The Muscular System: Lecture 17 Flashcards
muscle twitch
smallest muscle contraction; occurs in laboratory not in whole muscles of body
phases of twitch
latent period, contraction period, relaxation period
myogram
diagram of muscle twitch
latent period
time for action potential to propagate across sarcolemma
contraction period
repeated crossbridge cycles generate tension
relaxation period
calcium ion levels reduced in cytosol by SR pumps; tension diminishes
refractory period
begins at onset of latent period and ends at beginning of contraction period
muscle is unable to respond to further stimuli
refractory period in smooth and cardiac muscle
periods are as long as their contractions; must FULLY relax before contracting again
tension in twitch
varies with several factors: timing and frequency of stimulation, length of fiber at rest, type of muscle fiber
wave summation
increase in tension caused by repeated stimulation of muscle fiber by motor neuron
repeated stimulation results in progressively greater tension production
-pumps don’t have time to pump all released calcium ion back before restimulation, leading to cytosol increases with each new stimulation
unfused tetanus
stimulated about 50 times per second; fiber partially relaxes between stimuli
tension pulsates (individual twitches remain visible) and increases to about 80% of maximum
fused (complete) tetanus
stimulated about 80-100 times per second; fiber does not relax between stimuli
tension stays at nearly 100% of maximum
type I fibers
slow twitch
low myosin ATPase activity
extended periods of contraction, sustained oxidative ATP
well developed blood supply
dark meat
type II fibers
fast twitch
high myosin ATPase activity
powerful, quickly fatigues, sustained anaerobic ATP
smaller blood supply
light meat
Class I
slow oxidative, extensive blood supply
small to intermediate diameter
standing, sitting
Class IIa
fast oxidative glycolytic, less extensive blood supply
large diameter
walking, writing
Class IIx
fast glycolytic, limited blood supply
intermediate diameter
heavy lifting, sprinting
fastest!
motor units
single motor neurons with multiple axon branching
stimulate average 150 fibers
fibers within motor unit are of the same type
activation: recruitment, muscle tone, shivering
recruitment
more motor units recruited as required
muscle tone
alternating motor unit contractions to maintain muscle tone
shivering
random motor unit contractions to generate heat; brief normal hypertonia
isotonic concentric contraction
force generated by muscle greater than load, muscle shortens
isotonic eccentric contraction
force generated by muscle is less than load, muscle lengthens
isometric contraction
length of muscle does no change (static position)
muscle shapes
parallel, convergent, pennate, circular (sphincter), spiral, fusiform
muscle names
based on:
shape/appearance, size, structural characteristics, location, body region, points of attachment, action (flexion or extension)
skeletal muscle functions
locomotion, breathing, swallowing initiation, sound modulation, voluntary control over defecation and urination, shivering
functional groups of muscles
take cooperation of several individual muscles working group to perform movement;
agonists, antagonists, synergists, fixators
agonists
prime movers; provide most force for given muscle action
antagonists
usually on opposite sides of bones and joint where they meet; opposite action of agonist; allows for modulation and control of agonist movement
synergists
aid agonists by supplying supplemental force, minimizing unwanted movement; help stabilize joints; provide for more efficient movement
fixators
provide stabilizing force that anchors bone; provides movement efficiency and protection from injury due to unnecessary movements
lever system
three components: load or resistance, applied force that moves load, and pivot point (fulcrum)
first-class level
fulcrum sits between load and applied force; load moved in opposite direction than applied force
second-class lever
fulcrum is at one end of level, applied force is near other end, load is somewhere in between; load moved in same direction as applied force
third-class lever
fulcrum and applied force are close to one another at same end of lever; load in near other end, moved in same direction as applied force
myoplasticity
changes in muscle structure as result of changes in function related to physical training; changes within muscle fibers, do not involve changes in number of muscle fibers
satellite cells
cells that retain mitotic ability, can help repair injured skeletal muscle
endurance training
large increase in frequency of motor unit activation and moderate increase in force production (more repetitions with lighter weight)
primarily biochemical changes:
-increased oxidative enzymes and mitochondria
-increased fatigue resistance
-more efficient use of fuels
-increase in blood vessel network
resistance or strength training
moderate increase in frequency of motor unit activation and large increase in force production (fewer repetitions with heavier weight)
primarily anatomical changes
-number of myofibrils and diameter of muscle fibers increase
-decrease endurance
hypertrophy
number of myofibrils and diameter of muscle fibers increase
atrophy
decrease in number of myofibrils and size of fiber; decrease in oxidative enzymes caused by disuse of muscle
