CENTRAL REGULATION OF AUTONOMIC FUNCTIONS.
Change of functional condition of organs in the case of
stimulation of autonomic nerves
|
Symptoms |
Sympathetic
effecrs |
Parasympathetic
effecrs |
|
Pupil
of eye |
Increase |
|
|
Cardiovascular
system: heart
beat strength
of cardiac contractility |
Increase Increase |
Decrease Decrease |
|
Rate
of breathing Diameter
of bronchs |
Increase |
Decrease Decrease |
|
Digestive
tract: Salivation Motility Secretory
function Sphincters |
Increase,
viscous saliva Decrease Decrease Contract |
Increase,
liguid saliva Increase Increase Relex |
|
Vessels
of sceletal muscles Vessels
of skin Sweet
glands |
Increase Decrease Secretion |
– – – |
CRANIAL NERVES THAT CARRY PARASYMPATHETIC FIBERS. If the oculomotor nerve is
cut experimentally, the pupil dilates. The parasympathetic
fibers within the oculomotor nerve carry
nervous impulses that cause the pupil to constrict. Cutting the nerve destroys
the balance between parasympathetic
and sympathetic
innervation. The sympathetic
nervous impulses then cause the pupil to
dilate. The "drops" placed in the eye for optical examination apparently act in much the same way by
blocking the parasympathetic
nerve endings.
It has been mentioned that there are four cranial
nerves arising from the medulla that carry autonomic
fibers and therefore are a part of the craniosacral
system. These nerves are the facial glossopharyngeal, vagus, and accessory nerves. The facial nerve includes parasympathetic
fibers that are secretary to the lacrimal
gland and to the sublingual and submaxillary
salivary glands. The lacrimal gland
is supplied with postganglionic fibers from the sphenopalatine ganglion. The sublingual and submaxillary
salivary glands receive postganglionic fibers
arising in the submaxillary ganglion.
Preganglionic fibers in the glossopharyngeal
nerve extend outward to the optic
ganglion. Postganglionic fibers
arise in the otic ganglion and supply the parotid
salivary gland. These glands, including the lacrimal,
have a double innervation. They
derive their sympathetic innervation by
way of the superior cervical sympathetic ganglion and carotid plexuses. The
action of the two sets of nerves is not clear. Apparently they both contain
secretory fibers, but the secretory action of the parasympathetic system seems to be dominant. The vagus nerve contains
both motor and visceral afferent fibers. The motor fibers are long preganglionic fibers
that extend out to the organ supplied. Very short postganglionic fibers are contained within the organ. Motor fibers
are supplied to the larynx, trachea, bronchioles, heart, esophagus, stomach,
small intestine, and some parts of
the large intestine. Stimulation of the vagus acts as
an inhibitor to the heart, causing its rate of beating to slow or to
stop. To the muscles of the wall of the
digestive tract, branches of the vagus act as
accelerator nerves. Peristalsis is increased by parasympathetic stimulation. Parasympathetic
fibers to the glands of the digestive tract have regulatory function on
secretion, but food content of the stomach or intestine and hormones
circulating in the blood can also stimulate secretion.
Parasympathetic fibers from both the right and left vagus nerves enter the great plexuses of the sympathetic system. There is, however, a definite parasympathetic nerve supply to such organs as the pancreas, liver, and kidneys. Nervous
stimulation of these organs is, for the most part, merely regulatory. Hormones
in the blood normally cause the pancreas and liver to secrete, but stimulation
of the vagus increases the flow of pancreatic juice and bile. While sympathetic stimulation
of the kidneys by way of the splanchnic nerves results in vasoconstriction and
therefore reduced flow of urine, there are many other physiological factors that affect the function of the
kidneys. A part of the accessory nerve
contains visceral motor and cardiac inhibitory fibers. Certain types of allergy offer examples of overstimulation of the parasympathetic
system. Epinephrine can be used to counteract these
effects, since it is associated with the action
of the sympathetic system.
THE SACRAL AUTONOMICS. The sacral portion of the craniosacral system
is composed of preganglionic
fibers incorporated in the second, third, and fourth sacral nerves. The
fibers extend out to the pelvic plexuses, where they enter into close
relationship with fibers of the sympathetic system. Parasympathetic fibers innervate the urogenital organs and the distal part of the colon. Postganglionic fibers are considered to be in the organs supplied or in small ganglia
located close by. These parasympathetic fibers are motor to the muscles
of the distal two-thirds of the colon, to the rectum, and to the urinary
bladder. They carry vasodilator impulses to the
penis and clitoris. Inhibitory impulses pass to the internal sphincter muscle of the bladder and to the internal sphincter of
the anus.
