The back supports the weight of the body, allowing for flexible movement while protecting vital organs and nerve structures.

This article looks at the anatomy of the back, including bones, muscles, and nerves. It also covers some common conditions and injuries that can affect the back.

Click on the interactive model below to explore the anatomy of the back.

The back comprises the spine and spinal nerves, as well as several different muscle groups. The sections below will cover these elements in more detail.

Spine

The spine is composed of 33 bones called vertebrae, which stack together to form the spinal canal. This protects the spinal cord inside.

Facet joints connect each vertebra, with fluid supporting the free movement of these joints. A disk sits in-between each vertebra to cushion the bones from any shocks.

The spine consists of five sections. From the top of the spine to the bottom, these sections are:

  • The cervical spine: The cervical spine is the top part of the spine. It runs from the neck to the upper back. It consists of seven vertebrae. The cervical spine protects the nerves connecting to the brain, allowing the head to move freely while supporting its weight.
  • The thoracic spine: The thoracic spine is the middle part of the spine, connecting the cervical and lumbar spine. It has 12 vertebrae. The thoracic spine helps keep the body upright and stable.
  • The lumbar spine: The lumbar spine is the lower part of the back. It is made up of five larger vertebrae. These support most of the body’s weight.
  • The sacrum: The sacrum is the bottom part of the spine, which connects to the hip bones. The sacrum has five vertebrae fused together.
  • The coccyx: The coccyx is the base, or tailbone, of the spine. This consists of four vertebrae fused together. It joins to ligaments and muscles around the pelvis.

Ligaments are tough, flexible bands of connecting tissue that join bones to other bones.

Two of the main ligaments in the back are the anterior longitudinal ligament and the posterior longitudinal ligament. These two ligaments connect and support the spine from the neck to the lower back.

Spinal cord

The spinal cord runs from the neck down to the lower back. It consists of nerves that carry messages to and from the brain.

More specifically, the spinal cord allows the body to:

  • move freely
  • have an awareness of the position of limbs
  • feel sensations, such as heat, cold, and vibrations
  • regulate body temperature, blood pressure, and heart rate
  • carry out bodily functions, such as breathing, urinating, and having bowel movements

The spinal cord has five sections of spinal nerves branching off. These are:

  • the cervical nerves
  • the thoracic nerves
  • the lumbar nerves
  • the sacral nerves
  • the coccygeal nerves

Muscles in the back

There are three different groups of muscles in the back. These are called the superficial, intermediate, and intrinsic muscles. The sections below cover these in more detail.

Superficial muscles

The superficial, or extrinsic, back muscles allow for the movement of the limbs. These muscles include the:

  • trapezius
  • latissimus dorsi
  • levator scapulae
  • rhomboids

Intermediate muscles

The intermediate muscles connect to the ribs and support respiration. These muscles include the serratus posterior inferior and the serratus posterior superior.

Intrinsic muscles

The intrinsic, or deep, muscles allow for movements such as rotation and bending. These muscles include:

  • the iliocostalis
  • the longissimus
  • the spinalis
  • the semispinalis
  • the multifidus
  • the rotatores

A range of conditions can affect the back, including:

Abnormal curves in the spine

Abnormal curves in the spine can include:

  • Scoliosis: Scoliosis causes a sideways curvature of the spine. The spine may appear to form an “S” or “C” shape, rather than a straight line.
  • Kyphosis of the thoracic spine: People may also refer to this condition as hunchback. Kyphosis causes an abnormal outward curvature of the upper back.
  • Lordosis of the lumbar spine: People may refer to this condition as swayback. Lordosis creates an abnormal arch in the lower back.

Osteoporosis

Osteoporosis is a condition wherein the bones lose their density and become more fragile. This can cause the bones to fracture more easily.

Females and people over the age of 50 have a higher risk of osteoporosis. Osteoporosis of the spine can lead to back pain, structural irregularities, and height reduction.

Osteoarthritis

Osteoarthritis occurs when the cartilage that cushions bones wears down, causing the bones to rub against each other.

Osteoarthritis is the most common type of arthritis. It can affect the joints in the spine, causing stiffness and back pain.

Intervertebral disk degeneration

The intervertebral disks cushion the vertebrae. As people age, these disks can wear down. A decrease in this cushioning can cause pain.

Nerve compression

Compression of the sciatic nerve, or the spinal nerve root, can cause back pain. Pressure from surrounding tissue can irritate the nerve, causing pain, numbness, or tingling sensations.

These sensations can also radiate to other parts of the body, such as the buttocks and legs.

Injuries to the spine and spinal cord can happen for a variety of reasons, such as:

  • motor vehicle accidents
  • sporting injuries
  • physical violence
  • heavy falls
  • conditions that affect the spinal cord or the bones and nerves in the back
  • spinal tumors

Injuries to the spine include fractures and dislocations of the vertebrae. These injuries can also damage the spinal cord.

Some injuries to the vertebrae can include:

  • Compression fracture: In this type of fracture, external force pushes the spine forward and downward.
  • Burst fracture: This is a severe type of compression fracture, wherein the bones shatter and can damage the spinal cord.
  • Subluxation: Injury to the muscles and ligaments in the spine can cause the vertebrae to partially dislocate, which can also damage the spinal cord.
  • Dislocation: Tears or damage to the ligaments can cause the vertebrae to become dislocated or misaligned.
  • Fracture-dislocation: Severe ligament or soft tissue damage can cause a fracture or dislocation of the vertebrae. This can lead to damage of the spinal cord.

Other spinal cord injuries include ischemia, which is a decrease in blood flow to the spinal cord, and contusion, which refers to bruising of the spinal cord.

Herniated disk

If one of the disks that cushion the vertebrae becomes misaligned, bulges out, or ruptures, it is known as a herniated disk. Heavy lifting, straining, and twisting can cause a herniated disk.

This can cause back pain, particularly in the lower back. It can also cause numbing and tingling sensations, which may radiate out to other parts of the body.

Sprains and strains

Injuries can cause ligaments and muscles in the back to overstretch or tear, causing back pain. This can happen as a result of lifting incorrectly or straining the back.

Treatments for back conditions will vary depending on the cause. For mild conditions, a person may find that physical therapy and low impact, mobilizing exercises can help relieve the symptoms.

A doctor may recommend anti-inflammatory medication for certain conditions. For severe spinal irregularities or other conditions, corrective surgery may be necessary.

Hot and cold compresses, physical therapy, and pain medications may all help treat mild back injuries such as sprains. For significant injuries to the spine or spinal cord, a person may need surgery.

The back consists of the spine, spinal cord, muscles, ligaments, and nerves. These structures work together to support the body, enable a range of movements, and send messages from the brain to the rest of the body.

Conditions or injuries affecting the back can range from mild to severe. Mild conditions can cause aches, pain, or a reduction in mobility. Serious conditions can affect other bodily functions and nerve signals.

Treatments for back issues will vary depending on the severity of the condition and can include physical therapy, medication, and surgical procedures.