The Muscular System

Muscles Nearly ½ of your body mass is muscle Muscle is groups of fibers or cells bound together. Major Functions: Motion Maintenance of posture Stabilizes joints Produces heat By-product of muscle activity

Characteristics of Muscle Tissue Contract Ability to shorten & thicken Extensible Ability to be stretched/extended Excitable or have Irritability Can receive & respond to stimuli Elastic Ability to return to their original shape after contraction or extension

Types of Muscle Tissue Smooth Muscle Cardiac Muscle Skeletal Muscle Wall of internal organs & blood vessels Involuntary Generally squeeze the organ they surround to move material Ex. Digestive tract Cardiac Muscle Heart muscle – involuntary – striated Generates & conducts electrical impulses for rhythmic pumping Skeletal Muscle Allows movement – attaches to bone Voluntary – conscious control

Muscle Structure Muscle is made up of fibers Each fiber is made up of smaller units called myofibrils Myofibrils can be divided into units called sarcomeres Function units of muscles

Sacromeres Contractile units Aligned end to end along the length of the myofibrils Composed of smaller units called myofilaments Two types of myofilaments Myosin filament Thick filament Actin filament Thin filaments Arrangement of myofilaments produces the banding pattern (striations) in skeletal muscle.

Nerve Stimulation + Contraction Skeletal muscles must be stimulated by nerve impulses to contract One neuron may stimulate a few or hundreds of muscle cells Motor Unit One neuron & all the skeletal muscle cells it stimulates Nerve impulse releases a neurotransmitter (acetylcholine) that stimulates skeletal muscle. Generates an electrical current called an action potential The action potential travels from one end of the cell to the other causing the muscle to contract.

Muscle Contraction Sliding Filament Theory When signaled by a nerve impulse (release of Calcium ions into muscle fibers), the actin filaments slide toward one another, shortening the sacromeres & causing muscle to contract Myosin filaments do not move but acts as anchors to help the actin filaments move.

Types of Muscle Contractions Isotonic Muscles shorten and movement occurs force generated by a muscle while contracting, when the muscle lengthens and shortens during movement, with the force remaining constant Isometric Muscles do NOT shorten muscle contraction without the muscle or joints moving push against something that is immovable

Muscle Tone Results from a state of continuous partial contraction of portion of a skeletal muscle Essential for maintaining posture Flaccidity is a condition of less then normal tone. Atrophy is a decrease in size or wasting away of muscle tone Hypertrophy is an enlargement or overgrowth

Building Muscle…Exercise! Aerobic exercise results in stronger, more flexible muscles with greater resistance to fatigue Resistance or isometric exercise thickens fibers by adding more myofibrils More groups of myosin & actin Lactic Acid fermentation may occur during rigorous exercise due to low oxygen levels (oxygen debt) in the muscle cells. Causes a buildup of lactic acid & muscle cramps

Producing Movement Muscles produce movement by pulling on bones Muscles attach to bone at 2 points or more. The Origin – attached to immovable bone The Insertion – attached to the movable bone When a muscle contracts, the insertion moves toward the origin Work in opposing pairs One pulls one side of a bone The other “resets” the motion

Naming Skeletal Muscles Named on the basis of distinctive criteria: Direction of muscle fibers – rectus or oblique Relative size – maximus, minimus, or longus Location – temporalis or frontalis Number of origins – biceps or triceps Shape – deltoid (triangular) Location of origin & insertion – sternocleidomastoid Action of muscle – flexor, extensor, adductor

Muscles Named by Location frontalis – frontal bone lateralis – lateral or on the side tibialis anterior – front of tibia fibularis longus – near fibula supra – above infra – below sub - underneath

Shape: Muscles Named by Shape deltoid – triangle latissimus – wide teres - round trapezius – trapezoid serratus –saw-toothe orbicularis – circular

Muscles Named by Size Size: maximus – largest minimis – smallest vastus - huge longus – longest brevis – short major – large minor – small Example: Pectoralis Major

Muscles Named by Direction of Fibers Direction/Orientation: rectus (straight) - parallel to the muscle’s long axis ex: rectus abdominis transversus (transverse) – at right angles to the muscle’s long axis oblique – diagonal

Muscles Named for Number of Origins biceps – two origins ex: biceps brachii triceps – three origins ex: triceps brachii quadriceps – four origins

Muscles Named for Origin and Insertion Points sterno = sternum cleiodo = clavicle mastoid = location on the temporal bone sternocleiodomastoid muscle

Muscles Named for Action flexor carpi radialis – flexes wrist abductor magnus – abducts the thigh extensor digitorum – extends the digits levator – lifts a structure

Muscular System Disorders Fibrosis Formation of fibrous tissue where it normally does not exist Frequently occurs in damaged muscle tissue. Fibrositis Inflammation of fibrous tissue (ex: lumbago) Muscular Dystrophy Hereditary disease of muscles characterized by degeneration of individual muscle cells Abnormal contractions Include spasms, cramps, convulsions, & tics

Muscular System Disorders Tonic seizures involve increased muscle tone or stiffness. Clonic seizures rhythmic jerking which involve only one or a few twitches or jerks without any particular rhythm. Tetanus a medical condition characterized by a prolonged contraction of skeletal muscle fibers Tetany abnormal condition characterized by periodic painful muscular spasms and tremors caused by decreased calcium, vitamin D deficiency, or alkalosis, or following ingestion of alkaline salts.

Muscle and Tendon Injuries Strains injuries from overexertion or trauma which involve stretching or tearing of muscle fibers. often are accompanied by pain and inflammation of the muscle and tendon. Sprain the injury near a joint and involves a ligament Cramps painful muscle spasms or involuntary twitches. Stress-induced muscle tension may cause back pain and headaches.