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
Chapter 8 Muscles Muscular system – typically refers to skeletal muscle muscle (organ) – composed of muscle tissue, connective tissue and nervous tissue Functions of Muscles 1. Body movements 2. Maintain posture 3. Moving substances (mostly smooth) (GI and respiratory tract) 4. Generating heat (75% of ATP energy is lost as heat during contraction) 5. Pump blood (cardiac) TRIVIA! • How many muscles are there in the human body? – – • Answer: 640 Muscles The muscles make up about 40 % of the body mass. What is the longest muscle in the body? – – • Answer: The Sartorius The Sartorius runs from the outside of the hip, down and across to the inside of the knee. It twists and pulls the thigh outwards. What is the smallest muscle in the body? – – • Answer: The Stapedius The Stapedius is located deep in the ear. It is only 5mm long and thinner than cotton thread. It is involved in hearing. What is the biggest muscle in the body? – – Answer: The Gluteus Maximus The Gluteus Maximus is located in the buttock. It pulls the leg backwards powerfully for walking and running. Skeletal Muscle Movement • Movement – muscle move bones by pulling not pushing. – Synergists – any movement is generally accomplished by more than one muscle. All of the muscles responsible for the movement are synergists. – Prime Mover (agonist) = one most responsible for the movement – Ex. Push-up: see attachment Pushup.pdf • Movement cont. – Antagonists – muscles and muscle groups working in pairs – when one contracts the other relaxes (extends). – example: the biceps brachii flexes your arm and the triceps brachii extends your arm. Portions of a muscle origin • Origin: end of the muscle attached to the bone that remains stationary belly • Insertion: end of the muscle attached to the bone that moves • Belly: the fleshy part of the muscle between the tendons of origin and/or insertion insertion Categories of skeletal muscle actions • Categories Actions • • • • • • • • Increases the angle at a joint Decreases the angle at a joint Moves limb away from midline of body Moves limb toward midline of body Moves insertion upward Moves insertion downward Rotates a bone along its axis Constricts an opening Extensor Flexor Abductor Adductor Levator Depressor Rotator Sphincter Naming Skeletal Muscles Trapezius • Shape: – deltoid (triangle) – trapezius (trapezoid, 2 parallel sides) Deltoid – serratus (sawtoothed) – rhomboideus (rhomboid, 4 parallel sides) – orbicularis (circular) Serratus anterior Rhomboideus major Muscles Named by Location • Frontalis (over frontal bone) • Tibialis anterior (front of tibia) • Brachii (arm) • Lateralis (toward outside) tibialis anterior Muscles Named by Size • • • • • • maximus (largest) minimis (smallest) longus (longest) brevis (short) major (large) minor (small) Psoas minor Psoas major Muscles Named by Direction of Fibers • Rectus (straight) –parallel to long axis Rectus abdominis • Transverse • Oblique External oblique Muscles Named for Number of Origins Biceps brachii • Biceps (2) • Triceps (3) Muscles Named for Origin and Insertion Sternocleidomastoid originates from sternum and clavicle and inserts on mastoid process of temporal bone insertion origins Muscles Named for Action • Flexor carpi radialis (extensor carpi radialis) – flexes wrist • Abductor pollicis brevis (adductor pollicis) – abducts thumb • Adductor magnus – adducts thigh • Extensor digitorum – extends fingers Adductor magnus The 3 Types of Muscle Tissue 3 Types of Muscles Skeletal Muscle Smooth Muscle Cardiac Muscle Smooth Muscle • Fibers are thin and spindle shaped. • No striations • Single nuclei • Involuntary • Contracts slowly Smooth Muscle • Found in the circulatory system – Lining of the blood vessels • Found in the digestive system – Esophagus, stomach, intestine • Found in the respiratory system – Can regulate air flow • Found in the urinary system – Urinary bladder Cardiac Muscle • Cells are branched and fused with one another = intercalated discs • striatied • Each cell has a central nuclei • Involuntary • Intermediate contraction speed Cardiac Muscle • Healthy cardiac muscle NEVER fatigues Skeletal Muscle • Fibers are long and cylindrical • multiple nuclei • striatied • Voluntary • Rapid contraction speed Skeletal Muscle • Composed of striated muscle cells (muscle fibers) and connective tissue. – Most muscles attach to 2 bones that have a moveable joint between them. Connective tissue components: - Muscle fibers (cells) are soft and surprisingly fragile - Thousands of fibers are held together by fibrous connective tissue – provides the strength and support Tendon: thick dense connective tissue extension of the fascia attaching muscle to bone Aponeuroses – sheet-like structure of dense connective tissue connecting muscle to muscle Muscle Structure Terms: Outside to Inside • • • • • • • Fascia Epimysium Perimysium Fascicle Endomysium Muscle Fiber Myofibril Components of a Muscle Cell (Myofiber) • Sarcolemma – Cell membrane of a muscle fiber • Sarcoplasm – Cytoplasm of cell w/ large numbers of glycosomes (granules of stored glycogen) and significant amounts of myoglobin – Myoglobin • Oxygen binding pigment (protein) related to hemoglobin • T tubules – Deep invaginations