The Skeletal System Anatomy

The Skeletal System: Physiology


The Skeletal system includes every bone and joint in the body. Each bone is a complex living organ composed of many cells, minerals, and protein fibers. The skeleton acts as a scaffold by supporting and protecting the soft tissues that make up the rest of the body. The skeleton system also provides a connection point for the muscle to allow movements at the joints. The red bone marrow inside the bones creates a new blood cell. The bones act as the body’s warehouse for iron, calcium, and energy in the form of fat. Lastly, the skeleton grew throughout childhood and provided a framework for the rest of the body to grow.

Skeletal system Anatomy

The skeletal system is an adult body made up of 206 individual bones. These bones are arranged into two major divisions: the appendicular skeleton and the axial skeleton. The axial skeleton continues along the body’s midline axis and consists of 80 bones in the following regions.

  • Skull
  • Hyoid
  • Ribs
  • Auditory ossicles
  • Sternum
  • Ribs
  • Vertebral column

The appendicular skeleton is composed of 126 bones in the following regions:

  • Upper limbs
  • Pelvic girdle
  • Lower limbs
  • Pectoral (Shoulder girdle
Body Anatomy Bones Bone Anatomy Of The Human Body | Humananatomybody - Human Anatomy Library
Body Anatomy Bones Bone Anatomy Of The Human Body | Humananatomybody – Human Anatomy Library


The skull is made of 22 bones that are welded together except for the mandible. These 21 joined bones are separate in children to allow the skull and brain to grow but become fused later to give added strength and protection as an adult. The mandible remains the movable jaw bone and forms the only movable joint in the skull with the temporal one.

The ones of superior portion of the skull are also called the cranium and guard the brain against damage. The bones of the inferior and anterior parts of the skull are known as facial bones and support the eyes, mouth, and nose.

Hyoid and Auditory Ossicles

The hyoid is a small, U-shaped bone inferior to the mandible. The hyoid is the single bone in the body that does not form a joint with another bone- it is a floating one. The hyoid’s role is to help hold the trachea open and to create a bone connection to the tongue muscles.

The smallest bones in the body are the malleus, incus, and stapes- collectively, the auditory ossicles. These bones can be found in a small cavity within the temporal bone; they help to communicate and amplify sound from the eardrum to the inner ear.


Twenty-six vertebrae from the vertebral column of the human body. They are named after the region of the body.

  • Cervical (neck) – 7 vertebrae
  • Thoracic (chest) – 12 vertebrae
  • Lumbar (lower back) -5 vertebrae
  • Scarum – 1 vertebra
  • Coccyx (tailbone) – 1 vertebra

With the exclusion of the singular sacrum and coccyx, each vertebra is named for the first letter of its corresponding region and its position along the superior-inferior axis. An example is the most superior thoracic vertebra, called TI, and the most inferior is called T12.

Ribs and Sternum

The sternum, also recognized as the breastbone, is a thin, knife-shaped bone positioned along the midline of the skeleton’s anterior surface of the thoracic region. The sternum attaches to the ribs by a narrow band of cartilage named costal cartilage.

  • There are 12 pairs of ribs collectively with the sternum from the ribcage of the thoracic region. The first seven ribs are also known as “true ribs” because they connect the thoracic vertebrae right to the sternum through their band of Costa cartilage. Ribs 8, 9, and ten all connect to the sternum via cartilage attached to the seventh rib cartilage. These are considered “false ribs.” Ribs 11 and 12 are also “false ribs” but are also acknowledged as “floating ribs” because they are not joined to the sternum’s cartilage.

Pectoral Girdle and Upper Limb

The pectoral girdle attached the upper limb or arm bones to the axial skeleton, consisting of the left and right clavicles and the left and right scapulae.

The humerus is the bone in the upper arm. It forms the ball and socket joint within the shoulder with the scapula and forms the elbow joint with the lower arm bones. The radius and ulna are the two forearm bones. The ulna is the medial side of the forearm and forms a hand jointly with the humerus at the elbow. The radius enables the forearm and hand to turn over at the wrist joint.

The lower arm bones form the wrist joint with the carpals, a group of eight small bones that provide added flexibility to the wrist. The carpals are attached to the five metacarpals that form the bones of the hand and are connected to each of the fingers. Each finger holds three bones, known as phalanges, except for the thumb, which only has phalanges.


Pelvic Girdle and Lower Limb 

Created by the left and right hip bones, the pelvic girdle connects the lower limb (leg) bones to the axial skeleton.

The femur is the longest and largest bone in the body and the only one in the thigh (femoral) region. The femur makes the ball and socket hip joint with the hip bone and forms the knee joint with the patella and tibia. This area is commonly regarded as the kneecap; the patella is unique since it is one of the few bones that are not present when you are born. The patella forms in early childhood to strengthen the knee for crawling and walking.

The tibia and fibula are the bones of the lower. The tibia is much larger than the fibula and holds almost all of the body’s weight. The fibula is primarily a muscle connection point and is utilized to help maintain a person’s balance. The tibia and fibula articulate the ankle joint with the tail, one of the foot’s seven tarsal bones.


