Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

Self and Emotion 185

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

Fig. 9.1. Diagram of the autonomic nervous system. The spinal cord is the vertical
elongated structure on the far left. Solid circles outside of the cord are autonomic ganglia.
There are two sets of ganglia: (A) the sympathetic ganglia which receive neurons from
the thoracic and lumbar regions of the cord (thoraco-lumbar outflow) and are aligned
in parallel with the cord; (B) the parasympathetic ganglia which receive neurons from
the head (cranial) and the tail (sacral) regions of the central nervous system, and are dis-
tributed near the end organs away from the cord (cranio-sacral outflow). The first set of
ganglia contains sympathetic neurons, whereas the second contain parasympathetic neu-
rons. From the ganglia, post-ganglionic fibers come out to enervate the end organs (far
right). The general rule for neurotransmitters is: parasympathetic fibers (both pre- and
post-ganglionic) and sympathetic pre-ganglionic fibers release acetylcholine (ACh) (dot-
ted lines), whereas sympathetic post-ganglionic fibers (solid lines) release noradrenaline
(norepinephrine). Both sympathetic and parasympathetic outflows receive commands
from the hypothalamus in the brain through the spinal cord. The sympathetic outflow in-
cludes the adrenal medulla (a pair of endocrine glands located above the kidneys), which
receives pre-ganglionic fibers from the spinal cord and releases adrenaline (epinephrine)
into the bloodstream. Bear in mind that the autonomic nervous system also contains a
sensory component that reports end organ responses back to the brain; it is this type of
feedback sensation (interoception) that constitute the subjective aspect of an emotional
expression. [See Note 51: Cannon; after Bard, Note 52; courtesy Clark Univ. Press.]