Muscular System

KEY TERMS Abduction Fascia Adduction Flexion Cardiac muscle Insertion Circumduction Contract Contractibility Contracture Elasticity Excitability Extensibility Extension Fascia Flexion Insertion Involuntary Muscle tone Muscular system Origin Rotation Skeletal muscle Tendons Visceral (smooth) muscle Voluntary

Key Points Over 600 muscles make up the muscular system 45% of total body weight as an adult Contraction depends on myofilaments (actin and myosin) Sliding filament theory

Basic Anatomy of Skeletal Muscle Each muscle is an organ 100s to 1000s of muscle fibers per muscle Endomysium – fine sheath of connective tissue around each muscle fiber Perimysium – collagenic sheath around several muscle fibers bundled together (fascicles)

Characteristics of Muscles Excitability: the ability to respond to a stimulus such as a nerve impulse Contractibility: muscle fibers that are stimulated contract which causes movement Extensibility: the ability to be stretched Elasticity: allows muscle to return to its original shape after being contracted or stretched

Three Main Kinds of Muscle Cardiac muscle – forms the walls of the heart and contracts to circulate blood Involuntary muscle Visceral (smooth) muscle – found in internal organs of the body and contracts to cause movement in these organs Skeletal muscle – attached to bones and causes body movement Voluntary muscle

Functions of the Muscular System Movement – voluntary and involuntary Produce heat and energy for the body Help maintain posture by holding the body erect Protect internal organs Stabilization of joints

Muscle Attachments Tendons- Strong, tough connective-tissue cords. EX. Achilles tendon Fascia- Tough, sheet-like membrane that covers and protects the tissue. Origin- the end of the muscle attached to the non-moving bone. Insertion- the end of the muscle attached to the moving bone.

Muscle Movements Adduction: moving the body part toward the midline Abduction: moving the body part away from the midline Flexion: decreasing the angle between two bones, or bending Extension: increasing the angle between two bones, or straightening Rotation: turning a body part around its own axis Circumduction: moving in a circle at a joint

Anterior Upper Body

Posterior Upper Body

Anterior Lower Body

Posterior Lower Body

Muscular Information Muscle tone – the state of partial contraction Muscles are partially contracted even when not in use Atrophy – when muscles shrink in size and lose strength Due to injury or severe illness Contracture – a severe tightening of a flexor muscle resulting in bending of a joint

Diseases and Abnormal Conditions Fibromyalgia – chronic, widespread pain Symptoms: muscle stiffness, numbness or tingling in the arms or legs, fatigue, sleep disturbances, headaches, and depression Cause is unknown, but stress, weather, and poor physical fitness affect the condition Treatment: directed towards pain relief

Diseases and Abnormal Conditions Myasthenia Gravis Chronic condition where nerve impulses are not properly transmitted to the muscles Leads to progressive weakness and eventually paralysis Cause is unknown Thought to me an autoimmune disease with antibodies attacking the body’s own tissues No cure

Diseases and Abnormal Conditions Tendonitis (tendin/o + -itis) Inflammation of the tendon caused by excessive or repetitive use of a joint. Myalgia (my/o + -algia) Muscle tenderness or pain Myorrhexis (my/o + -rrhexis) Rupture of the muscle

Diseases and Abnormal Conditions Muscular Dystrophy Group of inherited disorders that lead to chronic, progressive muscular atrophy (shrinking, losing strength). Usually appears in childhood, most types lead to total disability and early death. No cure, but physical therapy is used to slows the progression.

Diseases and Abnormal Conditions Sprain Injury to a joint (ex. - ankle, knee, wrist). Frequently involves a stretched or torn ligament. Ligaments attach bone to bone. Strain Injury to the body of a muscle or the attachment of a tendon. Usually associated with overuse injuries. Tendons attach muscle to bone. Shin Splint Pain caused by muscle tearing away from the tibia. Usually caused by repeated stress to the lower leg.

Diseases and Abnormal Conditions Paralysis Loss of sensation and voluntary muscle movement due to disease or injury. Damage can be temporary or permanent. Paraplegia Paralysis of both legs and the lower part of the body. Spinal cord injury is below cervical vertebrae

Diseases and Abnormal Conditions Quadriplegia (quadr/i + -plegia) Paralysis of all four extremities. Spinal cord injury involves the cervical vertebrae. Above C5, respiration is affected. Hemiplegia (hemi + -plegia) Total paralysis on one side of the body. Usually associated with stroke or brain injury. Damage to one side of brain causes paralysis on the opposite side of the body.