recruited at a higher frequency.

Fewer fast motor units must be recruited at a lower frequency.

Slow motor units don't generate as much force as a fast motor unit, but they don't fatigue as quickly
You administered an experimental drug which inhibited the Ca++ ATPase pump on the SR (SERCA). As a result, your patient will be able to lift ________ afterload.
greater
Why do athletes "warm up" before a competition?
To increase intracellular calcium concentration in the myocytes

(Treppe/Staircase- Contractions increase in response to multiple stimuli of same strength- because increasing availability of Ca in sarcoplasm & HEAT increased as muscle contracts (muscle enzymes more efficient))
Fine gradation of the force of contraction of the biceps muscle during the lifting of this heavy load is facilitated by:
Activation of large numbers of motor units with relatively few cells
You notice that after holding this afterload for a period of time, your arm starts to hurt and it becomes difficult to hold the books. This occurs because:
ATP synthesis is insufficient in the muscle (physiological fatigue)
Muscle ______ before you stimulate it- determines force of contraction
Stretch
At optimum length lo- skeletal muscle has high/low passive force?
LOW
Cardiac muscle has high/low passive force at Lmax because?
HIGH, connective tissue
Predominance of fast-twitch fibers leads to increased contractile ____
Velocity
Predominance of slow-twitch fibers leads to increased contractile ____
Duration
Muscle contracts fastest when no load
Greater the load, ____ the latent period, ___ the contraction, ____ the duration of contraction
Longer, slower, shorter
If load is greater than ability of muscle to move it, velocity of shortening is _____
zero (isometric)
Fast twitch, slow twitch, smooth muscle- order these from greatest to least Vmax
Fast twitch
Slow twitch
Smooth muscle
characteristic of cardiac but not of skeletal muscle?
Gap junctions
characteristic of skeletal but not of cardiac muscle?
Tetany (Cardiac muscle cells have L-type slow Ca channels leading to plateau phase of AP --> LONG refractory period --> NO tetany)
Mechanism for Ca++ extrusion (remove Ca from cytoplasm) from the cardiac myocyte
Na/Ca antiport exchanger
SR Ca ATPase (70%)
Mitochondrial uptake
Catecholamines lead to what 3 effects?
positive lusotropic (relaxation rate)
positive inotropic (force of contraction)
positive chronotropic (frequency of contraction, increased heart rate)
Decreased force of cardiac muscle contraction can be accomplished by
Decreasing intracellular [Ca++]
What is required for CBC in smooth muscle?
Phosphorylated myosin head (by MLCK)
ATP available
sources of Ca for smooth muscle contraction (5)
VGCC
Stretch-activated Ca channels
Ca leak channels
Ligand-gated Ca channels
GPCRs
How are contraction of skeletal / cardiac/ smooth muscle regulated?
Skeletal & cardiac- Thin filament regulated- Ca binds troponin


Smooth- Myosin regulated:
Phosphorylation of myosin light chains --> activates myosin ATPase --> CBC
How does smooth muscle relax/ remove Ca?
- SERCA
- Ca pump in sarcolemma
- Na/Ca exchanger in sarcolemma
Myosin phosphatase
Smooth muscle contraction is terminated by
Dephosphorylation of Myosin light chain
Other sets by this creator