Axial and Appendicular Skeleton: Structure, Function, and Key Features

Axial Skeleton

Functions of the Axial Skeleton

• Support: Provides structural support for the body, maintaining posture and protecting internal organs.

• Attachment: Serves as an anchor for muscles, facilitating movement.

• Joints: Allows for articulation between bones, enabling flexibility and movement.

Types of Bones Found in the Skull

• Facial Bones: Protect and support entrances to the digestive and respiratory tracts.

  • Function: Provide attachment points for muscles that control facial expression and assist in manipulation of food.

  • Examples: Nasal, lacrimal, palatine, zygomatic, maxillae, inferior nasal conchae.

• Cranial Bones: Made up of 8 bones that form the cranium and enclose the cranial cavity.

  • Function: Protects the brain from injury.

  • Define calvaria: Roof of the skull formed by the occipital, parietal, and frontal bones.

  • Examples: Parietal, frontal, sphenoid, ethmoid.

• Associated Bones:

  • Hyoid: Supports the tongue and aids in swallowing.

  • Auditory ossicles: Transmit sound vibrations from the tympanic membrane to the inner ear.

Joints (Articulations) Between Skull Bones

Joints between skull bones are called sutures. They are immovable joints that fuse the bones of the skull.

• Coronal suture: Attaches frontal to parietal bones.

• Squamous suture: Attaches temporal and parietal bones.

• Sagittal suture: Attaches parietal bones.

• Lambdoid suture: Attaches occipital to parietal bones.

Special Skull Features

• Orbital Complex: Formed by several bones; houses the eyes.

• Nasal Complex: Formed by bones that enclose the nasal cavity.

• Paranasal Sinuses: Air-filled chambers connected to the nasal cavity; function in lightening the skull and humidifying air.

• Lower Jaw: The mandible; only movable bone of the skull.

Hyoid Bone

• Function: Supports the tongue and provides attachment for muscles associated with swallowing.

• Interesting Fact: The hyoid does not articulate directly with any other bone.

Auditory Ossicles

• Location: Within each middle ear cavity.

• Function: Play a key role in hearing by conducting vibrations from the tympanic membrane to the internal ear.

Fontanelles

• Where found: In the skulls of infants.

• Function: Allow for growth of the brain and skull during infancy.

• Details about anterior fontanelle:

  • Size: Largest fontanelle.

  • Nickname: "Soft spot" on a baby's head.

  • Closure: Typically closes by 18-24 months.

Vertebral Column

Structure and Regions

• Number of Bones: 26 vertebrae in adults.

• Regions:

  1. Cervical (7)

  2. Thoracic (12)

  3. Lumbar (5)

  4. Sacral (1, formed by fusion of 5 sacral vertebrae)

  5. Coccygeal (1, formed by fusion of 3-5 coccygeal vertebrae)

Spinal Curves

Region	Function	Primary/Secondary Curve
Thoracic	Accommodates thoracic organs	Primary
Sacral	Accommodates pelvic organs	Primary
Cervical	Balances the head	Secondary
Lumbar	Balances the weight of the trunk over the lower limbs	Secondary

Parts of a Vertebra

• Vertebral body: Main weight-bearing portion.

• Vertebral arch: Forms the vertebral foramen.

• Processes: Sites for muscle attachment and articulation.

Vertebral Foramen

• Definition: Opening formed by the vertebral arch; houses the spinal cord.

Intervertebral Discs

• Function: Cushion and separate vertebrae, allowing for movement and absorbing shock.

Cervical Vertebrae

• Key Features: Small body, large vertebral foramen.

• Atlas (C1): Supports the skull; allows nodding motion.

• Axis (C2): Has the dens; allows rotation of the head.

• Vertebra prominens (C7): Has a prominent spinous process.

Thoracic Vertebrae

• Key Features: Larger body, facets for rib articulation.

• How Many: 12 thoracic vertebrae.

• Each Connects To: A pair of ribs.

Lumbar Vertebrae

• Key Features: Largest vertebrae, thick body for weight bearing.

• How Many: 5 lumbar vertebrae.

Sacrum and Coccyx

• Sacrum: Formed by fusion of 5 sacral vertebrae; connects spine to pelvis.

• Coccyx: Tailbone; formed by fusion of 3-5 coccygeal vertebrae; provides attachment for ligaments and muscles.

Thoracic Cage

• Functions: Protects heart and lungs; supports shoulder girdle and upper limbs.

• Bones Involved: Sternum, ribs, thoracic vertebrae.

Appendicular Skeleton

Shoulder (Pectoral) Girdle

• Also Known As: Pectoral girdle.

• Bones/Parts Involved: Clavicle, scapula.

• Sternoclavicular Joint: Connects clavicle to sternum.

• Acromioclavicular Joint: Connects clavicle to scapula.

Upper Limb Bones

• Arm: Humerus.

• Forearm: Radius and ulna.

• Wrist: 8 carpal bones.

• Hand: Metacarpals (palm), phalanges (fingers).

• Thumb: Pollex; has only two phalanges.

Hip (Pelvic Girdle)

• Also Known As: Pelvic girdle.

• Bones Involved: Ilium, ischium, pubis.

• Joint Connecting Hip Bones in Front: Pubic symphysis; made of fibrocartilage.

• Joint Connecting Sacrum and Ilium: Sacroiliac joint.

• True Pelvis: Encloses pelvic cavity.

• False Pelvis: Supports abdominal organs.

Differences Between Female and Male Skeletons

Feature	Male	Female
Skull	Larger, more robust	Smaller, more delicate
Pelvis	Narrower, deeper	Wider, shallower

Lower Limb Bones

• Function: Support body weight and enable movement.

• Upper Leg: Femur.

• Kneecap: Patella.

• Lower Leg: Tibia and fibula.

• Ankle: Tarsal bones.

• Foot (Sole and Toes): Metatarsals and phalanges.

• Big Toe: Hallux; has only two phalanges.

• Function of Arches of the Foot: Distribute body weight and absorb shock during movement.

Additional info: Some details, such as the number of bones in each region and the specific features of certain joints, were inferred based on standard anatomical knowledge.