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MUSCLE • • • • I Kinds of muscle tissue A. smooth (visceral) 1) common in many invertebrates and in the viscera of vertebrates – 2) single nucleus – 3) slow contraction – 3-180 sec. – 4) involuntary – as in peristalsis ( wave-like contractions of muscle (intestine) B. Cardiac 1) heart 2) involuntary 3) 1-5 sec heart beat C. Skeletal ( striated) 1) makes up 40% of body weight 2) multinucleated 3) voluntary 4) mostly in limbs & body wall 5) fast reaction .1sec The word “striated” means striped. Skeletal muscle appears striped under a microscope. • • • • • • • • • • • • • – – II Connections A. individual 1) origin (a) end attached to the more stationary part of skeleton 2) insertion (a) end attached to the element moved by contraction B. as whole 1) tendon (cord-like) (a) muscle to bone 2) aponeuroses ( sheet-like) (a) muscle to bone C. sites of attachment 1) bone 2) cartilage 3) connective tissue III. Structure A. Connective tissue Covering 1) fascia (a) layers of connective tissue that separates an individual skeletal muscle from an adjacent muscle • • • • • • 2) epimysium (a) layer of connective tissue that closely surrounds a skeletal muscle 3) perimysium (a) separates muscle tissue into small compartments (fascicles) 4) endomysium (a) encloses muscle fibers within fasicle Muscles / Cells Sarcolemma = muscle fiber membrane Sarcoplasm = inner material surrounding fibers (like cytoplasm) Sarcoplasmic Reticulum - transport Myofibrils = individual muscle fibers, made of myofilaments Nucleus Sarcolemma Mitochondrion Sarcoplasm Myofibril Myofibrils are made of ACTIN = thin filaments MYOSIN = thick filaments Myofilaments ACTIN (thin) and MYOSIN (thick) -- form dark and light bands A band = dArk • thick (myosin) I band = lIght • thIn (actin) • B. Fibers – 1) a single cell that contracts in response to stimulation and then relaxes – when the stimulation ends – 2) thin elongated cylinders ( encased in a membrane (sarcolemma)) – 3) inside these fibers are myofibrils which enclose 2 types of protein filaments – (a) myosin - thick – (b) actin - thin – 4) the arrangement of these give skeletal muscle it’s striations – actin & myosin form a number of repeating sections within a myofibril. – Each section is known as a sarcomere; the functional unit of the – muscle. – (a) striation pattern – 1. I bands – 2. Z lines – 3. A bands It is important to remember the hierarchy fasicles myofibrils myofilaments actin myosin IV. Contraction A. Motor Unit – a motor neuron and all of the muscle fibers it innervates. 1.The CNS sends a signal (electrical impulse) down the axon of a neuron. 2. At the axon terminal, neurotransmitters are released; ACh- acetylcholine 3. Neurotransmitters cross the synapse carrying electrical impulses from the nerve to the muscle. 4. ACh stimulates the muscle to start contraction 5. Once stimulated muscle fibers innervated by the nerve will contract if stimulus is strong enough or not at all if not. “All or nothing Law” – No partial contraction. How Muscles Work with the Nervous System NEUROMUSCULAR JUNCTION - where a nerve and muscle fiber come together MOTOR END PLATE - folded area where muscle and neuron communicate SYNAPTIC CLEFT - gap between the neuron and motor end plate SYNAPTIC VESICLES - where neurotransmitters are stored *these are released into the cleft and tell the muscle to contract SLIDING FILAMENT THEORY (MODEL) The theory of how muscle contracts is the sliding filament theory. The contraction of a muscle occurs as the thin filament slide past the thick filaments. What is needed: ATP Calcium Myosin & Actin Acetylcholine Cholinesterase B. Sliding Filament Theory- Actin & Myosin filaments slide past one another shortening sarcomeres. Muscle fiber shortens 1. Stimulus begins when ACh is released @ neuromuscular junction. 2. The sarcoplasmic reticulum around the myofibril releases Ca+² 3.When Ca+² concentration rises, binding sites on actin open. 4.Cross bridges from myosin attach & pull on actin – sliding it 5. ATP binds to cross bridge releasing it from actin. 6. Ca+² & ATP keep the cycle going as long as they are present * When sarcomeres shorten, the thick and thin filaments do not change length. Rather, they slide past one another. Energy Source -ATP is produced by CELLULAR RESPIRATION which occurs in the mitochondria -Creatine phosphate increases regeneration of ATP * Only 25% of energy produced during cellular respiration is used in metabolic processes - the rest is in the form of HEAT. - maintains body temperature. • • C.Contraction requires energy 1) attached to the actin filament is ATP ( adenosine triphosphate) (a) only enough ATP in muscle for a 10 sec contraction then must use Glycolysis (b) Glycolysis – early phase of cell respiration (c) Cellular respiration is the conversion of glucose into ATP (our energy source) (d) glucose is the sugar we get from our food • • • • • • • • • 2) Glycolysis C6H12O6 + 6O2 6CO2 + 6H2O + ATP (a) 2 types 1. aerobic (with Oxygen) 19 times more efficient than without Oxygen (34 units of ATP) 2. anaerobic (without Oxygen) – Glycolysis is usually 2 units of ATP used when Oxygen can’t be supplied fast enough by the blood to keep up with the demand • • • • • • • • • • • • • D. Oxygen Debt 1. During Strenuous Exercise ATP can be used faster than it is produced. Oxygen is used to synthesize ATP for contraction. • • • • • • • • • • • • • • • E. Athletics 1) blood doping (a) extracting red blood cells and storing until approx. 