whole muscle topics Flashcards
an action potential in a muscle fiber lasts
1-2 msec
fiber contraction may take
100 msec or more
the muscle that takes the longest to contract is
soleus
a given motor neuron innervates
several muscle fibers
a given muscle fiber is innervated by
only one motor neuron
motor unit
one motor neuron plus all the muscle fibers it innervates
multiple fiber summation
increased muscle tension caused by increasing the number of motor units contracting simultaneously
tension
is the force exerted on an object by a muscle
load
is the force exerted on a muscle by the weight of the object
for a fiber to shorten, tension must
exceed load
isotonic contraction
muscle shortens while the load on it remains constant
isometric contraction
muscle develops tension but doesn’t shorten
twitch
contraction of a single muscle fiber in response to a single action potential
frequency summation
increased muscle tension that occurs when successive action potentials occur rapidly enough that the fiber has not completely relaxed from the prior twitch
treppe
a period of summation in which the strength of contraction rapidly increases as the rate of stimulation rises
“staircase effect”
unfused tetanus
maintained contraction at high stimulation rates in which muscle tension oscillates due to slight relaxations between stimuli
fused tetanus
maintained contraction at even higher stimulation rates in which no oscillations occur
muscle tone
the tautness that remains when the muscle is not actively moving a body part
tone results from
a low baseline rate of action potentials to the muscle coming from the spinal cord
a tetanically stimulated individual muscle fiber stretched to various lengths develops different
levels of tension
if a sarcomere is stretched so much that there is no overlap between actin and myosin,
no cross bridges can form (thus no tension)
if a sarcomere is stretched to the point that the amount of overlap between the myosin filament and the actin filament allows essentially all myosin heads to find binding sites on actin, then
there are maximal cross bridges pulling on actin, which means maximal tension produced
in a sarcomere, when actin filaments begin to overlap each other, this
interferes with the myosin head’s ability to find binding sites and exert force
at short sarcomere lengths, the Z lines collide with the ends of
myosin filaments and may even crumple it; resulting in tension dropping to very low levels
