L5 Muscular System PDF

Support and Movement 3: Muscular System HPHS4072 Anatomy and Physiology in Rehabilitation 1 Outline Skeletal Muscles Structure Mechanisms of Contraction Contractions of Skeletal Muscle Motor Unit Types of skeletal muscle...

Support and Movement 3: Muscular System HPHS4072 Anatomy and Physiology in Rehabilitation 1 Outline Skeletal Muscles Structure Mechanisms of Contraction Contractions of Skeletal Muscle Motor Unit Types of skeletal muscle 2 Introduction Muscle cells represent one of the four basic tissue types of the human body. The collective skeletal muscles of the body make up a substantial proportion of total body weight, about 40% of males and about 32% of females. Muscle tissues serve a range of functions. 3  Properties of Muscle I Contractility [contract] Ability of a muscle to shorten with force 2) Excitability Capacity of muscle to respond to a stimulus 3) Extensibility Muscle can be stretched to its normal resting length and beyond to a limited degree 4) Elasticity Ability of muscle to recoil to original resting length after stretched 4 Classification of Muscle * Ex consciously , “Voluntary” muscles: the actions can be directed by our thoughts via stomach nervous system (skeletal muscles); intestine... * can be involuntary > reflex unconsciously - “Involuntary” muscles: the actions are not under conscious control. 2 Their functions are directed by the autonomic nervous system (cardiac and smooth muscles); 5  cardiac muscle ↑ interculated disks > receive stimulate Types of Muscle Tissue - Skeletal muscle Y Attached to bones Nuclei multiple and peripherally located Striated, Voluntary and involuntary (reflexes) T Zuluh cli > - y Muscleeunicate eath other Smooth muscle stimulate 2) receive Walls of hollow organs, blood vessels, eye, glands, skin 2) S Single nucleus centrally located Not striated, involuntary, gap junctions in visceral smooth 1jh voluntaring music Cardiac music 3) Heart Single nucleus centrally located 2) one nucleus Striations, involuntary, intercalated disks 6  Skeletal Muscle Structure I Most distinctive feature of skeletal muscle is its striations and multinucleate 7 Skeletal Muscle Structure Sacro , myo > muscle - Skeletal Muscle (organ) Epimysium Perimysium Endomysium Nerve Fibrous connective tissue ↓ extend from tendons forms sheaths from tendon Scover - musche (epimysium) that extend around and into skeletal muscle Muscle fascicle Muscle fibers Blood vessels ↓ - : Muscle cell Inside the muscle this connective tissue divides muscle into columns called Epimysium fascicles Blood vessels and nerves Connective tissue around Tendon fascicles is called perimysium Endomysium Perimysium 8  Sucroplasmin Skeletal : muscle Sacro : muscle reticulum endominae I AISI Skeletal Muscle 11 I Structure LEA unit) (myosin) Muscle fibers are muscle cells II Il (Actin) Ensheathed by thin connective tissue layer called endomysium * muscle cell Plasma membrane is called sarcolemma sarem membran a call (fibrousetive tissafe II - # MATE Muscle fibers are similar to other cells except are multinucleate and striated 9  n is Skeletal muscle : *Multiple Smallest unit : largest unit : (muscle cell) 2) Muscle Fascicle > 3) Muscle Fibre > 4) Myofibril > 5) Sarcomere - - 1) Muscle - > - connective Tissues Connective Tissue (muscle's endoplasmic reticulum) (stored (a) Surrounded by : Epimysium Perimysium Endomysium Sarcoplasmic reticulum ThickSilament : Myosin (proteins) X myofclaments Contains : Myofibrils Sarcomeres Thin Actin - fascicle fibre filament : muscle musica Mechanisms of Contraction 10 Structure of Muscle Fiber Each fiber is packed with myofibrils 0. 001 mm - Myofibrils are 1µ in diameter and extend length of fiber Packed with myofilaments Myofilaments are composed of thick filament and thin filaments (work tyt) myosin that give rise to bands which activ underlie striations 11  Structure of a (lengthunchay Myofibril A band is dark, corresponds to the length of thick filaments (mostly myosin) - thin filament > - darker overlapping area X active no Light area at center of A band is thick a lame H zone heads(thick Cl band) / this myosin - cause = area where actin and Stricted myosin don’t overlap (thinfilment) activ A I band is light, corresponds to the distance between A bands, contain X Ovarlap thin filaments (mostly actin) X myosin lighter At center of I band is Z > - line/disc where actins attach ancha point activ of I band = DZ disc 12  Sarcomeres Are contractile units of skeletal muscle consisting of components between 2 Z discs M lines are structural proteins that anchor myosin during contraction * Titin is elastic protein attaching myosin to Z disc that contributes to elastic recoil of muscle Sarcomere I band A band ( myosin actin Contains: Thick filaments proteinin) Thin filaments Proteinin) Z line M line Titin Z line 13 H band Sliding Filament Theory of Contraction During contraction: A band A bands (containing actin), thin filament move # band contract length unchange closer to thick filament, do not shorten I bands shorten because they define distance band reduce between A bands of successive sarcomeres I L