week 3: 10.6 skeletal muscles produce increased tension by recruiting additional motor units Flashcards
why does regulating the number of stimulated muscle fibers control the tension of a skeletal muscle
the amount of tension produced by a muscle as a whole is the sum of the tensions generated by its individual muscle fibers as they are pulling together
isotonic contractions
muscle length changes with constant force
-tension increases and the skeletal muscle length changes
-lifting object, running
isometric contractions
length of the muscle does not change with a constant force
-muscle as a whole does not change length, tension produced never exeeds the load
e.g carrying bag, holding up head
concentric contraction
muscle shortens
eccentric contraction
muscle lengthens
motor unit
motor neuron and all the muscle fibers it controls
what does the size of a motor unit indicate
how fine or precise a movement can be
smaller motor units, 4-6 muscle fibers
precise control
eyes and fingers
large motor units
1000-2000 muscle fibers
precise control is not urgent
weight baring muscles of hips and thighs
why does the direction of pull exerted on the tendon not change when the number of activated motor units change
muscle fibers of each motor unit are intermingled
fasciculation
involuntary
synchronous contraction of a motor unit
recrutiment
smooth but steady increase in muscular tension produced by increasing the number of active motor units
when does peak tension occur
all motor units in the muscle contract in a state of complete tetanus
during a sustained contraction, motor units
activated on a rotating basis so some of them are resting and recovering while other are actively contracting
advantage of asynchronous motor unit summation
each motor unit can recover before it is stimulated again
muscle tone
some motor units are always active even when the entire muscle is not contracting
contractions do not produce enough tension to cause movement however they do tense and firm the muscle
why can skeletal muscles act as shock absorbers that cushion sudden impact
elastic nature of muscles and tendons
isotonic concentric contraction
muscle tension exceeds load and muscle shortens
isotonic eccentric contractions
peak tension developed is less than the load
muscle elongates due to the contraction of another muscle or the pull of gravity
movement of muscle fibers during isometric contraction
muscle as a whole does not shorten but the individual muscle fibers shorten as connective tissues stretch
why can you lift a light object more rapidly than a heavy object
load and speed of contraction are inversely related
why does it take longer more movement to begin if a load is heavier
muscle tension increases gradually
muscle tension must exceed load before shortening can occur
muscle relaxation- elastic forces
contraction ends, initial energy used in stretching tendons and distorting intracellular organelles is recovered as they recoil to their original dimensions
elasticity gradually helps return the muscle fibers in the muscle to their optimal resting length
muscle relaxation- opposing muscle contraction
contraction of opposing muscles can return muscle to original resting length
