LECTURE NOTES BY: PROFESSOR RODRIGUEZ

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1 LECTURE NOTES BY: PROFESSOR RODRIGUEZ Muscle Overview The three types of muscle tissue: These types differ in structure, location,, and means of activation Muscle Similarities Skeletal and smooth muscle cells are elongated and are called muscle Muscle contraction depends on two kinds of myos: o o Muscle terminology is similar o muscle plasma membrane o cytoplasm of a muscle cell o Prefixes,, and all refer to muscle Skeletal Muscle Tissue Packaged in skeletal muscles that attach to and cover the bony skeleton Has obvious stripes called Is controlled (i.e., by conscious control) Contracts rapidly but tires Is responsible for overall body Is extremely and can exert forces ranging from a fraction of an ounce to over 70 pounds Cardiac Muscle Tissue Occurs only in the Is striated like skeletal muscle but is not Contracts at a fairly steady rate set by the heart s allow the heart to respond to changes in bodily needs Smooth Muscle Tissue Found in the walls of hollow, such as the stomach, urinary bladder, and respiratory passages Forces through internal body channels It is not and is Functional Characteristics of Muscle Tissue, or the ability to receive and respond to stimuli the ability to shorten forcibly the ability to be stretched or extended

2 the ability to recoil and resume the original resting length Muscle Function muscles are responsible for all locomotion muscle is responsible for coursing the blood through the body muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs Muscles also maintain posture, stabilize joints, and generate heat Skeletal Muscle Each muscle is a discrete orga n composed of muscle tissue, blood vessels, nerve fibers, and connective tissue The three connective tissue sheaths are: o fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber o fibrous connective tissue that surrounds groups of muscle fibers called fascicles o an overcoat of dense regular connective tissue that surrounds the entire muscle Skeletal Muscle: Nerve and Blood Supply Each muscle is served by one nerve, an artery, and one or more veins Each skeletal muscle fiber is supplied with a nerve ending that controls contraction Contracting fibers require continuous delivery of oxygen and nutrients via arteries Wastes must be removed via veins Attachments Most skeletal muscles span joints and are attached to bone in at least two places When muscles contract the movable bone, the muscle s moves toward the immovable bone, the muscle s Muscles attach: o epimysium of the muscle is fused to the periosteum of a bone o connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis Microscopic Anatomy of a Skeletal Muscle Fiber Each fiber is a long, cylindrical cell with nuclei just beneath the sarcolemma Fibers are 10 to 100 µm in diameter, and up to hundreds of centimeters long! Each cell is a syncytium produced by fusion of cells

3 280 UNIT 2 Covering, Support, and Movement of the Body UNIT 2 Covering, Support, and Movement of the Body Microscopic Anatomy of a Skeletal280Muscle (a) Photomicrograph of portions Fiber (a) Photomicrograph of portions Nuclei Sarcoplasm has numerous glycosomes and a unique Nuclei oxygen-binding protein called myoglobin Dark A band of two isolated muscle fibersof(700 ). Notice the two isolated muscle obvious striations fibers (700 ). Notice the (alternating dark and light obvious striations bands). (alternating dark and light Dark A band Light Light Fibers contain the usual organelles, myofibrils, sarcoplasmic bands). reticulum, and T tubules Fiber Fiber Myofibrils Myofibrils are, rodlike (b) Diagram of part of a elements Sarcolemma They make up of the One the myofibrils. muscle volume muscle fiber showing the myofibrils. One (b) Diagram of part of a myofibril extends from muscle fiber the cut end of theshowing fiber. Sarcolemma myofibril extends from the cut end of the fiber. Mitochondrion The of9myofibrils within a Mitochondrion fiber is such that a perfectly aligned repeating series of 9 dark bands and light bands is evident Dark A band Thin (actin) Sarcomeres show the myos The region of a myofibril between two successive responsible for the Myos are of two types o o Myos: Banding Pattern (d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick s. Nucleus Dark A band Thin (actin) Light H zone A band Sarcomere Thick (myosin) Nucleus Thick (myosin) Myofibril H zone A band Sarcomere Thin (actin) Elastic (titin) s Thin (actin) (d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick s. Thick (myosin) Myosin thin s only H zone thick s only thick s linked by accessory proteins Outer edge of A band thick and thin Actin s overlap Z-disc coin-shaped sheet of proteins (connectins) that anatomy of a skeletal muscle fiber. (For a related image, see Figure 9.2 Microscopic A Brief Atlas of the Human Body, Plate 28.) the thin s and myofibrils to one another Myos: Banding Pattern thin s only H zone thick s only thick s linked by accessory proteins FigureCust: 9.2 Benjamin Microscopic anatomy of a skeletal muscle (For a related image, see # Cummings/CA Au: Marieb Pg.fiber. No. 280 C/M/Y/K Brief Atlas of the Human Body, PlateS4C 28.) Title: AAnatomy & Physiology Server: Short / Normal Outer edge of A band thick and thin s overlap DESIGN SERVICES OF CARLISLE Publishing Services Thin s do not overlap thick s in the lighter zone Lines appear darker due to the # Cust: Benjamin Cummings/CA Ultrastructure of Myos: Thick Filaments Title: Anatomy & Physiology Myosin Actin (e) Cross-sectional view of a sarcomere cut through in s extend different across locations. Thick (myosin) Elastic (titin) s (e) Cross-sectional view of a sarcomere cut through in different locations. the and partway into the A band Light s extend the entire length of an A band banding pattern. Each sarcomere extends from one to the next. Composed of made up of contractile proteins (c) Small part of one myofibril enlarged to show the myos responsible for the banding pattern. Each (c) Small part of one sarcomere extends from one Zmyofibril disc to enlarged the next.to The smallest unit of a muscle Myofibril Server: S4C Au: Marieb Pg. No. 280 C/M/Y/K Short / Normal Thick s are composed of the protein Each myosin molecule has a rodlike tail and two globular DESIGN SERVICES OF CARLISLE Publishing Services

