QS Study

The Reflexes that Control Heart Rate

Heart rate is the speed of the heartbeat measured by the number of contractions of the heart per minute. Cardiovascular reflex responses to visceral afferent stimulation are either excitatory or inhibitory. The beat-to-beat activity of the heart within the entire organism ought to be adjustable to the changing requirements of that organism. The automaticity of the heart is therefore subject to various neural stimuli that control the heart by either rising or diminishing its automaticity. Regulation of heart rate is controlled by various afferent and efferent nerves.

The reflexes regulate the heart rate are as follows:

(i) Cardio – inhibitory reflex/Baroreceptor reflex/Sino-aortic reflex: When blood pressure rises → stimulation of the baroreceptor occurs → sensory impulses from them stimulated vagal center → vagal tone increases → heart rate falls.

(ii) Vasomotor center through chemoreceptor reflexes/Anoxia: Degree of Hypoxia is directly proportional to the heart rate. Hypoxia stimulates the VMC through chemoreceptors. Then Impulse from VMC is transmitted through the sympathetic nervous system, which increases heart rate.

(iii) Bainbridge reflex / Cardio-accelerator reflex: An Ins venous return leads to an increase in heart rate especially when the heart rate is slow. This is known as Bainbridge reflex. Atrial pressure stimulates the Baroreceptor → afferent impulse is transmitted to medulla through vagus nerves →. Efferent impulse returns back to the heart through sympathetic and vagus nerve →↑ heart rate.

(iv) Cushing reflex: The reflex response to an increased intracranial pressure is called Cushing reflex.

Mechanism: Pressure in CSF ↑, Cerebral vessel are compressed, Cerebra blood flow reduced ↓, Ischaemia, (+) VMC, Systemic BP ↑,  Heart Rate ↑.

(v) Reflexes from other parts of the body: Sensory stimuli from other parts of the body like painful stimuli generally quicken heart rate.