Page 343 - Color_Atlas_of_Physiology_5th_Ed._-_A._Despopoulos_2003

Hypothalamus, Limbic System used to perceive and assess signals from the
“outer world” and from memories. Processing
The hypothalamus coordinates all autonomic of both types of input is important for be-
and most endocrine processes (! p. 266ff.) havior.
and integrates signals for control of internal Programmed behavior (! A). The lateral
milieu, sleep–wake cycle, growth, mental/ hypothalamus has various programs to control
physical development, reproduction and other lower hormonal, autonomic and motor
processes. This is reflected internally by
functions. The hypothalamus receives numer-
Central Nervous System and Senses organs (! p. 280). behavior.
numerous autonomic and hormonal activities,
ous sensory and humoral signals (! A). Pep-
and is reflected outwardly by different types of
tide hormones can circumvent the blood–
brain barrier by way of the circumventricular
Different programs exist for different behavioral re-
actions, for example:
Afferents. Thermosensors for control of body
! Defensive behavior (“fight or flight”). This pro-
temperature (! p. 224), osmosensors for regulation
gram has somatic (repulsive facial expression and
of osmolality and water balance (! p. 168), and glu-
posture, flight or fight behavior), hormonal (epi-
cose sensors for maintenance of a minimum glucose
nephrine, cortisol) and autonomic (sympathetic
concentration are located within the hypothalamus.
nervous system) components. Its activation results
Information about the current status of the internal
bition of insulin release, and a decrease in blood flow
from distant sensors, e.g., thermosensors in the skin,
to the gastrointestinal tract as well as to rises in car-
osmosensors in the liver (! p. 170), and stretch sen-
diac output, respiratory rate, and blood flow to the
sors in the cardiac atria (! p. 214ff.). The hy-
skeletal muscles.
12 milieu is neuronally projected to the hypothalamus in the release of energy-rich free fatty acids, the inhi-
pothalamus/circumventricular organs also contain
receptors for various hormones (e.g., cortisol and ! Physical exercise. The components of this pro-
angiotensin II), some of which form part of control gram are similar to those of defensive behavior.
loops for energy metabolism and metabolic ! Nutritive behavior, the purpose of which is to
homeostasis (e.g., receptors for cortisol, ACTH, CRH, ensure an adequate supply, digestion and intake of
leptin, and CCK). For functions related to growth and foods and liquids. This includes searching for food,
reproduction, the hypothalamus receives hormonal e.g. in the refrigerator, activation of the parasympa-
signals from the gonads and input from neuronal af- thetic system with increased gastrointestinal secre-
ferents that report cervical widening at the begin- tion and motility in response to food intake, post-
ning of the birth process and breast stimulation prandial reduction of skeletal muscle activity and
(suckling reflexes), among other things. similar activities.
! Reproductive behavior, e.g., courting a partner,
The limbic system (! A) and other areas of the neuronal mechanisms of sexual response, hormonal
brain influence hypothalamic function. The regulation of pregnancy (! p. 304), etc.
limbic system controls inborn and acquired ! Thermoregulatory behavior, which enables us
behavior (”program selection”) and is the seat to maintain a relatively constant core temperature
of instinctive behavior, emotions and motiva- (! p. 224), even in extreme ambient temperatures
tion (“inner world”). It controls the expression or at the high level of heat production during strenu-
ous physical work.
of emotions conveying important signals to the
environment (e.g., fear, anger, wrath, discom- Monoaminergic neuron systems contain neu-
fort, joy, happiness). Inversely, signals from the rons that release the monoamine neu-
environment (e.g., odors) are closely as- rotransmitters norepinephrine, epinephrine,
sociated to behavior. dopamine, and serotonin. These neuron tracts
The limbic system has cortical components extend from the brain stem to almost all parts
(hippocampus, parahippocampal gyrus, cin- of the brain and play an important role in the
gulate gyrus, parts of olfactory brain) and sub- overall regulation of behavior. Experimental
cortical components (amygdaloid body, septal activation of noradrenergic neurons, for ex-
nuclei, anterior thalamic nucleus). It has recip- ample, led to positive reinforcement (liking,
rocal connections to the lateral hypothalamus rewards), whereas the serotoninergic neurons
(chiefly used for recall of “programs”, see are thought to be associated with dislike. A
330 below) and to the temporal and frontal cortex. number of psychotropic drugs target mono-
Its connections to the cortex are primarily aminergic neuron systems.
Despopoulos, Color Atlas of Physiology © 2003 Thieme
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