Focus On: The Vertebral Column

The Human Vertebral Column is the complex structure of the skeletal system. Popularly known as the spine or backbone, the vertebral column consists of 24 articulating vertebrae and 9 fused vertebrae. The first vertebra is located at the base of the skull while the last one at the tailbone. The articulating vertebrae are divided into cervical, thoracic and lumbar vertebrae, such that, 7 vertebrae are located in the cervical, 12 in the thoracic and 5 in the lumbar regions. Between two articulating vertebrae there is an intervertebral disc. All the 9 fused vertebrae are located in the sacral region which consists of the sacrum and the coccyx. The sacrum has 5 while coccyx has 4 vertebrae.

So what are the functions of the Human Vertebral Column?

One of the major functions of the spine is to protect the spinal cord and its nerves. The two components are vital to the central nervous system of the body. The vertebral column consists of a canal formed by the vertebrae foramen where the nerves travel. The backbone and its ligaments create a network of protection that absorbs shock directed to the spinal cord.

The vertebral column provides strength and support for the entire body. The cervical vertebra bears the weight of the skull while the thoracic vertebra provides the strength and stability needed by the body. The lumbar vertebra carries most of the weight of the body. The spine's curvaceous nature, muscles, tendons and ligaments distribute the body's weight and adapt to its changes.

The spine allows for body movement. Its design and components such as muscle, tendons and ligaments allow the body to bend, stretch, rotate and lean. The first two vertebra of cervical, the atlas and axis, allow the head and neck to rotate.

The vertebrae column protects major organs of the body. Most ribs are attached to the thoracic vertebrae which together with sternum for the ribcage. The ribcage protects major organs such as the heart and lungs.

The spine improves blood supply in the body. It provides plenty of bones which produce red blood cells from within the bone marrow. The bone marrow is also responsible for the production of white blood cells, platelets and minerals.

And how is Human Vertebral Column structured?

The human vertebral column consists of two important parts: the vertebral body and the vertebral arch. The vertebrae body includes the anterior segment and a posterior part while the vertebrae arch consists of pedicles and laminae and encloses the vertebrae foramen.

The backbone presents four curves. The topmost curve is the cervical and covers parts of cervical and thoracic vertebrae. The convex forward curve forms when an infant starts to hold up its head and to sit upright. The next curve is the thoracic which includes most of the thoracic vertebrae. The concave forward curve is usually present at birth. Adjoining the thoracic curve is the lumbar curve which covers parts of the thoracic and sacral vertebrae. The convex anteriorly curve forms later when a child begins to walk. The last curve is the sacral and consists of the sacrum and coccyx vertebrae. The concave forward curve is present at birth.

Spinal Sections: The Thoracic Vertebrae

The thoracic vertebrae refer to the 12 vertebral segments that are designated as T-1 to T-12 that culminate into the thoracic spine.T-1 is found nearest to the skull whereas the rest can be found as you move down the vertebrae column. The thoracic vertebrae exhibit very little motion due to its firm attachment to the breastbone which is made up of the sternum and ribs.

It’s located between the cervical and the lumbar vertebrae and increases size-wise towards its lumbar counterpart. The lower vertebrae are larger than the upper ones. It’s worth noting that these vertebrae can be differentiated from the rest due to the facets that are present on the body sides which are required for articulation.

The vertebral columns T1-T10 are all connected to a two ribs. Each is located on both sides of the rib cage via the articular facets on transverse processes of the vertebrae. The ribs normally curve around the individual’s body and attaches to the body’s sternum. Consequently a rib cage is formed and responsible for protecting the body’s vital organs such as the lungs, the liver and the heart. The T11 and the T12 do not have facets like their counterparts and are shorter as well. They also resemble the lumbar vertebrae in terms of their function and size. ribs attached to the T11-T12 are responsible for protecting the kidneys from harm.

General features of the Thoracic Vertebrae

This video is a great way to learn about this section of the spine:

To summarise:

  • Its pedicles are backward and slightly upward directed. Its inferior notches are deeper and larger in size compared to other vertebral region.
  • The laminae are thick imbricated and broad. This means that there is an overlapping between the laminae and the subjacent ones.
  • The vertebral foramen is the fairly large opening posterior and is responsible for protecting the spine whereas the vertebral column is circular and quite small.
  • There are heart-shaped bodies are located in the middle section of the vertebral column.
  • The transverse processes are strong, thick and of fair length.
  • The superior articular processes on the other hand are thin plates that project upwards from the laminae and pedicles junctions.
  • Finally, the inferior articular processes are considerable fused to the laminae.

