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General Anatomy of the Spine
Functions of the Spine
The spine consists of vertebrae that support the body’s trunk while also enclosing the spinal cord. Understanding the general anatomy and functions of the spine (S.S.) is extremely important for patients with issues in this area.
This article provides an overview of the complex anatomy of the spine, covering the following topics:
- A general overview of spinal functions, including foramina and primary curves.
- A detailed description of individual anatomical components, including vertebrae, discs, the spinal cord, nerves, joints, muscles, and ligaments.
Regions of the Spine
The spine is typically divided into five main regions:
- Cervical
- Thoracic
- Lumbar
- Sacral
- Coccygeal
Each spinal region has distinct characteristics and functions.
Cervical Spine
The cervical spine is part of the human neck. It consists of seven vertebrae that protect the spinal cord, support the head, and allow for the neck’s significant flexibility.
- The first cervical vertebra is called the atlas, shaped like a ring.
- The second cervical vertebra is called the axis, which, as the name suggests, resembles an axis. It extends upward and fits into a specific position within the atlas.
- The atlas and axis allow the head to rotate, flex, and extend, accounting for about 50% of neck movement.
- The remaining cervical vertebrae (C3 to C7) do not have distinct anatomical features but are responsible for the other 50% of cervical mobility.
Thoracic Spine
The thoracic spine consists of 12 vertebrae, with the first located below the last cervical vertebra.
- As you move downward, the thoracic vertebrae increase in size: T1 is the smallest, while T12 is the largest.
- Each thoracic vertebra connects to a rib on the left and right, forming the rib cage when joined at the front with the sternum.
- The thoracic spine, along with the ribcage and sternum, protects the lungs and heart.
Lumbar Spine
The lumbar spine consists of five vertebrae (L1 to L5), increasing in size from top to bottom.
- The lumbar spine has greater mobility than the thoracic spine.
- Due to the orientation of its small joints, the lumbar spine primarily allows forward and lateral flexion, whereas rotational movement is limited compared to the thoracic spine.
Sacral Spine
The sacral spine (or sacrum) is commonly referred to as the tailbone in everyday language.
- It consists of five fused vertebrae (S1 to S5), forming a single bone.
- The sacrum connects the pelvis to the spine, acting as a link between the two.
- Below the sacrum is the coccyx.
Spinal Curvature
- When viewed from the front (frontal plane), the spine appears straight.
- When viewed from the side (sagittal plane), it has four curves classified as either kyphotic or lordotic.
- Kyphosis occurs naturally in the thoracic and sacral regions.
- Lordosis occurs naturally in the cervical and lumbar regions.
Vertebrae – Spinal Bodies
All vertebrae, except the first and second cervical ones, share the same fundamental structure:
- Outer layer: Cortical bone, which is hard, compact, and highly durable.
- Inner layer: Trabecular bone, which is softer and has a honeycomb-like structure.
- Bone marrow, located inside, produces red and some white blood cells.
Components of the Vertebrae
Each vertebra consists of the following elements:
- Vertebral body: The largest part, shaped like an hourglass, with a narrower middle section.
- Pedicles: Two small cylindrical structures extending from the vertebral body.
- Lamina: A bony plate extending between the pedicles, forming part of the vertebral canal.
Vertebrae – Processes and Facet Joints
- Each vertebra has seven processes extending from the lamina.
- Two articular processes per side (one facing up, one facing down) form the facet joints, which articulate with adjacent vertebrae.
- The facet joints are enclosed by a capsule filled with synovial fluid, acting as a lubricant.
- These joints:
- Facilitate movement and guide spinal motion.
- Limit excessive flexion and extension of the spine.
- Additional spinous and transverse processes provide attachment points for tendons and ligaments.
Vertebrae – Endplates
Other spinal structures include endplates, which are cartilage layers covering the top and bottom of each vertebral body.
- These plates surround and nourish the intervertebral discs by facilitating hydration and nutrient exchange.
Intervertebral Foramina
- The intervertebral foramen is the space between two adjacent vertebrae.
- This opening allows for the exit of spinal nerve roots, which then form nerve plexuses extending to the limbs.
Intervertebral Discs
Between the vertebral bodies are intervertebral discs, acting as shock absorbers. Their functions include:
- Absorbing movement-related loads.
- Holding vertebrae together.
- Receiving nutrients through osmosis from the endplates.
Each disc consists of:
- Annulus fibrosus (outer ring).
- Nucleus pulposus (inner core).
Annulus Fibrosus
- Structurally resembles a car tire:
- The outer ring is the annulus fibrosus.
- The soft center is the nucleus pulposus.
- It provides:
- Rotational stability.
- Compression resistance.
- Composed of collagen fibers, arranged in a woven pattern, similar to tire reinforcements, ensuring durability and stability.
Nucleus Pulposus
- The center of the disc contains a gel-like substance known as the nucleus pulposus.
- It distributes loads across the vertebrae.
- It is composed of:
- Water
- Collagen
- Proteoglycans
Spinal Cord and Nerve Roots
The spinal cord is an extension of the brain within the spinal canal:
- The brainstem, the lower part of the brain, transitions into the spinal cord at the upper cervical spine.
- The spinal cord extends to the L1 vertebra, after which it becomes the cauda equina (a bundle of nerve roots resembling a horse’s tail).
- Spinal nerves exit the spinal canal via intervertebral foramina and extend to the limbs.
The central nervous system consists of the brain and spinal cord, while the peripheral nervous system includes nerve roots, plexuses, and peripheral nerves.
Spinal Canal Stenosis
The spinal canal is the space between the vertebral body and lamina, housing the spinal cord. It may become narrowed (stenosis) due to:
- Disc herniation (bulging into the canal).
- Facet joint arthritis, leading to swollen joints occupying space in the spinal canal.
In such cases, the condition is referred to as spinal stenosis.
Χειρουργός Σπονδυλικής Στήλης
- Ο Χειρουργός Σπονδυλικής Στήλης/ Σκολίωσης Δρ. Ηλίας Χαρ. Παπαδόπουλος γεννήθηκε και μεγάλωσε στην Αθήνα. Αποφοίτησε με Άριστα από την Ιατρική Σχολή Αθηνών το 1994 και στη συνέχεια ειδικεύτηκε στην ορθοπαιδική, στην Α’ Ορθοπαιδική Κλινική του Πανεπιστημίου Αθηνών.
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