HYPOTHALAMUS
1.
Introduction :
The
hypothalamus is a part of the diencephalon.
2.
Situation :
Hypothalamus
lies in floor and lateral wall of the third ventricle.
3.
Structure :-
v
It
has been designated as the head ganglion of the autonomic nervous system
because it takes part in the control of many visceral and metabolic activities
of the body.
Anatomically , it includes
v
The
floor of the third ventricle, or structures in the interpeduncular fossa.
v
The
lateral wall of the third ventricle below the hypothalamic sulcus.
4.
Boundaries :-
v
The
base of the brain the hypothalamus is bounded as follows :
Anteriorly : - By the optic chiasma .
Posteriorly :- the posterior perforated substance ; and on
each side by the optic tract and crus cerebri.
Sagittal section of
the brain it is bounded anteriorly by the lamina terminalis;
Inferiorly : by the
floor of the third ventricle.
Posterosuperiorly
: By the hypothalamus sulcus.
5.
Parts of the hypothalamus :
The
hypothalamus is subdivided into optic, tuberal and mammillary parts. The nuclei
present in each part are as follows.
1.
Optic
part :
a.
Supraoptic
nucleus, above the optic chiasma.
b.
Para
ventricular nucleus, just above the supraoptic nucleus.
2.
Tuberal
part
a.
Ventromedial
nucleus.
b.
Dorsomedial
nucleus.
c.
Tuberal
nucleus, lateral to the ventromedial nucleus.
3.
Mammillary
part :
a.
Posterior
nucleus , caudal to the ventromedial and dorsomedial nuclei.
b.
Lateral
nucleus, lateral to the posterior nucleus.
The nuclei 3,4 and 6
are separated from nuclei 5 and 7 by the column of the fornix , the
mamillothalmic tract and the fasciculus retroflexus.
6.
Important connections :
A.
Afferents
:
1.
The
hypothalamus receives visceral sensations through the spinal cord and brain
stem .
2.
It
is also connected to several centres connected with olfactory pathways,
including the piriform cortex; with the cerebelleum ; and with the retina.
B.
Efferents
:
1.
Supra
opticohypophyseal tract from the optic nuclei to the pars posterior , the pars
tuberalis and the pars intermedia of the hypophysis cerebri.
2.
Mamillothalamic
tract.
3.
Mamillotegmental
tract (periventricular system of fibres).
7.
Functions of hypothalamus :
The
hypothalamus is a complex neuroglandular mechanism concerned with regulation of
visceral and vasomotor activities of the body. Its functions are listed below.
1.
Endocrine
control :
By forming releasing
hormones or release inhibiting hormones, the hypothalamus regulates secretion
of thyrotropin (TSH) , corticotropin (ACTH), somatotropin (STH), prolactin,
luteinizing hormone (LH), follicle stimulating hormone (FSH) and melanocyte
stimulating hormone by the pars anterior of the hypophysis cerebri.
2.
Neurosecretion
:
Oxytocin and
vasopressin are secreted by the hypothalamus and transported to the
infundibulum and the posterior lobe of the hypophysis cerebri.
3.
General
autonomic effects :
The anterior parts of
the hypothalamus chiefly mediate parasympathetic activity, and the posterior
parts, chiefly mediate sympathetic activity, but the effects often overlap.
Thus the hypothalamus
controls cardiovascular, respiratory and alimentary functions.
4.
Temperature
regulation :
The hypothalamus
maintains a balance between heat production and heat loss of the body.
5.
Regulation
of food and water intake :
The hunger or feeding
centre is placed laterally; the safety centre, medially.
Stimulation of the
feeding centre or damage of the satiety centre cause hyperphagia (over-eating)
leding to obesity.
6.
Sexual
behavior and reproduction :
Through its control
of the anterior pituitary, the hypothalamus controls gametogenesis, various
reproductive cycles.
7.
Biological
clocks :
Many tissues and
organ-systems of the body show a cyclic variation in their functional activity
during the 24 hours of a day .
8.
Emotion,
fear, rage,aversion, pleasure and reward:
These faculties are controlled by
the hypothalamus, the limbic system and the prefrontal cortax.
Applied anatomy :
1.
Obesity
: Frolich’s syndrome , or Laurence Moon-Biedl syndrome.
2.
Diabetes
insipidus.
3.
Diencephalic
autonomic epilepsy: - this is characterized by flushing, sweating, salivation,
lacrimation, tachycardia,retardation of respiratory rate, unconsciousness etc.
4.
Sexual
disturbance . either precocity or importance.
5.
Disturbance
of sleep .
6.
Hyperglycaemia
and glycosuria.
7.
Acute
ulcerations in the upper part of the gastrointestinal tract.
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