Question

Assertion: If we cut nerve supply to human heart, there will be no effect on heart beat. Reason: Human heart is myogenic in nature.

Short answer

The assertion is partially true - the human heart can generally continue to beat if its nerve supply is cut, due to its myogenic nature. However, the nerve supply can influence the rate of heart beats, so cutting it off might affect the heart beat rate.

Step-by-step solution

Understanding the Assertion

The assertion suggests that if the nerve supply to the human heart is cut, there will be no effect on the heart beat. So, one has to know how the human heart functions and what role nerve supply plays in heart beats.

Understanding the Reason

The reason stated is that the human heart is myogenic. 'Myogenic' means that the muscle tissue itself is responsible for its own rhythm and synchronization of its contractions. So, in the case of the heart, which is a muscular organ, it generates its own electrical impulses that lead to muscle contractions, allowing it to beat. This doesn't rely on nerve signals from the rest of the body.

Connecting the Assertion and the Reason

Linking the understanding from step 1 and 2, it can be concluded that since the human heart can generate its own rhythm thanks to its myogenic nature, it may continue to beat even if its nerve supply is cut off. However, this doesn't mean that nerve signals have no effect on the heart at all. Nerves from the nervous system can affect the rate of heart beats, but they aren't responsible for initiating them.

Key concepts

Myogenic Heart

The term 'myogenic' refers to the heart’s ability to generate electrical impulses independently. This ability allows the heart to beat without requiring signals from the nervous system.

The human heart possesses this intrinsic mechanism primarily due to specialized cells known as pacemaker cells. Found in the sinoatrial (SA) node, these cells spontaneously produce an electrical impulse.

• This impulse initiates a wave that travels across the heart, leading to muscle contractions.
• The heart can thus maintain a consistent rhythm, unaffected by external nerve connections.

This self-regulating nature underscores the robustness of the heart, providing a steady beat vital for sustaining life.

Nerve Supply to Heart

Although the heart is inherently myogenic, nerves play a key role in modulating the heart's rhythm. The autonomic nervous system innervates the heart, using two main components.

These are:

• The sympathetic nervous system, which increases the heart rate during stress or physical activity.
• The parasympathetic nervous system, which decreases the heart rate during rest.

Nevertheless, if the nerve supply is severed, the heart will continue beating at its inherent pace.

This showcases the heart's independence, as its primary function persists even without external neural inputs, albeit at a potentially different rate.

Heartbeat Regulation

Regulating the heartbeat is a sophisticated process involving both intrinsic and extrinsic factors. Intrinsic regulation stems from the myogenic nature of the heart, maintaining a basic rhythm autonomously.

Extrinsic factors come from the nervous system and hormones such as adrenaline, which can alter the heart's speed. Thus, while the heartbeat originates from within the heart, external factors finely tune it.

• During exercise, neural mechanisms increase the heart rate to supply more oxygen to muscles.
• In a calm state, the system slows the heart, conserving energy.

This dynamic adjustment ensures the heart meets the body's changing needs efficiently. Therefore, even though the heart can beat independently, its performance is profoundly affected by external regulation.