anaphy- sks

Anatomy and Physiology, 1e

Chapter 8: Axial Skeleton

Divisions of the Skeletal System

Section 8.1

Learning Objective 8.1.1

The Skeletal System

• Consists of all the bones, cartilage, and ligaments of the body

• 206 bones in adult skeleton

  • More in children

• Provides support for the body

• Aids in body movements

• Assists in calcium homeostasis

• Divided into axial and appendicular divisions

The Axial Skeleton (Figure 8.1)

• Forms vertical, central axis of the body

• Protects internal organs

• Allows movement of head, neck, back, and respiratory muscles

• Consists of 80 bones in total:

  • Skull

  • Vertebral column

  • Ribs

  • Sternum

The Appendicular Skeleton

• Forms upper and lower extremities

• Includes bones that attach extremities to axial skeleton

• 126 bones in total

• Discussed further in Chapter 9

The Skull

Section 8.2

Learning Objectives 8.2.1–8.2.4

Introduction to the Skull (Figure 8.2)

• Composed of 22 bones

• Bones are divided into two groups:

1. Cranial bones—surround and protect the brain

2. Facial bones—form the face, nasal cavity, mouth, and orbit

• Form openings called cavities

  • Contain soft organs

  • Decrease weight of skull

Bones of the Skull

• Cranial bones

  • Frontal bone (1)

  • Parietal bones (2)

  • Occipital bone (1)

  • Temporal bones (2)

  • Sphenoid bone (1)

  • Ethmoid bone (1)

• Facial bones

  • Mandible (1)

  • Maxillae (2)

  • Lacrimal bones (2)

  • Nasal bones (2)

  • Palatine bones (2)

  • Zygomatic bones (2)

  • Inferior nasal conchae (2)

  • Vomer (1)

Unpaired and Paired Skull Bones (Figure 8.3)

• Paired skull bones are found on the left and right sides

• Some bones are unpaired

Cavities of the Skull (Figure 8.4)

• Cavities house softer structures

• Cavities include:

  • Cranial cavity

  • Orbits

  • Nasal cavity

  • Oral cavity

  • Paranasal sinuses

Frontal Bone (Figure 8.5)

• Forms the forehead and part of cranium

• Bony markings:

  • Glabella

  • Supraorbital margin

  • Supraorbital foramen

Parietal Bones (Figure 8.6)

• Form superior lateral sides of the skull

• Articulate with frontal, temporal, and occipital bones

Occipital Bone (Figure 8.7)

• Forms posterior skull and posterior base of cranial cavity

• Bony markings:

  • External occipital protuberance

  • Superior nuchal line

  • Foramen magnum

  • Occipital condyles

Temporal Bones (Figure 8.8)

• Form lower lateral sides of skull

• Bony markings:

  • Squamous portion

  • Zygomatic process

  • Mastoid process

  • External acoustic meatus

  • Mandibular fossa

  • Articular tubercle

  • Styloid process

Sphenoid Bone (Figure 8.12)

• Forms much of the base of central skull and part of temples

• Bony markings:

  • Greater and lesser wings

  • Sella turcica

  • Pituitary fossa

  • Medial and lateral pterygoid processes

Ethmoid Bone (Figure 8.13)

• Forms part of orbit and nasal cavity

• Bony markings:

  • Perpendicular plate

  • Superior and middle nasal conchae

  • Crista galli

  • Cribriform plate

  • Olfactory foramina

Mandible (Figure 8.9)

• Forms lower jaw

• Only moveable bone of skull

• Bony markings:

  • Body, ramus, and angle

  • Coronoid and condylar processes

  • Mandibular notch

  • Mental foramina

  • Mental protuberance

Maxillary Bone (Figure 8.10)

• Also called the hard palate or maxilla

• Forms the upper jaw, most of the roof of the mouth, part of the orbit, and the lateral base of the nose

• Bony markings:

  • Alveolar processes

  • Infraorbital foramen

Lacrimal Bones (Figure 8.16)

• Lacrimal bones

  • Form part of orbit

  • Contain lacrimal glands that secrete tears

Palatine Bones (Figure 8.14)

• Form posterior portion of hard palate, medial part of orbit, and contributes to vertical section of nasal cavity

Zygomatic Bones (Figure 8.11)

• Known as the cheekbones

• Forms much of the lateral part of orbit

• Bony markings:

  • Temporal process

    • Unites with zygomatic process of temporal bone to form zygomatic arch

Vomer, Nasal, and Inferior Nasal Conchae Bones (Figures 8.18 and 8.16)

• Vomer

  • Forms part of nasal septum

• Nasal bones

  • Form bony base (bridge) and lateral walls the nose

• Inferior nasal conchae

  • Project into nasal cavity

The Articulated Skull (Figure 8.15)