24 hrs before activity (b) illegal in athletics since 1986 distance runners, skaters, etc. (c) military 1993 special forces at FT Bragg 1998 Australian defense forces scientist in study believed it increased endurance & alertness 2) altitude training (a) high altitude (>5000ft) training can lead to an increase in rbc (b) the atmospheric pressure is less decreasing the oxygen hemoglobin saturation. To make up for this the kidneys secrete a hormone(EPO) that stimulates rbc production in the marrow • • • • E. Reserve 1) ATP can be used faster than it is produced during strenuous exercise 2) muscles must build up a reserve supply (a) fibers store excess ATP on myosin filaments • • 2. Lactic Acid is a byproduct and accumulates when oxygen debt occurs can lead to muscle cramping. • • • • • • • • • • • • • (b) ATP combines with creatine to form creatine phosphate 1. creatine is a natural material that body secretes 2. often taken as a supplement by athletes and body builders * helps supply energy by increasing formation of ATP * can cause asthmatic symptoms and possibly kidney damage F. Steroids 1) promote signs of masculinity increased synthesis of muscle proteins 2) drawbacks organ damage males- hair loss, breast development, stunted height, females- deepening of voice, hair growth, male physique • • • • • • V. Interaction of skeletal muscles A. Skeletal muscles usually function in groups 1) prime mover– muscle that does the majority of work 2) synergist– muscles that assist the prime mover 3) antagonist– a muscle that causes the opposite reaction of a prime mover • 1. Threshold Stimulus Minimal strength required to cause a contraction Motor neuron releases enough acetylcholine to reach threshold 2. All-or-None Response Fibers do not contract partially, they either do or don't • • • • • • • B. All or None 1) a muscle either contracts or doesn’t ( can’t partially contract) C. Summation 1) force of several combined contractions are added together (a) whenever stimuli happen very frequently the muscle might not be able to relax 1. this sustained contraction is tetanic • • • • • • • • • VII. Kinds of Contractions A. Isotonic 1) muscle shortens and there is movement B. Isometric 1) tension with no movement C. tonic 1) long sustained contraction D. twitch 1) short rapid response to a stimulus • • • • VIII. Effects of Muscular exercise A. size change 1) atrophy- shrinking of muscle (lack of use) 2) hypertrophy – increase in muscle size ( use) 3. Motor Unit The muscle fiber + the motor neuron 4. Recruitment more and more fibers contract as the intensity of the stimulus increases 5. Muscle Tone Sustained contraction of individual fibers, even when muscle is at rest 6. Hypertrophy - muscles enlarge (working out or certain disorders) 7. Atrophy - muscles become small and weak due to disuse 8. Muscle Fatigue - muscle loses ability to contract after prolonged exercise or strain 9. Muscle Cramp - a sustained involuntary contraction 10. Oxygen Debt oxygen is used to create ATP, -- not have enough oxygen causes Lactic Acid to accumulate in the muscles → Soreness - • • • • • • • • • • • • • • • • • • B. respiration 1) rate increase (a) supply more Oxygen to muscles C. circulation 1) concentration of RBC increases (a) oxygen D. heart rate 1) increase (a) body demanding more blood E. blood pressure 1) increases (a) need for more blood to muscles F. body temperature 1) increases (a) 60% of energy is given off as heat H. urine production 1) decreases (a) need for extra water (dehydration) Location of Muscles A. Origin – immovable or fixed end of muscle. Head muscle. Most proximal end B. Insertion – movable end of muscle on other side of joint * Muscles may have more than one origin or insertion eg. Biceps Brachii – 2 origins * During Contration: insertion is pulled towards origin. 11. Origin and Insertion Origin = the immovable end of the muscle Insertion = the movable end of the muscle The biceps brachii has two origins (or two heads). What is rigor mortis? A few hours after a person or animal dies, the joints of the body stiffen and become locked in place. This stiffening is called rigor mortis. Depending on temperature and other conditions, rigor mortis lasts approximately 72 hours. The phenomenon is caused by the skeletal muscles partially contracting. The muscles are unable to relax, so the joints become fixed in place. What is tetanus? Tetanus causes cholinosterase to not break down the acetylcholine in the synapse. This results in a person's muscles contracting and not relaxing. A tetanus shot must be administered shortly after exposure to the bacteria. Once you develop tetanus, there is no cure. Interaction 1. Agonist (Prime mover) muscle primarily responsible for producing action. eg. Abducting arm- Deltoid contracts 2. Synergists – assist the prime mover by contracting also. 3. Antagonist – resist prime movers action and cause movement in opposite direction. Eg. Biceps / triceps • • • • • • • • • • • • • • • • • • • • • • • • • IX. Naming muscles A. direction of fibers 1) rectus III (a) rectus abdominus( stomach) 2) oblique /// (a) external oblique( ribs) B. location 1) temporalis (a) temporal bone C. relative size 1) maximus, minimus, longus, brevis, major, minor (a) gluteus maximus (b) gluteus minimus D. number of origins 1) biceps (a) 2 origins E. shape 1) trapezius (a) trapezoid shape F. origin and insertion 1) sternocleidomastoid (a) attached to sternum, clavicle, & mastoid process G. action 1) flexor digitorum (a) flexes digits