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 To hold the body erect/posture 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 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