VISCERAL NERVOUS SYSTEM ANATOMY VETS.pdf

ANATOMY

1. VISCERAL NERVOUS SYSTEM
T.KASIYANDIMA,T.MAGEJA,A.GAPARA,M.MANDIKIYANA,
T.CHIDANGWARA,Y.MABANDA,L.SEMBA,L.MUCHETU,K.MUZAMANI,
N.SITHOLE
BVSc,UZ

3. Introduction
ogoverns the visceral functions.
ohas many particular responsibilities, which may be defined as the maintenance of
the internal environment within the permissible limits
oConsists of visceral pathways can be divided into afferent and efferent pathways
oThe efferent pathways can be subdivided into sympathetic and parasympathetic
pathways.
oThe common concentration on the peripheral motor pathways distracts attention
from the central controlling structures and the afferent pathways that supply the
information necessary for appropriate responses.

4. THE HYPOTHALAMUS
•Is an important integration center of which the rostral part is concealed and the caudal
Part is exposed on the surface of the brain
•includes many areas of specialized function and responsibility.
•its functions must include the control of biological rhythms, appetite, water balance, body
temperature, cardiovascular performance, sexual behavior and activity, sleep, muscle
tension, and emotion.(limbic system)
•every body function has visceral implications and the hypothalamus must receive (and
coordinate) information from most other parts of the nervous system, including those of
somatic function.
•Information on the somatic activities is projected via the basal nuclei and relays on the
extrapyramidal motor pathways via the thalamic nuclei to which the somatic afferent
pathways lead.
•Information concerning visceral function is received from mesencephalic nuclei and the
reticular formation.

5. oThe nucleus of the solitary tract is the principal visceral sensory nucleus that receives
topographically organized input from major organ systems by way of the
glossopharyngeus(IX) and vagus(X) nerves.
oAs such it is the region of initial processing of visceral it is the region of initial
processing of visceral cardiovascular and respiratory, and gustatory information.
oThe hypothalamus regulates activity through both nervous and humoral mechanisms,
sometimes in combination.
oThe nervous pathways extend to the brainstem and spinal cord by direct routes or
multisynapticpathways within the reticular formation.
oOther projections provide a feedback to the forebrain routed through rostral thalamic
nuclei.
oThe humoral pathway operates through neurosecretorycells whose products may enter
the bloodstream directly for general distribution or whose products may be conveyed
specifically to the hypophysisby means of a system of portal vessels

7. THE HYPOPHYSIS
•Also known as pituitary gland suspended below the hypothalamus by the
infundibulum,
•consists of two parts the neurohypophysis(posterior lobe) and the
adenohypophysis
•comprises anterior and intermediate lobes.
•The three lobes produce or store several hormones
•The posterior lobe hormones (vasopressin and oxytocin) are produced by
neurosecretorycells within the supraopticand paraventricular nuclei of the
hypothalamus
•are conveyed along the axons for direct release into the neurohypophysial
capillary bed

8. VISCERAL AFFERENT PATHWAYS
•There are both “general” and special visceral afferent pathways,
•the latter is concerned with taste and smell.
•The receptors of the general visceral afferent pathway are found within viscera and
blood vessels;
•most are mechanoreceptors responsive to pressure, stretch, and, less commonly, flow,
•a minority are chemoreceptors responsive to such stimuli as the carbon dioxide
content of the blood.
•The fibers that convey impulses from these receptors travel within any conveniently
located nerve trunk, utilizing those of mainly somatic composition as well as those
whose other components are visceral efferent.

9. The bodies of the primary neurons are located within the dorsal root ganglia
of all spinal nerves (and the equivalent ganglia of certain cranial nerves);
•the axons project on interneurons and projection neurons within the
visceral afferent column of the spinal cord and brainstem
•Short chains of interneurons provide for simple visceral reflexes that have
their last two relays within the visceral efferent column and the peripheral
autonomic ganglia.
•The projection neurons form ascending pathways that follow somatic
systems, both lemniscaland extralemniscal, to end (like these) within
nuclei of the ventrocaudalthalamus.
•A final projection to the cortex may give rise to conscious perception,
although most visceral activity goes unnoticed

10. •The special visceral afferent pathway concerned with taste
follows a similar route to that taken by the general visceral
sensory modalities.
•The course from the taste buds within the facial,
glossopharyngeal, and vagusnerves terminates in the nucleus
of the solitary tract.
•The more complicated olfactory pathways are described
elsewhere

11. •Although most visceral activity occurs without conscious awareness, some
projections to the cerebral cortex give rise to conscious perception, such as
hunger, the sense of fullness of the rectum or the bladder.
•Pain arising from diseased inner organs may be confused with pain arising
from the surface of the body
•This is due to the exchange of information between the afferent visceral
pathway and the cutaneous somatic pathway.
•Each organ has its own reflection area, called head zone, on the body
surface, which in turn can be used to relieve pain of visceral origin
(massage, acupuncture).
•Similar reflex points on the skin exist for the skeletal system (joints, spine).

