4th June 2023

Neuroanatomy of the spinal cord

Basic spinal cord anatomy

The spinal cord extends from the medulla oblongata in the brainstem to the conus medullaris at the level of L1-L2 in the lumbar spine. It then forms a fibrous extension called the filium terminale, connecting the conus medullaris to the coccyx, stabilising the spinal cord. The filum terminale is surrounded by a bundle of nerves forming the cauda equina.

The spinal cord and brain are surrounded by three layers of membranes known as the meninges. The pia mater is the innermost layer, tightly adherent to the surface of the brain and spinal cord. The arachnoid mater is the middle layer, and the space between the pia and the arachnoid mater is called the subarachnoid space; this space contains CSF. The outermost layer is the dura mater. The epidural space refers to the area between the dura mater and the surrounding vertebral wall, and contains small blood vessels, lymphatics, and adipose tissue.

Ascending and descending tracts

Ascending and descending tracts in the spinal cord are pathways which enable sensory and motor information to be relayed between the brain, spinal cord, and peripheral nervous system. Knowing where these tracts decussate and their location within the white matter is helpful in the localisation of lesions affecting these pathways.

Ascending tracts

The three main sensory modalities entering the spinal cord and their respective tracts are:

1. Pain and temperature – Spinothalamic tract
2. Proprioception and stereognosis – Dorsal columns
3. Light touch – Combination of spinothalamic tract and dorsal columns 

The spinothalamic tract decussates almost immediately after entering the spinal cord; this means that a lesion of the tract will result in loss of pain and temperature sensation contralaterally, below the level of the lesion. The dorsal columns decussate at the junction between the spinal cord and brainstem; therefore, a lesion of the dorsal column causes a decrease in conscious proprioception and stereognosis ipsilaterally below the level of the lesion. All of these sensory pathways eventually decussate and then terminate in the thalamus, which communicates with the sensory cortex.

Descending tracts

The motor (corticospinal) pathway travels from the motor area of the cerebral cortex down through the brain stem, crossing at the level of the medial lemniscus. It synapses in the anterior horn (motor grey matter) of the spinal cord just prior to leaving the cord. Lesions of the corticospinal tract in the spinal cord will result in weakness on the ipsilateral side.

Cross sectional anatomy of the spinal cord.

Image Source: Wikimedia Commons (2010). Spinal cord tracts – English, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Spinal_cord_tracts_-_English.png (Accessed on: 11 January 2023).