Skeletal Muscle Fiber Structures & Sarcomere
axon terminal or synaptic bulb
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muscle myelin
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skeletal muscle mitochondria
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Actin
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.
Troponin
A globular protein that ssociated with tropomyosin as part of the thin filament of the sarcomere. Troponin binds Ca2+, which causes the conformaiton change in tropomyosin required to expose the myosin-binding sites on actin and initiate muscle contraction.
Tropomyosin
A helical protein that winds around actin helices in skeletal and cardiac muscle cells to form the thin filament of the sarcomere. In the absence of Ca2+, tropomyosin covers the myosin-binding sites on actin and prevents muscle contraction. When calcium is present, a conformation change in tropomyosin occurs so that the myosin-binding sites are exposed and muscle contraction can occur.
axon
A long, thin fiber that transmits signals away from the neuron cell body to other neurons, or to muscles or glands
Myofibril
A threadlike structure, extending longitudinally through a muscle fiber (cell) consisting mainly of think filaments (myosin) and thin filaments (actin, troponin, and tropomyosin)
H zone(s)
Are areas in the center of the A bands containing only thick filaments Contain myosin only Zones shrink during contraction
Troponin
At rest, what holds the tropomyosin molecule in place?
endomysium
Connective tissue surrounding a muscle fiber
Transverse (T) tubule
Folds of Sarcolemma that fold inwards across the muscle fibre and stick into the Sarcoplasm. These aid in spreading electrical impulses
I band(s)
Light bands containing thin filaments only and extend from the A Band of one sarcomere to the A Band of the next sarcomere.
M Line
Middle of sarcomere, holds thick filament in place
M line
Middle of sarcomere, holds thick filament in place midline of myosin fibers
skeletal muscle nucleus
Multiple nuclei in one cell (multinucleate) Dark structure inside endomysium
Myosin
The molecule on which ATPase (enzyme that breaks down ATP into ADP) is found.
motor end plate
The portion of the cell membrane at the neuromusclar junction; essentially the postsynaptic membrane at the synapse.
I band
The reginon of the sarcomere made up only of thin filaments. The I band is bisected by a Z line. I bands alternate with A bands to give skeletal and cardiac muscle a striated appearance. I bands get shorter (and may disappear completely) during muscle contraction.
H Zone
The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction.
H Zone & I Band
The region(s) of the sarcomere that shorten during muscle contraction.
sarcoplasmic reticulum
The smooth ER of a muscle cell, enlarged and specialized to act as a Ca2+ reservoir. The SR winds around each myofibril in the muscle cell.
Sarcomere
The unit of muscle contraction. Sarcomeres are bounded by Z lins, to which thin filaments attach. Thick filaments are found in the center of the sarcomere, overlapped by thin filaments over one another during contraction reduces the distance between Z lines, shortening the sarcomere.
Thin Filaments
These filaments are composed of actin, troponin, and tropomyosin.
synaptic vesicles
Tiny pouches or sacs in the axon terminals that contain neurotransmitters
H Zone
What is the area within that has only thick filament?
A band
What is the dark area that has both thick and thin filament?
Z disc
What is the end line for each sarcomere?
I Band
What is the light area that has only thin filament?
M line
What is the protein line that stabilize and support thick filament?
Troponin
Which molecule does calcium bind to?
Actin
Which molecule has an active site to which myosin heads bind?
motor neuron
a neuron that sends an impulse to a muscle or gland, causing the muscle or gland to react (ACh released by a somatic motor fiber stimulates a skeletal muscle Acetylcholinesterase (AchE)= Responsible for degrading ACh and stopping the stimulation of the muscle fiber)
Thin Filiments
composed of: 3 proten molecules (actin, troponin, tropmyosin made up of primarily actin
M line(s)
connects thick filaments in a sarcomere; also run perpendicular to the long axis
sarcomere(s)
contractile units within myofibrils, the smallest contractile unit of a muscle
A band(s)
dark areas, contain myosin and actin overlapping
terminal cisternae
dilated end-sacs of SR which cross the muscle fiber from one side to the other
myofibril
long protein cords that occupy sarcoplasm
Thick Filiments
made up of primarily myosin
sarcolemma
plasma membrane of a muscle fiber
Z Disc
provides anchorage for thin filaments and elastic filaments Separates the sarcomeres from each other A protein disc to which thin filaments and elastic filaments are anchored at each end of a sarcomere; appears as a narrow dark line in the middle of the I band.
synaptic cleft
tiny gap between synaptic knob and muscle sarcolemma
sarcoplasm
Cytoplasm of a muscle fiber/cell
triad
The T Tubule and two terminal cisternae associated with it
A Band
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
A band
The band of the sarcomere that extends the full length of the thick filament. The A band includes regions of thick and thin filament overlap, as well as a region of thick filament only. A bands alternate with I bands to give skeletal and cardiac muscle a striated apperance. The A band does not shorten during muscle contraction.
neuromuscular junction
The functional connection between the distal end of a nerve fiber and the middle of a muscle fiber ACh released, binds to ACh receptors ACh released by a somatic motor fiber stimulates a skeletal muscle
Z disc
Separates the sarcomeres from each other A protein disc to which thin filaments and elastic filaments are anchored at each end of a sarcomere; appears as a narrow dark line in the middle of the I band.
motor neuron
Somatic Motor Fibers: lead to the skeletal muscles