Muscle Tissue Ch. 10 Flashcards
Mesenchymal embryologic origins of bone, muscle, and dermis
- Sclerotome: bone
* Myotome: muscle•Dermatome: dermis
Types of Muscle
- Smooth muscle:lines walls of hollow organs, blood vessels, and glands
- Cardiac muscle: in walls of heart
- Skeletal muscle: makes up 40% the body’s mass and is attached to bone or to skin (e.g. with some facial muscles)
Similarities of Muscle Tissue
- Muscle contraction depends on two types of myofilaments with contractile proteins which generate contractile force
- actin
- myosin
Functional Features of Muscles
- Excitability: electrical nerve impulse stimulates the muscle cell to contract
- Contractility: long cells shorten and generate pulling force
- Extensibility: can be stretched back to its original length by contraction of an opposing muscle
- Elasticity: can recoil after being stretched
Smooth Muscle TissueCell shape and appearance
- Spindle-shaped cells with central nuclei•Elongated with tapered ends
- Arranged closely to form sheets
- No visible striations
Smooth Muscle
- Located mostly in walls of hollow viscera e.g., digestive tract, urinary tract, uterus, and glands and blood vessels
- Propels substances through internal hollow organs (e.g. the intestines) by alternating contraction and relaxation
- Squeezes fluids and other substances through glands
- Activity of smooth muscle in arterial walls influences blood pressure
- Involuntary control typically modulated by the autonomic nervous system
Cardiac Muscle Tissue
- Branching striated cells
- Generally uninucleate, but sometimes binucleate
- Cells branch and join/interdigitate at special cellular junctions called intercalated discs
Cardiac Muscle
- Located in walls of heart
- Contracts to propel blood into circulatory system
- Involuntary control through the autonomic nervous system
Skeletal Muscle Tissue
- Long, cylindrical cells
- Multinucleate
- Obvious striations and bands reflects a highly organized arrangement of myofilaments
Skeletal Muscle
•Skeletal muscles are attached to bones or to skin (e.g. with some facial muscles)
•Typically voluntary movement
•Facial expression
•Movement of upper and lower extremities
•Each muscle is an organ that consists mostly of muscle tissue
•Skeletal muscle also contains
-Connective tissue
-Blood vessels
-NervesFunctions of Skeletal Muscle
•Maintenance of posture—enables the body to remain sitting or standing
•Joint stabilization
•Heat generation
-Muscle contractions produce heat
-Helps maintain normal body temperature
Sheaths of connective tissue bind skeletal muscle and its fibers together
- Epimysium: dense irregular connective tissue surrounding entire muscle
- Perimysium: fibrous connective tissue that surrounds each fascicle (group/bundle of muscle fibers)
- Endomysium: within a fascicle, each muscle fiber is surrounded by a fine sheath of loose connective tissue consisting mainly of reticular fibers
Connective Tissue Sheaths in Skeletal Muscle
- The fibrous connective tissues (epimysium, perimysium, and endomysium) form sheaths that bind muscle fibers together and hold them in parallel alignment so they can work together to produce force
- The dense irregular connective tissue sheaths are continuous with tendons
- Tendons are connective tissue that joins skeletal muscles to bone
- When muscle fibers contract, they pull on the surrounding endomysium which in turn pulls on the perimysium, epimysium, and tendon
- Sheaths also provide elasticity and carry blood vessels and nerves
Typically, each skeletal muscle supplied by branches of:
- One nerve
- One artery
- One or more veins
- Nerves and blood vessels branch repeatedly in the intramuscular connective tissue, with the smallest branches serving individual muscle fibers
Muscle attachments
•Most skeletal muscles run from one bone to another•One bone will move, other bone remains fixed
•Origintends to be the more proximal muscle attachment and the insertiontends to be the more distal attachment
•Origin—less movable bone
attachment
•Insertion—more movable
bone attachment
