Spine Overview

Spine Anatomy Overview

The spine extends from the base of the skull to the posterior pelvis and is composed of 33 vertebrae, categorized into five segments: the cervical spine (C1-C7), thoracic spine (T1-T12), lumbar spine (L1-L5), sacrum (S1-S5), and coccyx (3-5). In adults, the sacrum and coccyx are fused, a feature visible in the accompanying image.
The primary function of the vertebral column is to protect the spinal cord within the vertebral canal and distribute the body's weight to the pelvis.
The spine exhibits a double-S shape with two types of curvature: kyphosis and lordosis. The cervical and lumbar regions exhibit lordosis, characterized by a concave posterior curve (curve inward). The thoracic and sacral regions exhibit kyphosis, with a convex posterior curve (curve outward).
Exaggerated versions of these curves, known as hyperlordosis and hyperkyphosis, can lead to back pain and altered posture. Scoliosis, an abnormal lateral curvature of the spine typically identified during adolescence, is another condition that can affect spinal alignment.

Vertebrae

There are features that are common to all vertebral segments and others that are unique to each level, which will be discussed in their respective sections.
The basic components of each vertebra include the vertebral body (anterior), vertebral arch (posterior), and vertebral foramen (middle, housing the spinal cord).
A primary role of the vertebral column is to support and bear the body's weight. Vertebral bodies connect (articulate) with one another via intervertebral discs (discussed below).
The vertebral arch encloses the spinal cord and consists of 2 pedicles (lateral), 2 laminae (posterior), 2 transverse processes (lateral), and 1 spinous process (medial).
On the superior and inferior sides of each vertebra, concavities called vertebral notches form intervertebral foramina, where spinal nerves and vessels exit the spinal canal.
Each vertebra also has articular processes located superiorly and inferiorly, which articulate with the adjacent vertebra to form facet joints (zygapophysial joints).
The term "pars interarticularis," meaning "the part between the articulations" describes the region located between the superior and inferior articular processes of 2 vertebrae.
The superior and inferior portions of the vertebral body are known as end plates, which are thin layers of hyaline cartilage that nourish the adjacent disk.

Clinical correlates:

- Spinous processes can be palpated to pinpoint specific spinal cord regions during procedures like spinal anesthesia or lumbar puncture.
- Laminectomy is a procedure involving surgical removal of both laminae to access the spinal canal.
- Over time, arthritis and the formation of osteophytes can narrow the intervertebral foramina, leading to compression of spinal nerves (known as radiculopathy).

Intervertebral Disc

Each vertebral body is connected to the next by an intervertebral disc made of cartilage.
The main function of the intervertebral disc is shock absorption.
Each disc consists of two parts: the annulus fibrosus, which forms the outer portion with concentric fibrocartilaginous fibers, and the nucleus pulposus, which forms the central portion containing a gelatinous mixture of water and proteoglycans.

Vertebral Ligaments

The vertebral column is supported by several ligaments, which may be injured and are important to know in the setting of spine procedures.
Anterior longitudinal = limits spine extension and supports the anterior portion of the intervertebral disc.
Posterior longitudinal = limits spine flexion
Ligamentum flavum = forms the posterior wall of the spinal canal.
Interspinous ligament = limits spine flexion.
Supraspinous ligament = limits spine flexion and connects the tips of the spinous processes.

During a lumbar puncture, a needle passes through the following structures to reach the target subarachnoid space: skin > adipose tissue > supraspinous ligament > interspinous ligament > ligamentum flavum > epidural space > dura mater > arachnoid mater.

Spinal Cord and Nerves

The central nervous system consists of the brain and spinal cord. The spinal cord's primary function is to transmit motor, sensory, and reflex signals to and from the body.
The spinal cord is located within the spinal canal (vertebral foramen) and runs from the brainstem until it terminates in the lumbar region of the spinal canal.
The conus medullaris is the inferior end of the spinal cord located around the L2 vertebral level. Inferior to the conus medullaris is the cauda equina, a bundle of spinal nerves that continue to run through the spinal canal and exit out of their respective intervertebral foramina.
The filum terminale is composed of pia mater and attaches the conus medullaris to the most inferior portion of the spinal canal for stability. The structures listed above are depicted and discussed in detail here.
There are 31 pairs of spinal nerves, each exiting the spinal canal based on its region:
- 8 cervical pairs: the first 7 exit superior to the cervical vertebrae, while the 8th exits below the 7th vertebra (there are 7 cervical vertebrae but 8 cervical spinal nerve pairs).
- 12 thoracic pairs: exit inferior to the 12 thoracic vertebrae.
- 5 lumbar pairs: exit inferior to the 5 lumbar vertebrae.
- 5 sacral pairs: exit inferior to the 5 sacral vertebrae.
- 1 coccygeal pair; exits the sacrum inferior to the first coccygeal segment.
Each pair of spinal nerves receives sensory input from specific skin regions known as "dermatomes" (shown in the accompanying image).

Vertebral Column Introduction

Vertebral Column Anatomy and Bones

References:

1: Anatomy and Physiology. OpenStax. Rice University. 2017. https://openstax.org/details/books/anatomy-and-physiology

2: Gray's Anatomy of the Human Body. Henry Gray. 1918. https://www.bartleby.com/107/

3: Youtube video: Vertebral Column Introduction

4: Youtube video: Vertebral Column Anatomy and Bones

Page updated

Google Sites

Report abuse