Axial Skeleton

Skull

The skull is a complex structure composed of several bones that protect the brain and form the structure of the face. It is divided into cranial and facial bones, each with distinct features and functions.

• Frontal Bone

  • Metopic suture: Fuses fully in childhood

  • Coronal suture: Connects frontal and parietal bones.

  • Supraorbital foramen: Passage for nerves and vessels.

  • Frontal sinus: Air-filled cavity within the frontal bone.

• Parietal Bone

  • Sagittal suture: Joins the two parietal bones.

• Occipital Bone

  • Lambdoid suture: Connects occipital and parietal bones.

  • Occipital condyles: Articulate with the first cervical vertebra.

  • Foramen magnum: Large opening for the spinal cord.

• Temporal Bone

  • Squamous suture: Joins temporal and parietal bones.

  • Mastoid process: Attachment for neck muscles.

  • Styloid process: Attachment for tongue and neck muscles.

  • Mandibular fossa: Articulates with mandible.

  • External auditory meatus: Ear canal opening.

  • Zygomatic process: Forms part of the cheekbone.

• Zygomatic Bone

  • Temporal process: Contributes to the zygomatic arch.

• Maxilla

  • Infraorbital foramen: Passage for nerves and vessels.

  • ""Maxillary sinus: Largest paranasal sinus.

• Palatine, Mandible, Vomer, Nasal, Lacrimal, Ethmoid, Sphenoid

  • Each bone has unique features such as mandibular condyle, mental foramen, crista galli, perpendicular plate, greater/lesser wings, and sella turcica.

Additional info: Differences in fetal skulls (fontanelles) are important for development and birth.

Spinal Column

The vertebral column supports the body and protects the spinal cord. It is divided into cervical, thoracic, lumbar, sacral, and coccygeal regions.

• Cervical Vertebrae (C1-C7)

  • Atlas (C1): Allows nodding motion ('yes').

  • Axis (C2): Allows rotation ('no'); has odontoid process (dens).

  • Secondary curvature develops in childhood.

• Thoracic Vertebrae (T1-T12)

  • Spinous process: Posterior projection.

  • Transverse processes: Articulate with ribs.

  • Primary curvature present at birth.

• Lumbar Vertebrae (L1-L5)

  • Spinous process: Short and thick.

  • Secondary curvature develops in childhood.

• Sacrum (S1-S5)

  • Bones fuse together.

  • Median sacral crest, transverse lines, auricular surface.

  • Primary curvature present at birth.

• Coccyx (Co1-Co4)

  • Bones fuse together to form the 'tailbone'.

Additional info: Study the three spinal deformities: scoliosis, kyphosis, and lordosis.

Thoracic Cage

The thoracic cage protects vital organs and supports respiration. It consists of the sternum and ribs.

• Sternum

  • Manubrium, body, xiphoid process.

• Ribs

  • Attach to thoracic vertebrae.

  • True ribs (1-7): Directly attached to sternum.

  • False ribs (8-12): Indirectly or not attached to sternum.

  • Floating ribs (11-12): Only attached to vertebrae.

Appendicular Skeleton

Pectoral Girdle

The pectoral girdle connects the upper limb to the axial skeleton and consists of the clavicle and scapula.

• Clavicle

  • Bumpy side is inferior; curved forward at sternal end, curved back at acromion end.

• Scapula

  • Coracoid process, spine, glenoid fossa, acromion process.

Arms/Hands

• Humerus

  • Head, deltoid tuberosity, medial/lateral epicondyles, capitulum, olecranon fossa.

• Ulna

  • Olecranon process, trochlear notch, coronoid process, styloid process.

• Radius

  • Head, radial tuberosity, styloid process.

• Carpals, Metacarpals, Phalanges

  • Carpals: Wrist bones.

  • Metacarpals: Palm bones.

  • Phalanges: Finger bones (proximal, middle, distal; pollex has only proximal and distal).

Pelvic Girdle/Coxal Bones

The pelvic girdle supports the lower limbs and protects pelvic organs. It consists of the ilium, ischium, and pubis.

• Ilium

  • Auricular surface, iliac crest, anterior/posterior superior/inferior iliac spines, greater sciatic notch.

• Ischium

  • Seat portion, ischial spine, ischial tuberosity, ischial ramus.

• Pubis

  • Pubic symphysis, obturator foramen, acetabulum (forms hip joint with femur).

Additional info: Differences between male and female pelvis are important for childbirth and locomotion.

Legs/Feet

• Femur

  • Head, neck, greater/lesser trochanter, gluteal tuberosity, medial/lateral condyle, linea aspera.

• Patella

  • Not present at birth; forms within the tendon of the quadriceps femoris muscle.

• Tibia

  • Medial/lateral condyle, tibial tuberosity, anterior crest, medial malleolus.

• Fibula

  • Head, lateral malleolus.

• Tarsals

  • Ankle bones; talus (between tibia and medial malleolus).

• Metatarsals

  • Bones before toes.

• Phalanges

  • Toe bones (proximal, middle, distal; hallux has only proximal and distal).

Joints and Movements

Structural and Functional Classes of Joints

Joints are classified based on their structure and function. Structural classes include fibrous, cartilaginous, and synovial joints. Functional classes are based on the degree of movement allowed: synarthroses (immovable), amphiarthroses (slightly movable), and diarthroses (freely movable).

• Fibrous joints: Bones joined by dense connective tissue; little to no movement.

• Cartilaginous joints: Bones joined by cartilage; limited movement.

• Synovial joints: Bones separated by a fluid-filled cavity; allow free movement.

Features of Synovial Joints

Synovial joints are the most movable type of joint in the body. They have a synovial cavity, articular cartilage, joint capsule, and supporting ligaments.

• Synovial cavity: Space filled with synovial fluid for lubrication.

• Articular cartilage: Covers bone surfaces to reduce friction.

• Joint capsule: Encloses the joint and maintains stability.

• Ligaments: Strengthen and support the joint.

• Movements allowed: Flexion, extension, abduction, adduction, rotation, and circumduction.

Example: The knee joint is a synovial joint that allows flexion and extension, as well as slight rotation.

Summary Table: Major Bones and Key Features

Additional info: This table summarizes the main bones and their distinguishing features for quick review.