What Does The Skeletal System Do?
Your skeleton is important for several reasons, some of which are obvious and some of which are not.
Mainly, of course, your skeleton supports your body and gives it structure. Without your skeleton, your body would collapse into a heap.
In addition, your skeleton serves as a point of attachment for your skeletal muscles, protects your internal organs and stores chemical energy and certain minerals, such as calcium and phosphorous. And don’t forget that blood cells are made in the bone marrow of your larger bones.
What Makes Up The Skeletal System?
The skeletal system in an adult body is made up of 206 individual bones. These bones are arranged into two major divisions: the axial skeleton and the appendicular skeleton.
The axial skeleton runs along the body’s midline axis and is made up of 80 bones in the following regions:
- Cervical (neck) – 7 vertebrae
- Thoracic (chest) – 12 vertebrae
- Lumbar (lower back) – 5 vertebrae
- Sacrum – 1 vertebra
- Coccyx (tailbone) – 1 vertebra
The skull is composed of 22 bones that are fused together except for the mandible. These 21 fused bones are separate in children to allow the skull and brain to grow, but fuse to give added strength and protection as an adult. The mandible remains as a movable jaw bone and forms the only movable joint in the skull with the temporal bone.
The bones of the superior portion of the skull are known as the cranium and protect the brain from damage. The bones of the lower front portion of the skull are known as facial bones and support the eyes, nose, and mouth.
Hyoid and Auditory Ossicles
The hyoid is a small, U-shaped bone found just below the mandible. The hyoid is the only bone in the body that does not form a joint with any other bone—it is a floating bone. The hyoid’s function is to help hold the trachea open and to form a bony connection for the tongue muscles.
The malleus, incus, and stapes — known collectively as the auditory ossicles — are the smallest bones in the body. Found in a small cavity inside of the temporal bone, they serve to transmit and amplify sound from the eardrum to the inner ear.
Twenty-six vertebrae form the vertebral column of the human body. They are named by region:
With the exception of the singular sacrum and coccyx, each vertebra is named for the first letter of its region and its position along the superior-inferior axis. For example, the most superior (highest) thoracic vertebra is called T1 and the most inferior (lowest) is called T12.
Ribs and Sternum
The sternum, or breastbone, is a thin, knife-shaped bone located along the midline of the anterior (front) side of the thoracic region of the skeleton. The sternum connects to the ribs by thin bands of cartilage called the costal cartilage.
There are 12 pairs of ribs that together with the sternum form the ribcage of the thoracic region. The first seven ribs are known as “true ribs” because they connect the thoracic vertebrae directly to the sternum through their own band of costal cartilage. Ribs 8, 9, and 10 all connect to the sternum through cartilage that is connected to the cartilage of the seventh rib, so we consider these to be “false ribs.” Ribs 11 and 12 are also false ribs, but are also considered to be “floating ribs” because they do not have any cartilage attachment to the sternum at all.
The appendicular skeleton is made up of 126 bones in the following regions:
- Pectoral (Shoulder) Gurdle
The pectoral girdle connects the upper limb (arm) bones to the axial skeleton and consists of the left and right clavicles and left and right scapulae.
The humerus is the bone of the upper arm. It forms the ball and socket joint of the shoulder with the scapula and forms the elbow joint with the lower arm bones. The radius and ulna are the two bones of the forearm. The ulna is on the medial side (closer to the body) of the forearm and forms a hinge joint with the humerus at the elbow. The radius allows 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 give added flexibility to the wrist. The carpals are connected to the five metacarpals that form the bones of the hand and connect to each of the fingers. Each finger has three bones known as phalanges, except for the thumb, which only has two phalanges.
Formed by the left and right hip bones, the pelvic girdle connects the lower limb (leg) bones to the axial skeleton.
The femur is the largest bone in the body and the only bone of the thigh (femoral) region. The femur forms the ball and socket hip joint with the hip bone and forms the knee joint with the tibia and patella. Commonly called the kneecap, the patella is special because it is one of the few bones that are not present at birth. The patella forms in early childhood to support the knee for walking and crawling.
The tibia and fibula are the bones of the lower leg. The tibia is much larger than the fibula and bears almost all of the body’s weight. The fibula is mainly a muscle attachment point and is used to help maintain balance. The tibia and fibula form the ankle joint with the talus, one of the seven tarsal bones in the foot.
