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 – 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