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Your skeleton includes all of the bones of your body, providing the internal supporting structure of the body. The skeleton is divided into the axial and appendicular skeletons. The adult axial skeleton consists of 80 bones that form the head and body trunk. Attached to this are the limbs, whose 126 bones constitute the appendicular skeleton.
Because of our upright stance, different functional demands are placed upon the upper and lower limbs. Thus, the bones of the lower limbs are adapted for weight-bearing support and stability, as well as for body locomotion via walking or running. In contrast, our upper limbs are not required for these functions. Instead, our upper limbs are highly mobile and can be utilized for a wide variety of activities. The large range of upper limb movements, coupled with the ability to easily manipulate objects with our hands and opposable thumbs, has allowed humans to construct the modern world in which we live.
You will learn more about the axial and appendicular skeletons throughout this lesson.
The axial skeleton forms the vertical, central axis of the body and includes all bones of the head, neck, chest, and back. It serves to protect the brain, spinal cord, heart, and lungs. It also serves as the attachment site for muscles that move the head, neck, and back, and for muscles that act across the shoulder and hip joints to move their corresponding limbs.
The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. The bones of the cranium are collectively referred to as the craniofacial bones. These can be subdivided into cranial and facial bones. Cranial bones form the brain casing, surrounding and protecting the brain. Facial bones underlie the facial structure, including the eye sockets, nose, upper and lower jaws, and more.
The craniofacial bones form multiple spaces within the cranium, some large and some small. For example:
The vertebral column is also known as the spinal column or spine. It consists of a sequence of vertebrae (singular, vertebra), each of which is separated and united by an intervertebral disc formed by connective tissue. Together, the vertebrae and intervertebral discs form the vertebral column. It is a flexible column that supports the head, neck, and body and allows for their movements. It also protects the spinal cord, which passes down the back through openings in the vertebrae.
The vertebral column originally develops as a series of 33 vertebrae. However, as humans develop, certain vertebrae fuse together, leaving the adult human with 24 vertebrae, plus the sacrum and coccyx. The vertebral column is subdivided into five regions, with the vertebrae in each area named for that region and numbered in descending order.
The thoracic cage, also referred to as the rib cage, forms the bony structure of the thorax, or chest. It consists of the 12 pairs of ribs and the associated cartilages. The ribs are attached posteriorly (toward the back) to the thoracic vertebrae. Anteriorly, most ribs are attached to the sternum, which is the elongated bony structure that anchors the anterior (front) thoracic cage. The thoracic cage protects the heart and lungs.
As you learned above, the appendicular skeleton includes all bones of the upper and lower limbs, plus the bones that attach each limb to the axial skeleton. These bones are divided into two groups: the bones that are located within the limbs themselves, and the girdle bones that attach the limbs to the axial skeleton. The bones of the shoulder region form the pectoral girdle, which anchors the upper limb to the thoracic cage of the axial skeleton. The lower limb is attached to the vertebral column by the pelvic girdle.
The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle. The clavicle (collarbone) is an S-shaped bone located on the anterior (front) side of the shoulder. You can easily palpate (feel with your fingers) the entire length of your clavicle.
The scapula (shoulder blade) lies on the posterior (back) of the shoulder. It is supported by the clavicle and articulates with the humerus (arm bone) to form the shoulder joint. The scapula is a flat, triangular-shaped bone with a prominent ridge running across its posterior surface. This ridge extends out laterally, where it forms the bony tip of the shoulder and joins with the clavicle. By following along the clavicle, you can palpate out to the bony tip of the shoulder, and from there, you can move back across your posterior shoulder to follow the ridge of the scapula.
The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive mobility of the entire pectoral girdle, which in turn enhances movements of the shoulder and upper limb.
The upper limb is divided into three regions:
There are 30 bones in each upper limb. The humerus is the single bone of the arm, and the ulna and the radius are the paired bones of the forearm. The base of the hand contains eight bones, each called a carpal bone, and the palm of the hand is formed by five bones, each called a metacarpal bone. The fingers and thumb contain a total of 14 bones, each of which is a phalanx bone of the hand.
The pelvic girdle (hip girdle) is the attachment point for each lower limb. This structure is formed by right and left coxal bones (also known as the hip bones; coxal, hip). Each coxal bone is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony pelvis is the pelvic girdle (the two coxal bones), the sacrum, and the coccyx.
The bones of the male and female pelvis have several clear differences that make the pelvis one anatomical piece of the body that allows for accurate sex determination. These differences relate to function and body size.
In general, the bones of the male pelvis are thicker and heavier, adapted for support of the male’s heavier physical build and stronger muscles. The greater sciatic notch of the male hip bone is narrower and deeper than the broader notch of females.
The female pelvis is adapted for childbirth, which is evidenced by it being wider than the male pelvis. The female sacrum is wider, shorter, and less curved, causing it to project less into the pelvic cavity. This creates a more rounded or oval-shaped pelvic inlet compared with males. The lesser pelvic cavity of females is also wider and shallower than the narrower, deeper, and tapering (becoming thinner) lesser pelvis of males.
Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination.
Like the upper limb, the lower limb is divided into three regions: the thigh, leg, and foot. While you may be used to referring to the entire lower limb as your “leg,” in anatomy, the term “leg” only refers to the portion of the lower limb between the knee and ankle. The thigh is the region of the lower limb located between the hip and knee joints. The leg is the region between the knee and ankle joints. Distal to (beyond) the ankle is the foot.
The lower limb contains 30 bones. The femur is the single bone of the thigh. The patella, or kneecap, is the bone found at the knee joint. The tibia and fibula are the paired bones of the leg. The bones of the foot are divided into three groups. The posterior portion of the foot is formed by a group of seven tarsal bones, whereas the midfoot contains five elongated metatarsal bones. The toes contain 14 small bones, each of which is a phalanx bone of the foot.
SOURCE: THIS TUTORIAL HAS BEEN ADAPTED FROM OPENSTAX “ANATOMY AND PHYSIOLOGY 2E”. ACCESS FOR FREE AT OPENSTAX.ORG/BOOKS/ANATOMY-AND-PHYSIOLOGY-2E/PAGES/1-INTRODUCTION. LICENSE: CREATIVE COMMONS ATTRIBUTION 4.0 INTERNATIONAL.