The tarsals are a group of seven small bones that form the posterior (rear) end of the foot and heel. The tarsals form joints with the five long metatarsals of the foot. Then each of the metatarsals forms a joint with one of the set of phalanges in the toes. Each toe has three phalanges, except for the big toe, which only has two phalanges.
Types of Bones
All of the bones of the body can be broken down into five types: long, short, flat, irregular, and sesamoid.
- Long bones
Long bones are longer than they are wide and are the major bones of the limbs. Long bones grow more than the other classes of bone throughout childhood and so are responsible for the bulk of our height as adults. A hollow medullary cavity is found in the center of long bones and serves as a storage area for bone marrow. Examples of long bones include the femur, tibia, fibula, metatarsals, and phalanges.
Short bones are about as long as they are wide and are often cubed or round in shape. The carpal bones of the wrist and the tarsal bones of the foot are examples of short bones.
Flat bones vary greatly in size and shape, but have the common feature of being very thin in one direction. Because they are thin, flat bones do not have a medullary cavity like the long bones. The frontal, parietal, and occipital bones of the cranium — along with the ribs and hip bones—are all examples of flat bones.
Irregular bones have a shape that does not fit the pattern of the long, short, or flat bones. The vertebrae, sacrum, and coccyx of the spine—as well as the sphenoid, ethmoid, and zygomatic bones of the skull—are all irregular bones.
The sesamoid bones are formed after birth inside of tendons that run across joints. Sesamoid bones grow to protect the tendon from stresses and strains at the joint and can help to give a mechanical advantage to muscles pulling on the tendon. The patella and the pisiform bone of the carpals are the only sesamoid bones that are counted 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.
An articulation, or joint, is a point of contact between bones, between a bone and cartilage, or between a bone and a tooth. Synovial joints are the most common type of articulation and feature a small gap between the bones. This gap allows a free range of motion and space for synovial fluid to lubricate the joint. Fibrous joints exist where bones are very tightly joined and offer little to no movement between the bones. Fibrous joints also hold teeth in their bony sockets. Finally, cartilaginous joints are formed where bone meets cartilage or where there is a layer of cartilage between two bones. These joints provide a small amount of flexibility in the joint due to the gel-like consistency of cartilage.
How Does The Skeletal System Work?
Some of the functions of the skeletal system are obvious, but some others are less so.
Perhaps the most obvious function of the skeletal system is to provide the rigid framework for the body. It is certainly difficult to envision what the human organism would resemble without the underlying support of the skeleton. The intricate arrangement of our bones allows us to achieve a uniquely upright posture. The “fit” of our bones where they form joints allows for complex movements while maintaining stability.
The vulnerable organs of the body, like the heart, lungs and brain, are protected by the skeleton from a variety of potential dangers. The spinal column combines the protective element of rigid bone with the maintenance of mobility between the spine segments to protect the delicate spinal cord. The skeletal system has a protective role over many of the body’s other organ systems.
While the muscular system is primarily responsible for body movements, the familiar movements of the human body are only made possible because the muscles are attached to the bones of the skeleton. This elaborate system of levers makes it possible for us to walk, run, jump, lift and climb. In this way, the skeletal system enables the muscular system to accomplish its necessary functions.
Bone marrow is that part of certain bones that is responsible for the production of blood cells. Both red and white blood cells are manufactured in bone marrow. That makes the skeletal system a necessary partner of the circulatory and immune systems. According to “The Anatomy and Physiology Learning System Textbook,” an average of 2.6 million red blood cells are produced in the bone marrow every second.
Blood levels of calcium and other minerals must remain at fairly consistent levels for nerves to conduct efficiently, for muscles to contract properly and for glands to help regulate bodily functions. When dietary intake is inadequate or when the blood levels of these minerals become low, the body can borrow minerals from the skeleton. This exchange of minerals between the bones and the blood is always in flux according to the changing needs of the body. So the skeletal system again plays a supporting role for the nervous, muscular and endocrine (glandular) systems.
What Can Go Wrong With Your Skeletal System?
Fracture, or breakage of a bone, is the most common skeletal injury. The breakage can be complete or partial, depending upon the intensity or severity of the impact and other pathological factors.
