The Skeletal System
• Skeleton comes from a Greek word meaning dried up body.
• Bone appears dead and dried up, but it is not!
• Bone is living tissue
• Newborn human has 350 bones
• Adult human has 206 bones
• Parts of the skeletal system
• Bones (skeleton)
• Joints
• Cartilages
• Ligaments (bone to bone)(tendon=bone to muscle)
Functions of Bones
- Support of the body (framework)
- Protection of soft organs
- Serve as levers (with help from muscles)
- Storage of minerals and fats (calcium)
- Blood cell formation
Bones of the Human Body
Two basic types of bone tissue
- Compact bone
- Dense/hard
- Spongy bone
- (Cancellous)
- Many open spaces
- Decrease wt of bone/contain red bone marrow
Classification of Bones on the Basis of Shape
- Long bones
- Typically longer than wide
- Have a shaft with heads at both ends
- Contain mostly compact bone
- Found in legs and arms
• Examples: Femur, humerus
- Short bones
- Generally cube-shape and small
- Contain mostly spongy bone
- Found in wrist, ankles, and toes
• Examples: Carpals, tarsals
- Flat bones
- Thin and flattened
- Usually curved
- Cover organs/provide surface for lg. muscle
- Thin layers of compact bone around a layer of spongy bone
• Examples: Skull, ribs, sternum
- Irregular bones
- Irregular shape
- Do not fit into other bone classification categories
• Example: Vertebrae and hip
Gross Anatomy of a Bone
- Diaphysis
§ Shaft
§ Composed of compact bone
- Epiphysis
§ Ends of the bone
§ Composed mostly of spongy bone
- Periosteum
§ Outside covering of the diaphysis
§ Fibrous connective tissue membrane
§ Serves as an attachment for muscle
- Arteries
§ Supply bone cells with nutrients
· Articular cartilage
§ Covers the external surface of the epiphyses
§ Made of hyaline cartilage
§ Decreases friction at joint surfaces
· Medullary cavity
§ Cavity of the shaft
§ Contains yellow marrow (mostly fat) in adults
§ Contains red marrow (for blood cell formation) in infants
Changes in the Human Skeleton
- In embryos, the skeleton is primarily hyaline cartilage
- During development, much of this cartilage is replaced by bone
- Cartilage remains in isolated areas
- Bridge of the nose
- Parts of ribs
- Joints
Bone Growth
- Epiphyseal plates allow for growth of long bone during childhood
- New cartilage is continuously formed
- Older cartilage becomes ossified
- Cartilage is broken down
- Bone replaces cartilage
- Bones are remodeled and lengthened until growth stops
- Grow longitudinally for height
- Bones grow in width to support weight
Epiphyseal Disc
• Growth plate
• The cartilage near the epiphyseal disc multiplies and eventually becomes ossified (turns to bone)
• As long as new cartilage continues to form the bone continues to lengthen.
• When the growth plate hardens and becomes ossified, growth stops
• Hormones play a big part in this
• Growth hormone stimulates growth
• Sex hormones stop growth
Bone Width
• Long after longitudinal bone growth has stopped, bones continue to grow in thickness and width.
• Bones are continuously being reshaped
Types of Bone Cells
- Osteocytes
- Mature bone cells
- Osteoblasts
- Bone-forming cells
- Osteoclasts
- Bone-destroying cells
- Break down bone matrix for remodeling and release of calcium
- Bone remodeling is a process by both osteoblasts and osteoclasts
Bone Remodeling
• A combined action of osteoblasts (bone forming cells) and osteoclasts (bone destroying cells)
• Osteoblasts deposit bone on the external bone surface
• Osteoclasts break down bone from the inside
Bone Fractures
- A break in a bone
- Types of bone fractures
- Closed (simple) fracture – break that does not penetrate the skin
- Open (compound) fracture – broken bone penetrates through the skin
- Bone fractures are treated by reduction and immobilization
- Realignment of the bone
Dislocation of joint
• Displacement of bones at the joint
• Often caused by impact trauma to that joint
• Can be more damaging and painful than a fracture
• Damage to the joint capsule and surrounding ligaments and tendons often takes much longer to heal than bone tissue.
Repair of Bone Fractures
- Hematoma (blood-filled swelling) is formed
- Break is splinted by fibrocartilage to form a soft callus
- Blood vessels grow into the hematoma
- Fibrocartilage callus is replaced by a bony callus
- Bony callus is remodeled to form a permanent patch
Skeletal System
Divided into two divisions
Axial skeleton ~ bones of the cranium, face, vertebral column, and bony thorax.
