Carotid sinus nerve

Carotid sinus nerve (a.k.a. the sinus nerve of Hering) is a branch of the glossopharyngeal nerve which innervates the carotid sinus and carotid body. It is a sensory nerve and contains general visceral afferent neurons.

Carotid sinus is a neurovascular structure formed by the dilatation of adjoining parts of common carotid and internal carotid arteries. It contains baroreceptors, which are stretch receptors, that get stimulated by the mechanical stretch caused by a rise in arterial blood pressure. They help mediate the carotid sinus baroreflex, wherein the general visceral afferent neurons within the carotid sinus nerve, transmit sensory information of stretch from the baroreceptors (in the carotid sinus) to the nucleus of tractus solitarius in the brainstem. The efferent signals are transmitted via the parasympathetic and sympathetic outflows to the heart and the blood vessels that bring about corresponding changes in heart rate and blood pressure to maintain these within physiological limits. For instance, an increased stretch would lead to reflex bradycardia and systemic vasodilation.

An additional structure innervated by the carotid sinus nerve includes the carotid body, which is a sensory chemoreceptor situated inside the adventitia of the bifurcation of common carotid artery. The chemoreceptors get stimulated by a decrease in arterial oxygen level and help mediate carotid chemoreflex, wherein the general visceral afferent neurons within the carotid sinus nerve, transmit sensory information of low blood oxygen saturation to the nucleus of tractus solitarius in the brainstem. The efferent outflow comprises of sympathetic neurons which increase the heart rate and blood pressure.