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Muscular System

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Han Nguyen

on 10 March 2011

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Transcript of Muscular System

Muscular System 3 Types of muscle:
1. Skeletal
2. Cardiac
3. Smooth Overall Characteristics of Muscles: 1. Muscle cells are elongated.
muscle cell = mucle fiber Function of Muscles: 2. 2. Contraction is due to microfilaments.
2 Microfilaments: actin and myosin 3. All muscle cells share terminology
Prefix myo refers to muscle
Prefix mys refers to muscle
Prefix sarco refers to flesh 1. Movement
2. Posture
3. Stabilize joints
4. Generate heat Characteristics:
1. attached by tendons to bones
2. multinucleate
3. striated
4. voluntary
5. surrounded and bundled by connective tissue wrappings Endomysium - CT sheath around a single muscle fiber Perimysium - membrane around a fascicle Fascicle - bundle of fibers Epimysium - covers entire skeletal muscle Epimysium blends into 2 types of connective tissue attachments:
1. Tendon - cord-like structure
2. Aponeuroses - sheet-like structure Sites of muscle attachment:
1. bones
2. cartilages
3. connective tissue coverings Characteristics:
1. no striations
2. spindle-shaped
3. single nucleus
4. involuntary
5. located in walls of hollow organs and vessels Characteristics:
1. has striations
2. located in heart
3. single nucleus
4. involuntary
5. cells joined at intercalated discs Microscopic anatomy of Skeletal Muscle Cells are multinucleate. Nuclei are pushed aside by myofibrils and are located just beneath the sarcolemma. specialized plasma membrane sarcoplasmic reticulum - specialized smooth endoplasmic reticulum bundle of myofilaments (actin) & (myosin) within the cell Myofilaments are arranged to give distinct bands (striations): I band - light band; distance between thick filaments (myosin) Z disc - midline of I band - ends of a sarcomere A band - dark band; total length of thick filaments (myosin) H zone - lighter central area of A band; distance between thin filaments (actin) M line - center of H zone Sarcomere - contractile unit of a mucle fiber Each myofibril is composed of bundles microfilaments:
myosin - thick filaments
actin - thin filaments Myosin filaments have heads called cross bridges when they link actin and myosin together during contraction Properties of Skeletal Muscle Activity
Irritability - ability to receive and respond to stimuli
Contractility - ability to shorten Nerve Stimulus to Muscles Skeletal muscles must be stimulated by a nerve impulse to contract A nerve cell may stimulate a few muscle cells or hundreds of them, depending on the particular muscle and the work it does. The mucles cells that are being stimulated is called a motor unit. Neuromuscular junction - association site of nerve and muscle Parts:
1. one neuron (nerve cell)
2. muscle cells stimulated by that neuron Synaptic cleft - gap between nerve and muscle
Area between nerve & muscle is filled with interstitial fluid Transmission of Nerve Impulse to Muscle Neurotransmitter - chemical released by nerve axon terminal upon arrival of nerve impulse The neurotransmitter for skeletal muscle is acetylcholine (ACh) Neurotransmitter attaches to receptors on the sarcolemma & cases it to become permeable to sodium (Na). Sodium rushing into the cell generates an action potential (electrical current) The action potential travels over the entire surface of the sarcolemma and stimulates the sarcoplasmic reticulum to release calcium (Ca). Calcium initiates "filament sliding" and the result is a muscle contraction. Once started, muscle contraction cannot be stopped (all or none). The cell is returned to its resting state through the sodium potassium pump (Na-K). Sliding Filament Theory of Muscle Contraction The release of calcium which was caused by the action potential causes the crossbridges of myosin to attach to actin and sliding begins. Each cross bridge attaches & detaches several times during a contraction, generating tension that pulls the actin toward the center of the saromere This continued action causes the sliding of the myosin along actin The result is that the muscle is shortened Muscles and Body Movements Muscles are attached to at least two points
1. Origin - attachment to a non-movable bone
2. Insertion - attachment to a movable bone During contraction, the insertion moves toward the origin Types of ordinary body movements: 1. Flexion - decrease the angle of 2 articulating bones. 2. Extension - increase the angle of 2 articulating bones 3. Rotation - bone rotates 4. Abduction - limb away from body 5. Adduction - limb toward body 6. Circumduction - limb moves in a circle Special movements - occurs only in a few joints: 1. Dorsiflexion - upward movement of ankle 2. Plantar flexion - downward movement of ankle 3. Inversion - turn sole of foot medial 4. Eversion - turn sole of foot laterally 5. Supination - palm is anterior 6. Pronation - palm is posterior 7. Opposition - thumb touches finger Types of muscles: 1. Prime mover - muscle with the major responsibility of movment;
it is active, contracted 2. Antagonist - opposes or reverses prime mover; relaxed and stretched 3. Synergist - help prime movers 4. Fixator - stabilizes the origin of a prime mover Criteria in Naming of Skeletal Muscles: 1. Direction of fibers 2. Size of muscle 3. Location of muscle 4. Number of origins 5. Location of origin and insertion 6. Shape of muscle 7. Action of muscle
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