Question

The frequency of action potentials sent from baroreceptors to the brain_________ when blood volume is decreased, resulting in __________ heart rate. a. increases, an increased b. increases, a decreased c. decreases, an increased d. decreases, a decreased

Short answer

The correct answer is c. decreases, an increased

Step-by-step solution

Understanding the role of baroreceptors

Baroreceptors are special sensors in the walls of blood vessels that detect changes in blood pressure. If blood volume decreases, these baroreceptors perceive a corresponding fall in blood pressure.

Frequency of action potentials.

In response to lowered blood pressure, the frequency of action potentials sent from the baroreceptors to the brain decreases.

Response to the decrease in blood volume

With a decrease in the frequency of action potentials, the brain perceives less pressure. It responds by stimulating mechanisms to increase the heart rate in an attempt to restore the blood pressure to normal.

Key concepts

Action Potentials in Baroreceptors

Baroreceptors play a crucial role in monitoring and regulating blood pressure in the body. They are stretch-sensitive mechanoreceptors primarily located within the carotid sinuses and aortic arch and are sensitive to the stretching of vessel walls caused by blood pressure changes.

When blood pressure increases, the walls of these vessels stretch more, activating the baroreceptors to generate more frequent action potentials. These action potentials are electrical signals that travel through the nervous system to the brain, particularly to the cardiovascular centers of the medulla oblongata.

Mechanism of Action Potential Generation

As the blood vessel walls stretch, ion channels within the baroreceptors open, leading to depolarization. This change in electrical charge triggers the generation of action potentials. The frequency of action potentials is directly proportional to the stretch—meaning the higher the pressure, the more frequent the action potentials. Conversely, when blood pressure drops, the frequency diminishes.

Blood Volume Decrease

Blood volume and blood pressure are directly related. When there is a decrease in blood volume, such as from bleeding, dehydration, or other causes, blood pressure typically falls. This condition can trigger a physiological response to restore homeostasis.

The Impact of Reduced Blood Volume

Reduced blood volume leads to less distension of the arteries where baroreceptors are located. As a result, the baroreceptors become less activated and generate fewer action potentials. The brain interprets this reduced signaling rate as an indication that blood pressure is too low, prompting corrective actions.

• Compensation Mechanisms: To combat the decreased blood volume—and consequently blood pressure—the body can initiate several responses, including releasing hormones like adrenaline, retaining water and sodium in the kidneys, and increasing the heart rate to attempt to raise the blood pressure back to an adequate level.

Heart Rate Regulation

Heart rate regulation is a dynamic process that ensures that the circulation meets the body's demand for oxygen and nutrients. It involves multiple sensors, pathways, and effectors, including the autonomic nervous system.

Autonomic Influence on Heart Rate

The autonomic nervous system, with its sympathetic and parasympathetic branches, plays a critical role in adjusting the heart rate. An increased heart rate is generally a result of enhanced sympathetic activity and reduced parasympathetic influence on the heart.

• Sympathetic Response: During a state of decreased blood volume and pressure, the sympathetic nervous system is activated. This causes the release of catecholamines, which increases heart rate and force of contraction, thus attempting to raise blood pressure.
• Parasympathetic Response: Conversely, when blood volume and pressure are high, the parasympathetic system predominates, slowing down the heart rate to reduce blood pressure and conserve energy.

Therefore, when baroreceptors detect a decrease in blood pressure due to reduced blood volume, the sympathetic response is to increase the heart rate, as the decreased rate of action potentials signals a need to elevate blood pressure.