Intervertebral disc

Small pads sit between the bones in your back.

These pads are called discs. They act like soft cushions. This helps your bones absorb shocks when you move.

Each disc has a tough outer ring. Inside the ring is a soft, gel center. This gel helps spread pressure evenly. It keeps the bones from getting hurt.

There are 23 discs in your spine. Some are in your neck. Others are in your middle back. Some are in your lower back.

As people get older, these discs change. They can lose water and get smaller. This might make a person shorter. These discs are very important for your back.

Your spine is made of many bones called vertebrae.

Small pads sit between these bones. These pads are called intervertebral discs. They have two main parts. The outer part is a tough ring. Scientists call this the anulus fibrosus. Inside the ring is a soft center. This center is a gel called the nucleus pulposus.

These discs do three big jobs. They let your bones move a little. They hold the bones together. They also act as shock absorbers. The gel center helps spread pressure. This keeps the bones safe from harm. There are 23 discs in a human spine. Six are in the neck. Twelve are in the middle back. Five are in the lower back.

Discs can change as you grow older. The gel center can lose water. This makes the discs smaller. This might make a person shorter. Sometimes the tough outer ring can bulge. This is called a herniated disc. It can press on a nerve. This might cause pain.

Your spine is a busy part of your body. It is made of many bones called vertebrae. Between these bones sit special pads called intervertebral discs.

These discs are very important for your movement. They act as joints that allow your bones to move slightly. They also work like ligaments to hold the vertebrae together. Most importantly, they act as shock absorbers for your spine. This helps protect your bones when you move around.

Each disc has a very specific way it works. It has a tough outer ring called the anulus fibrosus. This ring is made of layers of strong material called fibrocartilage. Inside this ring is a soft, gel-like center called the nucleus pulposus. The nucleus pulposus is actually a remnant of the notochord.

This gel center helps spread pressure in all directions. Because it spreads the pressure, it prevents damage to the bones. The gel helps keep the two vertebrae separated during activity.

There are many discs located throughout your back. A human spine has 23 of these discs in total. There are 6 discs in your neck, called the cervical region. You have 12 discs in your middle back, known as the thoracic region. There are also 5 discs in your lower back, called the lumbar region.

Doctors name these discs using the bones above and below them. For example, the disc between the fifth and sixth neck bones is C5-6.

Discs can change as a person gets older. When we are young, the discs have a blood supply. As adults, they have almost no direct blood supply. Over time, the gel center can lose water and shrink. This process is called degeneration. This shrinking can even make a person a little shorter as they age.

About 25% of people under age 40 show these changes. More than 60% of people over age 40 show them on an MRI.

Sometimes, a disc can bulge or move out of place. This is called a herniated disc, or a slipped disc. This happens when pressure deforms the outer ring. The gel center can then push outward. This might press on a nearby nerve. This can cause things like numbness or pain.

Other shapes like scoliosis can also change how the spine looks. Scoliosis is a curve in the spine that looks like the letter S.

An intervertebral disc is a specialized structure located between adjacent vertebrae in the vertebral column. These discs function as fibrocartilaginous joints, which are joints that allow for slight movement between bones. They serve several vital roles: they act as ligaments to hold the vertebrae together, they provide a surface for movement, and they function as shock absorbers for the spine.

By absorbing impact, they protect the vertebral column during physical activity. Without these discs, the bones of the spine would lack the necessary cushioning to handle the stresses of daily life.

The structure of the disc consists of two main parts: the anulus fibrosus and the nucleus pulposus. The anulus fibrosus is an outer fibrous ring made of several layers, or laminae, of fibrocartilage. This ring contains both type I and type II collagen. Type I collagen is concentrated toward the outer edge to provide extra strength. These stiff laminae are designed to withstand heavy compressive forces.

Inside this ring lies the nucleus pulposus, which is a gel-like center. This center contains loose fibers suspended in a mucoprotein gel. It is actually a remnant of the notochord, a structure from early development.

The mechanism of the disc relies on hydraulic pressure to protect the spine. When the body experiences compressive loads, the nucleus pulposus distributes that pressure evenly in all directions. This process prevents stress concentrations that could damage the vertebrae or their endplates. The gel center is composed of large vacuolated notochord cells, small chondrocyte-like cells, and collagen fibrils. It also contains aggrecan, which is a proteoglycan that binds to hyaluronan.

Aggrecan molecules have glycosaminoglycan (GAG) chains, such as chondroitin sulfate and keratan sulfate, attached to them. Because these aggrecan molecules are negatively charged, they increase oncotic pressure. This causes extracellular fluid to shift from the outside into the nucleus pulposus, keeping the disc hydrated.

Humans have 23 intervertebral discs distributed throughout the spine. There are 6 discs in the cervical region of the neck. The thoracic region, or the middle back, contains 12 discs. The lumbar region, located in the lower back, has 5 discs.

There is a disc between every pair of vertebrae, with one exception. The first cervical segment, called the atlas, is a ring around the axis. The axis is the second cervical segment and acts as a post. This allows the atlas to rotate so the neck can swivel.

Discs are identified by the vertebral bodies they sit between. For instance, the disc between the fifth and sixth cervical vertebrae is labeled "C5-6." While discs have a vascular supply to the cartilage endplates and the anulus fibrosus during development, this supply deteriorates quickly. In healthy adults, the discs have almost no direct blood supply. Doctors often use X-ray photographs to define the intervertebral disc space, which is the space between adjacent vertebrae. In healthy patients, this space matches the actual size of the disc.

Changes in the disc can lead to clinical issues, often termed discogenic when they cause pain. A herniated disc, or "slipped disc," occurs when unbalanced mechanical pressures deform the anulus fibrosus. This allows part of the nucleus pulposus to obtrude or bulge outward. This can happen due to trauma, peak physical performance, or chronic deterioration from poor posture.

When the material is forced laterally or posteriorly, it can press on nearby nerves. This may cause symptoms like numbness, paresthesia, or loss of muscle tone. Another type is vertical disc herniation, which involves the formation of Schmorl's nodes.

Degeneration is a normal part of aging, but it can change the disc's function. As people age, the nucleus pulposus dehydrates and the concentration of proteoglycans decreases. This limits the disc's ability to absorb shock and can lead to a decrease in overall human height. Approximately 25% of people under age 40 show evidence of degeneration. Beyond age 40, more than 60% of people show these changes on an MRI. Other spinal conditions like scoliosis, which is an S-shaped curvature, can also affect disc morphology by causing calcium deposits in the cartilage endplate.