Bones and Joints
There are 24 spinal bones that make up the human spine; these are known as vertebrae. The vertebrae are stacked on top of one another as they form the spinal column. This is the human body’s main upright support system.
The spine forms three curves on the sides. The neck is called the cervical spine and it curves slightly inward. The middle back is called the thoracic spine and it curves outward. The outward curve of the thoracic spine is known as the kyphosis. The lower back is known as the lumbar spine and it curves slightly inward. The inward curve of the spine is known as lordosis.
The lumbar spine is composed of lower five vertebrae. Doctors often call the vertebrae L1 to L5. The lowest vertebra which is the L5 connects to the top called the sacrum which is that triangular bone found at the base of the spine. This is found between the two pelvic bones. There are those that have the sixth or extra lumbar vertebra. This condition is not known to cause any kind of problem.
Every vertebra is formed by a vertebral body which is a round block of bone. The lumbar vertebral bodies are often taller and bulkier compared to the others in the spine. This is because the low back needs to withstand pressure brought about by the body weight and also from other activities like twisting, lifting, and carrying. Those large and more powerful muscles that are attached to the lumbar spine give extra force on lumbar vertebral bodies.
A bony ring is also attached to the back of every vertebral body. This ring is known to have two parts. There are two pedicle bones that are connected straight to the vertebral body. On the other hand, two lamina bones join all pedicles in completing the ring. It is the lamina bones that form the outer rim of this said bony ring. When the vertebrae are placed on top of each other, the bony rings tend to form a hollow tube that gets to surround the nerves and the spinal cord. The laminae are known to provide protection over the nerve tissues.
A bony knob shoots out from the point where the two lamina bones are merged at the back of the spine. Such projections are called spinous processes. They can be felt when you run your fingers up and down the spine. Each vertebra is also known to have two bony knobs that point to the sides, one on the left and another to the right. Such bony projections are known as transverse processes. Those projections found in the lower back are broader compared to the other parts of the spine because there are multiple large back muscles that are attached and they impart strong forces on them.
There are two facet joints found between the vertebrae of each spinal segment. These facet joints are found at the back of the spinal column. There are two facet joints in between every pair of vertebrae, one on every side of the spine. The facet joint is made of small and bony knobs that line up around the back of the spine. On the area where the two knobs meet, they all form a joint that connect the vertebrae. This alignment of the facet joints found in the lumbar spine allows for movement while you bend forward or back.
The surfaces of the facet joints are all covered by articular cartilage. This is that smooth and rubbery material that covers the joint ends. This also enables the bone ends to move against each other in a smooth fashion without any sort of friction.
A small tunnel is found on the left and right side of the vertebra and it’s called neural foramen. The plural term for is floramina. There are two nerves that leave the spine at every vertebra that pass the foramina, one on the left side and another on the right. Right in front of the opening the intervertebral disc is found. A herniated disc or bulged disc will be able to narrow the opening and put pressure on the nerve. The facet joint sits right at the back of the foramen. The bone spurs that form around the facet joint tend to project into the tunnel which narrows the hole and also pinches the nerve.
The hollow tube that’s formed by the bony rings found around the back of the spinal column surrounds the spinal cord. The spinal cord appears to be a long wire that’s composed of millions of nerve fibers. Same as the skull that protects the brain so are the bones found on the spinal column that protect the spinal cord.
The spinal cord goes down to the L2 vertebra. Below this part, the spinal canal has a bundle of nerves that goes right into the pelvic organs and the lower limbs. In Latin this is called cauda equine which means horse’s tail.
In between the vertebrae, there are two large nerves that branch out into the spinal cord, one on the left and another on the right side. The nerves go through the neural foramina of every vertebra. The spinal nerves group together in forming the main nerves that directly go to the limbs and the organs. The cauda equina or nerves of the lumbar spine lead to the pelvic organs and the lower limbs.
These are networks of fiber that put all the body cells together. Ligaments on the other hand are strong connective tissues that attach bone to the other bones in the body. There are a couple of long ligaments that connect the front and back parts of the vertebrae. The one that runs lengthwise down towards the front of the vertebral bodies is called the anterior longitudinal ligament. There are two other ligaments that run the entire length of the spinal canal. There’s also the posterior longitudinal ligament that is attached at the back of the vertebral bodies. There’s also the ligamentum flavum which is a long elastic band that connects to the lamina bone surfaces. The lumbar spine bones are also connected to the sacrum and the pelvis by thick ligaments.
There’s a special structure in the spine called the intervertebral disc which is composed of connective tissue. The disc’s fibers are formed by way of special cells that are known as collagen cells. These fibers are all lined up to form a nylon rope or a crisscrossed net.
The intervertebral disc is also composed of two parts, the nucleus which is the spongy center. This provides shock absorption within the spine. The nucleus is held in place by strong ligament strands that surround it.
Two Parts of the Intervertebral Disc.
These muscles found on the low back are arranged in what are known to be layers. The superficial layer which is closest to the skin’s surface is covered by a thick tissues known as fascia. The erector spinae or the middle layer come with strap-shaped muscles that all make up the chest, low back, and lower ribs. They all join the lumbar spine in forming a thick tendon connecting the low back bones, the pelvis, and the sacrum. The muscles’ deepest layers are attached to the surface of the spine, lower back, the pelvis, and sacrum. Such deepest muscles coordinate their actions with the abdomen’s muscles to make the spine steady.
Low Back Muscles
The Spinal Segment
You can look at the spinal segment to understand well the lumbar spine anatomy. Every spinal segment has two vertebrae that are all separated by the invertebral disc, small joints that link the spinal column, and the nerves that leave the spinal column at every vertebra.
The intervertebral disc is responsible for separating two vertebral bodies found in the spinal segment. It functions as a shock absorber. It protects the spine from gravity. It also offers spine protection during heavy activities like lifting, running, and jumping that put pressure on the spine.
Two facets connect the spinal segment. When the facet joints move together they usually bend and turn the low back.
There are many parts that make up the back anatomy. When you understand the structures and the regions of the lumbar spine you can take care of your health better and even get rid of your back problem.