•Muscles attach to origins and insertions via strong fibrous connective tissue that extend into fibrous periosteum of the bone
•Direct (fleshy) attachments—connective tissue fibers are short and muscles appear to attach directly to bone
•Indirect attachments—connective tissue extends well beyond the end of the muscle fibers to form a cord-like tendonor a flat sheet aponeurosis
•Bone markings present where tendons meet bones include tubercles, spines,trochanters, and crests
Microscopic & Functional Anatomy Skeletal Muscle Fiber = Muscle Cell
- Long, huge, cylindrical cell (= muscle fiber)
- Diameter is 10–100μm
- Length is several to dozens of centimeters
- Each cell formed by fusion of hundreds of embryonic cells, therefore, each cell (muscle fiber) is multinucleate
- Nuclei are peripherally located
Sarcolemma & sarcoplasma of the skeletal muscle fiber (cell)
- Plasma membrane is called a sarcolemma
* Cytoplasm is called sarcoplasm
Myofibrils
- long rod-shaped organelles within the sarcoplasm of the muscle cell/muscle fiber
- make up 80% of the sarcoplasm
- specialized contractile organelle
- contains contractile myofilament proteins (actin and myosin)
Sarcomeres
- long row of repeating segments in muscle fiber
- each sarcomere extends from one Z disc to the next Z disc and is basic functional unit of contraction in skeletal muscle
- Basic unit of contraction of skeletal muscle
- Sarcomere structure explains the pattern of striations in skeletal muscle fibers
Sarcomere
•Z disc (Z line): boundaries at the two ends of a sarcomere are Z discs (or Z lines)
•Thin (actin) filaments: extend from Z disc toward the center of the sarcomere
•Thick (myosin) filaments: located in center of the sarcomere and overlap the inner ends of the thin filaments is a cylindrical bundle of thick myosin filaments
•Thick myosin filaments contain ATPase enzymes to release energy required for muscle contraction
Sarcomere Structure
3•Both ends of thick filament are studded with knobs called myosin heads
Sarcomere Structure
- Z disc (Z line): boundaries at the two ends of a sarcomere are Z discs (or Z lines)
- I band: regions on either side of A band that contain only thin (actin) filaments; each I band is part of two adjacent sarcomeres and has a Z disc running through its center
- I band is visualized as a light band (isotropic)
- A band: full length of the thick (myosin) filament which includes inner end of overlapping thin (actin) filaments - its darker and thicker
- A band is visualized as a dark band (anisotropic)
- H zone: center part of A band with only thick filaments and where no thin filaments occur
- M line: dark line in center of H zone which contains tiny rods which hold the thick filaments together
Origins of names of myofibril elements
-will not ask the origin names on the test
•Z-lines (Z-discs): named from the German “Zwischenscheibe”, the disc in between the I bands•I-band: named for its isotropicproperties under a polarization microscope; visualized as a light band•A-band: named for its anisotropicproperties under a polarization microscope; visualized as a dark band•H-band: paler region in the A band; named from the German “heller”, which means brighter based on their properties under a polarization microscope •M-line: thin dark line inside H zone named from the German “Mittelscheibe”, the disc in the middle of the sarcomere, formed of tiny rods which hold the thick filaments together
Sarcoplasmic Reticulum & T Tubules
Sarcoplasmic Reticulum & T Tubules
Sarcoplasmic Reticulum (SR)
•A specialized smooth ER (endoplasmic reticulum) •Interconnecting sarcoplasmic reticulum (SR) tubules mainly run longitudinally and surround myofibrils
Sarcoplasmic Reticulum (SR)
- Other SR tubules called terminal cisternae form perpendicular cross-channels over the junction between each A band and its adjacent I bands
- The SR and terminal cisternae store large amounts of calcium ions that are released to stimulate the muscle to contract by triggering the sliding filament mechanism
T Tubules (transverse tubules)
