Muscle fiber
basic structural unit of muscle
individual cell with multiple nuclei
made up of bundle of myofibrils
3 Layers of Extracellular CT around muscle
1. epimysium-tough outer layer, surrounds muscle belly
2. perimysium-around each fascicle (bundle of fibers), has blood vessel supply
3. endoymysium-surrounds individual fibers, location of metabolic exchange btw. fibers and capillaries
Muscle Connective Tissue
composed mostly of collagen with some elastin fibers
3 layers that are interwoven and connect either directly or indirectly to the tendon
conveys contractile force to the tendon
Sarcolemma
cell membrane of a single muscle fiber
just inside the endomysium
Sarcomere
fundamental unit within a muscle fiber
A band-dark band, contains myosin and some actin (overlap)
H Zone-within the A band, contains only myosin
M Line-mid region of A band, connects myosin chains
I Band-light band, contains only actin
Actin
thin filament
Myosin
thick filament
Myosin heavy
globular head on myosin, involved in muscle contraction
Myosin light
thinner strand part of myosin, has regulatory role
Tropomyosin
thin strand of protein, has regulatory role
Troponin
globular protein that sits on top of tropomyosin, has regulatory role
Titin
runs from center of myosin to the Z discs
helps maintain length of myosin
structural role
plays role in developing passive tension
Motor Unit
a single motor neuron and all the muscle fibers it innervates
more fibers per unit = more force production
less fibers per unit = more precision
Phases of Sliding Filament Mechanism
1. excitation
2. coupling
3. contraction ( and recharging)
4. relaxation
Excitation Phase of Sliding Filament Mechanism
-AP at motor neuron arrives at NMJ
-ACh is released at NMJ, increasing the permeability of the sarcolemma to Na
-muscle AP
-depolarization of t-tubules reaching the sarcoplasmic reticulum, which releases Ca2+ into the sarcoplasm
Coupling Phase of Sliding Filament Mechanism
-Rest: myosin connected to actin weakly; troponin-tropomyosin is in the way
-during coupling, Ca2+ binds with troponin, pulling tropomyosin away
-allows for strong binding between actin and myosin, forming a cross bridge
Contraction Phase of Sliding Filament Mechanism
-during coupling, ATP is broken down into ADP + P + energy
-the energy that is released is used for cross bridge movement (contraction)
-to keep the process going, you must have Ca2+ and ATP available
-recharging: process of going from contraction back to
Relaxation Phase of Sliding Filament Mechanism
-absence of impulse at NMJ causes Ca2+ to be pumped back into the sarcoplasmic reticulum
-tropomyosin moves back to cover the actin-binding sites
-cross bridges are broken and contraction ceases
Concentric Contractions
Involves shortening of muscle
when force muscle > force resistance
actin filaments are pulled toward center of sarcomere
Types: gravity neutral, against gravity,with gravity but faster than gravity,with gravity and against resistance
Eccentric Contractions
involves lengthening of muscle
always involves a deceleration
when force resistance > force muscle
actin filaments are pulled away from center of sarcomere
ex: slowing down a follow through in sport
Isometric Contractions
no change in muscle length
force muscle = force resistance
Agonist
the mover
actively produces desired motion
may be concentric, eccentric, or isometric
Antagonist
oppose action the agonist
usually passively elongates the opposite muscle to permit the desired motion
Synergist
muscles that cooperate to perform the desired motion
Co-Contraction
simultaneous contraction of the agonist and antagonist
may enhance stability
ex: squat-co contraction of quads and hamstrings
Force-Couple
two or more muscles simultaneously produce forces in different linear directions to cause a rotation in the same direction
ex: anterior pelvic tilt-back extensors and hip flexors
posterior pelvic tilt-abdominals and hip extensors
Passive Insufficiency
inability to complete a ROM (passively) because the two joint antagonistic muscles cannot be elongated further
ex: knee extension ROM limited by tight hamstring
Tenodesis Grasp
-example of passive insufficiency
-when patient actively extends the wrist, the fingers automatically flex bc the flexors are stretched over the wrist and fingers
-when patient passively flexes wrist, fingers extend and hand opens for opposite reason. Fin
Fusiform Muscles
Parallel fibers
strap-type muscles
large ROM
ex: biceps brachii, sartorius
Pennate Muscles
fibers are oblique at an angle to the central tendon
large force
ex: rectus femoris, gastrocnemius
Physiological Cross Sectional Area
estimates the # of fibers in a muscle
measured perpendicular to fiber length
pennate muscles fit more fibers in a given PCSA
strength is related to # of fibers
therefore pennate muscles produce greater max force
Angle of Pull
fusiform muscles transmits full (100%) force to the tendon
pennate muscles transmit less than 100% depending on angle of fibers
Active Insufficiency
the inability of a two-joint muscle to produce maximum active tension because it has been placed in a shortened position
ex: cannot open jar with both wrist and fingers flexed
grip strength will be higher with wrist in slight extension
Active Tension
developed by muscle contractile elements
Passive Tension
developed by non contractile elements: tendons, connective tissue, titin
-includes parallel elastic component and series elastic component
Parallel elastic components
tissues that surround or lie in parallel with the active proteins
extracellular CT, structural proteins
Series elastic components
tissues that lie in series with active proteins
tendons, large structural proteins--titin
Passive Length Tension Relationship
passive tension (force) is greater when muscle is lengthened and stretched farther
Active Length Tension Relationship
optimal active tension (force) is produced when muscle is near 100% of resting length
-not too short or too long
Total Muscle Force
total force = passive tension + active tension
passive tension is more important at long muscle lengths where active tension is less-contributes to high eccentric muscle forces
Stored Passive Tension
-when muscle is stretched, tension is stored like a spring
-helps prevent the muscle from being damaged during maximal elongation
-is potential energy that is used during subsequent concentric contraction
Stretch Shortening Cycle
passive tension stored during rapid is stretch is "used" during a subsequent concentric contraction and increases the magnitude of the concentric contraction
ex: wind up phase, plyometrics
Torque Line of Pull
torque potential is largest when a muscle's line of action is at a right angle to the bony lever
Contraction Velocity
concentric-inverse relationship between velocity and force
eccentric-direct relationship between velocity and force
isometric-velocity is 0, higher force than concentric
Manual Muscle Testing
tests isometric contractions
Dynamometers
tests concentric contraction
measures strength throughout ROM and at different speeds of motion
All-or-None Phenomenon
when a motor neuron is stimulated all the fibers in the motor unit contract or none of the fibers contract
Size Principle of Motor Recruitment
smaller motor units are recruited first (they have a lower recruitment threshold)
as muscle force increases, larger motor unis are recruited
ensures "smooth" progression of muscle action
Type I muscle fibers
slow oxidative fibers
small motor units
slow twitch response-small amplitude, long duration
low force capability
fatigue resistant
Type IIB muscle fibers
fast glycolytic fibers
large motor units
fast twitch response-large amplitude, fast duration
high force capability
fatigue easily
have more titin-can produce more passive tension and therefore more total force