Exam 3 Whole Muscle Mechanics Flashcards
Tendons and CT of muscles are
vasoelastic
Viscoelasticity
ability of material to be deformed based on forced placed on it; help determine the mechanical properties of muscles during contraction and during passive extension
Contractile component of muscle
actin-myosin cross bridges
Series elastic component of muscle
Tendon + contractile proteins
Parallel elastic component
endo, peri, epimysium
Functions of viscoelastic components
keep muscle in ready position for contraction; assist muscles in smoothly transmitting tension during contraction; assist contractile elements return to resting position; prevent passive overstretch of contractile elements; assist muscle in generating forces
Characteristics and functions of series elastic component
tendons are in “series” with muscle fibers; whent eh SEC is stretch, energy is stored similar to stretching a spring (SEC increases tension generated in whole muscle by storing energy when stretched and releasing it as recoil); SEC provides for recoil of stretched muscle tissue to aid in return to resting length (aids in tension generation during active contraction)
Characteristics and functions of Parallel elastic component
Epimysium, perimysium, endomysium are in parallel with muscle fibers: act like a spring by storing energy when stretched; for muscles stretched beyond resting length, energy stored in PEC; PEC assisted in force production in stretched muscles
Concentric contraction
Muscle shortens during contraction
Eccentric contraction
muscle lengthens during contraction
Isometric contraction
Muscle length remains the same
All contractions have an isometric component when
Starting from rest (tension generating phase of concentric/eccentric contractions)
Isometric contraction
muscle does not shorten during contraction
Isotonic contraction
Muscle shortens but tension remains the same during contraction (concentric and eccentric contractions are considered to be isotonic)
Isokinetic contraction
Muscle shortens at the same rate, but contraction force differs throughout the range of motion
Resting sarcomere length
2.0-2.25 um; point of maximal force generation of sarcomere
Actin overlaps all myosin globular heads for full cross-bridging (no more cross-bridges available to increase tension)
As sarcomere lengthens beyond 2.25um , less than maximal tension can be produced (not all cross-bridge sites are capable of being bound)
At sarcomere length of 3.6 micrometers,
no overlap of myofilaments, thus no tension can be created
As sarcomere shortens < 2.0 um
less than maximal can be produced
between 1.65-2.0 um
thin filaments overlap each other (hinders the ability of actin to “slide” over myosin
At sarcomere length of <1.65 um
The thick filament (myosin) abuts the Z-line; minimal tension can be developed as there is no “room” for filaments to slide.
Passive tension
Tension is created by connective tissue of whole muscle when muscle is stretched; stretch of SEC and PEC of the muscle is responsible for this passive tension; Tension in SEC/PEC provide tension generation for stretched muscle to make up for sub-optimal length-tension of muscle fibers; most important in two-joint muscles (e.g. hamstrings, gastrocnemius, rectus femoris)
Active tension
tension developed by contractile elements of muscle; in whole muscle, the total strength of contraction is comprised of: actin-myosin sliding filaments (active tension), tension (passive) from PEC and SEC
Force velocity relationship
The force created by a muscle is dependent on the velocity of the muscle contraction
Concentric contraction, Force velocity relationship
The velocity of a shortening contraction is inversely proportional to the load applied (force produced)
Eccentric contraction, force velocity relationship
The velocity of a lengthening contraction is directly proportional to the load applied (force produced)
Isometric contraction, force velocity relationship
when the force created by the muscle equals the load applied to the muscle, no velocity of muscle contraction
Overall force(load) velocity relationship
force generation and speed of contraction are inverse for whole muscle.
