The Skeletal System Health Science I. Bone Facts Makes up the framework of the body Consists of 206 individual bones in the adult.

The Skeletal SystemHealth Science I

Bone Facts

•Makes up the framework of the body

•Consists of 206 individual bones in the adult

Functions of Skeletal System

• Support structure and provide shape• Protection• Allows for movement and anchorage of muscles• Provides mineral storage• Site of hemopoiesis• Blood cell formation in red marrow of long

bones

STUCTURE OF BONES

• Osteocytes• Microscopic cells of bones• Mature bone cell (osteocyte)

• Bone is made up of

• 35% organic - is a protein called collagen• degree of flexibility

• 65% inorganic - mineral salts (calcium) and water• Give bone its hardness and durability

Bone Formation

• Embryonic skeleton initially consists of collagenous protein fibers secreted by osteoblasts (primitive embryonic cells)• Later, cartilage is deposited between the

fibers• At 8 wks, ossification begins•Mineral matter begins to replace

cartilage, creating bone

Formation

• Infant bones are very soft and pliable because of incomplete ossification at birth• For example: soft spot on a baby’s head:

fontanel• Ossification due to mineral deposits will

continue through childhood making the bone hard and more capable of bearing weight

Structure of Long Bone

• A typical long bone contains a shaft: diaphysis• Hollow cylinder of hard, compact bone•Makes a long bone strong and hard yet

light enough for movement

• At each end is an epiphysis

Structure long bone cont

• In the center of the shaft is the medullary canal.• Filled with yellow bone marrow, mostly made of fat

cells• Marrow contains many blood vessels and some cells

which form WBCs, called leukocytes• Yellow marrow functions as a fat storage center

• Endosteum: • lining of the marrow canal that keeps the cavity

intact

Structure cont…

• Shaft is compact bone• ends of the shaft • are spongy bone (dissolved bone where less strength is

needed)

• Ends of the long bone contain the red marrow where some RBCs (erythrocytes) and some WBCs are made• Periosteum: tough fibrous tissue (outside covering of

bone) which contains blood vessels, lymph vessels, and nerves• Necessary for bone growth, repair, and nutrition

Last on Structure

•Covering the epiphysis is a thin layer of cartilage: articular cartilage•Acts as a shock absorber between 2 bones that meet to form a joint

Growth

• A bone increases its circumference by the addition of more bone to the outer surface of the diaphysis by osteoblasts• bone cells that deposit new bone• As girth increases, bone material is being

dissolved from the center: medullary canal (gets larger as diameter increases)

Growth

• Dissolution of bone from the medullary canal results from the action of cells called osteoclasts• Immense bone cells that secrete enzymes• Enzymes digest bony material, splitting the

bone minerals (calcium and phosphorus) and enabling them to be absorbed by the surrounding fluid

• Medullary canal eventually fills with yellow marrow

Growth

•Avg growth in females: 18 years•Avg growth in males: 20-21 years

Bone Types

• Four types:• 1. Long bones: found in upper and lower arms and

legs• 2. Flat bones: skull/head bones and ribs• 3. Irregular bones: bones of spinal column• 4. Short bones: wrist and ankle bones

PARTS OF THE SKELETON

•Axial• Skull, spinal column, ribs, sternum

(breast bone), and hyoid (U-shaped bone in the neck – tongue attached to it)

•Appendicular• Shoulder girdle, arms, wrists, hands, hip

girdle (pelvis), legs, ankles, and feet

Axial Skeleton

• Skull: cranium and facial bones• 22 bones total• Cranium houses and protects the brain• Facial bones guard and support the eyes, ears,

nose, and mouth• Some facial bones are made of bone and

cartilage for example the nose (which part is bone and which is cartilage?)

Cranium

• Cranial bones are thin and slightly curved• During infancy they are held together by an

irregular band of connective tissue called a suture• As the child grows, the connective tissue

ossifies and turns into hard bone• The dome shape gives better protection

than a flat surface, deflecting blows directed toward the head

8 Cranium Bones

• 1 frontal: forms the forehead• 2 parietal: form the roof and sides of the skull• 2 temporal: house the ears• 1 occipital: forms the base of the skull and contains

the foramen magnum (what is that?)• 1 ethmoid: (located b/t the eyes) forms part of the

nasal septum• 1 sphenoid: (resembles a bat) considered the key

bone of the skull; all other bones of the skull connect to it

14 Facial Bones

• 5 nasal• 2 are bones that form the bridge of the nose• 1 is the vomer bone which forms the lower part, or midline, of the nasal

septum• 2 are inferior concha which make up the side walls of the nasal cavity

• 2 maxilla: make up the upper jaw• 2 lacrimal: (in the inner aspect of the eyes) contain the tear ducts• 2 zygomatic: form the prominence of the cheek• 2 palatine: form the hard palate of the mouth• 1 mandible: lower jaw and the only movable bone in the face

Spinal Column/Vertebra

• Strong and flexible, supports the head, provides for attachment of the ribs, and encloses the spinal cord• Consists of small bones: vertebrae• Separated from each other by pads of cartilage tissue called

intervertebral disks• Cushions b/t the vertebrae and act as shock absorbers• During our lifetime they become thinner, accounting for

loss of height as we age

5 Sections of Vertebral Column

1. Cervical vertebrae2. Thoracic vertebrae3. Lumbar vertebrae4. Sacrum5. Coccyx

Cervical Vertebrae

• 7 total; located in the neck area• Atlas: the first cervical vertebra that

articulates, or is jointed, with the occipital bone; permits us to nod our heads• Axis: the 2nd vertebra; is the odontoid

process which forms a pivot on which the atlas rotates; permits us to turn our heads