4 two interwoven, heavy polypeptide chains two smaller, light polypeptide chains called cross bridges Ultrastructure of Myos: Thin Filaments Thin s are chiefly composed of the protein Each actin molecule is a polymer of globular subunits called G actin The subunits contain the sites to which myosin heads attach during contraction and are regulatory subunits bound to actin Sarcoplasmic Reticulum (SR) SR is an elaborate, endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril Paired terminal form perpendicular cross channels Functions in the regulation of intracellular levels Elongated tubes called T penetrate into the cell s interior at each A band junction T tubules associate with the paired terminal cisternae to form T Tubules T tubules are continuous with the They conduct impulses to the deepest regions of the muscle These impulses signal for the of Ca2+ from adjacent terminal cisternae Triad Relationships T tubules and SR provide tightly linked signals for muscle A double zipper of integral membrane proteins protrudes into the intermembrane space T tubule proteins act as sensors SR foot proteins are receptors that Ca2+ release from the SR cisternae Sliding Filament Model of Contraction s slide past the ones so that the actin and myosin s overlap to a greater degree In the relaxed state, thin and thick s overlap only Upon stimulation, myosin heads to actin and sliding begins Sliding Filament Model of Contraction Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate and propel the thin s to the of the sarcomere As this event occurs the sarcomeres, the muscle shortens Skeletal Muscle Contraction In order to contract, a skeletal muscle must: o Be stimulated by a o Propagate an electrical current, or, along its sarcolemma

5 o Have a, the final trigger for contraction Linking the electrical signal to the contraction is coupling Nerve Stimulus of Skeletal Muscle Skeletal muscles are stimulated by neurons of the somatic nervous system Axons of these neurons travel in nerves to muscle cells Axons of motor neurons branch profusely as they enter muscles Each axonal branch forms a junction with a single muscle fiber Motor Unit One neuron and all the cells that form junctions with its endings When a motor neuron is, all the muscle cells it supplies are activated to contract Each muscle consists of motor units Neuromuscular Junction The junction is formed from: o Axonal endings, which have small membranous sacs (synaptic ) that contain the acetylcholine (ACh) The motor end plate of a muscle, which is a specific part of the sarcolemma that contains ACh and helps form the neuromuscular junction Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the cleft Neuromuscular Junction When a nerve impulse reaches the end of an axon at the neuromuscular junction: o Voltage-regulated calcium channels open and allow Ca2+ to the axon o Ca2+ inside the axon terminal causes axonal to fuse with the axonal membrane Neuromuscular Junction This fusion releases ACh into the synaptic cleft via ACh diffuses across the synaptic cleft to ACh receptors on the Binding of ACh to its receptors initiates an in the muscle Destruction of Acetylcholine ACh bound to ACh receptors is quickly destroyed by the enzyme This destruction prevents continued muscle fiber contraction in the absence of additional stimuli Role of Acetylcholine (Ach) ACh binds its receptors at the motor end plate Binding opens chemically (ligand) gated channels Na + and K + diffuse out and the interior of the sarcolemma becomes less negative

