How is the vasomotor center structured?
The vasomotor center (VMC) is localized in the medulla oblongata.
The center includes two zones:
- Pressor zone (P).
- Depressor zone (D) — upon activation, it inhibits the pressor zone via inhibitory neurons and decreases cardiovascular activity.
The VMC participates in the reflex regulation of hemodynamics by receiving signals from vascular and cardiac receptors and transmitting commands via the autonomic nervous system.
How does the VMC lower high blood pressure?
This autoregulatory mechanism is called the depressor (baroreceptor) reflex. Its core purpose is to return blood pressure to baseline levels when it rises.
- Stimulus and reception: When blood pressure rises, baroreceptors of the aortic arch and carotid sinus are stimulated.
- Afferent pathway: The frequency of impulses (action potentials — ACh) increases along afferent fibers. The main conductor is the depressor nerve (N. depressor, a branch of the vagus nerve), which transmits the signal to the medulla oblongata.
- Central integration: In the VMC, the depressor region is excited, which inhibits the activity of the pressor region.
- Efferent pathway: The parasympathetic nervous system is activated (vagus nerve nuclei — N. vagus) and the sympathetic system is inhibited.
- Effect: Neural activity (NA) and cardiac function decrease — heart rate and contractility drop (bradycardia occurs). The tone of vascular smooth muscle decreases, leading to vasodilation. As a result, systemic blood pressure drops to the baseline level.
How does the VMC respond to increased venous pressure?
To adapt the heart to increased venous return, there is the unloading Bainbridge reflex (atrial stretch reflex). Its task is to return venous pressure (VP) to the baseline level.
- Stimulus and reception: Increased VP and blood volume in the openings of the venae cavae and the right atrium stimulate mechanoreceptors (stretch receptors).
- Afferent pathway: The increased frequency of action potentials (ACh) travels via vagus nerve fibers to the VMC.
- Central integration: In the medulla oblongata, the pressor region is excited and the depressor region is inhibited. Vagal nuclear tone decreases.
- Efferent pathway: The activity of the parasympathetic system (N. vagus) is inhibited. Simultaneously, the sympathetic nervous system (N. sympaticus) is activated. The sympathetic signal passes through the thoracic spinal cord (Th — Thoracic) to the heart.
- Effect: Neural activity (NA) increases — heart rate and contractility rise (tachycardia). The heart begins to pump the excess blood volume from the venous reservoir into the arterial system more rapidly, preventing congestion and lowering venous pressure.
Effectors and neurotransmitters of regulation
The reflex regulation scheme indicates the following neurotransmitters:
- Acetylcholine (ACh).
- Noradrenaline (NA).
Class and exam questions
Where is the vasomotor center located?
The vasomotor center (VMC) is located in the medulla oblongata.
What happens in the VMC when blood pressure rises?
When blood pressure rises, the depressor zone of the center is activated, which inhibits the pressor zone. This leads to the activation of the parasympathetic system, a decrease in cardiac activity, and vasodilation.
What is the essence of the Bainbridge reflex?
This is an unloading reflex that triggers when venous pressure rises and the right atrium stretches. The VMC activates the sympathetic system, causing tachycardia to pump blood into the arteries more quickly and lower venous pressure.
Which nerves serve as efferent pathways for the VMC?
Efferent signals are transmitted via the parasympathetic system (N. vagus) and sympathetic nerves (N. sympaticus). The sympathetic signal passes through the thoracic spinal cord.
What else to study on this topic
- Depressor reflex (baroreceptor reflex)
- Bainbridge reflex
- The autonomic nervous system in the regulation of blood circulation
- Vascular Bed Hemodynamics
Master the entire topic in the "Physiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on the topic "Vasomotor center (VMC)" and 4,128 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 114 video lessons on the subject
Other topics in "Physiology concepts"
Free video lessons: PhysiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.