The Muscular System

The Muscular System

• Muscle tissue found everywhere in the body

Muscle Types

• Three types of muscle tissue – skeletal, smooth, and cardiac

Smooth

Skeletal

Cardiac

Skeletal Muscle

– Usually attached to bones and are responsible for voluntary movement (voluntary muscle)

• Striated/striped – light and dark bands• Cells very large with many nuclei

Smooth Muscle

– Muscles not under voluntary control (involuntary muscle)

• One nucleus in cells and not striated• Found in organs and blood vessels• Helps move food through digestive tracts, decrease size in

pupils, as well as operate other organs in the body

Cardiac Muscle

– Muscle found in heart• Small, striated cells with one to two nuclei• Involuntary muscle found ONLY in the heart

Skeletal Muscle Structure

Skeletal muscle

Bundle of muscle fibers

Actin

Myosin

Sarcomere

Z disc

Muscle fiber (cell)

Myfibril

Muscle Contraction

• Contraction of a single muscle fiber is an all-or-none process – either the fiber completely contracts or it doesn’t

• The NUMBER of fibers stimulated by the nervous system to contract varies with the amount of work/strength needed

• Muscle fatigue caused by not enough ATP getting to muscle– Lactic cid fermentation kicks in = burning sensation in

muscles

How Muscles and Bone Interact

• Individual muscles can only PULL in one direction, so how does your arm move in two directions?

• Skeletal muscle is joined to bones by tendons, which pull on bones and make them work

• Several muscles surround each bone joint to allow pulling in different directions

How Muscles and Bone Interact (continued)

• Muscles work in opposing pairs – when one contracts, the other relaxes. Ex. Upper arm with biceps and triceps

– Biceps contracts = bend elbow (triceps relaxes)– Triceps contracts = extend elbow (biceps relaxes)

• Exercise is important to keep muscles firm and working properly; however, too much exercise all at once can tear and stress muscles and be painful

Opposing Muscle Pairs

Movement Movement

Biceps (relaxed)

Triceps (contracted)

Biceps (contracted)

Triceps (relaxed)

The Skin

The Skin – aka Integumentary System

• Largest sense organ in the body – deals with the sense of touch

Functions of the Skin

• Regulate internal body temperature (warming, cooling, sweating, etc.)

• Block the sun’s radiation with melanin

• Sense organ

• Produces essential vitamins – Vitamin D

• Protective layer to underlying tissues (invasion of microbes, chemicals, etc.)

Two Layers of the Skin

• Epidermis– Outermost layer – dead cells slough off – Has melanin pigments = skin color

• Dermis– Innermost layer– Helps insulate body– Contains blood vessels, nerves, nerve

endings, sweat glands, hair follicles, oil glands

Two Layers of the Skin

Hair follicle

Sweat pore

NervesHair

Epidermis

Dermis

Subcutaneous layer

Muscle

Sweat gland

Fat

Sebaceous gland