The number of cross-bridges formed between actin and myosin determines the amount of tension produced by a muscle. The length of a sarcomere is optimal when the zone of overlap between thin and thick filaments is greatest. Muscles that are stretched or compressed too greatly do not produce maximal amounts of power. A motor unit is formed by a motor neuron and all of the muscle fibers that are innervated by that same motor neuron. A single contraction is called a twitch. A muscle twitch has a latent period, a contraction phase, and a relaxation phase. A graded muscle response allows variation in muscle tension. Summation occurs as successive stimuli are added together to produce a stronger muscle contraction. Tetanus is the fusion of contractions to produce a continuous contraction. Increasing the number of motor neurons involved increases the amount of motor units activated in a muscle, which is called recruitment. Muscle tone is the constant low-level contractions that allow for posture and stability.
concentric contraction
muscle contraction that shortens the muscle to move a load
contraction phase
twitch contraction phase when tension increases
eccentric contraction
muscle contraction that lengthens the muscle as the tension is diminished
graded muscle response
modification of contraction strength
hypertonia
abnormally high muscle tone
hypotonia
abnormally low muscle tone caused by the absence of low-level contractions
isometric contraction
muscle contraction that occurs with no change in muscle length
isotonic contraction
muscle contraction that involves changes in muscle length
latent period
the time when a twitch does not produce contraction
motor unit
motor neuron and the group of muscle fibers it innervates
muscle tension
force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions
muscle tone
low levels of muscle contraction that occur when a muscle is not producing movement
myogram
instrument used to measure twitch tension
recruitment
increase in the number of motor units involved in contraction
relaxation phase
period after twitch contraction when tension decreases
tetanus
a continuous fused contraction
treppe
stepwise increase in contraction tension
twitch
single contraction produced by one action potential
wave summation
addition of successive neural stimuli to produce greater contraction
1. During which phase of a twitch in a muscle fiber is tension the greatest?
A) resting phase
B) repolarization phase
C) contraction phase
D) relaxation phase
C
1. Why does a motor unit of the eye have few muscle fibers compared to a motor unit of the leg?
Eyes require fine movements and a high degree of control, which is permitted by having fewer muscle fibers associated with a neuron.
2. What factors contribute to the amount of tension produced in an individual muscle fiber?
The length, size and types of muscle fiber and the frequency of neural stimulation contribute to the amount of tension produced in an individual muscle fiber.