The Axial Skeleton
The axial skeleton extends along the central axis of the body and is comprised of 80 bones, categorized into the following regions:
The Skull
The skull consists of 22 bones that are interconnected, with the exception of the mandible (lower jawbone). It is divided into two main sections:
- The upper part: Known as the cranium, this structure serves to protect the brain from injury.
- The lower and anterior part: These are referred to as the facial bones, which provide support for the eyes, nose, and mouth.
The Hyoid Bone and Auditory Ossicles
The hyoid bone is a small, U-shaped bone located at the base of the lower jaw. It is the only bone in the human body that is not connected to any other bone. The auditory ossicles, which include the malleus, incus, and stapes, are the smallest bones in the body. They function to transmit and amplify sound from the eardrum to the inner ear.
Vertebrae
The human spine consists of 26 vertebrae, organized as follows:
- Cervical vertebrae: Located in the neck, comprising 7 vertebrae.
- Thoracic vertebrae: Comprising 12 vertebrae in the upper back.
- Lumbar vertebrae: Comprising 5 vertebrae in the lower back.
- Sacrum: Comprised of 1 vertebra.
- Coccyx: Made up of 1 vertebra.
Ribs and Sternum
The sternum, a thin knife-shaped bone, is located along the midline at the front of the thoracic region of the skeleton. The ribcage consists of 12 pairs of ribs that, along with the sternum, form the protective ribcage.
The Appendicular Skeleton
The appendicular skeleton is composed of 126 bones, which include the bones of the arms, legs, and those that connect to the axial skeleton.
Pectoral Girdle
This region connects the arms to the axial skeleton and consists of two types of bones: the clavicles (collarbones) and the scapulae (shoulder blades), with one of each present on either arm.
Upper Limbs
Each arm comprises 30 bones, including:
- Humerus.
- Radius.
- Ulna.
- Carpal bones.
- Metacarpal bones.
- Phalanges.
Pelvic Girdle
Also known as the hip region, this area connects the legs to the axial skeleton and consists of the hip bones, with one present in each leg. Each hip bone is structured from three parts.
Lower Limbs
Each leg consists of 30 bones, which include:
- Femur.
- Tibia.
- Fibula.
- Patella.
- Tarsal bones.
- Metatarsal bones.
- Phalanges.
Cartilage
Cartilage is the second component of the skeletal system, composed of fibers embedded in connective tissue. Cartilage consists of two types of fibers: collagen and elastin fibers. There are three main types of cartilage:
- Hyaline cartilage
- Fibrocartilage
- Elastic cartilage