It’s worth noting that there are differences between the thoracic vertebrae in humans and other animals. For example it varies between humans and marsupial and koalas. In koalas they are 11 in number whereas in marsupials they are 13 in number.

Spinal Sections: The Lumbar Vertebrae

The lumbar vertebrae are the five bones which make up the portion of the spine in the lower back and sit below the thoracic region. The spine, 33 bones which extend from the skull to the pelvis is there to support the body's weight, holding the body upright; to allow flexibility and movement such as bending and twisting; and to protect the spinal cord. The S-shape of the spine acts as a natural shock absorber, preventing the head (and therefore the brain) from jarring during movement.

The Lumbar Vertebrae

The five lumbar vertebrae are numbered L1 at the top through to L5 at the bottom. They sit below vertebrae of the thorax, and above the sacrum and coccyx, which are in the pelvis region. The vertebrae in the lumbar region are sturdy bones, as they support all the upper body weight and provide a stable center of gravity. They also provide the flexibility and movement in the trunk, in combination with a range of ligaments and muscles.

Each Vertebrae is made up of three main areas:

  • The vertebral body is a roughly cylindrical shape. It is this part of the vertebrae that bears the weight. The top and bottom surfaces are flattened, with a rim around to provide grip to the intervertebral disc. Intervertebral discs, made from a jelly like substance with a fibrocartilage case, sit between each vertebra providing strength and flexibility and shock absorption.
  • The vertebral arch extends behind the vertebral body to form a ring, called the vertebral foramen, through which the spinal cord passes. In the lower back, the foramen is large and roughly triangular in shape.
  • The processes stick out from the vertebral arch to the side and downwards towards the rear, and provide link points for the various muscles and ligaments which support movement in this area of the back.

How are the Lumbar Vertebrae different from the other sections of the spine?

The spine is divided up into five sections: The seven cervical vertebrae are in the neck, they are smaller and more delicate than the other vertebrae, but have a large vertebral foramen. The twelve thoracic vertebrae are in the thorax and they have surfaces which articulate with the ribs. Then there are the five lumbar vertebrae. Below these are the five sacral vertebrae, which have fused by adulthood into one large bone in the pelvis with no intervertebral discs. Finally the coccygeal vertebrae, there are usually four, but sometimes 3 or 5, fused vertebrae with no intervertebral discs.

As usual, video is a great way to see things quickly and get clear visual explanations:

The main difference between the lumbar vertebrae and the others is their size. They are much larger, as they carry a lot of weight and absorb the stresses of carrying and lifting. The vertebral body is large and wide, thicker at the front that at the back. The vertebral foramen (the hole for the spinal cord) is triangular shaped, it's larger than in the vertebrae of the thorax, and slightly smaller than in cervical vertebrae. Lumbar vertebrae do not have the foramen transversarium as exists on cervical vertebrae, nor do they have the facets in the side of the body which are found in the thorax to provide articulation with the ribs.

Spinal Sections: The Cervical Vertebrae

Cervical vertebrae refer to seven bony rings located in the neck between the thoracic vertebrae in the trunk and the base of the skull. These bony rings form a continuous column between the chest and the skull. It is the Cervical vertebrae that sustain damage from a whiplash injury (leading to multiple whiplash injury claim each year!)

Functions of Cervical Vertebrae

This vertebrae process performs many essential functions that are paramount to the body survival.

(a) The various joints formed between the cervical vertebrae and the skull provides effective flexibility that allows the neck and the head to extend, flex and rotate.

(b) The various muscles attached to this vertebrae process provide ideal posture to the neck and head. There are considered to be the most effective muscles in maintaining body posture.

(c) The bony arches of these vertebrae processes protect essential blood vessels and nerves passing through the neck from any mechanical damage.

Main Features of Cervical Vertebrae

Each of these vertebrae is named according to its position from the first (superior) to the seventh (inferior). They are denoted as C1, C2, C3, C4, C5, C6 and C7. Details on each of these component parts of the spins, as follows:

Atlas (C1) - This refers to the vertebra inferior to the skull.

Axis (C2) - This refers to the second vertebra that facilitates side to side movement of the head. This happens because this vertebra provides the axis upon which the atlas and the skull rotate when the head moves side to side. The odontoid process gives the axis a very distinct shape. This process is a tooth like prominence that extends from its body superiorly towards the axis. This process provides the axis at the atlantoxial joint, upon which the atlas rotates.

