A Comprehensive Overview of the Skeletal System

Dr. Sandra El Hajj-MSc, N-MD, DHSc

What is the skeletal system?

The skeletal system's main function is to provide support and protection to the body while giving it shape and form. All human and animal movements require coordination of important body systems, particularly the skeletal system and muscular system. Without the proper function of each system, movement can't happen. The human skeletal system consists of many parts, which include all of the bones, cartilage tendons, and ligaments in the body. The human adult skeleton consists of a total of 206 bones, which make up about 20 percent of a person's body weight.

Differences in the skeletal system

Differences in the skeletal system’s structure exist depending on a person’s developmental growth. For instance, the skeleton of children as compared to adults contains more bones and tends to fuse as they grow older, like the bones of the skull. An adult has 206 bones, while a newborn baby has nearly 300 bones.

There are differences between the male and female skeleton as well. The male skeleton is usually longer and has a high bone mass as compared to the female skeleton. Male and female skulls show significant differences in structure. The male jawbone is typically angular and square-shaped at the chin area, while the female jawbone tends to be more rounded and pointed. Also, the female skeleton has a broader pelvis that plays an important role during pregnancy and childbirth.

The differences can be partly attributed to hormones, such as testosterone, which primarily influences the shape of men's bones and affects women's bone development. The high levels of estrogen that are released during female puberty cause an earlier closure of certain cartilage, which leads to the full development of the female skeletal system at around the age of 18. Male bone development ends at around age 21, which is why men have higher bone mass compared to women(1).

What are the parts of the skeletal system?

Anatomically, the human skeletal system can be divided into two parts: Theaxial skeletonand theappendicular skeleton. The axial skeleton protects the majority of the organs found at the upper part of the body through the vertebral column. The bones of the axial skeleton form a connected structure and are found in different areas such as the pelvic girdles and lower limbs or legs, pectoral girdles and upper limbs or arms(2).

The axial skeleton

The axial skeleton forms the upper vertical axis of the body excluding the arms and pectoral girdles. The axial skeleton has 80 bones (32-34 bones in the vertebral column, 12 pairs of ribs, 22 bones in the skull and seven associated bones). The axial skeleton is the most important part of the skeletal system because it protects the major organs like the brain, heart, liver and lungs. The axial skeleton is the main axis that supports the head, neck, back and chest.

The skull

The adult skull is made up of 22 bones which can be further classified by location:

• Cranial bonesform the bulk of the skull and protect the brain from any physical trauma.
• Facial bonesare made up of 14 bones found on the frontal area of the skull and make up the face. Facial bones give the face its form and shape.
• Auditory ossiclesare bones found within the inner ear canal. There are three auditory ossicles on each side of the head, known as the malleus (hammer), incus (anvil) and stapes (stirrup). These work collaboratively to channel sound waves from everything around you to the structures of the inner ear.
• The hyoidis a U-shaped bone that is found at the base of the jaw. It attaches to the muscles and ligaments in the neck.

Vertebral column

Another part of the axial skeleton is the vertebral column,which is made up of 26 bones. The vertebrae are the first 24 bones, then come the sacrum and coccyx (tailbone). The first 24 vertebrae can be divided accordingly:

• The cervical vertebrae, which is made up of the seven bones found in the head and neck
• The thoracic vertebrae, which is made up of the 12 bones found in the upper back
• The lumbar vertebrae, which is made up of the five bones that are found in the lower back

The combined vertebrae form the sacrum and coccyx. These help support the weight of the body while serving as connection points for various ligaments.

Thoracic cage

The thoracic cage is made up of the sternum (breastbone) and 12 pairs of ribs which form a protective structure around the organs of the upper torso, including the heart and lungs. Without the thoracic cage, human survival is not possible.

The appendicular skeleton

The appendicular skeleton is made up of bones that attach limbs to the axial skeleton. The appendicular skeleton is made up of 126 bones, which include bones of the upper and lower limbs, pectoral girdles, and the pelvic girdles. The appendicular skeleton facilitates movement, digestion, reproduction and excretion.

Pectoral girdle

The pectoral girdle consists of shoulder bones: The clavicle and the scapula. The pectoral girdle is where the arms attach to the axial skeleton.

Upper limbs

Upper limbs include bones of the arms and hands. Each arm contains 30 bones: The humerus (the long bone of the upper arm, the radius (one of two long bones of the forearm), which is found on the side where the thumb is located, the ulna (the second long bone of the forearm found on the pinky finger side), the carpals ( a group of eight bones found in the wrist area), the metacarpals (the five bones found in the middle area of the hand) and the phalanges (the 14 bones that make up the fingers).

Pelvic girdle

The pelvic girdle is made up of the bones that comprise the hips. This structure is where the legs attach to the axial skeleton. It consists of two hip bones that attach to each one of the legs. Each hip bone consists of three parts: The ilium, ischium and pubis. The Ilium is the hip’s upper bone, while the ischium is the curved section of the pelvic girdle (i.e. the base of each hip bone). The pubis is situated at the front part of the hip bone.

Lower limbs

The lower limbs include the bones of the legs and feet. Like the upper limbs, the lower limbs are also made up of different bone parts that maintain its structure and provide protection and motion. Each leg contains 30 bones which include the femur, tibia, fibula, patella, tarsals, metatarsals and phalanges.

• The femur is the large bone located at the upper leg.
• The tibia is the major bone of the lower leg that forms the shin.
• The fibula is the second bone in the lower leg, found in the outer leg.
• The patella is also known as the kneecap, which is responsible for knee extension.
• The ankle is made of seven bones called the tarsals.
• The middle area of the foot is made of five bones, called the metatarsals.
• The phalanges are 14 bones forming the toes.

