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The muscular system, Sliding filament theory of muscle contraction,…
The muscular system
Cardiac muscles: Cardiac muscle is only found in the heart
Cardiac muscle consists of branching, striated cells that interconnect in three-dimensional networks. Cardiac muscle is self-exciting (involuntary). Complex membrane junctions, called intercalated discs, join cells and
transmit the force of contraction from one cell to the next
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Pectoralis major: named for size and location; large size, located in
chest
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The cytoplasm of the distal end of the motor neuron contains numerous
mitochondria and synaptic vesicles storing neurotransmitters
Extensor digitorum: named for action; extends digits (fingers, toes)
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skeletal muscles: The Body contains over 600 skeletal muscles. This connective tissue extends beyond the ends of the muscle,
and gives rise to tendons that are fused to the peritoneum of bones. Skeletal muscles also have Layers of dense connective tissue, called fascia, surround and separate each muscle
Smooth muscles: Smooth muscle cells are elongated with tapered ends, lack striations (look
“smooth”), and have a relatively undeveloped sarcoplasmic reticulum. They Contain thick and thin filaments, but they are arranged more randomly
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Skeletal Muscle Fibers:
Each muscle fiber is a single, long, cylindrical muscle cell
Biceps brachii: named for number of attachments and location; has 2
origins/heads, and is found in the arm (brachium)
Sternocleidomastoid: named for attachments; attaches to sternum,
clavicle, and mastoid process
External oblique: named for location and direction of fibers; located
near outside of body, and fibers run at a slant
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Myofibrils are made up of many units called sarcomeres, joined end-to-end
I bands (light bands) are made up of actin filaments, which are anchored
to the Z lines
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The neuron communicates with the muscle fiber by way of chemicals called neurotransmitters, which are released at the synapse
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In the center of the A band is the H zone, which consists of myosin
filaments only
The M line, in the center of the H zone, consists of proteins that hold the
myosin filaments in place
The muscle fiber membrane in this area contains a specialized region
called the motor end plate, in which the sarcolemma is tightly folded
Each skeletal muscle fiber (cell) is functionally (not physically)
connected to the axon of a motor neuron, creating a synapse
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The neurotransmitters diffuse across the cleft, bind to the motor end
plate, and stimulate the muscle fiber to contract
When an electrical impulse reaches the end of the axon of a motor
neuron, synaptic vesicles release neurotransmitter into the synaptic cleft, the gap between the membranes of the neuron and muscle fiber
The head then releases, and attaches to the next binding site on the actin,
pulling this site toward the center As this occurs again and again, the filaments increase their overlap, and the sarcomere shortens from both ends
This binding causes the head to bend, pulling on the actin filament, and moving
it toward the center of the sarcomere
According to the sliding filament model of muscle contraction, during muscle
contraction, a myosin head attaches to a binding site on the actin filament,forming a cross-bridge
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The sarcolemma is stimulated. An implulse travels over
the surface of the muscle fiber and deep into the fiber through the transverse tubules.
The impulse reaches the sarcoplasmic reticulum, and
calcium channels open.
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Cross-bridges form, linking thin and thick filaments.
Calcium ions diffuse from the sarcoplasmic reticulum
into the cytosol and bind to troponin molecules.
The perimysium extends inward from the epimysium; it surrounds
bundles of skeletal muscle fibers, called fascicles, within each muscle
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Fascia blends with the epimysium, the layer of connective tissue
around each skeletal muscle
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