Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Types of muscle • Skeletal muscle Muscle structure and function – striated – voluntary • Smooth muscle Animal Science 123 Animal Growth & Development R. D. Sainz Lecture 09 • Cardiac muscle From: Frandson, RD. 1986. Anatomy and Physiology of Farm Animals. Lea & Febiger, Philadelphia. Smooth muscle • • • • No visible striations Spindle-shaped cells, central nucleus Network arrangement of cells Regulated by autonomous nervous system (involuntary) • Surrounding digestive tract, urogenital system, blood vessels Skeletal muscle • Striated (striped under low-power microscopy) • Multinuclear cells with peripheral nuclei (= fibers) • Fibers arranged in bundles or fasciculi, separated by connective tissue: – Endomysium – surrounds individual fibers – Perimysium – surrounds fiber bundles – Epimysium – surrounds entire muscle Cardiac muscle • Found only in heart • Network of cells, central nuclei • Contraction inherent & rhythmic – rate controlled by autonomic nervous system Skeletal muscle • Cell membrane = sarcolemma (plasma membrane + basement membrane + reticular fibers • Attachments: fleshy or tendons – Origin = least movable attachment (usually proximal) – Insertion = most movable attachment (usually distal) 1 From: Frandson, RD. 1986. Anatomy and Physiology of Farm Animals. Lea & Febiger, Philadelphia. From: Romans, JR, Costello, WJ, Carlson, CW, Greaser, ML, and Jones, KW. 1994. The Meat We Eat. Interstate Publishers, Danville, IL. Histology of skeletal muscle: organelles • Up to 100’s of nuclei, randomly distributed along fiber, just beneath sarcolemma • Mitochondria between contractile elements; concentration varies with fiber type • Ribosomes dispersed in sarcoplasm (very few on sarcoplasmic reticulum; few secreted proteins) • Sarcoplasmic reticulum ≈ endoplasmic reticulum, but also regulates [Ca2+] – action potential causes release of Ca2+ from sarcoplasmic reticulum, stimulates contraction • Transverse tubules (triads), continuous with sarcolemma • Contractile machinery = myofibril • Motor end-plate = neuromuscular junction From: Swatland, HJ. 1984. Structure and Function of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ. Myofibrils • From 100s to 1,000s per fiber • 12-14 aggregated proteins (ca. 55% of total muscle protein) • 2 main classes of filaments: thick and thin • thick filaments – 15 nm x 1,500 nm – mainly myosin • thin filaments – 6 nm x 1,000 nm – mainly actin, tropomyosin, troponin – anchored at the Z-disk, overlap with the thick filaments (A band) Source: Hill et al., 2004. Animal Physiology, Sinauer Associates, Sunderland, MA. 2 Sarcomere • Fundamental unit of muscle fiber • From Z line to Z line From: Swatland, HJ. 1984. Structure and Function of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ. Source: Hill et al., 2004. Animal Physiology, Sinauer Associates, Sunderland, MA. Fiber types • Based upon contraction speed and metabolic pattern • Slow-twitch, oxidative (SO) – AKA Type 1, β red – depend upon oxidative metabolism, ∴↑ mitochondria – ↓ fiber diameters – ↓ cell size (protein:DNA) – slower contraction speeds (≤ 100 msec) Fiber types Fiber types • Based upon contraction speed and metabolic pattern • Based upon contraction speed and metabolic pattern • Fast-twitch, glycolytic (FG) • Fast-twitch, oxidative-glycolytic (FOG) – AKA Type 2b, α white – depend upon anaerobic (glycolytic) metabolism, ∴ ↓ mitochondria – ↑ fiber diameters – fast contraction speeds (↑ myosin ATPase); ≥ 7.5 msec – – – – AKA Type 2a, intermediate, α red both oxidative and glycolytic capacity intermediate fiber diameters fast contraction speeds 3 Histochemical determination of fiber types • Slow, oxidative • Myosin ATPase staining – Slow, repetitive movements, e.g. postural muscles – Very resistant to fatigue – Acid or alkali preincubation – Fast – alkali-stable – Slow – acid-stable – Proportional to twitch speed • Fast, glycolytic – Rapid movements, heavy force generation – Easily fatigued; can go into O2 debt for short periods • Fast, oxidative-glycolytic – Adapted for rapid, repetitive movements – Recruited after SO fibers – Intermediate fatigue; recover faster than FG fibers • Succinate dehydrogenase (SDH) staining – Proportional to mitochondrial density Functions of different fiber types • Also: tonic muscle fibers (unusual) – Multiply innervated – Graded response to stimulation frequency (vs. propagated action potential) – Efficient isometric tension (e.g., anterior latissimus dorsi, holds wings against body) From: Swatland, HJ. 1984. Structure and Function of Meat Animals. Prentice-Hall, Inc., Englewood Cliffs, NJ. From: Gerrard, DE & Grant, AL 2003. Principles of Animal Growth & Development. Kendall/Hunt Pub. Co., Dubuque, IA From: Hedrick, HB, Aberle, ED, Forrest, JC, Judge, MD, and Merkel, RA. Kendall/Hunt Publishing Co., Dubuque, Iowa. Muscle contraction 1. Release of acetylcholine from nerve ending across synaptic cleft (20-30 nm) 2. Twitch response to action potential (ca. 2 msec later) a) ↑ Resting membrane potential (-90 mV → -10 mV) b) Action potential (Na+ influx); 2-4 msec, 5m/sec c) Refractory period 1-3 msec; repolarization (K+ efflux) 1994. Principles of Meat Science. Muscle contraction 1. Intracellular events a) propagation of action potential throughout plasma membrane (including transverse tubules) b) release of Ca2+ from sarcoplasmic reticulum into sarcoplasm & myofibrils c) Ca2+ combines with troponin & changes conformation of tropomyosin, allowing attachment of myosin heads to the actin filament (at the ADP site) 4 Muscle contraction d) Attachment changes the angle between the head & arm of myosin, forcing the filament to slide, shortening the sarcomere e) Changed angle exposes ATP, which is hydrolyzed, releasing energy and detaching the myosin head f) Myosin head bonds to the next ADP site on actin, as long as Ca2+ is present (ratchet theory) g) When stimulation ends, Ca2+ is sequestered by the sarcoplasmic reticulum (calsequestrin = transporter) h) ATP is therefore required for muscle relaxation 5