Muscular System Poudre High School Human AnatomyPhysiology Mr

Muscular System Poudre High School Human Anatomy/Physiology Mr. Bradley 1

The Muscular System · Muscles are responsible for all types of body movement · Three basic muscle types are found in the body · Skeletal muscle · Cardiac muscle · Smooth muscle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 2

Characteristics of Muscles · Muscle cells are elongated (muscle cell = muscle fiber) · Contraction of muscles is due to the movement of microfilaments · All muscles share some terminology · Prefix myo refers to muscle · Prefix mys refers to muscle · Prefix sarco refers to flesh Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 3

Skeletal Muscle striated, voluntary u Multi-nucleated – fibers in bundles u 1 -40 mm long, 10 -100 microns thick u 42% of male body weight, 36% in females u n General « 1. sarcoplasm – cytoplasm of muscle fibers « 2. sarcolemma – plasma membrane covering the muscle fibers « 3. location – any muscle attached to bones as well as in the tongue, the pharynx, and certain muscles of the eye « 4. functions – locomotion, posture, transport of blood and lymph, and heat production (85% of the body’s heat) 4

Cardiac Muscle n n heart muscle, involuntary branched fibers & striated Similar to skeletal muscles u Involuntary control u n purkinje fiber (conduction myofiber) u n n Stimulate actual contraction of the ventricles innervation – autonomic nervous system Functions u Move blood through the heart and through the vessels 5

Smooth Muscle n n n n Involuntary – maintenance of the body’s internal environment Nonstriated Spindle shaped 15 -500 microns long contractions are slow Location – in the walls of internal organs such as digestive organs, trachea, gall bladder, blood vessels, urinary and genital ducts, and the iris of the eye Functions – propulsion, expulsion, regulation of openings, and regulation the diameter of tubes / blood vessels 6

Characteristics of Muscle Tissue n Excitability – ability to receive and respond to stimuli n Contractility – ability to shorten and thicken n Extensibility – ability to stretch Elasticity – ability to return to the original shape n 7

q Skeletal Muscle Tissue Connective tissue components q Fascia – sheet or broad band of fibrous connective tissue superficial – under the skin Ø deep – holds the muscles together thus forming functional groups Ø Epimysium – fibrous connective tissue surrounding an entire muscle q Perimysium – covers a bundle of fibers called fascicles q Endomysium – surrounds each muscle fiber q Aponeurosis – the tendon that extends as a broad, flat layer around the skull or as a part of the abs – figure 78 14 q

Connective Tissue Wrappings of Skeletal Muscle · Endomysium – around single muscle fiber · Perimysium – around a fascicle (bundle) of fibers Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6. 1 9

Connective Tissue Wrappings of Skeletal Muscle · Epimysium – covers the entire skeletal muscle · Fascia – on the outside of the epimysium Figure 6. 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 10

n Nerve and Blood supply MUST HAVE: u Action Potential – the electric current stimulation necessary for contraction u Nerve impulse – causes the stimulation u Muscle action potential – the result u Blood to bring nutrients and oxygen, as well as to carry wastes « Generally there is one artery along with 1 or 2 veins to accompany each nerve 11

n n n Structure – Skeletal Muscle Fibers Sarcolemma – coverings Sarcoplasm – “stuff” inside – many nucleii, and mitochondria Sarcoplasmic reticullum – network of tubules similar to E. R. Transverse tubules – Perpendicular to the S. R. – open to exterior of the muscle fiber Myoglobin – reddish pigment similar to hemoglobin that carries 02 12

Fibers - continued n Myofibrils – Cylindrical structures that run longitudinally through the fibers and contain: thin myofilaments – Made mostly of actin (protein) and small amounts of tropomyosin and troponin u thick myofilaments – made mostly of myosin (protein) u « Shaped like a golf club « Heads are called cross-bridges 13

Microscopic Anatomy of Skeletal Muscle · Organization of the sarcomere · Thick filaments = myosin filaments · Composed of the protein myosin · Has ATPase enzymes Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 14

Microscopic Anatomy of Skeletal Muscle · Organization of the sarcomere · Thin filaments = actin filaments · Composed of the protein actin Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 15

More - fibers Sarcomeres – Basic compartments of myofilaments – functional unit u “A” bands – dark area composed of overlapping actin and myosin u “H” bands (zone) – narrow area in the center of the A band that contains only myosin u “I” bands – contains only actin u “Z” bands – (discs) – dense material between sarcomeres where the myofilaments attach 16

