muscle part 2 Flashcards
contraction produces…
tension
isometric contraction
no shortening, muscle tension increases but doesn’t exceed the load
isotonic contraction
muscle shortens because muscle tension exceeds the load
concentric contraction: shortens and does work (going up during push ups)
OR
eccentric contraction: muscle contracts as it lengthens (going down during a push up)
force and duration of contraction depend on…
frequency and intensity of stimuli
motor unit
a motor neuron and all muscle fibers it supplies. axons of motor neurons divide into a number of axon terminals that form neuromuscular junctions with each muscle fiber
twitch
briefest muscle contraction, just contraction and then relaxation
small motor unit
in muscle that control fine movements (fingers, eyes)
large motor units
in large weight bearing muscles (thighs, hips)
why can you control individual muscle cells?
- because of individual connections with motor endplates
- endomysium stops every cell from firing
motor unit contraction
contract asynchronously, helps prevent fatigue (allows us to hold heavier loads for longer w/o getting tired)
myogram
- latent period: time of endplate potential and excitation phase
- stimulus, then contraction phase
- contraction period: cross bridge formation, tension increases
- peak of graph is maximum tension, then calcium goes away, leading to a decrease in tension
- calcium is pumped back in by active transport
muscle twitch comparison
different strength and duration of twitches due to variation in enzyme function between muscles
more specifically:
if ATP can be broken down faster by ATPase, the muscle can twitch faster
gastrocnemius
springing, jumping
soleus
standing, walking
a single stimulus results in…
a single twitch
what happens if we increase the frequency of stimulus?
-muscle doesn’t have time to completely relax between stimuli
-calcium release stimulates further contraction (summation waves)
-further increase in stimulus frequency leads to incomplete tetanus
muscle cramp
complete tetanus:
when every myosin head is already attached because all the calcium has been dumped
what happens if we increase the intensity of a stimulus?
-stimulus must pass threshold (when first observable muscle contraction occurs)
-muscle contracts more vigorously as stimulus strength goes above threshold
-contraction force is controlled by recruitment
recruitment principle
brings more motor units so more cells are connected by motor neuron’s branches
importance: can control strength of contraction to meet the needs of the moment
size principle
motor units with larger and larger fibers are recruited as stimulus intensity incrases
size principle
motor units with larger and larger fibers are recruited as stimulus intensity increases
muscle tone
constant, slightly contracted state of all muscles
muscle’s source of energy for contraction
ATP is muscle’s only source for contraction
available stores of ATP are depleted in 4-6 seconds
how is ATP regenerated?
ADP into ATP by phosphorylation by creating phosphate (CP)
anaerobic pathway (glycolysis)
aerobic respiration (supplies most of ATP. but if not enough Oxy, muscle go through lactic acid fermentation)
