Muscular System ANATOMY & PHYSIOLOGY

Introduction  600 muscles that make up 40-45% of your body weight  Made up of bundles of muscle fibers (long, slender cells) held together by connective tissue  When stimulated by nerves they contract (become short and thick) which causes movement

Properties  Excitability-the ability to receive and respond to a stimulus  Contractility-the ability to shorten  Extensibility-the ability to be stretched  Elasticity-the ability to resume resting length after being stretched  Automaticity-the ability of a muscle to contract without a nerve supply

Functions  Movement  Locomotion/manipulation  Heartbeat  Moving substances through hollow organs  To hold the body erect/posture  Body heat – 85% of body heat  Joint stabilization  Some Internal organ protection

Types of Muscles CARDIAC, VISCERAL/SMOOTH, & SKELETAL

Types of Muscle  Skeletal  Striated  Voluntary  Smooth – unstriated – involuntary - visceral  Found in hollow organs like - digestive tract, blood vessels, and ducts leading from glands.  Purpose is to move fluids through these structures  Cardiac  Myocardium  Like striated muscle in appearance but like smooth muscle in function.

Cardiac Muscle  Forms walls of the heart  Contracts to circulate the blood  Striated with lots of mitochondria  Involuntary  Efferent nerves control the rate of contraction  Afferent nerves sense pain, spasm, & stretch  Contracts at a steady rate, except for brief, rapid bursts

Visceral/Smooth muscle  Found in the internal organs  Walls of hollow, visceral organs  No striations  Involuntary  Efferent neurons are less important  Afferent nerves are concerned with pain, spasm, and stretch  Steadies constant contractions, automaticity

Skeletal Muscles  40% of the body  Attaches to and cover the bony skeleton  Longest fibers  Striated  Voluntary  Efferent nerves send impulses for contraction  Afferent nerves send message to inform brain of degree of contraction  Contracts rapidly, tires easily; tremendous power, adaptable  Causes body movement

Methods of Attachment to Bone

Tendon  Strong, tough connective tissue cord  Example  Achilles tendon-attaches the gastrocnemius muscle on the calf of the leg to the heel bone

Fascia  A tough, sheet-like membrane  Covers and protects tissues  Example-lumbodorsal fascia which surrounds the deep muscles of the trunk & back

Aponeurosis  Flat sheet of fibrous connective tissue that connects muscle to bone or to other tissues

Origin & Insertion  When muscles attach to bones, one end becomes the origin and one end becomes the insertion  Origin – the end that does not move; usually proximal to insertion. Where the muscle begins.  Insertion – the end that moves when muscle contracts. Where the muscle ends.

Physiology of Skeletal Muscle Contraction

Muscle Tone  Steady partial contraction is present at all times  State of tension when awake  State of readiness to act; enables muscles for immediate response  Does not produce an active movement  Keeps muscles firm and healthy  Stabilizes the joints  Maintains posture

Muscle Tone continued  Loss of muscle tone  Can occur in severe illnesses such as paralysis & palsy  When muscles are not used for a long period of time – atrophy, waste away (degeneration & loss of mass)  Complete immobilization of muscle (complete bed rest or in a cast or loss of neural stimulation) – strength decreases 5% per day; paralysis=atrophy to ¼ the initial size; muscle tissue is replaced by fibrous connective tissue – muscle rehab is impossible; delayed with electrical stimulation

Muscle Tone continued  Lack of use can result in contracture (permanent contraction of the muscle due to spasm or paralysis)  Severe tightening of a flexor muscle  Results in bending of a joint  Fingers, wrists, and knees, as well as other joints can be affected

Muscle Tone continued  Muscle fatigue  Muscle is unable to contract  Tension drops to zero  Spasm – sudden involuntary contraction of a muscle  Clonic – a spasm alternating with relaxation  Tonic – sustained

Muscle Tone continued  Tetanus – a smooth, sustained contraction  Tetany – the result of low calcium  Increases the excitability of neurons  Loss of sensation, muscles twitching, convulsions  If untreated-spasms of the larynx, respiratory paralysis, and death can occur

Characteristics  Kinesiology  Muscles work in antagonistic pairs  Biceps brachii – elbow flexion  Triceps brachii – elbow extension  Contraction and relaxation  Muscle innervation  neuromuscular