skeletal, cardiac, smooth
3 types of muscle tissue
Excitability
Responsiveness to chemical signals, stretch, and electrical changes across the plasma membrane
Conductivity
Local electrical change triggers a wave of excitation that travels along the muscle fiber
Contractility
Shortens when stimulated
Extensibility
Capable of being stretched between contractions
Elasticity
Returns to its original rest length after being stretched
Skeletal Muscle
voluntary, striated muscle usually attached to bones
Striations
alternating light and dark transverse bands
Muscle Cell
a muscle fiber (myofiber) as long as 30 cm
Endomysium
Connective tissue surrounding a muscle fiber
Perimysium
Connective tissue surrounding a muscle fascicle
Epimysium
connective tissue surrounding entire muscle
Tendons
are attachments between muscle and bone matrix
Tendons
Continuous with collagen fibers of tendons
In turn, with connective tissue of bone matrix
Collagen
Stretches slightly under tension and recoils when released.
Resists excessive stretching and protects muscle from injury.
Returns muscle to its resting length.
Contributes to power output and muscle efficiency.
Sarcolemma
plasma membrane of a muscle fiber
Sarcoplasm
cytoplasm of a muscle fiber
myofibrils
long protein cords occupying most of sarcoplasm
Glycogen
carbohydrate stored to provide energy for exercise
Myoglobin
red pigment; provides some oxygen needed for muscle activity
multiple nuclei
flattened nuclei pressed against the inside of the sarcolemma
Myoblasts
stem cells that fused to form each muscle fiber early in development
Satellite cells
unspecialized myoblasts remaining between the muscle fiber and endomysium.
Play a role in regeneration of damaged skeletal muscle tissue.
Mitochondria
packed into spaces between myofibrils
Nucleus
A
houses DNA that codes for protein filaments
Muscle Fiber
B
a single muscle cell
Endomysium
C
covers individual muscle fibers
Striations
D
dark A bands and light I bands
sarcoplasmic reticulum (SR)
smooth ER that forms a network around each myofibril
terminal cisternae
dilated end-sacs of SR which cross the muscle fiber from one side to the other
SR
Acts as a calcium reservoir; it releases calcium through channels to activate contraction
T tubules
tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side
Triad
a T tubule and two terminal cisternae associated with it
Thick filaments
made of several hundred myosin molecules.
Each molecule shaped like a golf club:
Two chains intertwined to form a shaft-like tail
Double globular head
Thick filament composition
Heads directed outward in a helical array around the bundle.
Heads on one half of the thick filament angle to the left, while heads on other half angle to the right. Bare zone with no heads in the middle
thin filaments
String of globular (G) actin subunits each with an active site that can bind to head of myosin molecule
fibrous (F) actin
two intertwined strands
Troponin
small, calcium-binding protein on each tropomyosin molecule
Tropomyosin
each blocking six or seven active sites on G actin subunits
elastic filaments
Run through core of thin filament and anchor it to Z disc and M line
Help stabilize and position the thick filament
Prevent overstretching and provide recoil
Titin
huge, springy protein
myosin and actin
contractile proteins
tropomyosin and troponin
regulatory proteins bound to actin
regulatory proteins
Act like a switch that determines when fiber can (and cannot) contract
Contraction activated by release of calcium into Sarcoplasm and its binding to troponin
Troponin changes shape and moves tropomyosin off the active sites on actin
contractile proteins
do the work of contraction
Dystrophin
Links actin in outermost myofilaments to membrane proteins that link to endomysium
Dystrophin
Transfers forces of muscle contraction to connective tissue ultimately leading to tendon
Dystrophin
Genetic defects produce disabling disease muscular dystrophy
A bands (anisotropic)
Dark Bands
I bands (isotropic)
Light Bands
H band
not as dark; middle of A band; thick filaments only
M Line
middle of H band
Z disc
provides anchorage for thin filaments and elastic filaments. Bisects I band.
Sarcomere
segment from Z disc to Z disc
Functional contractile unit of muscle fiber
Sarcomeres
Muscle cells shorten because their individual __________ shorten
nerve
Skeletal muscle never contracts unless stimulated by a _____
denervation atrophy
shrinkage of paralyzed muscle when nerve remains disconnected
paralyzed
If nerve connections are severed or poisoned, a muscle is__________
somatic motor neurons
Nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles
Motor neuron
Each muscle fiber is supplied by only one __________
Motor Unit
one nerve fiber and all the muscle fibers innervated by it
muscle fibers of one motor unit
-Dispersed throughout muscle
-Contract in unison
-Produce weak contraction over wide area
-Provide ability to sustain long-term contraction as motor units take turns contracting
-Effective contraction usually requires contraction of several motor units at
200
Average motor unit contains ___ muscle fibers
Small motor unit
fine degree of control
Three to six muscle fibers per neuron
Eye and hand muscles
Large motor unit
more strength than control
Powerful contractions supplied by large motor units with hundreds of fibers
Gastrocnemius of calf has 1,000 muscle fibers per neuron
synapse
point where a nerve fiber meets its target cell
neuromuscular junction
when target cell is a muscle fiber
terminal branch
Each ___________ of the nerve fiber within the NMJ forms separate synapse with the muscle fiber
Synaptic Knob
swollen end of nerve fiber
Contains synaptic vesicles with acetylcholine (ACh)
synaptic cleft
gap between synaptic knob and sarcolemma
Schwann Cells
envelops and isolates NMJ
Excocytosis
Nerve impulse causes synaptic vesicles to undergo ________ releasing ACh into synaptic cleft
ACh recpetor
proteins incorporated into its membrane
Junctional Folds
beneath synaptic knob increase surface area holding ACh receptors
myasthenia gravis
Lack of receptors causes weakness in
Basal Lamina
thin layer of collagen and glycoprotein separating Schwann cell and muscle cell from surrounding tissues
AChE
Contains ______ that breaks down Ach, allowing for relaxation
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