Heart rate and its regulation

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 HEART RATE

Normal heart rate is 72/minute.

It ranges between 60 and 80 per minute.

 • Tachycardia is the increase in heart rate above 100/minute.

 • Bradycardia is the decrease in heart rate below 60/minute.

REGULATION OF HEART RATE

heart rate is regulated by the nervous mechanism; it consists of 3 components:

 1. VASOMOTOR CENTER (cardiac center)

 👉Vasomotor center is the nervous center that regulates the heart rate.

 👉it also regulates the blood pressure.

 👉 bilaterally situated in the reticular formation of medulla oblongata and lower part of pons.

 👉Vasomotor center is formed by three areas:

 I. VASOCONSTRICTOR AREA – CARDIOACCELERATOR CENTER

 • Vasoconstrictor area is situated in the reticular formations of medulla in floor of IV ventricle and it forms the lateral portion of vasomotor center.

 • It increases the heart rate and constrict blood vessels.

 • It is under the control of hypothalamus and cerebral cortex.

 II. VASODILATOR AREA – CARDIOINHIBITORY CENTER

 • also situated in the reticular formation of Medulla oblongata in the floor of IV ventricle. It forms the medial portion of vasomotor area.

 • decreases the heart rate and causes dilatation of blood vessels

 • When this area is removed or destroyed, heart rate increases.

 • is under the control of cerebral cortex and hypothalamus.

 It is also controlled by the impulses from baroreceptors, chemoreceptors and other sensory impulses

 III. SENSORY AREA

 • lies in nucleus of tractus solitarius in medulla and pons. and and forms posterior part of vasomotor center

 • this area controls the vasoconstrictor and vasodilator areas

 2. MOTOR (EFFERENT) NERVE FIBERS TO HEART

 Heart receives efferent nerves from both the divisions of autonomic nervous system.

 I. PARASYMPATHETIC NERVE FIBERS

 • It arises from the the dorsal nucleus of vagus

 • Vagus nerve is cardioinhibitory in function

 • carries inhibitory impulses from vasodilator area to the heart.

 • neurotransmitter substance known as acetylcholine

 II. SYMPATHETIC NERVE FIBERS

 • It arises from upper thoracic (T1 to T4) segments of spinal cord.

 • Sympathetic nerves are cardioaccelerators in function

 • carry cardioaccelerator impulses from vasoconstrictor area to the heart.

 • release of neurotransmitter substance, noradrenaline.

 3. SENSORY (AFFERENT) NERVE FIBERS FROM HEART

 • It passes through inferior cervical sympathetic nerve

 • Carry sensation of stretch and pain the heart to brain via spinal cord.


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