Appendicular skeleton ~ includes the bones of the pelvic girdles, the upper extremities and lower extremities.
The Axial Skeleton
- Forms the longitudinal part of the body
- Divided into three parts
- Skull
- Vertebral column
- Bony thorax
The Skull (28 bones) (18 names!)
- Sits on top of the vertebral column
- Two sets of bones
- Cranium (8 bones)
- Facial bones (14 bones)
- Bones are joined by sutures
- Only the mandible is attached by a freely movable joint
The Cranium
• Bony structure that encases and protects the brain.
• 8 bones
• Frontal Bone ~ forehead/upper part of the bony structure surrounding the eyes.
• Parietal Bone (2) ~ upper sides of the head and the roof of the cranial cavity (top of the head)
• Temporal Bones (2) ~ sides of the head, close to ears.
• Commonly called the temples
• Includes the external auditory meatus
• Opening for the ear
• Includes the zygomatic process
• Part of the cheekbone
• Occipital Bone ~ back and base of the cranium
• Includes the foramen magnum
• Foramen means hole
• Large hole for the brainstem/spinal cord
• Sphenoid Bone ~ forms sides of cranium and parts of orbits of the eyes
• Butterfly shaped
• Includes Sella Turcica (Turk’s Saddle)
• Where pituitary gland sits
• Ethmoid Bone ~ irregularly shaped bone located between the eye orbits
• Major supporting bone of the nasal cavity
• That’s it! No more cranium bones!
• 206 bones - 8 bones = 198 bones to go…
Facial Bones
• 14 bones
• Most of these bones come in pairs
• Only the mandible and vomer are single bones
• Mandible ~ the lower jaw bone
• Carries the lower teeth
• The anterior portion forms the chin
• Only freely movable joint in the skull
• Maxilla (2) ~ Upper jaw
• Two bones fused together
• Roof of the mouth
• Also form parts of the nasal cavity and eye orbits
• Palantine Bones (2) ~ form the posterior part of the hard palate and the floor of the nasal cavity.
• Failure of the palatine and/or maxillary bones to fuse causes a cleft palate.
• Zygomatic Bones (2) ~ the cheekbones
• Also forms a part of the orbits of the eyes
• Other Facial Bones
• Lacrimal Bones (2) ~ inner wall of eye sockets
• Nasal Bones (2) ~ bridge of nose
• Vomer ~ nasal septum
• Inferior Nasal Conchae (2)
• That’s it! No more facial bones!
• 198 bones - 14 bones = 184 bones to go…
Paranasal Sinuses
- Functions of paranasal sinuses
- Air filled cavities
- Lighten the skull
- Give resonance and amplification to voice
The Fetal Skull
- The fetal skull is large compared to the infants total body length
- Fontanelles – fibrous membranes connecting the cranial bones
- Allow the brain
to grow - Convert to bone within 24 months after birth
The Hyoid Bone
- U shaped
- Found in the upper neck
- The only bone that does not articulate with another bone
- Serves as a moveable base for the tongue
Middle Ear
• 3 Tiny bones ~ transmit vibrations
• All derived from Latin words
• Malleus (hammer)
• Incus (anvil)
• Stapes (stirrup)
• Smallest bone in the body
Middle Ear and Hyoid Bones
• That’s it!
• 184 bones - 4 bones = 180 bones to go…
The Vertebral Column
• The backbone or spine
• Consists of 26 bones called vertebrae
• Vertebrae separated by intervertebral discs (act as shock absorbers)
• The spine has a normal curvature
• Each vertebrae is given a name according to its location
• C1-C7 ~ in the neck region
• 7 cervical vertebrae
• T1-T12 ~ located in the chest region
• 12 thoracic vertebrae
• L1-L5 ~ located in the lower back
• 5 lumbar vertebrae
• Sacrum ~ curved bone of the lower back (posterior wall of the pelvis)
• fused sacral vertebrae
• 5 vertebrae at birth
• Coccyx ~ the tailbone
• 4 vertebrae at birth
• The vertebrae become larger as the vertebral column descends…..WHY?
• Vertebral foramen ~ opening for spinal cord.
• What is the opening for the spinal cord in the skull called?
• 180 bones - 26 vertebral column bones = 154 bones to go!
