(slide 1) Lecture Notes: Muscular System I. (slide 2) Introduction to Muscular System A) Tissues of the Muscular System: 1) Connective Tissues (a) dense fibrous (tendons and ligaments) 2) Nervous Tissue (a) Motor neurons 3) Muscle Tissue (a) Smooth muscle (1) spindle shaped cells (2) single nucleus (3) lacks striations (4) located in walls of hollow organs (BV, GI tract) (b) Cardiac muscle (1) short/branched (2) single nucleus (3) striations with intercalated discs (c) (slide 3) Skeletal muscle (1) structure: (a) multinucleate (b) striated (c) sarcolemma with acethylcholine (protein) receptors (d) Sarcoplasmic Reticulum: controls Ca 2+ release within sarcoplasm (2) function: voluntary contractions B) (slide 4) Functions of Muscles: 1) support upright and erect 2) movement bones, blink, facial expressions, breathing 3) heat (2 nd law of thermodynamics) 4) movement substances within tubes: blood, lymph, bolus, chime 5) protect internal organs by abdominal wall and pelvic cavity floor 6) articulation: stabilize joints Lecture Notes: Muscular System, page 1 of 11
C) (slide 5)Individual Skeletal Muscles are Organs 1) _ dense fibrous CT connect muscle to bone 2) _ CT covers entire muscle extends over muscle and becomes tendon 3) _ groups of individual muscle fibers D) (slide 6)Movements occur at articulations 1) contraction results in a movement muscles shorten and pull bones together 2) _ end of muscle attached to stationary bone 3) end of muscle attached to moving bone 4) (slide 7) antagonistic pair: describes muscles that work to produce opposite movements Note: other muscles function to assist/stabilize prime movers E) (slide 8) Isometric and Isotonic Contractions 1) Isometric contraction iso=same, metric = length 2) Isotonic contraction iso=same, tonic = tension Lecture Notes: Muscular System, page 2 of 11
F) (slide 9) Muscle Names 1) Size (a) gluteus maximus (b) pectoralis major 2) Shape (a) deltoid (b) Trapezius 3) (slide 10) Location/site of attachment (a) frontalis (b) brachialis (c) sternohyoid (d) pectoralis major (e) gluteus maximus 4) Direction of fibers (a) orbicularis oris (b) external oblique (c) transversus abdominus 5) Action (a) adductor lungus (b) flexors (c) extensors II. (slide 11) Steps Leading to a Muscle contraction A) Nervous System 1) _ brain or spinal cord determines an appropriate response is to get a muscle to contract 2) _ connects CNS to muscle fiber (a) (slide 12) dendrites: specialized membrane that conduct nervous impulse toward cell body (b) cell body: metabolic center (cytoplasm and nucleus) (c) axon: specialized process carries nervous impulse away from cell body ends with release of neurotransmitters (d) Note: nervous impulse always travels in one direction dendrite cell body axon Lecture Notes: Muscular System, page 3 of 11
B) (slide 14) Neuromuscular Junction: how CNS communicates with individual muscle fibers (1) (slide 15) Neuromuscular junction: space between the motor neuron axon terminus and the skeletal muscle fiber (2) Nervous impulse travels length of motor neuron reaching the axon terminus (one direction) (3) Acetylcholine (ACh) is released into neuromuscular junction/synaptic cleft by exocytosis (4) ACh diffuses through the cleft (5) ACh binds ACh receptors on the sarcolemma (6) (slide 16) Fate of ACh (a) acetylcholinesterase removes the message to contract (b) ACh is returned to motor neuron within vesicles to be re-used. Lecture Notes: Muscular System, page 4 of 11
C) (slide 17)Skeletal Muscle Fiber 1) Structure: (a) sarcolemma-cell membrane of a skeletal muscle fiber (b) Acetylcholine receptors: proteins located on the sarcolemma (c) Sarcoplasm: skeletal muscle fiber cytoplasm (d) Sarcoplasmic reticulum: modified SERT containing Calcium ions (e) Myofibrils: PROTEINS actin, myosin, troponin 2) (slide 18) Striations: formed from the arrangement of the myofibrils (actin/thin filament and myosin/thick filament) (a) _ (b) _ 3) (slide 19) _ smallest functional unit of a muscle fiber (smallest structural unit of a muscle fiber that can contract) Lecture Notes: Muscular System, page 5 of 11