PARASYMPATHETIC PLEXUSES. Enteric Plexuses the digestive
tube has its own intrinsic nerve supply,
consisting of the myenteric plexus,
located between the longitudinal and
circular muscles and a submucous plexus,
located under the mucous layer in the
sub mucosa. This part of the nervous system extends the entire length of the
digestive tube. It can be assumed that parasympathetic
fibers entering the wall of
the digestive tract are preganglionic fibers
that make synaptic connections with
neurons of the enteric system. Sympathetic fibers entering the muscular wall,
however, are postganglionic fibers and
terminate in the tissues that they supply without making synaptic connections.
The enteric plexuses function in maintaining
rhythmic peristaltic movement along the
digestive tract. Peristalsis is maintained if both sympathetic and parasympathetic nerve supply is cut. The nerves
of the autonomic system, however, exert a
regulatory effect.
SYMPATHETIC AND PARASYMPATHETIC RELATIONSHIPS. Autonomic effects are usually conditioned by other factors such as the presence of
hormones in the bloodstream or by circulatory
effects. The secretion of a gland can be
depressed by the stimulation of an inhibitor nerve; secretion can also be
depressed by vasoconstriction of blood
vessels supplying the gland, thus limiting its blood supply. While the
sympathetic system can be considered as an accelerator to the heart, the situation is reversed in the case of the action of the
autonomic system upon the digestive
tract. Here the action of sympathetic nerves depresses peristalsis and the secretion of digestive glands during emotional
excitement, while the parasympathetic system, as an accelerator, effects a return to
normal. When we speak of the sympathetic and parasympathetic
nerves as being antagonistic, we mean this in the sense of antagonistic
muscles. The nerves from the sympathetic and parasympathetic systems can produce opposite
effects, but they provide a correlated
adjustment to meet many physiological conditions. Autonomic effects are not always clearly antagonistic. The
accommodation reflex of the eye
whereby the lens and iris are adjusted to facilitate clear vision appears to be primarily a
parasympathetic function so far as the ciliary’s
muscle and the muscles of the iris
are concerned. The two sets of muscles of the iris seem to have a synergistic relationship, which causes them to contract or
dilate the pupil smoothly in a mild state of opposition to each other. The
pupil can also dilate in response to
an emotional state such as fear or pain. This is due to stimulation of the sympathetic system.
CHEMICAL TRANSMISSION AT AUTONOMIC FUNCTIONS
Transmission at the synaptic
junctions between pre- and postganglionic
neurons and between the postganglionic neurons and the autonomic effectors is chemically mediated. The principal transmitter agents involved
are acetylcholine and norepinephrine, although dopamine is also secreted by interneurons in
the sympathetic ganglia.
Chemical Divisions of the Autonomic Nervous System
On the basis of the chemical mediator released,
the autonomic nervous system can be
divided into cholinergic and noradrenergic divisions. The neurons that are cholinergic are (1) all preganglionic neurons;
(2) the anatomically parasympathetic postganglionic neurons; (3) the anatomically sympathetic postganglionic neurons which innervate sweat
glands; and (4) the anatomically sympathetic neurons which end on blood vessels
in skeletal muscles and produce vasodilatation when
stimulated. The remaining postganglionic sympathetic
neurons are noradrenergic. The adrenal
medulla is essentially a sympathetic ganglion in which the postganglionic cells have lost their axons and become specialized for secretion directly into the bloodstream. The cholinergic preganglionic neurons to these
cells have consequently become the
secret motor nerve supply of this gland.
RESPONSES
OF EFFECTOR ORGANS TO AUTONOMIC NERVE IMPULSES
General
Principles
On the basis of the chemical mediator released,
the autonomic nervous system can be
divided into cholinergic and noradrenergic divisions. The neurons that are cholinergic are (1) all preganglionic neurons;
(2) the anatomically parasympathetic postganglionic neurons; (3) the anatomically sympathetic postganglionic neurons which innervate sweat
glands; and (4) the anatomically sympathetic neurons which end on blood vessels
in skeletal muscles and produce vasodilatation when
stimulated. The remaining postganglionic sympathetic
neurons are noradrenergic. The adrenal
medulla is essentially a sympathetic ganglion in which the postganglionic cells have lost their axons and become specialized for secretion directly into the bloodstream. The cholinergic preganglionic neurons to these
cells have consequently become the
secret motor nerve supply of this gland.
