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STUDY GUIDE-MUSCLE TISSUE
I. OVERVIEW OF MUSCLE TISSUE
A. Types of Muscular Tissue
- Three types of muscle tissue. a. Skeletal Muscle: 1) Location: skeleton 2) Function: movement heat, posture 3) Appearance: striated, fibers parallel 4) Control: voluntary b. Cardiac Muscle 1) Location: Cardiac muscle tissue is found only in the heart wall 2) Function: pump blood 3) Appearance: Striated, central nucleus 4) Control: Involuntary (autorhythmic/hormones/neurotransmitters) c. Smooth Muscle 1) Location: GI tract, uterus, eye, blood vessels 2) Function: Peristalsis 3) Appearance: no striations, central nucleus 4) Control: Involuntary (autorhythmic) B. Functions of Muscular Tissue
- Producing body movements
- Stabilizing body positions
- Storing and moving substance within the body
- Generating heat (thermogenesis) C. Properties of Muscular Tissue
- Electrical excitability (action potentials)
- Contractility
- Extensibility
- Elasticity
II. STRUCTURE OF SKELETAL MUSCLE TISSUE
A. Connective Tissue Components a. Subcutaneous layer b. Endomysium, Perimysium, Epimysium c. Fascia is a sheet or band of fibrous connective tissue that is deep to the skin and surrounds muscles and other organs of the body. d. If, the connective tissue layers extend beyond the muscle to form a rope-like structure it is called a tendon, if they form a flat sheet it is called an aponeurosis. e. Clinical Connection: Fibromyalgia
- Nerve and Blood supply a. Skeletal muscles are well supplies with nerves and blood vessels. b. Capillaries are plentiful in muscular tissue B. Microscopic Anatomy of a Skeletal Muscle Fiber
- Microscopic anatomy of a skeletal muscle fiber. a. Sarcolemma, Transverse Tubule and sarcoplasm
- Transverse tubules are tiny invaginations of the sarcolemma that quickly spread the muscle action potential to all parts of the muscle fiber. b. Triad: transverse tubule, sarcoplasmic reticulum
- terminal cisternae
- The sarcoplasmic reticulum encircles each myofibril. It is similar to smooth endoplasmic reticulum in non-muscle cells and in the relaxed muscle, functions to store calcium ions.
- Sarcoplasm is the muscle cell cytoplasm and contains a large amount of glycogen for energy production and myoglobin for oxygen storage.
- Clinical Connection: Muscular hypertrophy, fibrosis and atrophy.
- Filaments and the sarcomere. a. A band, Z disc, M line, I band, H zone
- The darker middle portion is the A band consisting primarily of the thick filaments with some thin filaments overlapping the thick ones.
- The lighter sides are the I bands that consist of thin filaments only.
- Z disc passes through the center of the I band. (a) Exercise can result in torn sarcolemma, damaged myofibrils, and disrupted Z discs
B. The steps involved in the sliding filament mechanism of muscle contraction. a. ATP hydrolysis b. Attachment c. Power Stroke d. Detachment B. Excitation-Contraction coupling A. An increase in intracellular Ca++ starts the contraction B. Ca++ increase occurs because of release from the sarcoplasmic reticulum C. Ca++ active transport pumps restore the Ca++ D. Calesequestrin helps concentrate the Ca++ near the site for release for the sarcoplasmic reticulum E. Clinical connection: Rigor Mortis C. Length-Tension Relationship A. Length-tension indicates how the forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins. D. The Neuromuscular Junction A. The muscle action potential releases calcium ions from the sarcoplasmic reticulum that combine with troponin, causing it to pull on tropomyosin to change its orientation, thus exposing myosin-binding sites on actin and allowing the actin and myosin to bind together. a. The use of calcium ions to remove the contraction inhibitor and the joining of actin and myosin constitute the excitation-contraction coupling, the steps that connect excitation (a muscle action potential propagation through the T tubules) to contraction of the muscle fiber. b. Calcium ion active transport pumps return calcium ions to the sarcoplasmic reticulum. c. Clinical Connection: Electromyography โ measures the electrical activity of muscle cells. B. Show the general features of the neuromuscular junction that allows signals coming from the brain to be conveyed across the gap between the neuron motor cell and the sarcolemma of the muscle cell. a. Synaptic vesicles containing acetylcholine b. Motor end plate c. Sarcolemma
C. Describe the steps and components in the mechanism that cause a motor neuron action potential to result in a muscle cell action potential. a. Acetylcholine released from vesicles b. Binding to receptor c. Graded potential is elicited and then an action potential d. Acetylcholine is broken down D. Describe the interaction of acetylcholine with its membrane receptor E. Describe how binding by acetylcholine results in the simultaneous movement of Na+ and K+ F. Describe the movement of the action potential along the sarcolemma G. Several plant products and drugs selectively block events at the NMJ. H. Review the components of the action potential a. Depolarizing phase b. Repolarizing phase c. After-hyperpolarizing phase I. Connect the action potential phases to the open and closed status of membrane channels in the sarcolemma. J. Review the initiation of the action potential to the sarcolemma and subsequent propagation to the T-tubules. K. Summarize the major role players in the excitation-coupling mechanism a. Brain and associate neurons b. Acetycholine, receptors and enzymes c. Na+ and K+ channels and permeabilities d. Sarcolemma components e. Myofibril components (troponin, tropomyosin, myosin) f. ATP L. The inability of a muscle to maintain its strength of contraction or tension is called muscle fatigue; it occurs when a muscle has low calcium, creatine phosphate, oxygen and other nutrients. a. Elevated oxygen use after exercise is called recovery oxygen uptake (rather than the formerly used term oxygen debt).
