Chapter 10 - Muscle Tissue PDF

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Textbook and lecture notes for Human Anatomy taught by Melissa Jacobsen at Salt Lake Community College...

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Anatomy – Chapter 10; Muscle tissue 10.1 Properties of Muscle Tissue Excitability - very responsive to input from stimuli; can continue an electrical signal Contractility - cells shorten Elasticity - cells recoil to resting length Extensibility - cell can extend in opposition to the contracting 10.2 Characteristics of Skeletal Muscle Functions Body movement - bones of the skeleton move when muscles contract and pull on the tendons which attach the muscles to the bone Maintenance of posture - contraction of specific skeletal muscles stabilizes joints and helps maintain the body's posture or position Temperature regulation - energy is required for muscle tissue contraction and heat is always produced as a waste product of this energy usage (shivering) Storage and movement of materials (sphincters) - circular muscle bands contract at the openings/orifices of the gastrointestinal and urinary tracts Support - skeletal muscle is sometimes arranged in flat sheets or layers Gross anatomy > Endomysium - innermost connective tissue layer; delicate, areolar connective tissue layer; surrounds fiber bundles within fascicles > Perimysium - surrounds fascicles; dense irregular connective tissue sheath; high in blood vessels and nerves Fascicles - bundles of muscle fibers > Epimysium - layer of dense irregular connective tissue that surrounds the whole skeletal muscle > Deep fascia - an expansive sheet of dense irregular connective tissue that separates individual muscles, binds together muscles with similar functions, and forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels, and to fill spaces between muscles > Superficial fascia - composed of areolar and adipose connective tissue that separates muscle from skin Attachments Tendon - attaches muscle to bone, skin, or another muscle

Aponeurosis - thin, flattened sheet of tendon Origin - less mobile attachment of the muscle Insertion - more mobile attachment of the muscle Nerves (Innervation) - skeletal muscles contract because of neuron signals Microscopic anatomy Sarcolemma - plasma membrane of a muscle fiber; surrounds muscle fiber and regulates entry and exit of materials Sarcoplasm - cytoplasm of a muscle fiber; site of metabolic processes for normal muscle fiber activities Transverse tubules (T-tubules) - narrow, tubular extensions of the sarcolemma into the sarcoplasm, contacting the terminal cisternae; wrapped around myofibrils; quickly transports a muscle impulse from the sarcolemma throughout the entire muscle fiber Sarcoplasmic reticulum (SR) - smooth endoplasmic reticulum that are in contact with the transverse tubules; stores calcium ions needed for muscle contraction

Myofibrils - organized bundles of myofilaments; cylindrical structures as long as the muscle fiber itself; contain myofilaments that are responsible for muscle contraction Myofilaments Actin - thin filament; double-stranded contractile protein; binding site for myosin to shorten a sarcomere Myosin - thick filament; heads to grab onto actin and pull inward Crossbridges - where myosin head grabs onto actin Regulatory proteins: Troponin - regulatory protein that holds tropomyosin in place and anchors to actin; when calcium ions bind to one of its subunits, troponin changes shape, causing the tropomyosin to move off the actin active site, and this permits myosin binding to actin Tropomyosin - double stranded regulatory protein; covers the active sites on actin, preventing myosin from binding to actin when muscle fiber is at rest Sarcomere A-band - dark bands; one end of myosin to the other; contain the entire thick filament I-band - light band; no myosin, only actin, includes z disc contain thin filaments but no

thick filaments H-zone - only myosin; middle; a light, central region in the A band; only thick filaments are present M-line - myosin anchored in middle; a thin transverse protein meshwork structure in the center of the H zone of a relaxed fiber Z-disc - end of sarcomere; actin is attached; thin transverse protein structure in the center of the I band that serves as an attachment site for thin filament ends 10.3 Contraction of Skeletal Muscle Fibers Cross-bridge cycling Myosin grabs actin and pulls actin toward center of sarcomere ATP provides energy to detach myosin head and cock it back to original shape Process repeats (imagine pulling rope) Neuromuscular junctions - the point where a motor neuron meets and skeletal muscle fiber Synaptic knob - expanded tip of an axon Synaptic vesicles - small membrane sacs filled with molecules of acetylcholine (neurotransmitter) Acetylcholine - tells skeletal muscle to contract; exocytosis into synaptic cleft Synaptic cleft - narrow space separating the synaptic knob and the motor end plate ACh receptors - in the motor end plate act like doors that are normally closed; ACh opens -Muscle cells are excitable. They are similar to neurons because they can pass an electrical signal along the membrane (sarcolemma). T-tubule – allows electrical signal to pass to inner parts of cells Release of Calcium from SR Ca++ binds to troponin Troponin moves tropomyosin to expose active sites on actin Cross-bridge cycling occurs Other muscle physiology Motor units - a single motor neuron (tells muscles what to do) and the muscle fibers it controls; all of the fibers that neuron contracts will contract all the way

Isometric contractions - length is constant; tension is changing (pushing against a wall) Isotonic contractions - tension is constant; length is changing (lifting something up & down) 10.7b Actions of Skeletal Muscles Agonist - prime mover; contracts to produce a particular movement Synergist - a muscle that assists the agonist in performing its action Antagonist - a muscle whose actions oppose those of the agonist 10.8 The Naming of Skeletal Muscles Action (flexor, extensor, adductor, etc.) Location Attachments Orientation Shape and size Distinguishing feature 10.9 Characteristics of Cardiac and Smooth Muscle Cardiac muscle Striated? – yes Voluntary? – no Shape - one or two nuclei, Y-shaped Intercalated discs - gap junctions and desmosomes Autorhythmic - start their own contraction without neuron signal

Smooth muscle Striated? – no Voluntary? – no Shape - tapered on ends, wide in center (spindle or fusiform); central nucleus...