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Bones / Orthopedics

Anatomy of the Spinal Cord

By Dayyal Dg.Twitter Profile | Published: Monday, 24 April 2023
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Diagram showing herniated disc in human.
Diagram showing herniated disc in human. Freepik / @brgfx

The spinal cord is a critical part of the central nervous system, transmitting sensory and motor signals between the brain and the rest of the body. It is responsible for a variety of essential functions, including reflexes, sensation, and movement. In this article, we will take an in-depth look at the anatomy of the spinal cord, including its structure, function, and the different regions of the spinal cord.

Structure of the Spinal Cord

The spinal cord is a long, thin, tubular structure that extends from the brainstem to the lower back. It is protected by the vertebral column, which is made up of 33 vertebrae and intervertebral discs. The spinal cord is divided into five regions based on the vertebrae in which they are located, from top to bottom: cervical, thoracic, lumbar, sacral, and coccygeal.

The spinal cord is made up of both gray matter and white matter. The gray matter is located in the center of the spinal cord and is shaped like a butterfly. It contains cell bodies of neurons and interneurons, as well as dendrites and axons. The gray matter is divided into dorsal and ventral horns, which are responsible for relaying sensory and motor information, respectively.

The white matter surrounds the gray matter and contains myelinated nerve fibers that form tracts or pathways that connect different regions of the spinal cord and the brain. The tracts are organized into three regions: dorsal columns, lateral columns, and ventral columns. The dorsal columns carry sensory information from the periphery to the brain, the lateral columns contain motor fibers that control voluntary movements, and the ventral columns contain both sensory and motor fibers.

Meninges

The spinal cord is protected by three layers of protective membranes called the meninges. The outermost layer is the dura mater, a tough, fibrous membrane that forms the outermost layer of the spinal cord. It is attached to the periosteum of the vertebral column and provides a protective barrier against injury.

The second layer is the arachnoid mater, a thin, web-like membrane that lies between the dura mater and the pia mater. It is filled with cerebrospinal fluid (CSF), which helps to cushion the spinal cord against injury.

The innermost layer is the pia mater, a thin, delicate membrane that adheres to the surface of the spinal cord. It is highly vascularized and helps to provide nutrients to the spinal cord.

Nerve Roots

Nerve roots are the points at which nerves exit the spinal cord. Each nerve root is composed of two branches: a dorsal root, which contains sensory fibers, and a ventral root, which contains motor fibers. These two roots come together to form a spinal nerve, which carries both sensory and motor information to and from the periphery.

Cervical Region

The cervical region of the spinal cord is the uppermost part of the spinal cord and contains eight pairs of cervical nerves. These nerves are responsible for controlling the muscles of the neck and shoulders, as well as the diaphragm, which is essential for breathing.

Thoracic Region
The thoracic region of the spinal cord is located in the chest and contains 12 pairs of thoracic nerves. These nerves are responsible for controlling the muscles of the chest and abdomen, as well as the heart and lungs.

Lumbar Region

The lumbar region of the spinal cord is located in the lower back and contains five pairs of lumbar nerves. These nerves are responsible for controlling the muscles of the hips and legs, as well as the bladder and bowel.

Sacral Region

The sacral region of the spinal cord is located in the pelvis and contains five pairs of sacral nerves. These nerves are responsible for controlling the muscles of the lower legs, feet, and toes, as well as the sexual organs and anus.

Coccygeal Region

The coccygeal region of the spinal cord is the lowest part of the spinal cord and contains one pair of coccygeal nerves. These nerves are responsible for controlling the muscles of the anus and the skin around the coccyx.

Spinal Cord Function

The spinal cord is responsible for a variety of essential functions, including reflexes, sensation, and movement. It receives sensory information from the periphery and sends motor commands to the muscles and organs.

Reflexes

Reflexes are rapid, automatic responses to a stimulus that do not require conscious thought. They are essential for protecting the body from harm and maintaining balance and posture. Reflexes are controlled by the spinal cord and do not require input from the brain.

Sensation

The spinal cord is responsible for relaying sensory information from the periphery to the brain. Sensory information includes touch, temperature, pressure, pain, and proprioception (awareness of body position). The dorsal columns of the spinal cord carry sensory information from the periphery to the brain.

Movement

The spinal cord is responsible for controlling voluntary movement. Motor commands originate in the brain and travel down the spinal cord to the muscles and organs. The lateral columns of the spinal cord contain motor fibers that control voluntary movement.

Spinal Cord Injuries

Spinal cord injuries (SCI) can occur as a result of trauma, such as a car accident or a fall, or due to non-traumatic causes, such as a disease or infection. SCI can cause loss of sensation, movement, and reflexes below the level of injury, as well as bowel and bladder dysfunction.

The severity of an SCI depends on the level and extent of the injury. Injuries to the cervical region can result in quadriplegia, the loss of sensation and movement in all four limbs, as well as respiratory dysfunction. Injuries to the thoracic and lumbar regions can result in paraplegia, the loss of sensation and movement in the lower body.

Treatment for SCI includes surgery, rehabilitation, and assistive devices such as wheelchairs and braces. Research into new treatments, such as stem cell therapy and nerve regeneration, is ongoing.

Conclusion

The spinal cord is a critical part of the central nervous system, responsible for relaying sensory and motor signals between the brain and the rest of the body. It is protected by the vertebral column and surrounded by three layers of protective membranes called the meninges. The spinal cord is divided into five regions based on the vertebrae in which they are located and is made up of both gray matter and white matter. The spinal cord is responsible for reflexes, sensation, and movement, and spinal cord injuries can cause loss of sensation, movement, and reflexes below the level of injury. Treatment for SCI includes surgery, rehabilitation, and assistive devices, and research into new treatments is ongoing.

References

  1. Carlson, B. (2014). Human Embryology and Developmental Biology. Elsevier Health Sciences.
  2. Drake, R.L., Vogl, W., & Mitchell, A.W.M. (2014). Gray's Anatomy for Students. Elsevier Health Sciences.
  3. Kandel, E.R., Schwartz, J.H., & Jessell, T.M. (2012). Principles of Neural Science. McGraw-Hill Education.
  4. National Institute of Neurological Disorders and Stroke. (2021). Spinal Cord Injury: Hope Through Research.
  5. National Spinal Cord Injury Statistical Center. (2021). Facts and Figures at a Glance.
  6. Standring, S. (Ed.). (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. Elsevier Health Sciences.
  7. Waxman, S.G. (2013). Clinical Neuroanatomy. McGraw-Hill Education.
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