Interesting and Surprising Facts about the Human Skeleton
The human skeleton is an interesting and complex structure. It's not simply a scaffolding for our body or just a structure that enables us to move. The bones that make up the skeleton are made of living tissue that has vital functions.
In addition to supporting the body and allowing it to move, the skeleton protects organs, makes the blood cells and stores fat and minerals. Bones release minerals into the bloodstream and absorb them from the blood as needed. In addition, researchers are discovering that the skeleton makes chemicals that trigger effects not only in bones but also in other parts of the body.
There are two divisions of the skeleton - the axial skeleton and the appendicular skeleton. The axial skeleton is located in the midline of the body and is composed of the skull, the vertebral column or backbone, the sternum or breast bone and the ribs. It also includes smaller bones which aren't connected to the rest of the axial skeleton. These are the hyoid bone at the back of the throat and the ossicles in the middle ears.
The appendicular skeleton is made of the limbs and their associated bones. It includes the bones of the hands, arms, feet and legs as well as the pelvic bones, the scapula or shoulder blade and the clavicle or collar bone.
Bones in the Human Skeleton
The Vertebral Column
The Axial Skeleton
- The skull is made of the cranium and the facial bones.
- The cranium is made of eight bones that fit tightly together. There are fourteen facial bones.
- Some of the facial bones contain a space called a sinus which is filled with air and has a lining that produces mucus.
- Sinuses are connected to the nose via tubes called ducts.
- When skulls of people who died a long time ago are discovered, only the bridge of the noise remains. Like the ear lobes, the rest of the nose is made of cartilage, not bone. Cartilage decays faster than bone after death.
- The vertebral column is made of seven cervical vertebrae in the neck, twelve thoracic vertebrae in the upper back, five lumbar vertebrae in the lower back, five fused vertebrae in the sacrum at the back of the pelvis and three to five fused vertebrae in the coccyx, or tailbone.
- The first vertebra in the neck is called the atlas because it holds the head up. It's named after Atlas, an Ancient Greek deity who supported the world on his shoulders.
- Most people have twelve pairs of ribs.
- The first seven pairs of ribs are known as true ribs. They're connected to the vertebrae at the back and are joined via a strip of cartilage to the sternum or breast bone at the front.
- The next three pairs of ribs are known as false ribs because they are connected to another rib at the front of the rib cage instead of directly to the sternum.
- The last two pairs of ribs are known as floating ribs because they aren't attached to any other bone at the front of the rib cage.
- Some people have an extra rib known as a cervical rib. This arises from the last cervical vertebra and can be present on either side of the body or on both sides. The rib may be only partially developed.
- Most cervical ribs cause no problems. Occasionally they may press on nerves or blood vessels and contribute to a condition known as thoracic outlet syndrome.
The Hyoid Bone and the Ossicles
The hyoid bone and the ossicles are also part of the axial skeleton.
- The hyoid bone has a horseshoe shape and is located behind the throat.
- Unlike nearly all other bones, the hyoid bone isn't connected to another bone.
- The larynx, or voice box, houses the vocal cords that produce sound. The tongue and the hyoid bone allow a wider variety of vocalizations to be produced than the vocal cords on their own.
- The three tiny bones in the middle ear are called ossicles.
- The third ossicle is called the stapes and is the smallest bone in the body. It's only 2.8 mm in length.
- The stapes is also known as the stirrup because it looks like the stirrup used by horse riders.
- The ossicles vibrate as sound waves reach them from the outer ear. The ossicles transmit the vibrations to the fluid in the inner ear, which in turn stimulates hair cells. The hair cells then stimulate the auditory nerve, which sends nerve impulses to the brain. The brain creates the sensation of sound.
- Both the middle ear and the inner ear are located inside a bone of the skull. Only the outer ear is visible from the outside of the body.
The Skeletal System - Crash Course Biology
Some Appendicular Skeleton Facts
Sesamoid bones are located in tendons, which are the fibrous structures that connect muscles to bones. At least one sesamoid bone is present in everyone's body. This bone is the patella or kneecap, which is located in the front of the knee. Other sesamoid bones vary in number and position and may not be present in all people.
Some common sites for the location of sesamoid bones in addition to the knee are the wrist, the hands and the feet. With the exception of the patella, sesamoid bones are small in size. Despite this fact, sesamoid bones can break and may become inflamed, causing pain.
There are various theories for the function of sesamoid bones. One is that they improve the action of a tendon, acting as a fulcrum. Another is that they reduce friction in an area. Sesamoid bones on the bottom of the foot may assist with weight bearing.