• Anterior view of articulated skull

• Many of the bones of the skull can be identified anteriorly

Sutures

• Immobile joints filled with dense, fibrous connective tissue that attach cranial bones

  • Sagittal suture—connects the two parietal bones

  • Coronal suture—connects frontal bone to parietal bones

  • Lambdoid suture—connects parietal bones to occipital bone

  • Squamous suture—connects parietal and temporal bones

The Orbit (Figure 8.16)

• Protects the eyeball and muscles that move it

• Frontal, zygomatic, maxilla, ethmoid, lacrimal, palatine, and sphenoid bones contribute to orbit

• Optic canal allows entry of optic nerve

• Superior orbital fissure allows entry of blood supply

The Nasal Cavity, Septum, and Conchae (Figure 8.17)

• Nasal cavity is bordered by maxillae and nasal bones

• Nasal septum—divides nasal cavity

  • Formed by perpendicular plate of ethmoid, vomer, and septal cartilage

• Nasal conchae

  • Covered by mucous membranes

  • Warm, filter, and moisten inhaled air

The Nasal Septum (Figure 8.18)

• Divides nasal cavity

• Formed by union of three structures:

• Perpendicular plate of ethmoid bone

  • Vomer

  • Septal cartilage

Paranasal Sinuses (1 of 2) (Figure 8.19)

• Hollow, air-filled spaces found in frontal, maxillary, sphenoid, and ethmoid bones

• Connect to nasal cavity

• Add volume to skull without adding weight

• Allow resonance for voice

Paranasal Sinuses (2 of 2) (Figure 8.20)

• Named for the skull bone they are found in

  • Frontal sinus

  • Maxillary sinuses

  • Sphenoid sinus

  • Ethmoid sinus

Oral Cavity (Figure 8.21)

• Formed by maxillae, mandible, and palatine bones

• Teeth are embedded in alveolar processes

• Hard palate formed by palatine process of maxillae and horizontal plate of palatine bones

• Mandibular (mental) foramen allows entry of nerves and blood vessels to lower jaw

Lateral View of Skull (Figure 8.22)

• Zygomatic arch is formed by temporal process of zygomatic bone articulating with zygomatic process of temporal bone

  • Temporal fossa above zygomatic arch

  • Squamous suture unites parietal and temporal bones

Posterior View of Skull (Figure 8.23)

• Parietal bones are united by sagittal suture

  • Parietal bones and occipital bone are united by lambdoid suture

Inside the Cranial Cavity (Figure 8.24)

• Mostly occupied by the brain

  • Base of skull is divided into 3 fossae:

• Anterior cranial fossa

  • Middle cranial fossa

  • Posterior cranial fossa

Base of the Skull (Figure 8.25)

• Anterior cranial fossa

  • Contains crista galli and cribriform plates

  • Middle cranial fossa

    • Contains openings for blood vessels and nerves

  • Posterior cranial fossa

    • Contains internal acoustic meatus, hypoglossal canal, and jugular foramen

Openings of Middle Cranial Fossa

• Superior orbital fissure—passage for nerves to eyeball, associated muscles, and sensory nerves to forehead

  • Foramen rotundum—allows exit of major sensory nerve to face

  • Foramen ovale—allows exit of major sensory nerve to face

  • Foramen spinosum—entry of blood supply into cranial cavity

  • Stylomastoid foramen—exit of nerve to muscles of the face

  • Carotid canal—entry of blood supply to brain

  • Foramen lacerum—no structures pass through here

Openings of the Posterior Cranial Fossa

• Internal acoustic meatus – allows passage of the nerves for hearing and equilibrium and the nerve that supplies muscles of the face

  • Hypoglossal canal – allows passage of a nerve to the tongue (hypoglossal nerve, CNXII)

  • Jugular foramen – allows passage of several nerves and the jugular vein

Midsagittal Section of Skull (Figure 8.26)

• Frontal and parietal bones united by the coronal suture

  • Internal acoustic meatus of the temporal bone

  • Sphenoid sinus

  • Nasal septum

Brain-to-Body Size Ratio (Figure 8.27)

• Humans have a greater brain-to-body size ratio than other primates

  • Size of human neonate head is close to size of pelvic outlet, increasing difficulty of delivery

Development and Aging of the Skull

• Bones of skull are not fused at birth

  • Fontanelles

    • Also known as “soft spots”

    • Allow skull to change shape during birth

    • Allow for rapid growth of brain during infancy

  • Bones are not fully fused until adulthood

The Developing Skull (Figure 8.28)

• Early embryonic skull is mainly sheets of connective tissue

  • As bone ossifies, fontanelles remain to separate bones

  • During birth, bones may shift slightly and overlap

  • After birth, fontanelles and sutures eventually ossify

Application: Fusion Disorders

• Cleft lip results from partial or complete failure of upper lip to fuse together

  • Cleft palate results from failure of the hard palate to fuse completely

  • Craniosynostosis is the premature fusion of a suture line

    • Results in abnormal growth of skull and cranial deformity

Hyoid Bone (Figure 8.29)

• U-shaped bone located in superior part of neck

  • Does not articulate with other skull bones

  • Used primarily for muscle attachment

  • Due to location in the neck, it may be broken by strangulation.

