Ch-07-axial-skeleton-handout

Chapter 07: Axial Skeleton

Introduction

• The axial skeleton consists of 80 bones.

• Forms the longitudinal axis of the body.

• Functions of the axial skeleton:

  • Supports and protects the brain, spinal cord, and organs in trunk body cavities.

  • Provides attachment sites for muscles that can:

    • Adjust the position of the head, neck, and trunk.

    • Perform respiratory movements.

    • Stabilize or position parts of the appendicular skeleton that support the limbs.

Cranial and Facial Subdivisions of the Skull

• The skull is comprised of three main divisions:

  • Face: 14 bones.

  • Cranium: 8 bones.

  • Associated bones: 7 bones.

Cranial Bones

• Frontal bone

• Parietal bones (x2)

• Temporal bones (x2)

• Sphenoid

• Ethmoid

• Occipital bone

Facial Bones

• Lacrimal bones (x2)

• Nasal bones (x2)

• Vomer

• Mandible

• Zygomatic bones (x2)

• Maxillary bones (x2)

Not shown: palatine bones (x2), inferior nasal conchae (x2).

• Associated structures:

  • Hyoid bone

  • Auditory ossicles (x6).

Major Cranial Sutures

• Coronal suture: joint between frontal and parietal bones.

• Squamous suture: joint between temporal and parietal bones.

• Sagittal suture: joint between left and right parietal bones.

• Lambdoid suture: joint between occipital and parietal bones.

Cranial Cavity

• Contains:

  • Frontal bone

  • Ethmoid bone

  • Sphenoid bone

  • Temporal bone

  • Occipital bone

Cranial Fossae

• Anterior, Middle, Posterior

• Key Structures:

  • Olive

  • Internal acoustic meatus

  • Foramen magnum (spinal cord passage)

  • Various foramina allow passage of nerves and vessels (e.g. optic canal for optic nerve).

The Skull – Lateral and Anterior Views

Lateral View

• Notable Features:

  • External acoustic meatus

  • Mastoid process

  • Zygomatic arch

Anterior View

• The Nasal Complex and Paranasal Sinuses

  • Paranasal Sinuses: Frontal, Ethmoidal air sacs, Sphenoidal, Maxillary.

  • Nasal Septum: Perpendicular plate of ethmoid, Vomer.

  • Nasal Conchae: Superior, Middle, Inferior (with mucous membrane lining).

The Mandible

• Key Features:

  • TMJ: Temporal mandibular joint.

  • Ramus (side), Angle (turn), Body (front).

  • Contains alveolar part for tooth sockets.

The Hyoid Bone

• Unique as it does not articulate with any other bone.

• Functions:

  1. Supports the larynx (voice box).

  2. Attachment for muscles involved in swallowing and adjustment of speech.

Features of the Infant Skull

• Notable areas include 4 major fontanel areas:

  • Anterior fontanel

  • Posterior fontanel

  • Mastoid fontanels

  • Sphenoidal fontanels

  • Responsible for shape adjustments during birth and growth.

The Vertebral Column

• Composed of 26 bones:

  • 24 vertebrae: 7 cervical, 12 thoracic, 5 lumbar.

  • 1 sacrum (5 fused vertebrae).

  • 1 coccyx (3-5 fused vertebrae).

• Functions:

  • Encloses spinal cord.

  • Provides support and flexibility.

Cervical, Thoracic, and Lumbar Vertebrae

Cervical Vertebrae

• All possess transverse foramina (for blood vessels).

• C1 (Atlas) allows “yes” motion, while C2 (Axis) allows “no” motion.

Thoracic Vertebrae

• Characterized by slender spinous processes and rib articulation points.

Lumbar Vertebrae

• Large bodies for weight support, lack costal facets (rib attachment).

The Thoracic Cage

• Composed of:

  • Sternum

  • Twelve pairs of ribs

  • Costal cartilages

• Functions:

  • Forms walls of thoracic cavity.

  • Protects thoracic organs.

  • Provides attachment for muscles involved in breathing and movement of the pectoral girdle.

Sternum Structure

• Divided into:

  • Manubrium

  • Body

  • Xiphoid process

The Thoracic Cage – Ribs

• 12 pairs of ribs classified as:

  • True ribs (pairs 1-7): directly attached to the sternum.

  • False ribs (pairs 8-12): indirectly attached.

  • Floating ribs (pairs 11-12): not attached anteriorly.

Typical Rib Structure

• Contains:

  • Head

  • Neck

  • Tubercle

  • Angle

  • Shaft

  • Costal groove (for blood vessels and nerves).