Must Know Human Skeletal System Parts and Functions

Parts of the Skeleton

For many, the skeleton is a figure of creativity used in movies to scare viewers of the possibility of people rising from the dead. From an entertainment point of view, this might be true. After all, nothing is impossible when it comes to entertainment. Men have been witnessed to fly with absolutely nothing supporting them. A lot of things happen in entertainment, and that has consequently blurred the truth in many cases. In this case, the skeleton.

Scientifically, the skeleton is the supporting framework of most organisms. Not that all those organisms possess a skeleton like we do, but they do have a skeleton of their own variation that supports their survival, given the nature of the habitat where they are found. This is the reason why there are several types of skeletons.

The first kind of skeleton is the exoskeleton, found in a lot of invertebrates. The skeleton covers the outside of the organism’s body in order to protect the vital internal organs. In some organisms such as insects, the exoskeleton serves other purposes such as forming a surface for muscle attachment. Exoskeletons are usually small, although some variations are somewhat gigantic for their kind.

Endoskeletons are the most known and one of the most complex type of skeleton. It is typical in all vertebrates and mostly made of bones that support the framework of massive weight found in most vertebrates. Aside from the weight bearing function, endoskeletons also provide a surface for muscle attachment, as well as determining the shape of the organism.

The final kind of common skeletons is the fluid or hydrostatic skeleton. Basically, this kind of skeleton is a base for many organisms. It makes an organism rigid by filling it up with water. This may sound a little bizarre, but given that over 90% of the total weight of an average human is made up of water, it should make sense. Hydrostatic skeleton mostly exists in invertebrates, in saline conditions.

Other types of skeletons include pliant skeletons, rigid skeletons and cytoskeletons. As aforementioned, these varied kinds of skeletons are found in different organisms given the environment in which they live. This should make it relatively easier to understand why human beings possess an endoskeleton that supports their framework. The human skeleton is discussed in detail below.

Notably, the parts of the skeleton are self-outlining. Although the skeleton cannot physically be separated into their parts in a living human, it is for the sake of this discussion that we shall do so for easier understanding.

Below, we shall discuss each of the parts

Highlighting their various functions and special adaptations.

The Skull

Known to be one of the hardest, the skull serves quite a purpose that it cannot be judged for its stubborn hardness.It is quite obvious that the brain resides inside the skull, and, needless to say, the brain is quite delicate as it is important.

A typical skull

As can be see, the skull is not a single bone as thought by many. The skull is actually a collection of bones totalling to about twenty-two, that have fused together to form a rigid protective casing over the brain, its extensions and supporting organs. The labels in the diagram that are in bold are the names of the bones that make up the skull. The rest of the labels are the parts of these bones.

The term skull, therefore, includes the mandible, maxilla, zygomatic bone, lacrimal bone, nasal bone, frontal bone, parietal bone, occipital bone, sphenoidal bone, temporal bone, ethmoidal bone, the conchae and the vomer. The term cranium means the skull without the mandible. The cranialcavity has a roof also known as the cranial vault, and a floor which makes up the base of the skull. The facial skeleton is the front part of the skull, which is clearly shown on the diagram.

The skull, throughout its nature, has holes (commonly referred to as foramina) that allow it to communicate with the outside structures such as blood vessels and nerves. The largest foramina is known as the foramen magnum, which is found at the base of the skull. Foramen magnum allows the passage of the spinal cord among other structures. Numerous other foramina exist, especially at the base of the skull. These allow for maximum coordination of the central nervous system activities.

Of course, without even mentioning it, teeth are not considered to be part of the skull bones. This is because the bones technically play no role in the protective functions of the skull, neither are they actually fused to the skull bones as all other skull bones are fused and almost permanently connected to each other except in the case of serious fractures.

The Spine

picture of the spine
picture of the spine

After the skull, what else would a person expect? The spine, also known as the backbone, again, is made up of several bones that are not even fused with each other. Not many people have this fact misunderstood, but sure, there does exist several people who have never really known the spine. Below is a picture of the spine.

The spine is made up of 5 sections: the cervical, thoracic, lumbar, sacral and coccygeal. These regions, in layman, provided in the order already given, are the neck, chest, abdominal, and the tail region combining the last two. As mentioned, the spine is made up of separate bones known as vertebrae. The vertebrae in each region have their own specific characteristics that make them suitable for their functions.

There are seven cervical, twelve thoracic, 5 lumbar, 5 sacral and one coccygeal vertebrae. Each of the vertebrae in the regions is unique from any other vertebra in the whole organism. This is due to the varying nature of the spinal cord that the vertebrae work to protect. Although the vertebrae not only protect the spinal cord (as they have other functions such as providing posterior articulation surface for the ribs, the vertebrae primarily function to protect the spinal cord.