The tarsals are a group of seven smaller bones that make the posterior end of the foot and heel. The tarsals form joints with the five long metatarsals of the foot. Each of the metatarsals makes up the joints with one of the sets of phalanges in the toes. Each toe has three phalanges, but the big toe; only has two phalanges.

Microscopic Structure of Bones 

The skeleton makes up about 30 to 40% of an adult’s body mass. The skeleton mass consists of a nonliving bone matrix and many tiny bone cells. Roughly half of the bone matrix mass is water, while the other half is solid crystals of calcium carbonate, collagen protein, and calcium phosphate.

Living bone cells are found on the edges of bones and within small cavities inside the bone matrix. Even though living cells make up very little of the total bone mass, they have several vital roles in the functions of the skeletal system.

The bone cells enable the bones to:

Develop and Grow

Repair itself following an injury or due to daily wear

Break down to release their stored minerals

Types of Bones

Many different types of bones can be categorized into five types: long, short, flat, irregular, and sesamoid.

Long Bones are longer than wide; they are the major bones of the limbs. Long bones grow more than any other class of bones throughout childhood and are accountable for the bulk of our height as adults. A hollow medullary cavity is located in the center of long bones and serves as a storage area for bone marrow. Examples of long bones are the phalanges, metatarsals, femur, tibia, and fibula.

Short Bones are about short as they are wide and often curved or round. The tarsal bones in the foot or the carpal bones in the wrists are examples of short bones.

Flat bones – can vary significantly in shape and size. However, they have a common feature of being thin in one direction. Since they are thin, flat bones do not have a medullary cavity like long bones. The frontal, parietal and occipital bones of the skull and hip and rib bones are all examples of flat bones.

Irregular bones- have some shape or pattern that does not fit the pattern of long, short, or flat bones. The sacrum vertebrae, coccyx of the spine, and the ethmoid, sphenoid, and zygomatic bones of the skull are all irregular bones.

Sesamoid bones are formed after the birth inside of the tennis that runs along the joints. Sesamoid bones grow to shield the tendon against stress and strains at the joint and can help give a mechanical advantage to muscles pulling on the tendon. The patella and the pisiform bone or the carpals are the only sesamoid bones that are calculated as part of the 206 bones of the body. Other sesamoid bones can form in the joints of the hands and feet but are not present in all people.

Parts of the Bones


The body’s long bones encompass many unique regions due to how they grow and develop. At birth, each long bone is made of three individual bones divided by hyaline cartilage. Each end bone is called an epiphysis (epi = on; physis = to grow), while the center bone is called a diaphysis (dia = passing through). The epiphyses and diaphysis develop and grow towards one another and ultimately fuse into one bone. The region of the growth and eventual connection between the epiphysis and diaphysis is called the metaphysis (meta-after). Once the long bone parts have fused, the only hyaline cartilage left in the bone is located as articular cartilage on the ends of the bone that forms joints with other bones. The particular cartilage acts as a shock absorber and gliding surface linking the bones to facilitate movement at the joint.

Looking at a bone cross-section, numerous distinct layered regions make up a bone. The outside of a bone is blanketed in a thin layer of dense irregular connective referred to as periosteum. The periosteum has many strong collagen fibers that firmly anchor muscles and tendons to the bone for motion. Osteoblast cells and stem cells in the periosteum are incorporated in the growth and repair outside of the bone due to injury or stress. Blood vessels in the periosteum provide energy to the cells on the surface of the bone and penetrate into the bone itself to feed the cells inside the bone. The periosteum also contains nervous tissue and many nerve endings to make bone sensitive to pain when injured.
Deep inside the periosteum is the compact bone that composes up the hard, mineralized portion of the bone. Compressed bone is made of a matrix of solid mineral salts reinforced with tough collagen fibers. Many tiny cells called osteocytes exist in small spaces in the matrix ad help to preserve the durability and integrity of the compact bone.


Deep into the dense bone layer is a region of porous bone where the bone tissue grows in thin columns named trabeculae with spaces of red bone marrow. The trabeculae grow in a particular pattern to resist external stresses with the least amount of mass possible, retaining bones light but strong. Long bones have porous bones on their ends but have a deep medullary cavity in the center of the diaphysis. The medullary cavity holds red bone marrow during childhood, eventually turning into yellow bone marrow after puberty.


An Articulation, or joint, is the point of contact between bones, bone, and cartilage, a tooth and bone. Synovial joints are the most prevalent type of articulation and feature small bone gaps. These holes allow a free range of space and motion of the synovial fluid to lubricate the joint. Fibrous joints exist where bones are tightly joined and offer limited to no movement between the different bones. Fibrous joints also hold teeth in their sockets. Finally, cartilaginous joints are formed where bone meets cartilage or where there is a layer of cartilage in-between two bones. These joints provide a small quantity of flexibility due to the gel-like consistency of cartilage.

The Skeletal System: Physiology