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The Muscular System. Functions of Muscle Tissue. Movement Facilitation Thermogenesis Postural Support Regulation of Organ Volume Pumps Blood (HEART). Characteristics of Muscle Tissue. Contractility ability to become short and thick while producing movement.
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Functions of Muscle Tissue • Movement Facilitation • Thermogenesis • Postural Support • Regulation of Organ Volume • Pumps Blood (HEART)
Characteristics of Muscle Tissue • Contractility • ability to become short and thick while producing movement
Characteristics of Muscle Tissue • Extensibility • The ability of muscle tissue to be elongated or stretched • Smooth muscle
Characteristics of Muscle Tissue • Elasticity • ability to return to its normal resting length • Skeletal: from being shorter • Smooth: from being extended
Characteristics of Muscle Tissue • Excitability (irritability) • ability to receive and respond to a stimulus
Cardiac Muscle • Forms heart wall (myocardium) • Striated • Involuntary • Fibers quadrangular & branching • Centrally located nucleus • Sarcolemmas connected by intercalated discs • Gap junctions
Smooth (Visceral) Muscle • Walls of hollow internal surfaces such as: • Blood vessels/stomach • Urinary bladder/intestines • Non striated • Involuntary • Can be stretched to great lengths • Allows for tremendous size variability
Skeletal Muscle • Attached to bones • Striated • Voluntary • Multinucleated
Characteristics of Skeletal Muscle • Muscle origin: where muscle begins--tendon attaches to immovable bone (proximal) • Muscle insertion: where muscle ends--tendon attaches to moveable bone (distal) • Belly (gastr): fleshy portion of muscle between tendons
SKELETAL MUSCLE ORGANIZATION • Muscle fibers: elongated muscle cells • Endomysium: membrane around muscle fibers • Perimysium: membrane around fascicles • Epimysium: membrane around entire muscle (fascia)
Key terms • Sarcolemma = muscle cell membrane • Sarcoplasm = muscle cell cytoplasm
Key terms • Myofilaments --contain contractile elements of muscle fiber • Sarcomere: one section of contractile filaments
Actin • Thin Myofilaments • Receptor site for Ca+ • Anchored to the Z line • 2 regulatory proteins • Tropomyosin- follows contour of filament • Troponin = protein on tropomyosin
Myosin • Thick myofilaments • Globular head • AKA cross bridges • Overlap free ends of actin myofilaments • Shaped like a golf club
Sliding Filament Theory of Muscular Contraction • Due to an action potential, the actin and myosin myofilaments slide past one another, shortening the sarcomere • No change in length of myofilaments • H Zone narrows or disappears • I Band narrows or may disappear • A Band remains the same length
SLIDING FILAMENT THEORY OF MUSCLE CONTRACTION • SEE HANDOUT
Muscle--Nerve Interaction • Motor Neuron = nerve cell that excites muscle fiber • Axon – long, threadlike structure that transmits the impulse away from the cell body. • Motor Unit = motor neuron & all the muscle fibers it can effect
Neuromuscular Junction • Neuromuscular Junction = place between nerve & muscle fiber • Motor End Plate - location on muscle fiber next to the nerve
Muscle Nerve Interaction • Synaptic End Bulb - distal end of axon terminal • Synaptic Vesicles - membrane enclosed sacs within the synaptic end bulbs that store neurotransmitters
Acetylcholine • Acetylcholine (Ach) = neurotransmitter released to begin muscle contraction (action potential) • Acetylcholine Receptors—on motor end plate-makes membrane more permeable to Na+
Muscle Response to Nervous Stimuli • All or None Principle • Once a threshold stimulus is applied to a motor unit the muscle fibers innervated by that motor unit will contract to their fullest potential • Threshold Stimulus - the weakest stimulus from a neuron that will initiate a muscular contraction
Roles of Skeletal MusclesAgonist--Antagonist • Agonist (Prime Mover) • Main muscle • Antagonist • opposite movement
Roles of Skeletal MusclesSynergist • Synergist—assistsagonist • provides additional force
Roles of Skeletal MusclesFixator • Fixator (Stabilizer) • stabilizes a body segment • prime mover can act more effectively
Deltoid Location: “caps” the shoulder Action: shoulder abduction Biceps brachii Location: front of upper arm Action: elbow flexion Selected Superficial Skeletal Muscles (Anterior View) Pectoralis major Location: front of chest Action: shoulder adduction
More Anterior Muscles Sternocleidomastoid Location: front of neck Action: turn head to opposite side Diaphragm Location: beneath the ribs Action: breathing Quadriceps rectus femoris vastus medialis vastus lateralis vastus intermedius Location: front of thigh Action: hip flexion; knee extension
Trapezius Location: top of shoulder/neck Action: neck extension; elevation Triceps brachii Location: posterior upper arm Action: elbow extension Selected Superficial Skeletal Muscles (Posterior View) • Gastrocnemius • Location: calf • Action: plantarflexion
More Posterior Muscles • Hamstring Group • semimembranosus • biceps femoris • semitendinosus • Location: posterior thigh • Action: Hip extension; knee flexion • Gluteus maximus • Location: buttocks • Action: Hip extension • Latissimus dorsi • Location: mid back • Action: shoulder extension
Intramuscular Injections • Injections that penetrate the skin and subcutaneous tissue • Used for prompt absorption • Used when large doses are necessary • Preferred sites: • Gluteus medius muscle • Vastus lateralis muscle • Deltoid muscle
Fibromyalgia • Painful disorder of muscles, tendons, and surrounding soft tissue • Muscles feel like they have been pulled or overworked. • Sometimes muscles twitch & other times they burn. • Most patients say that they ache all over.
Muscular Dystrophies • Muscle destroying diseases • Degeneration of individual muscle fibers • Progressive atrophy of skeletal muscles • Due to a genetic defect
Shinsplints • Pain in the anterior lower leg • Tendonitis of tibialis posterior muscle • Inflammation of periosteum • Stress fracture of the tibia • Exaggerated enlargement of muscles within the epimysium • Pulling away of the periosteum from the underlying bone • Treatment: • RICE • Strengthen tibialis anterior muscle
Abnormal Contractions • Unintended muscular contraction not stimulated by normal mechanisms • May be caused by dehydration, electrolyte imbalances or neurological disorders & abnormalities • Examples--tic, twitch, spasm, Charlie horse
Myasthenia Gravis (MG) • A weakness of skeletal muscle • An auto-immune disorder • Caused by antibodies that block the Ach receptors at the motor end plate