Sprain is a severe painful injury to a ligament or tissue that covers a joint. It is one of the most common types of injuries of the skeletal system that occurs due to a sudden wrench that stretches or tears the tissues of the ligaments, causing swelling in the affected area.
Bursitis is a disorder that causes pain in the body’s joints especially shoulder and hip joints due to excessive activity of an arm or leg. Bursitis primarily occurs due to inflammation of the bursa, small fluid-filled bags which serve as lubricating surfaces for muscles to move over bones.
Of the many skeletal system disorders, osteoporosis is the most common disorder that occurs due to loss of bone tissue, hormonal imbalance, genetic disposition, etc. It’s commonly observed in elderly people and in women, and results from a reduction in calcium and phosphorous in the bones.
Osteomyelitis is an infection of bone marrow that occurs due to a certain strain of the Staphylococcus bacteria, transported by the blood to the bones from infected areas. Osteomyelitis is characterized by intense pain in the infected bone, fever, chills, nausea and weakness.
Arthritis is a common joint disorder caused by inflammation of the joints in the body. It’s characterized by pain, swelling, stiffness and tenderness in the infected part. Aging, injury, infection, mineral deficiency or hereditary factors are some common causes of arthritis.
Osteoarthritis is a degenerative joint disease caused due to breakdown and eventual loss of the cartilage of one or more joints. Osteoarthritis usually occurs in synovial joints (in the limbs) where the articular cartilage wears away, increasing friction, pain and stiffness in the joints during normal movement.
Rheumatoid Arthritis is a chronic, systematic inflammatory disorder of the synovial lining of joints. The joints are initially painful, swollen and are usually affected symmetrically but as rheumatoid arthritis progresses, the ligaments supporting the joints get ruptured, causing erosion of the bone and long term deformity of the joints.
Scoliosis is a skeletal system disorder which causes an abnormal curve (‘s’ or ‘c’ shape) of the spine or backbone. In most cases, the cause of scoliosis is unknown, however it becomes apparent during adolescence and usually affects girls more than boys.
Also called hunchback, Kyphosis a forward bending of the spine due to deformation of the bones in the upper part of the spine. It’s a spinal deformity caused by degenerative diseases like tuberculosis, syphilis, and rheumatoid arthritis.
Spina Bifida is a spinal defect present at the time of childbirth. In this, the spinal cord does not grow properly and the vertebrae and skin are unable to shape themselves around it. Spina Bifida results from an error in the development of the embryo due to intake of alcohol, excessive medications or over exposure to extreme heat a month after a woman becomes pregnant.
How Do Your Keep Your Skeletal System Healthy?
For a healthy skeletal system, follow these tips . . .
- Eat calcium-rich foods. The American Academy of Orthopedic Surgeons recommends that men and women get at least 1,000 mg of calcium each day. (Women older than 50 and teens need more calcium.) Milk, cheese and other dairy products contain calcium. Broccoli, kale, sardines, salmon, Brazil nuts, almonds, oranges and calcium-fortified foods are good sources of calcium as well. The American Academy of Orthopedic Surgeons indicates that getting 1,000 mg of calcium through diet alone may be difficult and therefore suggests a vitamin supplement as well.
And eat foods with vitamin D to assist in calcium absorption. The recommended daily amount of vitamin D is 15 micrograms for all adults up to age 70 and 20 micrograms for adults older than 70.. Foods with vitamin D include dairy, eggs, fatty fish such as salmon or tuna and fortified orange juice and cereal. Exposure to the sun triggers vitamin D synthesis to produce vitamin D, as well.
- Perform at least 30 minutes of weight-bearing exercise at least twice a week. Building muscle also increases bone density which prevents osteoporosis. You don’t necessarily need weights or equipment to build muscle. Pushups, squats and planks and other body-weight exercises strengthen muscles over most of the body.
- Protect your body. Wear your seat belt when driving and a helmet when using a motorcycle. Use headgear when engaged in sports that could lead to brain damage such as football, in-line skating, bicycling and horseback riding.
This article is part of a series called “Your Body: An Owner’s Manual” which explains how your body systems work and how to maintain them. The first article in the series included a picture of my wife, fitness coach Kathie Lamir, who exemplifies a healthy body. Pictures of Kathie were so well received that I have included one with each article in the series