Muscular System Chapter 8 Functional Divisions of Muscle

Muscular System Chapter 8

Functional Divisions of Muscle Control Ø Voluntary – Consciously controlled Ø Involuntary – l Automatically controlled l

Structural Types of Muscles Skeletal Cardiac Smooth

Skeletal Muscle Move appendages Ø Controls posture Ø Controls GI tract openings Ø Generates body heat Ø ØAttached to skeleton ØVoluntary movement ØStriated ØLong fibers ØMany nuclei ØStrongest contractions

Cardiac Muscle Found in the walls of the heart Ø Involuntary Movement Ø Roughly rectangular with branches that contact adjacent cells Ø Striated Ø Intercalated Discs = branching fibers that interconnect Ø l Ø Allow cardiac cells to function as a unit Does not fatigue or develop oxygen debt

Smooth Muscle In walls of hollow organs (GI tract and blood vessels) Ø Dilates pupils Ø Involuntary movement Ø Spindle-shaped Ø Not striated Ø Slowest and weakest contractions Ø No oxygen debt Ø

Tissue Characteristics Ø Excitability l Can receive and respond to stimuli Ø Contractility l Can shorten and thicken Ø Extensibility l Can stretch Ø Elasticity l Can return to original shape

Gross Anatomy of Muscles Ø Muscle Belly/Body l Medial section Ø Fascicle l Group of muscle fibers Ø Muscle l l Fiber 1 individual cell Up to 12 inches

Connective Tissues

Gross Anatomy of Muscles Ø Fascia l l Sheet or broad band of dense connective tissue Surrounds space between skin and muscles Ø Deep fascia surrounds muscle l l Supports muscles and hold them together as single units Serves as route for passage of blood vessels and nerves

3 Types of Connective Tissue Ø Epimysium l Outermost covering around entire muscle Ø Perimysium l Surrounds fascicles Ø Endomysium l Surrounds each individual fiber Ø Each of these types of connective tissue transmit blood vessels and nerves to muscle components

Tendons Ø Near bone three layers of connective tissues converge to form a thick band of dense connective tissue that extends from muscle to attach to bone.

Aponeurosis Ø Broad sheet of dense connective tissue Ø May attach muscle to bone or muscle to another muscle

Naming Muscles Ø Direction of muscle fibers: l Rectus (straight) : parallel to body midline, or long bone • Rectus abdominis l Oblique: run slanted • External obliques

Naming Muscles Ø Muscle Size: l Maximus: largest • Gluteus maximus l Minimus: smallest • Gluteus minimus l Longus: long • Adductor longus

Naming Muscles Ø Location: l Bone association • Frontalis, Temporalis Ø Number of Origins: l Biceps: • 2 l Triceps: • 3 l Quadriceps: • 4

Naming Muscles Ø Location of Origin and Insertion: l Sternocleidomastoid • • Origin = sternum and clavicle Insertion = mastoid process Ø Shape: Deltoid = triangle Ø Muscle Action Adductors, abductors, flexors, extensors

Fiber Organization Ø Parallel: (biceps brachii) l Found in most skeletal muscles l Fasicles are parallel to long axis l Fxn of muscle is parallel to individual cells l Entire muscle shortens by same % • Maximum shortening = 30%

Fiber Organization Ø Convergent: (pectoralis group) l Fibers are fanned, come together at a central point to pull on a tendon, tendonous sheet, or seam of collagen fibers l Versatile contraction direction • Stimulation of one group of fibers can determine direction of pull

Fiber Organization Ø Pennate: All fasicles form a common angle with the tendon l Contain more muscle cells than a parallel muscle l Pull at an angle – tendon movement is shorter than parallel l Generates more tension l

Fiber Organization Ø Pennate: l Unipennate: • Muscle cells on one side only l l Extensor digitorum longus Bipennate: • Fiber extends on both sides of tendon l l Rectus femoris Multipennate: • Tendon brances within the muscle l deltoids

Fiber Organization Ø Circular or Sphincter: (Pyloric Sphincter) l Concentrically arranged cells around an opening l Contraction produces a decrease in the diameter of an opening l Found at entrances and exits in digestive and urinary tracts

Large Small Muscle Fiber Myofibrils Myofilaments (Arranged in Repeating units called Sarcomeres)

Microscopic Anatomy Ø Sarcolemma l Plasma membrane of each fiber Ø Sarcoplasm l l Cytoplasm Contains myoglobin (protein – binds oxygen generates ATP; energy source)

Microscopic Anatomy Ø Myofibril specialized cylindrical organelle made of myofilament bundles l 1 -2 um diameter l up to several thousand in 1 fiber l covered by sarcoplasmic reticulum: specialized smooth ER, stores calcium ions l connects to other SR and to sarcolemma by T tubules l

Microscopic Anatomy Ø Myofilament l l Structural protein strands in myofibril Made up of mainly actin and myosin Ø Sarcomere l Basic unit of contraction

Sarcomere Anatomy A Band = area where thick and thin filaments overlap, dark striations Ø I Band = area where only thin filaments occur, light striations Ø Z Line = dense protein (connectin) extending perpendicular to length of myofibril l lies in the middle of each I-band l connect thin filaments and individual myofibrils to each other Ø

Sarcomere Anatomy Sarcomere = area between two Z lines H Zone = area in middle of A bands where there is no overlap of thin filaments l Only visible in relaxed muscles Ø M Line = fine (desmin) proteins l Connects middles of thick filaments l Found in middle of H Zone Ø Ø

Thick Myofilaments Ø Myosin l l l golf club shaped proteins with long tails and "fat" heads filament consists of staggered myosin macromolecules have actin binding sites and ATP binding sites with ATPase

