Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 33

Cardiovascular Regulatory Mechanisms 557

(RVLM; Figure 33–2). This region is sometimes called a vasomo-

tor area. The axons of RVLM neurons course dorsally and medi-

ally and then descend in the lateral column of the spinal cord to

the thoracolumbar intermediolateral gray column (IML). They

contain phenylethanolamine-

N

-methyltransferase (PNMT; see

Chapter 7), but it appears that the excitatory transmitter they se-

crete is glutamate rather than epinephrine. Neurovascular com-

pression of the RVLM has been linked to some cases of essential

hypertension in humans (see Clinical Box 33–1).

The activity of RVLM neurons is determined by many fac-

tors (see Table 33–2). They include not only the very impor-

tant fibers from arterial and venous baroreceptors, but also

fibers from other parts of the nervous system and from the

carotid and aortic chemoreceptors. In addition, some stimuli

act directly on the vasomotor area.

There are descending tracts to the vasomotor area from the

cerebral cortex (particularly the limbic cortex) that relay in

the hypothalamus. These fibers are responsible for the blood

FIGURE 33–1
Feedback control of blood pressure.
Brain
stem excitatory input to sympathetic nerves to the heart and vascula-
ture increases heart rate and stroke volume and reduces vessel diam-
eter. Together these increase blood pressure, which activates the
baroreceptor reflex to reduce the activity in the brain stem.

Baroreceptors

Heart rate

Stroke volume

Vessel diameter

Blood

pressure

Brain

stem

FIGURE 33–2
Basic pathways involved in the medullary control of blood pressure.
The vagal efferent pathways that slow the heart are
not shown. The putative neurotransmitters in the pathways are indicated in parentheses. Glu, glutamate; GABA,
γ
-aminobutyric acid; Ach, acetyl-
choline; NE, norepinephrine; IML, intermediolateral gray column; NTS, nucleus of the tractus solitarius; CVLM, IVLM, RVLM, caudal, intermediate,
and rostral ventrolateral medulla; IX and X, glossopharyngeal and vagus nerves.

Baroreceptor

afferents

(Glu)

(GABA)

Bulbospinal

pathway (Glu)

IX

X CVLM

IVLM

RVLM

NTS

Medulla

(Glu)

IML

Thoracic

cord

Arteriole

or venule

Adrenal

medulla

Postganglionic

sympathetic

neuron (NE)

Heart

Preganglionic

sympathetic

neuron (Ach)

Aortic

arch

Carotid

sinus