Download skin, bones, and muscles

SKIN, BONES, AND MUSCLES
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Skeletal system
 Contains 206 bones
 Functions of the skeletal system:
 Protects internal structures
 Provides attachment for muscles
 Produces red and white blood cells and platelets (in bone marrow)
 Axial skeleton – the central part of the skeleton that includes the skull, spine, ribs,
and sternum
 Appendicular skeleton – forms the appendages (or limbs) that hang from the axial
skeleton
 Structure of bone
 The dense, hard outer covering of bone is compact bone and provides most of
the support
 The porous, loosely structured network that makes up the inside of most bones
is spongy bone
 Some cavities within spongy bone are filled with a soft tissue called bone
marrow
 Red bone marrow produces all blood cells and platelets
 Yellow bone marrow in the hollow parts of long bones is mostly fat
 Periosteum – the tough exterior membrane that surrounds and protects bones;
it contains many blood vessels that supply nutrients to bones
 Osteocytes – bone cells
 Osteoblasts – bone-forming cells
 Osteoclasts – cells that break down bone; usually happens when there is
not enough calcium in the blood so bone is broken down to release the
calcium
 Haversian canals - very small, hollow tubes that carry blood vessels and
nerves from the periosteum through the entire bone
 Osteoporosis – a condition in which bone tissue is lost and bones can become
brittle and break easily
 Can be slowed by getting enough calcium, eating a balanced diet, and regular
exercise
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Joints
 Joint – where two bones meet; they are cushioned by pads of cartilage
 Ligaments – strong bands of connective tissue that hold together the bones in
a joint (connect bone to bone)
 Three types of joints:
 Immovable – permit little or no movement
 Example: cranial bones of the skull
 Slightly movable – permit limited movement
 Example: between the vertebrae of the spine and between the ribs
 Freely movable – joints that permit the most movement
 Types of freely movable joints:
 Ball-and-socket (hips and shoulders) - allows movement in every
direction
 Pivot (between head an d spine) - allows rotation
 Hinge (elbows, knuckles of fingers and toes) - allows bending and
straightening of joint
 Plane/gliding (wrists and ankles) - allows sliding or twisting
movement
 Between joints there is a tissue that secretes a lubricating fluid (synovial) and
cartilage to cushion the ends of the bones and reduce friction from the bones
moving past each other; degeneration of either of these can result in arthritis
(inflammation of the joint)
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Muscular System
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Tendons – strong connective tissue that attaches muscle to bone
Types of muscle tissue:
 Skeletal muscle – attached to the bones of the skeleton; they create voluntary
movement
 Smooth muscle – found in muscles that are usually not under conscious
control such as internal organs (moves food through digestive system), blood
vessels (changes their diameter), and pupils (constricting or dilating in
response to light)
 Cardiac muscle – found only in the heart; cardiac muscle cells can create their
own electrical current to stimulate coordinated contraction (other types of
muscle must wait for electrical stimulation to arrive from a nerve) so the heart
can beat as a whole
Flexor – a muscle that causes a joint to bend
Extensor – a muscle that causes a joint to straighten
Muscle structure
 Muscle tissue contains large amounts of contractile protein filaments called
actin (thin) and myosin (thick)
 Many strands of actin and myosin make up the myofibril  many myofibrils
make up a muscle fiber  many muscle fibers make up a muscle
Muscle contraction
 Myosin attaches to a binding site on the actin and pulls so that the myofibril
and muscle fiber are shortened = contraction
 The actin and myosin are moving in opposite directions during a muscle
contraction
 Needs ATP!!!
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Skin, hair and nails
 Largest organ of the body
 Protects body from injury and dehydration, first line of defense against
disease, and helps regulate body temperature
 Layers of skin:
 Epidermis – outermost layer of skin
 Cells from the epidermis are continuously shed are and replaced by
new cells that grow from below
 Melanin – pigment that helps determine skin color
 Keratin - protein that makes the skin tough and waterproof
 Dermis – functional layer of skin that contains hair follicles, nerve cells,
sweat glands, and blood vessels
 Arrector pili – muscle that is attached to hair follicles and makes hair
stand up when cold or afraid (goose bumps)
 Sebaceous glands – oil-producing glands
 Sweat glands help regulate body temperature
 Subcutaneous tissue – a layer of connective tissue (mostly fat) just below
the dermis
 Hair and nails are dead, keratin-filled cells produced from the epidermis