Biology · Body Fluids and Circulation · NEET
The human heart is myogenic. NCERT says normal heart activity is auto-regulated by specialised muscles (nodal tissue), hence the heart is called myogenic. The heartbeat begins in the muscle itself. A neurogenic heart (seen in many invertebrates like some crustaceans) needs a nerve to start each beat. All vertebrate hearts, including humans and frogs, are myogenic.
Because the heart is myogenic and its nodal tissue is autoexcitable. The muscle makes its own action potentials without any outside nerve. So even when removed and cut off from the brain, the isolated heart keeps beating rhythmically for some time using its own signal. This exact idea was asked in NEET 2017 (answer: heart is myogenic AND autoexcitable).
In a myogenic heart the beat starts in the cardiac muscle itself (nodal tissue / SAN). In a neurogenic heart the beat starts from a nerve ganglion, so it depends on a nerve for each contraction. Humans, all vertebrates, and molluscs have myogenic hearts. Many arthropods (like Limulus, crabs) have neurogenic hearts.
Nerves do not START the beat; they only MODIFY it. NCERT says a neural centre in the medulla oblongata moderates cardiac function through the autonomic nervous system. Sympathetic nerves speed the heart up; parasympathetic nerves slow it down; adrenal medullary hormones can also raise cardiac output. The beat itself is still born in the nodal muscle, so the heart stays myogenic.
Autoexcitable means the nodal muscle can generate action potentials on its own, with no external stimulus. This self-firing property of the nodal tissue is exactly WHY the heart is myogenic. The SAN fires the most action potentials (70–75 per minute), so it sets the pace and is called the pacemaker.
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
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:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. NCERT states the heart is auto-regulated by specialised muscles (nodal tissue), hence it is called myogenic. The beat starts in the muscle itself.
The nodal tissue, especially the sino-atrial node (SAN). It is autoexcitable, so it generates action potentials on its own and sets the heartbeat.
Many arthropods such as king crab (Limulus), prawns and crabs have neurogenic hearts, where the beat starts from a nerve ganglion. This is the opposite of the myogenic vertebrate heart.
Nerves do not start the beat; they only modify it. Sympathetic nerves speed it up, parasympathetic nerves slow it down, and the beat still originates in the nodal muscle.