f. The aerobic system will provide enough ATP for prolonged activity so long as sufficient oxygen and nutrients are available. V. CONTROL OF MUSCLE TENSION A. The Motor Unit A. A motor neuron plus all the muscle cells that innervate it a. A single motor unit has an average of 150 fibers being innervated by each motor neuron. B. Twitch contraction A. The brief contraction of all muscle fibers in a motor unit in response to a single action potential. B. Muscle contractions are recorded by a myogram C. Latent period : the delay following an action potential and the onset of contraction D. Contraction period : Ca++ binds to troponin and peak contraction is developed E. Relaxation period : time that Ca++ is transported back into the sarcoplasmic reticulum. F. Refractory period : the period of lost excitability C. Frequency of Stimulation A. The second contraction will occur stronger than the first B. Wave summation: stronger contractions caused by stimuli arriving at different times. C. Tetanus: unfused or incomplete โ sustained but wavering contraction. Fused or complete tetanus โ individual twitches cannot be detected. D. Motor Unit Recruitment A. Motor unit recruitment โ the process in which the number of active motor units increases. B. Clinical connection: Anaerobic training vs Aerobic training E. Muscle Tone A. Even at rest, a skeletal muscle exhibits muscle tone, or a small amount of tension B. Clinical Connection: Hypotonia and Hypertonia F. Isotonic and Isometric Contractions A. Isotonic contraction โ tension is constant while the muscle changes length a. Concentric isotonic contraction โ when the length of the muscle shortens and the object is moved b. Eccentric Isotonic contraction โ when the length of the muscle increases or lengthens during contraction B. Isometric contraction โ muscle contracts but does not change length
VI. SKELETAL MUSCLE FIBER TYPES
A. Types of skeletal muscle fibers A. Slow oxidative fibers a. Small, dark red, fatigue resistant B. Fast oxidative-glycolytic fibers a. Intermediate size, dark red, moderately resistant to fatigue b. Use the cross section to show how must skeletal muscles are mixtures of all types. C. Fast Glycolytic fibers a. Low myoglobin content, few blood capillaries and appear white in color. D. Distribution and Recruitment of different types of fibers a. Most skeletal muscles are mixtures b. Within a motor unit, all muscle fibers are of the same type B. Exercise and Skeletal Muscle Tissue A. Effective stretching a. Stretching is most effective when the muscles are warm, it is important to warm up before stretching B. Strength Training a. The process of exercising a muscle and adding resistance for the purpose of strengthening the musculskeletal system. b. Clinical Connection: Anabolic Steroids C. Cardiac Muscle Tissue A. Intercalated discs โ contain desmosones and gap junctions that allow muscle action potentials to spread from one muscle fiber to another B. Contractions last 10 15 times longer than skeletal muscle C. Mitochondria are larger and more numerous D. Smooth muscle Tissue A. Usually activated involuntarily B. Single unit โ contract as one single unit, similar to cardiac muscle C. Multiunit โ consists of individual fibers that contract independently D. Microscopic Anatomy of Smooth Muscle a. Thick in the middle and tapered at the end b. Contain intermediate filaments in addition to thick and think filaments c. Filaments are connected to structures called dense bodies which are functionally similar to Z discs.
C. Abnormal Contractions of Skeletal Muscle: a. Spasm b. Cramp c. Tic d. Tremor e. Fasciculation f. fibrillation D. Exercise-Induced Muscle damage a. Exercise-induced muscle damage b. Delayed onset muscle soreness (DOMS)
