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Depressor Reflex

Reflexus depressorius

For medical students2 min readUpdated 2026-10-10

The depressor reflex (also known as the baroreceptor reflex) is a fundamental physiological self-regulatory mechanism aimed at reducing abnormally high blood pressure. The primary function of this mechanism is to rapidly return hemodynamic parameters to baseline levels.

StimulusIncreased blood pressure
ReceptorsBaroreceptors of the aortic arch and carotid sinus
CenterVasomotor center of the medulla oblongata
ResultReduction of blood pressure to normal values

Initiating the Reflex: Stimulus and Afferent Pathway

Every reflex begins with a stimulus. For the depressor reflex, the specific stimulus is a sudden increase in systemic blood pressure. This pressure surge leads to mechanical stretching of the vessel wall.

Sensitive nerve endings, known as baroreceptors, are located in key reflexogenic zones: the aortic arch and the carotid sinus. When the vessel is stretched, these receptors are instantly stimulated, generating a nerve impulse. The higher the blood pressure rises, the greater the frequency of firing along the afferent (sensory) fibers.

The primary pathway transmitting this signal upward is the depressor nerve (N. depressor), which is a branch of the vagus nerve. Through this nerve, the stream of impulses rapidly heads toward brain structures for subsequent processing.

Central Regulation: Function of the Vasomotor Center

The afferent signal reaches the medulla oblongata, which houses the vasomotor center (VMC). This center has a complex structure and is functionally divided into zones that operate reciprocally (mutually exclusive principles).

Impulses arriving from the baroreceptors activate the depressor area of the center. Once the depressor region is excited, it immediately exerts an inhibitory influence on the pressor area. Thus, mechanisms that lower blood pressure are activated simultaneously while structures that could raise it are suppressed. This strict balance allows the nervous system to precisely adjust the state of circulation.

Efferent Pathway and Target Organ Response

Following information processing in the medulla oblongata, a response command is formed and transmitted to the effector organs via the autonomic nervous system. This process proceeds along two parallel pathways:

  1. Activation of the parasympathetic system. Excitation of the vagus nerve (N. vagus) nuclei occurs, with impulses directed toward the heart.
  2. Inhibition of the sympathetic system. Signals maintaining vascular tone and cardiac activity are blocked at the level of the spinal cord and sympathetic ganglia.

As a result, the function of the main target organs changes:

The logical outcome of decreased cardiac output and dropped vascular resistance is the normalization of systemic blood pressure.

Mnemonic

It is easy to remember the autonomic nervous system response using the "brake and gas" principle: when blood pressure is high, the body steps on the "brake" (exciting the parasympathetic system and depressor center) and releases the "gas" (inhibiting the sympathetic system and pressor center).

Frequently asked questions

Through which nerve does afferent impulse traffic from the carotid sinus travel?

Afferent impulse traffic from the carotid sinus is carried out via Hering's depressor nerve.

Main conduction pathways:

  • Hering's nerve (sinus nerve) — branches directly from the carotid sinus receptors.
  • Glossopharyngeal nerve (n. glossopharyngeus) — incorporates fibers of Hering's nerve, through which impulses enter the vasomotor center of the medulla oblongata.
Which neurotransmitters are released in the effector synapses of target organs during the depressor reflex?

The following neurotransmitters are indicated for the autonomic nervous system links in target organ effector synapses:

  • Acetylcholine — released by postganglionic parasympathetic nerve endings. During the depressor reflex, the parasympathetic system is excited; the cardiac effect is inhibition of cardiac activity, decreased heart rate/bradycardia.
  • Norepinephrine — the neurotransmitter of postganglionic sympathetic nerve endings. During the depressor reflex, the sympathetic nervous system is inhibited; net effects include decreased vascular tone and reduced blood pressure.
Where are the receptors that trigger the depressor reflex located?

Baroreceptors responding to increased pressure are localized primarily in the walls of the aortic arch and the region of the carotid sinus.

Through which nerve does the afferent signal travel to the brain?

Impulses from the vessels are transmitted to the medulla oblongata via the depressor nerve (N. depressor), which is a branch of the vagus nerve.

What does the efferent signal lead to in this reflex?

The efferent signal causes a decrease in heart rate and contractility (bradycardia), as well as relaxation of vascular smooth muscle, leading to vasodilation.

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