Muscle Phys - Review Flashcards
Major physiological functions of skeletal muscle
Execute body movement
Establish and maintain posture
Accomplished by shortening or lengthening muscle distance between connections to bone
Key properties of all muscle types
Contractibility
Excitability
Extensibility
Elasticity
Skeletal muscle
Attaches to bones
Voluntary and involuntary control
Multinucleated (peripheral location)
Striated, bands perpendicular to long axis of fibers
Cardiac muscle
Single nucleus, centrally located
Striated, involuntary contraction, intercalated disks
Smooth muscle
Walls of hollow organs, blood vessels, eyes, glands, skin
Single nucleus, centrally located
Not striated, involuntary contraction, gap junctions in visceral smooth
Coordination in muscle function
Receiving an excitatory stimulus via intracellular signal
Activates shortening machinery in cell (contraction)
Relaxation removes the extra/intracellular stimuli to contract & reverses excitation coupling
Muscles relaxed can stretch passively
Depolarization
Action of ACh signaling the NMJ to transit Na & K to depolarize the resting membrane potential. This leads to muscle excitability and contraction & can cause adjacent voltage sensitive Na channels to depolarize & spread the signal, propagating down the cell
Depolarization
Repolarization
Hyperpolarization
De - influx of Na into the cell
Re - efflux of K out of cell
Hyper - overshoot of K efflux out of cell
Excitation - contraction coupling involves
Is a mechanism which spreading action potential is coupled to muscle fiber contractions
Sarcolemma
T tubules
Release of Ca from sarco retic
Dihypropyridine receptor
In sarcolemma or t tubules
Voltage sensitive channel, opens w depolarization
Allows slow influx of calcium from extra cell
Interacts w and activates RyR
Ryanodine receptor (RyR)
In sarco retic
Opens when directly activated by DHPR
Allows release of Ca++ stores in SR into sarcoplasm where it can activate contractile machinery
Contractile machinery
Thin myofilaments - actin, anchored by z disks
Thick myofilaments - myosin
Pathway of action potential to muscle contraction
Action potential enters sarcolemma via t tubules
Ca++ is released from the SPR into the plasma
Ca interacts with sarcomere: binds to troponin, activates/reveals the G actin binding site, myosin attaches to active sight forming a cross bridge
Cross bridge cycling
Resting fiber cross bridge not attached to actin
Ca enters and cross bridge binds to actin
Power stroke involves change in orientation of myosin head cross-bridge & dissociation of ADP & P
New ATP binds to myosin head, allowing it to release from actin
ATP is hydrolyzed, causing cross bridge to return to its original orientation
What mechanisms account for variation in force in muscle contraction?
Engaged number of motor units
Alteration of frequency of stimulation
Length of muscle prior to arrival of stimulus to contract
Adaptation to exercise
Motor unit
Motor neuron plus all muscle fibers with which it forms synapses
Graded contractions
Varying degrees of force generation, produced by variations in the number of motor units activated - controlled by CNS
Innervation ratios
Fibers per neuron, vary anatomically consistent with the functional requirements of muscle in question
Length tension relation in single muscle fiber
Tension generation varies based on length of muscle when signal was received.
Opportunity for greatest contraction is at resting length
Length tension relation in muscle unit + tendons
Force generation capacity increases when muscle initially is slightly stretched. Active tension supplements the recoils of passive tension that has been stretched
Fast fibers
High myosin ATPase activity, rapid cross bridge cycling & high shortening velocity. Rapid fatigue
Slow fibers
Low myosin ATPase activity & lower shortening velocity. Fatigue slowly
Oxidative fibers
Have numerous mitochondria, high capacity of oxidative phosphorylation. ATP production dependent on blood borne oxygen & fuel; contain myoglobin, increase rate of oxygen capture in fiber
Glycolytic fibers
Fewer mitchondria, high concentration of glycolytic enzymes & glycogen. Larger w more thick/thin filaments = more tension. Fatigue rapidly
Effects of exercise on skeletal muscle
Contractile activity increases (hypertrophy, # if myofilaments, capacity for ATP production)
Low intensity = oxidative fiber (^ mitochondria & cap)
High intensity = glycolytic fibers (^diameter of actin/myosin, ^ production of glycolytic enzymes