6 This event is called Action Potential A transient depolarization event that includes of a sarcolemma (or nerve cell membrane) and the propagation of an action potential the membrane Excitation-Contraction Coupling Once generated, the action potential: o Is along the sarcolemma o Travels down the T o Triggers Ca 2+ from terminal cisternae Ca 2+ binds to and causes: o The action of tropomyosin to cease o Actin active sites to be exposed Excitation-Contraction Coupling Myosin cross bridges attach and detach Thin s move toward the of the sarcomere Hydrolysis of ATP powers this cycling process Ca2+ is into the SR, tropomyosin is restored, and the muscle fiber Role of Ionic Calcium (Ca 2+ ) in the Contraction Mechanism At low intracellular Ca 2+ concentration: o blocks the binding sites on actin o Myosin cross bridges cannot to binding sites on actin o The state of the muscle is enforced At higher intracellular Ca2+ concentrations: o Additional calcium binds to (inactive troponin binds two Ca2+) o Calcium-activated troponin binds an additional two Ca2+ at a separate regulatory site Calcium-activated troponin undergoes a change This change moves away from actin s binding sites Myosin can now bind and cycle This permits (sliding of the thin s by the myosin cross bridges) to begin Contraction of Skeletal Muscle Fibers Contraction refers to the of myosin s cross bridges (force-generating sites) Shortening occurs when the generated by the cross bridge exceeds forces opposing shortening Contraction ends when cross bridges become, the tension generated declines, and relaxation is induced

7 Two Types of Skeletal Muscle: o Many capillaries, high myoglobin o Contracts fairly slowly o Can sustain contraction o Fewer capillaries, less myoglobin o Contracts quickly o Cannot sustain contraction Motor Unit: The Nerve-Muscle Functional Unit A motor unit is a motor neuron and all the muscle fibers it supplies The number of muscle fibers per motor unit can vary from four to several hundred Muscles that control fine movements (fingers, eyes) have small motor units Motor Unit: The Nerve-Muscle Functional Unit Large weight-bearing muscles (thighs, hips) have large motor units Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle Contraction of Skeletal Muscle (Organ Level) Contraction of muscle fibers (cells) and muscles (organs) is similar The two types of muscle contractions are: o contraction increasing muscle tension (muscle does not shorten during contraction) o contraction decreasing muscle length (muscle shortens during contraction) Isotonic Contractions In isotonic contractions, the muscle changes in (decreasing the angle of the joint) and moves the load The two types of isotonic contractions are concentric and eccentric o contractions the muscle shortens and does work o contractions the muscle contracts as it lengthens Isometric Contractions Tension to the muscle s capacity, but the muscle shortens nor lengthens Occurs if the is greater than the the muscle is able to develop Muscle fatigue the muscle is in a state of physiological inability to contract Muscle fatigue occurs when: o ATP fails to keep pace with ATP o There is a relative deficit of ATP, causing o Lactic acid in the muscle o Ionic are present Intense exercise produces rapid muscle (rapid recovery)

8 Na + -K + pumps cannot restore ionic balances enough Low-intensity exercise produces slow-developing fatigue SR is damaged and Ca 2+ is disrupted Oxygen Debt Vigorous exercise causes dramatic changes in muscle chemistry For a muscle to return to a resting state: o Oxygen reserves must be o Lactic acid must be converted to acid o Glycogen stores must be o ATP and CP reserves must be resynthesized the extra amount of O 2 needed for the above restorative processes Heat Production During Muscle activity Only of the energy released in muscle activity is useful as work The remaining 60% is given off as Dangerous heat levels are prevented by radiation of heat from the skin and sweating Force of Muscle Contraction The force of contraction is by: o The number of muscle contracting the more motor fibers in a muscle, the stronger the contraction o The relative of the muscle the bulkier the muscle, the greater its strength o Degree of muscle muscles contract strongest when muscle fibers are % of their normal resting length Smooth Muscles Composed of spindle-shaped with a diameter of 2-10 µm and lengths of several hundred µm the coarse connective tissue sheaths of skeletal muscle, but have fine endomysium Organized into two layers ( and ) of closely apposed fibers Found in walls of hollow (except the heart) Have essentially the same mechanisms as skeletal muscle Peristalsis When the layer contracts, the organ dilates and contracts When the layer contracts, the organ elongates alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organ