Structure Function Of Axial Skeleton

The axial skeleton consists of the 80 bones in the head and trunk of the human body. It is composed of several parts; the human skull, the sternum, the rib cage, and the vertebral column. There are also some major bones included in this skeleton. The skull, which is located on top of the vertebral column, is one. The axial skeleton and the appendicular skeleton together form the complete skeleton.

The axial skeleton transmits the weight from the head, the trunk, and the upper extremities down to the lower extremities at the hip joints, and is therefore responsible for the upright position of the human body. Most of the body weight is located in back of the spinal column which therefore has the erector spinae muscles and a large amount of ligaments attached to it resulting in the curved shape of the spine. The 366 skeletal muscles acting on the axial skeleton position the spine, allowing for big movements in the thoracic cage for breathing, and the head, where they control the minute and complex facial movements.

Adults have 12 pairs of ribs, which run between the sternum and the thoracic cage. The ribs are flat bones that create a protective cage around the heart and lungs. An individual will have seven pairs of ribs that both attach to the sternum and vertebrae. These are true ribs. They will also have three pairs that attach from the vertebrae to a cartilage attachment on the sternum and two that attach to the vertebrae but are free as they have no second attachment. These are free ribs.

The spine is made up of five different areas; cervical (7), thoracic (12), lumbar (5), sacrum (5), coccyx (4). The seven cervical vertebrae make up the neck and run down to the shoulders. The twelve thoracic vertebrae make up the chest area and the five lumbar vertebrae make up the lower back. The sacrum consists of five vertebrae and these are fixed together and they form a joint with the pelvis and the coccyx is four bones joined together, which are remnants of when we had a tail.

The appendicular skeleton is composed of 126 bones in the human body. The word appendicular is the adjective of the noun appendage which itself means a part that is joined to something larger. Functionally it is involved in locomotion (Lower limbs) of the axial skeleton and manipulation of objects in the environment (Upper limbs).

The appendicular skeleton is divided into six major areas and contains bones such as; shoulder girdle (scapula and clavicle), the pelvic girdle, upper and lower limbs.

It is important to realize that through anatomical variation it is common for the skeleton to have many extra bones (sutural bones in the skull, cervical ribs, lumbar ribs and even extra lumbar vertebrae).

Their functions are to make locomotion possible and to protect the major organs of locomotion, digestion, excretion, and reproduction.

The appendicular skeleton of 134 bones and the axial skeleton of 80 bones together form the complete skeleton of 206 bones in the human body. Unlike the axial skeleton, the appendicular skeleton is unfused. This allows for a much greater range of motion.

The bones colored red are the bones in the appendicular skeleton.

Fibula

Tibia

Patella

Femur

Carpals, Metacarpals, phalanges

Ulna

Radius

Humerus

Scapula, clavicle

Ischium, illium, pubis

Tarsals, metatarsals, phalanges

The functions of the major bones of the appendicular skeleton.

Clavicle

This bone connects the upper arm to the trunk of the body. One end is connected to scapula. The role of the clavicle is to keep the scapula the correct distance from the sternum.

Scapula

This bone is at the back of the body. The scapula provides points of attachment for many of the muscles of the upper back and arms.

Arm

This consists of three bones; the humerus (upper arm), the radius and the ulna (lower arm). The ulna forms the elbow joint with the humerus and runs to the little finger. The radius is positioned opposite the ulna and runs to the thumb side. When the hand moves the radius moves across the ulna.

Hand

The hand has three areas made up with different types of bones. First, wrist is made up of eight bones called carpals, which are small bones made up into two rows of four; the five long bones between the wrist and fingers are called metacarpals and the bones of the fingers are phalanges. There are fourteen phalanges in all with three in each finger and two in the thumb.

Pelvis

The pelvis protects and supports the lower internal organs, including the bladder, the reproductive organs, and also in pregnant women, the developing foetus. The pelvis is made up of three bones, the ilium, pubis and Ischium, which have become fused together to form one main area.

The Leg

The leg consists of four bones; the femur is the longest bone in the body and forms the knee joint with the tibia, which is the weight-bearing bone of the lower leg; the fibula is the non- weight bearing bone of the lower leg and helps the ankle; the patella is the bone that floats over the knee. It lies within the patella tendon and smoothes the movement of the tendons over the knee joint.

The Foot

Like the hand that has three areas, so does the foot. The seven tarsals form the ankle, the five metatarsals travel from the ankle to the toes and the fourteen phalanges which make up the toes. There are three in each toe and two in each big toe.

