Which of the following reflexes would be considered abnormal in an adult?
a. Biceps reflex
b. Plantar reflex
c. Anal reflex
d. Babinski’s reflex
The Correct Answer and Explanation is:
The correct answer is: d. Babinski’s reflex
Explanation
The Babinski reflex is a diagnostic sign that involves stroking the sole of the foot and observing the response of the toes. In infants, a normal response is dorsiflexion of the big toe (upward movement) and fanning out of the other toes. This is due to the immaturity of the corticospinal tract, a major pathway for motor control.
However, in adults, the normal response is plantar flexion of the toes (downward movement). If an adult exhibits dorsiflexion of the big toe and fanning of the other toes—a positive Babinski sign—it is considered abnormal and suggests neurological dysfunction, particularly involving the upper motor neurons of the corticospinal tract. This could indicate conditions such as multiple sclerosis, stroke, spinal cord injury, or brain tumors.
In contrast, the biceps reflex, plantar reflex, and anal reflex are typically normal reflexes in a healthy adult:
- Biceps reflex (elicited by tapping the biceps tendon) results in flexion of the elbow. It assesses the integrity of the C5-C6 spinal segments.
- Plantar reflex (not to be confused with the Babinski sign) involves stroking the sole of the foot and observing a normal downward curling of the toes.
- Anal reflex (or anal wink) involves contraction of the anal sphincter in response to stimulation of the perianal skin and is used to assess the integrity of the S2–S4 spinal segments.
Thus, while the Babinski reflex is normal in infants up to about 1–2 years old, its persistence or appearance in adults is a red flag for potential central nervous system pathology. Therefore, Babinski’s reflex is considered abnormal in an adult, making option d the correct answer.