The smooth muscle in the walls of the hollow viscera is generally
innervated by both noradrenergic and cholinergic fibers, and activity in one of
these systems increases the intrinsic activity of the smooth muscle whereas
activity in the other decreases it. However, there is no uniform rule about
which system stimulates and which inhibits. In the case of sphincter muscles,
both noradrenergic and cholinergic innervations are excitatory, but one
supplies the constrictor component of the sphincter and the other the dilator.
There
is usually no acetylcholine in the circulating blood, and the effects of
localized cholinergic discharge are generally discrete and of short duration
because of the high concentration of acetylcholinesterase
at cholinergic nerve endings. Norepinephrine spreads farther and has a more
prolonged action than acetylcholine. The epinephrine and some of the dopamine
come from the adrenal medulla, but much of the norepinephrine diffuses into the
bloodstream from norad-renergic nerve endings.
Cholinergic
Discharge
In a general way, the functions promoted by activity in the cholinergic
division of the autonomic nervous system are those concerned with the
vegetative aspects of day-to-day living. For example, cholinergic action favors
digestion and absorption of food by increasing the activity of the intestinal
musculature, increasing gastric secretion, and relaxing the pyloric sphincter.
For this reason, and to contrast it with the ''catabolic'' noradrenergic
division, the cholinergic division is sometimes called the anabolic nervous system.
Noradrenergic
Discharge
The
noradrenergic division discharges as a unit in emergency situations. The
effects of this discharge are of considerable value in preparing the individual
to cope with the emergency, although it is important to avoid the teleologic fallacy involved in the statement that the
system discharges in order to do this. For example, noradrenergic discharge
relaxes accommodation and dilates the pupils (letting more light into the
eyes), accelerates the heartbeat and raises the blood pressure (providing
better perfusion of the vital organs and muscles), and constricts the blood
vessels of the skin (which limits bleeding from wounds). Noradrenergic
discharge also leads to lower thresholds in the reticular formation
(reinforcing the alert, aroused state) and elevated blood glucose and free
fatty acid levels (supplying more energy). On the basis of effects like these,
Cannon called the emergency-induced discharge of the noradrenergic nervous
system the ''preparation for flight or fight.''
The
emphasis on mass discharge in stressful situations should not obscure the fact
that the noradrenergic autonomic fibers also subserve
other functions. For example, tonic noradrenergic discharge to the arterioles
maintains arterial pressure, and variations in this tonic discharge are the
mechanism by which the carotid sinus feedback regulation of blood pressure is
effected. In addition, sympathetic discharge is decreased in fasting animals
and increased when fasted animals are refed. These
changes may explain the decrease in blood pressure and metabolic rate produced
by fasting and the opposite changes produced by feeding.
Adrenergic Fibers The terminal filaments of most sympathetic postganglionic neurons produce an
adrenalin-like substance and are classified as adrenergic.
Sympathetic fibers to sweat
glands, blood vessels of the skin, and to
the arrestors pylorus muscles are exceptions. These postganglionic fibers enter spinal nerves through the gray rami and
reach the skin incorporated in peripheral nerves.
The effects of norepinephrine,
in conjunction with epinephrine, can be general and widespread. There is experimental evidence that
the chemical substance resulting from excitation of sympathetic postganglionic fibers is carried by the
bloodstream and can affect organs remote from the point of origin. It is
interesting to note that the sympathetic
ganglia and the modularly portion of the adrenal gland have the same embryonic origin. They both arise from neural crest cells.
Cholinergic Fibers Parasympathetic
fibers also produce a chemical mediating substance. In this case the substance is acetylcholine,
which is promptly converted to choline and
acetic acid by the action of an enzyme called cholinesterase. Since acetylcholine does
not remain in its most active state for any great length of time, it is
probable that its effects are entirely local. Unlike norepinephrine, it is probably not carried by the bloodstream.
All preganglionic fibers,
whether sympathetic or parasympathetic, have
been shown to liberate a cholinergic substance,
probably identical with acetylcholine. This
means that the transmission of the nervous impulse across the point of synapse between the preganglionic and postganglionic fiber
is accomplished by the production of acetylcholine.
