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

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 Contraction Events (refer to handout)

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 Muscles Agonist--Antagonist Agonist (Prime Mover) Main muscle Antagonist opposite movement

Roles of Skeletal Muscles Synergist Synergist—assists agonist provides additional force

Roles of Skeletal Muscles Fixator Fixator (Stabilizer) stabilizes a body segment prime mover can act more effectively

Selected Superficial Skeletal Muscles (Anterior View) Deltoid Location: “caps” the shoulder Action: shoulder abduction Biceps brachii Location: front of upper arm Action: elbow flexion Pectoralis major Location: front of chest Action: shoulder adduction

More Anterior Muscles Sternocleidomastoid Quadriceps Diaphragm 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

Anterior Skeletal Muscles

Selected Superficial Skeletal Muscles (Posterior View) Trapezius Location: top of shoulder/neck Action: neck extension; elevation Triceps brachii Location: posterior upper arm Action: elbow extension 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

Posterior Skeletal Muscles

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

Muscle Diseases and Disorders

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.

FIBROMYALGIA PAIN POINTS

Muscular Dystrophies Muscle destroying diseases Degeneration of individual muscle fibers Progressive atrophy of skeletal muscles Due to a genetic defect

Muscular Dystrophy in lower limbs

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

Shinsplints

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

Myasthenis gravis eye droop

The End