The Bony Thorax (Thoracic Cage)
- The chest region
- Forms a cage to protect major organs
- Composed of sternum, ribs and thoracic vertebrae.
- Sternum ~ breastbone.
- Dagger-shaped bone located along the midline of the anterior chest.
- Ribs ~ 12 pairs of ribs attach posteriorly to the thoracic vertebrae
- True ribs ~ first 7 pair
- False ribs ~ last 5 pairs
That is it for the axial skeleton!
• 154 bones - 24 ribs -1 sternum = 129 bones to go!!!
The Appendicular Skeleton
- Limbs (appendages)
- Pectoral (shoulder) girdle
- Pelvic girdle
The Pectoral (Shoulder) Girdle
- Composed of two bones
- Clavicle – collarbone
- Scapula – shoulder blade
- These bones allow the upper limb to have exceptionally free movement
Bones of the Upper Limb
- The arm is formed by a single bone
- Humerus
- Head of humerus allows for rotation
- The forearm has two bones
- Ulna
- Radius
Radius
• Radius ~ locate on the lateral or thumb side when the palm of the hand is facing forward.
Ulna
• Ulna~ the longer of the two forearm bones.
• Located on the medial or little finger side of the forearm.
Bones of the Upper Limb
- The hand
- Carpals – wrist
- Metacarpals – palm
- Phalanges – fingers
Bones of the Pelvic Girdle
- Composed of two coxal bones (hip bones)
- Composed of three pair of fused bones
- Ilium
- Ischium
- Pubis
- The total weight of the upper body rests on the pelvis
- Protects several organs
- Reproductive organs
- Urinary bladder
- Part of the large intestine
Bones of the Lower Limbs
- The thigh has one bone
- Femur – thigh bone
- Patella ~ knee cap
- Triangular bone located within a tendon that passes over the knee.
- The leg has two bones
- Tibia ~ shin bone
- larger
- Fibula
- Long and thin
- The foot
- Tarsal (7)– ankle
- Metatarsals (5)– sole/instep
- Phalanges (14) – toes
Joints
- Articulations of bones
- Functions of joints
- Hold bones together
- Provide flexibility
- Ways joints are classified
- By their function
- By their structure
Functional Classification of Joints
- Synarthroses – immovable joints
- Amphiarthroses – slightly moveable joints
- Diarthroses – freely moveable joints
Structural Classification of Joints
- Fibrous joints
- Generally immovable
- Cartilaginous joints
- Immovable or slightly moveable
- Synovial joints
- Freely moveable
Fibrous Joints
- Bones united by fibrous tissue – synarthrosis or largely immovable.
Cartilaginous Joints – mostly amphiarthrosis
- Bones connected by cartilage
- Examples
- Pubic
symphysis - Intervertebral
joints
Synovial Joints
- Articulating bones are separated by a joint cavity
- Synovial fluid is found in the joint cavity
- Reinforced by ligaments
- 6 Types of Synovial Joints
Hinge joint
· Movement is like two boards joined together by a hinge
· Movement in one direction
· Elbow, knees, fingers
Ball and Socket Joint
· When ball-shaped end of one bone fits into the cup-shaped socket of another
· Bones can move in many directions
· Shoulder, hip
Pivot Joint
· Allows for rotation around the length of a bone.
· Allows only for rotation
· Head (side to side “no” action)
· Forearm joints (palms) supination/pronation
Saddle Joint
· When the surfaces of both articulation bones are saddle-shaped
· Concave/convex
· Thumb
· Wide range of motion
Gliding Joint
· Interaction of flat surfaces of articulating bones
· Limited but complex movement
· Wrist, ankle
Condyloid Joint
· Oval-shaped articular surface of one bone fits into the oval-shaped depression of another
· Mandible, knuckles
Inflammatory Conditions Associated with Joints
- Bursitis – inflammation of a bursa usually caused by a blow or friction
- Tendonitis – inflammation of tendon sheaths
- Arthritis – inflammatory or degenerative diseases of joints
- Over 100 different types
- The most widespread crippling disease in the United States
Clinical Forms of Arthritis
- Osteoarthritis
- Most common chronic arthritis
- Probably related to normal aging processes
- Rheumatoid arthritis
- An autoimmune disease – the immune system attacks the joints
- Symptoms begin with bilateral inflammation of certain joints
- Often leads to deformities
- Gouty Arthritis
- Inflammation of joints is caused by a deposition of urate crystals from the blood
- Can usually be controlled with diet
- Red meat and wine are high in uric acid.
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