overlapping) H band D gone I band H bands (containing myosin) shorten Muscle contraction occurs because thin filaments slide over and between thick filaments towards center: Shortening distance from Z disc to Z disc 14  artin along its length myosin pulls Cross Bridge (Cycle) Cat releases 1) Sliding Filament theory Ca 1) sarcoplasmic reticulum - 2) Nerve Tropin tropomyosin impulse-release Cat + +iv) binds 2) ATP ADP + P- > cooktbird * The zone of myosin ↑ ATP- > ADP + P stroke & actin overlap ADD released) ADP + P leave power ATP bind-release activ ↓ > - myosin > pull autintyt activa [ mysfilament LoverGl mitsin filament venileentrative VATP 15 Cross Bridge 16 Cross Bridge 17 Control of Contraction Control of cross bridge attachment to actin is via troponin-tropomyosin system Serves as a switch for muscle contraction and relaxation The filament tropomyosin lies in grove between g double row of G-actins (that make up actin thin filament) Troponin complex is attached to tropomyosin at intervals of every 7 actins [7 actions > - Troponing In relaxed muscle, tropomyosin blocks binding sites on actin so crossbridges can’t occur This occurs when Ca2+ levels are low Contraction can occur only when binding sites are exposed 18 Summary of the sliding filament theory of contraction Cross bridge Cycle 1. A myofiber, together with all its myofibrils, shortens by movement of the insertion toward the origin of the muscle. 2. Shortening of the myofibrils is caused by shortening of the sarcomeres – the distance between Z lines is reduced. 3. Shortening of the sarcomeres is accomplished by sliding of the myofilaments – the length of each filament remains the same during contraction. 4. Sliding of the filaments is produced by asynchronous power strokes of myosin cross bridges, which pull the thin filaments (actin) over the thick filaments (myosin). 5. The A bands remain the same length during contraction, but are pulled toward the origin of the muscle. 6. Adjacent A bands are pulled closer together as the I bands between them shorten. 7. The H bands shorten during contraction as the thin filaments on the sides of the sarcomeres are pulled toward the middle. 19 Excitation-Contraction Coupling Neuromuscular Junction (NMJ) Muscle receive singal Includes the single synaptic ending of the motor Y mitochondria neuron innervating each muscle fiber(cell) and underlying specializations of sarcolemma cell muscle coll membrane of Place on sarcolemma where NMJ occurs is the motor end plate fibre - on e One muscle neuromuscula junction 20 junction # exocytosis Enzyme 21 Excitation- Contraction Coupling Skeletal muscle sarcolemma is excitable a Conducts Action Potentials >open - Cr Chn Release of ACh at NMJ causes large depolarizing end-plate potentials and APs in muscle APs race over sarcolemma and down into muscle via T tubules # c channel SR- Store cat 22 Excitation- Contraction Coupling T tubules are extensions of sarcolemma Ca2+ channels in SR 4 are mechanically linked to channels in T tubules 3 APs in T tubules cause release of Ca2+ from cisternae via V-gated and Ca2+ release channels Called electromechanical release channels are 10X larger than V- gated channels 23  Da helphind Excitation- Contraction Coupling inside mussie cell > - space 24 Relationship of the Action I Potential 2 Relationship of the action potential, the increase in intracellular 3) Tension [Ca2+ ], and muscle oh musch contraction in skeletal contraction muscle. 25 Muscle Relaxation (stop) Action potentials cease. Ca2+-ATPase pumps move Ca2+ back into SR. No more Ca2+ is available to bind to troponin C, so no more cross bridges are formed. 26  1) motor neuron Consist : 2) muscle fibre it control Motor Unit Each motor neuron branches to innervate a variable number of muscle fibers 3 different motor units A single motor unit: includes a branched motor axon and the all muscle fibers it innervates 27 1) Motor Unit When a motor neuron is activated, all muscle fibers in its motor unit contract Number of muscle fibers in motor unit varies according to degree of fine control capability of the muscle Contraction strength comes from motor unit recruitment. I nerve to one fibre musica Finer muscle control requires smaller motor units (fewer muscle fibers). ↑ density ofhere The eye muscles may have ~20 muscle fibers/motor units. Larger, stronger muscles may have motor units with thousands of muscle fibers. Control and strength are trade-offs. 28 I Muscle Tone Muscle tension at rest > - * Injury Spina corr- timuscletone of brain & Skeletal muscle exhibits muscle tone (tonos = tension) at rest Due to weak, involuntary contractions of its motor units Established by neurons in the brain and spinal cord that excite the muscle’s motor neurons Flaccid: RE fore > - no muscle When the motor neurons serving a skeletal muscle are damaged or cut Small groups of motor units alternatively active and inactive in a constantly shifting pattern  keeps skeletal muscles firm, not result in a force strong enough to produce movement Important in smooth muscle tissues E.g. the walls of blood vessels, GI tracts 29 Muscle Tone ↑E activation Hypotonia: Decreased or lost muscle tone > two little resting muscle - Flaccid muscles are loose and appear flattened rather than rounded Certain disorders of the nervous system and disruptions in the balance of electrolytes  flaccid paralysis無⼒肢體麻痺症 · activation too much resting muscle Hypertonia: Increased muscle tone > - spasticity reflex Increase in tendon reflexes and pathological reflexes u Certain disorders of the nervous system and electrolyte disturbances  spastic paralysis paralysis, partial paralysis Rigidity ↑ reflex Reflexes are not affected 30  Types of Muscle Contractions 1) Reflexive 2) Tonic (normal muscle tone 4) 3) 3) Isometric 4) Isotonic t 4b) 4a) Concentric 4u) contract 4b) Eccentric 31  intain posture stable reflexion - T ⑭ Elexive I - muscle / contractions I ⑮metric Tonic & I / essentric Concentric I ⑳teni Se O muscle / length shorten While generating force - ⑪let e Types of Skeletal Muscle 32  > VO metabolism - Aerobic Slow twitch Type I Fibers > - > - low myosin at pace > Small - diameter activity > - less fore Also called red slow oxidative fibers -TATP > On Vaerobic respiration - - > resistance to - fatigue Adapted to contract slowly without fatigue Uses mostly aerobic respiration O2 inblood Has rich capillary supply, many mitochondria, and aerobic enzymes Has lots of myoglobin (O2 storage molecule) Gives fibers red color Have small motor neurons with small motor units  Fast-twitch - Type II Fibers Type IIX fibers also called white fast glycolytic fibers XO2 glycolytic glycolytic Adapted to contract fast using anaerobic metabolism Has large stores of glycogen, few capillaries and mitochondria, little myoglobin Type II A fibers also called red fast oxidative light red vOt Adapted to contract fast using aerobic metabolism 1 mitochondria ·; Aerobic metabolism Intermediate to Type I and Type IIX Have large motor neurons with large motor units Type IIX TypeT Type IIA Muscle Repair Y Skeletal muscles have stem cells called satellite cells located near muscle fibers. These can fuse to damaged muscle cells and repair them or fuse to each other to form new muscle fibers. ALE E Myostatin is a paracrine regulator that inhibits satellite cells. 36 Muscle Decline with Aging Reduced muscle mass (usually type II fibers) Can be helped with strength training Reduction in capillary blood supply Can be helped with endurance FIS] training Fewer satellite cells, increased myostatin production 37 Production of Movement by Muscles 38 How Skeletal Muscles Produce Movements Muscle attachment Origin: attachment of a muscle’s tendon to the stationary bone Insertion: attachment of the muscle’s other tendon to the movable bone Belly (Body): fleshy portion of the muscle between the tendons 39 Example: Biceps brachii Origin of short head Apex of coracoid process Origin of long head Supraglenoid tubercle of scapula 40  Example: Biceps brachii Insertion Tuberosity of radius, aponeurosis of biceps brachii Nerve supply Musculocutaneous nerve (C5,6,7) Actions of muscle Flexion of shoulder Flexion of elbow 41  The main muscle responsible for movement in a given direction is the agonist (Prime mover) Skeletal Muscles Flexors and extensors; abductors and adductors that work together are antagonists Ill antagonist 42 How Skeletal Muscles Produce Movements Lever system and leverage a rigid structure that can move around a fixed point called a fulcrum (F) acted on at two different points by two different forces Effort (E), which causes movement Load (L) or resistance, which opposes movement 43 Muscle shapes Fusiform Strength of a muscle and the direction of its pull are determined partly by the orientation of its muscle fibres  Domain Examples Shape Deltoid, Rhomboideus Nomenclature: Size Gluteus maximus, gluteus minimus how muscles Location Supraspinatus, infraspinatus are named Action Supinator, pronator Attachment Sternocleiodomastoideus 45 Homeostatic Imbalance Disorders Abnormal Contractions of Skeletal Muscle Spasm · Sudden involuntary contraction of a single muscle in a large group of muscles Cramp: painful spasmodic contraction, caused by inadequate blood flow to muscles, overuse of a muscle, dehydration, injury, holding a position for prolonged periods, and low blood levels of electrolytes, such as potassium. Tic E (mostly in neck head) & Spasmodic twitching made involuntarily by muscles that are ordinarily under voluntary control E.g. Twitching of the eyelid and facial muscles Tremor (shaking) Rhythmic, involuntary, purposeless contraction  produces a quivering or shaking movement 46 Homeostatic Imbalance Disorders Exercise-induced Muscle Damage Torn sarcolemmas in some muscle fibers, damaged myofibrils, and disrupted Z discs Delayed onset muscle soreness (doms) 12 to 48 hours after strenuous exercises Accompanied by stiffness, tenderness, and swelling Microscopic muscle damage appears to be a major factor Increases in blood levels of proteins (myoglobin, creatine kinase) Muscle fibers undergo repair: new regions of sarcolemma are formed to replace torn sarcolemmas, and more muscle proteins are synthesized in the sarcoplasm of the muscle fibers cell Satelliate 47