Unit Four: The Circulation Chapter 18: Nervous Regulation of the Circulation, and Rapid Control of Arterial Pressure Guyton and Hall, Textbook of Medical Physiology, 12 edition

Autonomic Nervous System Sympathetic Nervous System Sympathetic innervation of the blood vessels Sympathetic nerve fibers to the heart Sympathetic vasoconstrictor system Parasympathetic Control of Heart Function

Autonomic Nervous System Sympathetic Nervous System Fig. 18.1

Autonomic Nervous System Sympathetic Nervous System Fig. 18.2 Sympathetic innervation of the systemic circulation

ANS (cont.) Vasomotor Center in the Brain and its Control of the Vasoconstrictor System Located bilaterally in the reticular substance of the medulla and lower third of the pons; contains 1. vasoconstrictor area 2. vasodilator area 3. sensory area

Fig. 18.3 Areas of the brain that play important roles in the nervous regulation of the circulation. Dashed lines represent inhibitory pathways.

ANS (cont.) Continuous partial constriction of the blood vessels is normally caused by sympathetic vasoconstriction (Fig. 18.4) Control of heart activity by the vasomotor center Control of the vasomotor center by higher nerve centers (Fig. 18.3) Norepinephrine-the vasoconstrictor substance

Fig. 18.4 Effect of total spinal anesthesia on the arterial pressure, showing marked decrease in pressure resulting from loss of “vasomotor” tone

Role of the Nervous System in Rapid Control of Arterial Pressure Most arterioles of the systemic circulation are constricted The veins are especially strongly constricted The heart is directly stimulated by the ANS, further enhancing cardiac pumping

Role of the Nervous System in Rapid Control of Arterial Pressure Rapidity of Nervous Control of Arterial Pressure Increase in arterial pressure during muscle exercise and other types of stress Reflex Mechanism for Maintaining Normal Arterial Pressure Baroreceptor Reflexes

Baroreceptor Reflexes Physiological Anatomy and Innervation Fig. 18.5

Baroreceptor Reflexes (cont.) Response to Arterial Pressure Fig. 18.6

Baroreceptor Reflexes (cont.) Circulatory Reflex Initiated by Baroreceptors Vasodilation of the veins and arterioles Decreased heart rate and strength of contraction Fig. 18.7 Typical carotid sinus reflex effect on aortic arterial pressure by clamping both common carotid arteries

Baroreceptor Reflexes (cont.) Functions of the Baroreceptors During Changes in Body Posture Pressure “Buffer” Function of the Baroreceptor Control System

Baroreceptor Reflexes (cont.) Fig. 18.8 Two hour records of arterial pressure in a normal dog and in the same dog several weeks after the baroreceptors have been denerved

Baroreceptor Reflexes (cont.) Fig. 18.9 Frequency distribution curves of the arterial pressure for a 24 hr period in a normal dog and in the same dog several weeks after the baroreceptors have been denerved

Baroreceptors (cont.) Control of Arterial Pressure by the Carotid and Aortic Chemoreceptors Effect of the lack of oxygen on arterial pressure Atrial and Pulmonary Artery Reflexes Regulate Arterial Pressure Atrial Reflexes That Activate the Kidneys- the volume reflex Atrial Reflex Control of Heart Rate- the Bainbridge Reflex

CNS Ischemic Response Control of Arterial Pressure by the Brain’s Vasomotor Center in Response to Diminished Brain Blood Flow Importance of the CNS ischemic response as a regulator of arterial pressure Cushing Reaction to increased pressure around the brain

Nervous Control of Arterial Pressure Abdominal Compression Reflex Increased Cardiac Output and Arterial Pressure Caused by Skeletal Muscle Contraction During Exercise Respiratory Waves in the Arterial Pressure Arterial Pressure “Vasomotor” Waves Oscillation of the baroreceptor and chemoreceptor reflexes b. Oscillation of the CNS ischemic response