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Muscle Anatomy and Physiology
Chapters 9-10
40
Anatomy
Undergraduate 1
11/28/2010

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Term
Sarcolemma
Definition
Plasma membrane
Penetrates into the cell interior to form a transverse T Tubule.
Resting sarcolemma is polarized
Term
Thin Filaments
Definition
Made up of actin molecules called G actin
Term
Myosin Heads
Myosin Tails
Definition
Myosin heads are 2 small, light polypeptide chains that act as cross-bridges during contraction
Binding sites for actin thin filaments
Binding sites for ATP
ATP enzymes
Term
Thick filaments
Definition
Surrounded by a hexagonal arrangement of 6 thin filaments
Composed of myosin which is made up of a rod-like tail and 2 myosin heads(cross-bridges)
Contains 200 myosin molecules that are bundled so the tails make up the central unit and heads face outward at the opposite end
Term
G actin (Globular)
Definition
Forms a chain of long filaments called F actin which is coiled into a helix structure
Term
Troponin
Definition
A 3 subunit protein that binds to tropomyosin and functions in holding tropomyosin in place on the G actin strand
Term
T Tubules
Definition
Conduct nerve impulses to the deepest regions of the muscle cells and sarcomere. Impulses trigger the release of calcium from adjacent terminal cisternae
Term
Sarcoplasmic Reticulum
Definition
Smooth endoplasmic reticulum that surround myofibril
Terminal cisternae are large perpendicular cross-channels
Regulates intracellular calcium levels and can store or release calcium(when fiber contracts
Term
Fasicles
Definition
Bundles of muscle fibers
Term
Endomysium
Definition
Meaning within the muscle
CT surrounding each individual muscle fiber
Is areolar CT
Term
Epimysium
Definition
Meaning outside the muscle
Overcoar of dense irregular CT that surrounds the whole muscle
Term
Perimysium
Definition
Fibrous CT surrounding fascicles
Term
Special Characteristics of Muscle Tissue
Definition
Excitability
Contractility
Extensibility
Elasticity
Term
Muscle Functions
Definition
Movement of bones or fluids
Maintaining posture and body position
Stabilizing joints
Heat generation
Term
Insertion
Definition
Point of muscle attachment that is moveable during contraction
Term
Origin
Definition
Point of muscle that is relatively fixed during contraction.
In limb m uscles origin usually lies proximal to insertion
Term
Sarcomere
Definition
Smallest contractile unit of a muscle fiber
The region of a myofibril between 2 successive Z discs
Composed of thick and thin myofilaments
Term
Skeletal Muscle Fibers
Definition
Long cylindrical cell with multiple muclei beneath the sarcolemma
Cytoplasm of muscle cells called sarcoplasm which contains large amounts of stored glycogen
1 muscle fiber composed of several hundred myofibrils responsible for contraction
Term
Myofibrils
Definition
Run parallel to length
Densely packed, rodlike elements 80% of cell volume
Exhibit striations: perfectly aligned repeating series of A & I bands
Term
Glycosomes
Definition
Granules of stored glycogen provide glucose during periods of muscle cell activity
Term
Myoglobin
Definition
A red pigment that stores oxygen
Term
Titin
Definition
Protien that connects thick filaments to thin filaments of adjacent sarcomeres
Term
Z line (discs)
Definition
Anchors thin filaments and connects each myofibril to the next
Term
A bands
Definition
Made of thick filaments
Has a lighter stripe in midsection
Called H zone where no thin filaments are present
H zone becomes smaller during contraction
A band does not change size during contraction
Term
I Bands
Definition
Made of thin filaments which extend across the I band and partway into the A band
A dark M line bisects each H zone
Term
Events at the Neuromuscular Junction
Definition
Nerve impulse arrives at axon terminal
ACh released and binds with receptors on the sarcolemma
Electrical events lead to the generation of an action potential
Term
Events in the Generation of and Action Potential
Definition
Local depolarization
1. Ach binding opens chemically gated ion channels
2. Simultaneous diffusion of Na+ and K+
3. More Na+ diffuses so the interior of the sarcolemma becomes less negative
4. Local depolarization
Term
Events in the Generation of an Action Potential
Definition
2. Generation and propagation of an action potential
End plate potential spreads to adjacent membrane areas.
Na+ channels closed and voltage-gated K channels open
Na+ influx decreases the membrane voltage toward a critical threshold
If threshold is released an action potential is generated
Term
Events in the Generation of and Action Potential
Definition
Repolarization
Term
Contraction
Definition
Does not necessarily cause shortening of the fiber
Shortening occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing shortening
Term
Sliding filament model of contraction
Definition
During contraction myosin heads bind to actin, detach, and bind again to propel the thin filaments toward the M line.
As H zones shorten and disapear sarcomeres shorten, muscle cells shorten, and the whole muscle shortens
Term
Requirements for Skeletal Muscle Contraction
Definition
Activation
Excitation-contraction coupling
Term
Events at the Neuromuscular Junction
Definition
Skeletal muscles are stimulated by somatic motor neurons
Each axon ending forms a neuromuscular junction with a single muscle fiber
Term
Isometric contraction
Definition
No shortening muscle tension increases but does not exceed the load
Term
Isotonic contraction
Definition
Muscle shortens because muscle tension exceeds the load
Term
Motor Unit
Definition
A motor neuron and all muscle fibers it supplies
Term
Muscle twitch
Definition
Response of a muscle to a single, brief threshold stimulus
Term
Muscle tone
Definition
Constant, slightly contracted state of all muscles
Keeps muscles healthy
Term
ATP is regenerated by:
Definition
Direct phosphorylation of ADP by creatine phosphate
Anaerobic pathway(glycolysis)
Aerobic respiration
Term
Muscle Fatigue
Definition
Occurs when there are Ionic imbalances and when prolonged exercise damages the SR and interferes with Ca2+ regulation and release
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