Muscular SystemANATOMY & 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