The Funny Bone
The "funny bone" is actually the ulnar nerve. This is a very long nerve that travels from the neck down the arm to the hand. It's well protected over most of its route but is less protected at the elbow. If we hit our elbow in a certain place we may push the ulnar nerve against bone. This produces a strange sensation of numbness, tingling and pain that travels down the forearm. People often say that they have "hit their funny bone" when they experience this event. The term may have arisen due to the funny or strange sensation that is produced or because it happens at the bottom of the upper arm bone, whose technical name is the humerus. This name makes some people think of the word "humourous".
Structure of Bone
There are two types of bone tissue - compact bone and spongy bone. Spongy bone is also known as cancellous or trabecular bone. Compact bone is found in the outer part of bones and spongy bone is located in the inner part.
Compact bone is made of "building blocks" called osteons. Osteons are made of calcium, phosphate and protein, a mixture that is known as bone matrix. Each osteon has a central canal, also called the Haversian canal, which contains blood vessels, a lymphatic vessel and a nerve. The bone cells are located in small spaces in the osteon known as lacunae. The lacunae are arranged in concentric circles around the central canal. Tiny passageways called canaliculi connect the lacunae to each other.
Spongy bone consists of a mesh-like structure with spaces in between the bars and plates of the mesh. These spaces are often filled with bone marrow. The solid part of spongy bone contains bone matrix, lacunae and canaliculi, but these aren't arranged in osteons.
Microscopic Structure of Bone
Functions of Bones
- The cells in bone are the osteocytes, which are mature bone cells, the osteoblasts, which build bone, and the osteoclasts, which break down bone.
- Bone is continually being remodelled by the osteoblasts and osteoclasts.
- When bone is broken down, minerals are released into the bloodstream. When bone is made, minerals are absorbed from the bloodstream. The chief minerals in bone are calcium and phosphorus.
- Unfortunately, as we age the osteoblasts become less active while the osteoclasts are relatively unaffected. This is especially true in women who are past menopause. Bone may be lost as a result. Exercise - especially weight-bearing exercise - can stimulate the activity of osteoblasts and restore some of the lost bone.
- Red bone marrow contains stem cells that produce the red blood cells, white blood cells and platelets.
- In a newborn baby all the bone marrow is red. As a person grows, some of their red bone marrow is gradually replaced by yellow bone marrow. This type of bone marrow stores fatty acids instead of making blood cells.
- In adults, red bone marrow is located in the spongy bone at the ends of the humerus and femur and in the skull, sternum, ribs, vertebrae and hip bones.
- In cases of serious blood loss, the body can convert yellow bone marrow into red bone marrow.
- Red bone marrow makes about 2 million red blood cells every second. These are used to replace the old and damaged red blood cells destroyed by the liver.
- When muscles contract, they exert a pulling force on tendons. The tendons in turn pull on bones, enabling the body to move.
- The skeleton protects vital organs and tissues. For example, the cranium protects the brain, the vertebrae protect the spinal cord and the rib cage protects the heart and the lungs.
The Three Types of Joints - Learning Through Song
- The bones of the skeleton are connected to other bones via joints.
- Joints are classified as movable, slightly movable and immovable.
- Fibrous joints (synarthroses) are immovable. The bones are joined by fibrous connective tissue and there is no cavity between the bones. The joints between the skull bones are fibrous joints.
- Cartilaginous joints (amphiarthroses) are slightly movable. The bones are joined by cartilage and there is no cavity between the bones. The intervertebral disks located between the vertebrae are cartilaginous joints.
- Synovial joints (diarthroses) are movable and are the most common type of joint in the body. The bones are joined together via ligaments and there is a fluid-filled cavity between the bones. Some examples of this type of joint are those found in the shoulder and hip joints, the elbow and ankle joints and the finger and toe joints.
- Synovial joints are classified into other categories based on their structure and type of movement.
Some Strange Facts about Skeletons
- A baby is born with about 300 "bones", although some of these bones are made of cartilage. As the baby grows, a lot of the cartilage ossifies, or turns into bone, and some of the bones fuse. As a result, an adult has only about 206 bones, even though their body is bigger than a baby's.
- Teeth are considered to be part of the skeletal system, although they are made of dentine and enamel instead of bone and have a different function from the rest of the skeletal system.
- According to Guinness World Records, Evel Knievel holds the record for the largest number of broken bones in a lifetime. Knievel was a stunt performer who was born in 1938. By the end of 1975 he had suffered from 433 broken bones. He retired from major competitions in 1976.
© 2014 Linda Crampton
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