sinusnerve

The sinusnerve, also known as the carotid sinus nerve or Hering's nerve, is a small sensory branch of the glossopharyngeal nerve (cranial nerve IX) that supplies the carotid sinus and, to a lesser extent, the carotid body. It carries afferent information from the arterial baroreceptors and chemoreceptors in the carotid sinus to the brainstem.

Anatomy and function: The sinusnerve arises from branches of CN IX in the neck and projects to the carotid sinus, transmitting sensory signals to the nucleus tractus solitarius in the medulla. Its primary role is in the baroreceptor reflex, whereby changes in arterial pressure are detected by the carotid sinus. When arterial pressure rises, increased firing from the sinusnerve leads to a autonomic response that reduces sympathetic outflow and increases parasympathetic activity, resulting in lowered heart rate and vasodilation to help restore blood pressure. Carotid body chemoreceptors, which detect changes in blood oxygen, carbon dioxide, and pH, also send information through related pathways that influence respiratory and cardiovascular reflexes.

Clinical significance: The carotid sinus nerve is involved in procedures such as carotid sinus massage, which can transiently slow the heart or reduce blood pressure by enhancing baroreflex activity. Hypersensitivity of the carotid sinus (carotid sinus syndrome) can cause syncope with minimal stimulation and is of particular concern in older individuals or those with carotid artery disease. Injury or surgical manipulation of the sinusnerve can impair baroreceptor signaling and blood pressure regulation.

History and terminology: The nerve is frequently referred to as the carotid sinus nerve and is commonly described as Hering's nerve in classic anatomical texts.