Vertebral arch - This refers to a thin ring of bone that surrounds the transverse foramina and the vertebral. It plays a critical role of providing space of the spinal cord and the meninges as they pass via the neck.

Transverse foramina - These surround the vertebral veins and arteries. They work along with jugular veins and carotid arteries, to transport blood to and from the brain. Transverse process is located on the right and left lateral sides of each vertebra. This process forms the insertion point for muscles of erector spinae. These muscles are essential in flexing and extending the neck.

Spinous process - This is among the various bony processes that extend from vertebral arch and is essential for muscle attachment and movement of the neck. It extends from the posterior of the arch and serves as a connection point for muscles such as spinalis and trapezius. These muscles are vital in extending the neck.

The body - This refers to a thickened region of bone that lies anterior to the vertebral foramen. It forms the main bone mass in all vertebrae apart from the atlas. The body supports most of the weight of the tissues of the neck and head. It is also very effective in boosting the vertebral.

Intervertebral disks - These are essential in providing slight flexibility to the neck. They are made of rubbery fibro cartilage and they lie between the vertebral bodies.

Flattened facets - These are essential in allowing movement among the vertebrae. They form joints with the skull and neighboring vertebrae.

Other Features of C3 to C7 Vertebrae

1. Laminae- These are usually thinner and narrow above than below.

2. The pedicles-These are attached backward and laterally. They are usually attached to the body midway between the lower and upper boarders. This makes the superior vertebra notch deeper than inferior.

3. The lower surface is usually convex from side to side and concave from front to back. They present shallow concavities which receives the corresponding lips of the underlying vertebra.

4. The upper surface is concave transversely and presents a projecting lip on either side.

In conclusion, the Cervical vertebrae are essential in maintaining straight spine and good body posture. They are also paramount in providing attachment for neck muscles.They also provide excellent flexibility that allows the neck and head to extend and rotate. Without the cervical vertebrae, you'd be a gelatinous mass, quivering on the floor, so be thankful for C1 to C7!

Here's the icing on the cake, a video that graphically shows what is stated above:

Focus On: The Coccyx

coccyx

The coccyx is actually the very bottom part of the spine. It may also be called a tailbone and is the final segment in the vertebral column. The structure of the coccyx may be anywhere from three to five vertebrae, but will vary from person to person. The top coccyx vertebrae connects with the sacral bone and each of the three first segments are connected, although they are separate bones. However, the movement between these bones is minimal, and they rarely experience much movement. Additionally, the first bone is the largest and then the remaining bones become smaller with the final piece of bone usually being extremely small.

Although the coccyx does not appear to have any practical function, it does play an important role in the spinal column. Many of the body's muscles, tendons, and ligaments attach to these bones, so it plays a role in structure. Additionally, the coccyx is the base of the spine and supports all the vertebrae above it. When a person is sitting, the coccyx is mainly responsible for bearing weight, especially when leaning backward.

The coccyx also plays an important role in walking because of the muscles and ligaments attached to the end of the spinal column. When a person has a fractured tailbone, they may experience difficulty sitting, walking, and using the lower part of their bodies easily.

While the structure of the coccyx is extremely small and it does not move, your tailbone serves as an attachment and also supports the rest of the body. Located at the end of the spine, the coccyx is often thought of as a left-over from a vestigial tail. However, this part of the spinal column still plays an important function in structure and movement.

Erector Spinae = Straight Spine

erector spinae

The muscular system performs some of the most basic functions of the human body and what goes on within it is more complex and astonishing than most would care to imagine. Of the various muscle groups that make up the muscular system, the Erector Spinae is probably the least known. This group of muscles comprise of small muscles and tendons, which form two different groups of muscles that are located on either side of the spine. Therefore, the erector muscles are two groups of muscles that extend throughout the thoracic, lumbar and cervical regions of the body.

Being a group of muscles, the Erector Spinae is made up of three muscles; the iliocostal muscles, spinal muscles and the longissimus dorsi muscles, with the latter being the longest back muscle. The muscle is divided in to three smaller muscles, which are; the capitis, the thoraces and the cervices. The capitis is responsible for holding the head erect, while the thoraces and cervices assist in the motion of backward and sideward bending and bending the top of the neck respectively. Similar to the longissimus, the spinal muscles consists of the spinal cervices and the spinal thoracic. These three groups of muscles assume varying shapes and structure within the vertebral column. In the sacral region the erector group of muscles is narrow and pointed whereas in the lumbar region it is larger and forms a thick fleshy mass. The muscles reduce in size as they approach the vertebrae and ribs.