Compact bone or (cortical bone)

Cortical bone, synonymous with compact bone, is one of the two types of osseous tissue that form bones. Cortical bone facilitates bone’s main functions: to support the body, protect organs, provide levers for movement, and store and release chemical elements, mainly calcium and phosphorous. As its name implies, cortical bone forms the cortex, or outer shell, of most bones. Again, as its name implies, compact bone is much denser than cancellous bone, which is the other type of osseous tissue. Furthermore, it is harder, stronger and stiffer than cancellous bone. Cortical bone contributes about 80% of the weight of a human skeleton. The primary anatomical and functional unit of cortical bone is the osteon. Properties of cortical bone studies using MRI and CT scan are the main field of research in recent years.

Cancellous bone

Cancellous bone, synonymous with trabecular bone or spongy bone, is one of the two types of osseous tissue that form bones. Compared to compact bone, which is the other type of osseous tissue, it has a higher surface area but is less dense, softer, weaker, and less stiff. It typically occupies the interior region of bones. Cancellous bone is highly vascular and frequently contains red bone marrow where hematopoiesis, which is the production of blood cells, occurs. The primary anatomical and functional unit of cancellous bone is the trabecula.

Types of Bones

There are 5 types of bone found within the human body. These are long, short, flat, irregular and sesamoid.

Long Bones

Long bones are some of the longest bones in the body, such as the Femur, Humerus and Tibia but are also some of the smallest including the Metacarpals, Metatarsals and Phalanges. The classification of a long bone includes having a body which is longer than it is wide, with growth plates (epiphysis) at either end, having a hard outer surface of compact bone and a spongy inner known as cancellous bone containing bone marrow. Both ends of the bone are covered in hyaline cartilage to help protect the bone and aid shock absorption.

The femur – a long bone

Short Bones

Short bones are defined as being approximately as wide as they are long and have a primary function of providing support and stability with little movement. Examples of short bones are the Carpals and Tarsals in the wrist and foot. They consist of only a thin layer of compact, hard bone with cancellous bone on the inside along with relatively large amounts of bone marrow.

The carpals – short bones

Flat Bones

Flat bones are as they sound, strong, flat plates of bone with the main function of providing protection to the body’s vital organs and being a base for muscular attachment. The classic example of a flat bone is the Scapula (shoulder blade). The Sternum (breast bone), Cranium (skull), Pelvis and Ribs are also classified as flat bones. Anterior and posterior surfaces are formed of compact bone to provide strength for protection with the centre consisting of cancellous (spongy) bone and varying amounts of bone marrow. In adults, the highest number of red blood cells are formed in flat bones.

The scapula – a flat bone

Irregular Bones

These are bones which do not fall into any other category, due to their non-uniform shape. Good examples of these are the Vertebrae, Sacrum and Mandible (lower jaw). They primarily consist of cancellous bone, with a thin outer layer of compact bone.

Vertebrae – irregular bones

Sesamoid Bones

Sesamoid bones are usually short or irregular bones, imbedded in a tendon. The most obvious example of this is the Patella (knee cap) which sits within the Patella or Quadriceps tendon. Other sesamoid bones are the Pisiform (smallest of the Carpals) and the two small bones at the base of the 1st Metatarsal. Sesamoid bones are usually present in a tendon where it passes over a joint which serves to protect the tendon.

The patella – a sesamoid bone

Specific uses for specific bones

Specific bones in the body are designed for their own purpose. The femur is the largest bone in the human body. The reason for this is that it has a great number of muscles attached to its surface. These muscles are needed in order for the leg to be able to move. It also has to bear some of the weight of the upper body. The shoulder is another bone that has its own purpose. Its purpose is to allow rotational movement of the upper arm. As a ball and socket joint it does this. It is also a surface for the muscles that allow attaching to. Without these muscles this movement would be impossible. The elbow and the knee can be used as an example of bones of the body that have many functions. The knee is made up of two parts the patella is the part of the knee that allows movement and it rests on a bursae. The second part is the joining of the femur and the tibia and the fibula. This is a meeting of many bones and many muscles and all these muscles control things like the movement of the ankle and the foot.

The different types of joints

A place where two bones join or meet is called a joint or articulation. A joint is held together with ligaments and these give the joint stability. Joints are placed into three categories depending on the amount of movement available. Fixed/fibrous; these joints allow no movement. These joints can be found between the plates of the skull.

Slightly moveable/cartilaginous; these allow a small amount and are held in place by ligaments and are cushioned by cartilage. These types of joints can be found between the vertebrae of the spine.

Moveable/ synovial; there are six types of this joint all with varying degrees of movement. The six types of joint are: hinge, ball and socket, pivot, condyloid, sliding, and saddle. A synovial joint is made up of several components;

Synovial capsule – keeps the contents of the synovial joint in place.

Synovial membrane – releases synovial fluid onto the joint.

Synovial fluid – a thick oily substance that helps lubricate the joint and allows free movement.

Articular cartilage – a bluish-white covering that protects the end of the bones from wearing down.