However, the spinal cord also functions in weight bearing. This is easy to tell as the spinal cord ends at the level of the second thoracic vertebra in adults, whereas there are vertebrae even after the end of the spinal cord. Due to this weight bearing function, the spinal cord is therefore not straight. It has curvatures of two kinds: primary and secondary. Primary curvature is known as lordosis present in the cervical and lumbar regions; and secondary known as kyphosis is found on the thoracic and sacral regions. Any other curvature is classified as an abnormality as seen in scoliosis which is sideway curvature of an S or C shape.

Notice that the sacral vertebrae are fused, as well as the coccygeal.

If you experience back pain, it is most likely because your spine has been suffering from an awful posture for quite some time. You therefore need to adapt a better posture and practise stretching in order to be able to free yourself of this seemingly inevitable problem.

Before the spinal cord ends, I believe it is worth mentioning that people of advanced age tend to get shorter over time. A surprising fact is that the spine is responsible for this behaviour. This is because between any two vertebrae except fused ones, there exists a disk of cartilage known as the intervertral disk. Because it is made of cartilage, it tends to get compressed by the weight of the body impacted on it by gravity due to its spongy nature. This means that if one was to go live in space, it is likely that he or she would come back taller despite the person’s age.

The Upper Limb

The Upper Limb
The Upper Limb

The upper limb, as most can guess, is basically the hand. Well, it doesn’t just end at the hand. It has a lot more to it, which is why it attained a name other than the layman’s term. The upper limb, anatomically speaking starts from the scapula to the fingertips.  This is the illustration of what the upper limb stands for.

The bones of the upper limb are the scapula, humerus, ulna, radius, carpals, metacarpals and phalanges. All these bones work in coordination to handle the activities of the upper limb such as grasping objects, throwing objects and clapping. Each of the bones plays its own specific role in making sure these are achieved however.

The scapula, attached to the back, makes sure that the humerus gets a decent attachment position. Aside from that, the scapula also supports the clavicle which connects the upper limb to the chest, specifically to the sternum (or the manubrium of the sternum). The scapula is a generally flat bone with a single spine on its posterior surface, thus making it suitable for muscular attachments.

After the scapula, come the humerus. The supports the general arm as it provides an attachment surface for many muscles, including some of the triceps and biceps. Aside from that, it connects the arm to the forearm through its attachment to the ulna at the elbow joint. The elbow joint is another structure worth mentioning. It forms the cubital fossa at the front and is made up of the humerus and ulna only (the radius joins onto the ulna just below the elbow joint). This joint allows for adduction, abduction, flexion and extension as well as rotation of the forearm.

The ulna and radius are the bones of the forearm. They support the forearm, as well as provide an attachment surface for forearm muscles. They also form the wrist joint with the 8 carpals. The presence of multiple joints at the wrist joint is one of the reasons why it is so flexible when it comes to flexion, extension and rotation.

The metacarpals form the palm and extend further to support the digits or the fingers. This forms a perfect framework needed for the flexibility of the palm, its ability to be completely folded into a fist among other properties.

Notice that the general flexibility of the whole hand is mainly resulting from the glenohumeral joint between the glenoid cavity of the scapula and the humerus. This is because the glenoid cavity is shallow and lacks ligaments that would hold the joint tight. Consequently, resulting from its flexibility, this joint is one of the most dislocated joints in the body. You are advised to be careful using your hand therefore.

The Lower Limb

The Lower Limb
The Lower Limb

The upper limb is made up of the fused hip bones, the femur, tibia and fibula, tarsals, metatarsals and phalanges. All these bones, like those of the upper limb, work together in coordination to achieve tasks such as running, kicking and standing. The hip bone, like the scapula provides an attachment for the femur, through the hip joint which is directly aided by the acetabulum.

The femur, the largest bone in the body follows. It is one of the main supporting structures when it comes to weight bearing when a person is standing upright. This is because it is strong (it is actually as hard as concrete) and forms a very stable joint at the hip. It is therefore hard to dislocate, a fact that makes it a good weight bearing factor. Aside from that, it provides an attachment surface the hamstrings among other femoral muscles.

Forming the knee joint at the front and the popliteal fossa at the back, the femur attaches to both tibia and fibula unlike humerus. The knee joint is a complex hinge joint. It is classified as complex since it allows a little rotation unlike a typical hinge joint that only allows movement in one plane.

Down from the knee joint, we meet tibia and fibula, the bones of the leg. These bones form a strong compartment that supports the femur in bearing the body weight, as well as connecting it the foot that does that actual bearing, especially on the plantar surface.

Conclusion

The interconnections between the parts of the skeleton is important in understanding the human skeleton. Notice how the skeleton is designed to bear the body weight, as well as protect some of the vital organs.

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