Eccentrics are slower than isometrics (eccentrics can develop more tension than isometrics)
Isometrics are slower than concentrics (isometrics can develop more tension than concentrics)
Contraction speeds and force generated:
faster eccentric contractions develop more tension than slower ones
faster concentric contractions develop less tension than slower ones
Variable rates of ______ contraction speed occurs among different types of muscles
Isometric
(e.g how quickly can a muscle fiber fully contract)
Examples: ocular muscle (rapid eye movement)
Gastrocnemius (run, jump)
Soleus (postural control)
Fast vs. Slow fibers
some muscle fibers contract rapidly following depolarization, while others are slower to contract following depolarization
Slow fibers (type I fibers)
Smaller fibers
Extensive vasculature to deliver oxygen (numerous mitochondria to aerobically create ATP)
Large amounts of myoglobin (protein similar to hemoglobin, binds oxygen and stores it until needed)
Myoglobin gives muscle red appearance (red muscle); low levels myoglobin = white muscle composed of mainly fast fibers
fast fibers (type II fibers)
larger fibers (compared to slow fibers) for increased strength of contraction
More extensive SR for rapid release of calcium
Abundance of glyolytic enzymes for fast energy release via glycolysis
Less extensive blood supply and fewer mitochondria (fast gibers are not reliant on oxygen delivery for contraction as compared to slow twitch fibers)
Fiber with slow twitch time
Slow twitch (type I)
Fiber that is highly fatigue resistant
slow twitch (type I)
Fiber with fast twitch time
fast twitch (type II)
fiber that is less fatigue resistant (more easily fatigable)
Fast twitch (type II)
intermediate twitch speed with some fatigue resistance
Fast twitch, type IIa
Fastest twitch speed with minimal fatigue resistance
Fast twitch fiber type IIb
muscle fiber type is determined by
the motoneuron that innervates it
fiber type in muscles is _____ determined
genetically
All muscle fibers of a motor unit are
of one fiber type
Muscle Fiber summation
Summation = adding of individual muscle fiber twitch contractions to increase the intensity of whole muscle contraction
Frequency summation
increasing frequency of twitch contractions to create a full tetanic contraction of muscle;
Successive twitch contractions in muscle fibers than result in whole muscle contraction (full fiber contraction),
Stimulation rate is high enough (APs from motoneuron) such that one fiber twitch contraction is not completed before the next twitch is induced
Contraction force is added and twitches are summed into one smooth contraction;
Increased rate of stimulation by motoneuron creates continued level of calcium in sarcoplasm (calcium allows for continued cross-bridge cycling)
Multiple fiber summartion
Increasing number of motor units contraction simultaneously to generate a tetanic contraction
Muscle fiber summation: motor unit recruitment
Each motorneuron synapses with a number of muscle fibers; when active, each motorneuron stimulates it’s entire group of muscle fibers (motor unit) to contract
Motor unit
A single motoneuron and all muscle fiber innervated; average MU size is 80-100 fibers per motoneuron (motor unit size varies from 2-3 fibers to 2000 muscle fibers per motorneuron)
Motorneurons innverate fibers
that are dispersed throughout the entire muscle (fibers are not all adjacent to each other but spread out throughout the muscle)
Smaller motor units create more precise control of muscle contractions and movements (e.g.s extra ocular muscles, index finger, thumb)
Larger motor units allow easy excitation of numerous fibers for more powerful contractions (e.g. gluteus maximus, quadriceps)
Size Principle of motor unit recruitment
Size of motor units affects the order of unit recruitment during muscular contractions
For weak contractions, smaller MUs are recruited first (mostly type I fibers) - allows for more precise control of weak contractions
As the force of contraction increases, larger MUs are then recruited (mostly type II fibers)
Overall MUs are activated asynchronously to sustain a smooth contraction
Muscle tone
At rest, muscles maintain a certain amount of tautness; Signals from spinal cord and muscle spindles control motorneuron excitation of muscle to maintain tone
Muscle Spindles
specialized muscle fibers that provide sensory information regarding stretching of muscle
Increased resistance to passive stretch (tone) is related to
dysfunction in the spindle-sensory system; common occurrence in CNS disorders, especially those involving the brain; also loss of descending motoneuron inhibition
Energy storage sources for contraction
ATP
Phophocreatine
Glycolysis
Aerobic Metabolism
ATP (energy storage sources for contraction)
first source used, maintains full contraction for 1-2 seconds
Phosphocreatine (creatine phosphate)
After ATP
Next energy source utilized; transfers high energy phosphate to ADP to make ATP
Creates additional 5-8 seconds of full contraction
Glycolysis (energy storage sources for contraction)
Rapid production of ATP from stored glycogen; additional 1-2 minutes of full contraction
Aerobic metabolism (energy storage sources for contraction)
sustains prolonged contractions; sustains contractions for mins. to hours.
