Skeletal System

The Axial Skeleton

Skeletal System – Framework of the human Body

Has approximately 206 bones

Comparable in strength to reinforced concrete

Self-RepairingProduces blood cells

Reservoir for minerals such as calcium and phosphorus

Bones of the Head – Head is divided into two main parts, cranial and facial bones.

Cranial Bones

Cranium - The brain case that composes the top, sides, and rear of the skull.

Frontal Bone (forehead), Parietal Bones (top of the head), Temporal Bones (sides of the head), Occipital Bone (back of the head)

Suture – The joints where cranial bones are fused tightly together. Also help absorb shock from a blow to the head.

Fontanels – The cranial bones in an infant’s skull are not fused tightly together yet,

but they do have tough membranes that are called fontanels or “soft spots.”

These “soft spots” allow for the baby’s head to flex, without breaking during natural birth. They also allow the child’s skull to grow larger.

Facial Bones

Maxillary Bones – Forms the central portion of the face and serve as the attachment to your upper teeth

Mandible – Forms the lower jaw and holds the lower teeth. It is the only movable bone in the skull and is held to the cranium by ligaments.

Ligaments – Tissues that join bones to other bones

Sinuses – Hollow spaces in certain bones of the skull. They help give your voice different qualities

and allows for the skull to be lighter than if it were made of solid bone.

Middle Ear Bones – The smallest bones in the body are the Malleus (Hammer), Incus (Anvil), and stapes (stirrup).

These are the mechanical linkage between the eardrum and the cochlea, which amplifies vibrations allowing you to hear.

Bones of the Spine

Vertebral Column – (a.k.a. spine, spinal column, or backbone) The support to which all the other parts of the skeleton are attached.

Made up of 26 individual bones called vertebrae. Hollow cavities along the back of each vertebra form

a long vertical tunnel through the spine that encloses the spinal cord

Intervertebral Disks – Disks of flexible cartilage, which allow the spine to bend and twist and absorb shock.

Cervical Vertebrae – (Referring to the neck) The 7 vertebrae that form the neck.

Atlas – Top vertebra that has special bearings that allow the head to rotate up and down

Axis – Vertebra located just under the Atlas that allows the Atlas to swivel left and right.

The other vertebrae allow for a little movement, but most of it happens with these two vertebrae.

Thoracic Vertebrae – (referring to the chest) Serve as attachments for the rib cage

Lumbar Vertebrae – (Referring to the lower back) The largest of the vertebrae because they have to support the entire upper body.

Pelvic/Sacral Vertebrae – (Referring to the sacrum) 9 vertebrae that make up the Sacrum and the Coccyx

Sacrum – 5 Vertebrae that fuse together in adults. It is joined to the hip bones and forms the base of the spine

Coccyx – (Tailbone) 4 Vertebrae that fuse together in adults. Serves as attachments for muscles that allow us to stand upright

Curvature of the Spine – the spine is designed to have a natural S curve if you look at it from the side.

This allows the spine to have more flexibility and strength.

Scoliosis – Severe lateral (sideways) curvature of the spine

Kyphosis - (Humpback, Hunchback) Excessive thoracic curvature

Lordosis - (Swayback) Excessive lumbar curvature

Bones of the Chest

Thoracic Cage – Bones that protect the thoracic cavity

Ribs – Long curved bones that attach directly to the thoracic vertebrae in the back and indirectly

by the costal cartilages to the sternum (breastbone) in the front

Costal Cartilages – Connect the ribs to the Sternum. Allows for the Thoracic Cage to expand and contract during breathing.

True Ribs – Costal Cartilage connects directly to the Sternum

False Ribs – Costal Cartilage connects to Costal Cartilage of other ribs

Floating Ribs – Have no Costal Cartilage at all

Bones of the Shoulders – Are known as the pectoral girdle

Clavicle – (collarbone) Anchors the whole arm to the axial skeleton

Scapula – (shoulder blade) not rigidly fixed to the axial skeleton, which gives them more mobility.

Bones of the Upper Extremities (Arms) – Designed for both strength and dexterity

Humerus (Ha ha) – Makes up the upper arm and is connected to the scapula.

Ulna – On the same side as your little finger, attached to the humerus in a hinge-like joint.

Radius – Same side as your thumb, attached to the ulna and humerus, which allows it to rotate around the ulna

Designed to let your arm twist clockwise and counter-clockwise

Carpals - Bones in the wrist

Metacarpals – 5 Bones that branch off from the carpals.

Phalanges – Form the fingers and thumb

Bones of the Pelvis – The bodies lower appendages are connected to the axial skeleton by the pelvis

Pelvic Bones – Attach to the sacrum and forms a rigid ring of bone that supports the body

Bones of the Lower Extremities (Legs) – Theses bones are thicker and stronger because

they have to hold the body’s weight when the body is standing, running, and jumping.

