Chapter 6 The Skeletal System

Skeletal system

Consists of 206 bones (in adults), joints, cartilage and ligaments.

Functions of the skeleton

1. support

2. protection of soft body parts

3. Blood cell production

4. Storage of fats & minerals

5. Movement, using muscles & joints.

Classification of bones

-Long

-short

-flat

-irregular

-round

Long bone

longer than they are wide (femur)

Short bone

Cube shaped (tarsal)

Flat bones

Plate-like, with broad surfaces

Irregular bone

Varied shapes

Round bone

Circular in shape (patella)

Periosteum (long bone)

Tough, connective tissue covering that contains blood vessels.

-continuous with tendons (connect muscle to bone) and ligaments (connect bones to bones)

Epiphysis (long bone)

Expanded portion at the ends of bones; made of spongy bone.

Diaphysis (long bone)

Portion between the epiphysis; the shaft; made of compact bone.

medullary cavity (long bone)

hollow portion of diaphysis containing yellow marrow (fat).

articular cartilage

Layer of hyaline cartilage at articulations (where bones join together).

Endosteum

Lines medullary cavity and the spaces of spongy bone.

Red bone marrow

Found in spongy bone in adults; where hematopoiesis (production of red blood cells) occurs.

Anatomy of a long bone

Epiphysis

Diaphysis

medullary cavity

epiphysial line

Compact bone

Made of osteons, which are made of lamellae (concentric layers of matrix) containing collagen fibers and mineral salts.

Lacunae

Contain bone cells - osteocytes.

Canaliculi

Small canals that connect osteocytes to each other and blood supply and nerves.

Central canal

contains blood vessels and nerves

perforating canals

run from the periosteum to the central canal of each osteon

Compact bone

compact bone structure

Spongy bone

-Also called cancellous bone.

-contains bony bars & plates called trabeculae.

-trabeculae follow lines of stress, giving bones strength.

spongy bone

Types of bone cells

1. Osteoprogenitor cells

2. Osteoblasts

3. Osteocytes

4. Osteoclasts

osteoprogenitor cells

Unspecialized cells found in the periosteum, endosteum and central canals.

Osteoblasts

Bone forming cells, created from osteoprogenitor cells.

Osteocytes

Mature bone cells, prior osteoblasts.

Osteoclasts

Bone resorption; calcium and phosphorus removed from bone is deposited into the blood.

Ossification

-formation of bone.

1. Instramembranous ossification:

-spongy bone forms between 2 sheets of fibrous connective tissue.

-forms bones of the skull.

2. Endochondral ossification:

-forms most bones of human body.

-hyaline cartilage models are replaced by spongy bone and then compact bone.

Endochondral ossification of a long bone

Epiphyseal plate

-band of hyaline cartilage in epiphysis of Long bones.

-allows the bone to grow in length.

-Long bone growth continues until place is ossified.

Appositional growth

Increase in bone diameter.

Remodeling of bones

-bone is continually being broken down and built up again

-osteoclasts remove worn cells and deposit calcium in the blood

-osteoblasts remove calcium from the blood and form new bone

-eventually, they surround themselves with matrix and become trapped in lacunae; they then mature into osteocytes.

-proper levels of calcium needed to prevent osteoporosis.

-Ca promotes the work of osteoblasts.

Surface features of bones

Tissues of the Skeleton

compact and spongy bone, cartilage, and dense connective tissue

Axial skeleton

-lies in midline of body

-bones of axial skeleton:

-skull

-hyoid bone

-vertebral column

-thoracic cage

-middle ear bones

Major bones of the axial skeleton

Skull

-formed by the cranium and facial bones.

-cranium is composed of 8 bones:

1. Frontal bone (1)

2. Parietal bone (2)

3. Occipital bone (1)

4. Temporal Bones (2)

5. Sphenoid bone (1)

6. Ethmoid bone (1)

Skull Anatomy

Skull Anatomy

Frontal bone

Parietal bone

Occipital bone

Occipital bone (1)

-foramen (rounded opening) magnum.