All of these bones are interconnected to allow for motion, maintenance of shape and form of the lower limbs, and to allow coordination of movements of each part.

What are the functions of the skeletal system?

The skeletal system plays an essential role in our survival. The main function of the skeletal system is to provide support for the body (e.g. how the spinal column provides support for the head and torso, allowing us to stand straight, bend backward, forwards or sideways(3). However, the skeletal system has several additional functions.

Protects vital internal organs from trauma and other injuries

One of the most important functions of the skeletal system is to protect vital organs. The skeletal system keeps major organs in place and ensures that these organs are protected from any trauma and can function as they should. This is evident with the skull protecting the brain, and the thoracic cage protecting the heart and lungs.

Allows mobility and locomotion

Bones of the body coordinate with skeletal muscles and other skeletal system components to enable the body to move from one place to another and do multiple movements such as walking, running, dancing, sitting, standing and jumping. Muscles are attached to bones through tendons, which allows the body to move in many different ways with flexibility.

Aids in hematopoiesis

Hematopoiesis is defined as the production of all types of blood cells. It involves the hematopoietic system, which includes organs and tissues such as the bone marrow, liver and spleen. However, it is important to know that in adults, the production of red blood cells, white blood cells and platelets occurs primarily in the bone marrow. Conditions affecting the bone marrow may affect the production of blood cells.

Stores minerals and nutrients

Bones store essential minerals and mineral salts such as calcium, phosphorus and calcium phosphate, which provide firmness to the bones. Bones also store fat in yellow bone marrow.

Conditions of the skeletal system

Any injuries to bones, ligaments, tendons or cartilage can greatly affect the normal function of the body. The human skeletal system is usually not very vulnerable to diseases unless it is damaged due to physical trauma or internal infections. However, it is susceptible to osteoporosis, deformities at the time of birth and improper growth of one or more bones due to lack of minerals. It can also be affected by DNA mutations of its cellular components, which may lead to tumor development(4).

Fractures

Fractures (broken bones) typically occur due to a severe injury or trauma causing breakage in the bone. Fractures occur from incidences such as vehicular accidents, falls and physical assault. Normally, a fracture requires the immediate intervention of orthopedic doctors or orthopedic surgeons in cases that involve surgery.

Metabolic bone diseases

Metabolic bone diseases affect the bone’s strength and integrity, both of which are the result of a deficiency in vitamin D, some loss in bone mass or the use of certain medications like steroids and chemotherapy.

Arthritis

Arthritis is a condition that leads to the inflammation of the joints. It results in pain and limits the movement. Arthritis can be caused by a breakdown of cartilage found in joints, autoimmune conditions or infection.

Cancer

Cancer can develop in the tissues of the bone or the cells produced by bones. This condition is usually rare, chronic and requires intensive treatment.

Spinal curvatures

Spinal curvature is a condition that causes the spine to have an abnormal curve deviant from its usual shape. There are three main types of spinal curvature which include: Kyphosis (resulting in a rounded upper back), lordosis, which causes the lower back to curve inward and scoliosis, which causes an s- or c-shaped curve in the spine.

Linking the skeletal system to muscles and ligaments

Human survival is dependent on the effective interaction and function of all the body’s systems. The function of one system is interconnected and dependent on other systems, and this is certainly the case for the skeletal and muscular system. The bones provide a solid frame and form to support the body as well as protect the internal organs.

The bones are connected to joints, which allows for movement of individual limbs as well as the movement of the entire body. The muscular system connects to the bones and works with connective tissue at the joints to allow for movement. The muscles connect to the nervous system and allow nerve signals to be sent to, and received from, the brain.

The bones and muscles are supported by connective tissue, which plays an integral role in structural support. Ligaments connect bones to other bones and keep the skeletal system supported while allowing movement at the joints. Tendons connect muscles to bone and support compressive force allowing the flexibility needed for wear and tear activities.

To facilitate the brain signals necessary for musculoskeletal movement, the motor neurons connected to individual muscle fibers must function properly. The nerve impulses transport neural information to the muscles, leading to muscle contraction. As the muscles contract, the connective tissue at the joint draws the bone into movement along the designated pathway dictated by the skeletal structure of the joint.

Supporting healthy bones and joints

The skeletal system, being of major importance, is the main support for the human body. Just like for any other system, it needs care and maintenance to ensure its proper functioning. The most essential element is vitamin Dm which you can easily obtain from daily exposure to sunlight. In as little as 15 minutes, you can give your body all it needs from vitamin D. Keep in mind that your body is not capable of benefiting from this vitamin when wearing sunscreen or when behind glass or window.

Food and exercise can also play a major role in the wellbeing of your skeletal system. When you work out, you are helping your bones maintain a proper mass while reducing bone losscaused by aging. This prevents osteoporosis while improving muscle strength, balance and coordination. Altogether, they help individuals maintain a healthy posture, preventing falls and possible fractures. The food you eat can lead to either strong bones or weaker ones. Your skeletal system needs calcium. You can obtain this mineral by adding milk and dairy products, green leafy vegetables, nuts, enriched flour and fatty fish to your diet.

In summary

The skeletal system is a very important system that supports and protects the body while giving it shape and form. It is composed of connective tissues including bone, cartilage, tendons and ligaments. The skeletal system functions mainly for providing mobility and structure. However, it also functions to store minerals and nutrients, aids in hematopoiesis, and protects vital organs.

Conditions associated with the skeletal system include fractures, metabolic bone diseases, arthritis, cancer, and spinal curvatures. Tendons, bones, joints, ligaments, and muscles work together to produce various movements. Since the skeletal and muscular systems both support each other, injury to each part of the whole system has an immediate effect on the other.