What is the Reticulospinal Tract?

Reticulospinal Tract: Coordinating Reflexes, Posture & Rhythmic Movement

The reticulospinal tract is a crucial pathway in the central nervous system, conveying motor commands from your brainstem to your spinal cord. This tract has an important role in maintaining posture, initiating locomotion, and regulating reflexes. It originates from the reticular formation, which is a network of neurons in the brainstem that acts as an integration center, receiving inputs from both cortical (voluntary) and subcortical (involuntary/automatic) regions.

Anatomy and Origin of the Reticulospinal Tract

The reticulospinal tract originates from the reticular formation, which is a complex network of nuclei located in your brainstem. Moreover, lateral and medial reticulospinal tracts are the two most common reticulospinal pathways:

• Medial (Pontine) Reticulospinal Tract : This tract originates from the pontine reticular formation and descends ipsilaterally (i.e., on the same side of the body) through the anterior funiculus in the spinal cord. The medial reticulospinal tract mainly facilitates the extensor motor neurones.
• Lateral (Medullary) Reticulospinal Tract : This tract stands to inhibit extensor muscles and facilitate flexors. Thus, the lateral reticulospinal tract inhibits antigravity extensors to allow for voluntary, flexor-dominant movements and contributes to coordinated motor control.

Functions and Neurological Roles of the Reticulospinal Tract

The reticulospinal tract provides a few physiological motor and regulatory functions:

• Postural Control : It regulates the tone of proximal limb and axial muscles to ensure stability in standing postures and moving postures, such as walking. The medial tract is important in maintaining upright postural stability against gravity.
• Locomotion : This tract works in conjunction with the corticospinal tract and central pattern generators (CPGs) in your spinal cord for initiating movement and continued rhythmic movements, such as walking. One way this tract mediates locomotion is that it helps synchronise bilateral limb movements by regulating networks in the spinal cord.
• Reflex Modulation : This tract also plays a regulatory role concerning spinal reflexes. It accomplishes this by acting on the interneurons in the spinal cord to boost or dampen reflexive responses, depending on the situational demands.
• Autonomic and Respiratory Regulation : The reticulospinal tract has indirect effects on autonomic regulation. It is not its primary function. Rather, it integrates with other pathways that feed into cardiovascular and respiratory centres.

Clinical Significance and Disorders of the Reticulospinal Tract

Damage to this tract can lead to motor control and coordination difficulties in individuals with neurological conditions such as stroke, traumatic brain injury, and neurodegenerative diseases. These challenges may present clinically in the following ways:

• Spasticity and Hyperreflexia : Following upper motor neurone injury (e.g., after stroke), the reticulospinal tract could contribute to overactivity due to a lack of inhibition from the higher centres, which may increase muscle tone and elicit hyper-reflexive responses.
• Impaired Postural Reflexes : Lesions affecting the medial reticulospinal tract may impair a subject's stability. Lesions affecting the medial tracts may not provide a good sense of stability; when combined with anti-gravity movement against a perturbed position, individuals may demonstrate increased fall risk.
• Motor Recovery : Based on the retrospective evidence, this tract may indirectly contribute to motor recovery following an injury to a descending corticospinal tract pathway. The reticulospinal tract serves as an alternative pathway that helps maintain voluntary movement by preventing disturbances, especially when other motor pathways are impaired.

Rehabilitation strategies, such as task-specific training and neuromodulation, are increasingly focusing on enhancing reticulospinal activity to support recovery in patients with corticospinal tract damage. However, this pathway does not carry the same specificity found in the corticospinal pathway. Imprecise reticulospinal input may produce crude, stereotyped movements characterized by abnormal limb synergies (e.g., mass flexion patterns), which lack the fine motor control typically mediated by the corticospinal tract.

The reticulospinal tract is a major element of the motor system and serves as a connection between automatic postural adjustments to the cortical areas that plan voluntary movements. It provides a transitional opportunity to integrate cortical, sensory, and subcortical signals for fluent, stable, and adaptable human movement.