Problem 110 - Objective Biology for NEET

Question

Parasympathetic neural signal decreases the cardiac output by (a) Decreasing the rate of heartbeat (b) Decreasing the speed conduction of action potential (c) Both (a) and (b) (d) Increasing adrenal medulla hormones secretion

Step-by-Step Solution

Answer

The correct answer is (c) Both (a) and (b). The parasympathetic neural signal decreases both the rate of heartbeat and the speed conduction of action potential.

Step 1: Understanding the Parasympathetic Nervous System

The Parasympathetic Nervous System is a part of the Autonomic Nervous System. It is responsible for 'rest and digest' functions. That means, it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.

Step 2: Effect on Heart Rate

The Parasympathetic Nervous System decreases the heart rate. This happens because it releases a neurotransmitter called Acetylcholine which slows the pulse.

Step 3: Effect on Speed Conduction of Action Potential

The Parasympathetic Nervous System also decreases the speed conduction of action potential. This happens due to the aforementioned Acetylcholine limiting the speed of electrical impulses travelling through the heart.

Step 4: Achieving the Answer

With the above information, it is evident that both the heart rate and speed conduction of action potential decrease under the influence of the parasympathetic neural signal. So, the correct answer is (c) Both (a) and (b).

Key Concepts

Cardiac Output

Cardiac output is an essential indicator of heart performance. It is the volume of blood the heart pumps out per minute. Generally, cardiac output can be calculated by multiplying the heart rate and stroke volume. Here, heart rate refers to the number of beats per minute, while stroke volume is the amount of blood pumped with each beat.

• An increase in either heart rate or stroke volume leads to a higher cardiac output.
• Conversely, when the heart rate or stroke volume drops, cardiac output decreases.

The parasympathetic nervous system's role becomes evident in controlling cardiac output, as it primarily works to decrease heart rate through its calming signals to the heart.

Heart Rate

Heart rate determines how many times the heart beats in a minute and is crucial for maintaining proper blood circulation in the body. Different factors can influence heart rate, including physical activity, emotional stress, and neural regulation.

• Parasympathetic Nervous System: It plays a significant role in slowing down the heart rate, primarily through the release of acetylcholine, a neurotransmitter that connects with heart cells to reduce beats per minute.
• When the parasympathetic nervous system is active, you would typically experience a slower heart rate, aiding in energy conservation and facilitating recovery.

A decreased heart rate means the heart doesn't have to work as hard, although it pumps less frequently. This is typically seen in resting and relaxed states.

Action Potential

Action potentials are critical electrical impulses that pass through nerve fibers to initiate contraction in heart muscle cells. They determine the pace at which your heart beats by controlling the rhythm of cardiac cycles.

• Speed of Conduction: The rate at which these action potentials move along the heart's conduction pathways can significantly affect heart function.
• Parasympathetic Influence: Through the influence of acetylcholine, the parasympathetic nervous system can slow down these action potentials, leading to a reduced heart rate and cardiac output.

Thus, alterations in action potential conduction speeds are part of how the body regulates the heart's activity, adapting to different states like rest or stress.

Autonomic Nervous System

The Autonomic Nervous System (ANS) manages involuntary body processes like heart rate, digestion, and respiratory rate. It's divided into two parts: the sympathetic nervous system and the parasympathetic nervous system.

• Sympathetic Nervous System: Often known as the "fight or flight" system, it prepares the body for stressful situations by increasing heart rate, among other functions.
• Parasympathetic Nervous System: Known as the "rest and digest" system, it counteracts the sympathetic system effects by slowing the heart rate and aiding with digestion.

Understanding the balance between these two systems is paramount as they operate continuously to maintain homeostasis. Their influence on heart rate and cardiac output is vital in managing overall cardiovascular health.