Osseous System: Structure and Functions of Bones of the Axial and Appendicular Skeleton

The osseous system, also known as the skeletal system, is a complex network of bones that supports and protects the body’s organs, facilitates movement, stores and releases minerals and fat, and produces blood cells. The skeletal system is divided into two main parts: the axial skeleton and the appendicular skeleton. Each part consists of specific bones that have unique structures and functions.

1. Axial Skeleton

The axial skeleton forms the central axis of the body and includes bones that protect the brain, heart, and lungs. It provides support and stability for the body.

Bones of the Axial Skeleton:

• Skull (Cranium and Facial bones)
• Vertebral Column (Spine)
• Ribs
• Sternum

Structure and Function of the Axial Skeleton:

1. Skull:
   • Structure: The skull consists of 22 bones, divided into two main regions:
     • Cranium: The upper part of the skull, protecting the brain, composed of 8 bones (e.g., frontal, parietal, temporal, occipital).
     • Facial bones: 14 bones that form the face, including the nasal bones, maxilla, zygomatic bones, and mandible.
   • Functions:
     • Protection: Protects the brain and sensory organs.
     • Support: Supports structures like the eyes, ears, and nose.
     • Attachment sites: Provides attachment points for muscles involved in facial expression and chewing.

1. Vertebral Column (Spine):
   • Structure: The vertebral column consists of 33 vertebrae, which are grouped into regions:
     • Cervical region: 7 vertebrae in the neck.
     • Thoracic region: 12 vertebrae in the chest region, each attached to a rib.
     • Lumbar region: 5 vertebrae in the lower back.
     • Sacral region: 5 fused vertebrae forming the sacrum.
     • Coccygeal region: 4 fused vertebrae forming the coccyx (tailbone).
   • Functions:
     • Support: Supports the head and torso.
     • Protection: Encases and protects the spinal cord.
     • Flexibility: Provides flexibility and allows for movement, such as bending and twisting.
     • Shock absorption: The intervertebral discs between vertebrae act as shock absorbers.
2. Ribs:
   • Structure: There are 12 pairs of ribs that form the rib cage. They are classified into:
     • True ribs (1–7): Directly attach to the sternum via costal cartilage.
     • False ribs (8–10): Indirectly attach to the sternum.
     • Floating ribs (11–12): Do not attach to the sternum or other ribs.
   • Functions:
     • Protection: Protects the heart, lungs, and other thoracic organs.
     • Respiration: Facilitates the expansion and contraction of the lungs during breathing.

1. Sternum:
   • Structure: The sternum, also known as the breastbone, is a flat bone located in the center of the chest. It consists of three parts:
     • Manubrium: The upper portion that articulates with the clavicles and first ribs.
     • Body: The middle portion that articulates with ribs 2 through 7.
     • Xiphoid process: The small, cartilaginous lower tip.
   • Functions:
     • Protection: Protects the heart and lungs.
     • Attachment: Serves as the attachment point for ribs and the clavicle.

2. Appendicular Skeleton

The appendicular skeleton is responsible for facilitating movement. It includes the bones of the limbs and the structures that connect the limbs to the axial skeleton.

Bones of the Appendicular Skeleton:

• Shoulder girdle (Clavicle and Scapula)
• Upper limbs (Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges)
• Pelvic girdle (Hip bones or coxal bones)
• Lower limbs (Femur, Patella, Tibia, Fibula, Tarsals, Metatarsals, Phalanges)

Structure and Function of the Appendicular Skeleton:

1. Shoulder Girdle (Pectoral Girdle):
   • Structure: Composed of the clavicle (collarbone) and scapula (shoulder blade).
   • Functions:
     • Connection: Connects the upper limbs to the axial skeleton.
     • Movement: Provides a stable yet flexible platform for arm movements.
2. Upper Limbs:
   • Humerus: The long bone of the upper arm.
   • Radius: One of the two bones of the forearm, located on the thumb side.
   • Ulna: The other bone of the forearm, located on the pinky side.
   • Carpals: The 8 bones of the wrist.
   • Metacarpals: The 5 bones forming the palm of the hand.
   • Phalanges: The 14 bones of the fingers.
   • Functions:
     • Movement: Facilitates arm and hand movement, enabling a wide range of motions such as gripping, lifting, and pushing.
     • Support: Supports the weight and activities of the upper limbs.
3. Pelvic Girdle (Hip Bones):
   • Structure: Composed of two coxal bones (hip bones), which are fused together at the pubic symphysis. Each coxal bone consists of three fused bones: the ilium, ischium, and pubis.
   • Functions:
     • Support: Supports the weight of the body and transfers it to the lower limbs.
     • Protection: Protects the reproductive organs, bladder, and lower digestive tract.
     • Movement: Facilitates movement and mobility of the lower limbs.
4. Lower Limbs:
   • Femur: The longest and strongest bone in the body, located in the thigh.
   • Patella: The kneecap, which protects and maintains the knee joint.
   • Tibia: The larger of the two bones in the lower leg, responsible for bearing weight.
   • Fibula: The smaller bone in the lower leg, provides support but does not bear weight.
   • Tarsals: The 7 bones that make up the ankle and the heel.
   • Metatarsals: The 5 bones that form the arch and ball of the foot.
   • Phalanges: The 14 bones of the toes.
   • Functions:
     • Movement: Allows for walking, running, jumping, and other motions involving the lower body.
     • Support: Supports the weight of the body during standing, walking, and running.
     • Balance: The lower limbs, particularly the feet, are essential for maintaining balance and stability.

Summary of the Structure and Functions of the Bones

The skeletal system plays an essential role in the overall structure and function of the human body. The axial skeleton serves as the central framework for protecting critical organs, while the appendicular skeleton is involved in movement and mobility. The bones in both parts of the skeleton are structured to provide support, facilitate movement, and protect vital organs, all of which are vital for everyday activities and overall body function. Understanding the structure and functions of bones within these two skeletal regions is crucial in fields such as anatomy, healthcare, and physical therapy.