Muscular System

KEY TERMS

• Abduction• Adduction• Cardiac muscle• 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

1. Cardiac muscle – forms the walls of the heart and contracts to circulate blood• Involuntary muscle

2. Visceral (smooth) muscle – found in internal organs of the body and contracts to cause movement in these organs• Involuntary muscle

3. 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.