Thoracic and Lumbar Vertebrae

• Thoracic: 12 total; located in the chest area•Articulate with the ribs

• Lumbar: 5 total; located in the back•Have large bodies that bear most of

the body’s weight

Sacrum and Coccyx

• Sacrum: wedge-shaped bone formed by 5 fused bones• Forms the posterior pelvic girdle and serves as

an articulation point for the hips

• Coccyx: known as the tailbone• Formed by 4 fused bones

Ribs and Sternum figure 6-7

• Thoracic area protected and supported by the thoracic vertebrae, ribs, and sternum• Sternum: (breastbone) is divided into 3 parts: • upper region (manubrium), the body, and a

lower cartilaginous part: the xiphoid process• Attached to each side of the upper region , by

means of ligaments, are the 2 clavicles(collar bones)

continued

• Human body contains 12 pairs of ribs• 7 pairs of costal cartilages join 7 pairs of ribs

directly to the sternum• True ribs

• Next 3 pairs are attached to the 7th rib (instead of the sternum) by their costal cartilages• False ribs

• Last 2 pairs are not connected to costal cartilages or sternum• Floating ribs

The Appendicular Skeleton

Upper Extremitiesshoulder girdlesarmswristhands

Lower Extremitieship girdlelegsanklesfeet

Shoulder Girdle

• Also called pectoral girdle• Consists of 4 bones • 2 clavicles (collar bones)• 2 triangular scapulae (shoulder bones)

• Clavicles help to brace the shoulders and prevent excessive forward motion• Scapulae permit the attachment of muscles that

assist in arm movement and serve as a place of attachment for the arms

Arm

• Consists of the humerus, radius, and ulna

• Humerus• Upper arm – 2nd largest in body• Upper end articulates with the scapulae

• Forearm• Radius on thumb side (RADIAL PULSE SITE)• Rotates around the ulna- good flexibility

• Ulna on pinky side• Limited movement• Olecranon process(FUNNY BONE) articulates with the humerus

Hand• Has 27 bones • Carpals (wrist bone): consists of 8 small bones arranged in 2

rows

• Metacarpals (5)

• Phalanges (14) – each finger has 3, the thumb has 2

Pelvic Girdle • 3 bones in youth• ilium, ischium, and pubis• Eventually fuse with the sacrum to form a

bowl-shaped structure (the pelvic girdle)• Eventually the 2 sets of bones form a joint with the bones in

the front: symphysis pubis and with the sacrum in the back: sacroiliac joint

Male vs Female Pelvis• Female pelvis is

wider• Necessary for

childbirth

• Male pelvis is heavier

Upper Leg

• Femur (thigh)• LONGEST and STRONGEST bone in body• Upper part of the femur has a smooth,

rounded head• Fits neatly into a cavity of the ilium

known as the acetebulum, forming a ball and socket joint

Lower Leg

• Consists of 2 bones:• Tibia: largest of the 2• Fibula

• The patella (kneecap) is found in front of the knee joint; it is a flat, triangular, sesamoid bone• Formed in the tendons of the quadricep in front of the femur• 4 bursae surround the patella which serve to cushion the knee joint

Sesamoid Bone

• Found where a tendon passes over a joint• Holds the tendon slightly

farther away from the center of the joint and thus increases its movement• Prevents the tendon from

flattening into the joint as tension increases

Ankle

• 7 tarsal bones which provide a connection b/t the foot and leg bones• Largest ankle bone is the heel bone or calcaneus• Tibia and fibula articulate with a broad tarsal

bone called the talus• Movement is a sliding motion, allowing the foot

to extend and flex when walking

Foot • Has 5 metatarsal bones • Arranged to form 2 distinct arches• One runs longitudinally from the calcaneus to the

head of the metatarsals: longitudinal arch• Other lies perpendicular to the longitudinal arch:

transverse arch• Arches strengthen the foot and provide flexibility and

springiness to the stride• Strong ligaments and leg muscle tendons help to

hold the foot bones in place

Foot continued

• Arches can “fall” d/t weak foot ligaments and tendons• Downward pressure by weight of the body slowly

flattens them, causing fallen arches or flatfeet• Cause a good deal of stress and strain on the foot

muscles• Factors leading to it may be: fatigue, overweight,

poor posture, and improperly fitting shoes

Foot…

• Toes are similar in composition to the fingers• There are 3 phalanges but the big toe has

2• Total of 14 phalanges in each foot

Types of Motion

• Flexion: act of bringing 2 bones closer together which decreases the angle b/t the 2 bones• Extension: act of increasing the angle b/t 2 bones, which results

in a straightening motion• Abduction: movement of an extremity away from the midline• Adduction: movement toward the midline• Circumduction: includes flexion, extension, abduction, and

adduction• Rotation: movement that allows a bone to move around 1 central

axis (for example: turning your head from side to side = pivot)• Pronation: the forearm turns the hand so the palm is downward

or backward• Supination: the palm is forward or upward