Chapter 3 - Muscle Flashcards
fusiform muscle
fibers running parallel to each other and the central tendon
pennate muscle
approach central tendon obliquely
- more muscle fibers
- may be unipennate, bipennate, multipennate
muscle fiber
structural unit of muscle
- individual cell with multiple nuclei
- cell is surrounded by connective tissue(endomysium)
epimysium
surrounds muscle belly(bunches of fascicles)
- tightly woven collagen bundles highly resistive to stretch
perimysium
beneath the epimysium
- surrounds fascicles = bunch of muscle fibers together
- provides conduit for vessels and nerves
endomysium
surrounds individual muscle fibers
- partly connected to perimysium
- connections to muscle fibers allow for transmission of force to tendon
physiologic cross-sectional area
amount of contractile protein available to generate force
- maximal force production is proportional to the sum of the cross-sectional area of all the fibers
- increase area = increase max force
pennation angle
angle of orientation between fiber and tendon
- if greater than zero, then less from the muscle is transmitted to tendon
- can produce greater max force than fusiform muscles of similar size(fit more fibers)
elasticity
temporarily stores part of the energy used to create the stretch
- helps prevent injury during maximal elongation
viscosity
rate-dependent resistance encountered between surfaces of adjacent fluid-like tissues
muscle ideal resting length
length that allows the greatest number of crossbridges and therefore the greatest potential force
- as the sarcomere is lengthened or shortened from resting length, number of potential crossbridges decreases which yields less force production with max muscle activation
total length-tension curve
combines the active and passive length-tension curves
- allows for a large range of muscle force over a wide range of muscle length
- at shortened lengths, active force dominates
- passive tension begins to contribute as muscle is stretched beyond resting length
- passive tension dominates at end range of stretch
isometric state
there is no movement
- internal torque = external torque
- static state
max effort concentric activation
muscle force is inversely proportional to the velocity of muscle shortening
max effort eccentric activation
muscle force is directly proportional to the velocity of muscle lengthening
motor unit
the alpha motor neuron and all muscle fibers innervated by it
- must first recruit the motor neuron then select rate of sequential activation
- smaller motor neurons are recruited first, then bigger
small motoneurons(SO)
twitch responses long in duration and low in amplitude
- slow to respond to a stimuli
- oxidative
- show relatively little fatigue
large motoneurons(FF or FG)
twitch responses brief in duration and high in amplitude
- fast and fatigued
- fast and glycolytic
intermediate sized motoneurons(FOG)
between slow and fast
- fast and fatigue resistant(FR)
- combined oxidative and glycolytic
rate coding
rate of excitation
- muscle fiber twitch last longer than an action potential
- subsequent action potentials can occur prior to the muscle twitch relaxing
- muscle twitches summate and generate more peak force
- motor units activated at high rates are capable of generating greater overall force than the same number of motor units activated at lower rates
fused tetanus
the greatest force level that is possible for a muscle fiber
muscle fatigue
force will decrease even though the rate of activation remains the same
- nervous system compensates for fatigue by increasing rate of activation or recruiting more motoneurons
- rest periods allow muscle to return to normal performance
- type and intensity of contraction influences rest period needed
- Rapidly fatigued = secs to minutes
- slowly fatigued = hours
central fatigue
affected by psychological factors such as sense of effort, physiological factors influencing descending pathways
- verbal encouragement may help temporarily
peripheral fatigue
neurophysiological factors at level of motoneuron
- gradual reduction in acetylcholine release
DOMS
delayed onset muscle soreness
- more severe after repeated eccentric exercise
- peaks 24-72 hours after exercise
- caused by disruption of sarcomeres and damage to cytoskeleton within and around muscle fiber
changes in muscle with strength training
neuromuscular system adapts
- plasticity
- muscle hypertrophy and increased strength(actin and myosin laid down)
- eccentric activations produce greater force and more effective in promoting muscle hypertrophy
muscle hypertrophy
results from increased protein synthesis within muscle fibers which leads to increased cross-sectional area of the whole muscle
- primary cause of increased muscle mass
- limited evidence of an increase in number of muscle fibers
- greatest in fast twitch(type 2) fibers
nervous system adaptation with strength gains
increased area of activity with cortex
- increased motor neuron excitability
- greater discharge frequency of motor units
- decreased neural inhibition
- increased muscle strength with imagery training
- increased strength in contra-lateral, non-exercised side
- strength gains due to more than just hypertrophy
isometric exercise
a muscle contraction against a load which is immovable
- muscle length remains constant
- no joint movement
- static or nonmoving contraction
- zero speed, body segment does not move
isotonic exercise
muscle contracts against a mechanical system which provides a constant load as the body segment moves against this constant load
- the load remains the same, but the tension of the muscle changes
- dynamic or moving contraction
- constant resistance
- can be varying speed
isokinetic exercise
dynamic contraction
- varying resistance
- force exerted varies according to physiological and leverage factors(joint angle)
- constant speed = speed is controlled so that the body segment moves at the same speed throughout the ROM