As we have indicated, postganglionic sympathetic fibers to the sweat glands and to smooth
muscles of the skin are cholinergic. These
fibers are carried by peripheral
nerves. Voluntary motor nerves to skeletal muscles are also cholinergic. On the basis of chemical transmitter substances it appears that the
division of the autonomic system into
sympathetic and parasympathetic is
somewhat artificial.
MEDULLA OBLONGATA
Control of Respiration, Heart Rate, & Blood Pressure
The medullary centers for the autonomic reflex control
of the circulation, heart, and lungs are called the vital centers because
damage to them is usually fatal. The afferent fibers to these centers originate
in a number of instances in highly specialized visceral receptors. The
specialized receptors include not only those of the carotid and aortic sinuses
and bodies but also receptor cells that are apparently located in the medulla
itself. The motor responses are graded and delicately adjusted and include
somatic as well as visceral components.
Other Medullary Autonomic Reflexes
Swallowing, coughing, sneezing, gagging, and vomiting are also reflex
responses integrated in the medulla oblongata. Coughing is initiated by
irritation of the lining of the respiratory passages. The glottis closes and
strong contraction of the respiratory muscles builds up intrapulmonary
pressure, whereupon the glottis suddenly opens, causing an explosive discharge
of air. Sneezing is a somewhat similar response to irritation of the nasal
epithelium. It is initiated by stimulation of pain fibers in the trigeminal
nerves.
RELATION OF HYPOTHALAMUS TO AUTONOMIC FUNCTION
Many years ago, Sherrington called the hypothalamus "the head
ganglion of the autonomic system." Stimulation of the hypothalamus
produces autonomic responses, but there is little evidence that the
hypothalamus is concerned with the regulation of visceral function per se.
Rather, the autonomic responses triggered in the hypothalamus are part of more
complex phenomena such as rage and other emotions.
"
Stimulation of the superior anterior hypothalamus occasionally causes
contraction of the urinary bladder, a parasympathetic response. Largely on this
basis, the statement is often made that there is a "parasympathetic center
" in the anterior hypothalamus. However, bladder contraction can also be
elicited by stimulation of other parts of the hypothalamus, and hypothalamic
stimulation causes very few other parasympathetic responses. Thus, there is
very little evidence that a localized "parasympathetic center"
exists. Stimulation of the hypothalamus can cause cardiac arrhythmias, and
there is reason to believe that these are due to simultaneous activation of
vagal and sympathetic nerves to the heart.
Sympathetic Responses
Stimulation of various parts of the hypothalamus, especially the lateral
areas, produces a rise in blood pressure, pupillary dilatation, piloerection, and other signs of diffuse noradrenergic
discharge. The stimuli that trigger this pattern of responses in the intact
animal are not regulatory impulses from the viscera but emotional stimuli,
especially rage and fear. Noradrenergic responses are also triggered as part of
the reactions that conserve heat.
Low-voltage electrical stimulation of the middorsal
portion of the hypothalamus causes vasodilatation in muscle. Associated
vasoconstriction in the skin and elsewhere maintains blood pressure at a fairly
constant level. This observation and other evidence support the conclusion that
the hypothalamus is a way station on the so-called cholinergic sympathetic
vasodilator system, which originates in the cerebral cortex. It may be this
system, which is responsible for the dilatation of muscle blood vessels at the
start of exercise.
Stimulation of the dorsomedial
nuclei and posterior hypothalamic areas produces increased secretion of
epinephrine and norepinephrine from the adrenal medulla. Increased adrenal
medullary secretion is one of the physical changes associated with rage and
fears and may occur when the cholinergic sympathetic vasodilator system is
activated. It has been claimed that there are separate hypothalamic centers for
the control of epinephrine and norepinephrine secretion. Differential secretion
of one or the other of these adrenal medullary catecholamines
does occur in certain situations, but the selective increases are small.
RELATION TO SLEEP Lesions of the posterior hypothalamus cause prolonged sleep,
and stimulation of the dorsal hypothalamus in
conscious animals causes them to go to sleep. These observations have led
to consideralable speculation
about the existence of 'sleep centers" a ' 'wakefulness
centers '' in the hypothalamus.
