Loss of anal reflex suggests a lesion at which spinal segment levels?

Loss of anal reflex suggests a lesion at which spinal segment levels?

• A. Thoracic 8, 9, and 10
• B. Thoracic 10, 11, and 12
• C. Lumbar 5 and Sacral 1
• D. Sacral 2, 3, and 4

Answer: (D)

The anal reflex (anal wink) is a sacral reflex arc controlled by the spinal cord segments S2–S4 via the pudendal nerve to the external anal sphincter. Sensory input from the perianal skin travels to these sacral segments, and motor output goes from Onuf’s nucleus in S2–S4 through the pudendal nerve to cause contraction of the external anal sphincter. If these sacral levels are damaged or the pudendal pathways are affected, the reflex is lost. Lesions higher up in the thoracic region would not abolish this reflex because the reflex arc is localized to the sacral cord and its nerves. Among the options, only the sacral segments 2 through 4 encompass the necessary components of the reflex arc, so loss of the anal reflex points to involvement of those sacral levels.

The anal reflex (anal wink) is a sacral reflex arc controlled by the spinal cord segments S2–S4 via the pudendal nerve to the external anal sphincter. Sensory input from the perianal skin travels to these sacral segments, and motor output goes from Onuf’s nucleus in S2–S4 through the pudendal nerve to cause contraction of the external anal sphincter. If these sacral levels are damaged or the pudendal pathways are affected, the reflex is lost. Lesions higher up in the thoracic region would not abolish this reflex because the reflex arc is localized to the sacral cord and its nerves. Among the options, only the sacral segments 2 through 4 encompass the necessary components of the reflex arc, so loss of the anal reflex points to involvement of those sacral levels.