Human root and cord potentials evoked by Achilles tendon tap

Area of Science:

• Neuroscience
• Physiology
• Biomedical Engineering

Background:

• Understanding neural pathways is crucial for diagnosing and treating neurological disorders.
• The Achilles tendon reflex and H-reflex are valuable tools for assessing sacral spinal cord function.

Purpose of the Study:

• To compare the sacral spinal cord responses to mechanical (Achilles tendon tap) and electrical (posterior tibial nerve stimulation) stimuli.
• To investigate the differences in conduction times and delays within the sacral cord for these two reflex pathways.

Main Methods:

• Recorded epidural lumbosacral root and sacral spinal cord potentials in 24 healthy adults.
• Utilized mechanical tapping of the Achilles tendon and electrical stimulation of the posterior tibial nerve.
• Analyzed averaged responses and compared latencies and conduction times.

Main Results:

• Electrical stimulation readily evoked dorsal and ventral root responses.
• Mechanical stimulation produced a late, small ventral root response with two negative deflections.
• Mechanical stimulation resulted in a 4.0 msec delay in ventral root responses and Soleus reflexes compared to electrical stimulation.
• Sacral cord conduction delay was 1.8 msec for the H-reflex and 4.1 msec for the Achilles tendon reflex.

Conclusions:

• The Achilles tendon reflex exhibits a significantly longer sacral cord conduction delay than the H-reflex.
• This prolonged delay may be attributed to the oligosynaptic nature of the Achilles tendon reflex or dispersed afferent volleys.
• Findings provide insights into the differential processing of sensory information within the sacral spinal cord.