The Skeletal System

The Skeletal System

Parts of the skeletal system Bones (skeleton)—206 bones in human body Joints Cartilages Ligaments

Two subdivisions of the skeleton Axial skeleton—skull, vertebral column and

thoracic cage Appendicular skeleton—pectoral girdle,

upper limbs, pelvic girdle and lower limbs

Axial Skeleton

Pubic or Coxal Bone Pubis

illium

ischium

Talus

The Skull

Mandibular condyle

Axial Skeleton—Skull

Two sets of bones Cranium Facial bones

Bones are joined by sutures

Only the mandible is attached by a freely movable joint

The Skull

Axial Skeleton—Skull

Skull: at birth—not completely developed

Cranial bones separated by fibrous membranes called fontanels or soft spots

They allow for compression in birth canal

They are eventually replaced wit bones and become sutures.

Sinuses

Hollow portions of bones surrounding the nasal cavity

Functions of paranasal sinuses Lighten the skull Give resonance

and amplification to voice

Hyoid bone

The only bone that does not articulate with another bone

Serves as a moveable base for the tongue

Aids in swallowing and speech

Axial Skeleton—Vertebral Column Extends from the

skull to the pelvis Composed of

vertebrae (24) Supports the

head and trunk of the body

Protects the spinal cord

Types of vertebrae Cervical (7) Thoracic(12) Lumbar(5) Sacrum (1) Coccyx (1)

Axial Skeleton—Vertebral Column

Supports the shoulder girdle and arms

Protects the visceral organs in chest and upper abdomen

Made of Ribs (12 pair—2 float) Sternum (1 long bone

with 3 divisions)

Axial Skeleton—Thoracic Cage

Appendicular Skeleton

Appendicular Skeleton—Pectoral Girdle Supports arms Made of

Clavicle (2) Scapula (2) Humerus (upper arm) Radius (lower arm) Ulna (lower arm, elbow) Olecranon process (on

ulna) Hand—carpals (wrist),

metacarpals (hand) and phalanges (fingers)

Appendicular Skeleton—Pelvic Girdle

2 coxal bones that come together to form the pelvis

Strong stable support for vertebral column

Attaches lower limbs to axial skeleton

Made of Ilium Ischium Pubis

Gender differences of the pelvis

Femur (thigh) Patella (kneecap) Tibia (lower leg-shin) Fibula (lower leg-

lateral) Foot—tarsals (ankle),

metatarsals (foot) and phalanges (toes) Calcaneus (heel bone-large tarsal) Talus-where tibia articulates with tarsals

Appendicular Skeleton—Lower Limbs

Types of bones

Long Bones Short Bones Flat Bones Irregular Bones

Long Bones

Parts of a long bone Epiphysis: end of the

bone that forms a joint with another bone

Epiphyseal disk: dark line at epiphysis where growth takes place

Articular cartilage: cartilage that covers the ends of bones. Serves to cushion and decrease friction

Long Bones

Diaphysis: the main shaft of the bone

Medullary Cavity: contains bone marrow, a specialized soft connective tissue Red bone marrow makes

RBC’s, WBC’s and platelets Yellow bone marrow stores

fat Periosteum: tough vascular

covering of the bone that functions to form and repair bone tissue

Long Bones

Compact bone: tightly packed tissue that makes up the diaphysis; very strong

Spongy bone: spongy inner portion of the bone that makes up the epiphysis; helps reduce the weight of the bone; provides strength at the ends of bones.

Microscopic Structures of Bones

Microscopic Structure of Bones

Osteocytes: mature bone cells that are arranged around canals called Haversian canals

Haversian canals hold blood vessels and nerves.

Osteocytes secrete calcium and phosphorus that form extracellular matrix that is very hard.

Lamellae-layers of calcified matrix

Lacunae- holes in lamella where bone cells are

Canaliculus-canals so bone cells can touch each other.

Microscopic Structure of Bones

Types of bone cells Osteoblasts:

bone forming cells Osteoclasts:

bone destroying cells—break down bone for remodeling and release calcium in response to parathyroid

Formation of 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 (Ossification)

Epiphyseal plates allow for lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified

Cartilage is broken down Enclosed cartilage is digested away, opening

up a medullary cavity Bone replaces cartilage through the action of

osteoblasts

Bone Growth (Ossification)

Bones are remodeled and lengthened until growth stops Bones are remodeled in response to two

factors Blood calcium levels Pull of gravity and muscles on the skeleton

Bones grow in width (called appositional growth)

Long Bone Formation and Growth

Figure 5.4a, step 1

Bone startingto replacecartilage

In an embryo

Bone collar

Hyalinecartilagemodel

(a)

Long Bone Formation and Growth

Figure 5.4a, step 2

Bone startingto replacecartilage

In a fetusIn an embryo

Growthin bonelength

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

(a)

Long Bone Formation and Growth

Figure 5.4a, step 3

Bone startingto replacecartilage

Epiphysealplatecartilage

Articularcartilage

Spongybone

In a childIn a fetusIn an embryo

New boneforming

Growthin bonewidth

Growthin bonelength

Epiphysealplate cartilage

New boneforming

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

(a)

Broken Bones

Fracture—break in a bone

Types of bone fractures Closed fracture—

break that does not penetrate the skin

Open fracture—broken bone penetrates through the skin

Bone fractures are treated by reduction and immobilization

Steps to healing broken bones

Hematoma (blood-filled swelling) is formed Break is splinted by fibrocartilage to form a callus Fibrocartilage callus is replaced by a bony callus Bony callus is remodeled to form a permanent patch

Types of Breaks

Greenstick Fracture—incomplete fracture, only one side of the bone is broken, causes bone to bend, common in children

Types of Breaks

Hairline fracture-- incomplete fracture—it is a crack that does not break all the way through

Types of Breaks

Transverse simple fracture—complete fracture—occurs when the bone is broken into two fragments and the break is straight across

Types of Breaks

Oblique simple fracture—complete fracture—occurs when bone is broken into 2 fragments and the break is at an angle

Types of Breaks

Spiral simple fracture—complete fracture—occurs when the bone is broken into 2 fragments and the break is at an angle that is twisted

Types of Breaks

Comminuted—complete fracture—it is a break that has many fragments

Types of Breaks

Compression fracture– bone is crushed, common in skull and vertebral column