Visceral Reflexes

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The ANS is responsible for the body's visceral reflexes— unconscious, automatic, stereotyped responses to stimulation, much like the somatic reflexes discussed in chapter 14 but involving visceral receptors and effectors and somewhat slower responses. Some authorities regard the visceral afferent (sensory) pathways as part of the ANS, while most prefer to limit the term ANS to the efferent (motor) pathways. Regardless of this preference, however, autonomic activity involves a visceral reflex arc that includes receptors (nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli), afferent neurons leading to the CNS, interneurons in the CNS, efferent neurons carrying motor signals away from the CNS, and finally effectors.

For example, high blood pressure activates a visceral baroreflex.2 It stimulates stretch receptors called barore-ceptors in the carotid arteries and aorta, and they transmit

2baro = pressure

Saladin: Anatomy & I 15. The Autonomic Nervous I Text I © The McGraw-Hill

Physiology: The Unity of and Visceral Reflexes Companies, 2003 Form and Function, Third Edition

Chapter 15 The Autonomic Nervous System and Visceral Reflexes 565

signals via the glossopharyngeal nerves to the medulla oblongata (fig. 15.1). The medulla integrates this input with other information and transmits efferent signals back to the heart by way of the vagus nerves. The vagus nerves slow down the heart and reduce blood pressure, thus completing a homeostatic negative feedback loop. A separate autonomic reflex arc accelerates the heart when blood pressure drops below normal.

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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