Question

Identify the inputs to cardiac center which affect the heart rate.

Identify the factors that affect cardiac output.

Answer 1

Heart rate is regulated by the nervous mechanism, which consists of three components:
A. Vasomotor center
B. Motor (efferent) nerve fibers to the heart
C. Sensory (afferent) nerve fibers from the heart.
VASOMOTOR CENTER – CARDIAC CENTER
Vasomotor center is the nervous center that regulates the heart rate. It is the same center in brain, which regulates the blood pressure. It is also called the cardiac center.
Vasomotor center is bilaterally situated in the reticular formation of medulla oblongata and lower part of pons   Areas of Vasomotor Center
Vasomotor center is formed by three areas: 1. Vasoconstrictor area
2. Vasodilator area
3. Sensory area.
VASOCONSTRICTOR AREA – CARDIOACCELERATOR CENTER
Situation
Vasoconstrictor area is situated in the reticular formation of medulla in floor of IV ventricle and it forms the lateral portion of vasomotor center. It is otherwise known as pressor area or cardioaccelerator center.
Function
Vasoconstrictor area increases the heart rate by sending accelerator impulses to heart, through sympathetic nerves. It also causes constriction of blood vessels. Stimu­ lation of this center in animals increases the heart rate and its removal or destruction decreases the heart rate.
Control
Vasoconstrictor area is under the control of hypothala- mus and cerebral cortex.
VASODILATOR AREA – CARDIOINHIBITORY CENTER
Situation
Vasodilator area is also situated in the reticular formation of medulla oblongata in the floor of IV ventricle. It forms the medial portion of vasomotor center. It is also called depressor area or cardioinhibitory center.
Function
Vasodilator area decreases the heart rate by sending inhibitory impulses to heart through vagus nerve. It also causes dilatation of blood vessels. Stimulation of this area in animals with weak electric stimulus decreases the heart rate and stimulation with a strong stimulus stops the heartbeat. When this area is removed or destroyed, heart rate increases.
Control
Vasodilator area is under the control of cerebral cortex and hypothalamus. It is also controlled by the impulses from baroreceptors, chemoreceptors and other sensory impulses via afferent nerves.
SENSORY AREA
Situation
Sensory area is in the posterior part of vasomotor center, which lies in nucleus of tractus solitarius in medulla and pons.
Function
Sensory area receives sensory impulse via glosso­ pharyngeal nerve and vagus nerve from periphery, particularly, from the baroreceptors. In turn, this area controls the vasoconstrictor and vasodilator areas.

factors that affect cardiac output.
1. Venous return
2. Force of contraction
3. Heart rate
4. Peripheral resistance.