Hinge joint

This is a diagram of a knee. This joint is a hinge joint. The hyaline cartilage on the end of the femur is used as an articulating surface when rubbing with the medial meniscus. This movement, controlled by the lateral collateral ligament, is what enables us to be able to walk. The movement of walk is the only movement of this joint and it is flexion (when the joint is pulled back by the lateral collateral ligament) and extension (when the leg swings forward to full extension by the lateral collateral ligament). A sporting example of this range of movement is the kicking of a football or rugby ball.

Ball and socket

This is a diagram of a shoulder joint, which is a ball and socket joint. The humeral head is covered in hyaline cartilage and is used as a rubbing surface against the inside of the socket. The range of movement for this joint is flexion, extension, abduction, adduction, circumduction and rotation. A sporting example of the use of this joint is hitting a serve in tennis.

Condyloid joint

This type of joint can be found at the wrist. It allows movement in two different planes; this is called biaxial. It allows you to bend and straighten the joint (flexion and extension). A sporting example of this joint is using a foil in the sport fencing.

Pivot joint

This joint can be found in the top two vertebrae of your neck. These two vertebrae are call the atlas and axis. It only allows rotational movement. For example it only lets you move your head from side to side as if you were saying no. A sporting example of this joint is the heading of a football.

Saddle joint

This joint is found only in the thumbs. It allows movement in three planes, backwards, forwards, from side to side and across. These plains of movement are called, Sagittal Plane, Frontal Plane, and Transverse Plane. This joint is specific to only humans. It gives us “manual dexterity”. This enables us to hold a cup or to write, among many other skills. A sporting example of the use of this joint is the griping of a racket handle in badminton.

Gliding joint

This type of joint can be found in the carpal bones of the hand and the tarsal bones in the ankle. These types of joint occur between the surfaces of two short or long bones. They allow very limited movement in a range of directions. A sporting example of the use of this joint is the applying of spin to a pass in rugby.

Contrast and Comparison of synovial joints.

All these synovial joints allow different ranges of movement. They are all in different places and the joint that is there is designed specifically for that function. Without that joint the body would cease to be the perfect machine that we all rely on. This happens to us when we suffer an injury somewhere in our bodies. These joints allow us different ranges of movement because of all the different bones that they are made up of and their composition. An example of this would be that a ball and socket joint could take the place of a gliding joint and keep the exact function. All the joints in the body are there for the one purpose that they do. This could be seen as a disadvantage but when you have something that foes its job so well, why would want to replace?

Effects of exercise on the skeletal system

If we were to train for a period of about three months we will start to experience some adaptations to our skeletal system: an increase in bone density, stronger ligaments, and a thickening of the hyaline cartilage at the end of the bones. The bones become denser if we perform a lot of weight-bearing exercises, which is where we put force through a bone. An example of this is if we did a lot of walking or running, it places force through the tibia, fibula, and femur, and the body will respond by laying down higher amounts of cartilage and calcium to strengthen the bones. Weight-bearing exercise will also increase osteoblast activity, which means that more bone is being built or being laid down. As the ligaments become stronger due to the higher amounts of collagen being laid down, they also increase the stability of the joints and make them less prone to injury. All the following activities can help stave off such specific bone conditions like osteoporosis; running, skipping, brisk walking, aerobics, tennis. However, there can be some negative long term effects on your skeleton from specific sports. Here is an example from the sport of tennis and the common injury, tennis elbow. The most common cause of tennis elbow is repeated overuse of your arm. Playing tennis three times in a week when you haven’t played for some time is the sort of overuse that could cause tennis elbow. However, most people who develop tennis elbow haven’t been playing tennis. A range of different activities that involve repeated hand, wrist and forearm movements is more often the cause. This includes activities like using a screwdriver, using vibratory work equipment (such as a drill), or even using a keyboard. Rarely, tendon damage can happen after a single and often minor incident, such as lifting something heavy or taking part in an activity which you don’t do very often, such as painting and decorating. These activities can cause a tear in your tendon.

Short term effects of sport on the skeletal system

A short term affect of exercise on the skeleton is an increase in the secretion of synovial fluid from the joints. Another effect is that the area of the joint may be warmed up and may be easier to move. The joints ligaments and tendons may also become suppler as a result of this. This affects the skeleton by creating the need to replace this lost glucose and thus regaining the lost energy.

As we can see there are some differences between the long and short term effects of doing exercise. You can suffer injuries from both and they can have long or short term effects on your body. A plus side is that your body rebuilds itself quickly and can become healthier and fitter through the use of exercise. Therefore the next time you go to do the sporting activity, you are able to perform better. You should not, though, do to much lengthy exercise for a great period of time as this can also have the undesired affect of stress on the skeleton. You should not do to much light exercise as this can have the affect of your body not benefiting from the exercise. Instead you should try and mix up the exercise routine you do so that you can gain the greatest possible outcome of health and fitness for your body.