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Phys. Skeletal muscle contraction
skeletal muscle contraction
27
Physiology
Graduate
09/03/2010

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Term
a muscle twitch is the response of a muscle to a single, brief ___ ___.
Definition
- threshold stimulus
Term
3 phases of a muscle twitch are:
Definition
- latent period- first few milliseconds after stimulation when excitation contraction coupling is taking place
- contraction period- cross bridges actively form and muscle shortens
- period of relaxation- calcium is reabsorbed into SR and muscle tension goes to 0
Term
for the extraocular eye muscle the time from stimulation to peak contraction is ___ msec. for the gastrocnemius it is __ msec. And for the soleus it is __ mssec.
Definition
- 8 msec
- 40 msec
- 90 msec
Term
graded muscle responses:
Definition
- variations in degree of muscle contraction
- required for proper control of skeletal movement
Term
muscle responses are graded by:
Definition
Changing the frequency of stimulation
Changing the strength of the stimulus
Term
a single stimulus results in a single contractile response called a ___
Definition
twitch
Term
frequently delivered stimuli without complete relaxation b/w results in :
Definition
wave summation- increased contractile force
Term
more rapidlly delivered stimuli result in ___ ___. If stimuli are given quick enough you can get ___.
Definition
- incomplete tetanus
- complete tetanus
Term
Staircase effect:
Definition
increased contraction in response to multiple stimuli of same strength

- contraction increases b/c more calcium is available in the sarcoplasm
- muscle enzyme systems become more efficient b/c increased heat as muscle contracts

see slide 79 and 80 skeletal muscle lecture and know picture
Term
the force exerted by a contracting muscle on an object is referred to as:
Definition
tension
Term
___ occurs when the tension generated by cross bridging exceeds the forces opposing this.
Definition
shortening
Term
passive tension:
Definition
- force you can measure in a relaxed muscle
- due to amount of stretch in muscle
Term
muscle tone
Definition
- relaxed msucles are almost always slightly contracted due to spinal reflexes activating motor units
Term
load:
Definition
- weight or reciprocal force exerted by an object on a muscle
Term
preload:
Definition
load on muscle in relaxed state prior to stimulation
Term
the greater the preload, the greater the ___ ___, and the greater the ___ ___.
Definition
- preload stretch
- passive tension
Term
afterload:
Definition
load the muscle is trying to move or work against during stimulation
Term
if a muscle has a preload, then the afterload the muscle must generate upon stimulation =
Definition
afterload= preload tension+ additional tension of the weight
Term
look at slide 83 on skeletal muscle lecture for preload and afterload diagram
Definition
Term
With an isotonic contraction, the ___ stays constant but the muscle may __ or ___ during the contraction. this is common where?
Definition
- tension
- shorten
- lengthen
- finger and hand movements
Term
concentric isotonic contraction:
Definition
- the tension stays constant
- the muscle shortens and does work
Term
eccentric isotonic contractions:
Definition
- the tension is constant
- the muscle contracts as it lengthens
- example= lowering weight during curls, putting down book, walking down hill, skiing
Term
with eccentric contraction you get delayed soreness and then ____.
Definition
hypertrophy
Term
isometric contraction:
Definition
- tension increases to muscle capacity but the muscle does not shorten or lengthen
Term
isometric contraction occurs if the ___ is greater than the ___ the muscle is able to develop.
Definition
- load
- tension
Term
no work is done with isometric contraction. these contractions are used to ___ and __ force. give example:
Definition
- generate
- maintain
- postural muscles maintain a constant tension without changing length
Term
Most contractions are:
Definition
- a mixture b/w iosmetric and isotonic
- first have an isometric contraction until enough force is generated, then you have an isotonic contraction where muscle is shortening at a constant force
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