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Muscle Tissue

Muscle Tissue. Chapter 10. Muscle Tissue. Muscle is one of the 4 primary types of tissue. It is subdivided into skeletal , cardiac and smooth muscle. Skeletal Muscle Tissue. The 5 functions of skeletal muscles are: To produce skeletal movement. To maintain posture and body position.

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Muscle Tissue

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  1. Muscle Tissue Chapter 10

  2. Muscle Tissue • Muscle is one of the 4 primary types of tissue. • It is subdivided into skeletal, cardiac and smooth muscle

  3. Skeletal Muscle Tissue The 5 functions of skeletal muscles are: • To produce skeletal movement. • To maintain posture and body position. • To support soft tissues. • To guard the entrances and exits of the body. • To maintain body temperature.

  4. Functional Anatomy of Skeletal Muscle • Organization of Connective Tissues

  5. Organization of Connective Tissues • Muscles have 3 layers of connective tissues • epimysium • perimysium • Endomysium • the endomysium, perimysium and epimysium come together to form a tendon (a bundle) or an aponeurosis (a sheet).

  6. Skeletal Muscle Fibers • Long fibers develop through the fusion of mesodermal cells (myoblasts) until they become very large and contain hundreds of nuclei • The 2 types of myofilaments are: • thin filaments: made of the protein actin, and • thick filaments: made of the protein myosin

  7. Sarcoplasmic Reticulum • involved in transmitting the action potential to the myofibril • Triad • Terminal cisternae • T tubules

  8. Striated • thin filaments (I bands) • thick filaments (A bands )

  9. Thin filaments contain 4 proteins • F actin (2 twisted rows of globular G actin. Active sites on G actin strands bind to myosin.) • nebulin (holds F actin strands together) • tropomyosin (a double strand, prevents actin-myosin interaction) • troponin (a globular protein, binds tropomyosin to G actin, controlled by Ca++)

  10. Thick Filaments • Twisted myosin subunits. • The tail binds to other myosin molecules. • The free head, made of 2 globular protein subunits

  11. Sliding Filaments and Muscle Contraction • The thin filaments of the sarcomere slide toward the M line, in between the thick filaments. This is called the sliding filament theory. The width of the A zone stays the same, but the Z lines move closer together.

  12. The Control of Skeletal Muscle Activity • Neural stimulation occurs at the neuromuscular junction (NMJ) • Acetylcholine (ACh) • Acetylcholinesterase or AChE

  13. Excitation - Contraction Coupling • The Contraction Cycle has 5 steps: • 1. Exposure of active sites • 2. Formation of cross-bridges • 3. Pivoting of myosin heads • 4. Detachment of cross-bridges • 5. Reactivation of myosin Movie

  14. Relaxation • Since AChE quickly breaks down ACh, the duration of a contraction depends on: 1. the duration of the neural stimulus 2. the number of free calcium ions in the sarcoplasm 3. the availability of ATP

  15. Key • Skeletal muscle fibers shorten as thin filaments interact with thick filaments and sliding occurs. • The trigger for contraction is the appearance of free calcium ions in the sarcoplasm; the calcium ions are released by the sarcoplasmic reticulum when the muscle fiber is stimulated by the associated motor neuron. • Contraction is an active process; relaxation and return to resting length is entirely passive.

  16. Tension Production by Muscle Fibers • All-or-none principal • Tension produced by the contraction of an individual muscle fiber can vary

  17. Length-Tension Relationships • There is an optimum amount of overlap to produce the greatest amount of tension

  18. Frequency of Stimulation • A single neural stimulation produces a single contraction or twitch which lasts about 7-100 milliseconds. • Sustained muscular contractions require many repeated stimuli

  19. Twitches are divided into 3 phases • The latent period before contraction. The action potential moves through the sarcolemma, causing calcium ions to be released. • The contraction phase: Calcium ions bind to troponin, tension builds to a peak. • The relaxation phase: Calcium levels fall, active sites are covered, and tension falls to resting levels.

  20. Twitch types • Treppe • Summation of twitches • Incomplete tetanus • Complete tetanus

  21. Tension Production by Skeletal Muscles The amount of tension a whole muscle can produce depends on: • The internal tension produced by the muscle fibers • The external tension the muscle fibers exert on their elastic extracellular fibers (series elastic elements such as tendons) • The total number of muscle fibers stimulated

  22. 2 basic patterns of muscle tension: • Isotonic contraction • Isometric contraction.

  23. Muscle Relaxation and Return to Resting Length • Elastic forces are the pull of the elastic elements returning to normal length. • Opposing muscle contractions reverse the direction of the original motion, the work of opposing muscle pairs. • Gravity can take the place of opposing muscle contraction to return a muscle to its resting state.

  24. ATP and CP Reserves • ATP is the active energy molecule • Creatine phosphate (CP) stores of energy in cell. • energy in creatine phosphate is used to recharge ADP to ATP

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