RELATION TO CYCLIC PHENOMENA
Lesions of the suprachiasmatic nuclei disrupt the circadian rhythm in the secretion of ACTH and melatonin. In addition, these
lesions interrupt estrous cycles and activity patterns in laboratory animals. The suprachiasmatic nuclei receive an important input from the
eyes via the retinohypothalamic
fibers, and it appears that they normally function to entrain various body rhythms to the 24-hour light-dark cycle.
There is a prominent serotonergic input from the raphe
nuclei to the supra-chiasmatic nuclei, but the exact relation of this input
to their function is not known. Feeding
& Satiety Centers Hypothalamic regulation of the appetite for
food depends primarily upon the interaction of 2 areas: a lateral "feeding center" in the bed nucleus of the medial forebrain bundle at its junction with the pallid hypothalamic fibers, and a medial "satiety center" in the ventromedial nucleus.
Stimulation of the feeding
center evokes eating behavior in conscious
animals, and its destruction causes severe, fatal anorexia in otherwise healthy animals.
Stimulation of the ventromedial nucleus
causes cessation of eating, whereas lesions in this region cause hyperphagia and, if the food supply is abundant, the syndrome of hypothalamic. Destruction of the feeding center
in rats with lesions of the satiety center
causes anorexia, which indicates that the satiety center-functions by
inhibiting the feeding center.
ANATOMIC CONSIDERATIONS
The term limbic lobe or limbic system is applied to the part of the
brain that consists of a rim of cortical tissue around the hilus
of the cerebral hemisphere and a group of associated deep structures – the
amygdala, the hippocampus, and the septal nuclei. The
region was formerly called the rhinencephalon because
of its relation to olfaction, but only a small part of it is actually concerned
with smell.
LIMBIC FUNCTIONS
Stimulation and ablation experiments indicate that in addition to its
role in olfaction, the limbic system is concerned with feeding behavior. Along
with the hypothalamus, it is also concerned with sexual behavior, the emotions
of rage and fear, and motivation.
Autonomic Responses & Feeding Behavior
Limbic stimulation produces autonomic effects,
particularly changes in blood pressure and respiration. These responses are
elicited from many limbic structures, and there is little evidence of
localization of autonomic responses. This suggests that the autonomic effects
are part of more complex phenomena, particularly emotional and behavioral
responses. Stimulation of the amygdaloid nuclei
causes movements such as chewing and licking and other activities related to
feeding. Lesions in the amygdala cause moderate hyperphagia,
with indiscriminate ingestion of all kinds of food.
Pilomotor reflex
To make a thermal (ice) or mechanical stimulus of skin in area of
trapezoidal muscle. Pay attention on development of anserine skin on the part
of the body. Rise of intensive anserine skin on the whole body testifies of increased
of irritation of the sympathetic nervous system (slight anserine skin testifies
of normal reaction). It is known, that pileous
muscles of head and neck are connected with I-III thoracic segments, pileous muscles of hands are connected with IV-VII thoracic
segments, pileous muscles of trunk are connected with
VIII-IX thoracic segments.
Functional significance of posterior hypothalamus
(stereotaxic research)
To determine stereotaxic coordinates of posterior hypothalamus. To
narcotize a rat and fix it on a table. Put the identeferentive
electrode into the cervic muscles of a rat. The
active electrode into the electrodo-holder and lead
it into the posterior hypothalamus.
To count a quantity of respiratorical movements during one minute. To make the stimulation
and then count a quantity of respiratorical movements
once more.
AUTONOMIC CIRCULATORY EFFECTS. Vasoconstriction is a function of the sympathetic
system. Although vasodilation may be a
function of the parasympathetic system,
experimental results are not conclusive. It appears that sympathetic nerves also can include vasodilator
fibers. Other factors can influence the
blood vessels, such as hormones circulating in the blood stream, the CO2
content of the blood, and temperature.
Sympathetic fibers are conveyed to the blood vessels
of the arms and legs by way of the spinal nerves of the central nervous system
supplying these regions. Vasoconstriction can
be localized or general. In an emergency calling tor quick action, general vasoconstriction causes a rise in blood
pressure. At the same time Vasoconstriction may
reduce the flow of blood to the digestive tract in a localized area. Muscular exercise requires an increased flow of
blood to the skeletal muscles and, therefore,
vasodilation of the blood vessels
supplying them. Coronary arteries supplying the heart muscle are dilated also.
