The spinal cord is a tubular structure composed of nervous tissue that extends from the brainstem and continuing distally before tapering at the lower thoracic/upper lumbar region as the conus medullaris. The spinal cord is anchored distally by the filum terminale, a fibrous extension of the pia mater anchoring the spinal cord to the coccyx. Protecting the spinal cord is the surrounding cerebrospinal fluid (CSF), supportive soft tissue membranes and meninges, and the osseous vertebral column. A basic knowledge of the structure and function of the spinal cord and spinal column is essential for healthcare providers as the recognition of characteristic clinical signs and symptoms is imperative for the appropriate treatment of patients presenting with a wide range of clinical symptoms.
Meninges and Spaces
After the 3rd week of development, there is a fusion of the neural folds into a tube (neurulation); the neural tube then closes completely at day 28 and forms the brain and the spinal cord.
The caudal neural tube's cross-sectional view initially appears diamond shaped, lined by neuroepithelial cells, which divide and multiply into neuroblasts that populate surrounding areas called the mantle zone, which eventually forms the gray mater. Divided neuroepithelial cells now form the ependymal lining of the central spinal canal with roles in CSF production.
The mantle zone differentiates into - basal plate, alar plate, and intermediolateral plate. More lateral parts form into the marginal zone which becomes the white mater with ascending and descending myelinated fibers.
The basal plates differentiate into the anterior or ventral gray horn. Multipolar neurons in the anterior horn are first-order neurons and give off motor fibers that exit the spinal segments and become myelinated by Schwann cells (derivative of neural crest cells).
The alar plates differentiate into the posterior or dorsal gray horn. They comprise second order pseudo-unipolar neurons, which receive sensory communication from first-order neurons derived from neural crest-derived dorsal ganglia.
The intermediolateral plates in cervical and thoracic regions are populated by pre-ganglion neurons which give off fibers exiting ventrally onto the sympathetic trunk.
Radiculo-medullary branches from the anterior and posterior spinal arteries and the costocervical trunk anastomose to supply the cervical region of the spinal cord. The thoracolumbar segments of the spinal cord receive extra arterial blood supply through radiculo-medullary branches of segmental arteries from the aorta; of note is the great radicular artery called Adamkiewicz artery. It has a variable origin arising anywhere between T9 and L5 vertebra.
There are 31 spinal nerve pairs (mixed) that arise from the intervertebral foramen on both sides of the vertebral column.
Nerves from the lower spinal segment exit terminal to the conus medullaris and form the cauda equina.
Ventral spinal nerve roots - make up the motor component of the spinal innervation with rootlets arising from the anterior horn of the spinal segment, sending motor impulses to muscles and joints, etc
Dorsal spinal nerve roots - make up the sensory component, with the dorsal ganglia sending sensory impulses via nerve rootlets to the posterior horn of spinal segments.
In general, the extent of disability depends on the level of injury and underlying degree of severity of the corresponding clinical pathology. For example, injuries at the levels of the cervical segment affect both upper and lower limbs while lesions from thoracic segments downwards affect the lower limb.
Spinal cord injury (SCI) patterns
Incomplete spinal cord injuries (SCIs)