Anatomy Insight - Spine Anatomy

Spine Anatomy

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The spine is composed of:

Vertebrae
Intervertebral disks
Facet joints
Spinal cord and nerves
Soft tissues

The spine, or backbone, is a long column of bones that extends from the neck to the lower back.

It supports the body and connects various parts of the musculoskeletal system, including bones and muscles. The spine lets a person to sit, stand, walk, twist, and bend.

Vertebrae

The spine is made up of 33 small bones called vertebrae. These bones are stacked on top of each other to make a tunnel called the spinal canal. This tunnel protects the spinal cord and nerves inside.

Most of the vertebrae can move to help you bend and twist. But the ones at the very bottom (called the sacrum and coccyx) are stuck together and don’t move.

Image by Anatomy Standard, cropped from the original, licensed under CC BY-NC 4.0

Intervertebral disks

Between each spine bone, there’s a round, flat cushion called a disk. These disks act like shock absorbers to protect your spine.

Each disk has a soft, jelly-like center and a tougher outer ring. If too much pressure builds up, the soft center can push out and touch nearby nerves. This can cause pain, like sciatica.

Facet joints

Facet joints are the small joints between the bones in your spine.

They’re covered with smooth cartilage, which helps the bones slide over each other. These joints let you twist and turn while keeping your back steady.

Image by Anatomy Standard, cropped from the original, licensed under CC BY-NC 4.0.

Soft tissues

Ligaments hold the spine bones together.
Muscles support the spine and help you move.
Tendons connect muscles to bones and help stop injuries while you move.

Spinal cord and nerves

The spinal cord is a thick bundle of nerves that runs through the middle of the spine, from your head to your lower back.

It sends messages between your brain and your body.
Thirty-one pairs of nerves branch out from the spinal cord through small openings in the spine. These nerves help you move and feel things.

The segments of the spine

Your spine is made up of 33 small bones called vertebrae, and these are divided into 5 main sections, going from the neck down to the tailbone:

Cervical spine (neck): This is the top part of the spine and has seven vertebrae, labeled C1 to C7. These bones help your head move so you can turn, tilt, and nod. This part of the spine curves inward like the shape of a “C,” which is called a lordotic curve.
Thoracic spine (middle back): The thoracic spine has 12 vertebrae, from T1 to T12. Your ribs connect to these bones. This section curves outward in a slight “C” shape going the other way, which is called a kyphotic curve.
Lumbar spine (lower back): The lumbar spine includes five vertebrae, L1 to L5. This part supports the upper spine, connects to the hips, and holds most of your body weight. It also helps with movements like lifting and bending. It curves inward like the neck, forming another lordotic curve.
Sacrum: The sacrum is a triangle-shaped bone made from five vertebrae (S1 to S5) that are joined together and don’t move. It connects the spine to the hips. Together with the hip bones, it forms a ring called the pelvic girdle.
Coccyx (tailbone): The coccyx is at the very bottom of the spine. It’s made of four small bones that are fused together. Muscles and ligaments from the pelvic floor are attached to the coccyx.