Page 752 - Fundamentals of anatomy physiology

Chapter 20 The Heart 739

Figure 20–20 Factors Affecting Cardiac Output. heart transplant continues to beat unless it is kept chilled in a
preservation solution.

Factors Affecting Factors Affecting Autonomic Innervation
Heart Rate (HR) Stroke Volume (SV)
The sympathetic and parasympathetic divisions of the auto-

Autonomic Hormones End-diastolic End-systolic nomic nervous system innervate the heart by means of the nerve
innervation volume volume network known as the cardiac plexus (Figure 16–8, p. 574, and

Figure 20–21). Postganglionic sympathetic neurons are located

HEART RATE (HR) STROKE VOLUME (SV) ‫ ؍‬EDV ؊ ESV in the cervical and upper thoracic ganglia. The vagus nerves
(N X) carry parasympathetic preganglionic fibers to small gan-

glia in the cardiac plexus. Both ANS divisions innervate the SA

and AV nodes and the atrial muscle cells. Both divisions also

innervate ventricular muscle cells, but sympathetic fibers far

CARDIAC OUTPUT (CO) ‫ ؍‬HR ؋ SV outnumber parasympathetic fibers there.
The cardiac centers of the medulla oblongata contain the

autonomic headquarters for cardiac control. p. 496 The

cardioacceleratory center controls sympathetic neurons that

increase the heart rate. The adjacent cardioinhibi-

Figure 20–21 Autonomic Innervation of the Heart. tory center controls the parasympathetic neurons
that slow the heart rate. Reflex pathways regulate the

Vagal nucleus cardiac centers. They also receive input from higher
centers, especially from the parasympathetic and
Cardioinhibitory sympathetic headquarters in the hypothalamus.
center

Cardioacceleratory &T i p s T r i c k s
center To remember the effect of the sympathetic ner-

Medulla vous system on cardiac performance, remember 20
oblongata that sympathetic input speeds and strengthens

Vagus (N X) the heartbeat.

Sympathetic Spinal cord Cardiac Reflexes. Information about the status
of the cardiovascular system arrives over visceral
Sympathetic Parasympathetic sensory fibers accompanying the vagus nerve and
preganglionic the sympathetic nerves of the cardiac plexus. The
Parasympathetic cardiac centers monitor baroreceptors and che-
fiber preganglionic moreceptors innervated by the glossopharyngeal
Sympathetic ganglia fiber (N IX) and vagus (N X) nerves. pp. 525, 526 On
(cervical ganglia and Synapses in the basis of the information received, the cardiac
cardiac plexus centers adjust the heart’s activity to maintain ad-
superior thoracic Parasympathetic equate circulation to vital organs, such as the brain.
ganglia [ T1–T4]) postganglionic
Sympathetic fibers The cardiac centers respond to changes in blood
pressure as reported by baroreceptors, and to changes
postganglionic fiber in arterial concentrations of dissolved oxygen and
carbon dioxide as reported by chemoreceptors. For
Cardiac nerve example, a decline in blood pressure or oxygen con-
centrations or an increase in carbon dioxide levels
generally means that the heart must work harder to
meet the demands of peripheral tissues. The cardiac
centers then call for an increase in cardiac activity.
We detail these reflexes and their effects on the heart
and peripheral vessels in Chapter 21.