Twitch=
contractile response of a single muscle fiber to a muscle fiber to a muscle impulse
Threshold stimulus
minimal strength required to cause contraction
Latent period
brief delay between time of stimulation and the beginning of contraction (2 msec)
Period of contraction
muscle contracts reaction time is 40 msec
Period of relaxation
muscle relaxes reaction time is 50 msec
Refractory period
period of lost excitability (time in which you cant make another action potential) reaction time is 5 msec
Myogram=
recording of a twitch contraction
All or none principle
- whole muscle fiber contracts or not (no halfsies)
- each muscle fiber generates same force in a contraction
-whole muscles though, have varying size of contractions
Strength of Contraction (reasons why some muscles are stronger than others)
- Frequency of stimulation of individual fiber
- Number of muscle fibers making up whole muscle
Summation
- application of a series of stimuli of increasing frequency
- complete relaxation cannot occur combining individual twitches
- contraction becomes sustained
Tetanic contraction
- frequency of stimulation occurs often enough that partial relaxation cannot even take place
- most common and used for usual body movements
- also accounts for muscle tone
- small, sustained contractions not causing body movements
- Mostly helps to maintain posture
What are the different types of contractions
- Isotonic
- Eccentric
- Isometric
Isotonic (def)
muscle contracts and changes length
Isotonic
- Most common type moving bones
- Muscle tension is constant and muscle shortens
Eccentric (def)
“lengthening” contraction
Eccentric
- type of isotonic
- cross bridges are not generating enough force to shorten the muscle (resistance is stronger)
- tension is not constant
Isometric (def)
muscle contracts but does not change length
Isometric
- no body movement, just stabilizing positions
- pushing on a wall
- tension is constant
Cramps
= painful spasmodic contraction
- caused by prolonged physical activity or prolonged cold
- insufficient amount of ATP/ lactic acid build up
- Ca^2+ does not return properly to the sarcoplasmic reticulum prevents muscle from relaxing
Muscle strain/ Pull/ Tear
- overstretched of muscle fibers causing tearing
- can also tear fascia
- severity is determined by tear and amount of lost usage
Atrophy
= muscle fibers decrease in size
- due to extreme inactivity
- can decrease muscle strength by 5% each day
- eventually is replaced by fibrous connective tissue
and cannot be rehabilitated -> muscle cannot divide
- takes about 2 years immobilization
Rigor Mortis
= few hours after death
- loss of ATP (because u ded) and excessive leakage of Ca^2+ -> SR no longer controlling flow
- cross bridges do not let go of actin causing stiffening
- can continue for 72 hours until tissue starts to decompose