D) (slide 20) Sliding Filament Theory much supported (experimentally) hypothesis of how skeletal muscle cells generate a contraction 1) At rest: actin and myosin cannot interact 2) (slide 21) Myosin: globular protein (a) gets energy from ATP (b) myosin binds actin (c) uses energy to pull actin toward center of sarcomere Lecture Notes: Muscular System, page 6 of 11
3) (slide 22)Events (a) acetylcholine binds acetylcholine receptors on sarcolemma (b) SR releases Calcium ions into sarcoplasm (c) calcium binds troponin to move exposing the myosin active site on actin (d) (slide 23) _ myosin binds actin (e) myosin swings toward center of sarcomere pulling actin toward center/shortening (f) _ (g) myosin releases actin and repeats crossbridge, powerstroke, ATP (h) continues as long as Calcium ions present Lecture Notes: Muscular System, page 7 of 11
III. (slide 26) Energy for muscle contraction: A) ATP 1) ATP myosin ADP + P + Energy 2) Energy used to shorten sarcomere 3) some energy lost as heat (2 nd law of thermodynamics) B) (slide 27) Aerobic Cellular Respiration 1) mitochondria 2) requires oxygen 3) Glucose + 6 O 2 6 CO 2 + 6 H2O 4) hemoglobin 5) _ muscle fiber protein that can store small amounts of oxygen within muscle cells 6) glucose 7) _ 8)_ storage form of glucose within skeletal muscle cells enter Kreb s as long as oxygen available C) (slide 28) Anaerobic sources of ATP 1) anaerobic no oxygen required in any of the chemical reactions 2) Fermentation (a) glycolysis glucose pyruvate (b) fermentation pyruvate lactic acid 2 ATP per glucose 0 ATP per glucose (c) lactic acid accumulates (2-3 minutes) (1) acidic ph (2) glycolytic enzymes slow (decrease ATP production) 3) (slide 29) _ results as oxygen depleted and fermentation fails to meet ATP demands 4) _ payback as oxygen becomes available, use oxygen to make ATP Lecture Notes: Muscular System, page 8 of 11
D) (slide 30) high energy compound in muscle cells carries high energy phosphate group that can be transferred directly to ADP to make ATP Creatine + Phosphate Creatine-Phosphate Creatine-Phosphate + ADP ATP + Creatine Note: provides about 8 seconds worth energy during intense activity IV. (slide 31) Whole muscle contraction A) Athletics and muscle contraction: 1) Exercise and muscle size Use it or lose it 2) decrease in muscle size due to lack/mild contractions can lead to muscle shortening leaving body in contorted positions 3) _ increase in muscle size due to forceful contractions over prolonged periods (increase number myofibrils/sarcomeres) B) Slow-twitch and fast-twitch muscle fibers Slow Twitch Muscle Fibers Aerobic Steady force Lots mitochondria and myoglobin Dark Lots capillaries Resistant to fatigue Glycogen reserves Fat Reserves Endurance activities Fast Twitch Muscle Fibers Anaerobic Explosions of energy Few mitochondria and myoglobin Light Few capillaries Fatigues rapidly Little energy reserves Weight lifting/brief Lecture Notes: Muscular System, page 9 of 11
C) Muscle Twitch 1) _ initiates a response 2) _ minimum amount of stimulus required to initiate contraction, minimum amount of ACh to begin contraction 3) _ time between threshold and contraction time for calcium to interact with troponin so cross-bridges can form 4) _ myosin forming crossbridge using ATP to continue powerstrokes and sarcomere shortening/generating force 5) _ calcium removed and troponin prevents cross-bridge formation so muscle returns to resting length D) _ either a muscle fiber contracts or it doesn t E) _ even in relaxes state, a few muscle fibers constantly contracting F)_ situation where another stimulus initiates a contraction before muscle returned to resting length G) _ maximum sustained contraction (may) continue until muscle fiber fatigues Lecture Notes: Muscular System, page 10 of 11
H) Whole muscle contractions vary depending on the number of individual skeletal muscle fibers that contract 1) _ single motor neuron and all the muscle fibers it innervates 2) _ depending on the amount of stimulus, more and more motor units are stimulated to increase the strength/force of the contraction Lecture Notes: Muscular System, page 11 of 11