Horner syndrome results from disruption of which autonomic output?

Horner syndrome results from disruption of which autonomic output?

• A. Disruption of the sympathetic output
• B. Disruption of the parasympathetic output
• C. Disruption of somatic motor output
• D. Disruption of central cholinergic output

Answer: (A)

Horner syndrome reflects loss of the sympathetic output to the eye and face. The oculosympathetic pathway travels from the hypothalamus down to the spinal cord, then up to the superior cervical ganglion, and from there its fibers ride along the carotid arteries to reach the pupil dilator muscle and the sweat glands of the face. When this pathway is disrupted, the eye shows miosis (pupil constriction) due to loss of sympathetic dilation, and the eyelid droops modestly because Müller's muscle (which helps lift the eyelid) loses sympathetic input. The face may be less sweaty on the affected side due to loss of sympathetic innervation to sweat glands. These signs point to sympathetic disruption, not parasympathetic, somatic motor, or central cholinergic outputs. If the parasympathetic system were affected, you would expect pupil dilation rather than constriction.

Horner syndrome reflects loss of the sympathetic output to the eye and face. The oculosympathetic pathway travels from the hypothalamus down to the spinal cord, then up to the superior cervical ganglion, and from there its fibers ride along the carotid arteries to reach the pupil dilator muscle and the sweat glands of the face. When this pathway is disrupted, the eye shows miosis (pupil constriction) due to loss of sympathetic dilation, and the eyelid droops modestly because Müller's muscle (which helps lift the eyelid) loses sympathetic input. The face may be less sweaty on the affected side due to loss of sympathetic innervation to sweat glands. These signs point to sympathetic disruption, not parasympathetic, somatic motor, or central cholinergic outputs. If the parasympathetic system were affected, you would expect pupil dilation rather than constriction.