Femur – Makes up the upper leg/thigh, connected to the pelvic bone at the hip

Tibia – (Makes a T) The main weight-bearing bone of the leg, connected to the femur at the knee

Fibula – Smaller than the tibia, connected to the tibia at the knee

Patella – (kneecap) Acts as a brace for the tendon to straighten the leg

Tendon – Strong tough fibers that connect muscle to bone

Tarsal Bones – Bones in the ankle that allow the foot to rotate left and right

Talus – Tarsal bone that connects to the tibia and fibula

Calcaneus – Tarsal bone that forms your heel

Metatarsals – 5 bones that branch off from the tarsal bones

Phalanges – Form the toes of the foot

The Design of Bone

Diaphysis – The shaft of a long bone

Epiphysis – The bulged ends of a long bone

Periosteum – The outside protective covering of the bone

Compact Bone – Dense outer shell of the bone. Gives the bone strength and rigidity

Spongy Bone – A lightweight porous bone inside the epiphysis.

Looks like sponge, but does not feel like sponge

Spaces in spongy bone are where the red marrow is found

Red Marrow – Tissue that produces red and white blood cells

Medullary Cavity – Hollow cylindrical shaped opening in the bone shaft

Holds the red marrow in infants and children, but yellow marrow for adults

Yellow Marrow – A fatty substance used to store fats

Osteoclasts – Cells that move through your bones removing old material making room for new

Carve out little tunnels called Haversian canals lengthwise through the bone

Osteoblasts – Cells that move through the Haversian canals and construct new collagen and Hydroxyapatite

This process was designed to keep our bones strong and resilient

Nutrition

Bones need certain vitamins and minerals to be healthy. Some of the major factors are calcium, phosphorus, and vitamins A, C, and D.

Calcium and Phosphorus make up the inorganic (nonliving) portion of the bone

Vitamin D allows the Calcium and Phosphorus to be absorbed into the body

Your skin can make vitamin D in the presence of sunlight

Vitamin A – Helps bones develop

Vitamin C – Allows osteoblasts to produce collagen

Exercise

Osteoblasts and Osteoclasts can sense which part of the bone is under stress and strengthen each bone accordingly

Wolff’s Law – Bones adjust their shapes to the physical stress placed upon them

Bones of athletes are then bigger then those of non-athletes

Bones of astronauts loose their bone mass when in space, unless special exercises are done

Atrophy – The wasting away or shrinking of bone or muscle do to lack of use.

Construction

When you are developing your osteoblasts form your bones in a process called ossification

Ossification – The process of changing cartilage to bone

Fracture – Where bones break or crack

Transverse – When a bone breaks cleanly in two

Greenstick – Bone bends or breaks but is held together by collagen fibers

Spiral – When a bone is twisted in half

Comminuted – Part of the bone is shattered

Simple – When a bone breaks but does not pierce the skin

Compound – When a broken bone breaks through the skin

Repair

Bone heals with its own cells and not with scar tissue

When a bone is broken there is much internal bleeding

The blood clots to stop the bleeding

New blood vessels are formed around the break to provide nutrients to the area

Osteoblasts and Osteoclasts start to work forming new bone

Cartilage and collagen form in the gap between the broken ends

Osteoclasts move through the break collecting and breaking down bone fragments

Osteoblasts move through the cartilage and making it into spongy bone

Both then work to form compact bone where needed and get rid of excess bone.

Joints of the Skeleton

Joints – Place where bones join or articulate

Immovable (Fixed)– Joints that are rigid

Slightly Movable – Some bending or twisting is possible

Freely Movable – Allow wide range of motion

Structure

Articular Cartilage – Slippery type of cartilage that allows the bones to move smoothly

Synovial Fluid – Lubrication of the articular cartilage

Ligaments – Connect bone to bone and totally encase the joint and creates the joint capsule

Joint Capsule – Serves as a container for the synovial fluid

Types of Joints (Pictures on p. 145)

Hinge Joint – Allows the bone to move back and forth in a single plane

Examples: Elbow, Knee, Fingers

Ball-and-socket Joints – Rounded head of the bone fits into the hollow socket, allows the bone to move in two plane and rotate

Examples: Hip and Shoulder

Pivot Joint – A bone rotates in place against another bone

Examples: Radius at Elbow

Ellipsoid (Condyloid) Joint – Allows bone to move up, down, left, and right, they have a convex head that fits into a

concave portion of another bone.Examples: Base of Fingers

Gliding Joint – One bone slides across the surface of another

Examples: Carpals, Tarsals, Vertebrae

Saddle Joint – Allows bone to move in two planes, has two saddle shaped ends that fit together.

Examples: Base of Thumb

Problems of the Joints

Arthritis – inflammation of the joints, a common degenerative condition of the joints

Osteoarthritis – Where the articular cartilage is worn out between bones. Worst when it is in the hip

Rheumatoid Arthritis – The body’s immune system attacks the tissue of the joint, may cause damage to the articular cartilage,

abnormal growths in connective tissue, or ossification of the joint

Sprain – Ligaments in a joint are overstressed

Dislocation – Joint is stressed to the point of being popped out of alignment

Torn Ligaments – Usually does not tear completely and will regenerate with rest,

if torn completely, they must be surgically reattached