Biology · Body Fluids and Circulation · NEET
The brain does NOT start the heartbeat. The heart is myogenic, meaning the beat is generated by the SA node (nodal tissue) inside the heart itself. That is why a frog's heart keeps beating even after it is removed from the body. The neural centre in the medulla oblongata only moderates (adjusts) this beat through the autonomic nervous system. So nerves are modifiers, not the pacemaker.
Sympathetic nerves increase the heart rate, increase the strength of ventricular contraction, and therefore increase cardiac output. Parasympathetic nerves do the opposite: they decrease the heart rate, decrease the speed of conduction of the action potential, and therefore decrease cardiac output. Simple way to remember: Sympathetic = accelerator, Parasympathetic = brake.
The medulla oblongata. NCERT clearly states a special neural centre in the medulla oblongata moderates cardiac function through the autonomic nervous system. It is NOT the cerebrum, cerebellum or hypothalamus. This is a very common trap in options.
It is the adrenal MEDULLA. Its hormones (adrenaline and noradrenaline) can increase cardiac output. The adrenal cortex (which makes cortisol, aldosterone, etc.) does NOT directly regulate heart rate. NEET 2025 tested exactly this by putting 'adrenal cortical hormones' as a wrong option.
These two facts do not conflict. Myogenic means the origin of the beat is muscular (SA node), so the heart is self-exciting. But how fast or strong that beat runs can still be tuned up or down by the autonomic nerves and by adrenal medullary hormones. Origin = heart; adjustment = nerves and hormones.
Cardiac activities of the heart are regulated by: A. Nodal tissue B. A special neural centre in the medulla oblongata C. Adrenal medullary hormones D. Adrenal cortical hormones Choose the correct answer from the options given below:
Frog's heart when taken out of the body continues to beat for some time. Select the best option from the following statements: (a) Frog is a poikilotherm (b) Frog does not have any coronary circulation (c) Heart is 'myogenic' in nature (d) Heart is autoexcitable Choose the correct option:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The human heart is myogenic. The beat originates in the nodal tissue (SA node), not from nerves. Nerves and hormones only speed it up or slow it down.
The parasympathetic nerve (vagus supply) slows the heart. It decreases heart rate, decreases the speed of conduction of the action potential, and lowers cardiac output.
Adrenal medullary hormones (adrenaline and noradrenaline) increase cardiac output. Remember it is the adrenal medulla, not the adrenal cortex.
A special neural centre in the medulla oblongata moderates cardiac function through the autonomic nervous system, increasing or decreasing heart rate as the body needs.
NEET repeatedly frames statement-based and 'regulated by' questions (2017, 2025) that mix correct terms with traps like cerebrum, adrenal cortex or ANS confusion. Knowing the exact NCERT wording secures easy marks.