- T tubules: deep invaginations of sarcolemma which run through each pair of terminal cisterns
- Triad:complex of the T tubule flanked by two terminal cisterns
Mechanism of Contraction
- Nerve-generated impulses travel along the sarcolemma of the muscle fiber
- T tubules are connected to and communicate with the sarcolemma and conduct each impulse to the deepest regions of the muscle fiber, thus allowing the deep lying myofibrils to contract at the same time as the superficial ones
- Impulses traveling down the T tubules stimulate the release of calcium ions from the terminal cistern to trigger muscle contraction
- After contraction, calcium is pumped back into sarcoplasmic reticulum for storage
Mechanism of Contraction
- Sliding filament mechanism explains concentric contraction which causes muscle to shorten to move arms & legs
- Initiated by release of calcium ions from the sarcoplasmic reticulum
- Powered by ATP
sarcolemma > myofibrils > contraction
Mechanism of Contraction
WILL BE ON EXAM
- Myosin heads attach to thin (actin) filaments at both ends of a sarcomere and pull thin filaments toward the center of the sarcomere by swiveling inward
- The thin filament merely slides over the thick filament
- Thin and thick filaments do not shorten
Sliding Filament MechanismContraction changes the striation pattern
KNOW THIS CUZ WILL BE ON EXAM
understand slide about sliding filament it is the one with the diagram
•Fully relaxed: thinfilaments partially overlap thickfilaments
•Contraction: thinfilaments overlap of thickfilaments is increased
-Z discs move closer together
-Sarcomere length shortens
-I bands shorten
-H zone disappears
-A band remains the same length
Muscle extension
•Muscle is stretched (extended) by a movement that is opposite of that which contracts it
Titin
- A spring-like elastic molecule in sarcomeres
- Resists overstretching of muscles
- Holds thick filaments in place
- Unfolds when muscle is stretched
Motor Neuron Innervation of Skeletal Muscle
- Neuromuscular junctionis the point where nerve ending and muscle fiber meet
- Axon terminalsat ends of axons where acetylcholine neurotransmitter is released
- Synaptic cleftis space between axon terminal and sarcolemma
Motor Innervation of Skeletal Muscle
- Nerve impulse stimulates release of acetylcholine into the synaptic cleft
- Acetylcholine stimulates changes in the sarcolemma that excite the muscle fiber and this stimulus is carried down the T tubules which trigger terminal cisternae to release calcium with initiates fiber contraction
Types of Skeletal Muscle Fibers
•Skeletal muscle fibers are categorized according to two characteristics
–How they manufacture energy (ATP)
–How quickly they contract
- Oxidative fibers—produce ATP aerobically; small diameter and contract relatively slowly
- Glycolytic fibers—produce ATP anaerobicallyby glycolysis; larger diameter and contract faste
Type I, slow twitch, or “red” muscle
- Type I, slow twitch, or “red” muscle, is dense with capillaries and is rich in mitochondria and myoglobin, giving the muscle tissue its characteristic red color.
- It can carry more oxygen and sustain aerobic activity using fats or carbohydrates as fuel.
- Slow twitch fibers contract for long periods of time but with little force.
- Used for postural maintenance e.g., holding head up and endurance exercises e.g., long distance running.
Type ll, fast twitch, or “white” muscle
WILL NOT ASK QUESTION ABOUT TYPE ONE OR TYPE TWO ON EXAM
- Type II, fast twitch muscles vary in both contractile speed and force generated.
- Fast twitch fibers contract quickly and powerfully but fatigue very rapidly, sustaining only short, anaerobic bursts of activity before muscle contraction becomes painful. •They contribute most to muscle strength and have greater potential for increase in mass.
- Type IIA is fast twitch oxidative
- Type IIB is fast twitch glycolytic, which is anaerobic “white” muscle that is least dense in mitochondria and myoglobin; in small animals (e.g., rodents) this is the major fast muscle type, explaining the pale color of their flesh.
