Chapter_10_Muscular_Tissue.pdf

Chapter 10 – Muscular System 1) Introduction a) 3 types of muscular tissue Muscle Type Skeletal Nuclei/Cell multiple Striated Y Voluntary Y Cardiac 1-2 Y (lightly) N (involuntary) Smooth 1 N N (involuntary) Shape Tubular Branched Intercalated disks Gap junctions Spindle Location Skeletal muscle: tru...

Chapter 10 – Muscular System 1) Introduction a) 3 types of muscular tissue Muscle Type Skeletal Nuclei/Cell multiple Striated Y Voluntary Y Cardiac 1-2 Y (lightly) N (involuntary) Smooth 1 N N (involuntary) Shape Tubular Branched Intercalated disks Gap junctions Spindle Location Skeletal muscle: trunk, arms, legs Heart Esophagus, Gastrointestinal tract, blood vessels, sphincter muscles 2) Properties of Muscle Tissue a) Excitability – ability to be stimulated to contract (via neurotransmitter, hormones, electrical/chemical stimulants) b) Contractility – ability to contract/shorten c) Elasticity – ability to return to shape d) Extensibility – ability to be stretched without being damaged 3) Skeletal Muscle Bundles a) Contains all four tissue types (muscle belly connected by tendons to the skeleton with neurovascular innervation) b) Striated – areas of overlap of myofilaments 4) Skeletal Muscle Functions a) Support/Maintenance of Posture b) Movement c) Temperature Regulation d) Storage & Movement of materials/fluids (blood & lymph) e) Protects internal organs f) Express emotion (facial) 5) Hierarchy of Skeletal Muscle Composition / Structural Organization i) Muscle belly ii) Fascicles iii) muscle fibers = cell iv) myofibrils (made up of sarcomeres end to end) v) myofilaments: thin (actin & others) & thick (myosin) 6) Connective Tissue Components a) Each muscle has 3 layers of concentric connective tissue that is comprised mainly of collagen and elastic fibers. i) Provides protection, sites for blood vessel and nerve distribution, and a means of attaching the muscle to the skeleton. ii) Layers of connective tissue (1) Epimysium – dense irreg CT, encases ms belly, anchors to tendon (may also anchor nn’s, vessels) (2) Perimysium – dense irreg CT, separates fascicles, anchors neurovascular bundles (3) Endomysium – areolar CT (delicate), w/in fascicle, b/n (surrounds) fibers, electrically insulates muscle fibers (4) Superficial fascia – dense CT, surrounds each muscle, separates muscles (a) Superficial fascia – encases groups of muscles, subcutaneous layer of areolar CT (b) Deep fascia – separates individual muscles, dense CT 7) Muscle Fiber Terminology a) Sarco: flesh/muscle (like cyto = cell) (1) Sarcolemma = plasma membrane of muscle fiber (2) Sarcoplasm = “cytoplasm” of muscle (3) Sarcoplasmic reticulum = “endoplasmic reticulum” of cell (storage site of Ca2+) (4) Sarcomere = contractile unit of a myofibril b) Two structures unique to muscle fibers i) T-tubules: extension of sarcolemma going deep into the muscle ii) Terminal cisternae c) Mitochondria: in sarcoplasm (provide ATP for muscle contraction) d) Multinucleated e) Myo: muscle (1) Myoglobin: replaces hemoglobin, ↑’d affinity for O2 at higher temp (2) Myofibril: contracting fiber, runs entire length of cell, many per cell (a) Myofilaments – cylindrical protein fibers making up the sarcomere in the myofibril (i) Thick Filaments 1. Myosin – elongated tail w/ golf club head a. Twice as thick as thin filaments b. 2 myosin tails coil around each other > free heads c. Binding site for actin (thin filament) and another for ATP d. Forms cross-bridge as it attaches to actin (thin filament) (ii) Thin Filaments 1. Actin – double stranded helix pearl necklace (F-actin, G-actin), attachment sites for myosin 2. Tropomyosin – rope covering myosin binding sites 3. Troponin – 3 protein snow man regulatory proteins f) Organization of thick and thin filaments i) Its organization is the cause for striation in skeletal muscle ii) A bands – isotropic, area of thick filament iii) I bands – area of no overlap (1) Titin – protein binding myosin to z-disc (z-band) iv) Components of A & I bands (1) H zone (H band) – only thick filaments, area of non-overlap between actin of same sarcomere, includes M line (2) M line – proteins in middle of sarcomere, anchoring myosin tails join together (3) Z disc (Z band) – proteins separating sarcomeres, anchors thin filaments v) Sarcomeres arranged head to tail (side to side), the length of the myofibril. 8) Motor unit = motor neuron (nerve fiber) + all the muscle fibers it innervates i) Motor neuron can stimulate a few (50) to 2,000 ms fibers (1) Eye – few (2) Quadriceps – several hundred ii) All or none response: (1) all muscle fibers of a motor unit contract at the same time (2) graded response by number of motor units recruited. (3) All ms fibers have only one connection (nerve) to the nervous system iii) Recruitment (1) Smallest MU’s recruited first (2) As demand ↑’s > size of MU recruitment ↑’s (to ↑ load or velocity) (3) As fatigue sets in, can no longer recruit MU’s 9) Neuromuscular junction (NMJ) – contact site of motor neuron on muscle fiber (a) Components (i) Synaptic knob - end of axon, secretes neurotranmitter (NT) (ii) Synaptic vesicles - contain neurotransmitter (iii) Synaptic cleft - space b/n synaptic knob/terminal & post synaptic membrane (iv) Motor end plate (MEP) = post synaptic membrane on muscle (v) Ach receptors - on MEP, receives NT (vi) Acetylcholinesterase (AChE) = NT released that stimulates the muscle 10) Mechanism of Skeletal Muscle Contraction a) Motor neuron releases neurotransmitter acetyl choline (ACh) at neuromuscular junction b) Ach binds to receptor at motor end plate initiating muscle impulse c) Signal sent across sarcolemma, down t-tubule d) Sarcoplasmic reticulum releases Ca2+ e) Sliding Filament Model activated https://youtu.be/0kFmbrRJq4w (1) Ca2+ becomes available and attaches to troponin (2) Troponin pulls tropomyosin rope off actin, exposing myosin binding site (3) Attachment: myosin (containing ADP + Pi) binds to exposed binding site, releasing Pi (4) Power stroke: myosin uses ADP as energy pulling actin toward center, releasing ADP (5) Detach/Release: (a) new ATP binds to myosin, allowing it to let go of actin. (b) ATP splits (hydrolyzes) into ADP + P and reaches back into starting position (c) Calcium returns to sarcoplasmic reticulum (6) Repeat 11) Fuel sources (in order of which is used first) a) Creatine phosphate (stored in muscle) ↔ creatine + ATP [anaerobic] – fastest, < 5 sec (football play), submaximal contraction b) Glycogen (stored in muscle) ↔ lactate + 2 ATP/glucose [anaerobic fermentation] i) Lactate buildup > soreness, requires O2 to convert 80% of it back to glucose for storage in liver (Oxygen debt) c) Glycogen (stored in muscle, recruited from liver) > CO2 + H20 + 36 ATP/glucose [aerobic respiration] d) Fat > converted to intermediate molecules used in aerobic pathway, slowest, endurance Size of fiber Type I (SO) small Type IIa large Speed of twitch 2-3x’s slower ↑ Large (2x’s SO) ↑↑ Aerobic capacity ↑↑ Myoglobin / Mitochondrion ↑↑ Force ↓↓ Fatigue Resistance ↑↑ Color ↔ ↔ ↔ ↔ Red (dark meats) pink ↓ ↓↓ ↑↑ ↓↓ white (FOG) Type IIb (FG) 12) Types of Muscle Fibers a) Slow-Twitch (Type I, SO) – aerobic pathways (glucose & fat aerobic respiration) i) Motor units have fewer fibers ii) Dark in color – many mitochondria & myoglobin, dense capillary beds iii) Small MU’s: slower iv) ↑ (endurance - ↑ reserve of glycogen and fat v) ↓ force production b) Fast Oxidative (Type IIa, FOG) i) Intermediate of Type I and Type IIb ii) Similar to fast but more mitochondria, iii) “Wash Theory” Can convert IIb (white sock) > IIa (pink sock), but not I > IIa (1) Marathoners can be made, sprinters are born c) Fast-Twitch (Type IIb/x, FG)– anaerobic pathways (creatine, glucose in fermentation stored in muscle i) Strength – explosive energy: large MU’s ii) Light in color – fewer mitochondria, little/no myoglobin, fewer blood vessels iii) Fatigue quickly iv) Twice the size of slow twitch Energy System aerobic aerobic and anaerobic anaerobic 13) Distribution of Three Muscle Fiber Types a) Usually, skeletal muscles = all 3 muscle fiber types, but varies from muscle to muscle b) Single MU- has single type of fibers c) Postural muscles – slow twitch (soleus) d) Eye and hand – fast twitch only 14) Types of Muscle Contractions a) Isotonic: force/tension remains constant as length change i) Concentric – muscle contracts as it shortens (1) Force of contraction > force of load ii) Eccentric – muscle contracts as it lengthens (lowering weight – ie. bench press lowering) (1) We are 1.3-1.5 x’s stronger eccentrically than concentrically (2) Rips myosin from actin > ↑ ms repair > ↑ strength (3) Force of contraction < force of load b) Isometric – maintains same length (not moving): i) force of contraction = force of load 15) Amount of Muscle Tension is Dependent on 2 Factors a) Recruitment: ↑MU > ↑ force produced b) Rate of Recruitment (Coding frequency): how rapidly the nervous system stimulates the muscle 16) Exercise a) The relative ratio of fast glycolytic (FG) and slow oxidative (SO) fibers in each muscle is genetically determined >account for individual differences b) Hypertrophy - ↑ in myofilaments (not in # of cells) i) Result of weight training c) Atrophy - ↓ in # of myofilaments i) Result of detraining, shrinkage (can be regained) d) Fatigue is a result of i) Calcium depletion ii) Peripheral fatigue at axon of motor neuron, ↓Na+/K+ iii) ↓ neurotransmitters (Ach) 17) Cardiac Muscle a) Autorhythmicity: ability to generate own spontaneous potentials b) Intercalated discs i) Gap junctions ii) Desmosomes c) Branched fibers i) Fibers are short and flat ii) 1-2 nuclei iii) Endomysium present; lacks perimysium and epimysium 18) Smooth Muscle a) 2 types i) Visceral (single-unit) (1) Skin, sheaths of aa’s/vv’s, stomach, GI, uterus, urinary bladder (2) Gap junctions spread activating potential for quick response (3) Activated by neurotransmitters, hormones, autorhythmic fiber ii) Multi-unit smooth muscle (1) Individual fibers, each with its own motor neuron terminal (2) Few gap junctions: stimulation causes only that one particular fiber to fire (3) Large vessels (aorta, large arteries), arrector pili, iris (diameter), and ciliary bodies attaching to lens 19) Aging a) 10% muscle loss between ages 30-50 b) 40% muscle mass lost by age 80