The action of the sympathetic system is supported by epinephrine in the bloodstream. Central Regulation of Visceral Function
The levels of autonomic
integration within the central nervous system are arranged, like their
somatic counterparts, in a hierarchy. Simple reflexes such as contraction
of the full bladder are integrated in the spinal cord. More complex reflexes that regulate respiration and blood pressure
are integrated in the medulla oblongata. Those
that control papillary responses to light and accommodation are integrated in
the midbrain. The complex autonomic mechanisms that maintain the chemical
constancy and temperature of the internal environment are integrated in the
hypothalamus. The hypothalamus also functions with the limbic system as a until that
regulates emotional and instinctual behavior.
Autonomic Reflexes of Spinal cord
Reflex
contractions of the full bladder and rectum occur in spinal animals and humans,
although the bladder is rarely emptied completely. Hyperactive bladder reflexes can keep the bladder in a shrunken state
long enough for hypertrophy and fibrosis of
its wall to occur. Blood pressure is generally normal at rest, but the precise
feedback regulation normally supplied by the baroreceptor reflexes is absent and wide swings in pressure are common.
Bouts of sweating and blanching of the skin also occur.
Sexual Reflexes of Spinal cord other
reflex responses are present in the spinal animal,
but in general they are only fragments ol patterns
that are integrated in the normal animal into purposeful sequences. The sexual
reflexes are example. Coordinated sexual activity depends upon a series of
reflexes integrated at many neural
levels arc is absent after cord transection. However,
genital manipulation in male spinal animals and humans produces erection and
even ejaculation. In female spina dogs,
vaginal stimulation causes tail deviation and movement of the pelvis into the copulatory
position.
Neurosecretion.
The hormones of the posterior
pituitary gland are synthesized in the cell bodies of neurons in the supraoptic and
paraventricular nuclei and transported
down the axons of these neurons to the posterior lobe. Some of the neurons make oxytocin
and others make vasopressin, and oxytocin-containing
and vasopressin-containing cells are found in both
nuclei. The neurons also conduct action potentials, and action
potentials reaching the endings of the axons trigger release of the hormones by Ca:+-dependent
exocytosis. Oxytocin and vasopressin are neural hormones, ie, hormones secreted into the circulation by nerve cells.
The term neurosecretion was originally coined to describe the secretion of
hormones by neurons.
Effects of vasopressin because its principal physiologic effect is the retention of water by the kidney, vasopressin is often called the antidiuretic
hormone (ADH). It increases the permeability of the collecting ducts of
the kidney, so that water enters the hypertonic interstitium
of the renal pyramids. The urine becomes concentrated and its volume
decreases. The overall effect is therefore retention of water in excess
of solute; consequently, the effective osmotic pressure of the body fluids is decreased.
Effect of Oxytocin on the Breast in mammals, an important physiological effect of oxytocin is on the myoepithelial cells, smooth muscle-like cells that line the ducts of the breast. The hormone makes these cells
contract, squeezing the milk out of the
alveoli of the lactating breast into the large ducts (sinuses) and thence out
the nipple. Oxytocin causes contraction
of the smooth muscle of the uterus. Feature
of Hypothalamic Control Anterior
pituitary secretion is controlled by chemical
agents carried in the portal hypophyseal vessels
from the hypothalamus to the pituitary.
These substances have generally been referred to as releasing and inhibiting
factors, but they are now commonly called hypophysiotropic
hormones. The latter term seems appropriate,
since they are secreted into the bloodstream and act at a distance from
their site of origin. There are 7 relatively well established hypothalamic releasing and inhibiting hormones:
corticotropin-releasing hormone
(CRH); thyrotropin-releasing hormone (TRH); growth hormone-releasing hormone (GRH);
growth hormone-inhibiting hormone (GIH; also called somatostatin); luteinizing hormone-releasing hormone (LHRH); prolactin-releasing
hormone (PRH); and prolactin-inhibiting hormone (PIH) Hypothalamus and temperature regulation Anterior
hypothalamus response to heat. Posterior hypothalamus
response to cold. Afferents go from cutaneous cold receptors, temperature-sensitive cells in hypothalamus.
References:
1. Review of Medical
Physiology // W.F. Ganong. – Twentieth edition, 2001.
– P. 217-223, 226-229, 232, 233, 242.
2. Textbook of Medical
Physiology // A.C. Guyton, J.E. Hall. – Tenth edition, 2002. – P. 364, 632,
681-684, 697-707, 736.