-occipital condyles.

Occipital bone

foramen magnum

Temporal Bones

Temporal bones (2)

-external acoustic meatus.

-mandibular fossa

-mastoid process

-styloid process

-zygomatic process.

Temporal bone

mastoid process

Sphenoid bone

Sphenoid bone (1) (butterfly)

-sella turcica.

Ethmoid bone

Ethmoid bone (1) (medial sides of orbits, nasal septum)

-Christa Gali

-cribriform plate

-perpendicular plate

-superior & middle nasal conchae

Saggital section of skull

Sphenoid Bone

Temporal bone

ethmoid bone

Bones of cranium

-sutures: immovable joints between cranial bones.

-fontanels: membranous regions in newborns where cranial bones have not yet fused together.

coronal suture

sagittal suture

Lambdoidal suture

Squamosal suture

Sinuses in skull bones

-mucous membranes-lines air spaces within the bones.

-reduce the weight of skull.

-give the voice a resonant sound.

-paranasal sinuses - empty into the nose.

Paranasal sinuses

Located in : maxillary, frontal, ethmoid, sphenoid

paranasal sinuses

Mastoid sinuses

Drain into middle ear.

Mastoid sinuses, mastoiditis

Sinusitis

Sinus infection; mastoiditis.

Bones of the face

1. Maxillae (2)

2. Palatine bones (2)

3. Zygomatic bones (2)

4. Lacrimal bones (2)

5. Nasal bones (2)

6. Vomer bone (1)

7. Inferior nasal conchae (2)

8. Mandible (1)

Maxillae (2)

-alveolar process (tooth sockets)

-palatine process (hard palate-roof of mouth) (cleft palate)

Zygomatic bones (2)

-temporal process

-zygomatic arch

Maxillae (maxillary bones)

palatine bone

Zygomatic bone

Lacrimal bone

Nasal bone

Mandible

-only movable bone of the skull.

-mandibular condyle

-coronoid process

-alveolar process

Mandible

Hyoid bone

-superior to larynx.

-only bone In the body that does not articulate with another bone.

-anchors to the tongue.

-site of attachment for muscles associated with swallowing.

Hyoid bone

Vertebral column

Consists of separate vertebrae separated by intervertebral disks.

Functions of vertebral column

1. Forms body's vertical axis.

2. Supports rib cage.

3. Serves as point of attachment for pelvic girdle.

4. Protects spinal cord.

Curvatures of spine

Vertebral bones

- 7 cervical (neck)

- 12 thoracic (chest)

- 5 lumbar (lower back)

- 5 sacral (fused)

- 3 to 5 coccygeal (fused)

Normal curvatures of spine

-cervical & lumbar : convex anteriorly

-thoracic & sacral : concave posteriorly

-provide support & balance.

Abnormal curvature of spine

1. Lordosis : exaggerated lumbar curvature.

2. Kyphosis : increased roundness of thoracic curvature.

3. Scoliosis : lateral curvature; occurs most often in thoracic region.

Abnormal curvatures of spine

intervertebral discs

fibrocartilage pads between vertebrae.

-prevent vertebrae from grinding against one another.

-absorb shock

-allow motion between vertebrae

-can slip or rupture (herniated disk).

intervertebral discs

Vertebrae structure

-Body : large, anterior portion.

-vertebral foramen : canal for spinal cord

-bony projections : sites for muscle attachment.

-spinous process (spine) : posterior projection (c7-chin to chest)

-transverse process : lateral projections.

Vertebrae

Cervical Vertebrae

-C1-C7

-C7 also called the vertebra prominens.

-have transverse foramina & short spines.

-Atlas (c1) : supports head; allows head movement up and down.

-Axis (c2) : serves as pivot for atlas; allows head movement from side to side. (has odontoid process, or dens!)

C1 Atlas

C2 Axis

Atlas & Axis

thoracic vertebrae

-T1-T12

-Long slender spines and costal facets.

lumbar vertebrae

-L1-L5

-massive bodies & square spines.