What is the neurotransmitter for sympathetic innervation of the heart?

• A. Acetylcholine
• B. Norepinephrine
• C. Dopamine
• D. Serotonin

Answer: (B)

The neurotransmitter responsible for sympathetic innervation of the heart is norepinephrine. In the sympathetic nervous system, norepinephrine is released from sympathetic nerve endings and acts on adrenergic receptors in the heart, leading to an increase in heart rate and contractility. This process is part of the body's "fight or flight" response, where the heart needs to pump more blood to prepare for physical activity or stress.

Norepinephrine binds primarily to beta-1 adrenergic receptors located in the cardiac tissue, leading to enhanced cardiac function. This is crucial for understanding how the body's autonomic nervous system regulates heart activity, especially during times of increased demand.

Other neurotransmitters listed, such as acetylcholine, play roles in different aspects of the autonomic nervous system, like parasympathetic innervation, but do not mediate sympathetic responses in the heart. Dopamine and serotonin have their own distinct functions and are not directly involved in sympathetic stimulation of cardiac activity. Understanding these distinctions clarifies the role of norepinephrine specifically in the context of sympathetic cardiac innervation.