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