12. VISCERAL EFFERENT PATHWAYS
•the efferent component of the visceral nervous system is arranged
in two divisions,sympatheticand parasympathetic
•Distinguished by morphology, pharmacology, and physiology.
•The final conducting pathway of both divisions includes two motor
neurons in succession:
•the first has its perikaryonwithin the central nervous system, and
the second is stationed within a peripheral ganglion (Figure 8–53).
•The two are most frequently distinguished as preganglionic and
postganglionic neurons and together are equivalent to the lower
motor neuron of the somatic system.

13. •The preganglionic neurons of the sympathetic division are
located within the lateral (visceral efferent)
•column of the spinal cord between the first thoracic and
middle lumbar segments (with some interspecific variation
•The postganglionic neurons are found in paravertebral ganglia
of the sympathetic chain or subvertebralganglia on the aorta;
both groups are relatively close to the cord.

14. •The parasympathetic preganglionic neurons are restricted to
the nuclei of origin of the oculomotor, facial, glossopharyngeal,
and vagusnerves within the brainstem
•And also the lateral columns of certain sacral segments of the
cord.
•The postganglionic neurons are stationed within small ganglia
in close proximity to or actually incorporated within the walls
of the organs they supply

15. •The transmitter substance at the last sympathetic relay is
norepinephrine and that of the parasympathetic division is
acetylcholine
•Stimulation of the sympathetic pathways results in an increase
in blood pressure, heart rate and respiratory rate, dilatation of
the pupils, while at the same time gut motility and intestinal
gland activity are decreased.

18. Limbic system
ois applied to a collection of brain structures involved with emotional behavior andHas
cortical and subcortical components
oThe cortical part comprises interconnected telencephalicstructures on the medial and basal
aspect of the hemispheres. namely the cingulate gyri, the piriform lobe and the
hippocampus.
oThe subcortical part includes components of the diencephalon (habenula, hypothalamus,
thalamus), midbrain (interpeduncular and tegmental nuclei) and the amygdaloidbody.
oit is often considered to be primarily a “visceral brain” because its major functions are
expressed by visceral motor activity.
oalso triggers emotional behaviour, such as fear, aggression and apparent pleasure and has
great input on thirst, hunger and sexual behaviourand is closely related to the reticular
formation

19. Limbic system
oOlfactory impulses passing by way of the piriform lobes may influence many structures of
the system.
oOf all the sensory inputs, olfaction exhibits the most profound effects on visceral motor
activities that are associated with emotional behavior such as eating, rage, sexual activity,
fear, and drinking.
oThe system also receives optic, auditory, extroceptive, and introceptivestimuli.
oThe efferent pathways from the cortical regions involve nearly all the subcortical nuclei of
the system.
oA major portion of the influences of the limbic cortex is mediated through the efferent
systems of the amygdaloidnuclei.
oElectrical stimulation of the amygdala produces a wide variety of visceral and somatic
reactions and many behavioral reactions such as aggression and anxiety

20. Limbic system
oThe types of behavior most influenced by the limbic system are those essential for
the preservation of the individual or the species.
oThe hippocampus probably plays the predominant part in the limbic system’s
control of emotional expression and behavior through regulation of autonomic,
endocrine, and somatic functions.
oIt is also concerned with memory functions, such as the processing of recently
acquired memory and its more permanent consolidation.
oIn its activities the limbic system is closely associated with the reticular formation of
the brainstem.

21. CLINICAL CORRELATIONS
AUTONOMIC REFLEXES -Neurological examination
oThe pupillary light reflex-assessment of CNII and CNIII.
-Light into an animal’s eye
-Stimulation of photoreceptors in the retina
-Sensory info conveyed via optic nerve to the brainstem
-Parasympathetic cholinergic neurons activated
-Stimulation of the constrictor smooth muscle of the iris
-Pupillary vasoconstriction (miosis)