Thin Myofilaments Ø Actin l l l anchored to Z lines kidney bean shaped monomers; polymerized into long chains tropomyosin coils around actin troponin binds to tropomyosin and to actin Tropomyosin/Troponin Complex blocks active sites on actin chains 6 thin filaments are arranged as a hexagon around each thick filament

Sliding Filament Theory Ø Thin filaments slide over thick filaments Ø Z lines pull together Ø I band H zone shorten Ø A band stays same length

Resting Muscle Ø Calcium ions are stored in SR Ø ATP is bound on thick filaments Ø Troponin is blocking myosin binding site on actin

Sliding Filament Theory v v v Impulse arrives at neuromuscular junction Ach reaches receptors in muscle cell, signals ion channels to open Sodium flows into cell Action potential travels down T-tubules Signals SR to release calcium

Sliding Filament Theory v Ca 2+ binds to troponin molecules in the thin filaments (actin) v Troponin moves laterally to uncover binding site for myosin v Cross bridge attachment v Myosin binds to actin v Ca 2+ also activates splitting of ATP v Leaves ADP and PO 4 hanging on myosin

Sliding Filament Theory v Power stroke v Energy released from splitting ATP is used to tilt myosin head v Tilting heads pull actin forward v Much energy is lost as heat v ADP and PO 4 are released from head

Sliding Filament Theory v Rigor Complex v Myosin head remains attached to actin v More ATP binds to myosin causing detachment v Cycle repeats, shortening sarcomeres

Sliding Filament Theory

Sliding Filament Theory SDSU Biology 590 - Actin Myosin Crossbridge 3 D Animation

Returning to Rest Cholinesterase inactivates acetylcholine v Calcium ions return to sarcoplasmic reticulum by active transport v All cross bridges are broken and thin filaments are allowed to slide back to original positions v

Skeletal Muscle Contraction Physiology Ø Motor unit l Motor neuron and all of the muscle fibers it stimulates Ø Motor neuron l Nerve cells that carry action potentials to skeletal muscle fibers Ø Neuromuscular junction l Specialized site where neuron and muscle come together

Muscle Metabolism Ø Stored ATP is energy source Ø ATP generated by l Phosphorylation of ADP • Anaerobic Fermentation • Aerobic Respiration (Most ATP generated)

Phosphorylation of ADP Ø Once contraction begins stored ATP is used up in a matter of seconds Ø ADP and creatine phosphate stored in muscles l High energy molecule Ø Creatine phosphate is broken down Ø Energy released is used to regenerate ATP

Anaerobic Cycles Ø Oxygen is not required Ø Use stored glycogen Ø Lactic acid formed Ø Produces ATP quickly in small amounts Ø Short-term vigorous exercise l Used up within minutes

Aerobic Respiration Ø Requires oxygen Ø Produces most ATP over long period of time Ø Mitochondria Ø Energy for hours Ø Prolonged activities where endurance is important

Muscle Fatigue Ø Physiological inability of muscle to contract l l Build up of lactic acid lowers cell’s p. H Cell becomes unresponsive to stimulation Ø Relative deficiency of ATP Ø Accumulation of lactic acid Ø Cramps: inability to relax l Lack of ATP stops active transport of Ca++ into SR

Oxygen Debt Ø Temporary lack of oxygen availability Ø Causes accumulation of lactic acid l Muscles feel sore Ø Repaid when additional oxygen is taken in after exercise (heavy breathing) Ø Lactic acid converted to pyruvic acid Ø Synthesize ATP and creatine phosphate Ø Slow process (hours)

Stimuli All or none law l When muscle fiber is stimulated it will contract fully or not at all Ø Threshold stimulus = weakest stimulus that can initiate a contraction Ø Subthreshold stimulus = too weak to cause a contraction

Motor Units Motor Unit: one motor neuron + muscle fibers it stimulates - avg. = 150 Contraction Strength - how many - how frequently Recruitment: Stronger stimuli increases # of motor units activated

Types of Muscle Contraction Ø Twitch l l Rapid response to a single stimulus that is slightly over the threshold 1/10 th of a second Myograph

Types of Muscle Contraction Ø Treppe l l Produces single twitches that rapidly follow each other First few progessively increase in force May allow muscle to “warm-up” “Staircase” phenomenon

Types of Muscle Contraction Ø Wave summation l l l Muscle receives second stimulus before the first contraction cycle is complete Second contraction will be stronger Increased Force: Contraction may be up to 4 times as great as that achieved by a series of twitches

Types of Muscle Contraction Ø Tetanus l Series of stimuli bombard muscle before each contraction cycle can reach completion • 20 – 30 per second l Wave summation reaches maximum value and is sustained until stimuli stops

Types of Muscle Contraction Ø Incomplete tetanus l Partial relaxation occurs between stimuli Ø Complete tetanus l l l 30 -50 stimuli per second Contraction is maintained without any relaxation Lockjaw = severe cramping

Types of Muscle Contraction Ø Isotonic contractions l l Produces movements as the muscle pulls an attached structure toward a more stationary structure Tension held constant until muscle relaxes Produces body movement Provides greater muscle enlargement and endurance

Types of Muscle Contraction Ø Isometric Contraction l l Produces muscle tension Muscle does not shorten • No body movement • Ex: Push against a wall l Muscles contract and tense but no movement

Group Action Example: Ø Prime Mover l triceps brachii Relax during action Ø Synergist l biceps brachii Cause desired action Ø Antagonist l Elbow forearm muscles Steady movement Ø Fixators chest, back, shoulder Stabilize origin of the prime mover

Muscle Development and Coordination Ø Direction: Cephalic Caudal l Gross Motor Fine Motor l Lift head…. sit up…. grab large objects…. Pinch! (9 months)…. walk l