of membrane which allow depolarization of the membrane to quickly penetrate to the interior of the cell • Multiple nuclei • Multiple mitochondria – Produce ATP (energy) for the cell by cellular respiration • Myofibrils – Cylindrical organelles which contain contractile proteins Components of a Myofibril • Sarcomere = single contractile unit of a myofibril – Hundreds end to end per myofibril • Actin = thin filaments (protein) – Filaments pulled during contraction • Myosin = thick filaments (protein) – Contain ATPase – Studded w/ myosin heads • Z disc (line) = actin attachment site • M line = myosin attachment • A Band = dark band of myosin (and actin overlap) • I Band = light band of only actin fibers • H zone = only myosin filements – Disappears during contraction Muscle contraction • A muscle cell must be stimulated by a neuron to contract • Motor unit = a motor neuron and all the muscle fibers it stimulates (on ave. 150) • Neuromusclar junction = site where a neuron’s axon meets the muscle fiber – DO NOT actually touch – gap between them called synaptic cleft • During contraction the myofilaments slide over each other increasing overlap = sliding filament theory Sequence of event in muscle contraction: 1. Nerve impulse reaches end of motor neuron 2. Neurotransmitter acetylcholine (ACh) released and diffuses across synaptic cleft 3. ACh binds with receptors on sarcolemma causing depolarization of membrane (causes action potential) 4. Action potential travel along sarcolemma and down T tubules 5. Changes permeability of sarcoplamic reticulum, opening protein channels allowing Ca ions to flood into sarcoplasm 6. Ca binds to actin filaments changing shape and exposing active sites 7. Myosin heads bind to active sites forming cross bridges 8. ATP is broken down and energy released flexes the myosin head pulling the actin filaments 9. Actin filaments are pulled toward each other shortening the sarcomere by pulling the Z lines towards each other (H zone disappears) Sequence for return to resting state: • Ach in synaptic cleft broken down • Calcium ions pumped back into sarcoplasmic reticulum by active transport (requires ATP) • Active sites on actin are again covered • Actin filaments slide back to original position • Extra fact: Botulism blocks the release of Ach stopping motor neuron stimulation of respiratory muscles Fueling Muscle Contraction: 1. Use available ATP - Very limited supply 2. Use Creatine Phosphate - 4-6x more abundant then ATP - contains a high-energy phosphate bond - can quickly convert ADP back into ATP in mitocondria - again supply is limited 3. Convert glucose into ATP - using cellular (aerobic) respiration - from blood or glycogen - also occurs in mitochondria and requires oxygen 34-36 Oxygen Debt: During rest or moderate activity respiratory and cardiovascular system supply sufficient oxygen to muscles. During heavy activity it cannot - eventually converts to anaerobic respiration Lactic acid fermentation occurs – lactic acid must be removed by blood and reconverted in liver to glucose (requires oxygen) Creates oxygen debt: = amount of oxygen required for liver to convert lactic acid to glucose + oxygen required for muscle cells to restock ATP and creatine phosphate - slow to repay – may take several hours Muscle fatigue: - After prolonged activity muscle may lose ability to contract = fatigue - Usually result of high lactic acid buildup in muscles - Lowers pH and muscles no longer respond to stimulus - Lactic acid also stimulates pain receptors and muscle soreness occurs Benefits of exercise: Aerobic: (lead to resistance to fatigue) - more capillaries form around muscle - more mitochondria and myoglobin in cells - more metabolic enzymes produced (glycolysis) - heart becomes stronger - more RBC’s produced - respiratory system increases efficiency Resistance: - muscle cells produce more myofilaments (increase mass) - connective tissue increases in thickness - capable of contracting w/ more force - resting metabolic rate increases Graded Responses: • Multiple fiber summation – – Weak signal from CNS stimulates small motor units first – As signal strength increases, more motor units are excited = recruitment – more and larger motor units are activated, the force of muscle contraction becomes progressively stronger – Maximal tension = all possible motor unit are activated • Frequency summation – - in skeletal muscles, the force exerted by the muscle is controlled by varying the frequency at which action potentials are sent to muscle fibers - twitch = single contraction lasting fraction of a second - if next action potential arrives before complete relaxation the force of twitches combines - tetanus – sustain contraction lacks even partial relaxation Myogram Concentric: Force is greater than load – muscle shortens Eccentric: Force is weaker than load – muscle lengthens slowly Isometric: Force is equal to load – Muscle length remains same Types of Fibers • Slow Oxidative Fibers – Dark red – Large amounts of myoglobin and mitochondria – Aerobic respiration • Fast Glycolytic Fibers – Low myoglobin content – Few mitochondria – Anaerobic movement Typical person = 50/50 Elite sprinters – as much as 80% fast twitch Elite marathoners – as much as 80% slow twitch