The Vertebral Column

Regions of the Vertebral Column (Figure 8.30)

• Twenty-four vertebrae in total plus the sacrum and the coccyx

  • Five regions of vertebral column:

    • Cervical (7)

    • Thoracic (12)

    • Lumbar (5)

    • Sacral (5 fused vertebrae)

    • Coccygeal (4 fused vertebrae)

Curvatures of the Vertebral Column (Figure 8.31)

• Four curvatures increase strength, flexibility, and shock absorption

  • Cervical curve (posteriorly oriented)

  • Thoracic curve (anteriorly oriented)

  • Lumbar curve (posteriorly oriented)

  • Sacrococcygeal curve (anteriorly oriented)

Curvature Abnormalities

• Kyphosis – excessive posterior curvature of thoracic region

  • Lordosis – excessive anterior curve of lumbar region

  • Scoliosis – abnormal lateral curvature of vertebral column

General Structure of a Vertebra

• Components of a typical vertebra:

  • Vertebral body

  • Vertebral arch

    • Pedicles

    • Lamina

  • Vertebral foramen

  • Transverse, spinous, and articular processes

  • Intervertebral foramen

Articulated Vertebrae (Figure 8.32)

• Intervertebral discs are between the bodies of each vertebra

  • Superior and inferior articular processes unite the vertebrae posteriorly

  • Intervertebral foramen allows spinal nerves to exit

Cervical Vertebrae (Figure 8.33)

• Seven cervical vertebrae

  • Small vertebral bodies

  • Transverse foramina for vertebral arteries

  • Bifid spinous processes

Atlas and Axis (Figure 8.34)

• C1 and C2 allow rotation of the head

  • C1 = atlas

    • Allows head to move in a “yes” motion

• C2 = axis

  • Contains the dens

  • Allows head to move in a “no” motion

Thoracic Vertebrae (Figure 8.35)

• Twelve thoracic vertebrae

  • Vertebral bodies increase in size as you descend the spinal column

• Long, downward angled spinous processes

  • Articulate with ribs

Ribs Articulate with Thoracic Vertebrae (Figure 8.36)

• Bodies of thoracic vertebrae articulate with heads of ribs

  • Transverse processes of thoracic vertebrae articulate with rib tubercles

Lumbar Vertebrae (Figure 8.37)

• Five lumbar vertebrae

  • Largest vertebral bodies

  • Short, blunt spinous processes

Sacrum and Coccyx (Figure 8.38)

• Sacrum is a thick triangular shaped bone

  • Formed by fusion of 5 vertebrae

  • Median sacral crest

  • Sacral promontory on superior portion of sacrum

  • Openings are called sacral foramina

• Coccyx is formed by fusion of 4 vertebrae

Intervertebral Disks (Figure 8.39)

• Fibrocartilage pads between vertebrae

  • Anulus fibrosus – fibrous outer layer

  • Nucleus pulposus – soft, gel- like

  • Anchor vertebrae to each other

  • Cushion and allow movement

The Thoracic Cage

Sternum (Figure 8.40)

• Parts of sternum

1. Manubrium

   • Clavicular notch

   • Suprasternal notch

2. Body

   • Joins to manubrium at sternal angle

3. Xiphoid process

   • Clavicles and some ribs

attach to sternum

Ribs (Figure 8.41)

• Twelve pairs of curved flat bones

  • Costal cartilage articulates some to the sternum anteriorly

• Bony features:

  • Head, neck, body, tubercle, and angle of the rib

  • Costal groove

Types of Ribs

• Only some ribs have costal cartilage

  • True ribs (1–7)—costal cartilage directly attaches to sternum

  • False ribs (8–12)—costal cartilage does not attach to sternum

  • Floating ribs (11–12)—do not have costal cartilage

Summary

• At the end of this chapter, you should be able to:

  • Discuss and identify the cranial bones of the skull.

  • Discuss and identify the facial bones of the skull

  • Identify bony markings of the skull and their functions.

  • Describe the structure of a typical vertebrae.

  • Discuss the anatomy of the sternum and ribs.