Lecture 8 Flashcards
What is the earliest part in muscle stimulation where there is no change in sarcomere length?
Latent period
The Latent Period is everything between
The formation of a graded potential in the sarcolemma of muscle cell to the power stroke of the myosin
The end of the latent period is marked by the
First change in force
Muscle contracts and sarcomeres shorten during the
Contraction period
Relaxation Period is when the
Muscle relaxes and sarcomere returns to its relaxed length
Why does the muscle relax?
Acetylcholinesterase breaks down acetylcholine and force decreases during the Relaxation Period
The amount of force generated by a muscle during contraction is the result of the
Number of activated motor units
Motor Units consist of
The motor neuron and any muscle cells that neurons are connected to it
A large muscle would have
Many motor units
A small muscle has
Fewer motor units
In Isotonic Contraction, the force generated by the muscle is
Greater than the load
Isotonic Contraction results in
Muscle shortening
In Isotonic Contraction, the force generated by muscle is always equal to
The load trying to be moved
What is Isometric Contraction?
Load is greater than the force generated by the muscle and muscle does not shorten (because the object is too heavy)
What happens in Isometric Contraction?
Tension develops in the muscle as the myosin tries to pull on the actin, but sarcomeres do not shorten because the muscle is too weak to move the load
The force that a muscle generates also depends on
How frequently the muscle is stimulated by action potentials from the nervous system
Multiple APs arriving at the muscle in quick succession can
Activate more motor units than a single AP would, resulting in contractions that generate more force
Summation is when
Muscle is restimulated by a second AP before it fully relaxes, generating more force
Tetanus is when
A muscle is stimulated so rapidly that it does not relax at all
Summation and Tetanus occur because
Each additional AP releases new Calcium ions from the Sarcoplasmic Reticulum, which in turn increases the number of actin-myosin cross bridges and powerstrokes to generate more force
Contraction Velocity describes
How long it takes for the muscle to go from its relaxed length to contracted length
Heavier loads require
More motor units to be activated, which takes more time, slowing contraction velocity
