The Axial Skeleton

  • The skeletal system is a complex framework consisting of:

    • Bones: Rigid structures that form the body's framework.

    • Tendons: Connective tissues that attach muscles to bones, enabling movement.

    • Ligaments: Tough bands of tissue that connect bones to other bones, providing joint stability.

    • Cartilages: Flexible tissues that cover the ends of bones at joints, facilitating smooth movement and acting as a shock absorber.

  • The skeletal system is classified into 2 main sections:

    • Axial Skeleton

    • Comprises 80 bones, providing the central axis of the body.

    • Includes vital structures:

      • Skull: Protects the brain and supports facial structure.

      • Thorax: Contains the rib cage which protects the heart and lungs.

      • Vertebral Column: Supports the body, encases the spinal cord, and allows for flexibility and movement.

    • Appendicular Skeleton

    • Comprises 126 bones, supporting the limbs and their attachments to the body.

    • Includes structures:

      • Limbs: The upper and lower extremities including arms and legs.

      • Pectoral Girdle: Connects the arms to the body and consists of the clavicle and scapula.

      • Pelvic Girdle: Attaches the legs to the axial skeleton and supports the weight of the upper body during locomotion.

    • Total of 206 separate bones in the human body, which are categorized based on their shape: long, short, flat, and irregular bones.

Axial Skeleton

  • Key Characteristics:

    • Forms the longitudinal axis of the body, essential for maintaining posture and balance.

    • Functions of the axial skeleton include:

      • Support: Provides structural support, bearing the weight of the body.

      • Protection: Encases and protects vital organs of the head, neck, and trunk, such as the brain, heart, and lungs.

      • Muscle Attachments: Serves as a point of attachment for muscles connecting to the appendicular skeleton, facilitating movement and stability.

  • Total Number of Bones: 80

  • Components Included:

    • Skull: Composed of cranial and facial bones that serve protective and supportive functions.

    • Cranium: Encloses and protects the brain.

    • Facial Bones: Form the structure of the face and provide attachment points for facial muscles.

    • Middle Ear Bones: Tiny bones (ossicles) that transmit sound vibrations.

    • Hyoid Bone: Supports the tongue and is the only bone in the body not directly attached to another bone.

    • Vertebral Column: Consists of vertebrae, intervertebral discs, and ligaments, allowing for flexibility and protection of the spinal cord.

    • Thoracic Cage (Rib Cage): Comprises ribs and sternum, protecting the thoracic cavity's organs and aiding in respiration.

    • Supplemental Cartilages: Supports structures such as the ribs and windpipe.

Skull

  • Main Functions of the Skull:

    • Provides protection and structural support for the openings to the digestive and respiratory tracts.

    • Offers muscle attachment points that enable facial expressions, mastication (chewing), and speech.

    • Except for the mandible, all skull bones are connected by immovable joints called sutures, which solidify the skull structure as the individual matures.

  • Total Number of Skull Bones: 22

    • Facial Bones: 14, including key structures that shape the face and house the teeth.

    • Cranial Bones: 8, providing a protective case for the brain.

    • Associated Bones: 7 (includes auditory ossicles and the hyoid bone).

  • Associated Bones:

    • Auditory Ossicles: 6 tiny bones involved in hearing, each essential for sound transmission.

    • Hyoid Bone: 1, crucial for speech and swallowing functions.

Facial Bones (Total 14)

  • Components of the facial bones include:

    • Maxilla (2 bones): Form the upper jaw and contain the maxillary sinuses; important for the structure of the mouth and face.

    • Palatine (2 bones): Contribute to the formation of the hard palate and the floor of the nasal cavity.

    • Zygomatic (2 bones): Also known as cheekbones, they define the lateral aspect of the face.

    • Lacrimal (2 bones): Smallest facial bones located in the medial wall of the orbits, aiding in tear drainage.

    • Nasal (2 bones): Bridge of the nose, supporting its structure.

    • Inferior Nasal Concha (2 bones): Contribute to the lateral walls of the nasal cavity, enhancing airflow and filtration.

    • Vomer: 1 bone, forms part of the nasal septum.

    • Mandible: 1 bone, lower jaw; features include ramus, mandibular condyle, coronoid process, and alveolar processes for tooth attachment.

Cranial Bones (Total 8)

  • Components of the cranial bones include:

    • Frontal Bone: 1, forms the forehead and contributes to the orbits of the eyes.

    • Parietal Bones: 2, located on the sides of the skull, contributing to its dome-like structure.

    • Temporal Bones: 2, house structures of the ear and protect the sides of the skull; feature mastoid process and external acoustic meatus.

    • Occipital Bone: 1, forms the back and base of the skull; contains the foramen magnum for spinal cord passage.

    • Sphenoid Bone: 1, a keystone bone that articulates with all other cranial bones and contains sinus cavities.

    • Ethmoid Bone: 1, located between the orbits, helps form the nasal cavity's structure and sinus drainage.

Sutures in the Skull

  • Main sutures include:

    • Sagittal Suture: Connects the two parietal bones.

    • Squamous Suture: Joins the parietal bones to the temporal bones.

    • Coronal Suture: Connects the frontal bone to the parietal bones.

    • Lambdoid Suture: Connects the occipital bone to the parietal bones.

Major Foramina in the Skull

  • Key foramina include:

    • Foramen ovale: Allows passage of the mandibular nerve.

    • Jugular foramen: Transmits the internal jugular vein and cranial nerves IX, X, and XI.

    • Foramen lacerum: Pertains to several neurovascular structures.

    • Carotid canal: Provides passage for the internal carotid artery.

    • Foramen magnum: The largest opening where the spinal cord enters the skull.

Infantile Skulls

  • At birth, the skull is not fully developed, consisting of soft and flexible bony segments.

  • Fibrous Membranes connect the cranial bones, known as fontanels:

    • Posterior Fontanel: Closes around 2 months post-birth.

    • Sphenoidal Fontanel: Closes around 3 months postpartum.

    • Mastoid Fontanel: Closes around 12 months.

    • Anterior Fontanel: Closes around 2 years, allowing for brain growth and skull adjustments.

Associated Bones

  • Hyoid Bone:

    • Located in the neck, supports the tongue and its muscles, crucial for swallowing and speaking.

  • Auditory Ossicles:

    • Located in the middle ear cavity and considered part of the temporal bone.

    • Function: Move sound vibrations to the inner ear, functioning in the sense of hearing.

    • Components include:

      • Malleus: Hammer-shaped bone attached to the tympanic membrane.

      • Incus: Anvil-shaped bone that transmits sound from the malleus to the stapes.

      • Stapes: Stirrup-shaped bone that contacts the inner ear, facilitating sound transduction.