Though rarely given the attention they deserve, the Erector Spinae muscles are responsible for some of the most basic functions of the muscular system. Key among them is the extension of the vertebral column. In simple terms, the erector muscles are responsible for the body’s ability to stand/sit upright and learn to one side. Therefore the muscles are essential for good posture while sitting down or standing. Most back problems and chronic illnesses are associated to weak erector muscles.

To most people the waist is responsible for their ability to bend forward. However, contrary to this notion, the body’s ability to bend forward is due to the resistance provided by the Erector Spinae. This resistance provides control that is essential in bending forward. This is one of the basic, yet essential functions of this group of muscles. In addition, to this the erector group of muscles acts as a powerful extensor that allows the back to return to an erect position. Therefore the simple task of bending would be impossible were it not for this group of muscles.

Bending forward until fingertips touch the floor is a popular exercise for the reduction of abdominal fat. For this exercise to be possible the Erector Spinae has to be involved. When bending the erector muscles are usually relaxed. However, on the reversal movement this group of muscles together with the hamstring and Gluteus maxim muscles extends the back causing the spine to straighten. This muscular movement is integral in any exercise that involve leaning, sitting, standing or any other movements that will affect the vertebrae column of the body. This is why the erector muscles are important in movement.

The Erector Spinae, like all other body organs are susceptible to damage when not used properly. The weakening of the muscles can be caused by a myriad of things, key among them bending from the waist while lifting heavy objects. This puts too much strain on the back and thus weakens the muscles that run down the back. Similarly, hunching over a keyboard for a lengthy period of time leads to weakening of the erector muscles. To prevent damaging the muscles training of the lower back is crucial. Squats and dead lifts are known to be good for training the lower back and strengthening the muscles.

The three groups of muscles that comprise the Erector Spinae function as a unit and therefore activities that focus on the whole torso are good for strengthening the erector muscles. Yoga and pilates help in relieving of tightness in the erector muscles and thus improve posture. In conclusion the erector muscles dictate most of the body’s basic movements and actions. These muscles are thus integral in maintaining a good body posture. Additionally, the muscles, just like all other muscles in the body, are used mainly during exercises such as squats.

Sacrum: Base Of The Spine

sacrum

The sacrum, also referred as the sacral region, is a triangular bone found at the spine’s base and at the back section in the pelvic cavity. It inserts into the pelvic cavity like a wedge between two hip bones. The sacrum’s upper most part connects with the lumbar vertebrae and its lower section with the coccyx, also called tailbone. It starts as five unfused vertebrae which then start fusing at the age of 16 to 20. The vertebrae then fuse into a single bone at an approximate age of 30 to 34. It has several openings that on its sides where blood vessels and nerves run.

Functions of the Sacrum

It is concave-shaped on its interior surface to provide ample space in the pelvic cavity. It also differs depending on one’s gender. The female sacrum tends to be wider, shorter, and more curved to its posterior than their counterpart’s male sacrum. The female’s sacrum unique features give it the necessary conditions for the delivery of the baby/ fetus during childbirth.

The sacrum together with the fifth lumbar vertebrae forms the fibro cartilaginous lumbosacral joint on its wide superior end. To its inferior end, the sacrum and the tailbone form a fibro cartilaginous sacro-coccygeal joint. To its left and right sides, it forms sacroiliac joints with iliac from the hip bones to yield a rigid pelvis. Several ligaments bind to the sacroiliac joints to solidify the pelvis and stabilize its motion.

The sacral region gives way to several nerves originating from the lower end of the spinal cord, as well as, those of the caudal equine. The nerves from the vertebral foramen enter it through the sacral canal and exit as branches through four holes on its sides. The holes, called sacral foramina or sacral hiatus, located at the inferior end sacrum are vital for protection and also provide a through way for the nerves.

The sacrum is required for the proper functioning of the muscular, nervous, skeletal, and the reproductive system, and in particular, the female system. While acting as the pillar of the pelvis, it binds the hip bones near the posterior side. It also supports the spinal column’s base as it fuses with the pelvis. Most of the hip joint muscles such as the Piriformis, Illiacus, and Gluteus Maximus have their origins from the sacrum’s surface and rely on it when they pull to move the legs. Lastly, the sacrum contributes to the formation of pelvic cavity. Pelvic cavity then helps in supporting, as well as, protecting the delicate organs contained in the abdominopelvic cavity.

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