Muscle 5 Flashcards
The force developed by a muscle fibre is increased by…
summation of multiple twitches
motor unit
a single motor neuron and all the muscle fibres it innervates
motor neuron pool
the group of all motor neurons innervating a single muscle
Weak stimulus to motor neuron pool recruits…..first
smallest motor neurons
small-diameter motor neuron
Rm is high and conduction velocity is low (slow-twitch, type I)
large-diameter motor neuron
Rm is low and conduction velocity is high (fast-twitch type II)
size principle
all muscle fibres within one motor unit are the same type
small motors units
small motor neurons; slow-oxidative
intermediate motor units
intermediate size motor neurons; fast-oxidative-glycolytic
large motor units
large morot neurons; fast glycolytic
Asynchronous recruitment
the CNS modulates firing rates of upper motor neurons to allow different motor units to maintain contraction in order to prevent fatigue
tension
the force tending to pull the attachment points of a muscle toward one another
isotonic contraction
the muscle contracts, shortens, and creates force to generate movement
isometric contraction
muscle contracts but does not shorten; creates force without moving a load
two kinds of isotonic contractions
concentric and eccentric
concentric contraction
muscle shortens while generating force
eccentric contraction
muscle lengthens with generating force
eccentric contraction acts to….
decelerate the joint at the end of a movement
How do the sarcomeres shorten during isometric contraction without the muscle changing length?
elastic elements in tendons and connective tissue around muscle fibres
myosatellite cells
involved in muscle repair and may form new muscle fibres (occurs in development)
satellite cells
in response to an injury, become activated and proliferate
Two proposed mechanisms by which muscle mass may be increased
hypertrophy and hyperplasia
hypertrophy
When skeletal muscle is subjected to an overload stimulus, it causes perturbations in muscle fibres and the related extracellular matrix
hypertrophy leads to..
-increase in size and number contractile proteins, sarcomeres, sarcoplasmic storage
sarcopenia
muscle loss due to age
cachexia
weakness and/or wasting due to chronic disease