Microscopic Anatomy of Skeletal Muscle · Myofibril · Bundles of myofilaments · Myofibrils are aligned to give distrinct bands · I band = light band · A band = dark band Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 17

Microscopic Anatomy of Skeletal Muscle · Sarcomere · Contractile unit of a muscle fiber Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 18

Microscopic Anatomy of Skeletal Muscle · Myosin filaments have heads (extensions, or cross bridges) · Myosin and actin overlap somewhat Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 19

Microscopic Anatomy of Skeletal Muscle · At rest, there is a bare zone that lacks actin filaments · Sarcoplasmic reticulum (SR) – for storage of calcium Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 20

Muscle Contraction n Sliding filament mechanism – u The myofilaments slide inward towards the center of the sarcomere so the sarcomere shortens but the myofilaments DO NOT! u Sufficient Ca 2+ and adequate energy are required (ATP) 21

The Sliding Filament Theory of Muscle Contraction · Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament · Myosin heads then bind to the next site of the thin filament Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 22

The Sliding Filament Theory of Muscle Contraction · This continued action causes a sliding of the myosin along the actin · The result is that the muscle is shortened (contracted) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 23

Neuromuscular Junction (Motor-end plate) n Consists of a motor neuron and the muscle fibers it stimulates Precise movements require 10: 1 or less fiber to MEP ratio « Gross movements may have as many as 2000: 1 ratio « u u Synaptic vesicles – Sacs at the end of the axon of a neuron Synaptic cleft – The space between the axon and the sarcolemma of the muscle fiber Acetylcholine(ACh) – A neurotransmitter that is released as a result of Ca 2+ from the interstitial fluid « Changes the permeability (especially to Na+) « Carries the impulse to receptors on sarcolemma Cholinesterase(ACh. E) – found in the synaptic cleft « Deactivates ACh within 1/500 of a second by breaking it into acetate and choline thus preventing continuous stimulation 24

Neuromuscular Junction – cont. 25

1. Physiology of contraction The relaxed muscle is low in Ca because the S. R. has 2+ calcium active pumps to remove it from the sarcoplasm. 2. When the action potential travels along the sarcolemma Ca 2+ channels open in the S. R. and a flood of Ca 2+ move into the sarcoplasm around the thick and thin myofiliments 3. Ca 2+ combine with troponin changing it’s shape thus the troponin –tropomyosin complex move away from the bonding sites on actin (exposed) 4. ATP attaches to the myosin crossbridges 5. A portion of each myosin head acts as ATPase (enzyme) which splits ATP into ADP+P 6. The myosin head becomes energized 26

Physiology of contraction – cont. 7. This causes the myosin heads to bind to the binding sites on the troponin- tropomyosin complex 8. Now the heads pivot causing the “power stroke” of muscle contraction. 9. As the thin filaments draw past the thick filaments they release ADP 10. ATP reforms and returns to the myosin crossbridges and the myosin detaches from the actin. ( about ½ of the crossbrides are bound and ½ are preparing to bind at any one time) * * As long as ATP is available and the Ca 2+ is high the contraction will repeat. 27

Relaxation n 2 changes permit the muscle to relax u ACh is broken by ACh. E which prevents the action potential by stopping Ca 2+ release u Calcium active transport pumps remove the Ca 2+ from the sarcoplasm rapidly « At death Ca 2+ leaks and causes rigor mortis – no ATP to release the actin from the myosin 28

n Energy for muscle contraction ATP is the immediate energy source but the muscle only contains enough for 5 -6 seconds of sustained activity. u Creatine Phosphate – high energy molecule found in muscles that can break down into creatine, phosphate, and energy to form enough ATP to last for 15 more seconds. u Now we must access glucose for energy - respiration « Glucose is stored as glycogen in the muscle « Glycogen is broken into 2 pyruvic acids(glycolysis) anaerobically (no O 2 needed) – this requires 2 ATP but it produces 4 ATP – 30 -40 seconds of energy - 29

Energy for muscle contraction « Pyruvic acid enters the mitochondria to be catabolized into C 02 and water – Aerobic (02 required) « This is called the Krebs cycle or the citric acid cycle « This will occur 100, 000 times/second as long as there is pyruvic acid and O 2 available « Each cycle will produce 36 – 38 ATP 30