the hypothalamic functions

1. of the brain
THE HYPOTHALAMUS
The hypothalamus is a small part of the brain weighing
about 5 grams. It bounds the ventral half of the 3rd ventricle
and lies below the thalamus.
On its inferior pole,it is connected with the pituitary
gland.the afferent and efferent connections of the
hypothalamus show that it is a vital integration centre for the
somatic,autonomic and endocrine functions.

2. Ventral hypothalamus is reciprocally connected to the upper
midbrain,the limbic midbrain and the limbic system.It receives
afferent inputs from all parts of the body through the spinal
cord,medulla oblongata and the reticular formation of the brain stem.
These pathways project into the hypothalamus either through the
thalamus or limbic midbrain area.Efferent connections from the
hypothalamus link it with autonomic and somatic nuclei in the
reticular formation.

3. The medial hypothalamus also makes a reciprocal connections with
the lateral hypothalamus and receives direct afferent inputs from
non-hypothalamic parts of the brain.
Special neurons in the medial hypothalamus measure the
concentration of important constituents of the blood or cerebrospinal
fluid. In this way, the medial hypothalamus monitors the internal
milieu(internal environment).
Such receptors measure blood concentration of glucose, salts,
endocrine hormones or the temperature of blood

4. The efferent connections from the medial hypothalamus to the
hypophysis are neuronal to the neurohypophysis (the
hypothalamohypophysial tract) and hormonal to the
adenohypophysis(anterior pituitary gland) through the portal
hypophysiavessels.
The hypothalamus is made up of many hypothalamic nuclei and each
of these nuclei have been associated with specific functions.

5. HYPOTHALAMIC NUCLEI THEIR FUNCTIONS
Hypothalamic nuclei Functions.
 Supraoptic nuclei -Vsaopresin release(ADH)
 Paraventricular nuclei -Oxytocin release (Pitocin)
 Medial preoptic area -Bladder contraction,decreased heart
rate &blood pressure
 Posterior preoptic and anterior
Hypothalamic areas -Body temperature regulation

6. Hypothalamic nuclei Functions (contd)
 Mamilary body -Feeding reflexes
 Lateral hypothalamic area -Thirst & hunger
 Ventromedial nucleus -Satiety,neuroendocrine control
 Periformical nucleus -Hunger,rage,increased blood
pressure
 Dorsomedial nucleus -Gastrointestinal stimulation
 Posterior hypothalamus -Raised BP,pupillary
dilation,shievering.

7. Functions of the hypothalamus
The major functions of the hypothalamus are listed below:
a. Autonomic function
b. Cardiovascular function
c. Circadian rhythm(cyclic phenomenma)
d. Hunger
e. Thirst
f. Posterior pituitary secretion

8. g.Anterior pituitary secretion
h.Temperature regulation
I.Sexual behavior
j.Defense reaction –rage,fear
k.Sleep

9. ELECTROENCEPHALOGRAM (EEG)
EEG is the study of electrical activities of the brain. EEG is the
graphical recording of electrical activities of the brain. Electrical
activity of the brain is complicated when compared to that of a single
nerve fibre or neuron,this is due to the involvement of large number
of neurons and synapses.
German Psychiatrist Hans Berger was the first one to analyse the EEG
waves systematically and hence the EEG waves are referred to as
Berger waves.

10. Significance of EEG
EEG is useful in the diagnosis of neurological and sleep disorders.Its
pattern is altered in the following neurological disorders :
1. Epilepsy ,which occurs due to excessive discharge of impulsesfrom
cerebral cortex
2. Disorders of midbrain affecting ascending reticular activating
system (ARAS)
3. Subdural hematoma during which there is collection of blood in
subdural space over the cerebral cortex

11. Method of Recording EEG
Electroencephalograph is the instrument used to record EEG. The
electrodes called scalp electrodes from the instrument are placed
over unopened skull or over the brain after opening the skull or by
piercing into brain.
Electrodes are of two types,Unipolar and Bipolar electrodes. While
using bipolar electrodes,both the terminals are placed in different
parts of the brain. When using unipolar electrode, the active
electrode is placed over over cortex and the inactive electrode is kept
on some part of the body away from cortex.

12. Waves of EEG
Electrical activity recorded by EEG may have synchronized or
desynchronized waves. Synchronized waves are the regular and
invariant waves,whereas dysnchronized waves are irregular and
variant waves.
In normal persons,EEG has three frequency bands:
1. Alpha rhythm/waves
2. Beta rhythm /waves
3. Delta rhythm/waves

13. In addition to these three types of waves, EEG in children shows
theta waves.
Alpha Rhythm/waves :
Alpha waves consists of rhythmical waves,which appear at a frequency
of 8 to 13Hz with the amplitude of 50µV.Alpha waves are synchronized
waves.
Alpha rhythm is obtained in inattentive brain or mind as in
drowsiness,/slight sleep with closed eyes.

14. It is abolished by visual stimuli or any other type of stimuli or by
mental effort.So,it is abolished when eyes are opened.
Alpha Block :Alpha block is the replacement of synchronized alpha
waves in EEG by desynchronized and low voltage waves when the
eyes are opened.
The desynchronized waves do not have specific frequency.It occurs
due to any form of sensory stimulation of mental concentration,such
as solving arithmetic problems.

15. Beta Rhythm :
This includes high frequency waves of 15 to 60 Hz,but the amplitude is
low,i.e 5 to 10µV.Beta waves are desynchronized waves and are
recorded during mental activity or mental tension or arousal state.It is
not affected by opening the eyes.
Delta Rhythm/waves – This includes waves with low frequency and
high amplitude .The waves have the frequency of 1 to 5Hz with the
amplitude of 20 to 200 µV .It is commom in early childhood during
waking hours. In adults,it appears mostly during deep sleep.

16. Presence of Delta waves in adults during conditions other than sleep
indicates the pathological process in brain like tumor,
epilepsy,increased intracranial pressure and mental deficiency or
deoression.These waves are not affected by opening the eyes.
Theta waves-theta waves are obtained generally in children below
5years of age. These waves are of low frequency and low voltage
waves. The frequency of theta waves is 4 to 8 Hz and the amplitude is
about 10µV.

17. PHYSIOLOGY OF SLEEP
Sleep is the natural periodic state of rest for mind and body with
closed eyes characterized by partial or complete loss of consciousness
.Loss of consciousness leads to decreased response to external stimuli
and decreased body movements.
Depth of sleep is not constant throughout the sleeping period. It
varies in different stages of sleep. Sleep can also be defined as a state
of unconsciousness from which the person can be aroused by sensory
or other stimuli. It is different from coma, which is unconsciousness
from which a p[erson cannot be aroused.In other words,sleep is an
alteration of,rather than loss of consciousness .

18. Sleep Requirement
Sleep requirement is not constant. However,average sleep
requirement per day at different different age group is :
1. New born infants :18 to 20 hours
2. Growing children : 12 to 14 hours
3. Adults :7 to 9 hours
4. Old persons :5 to 7hours

19. Physiological changes during sleep
During sleep,most of the body functions are reduced to basal
level.The following are important changes in the body during sleep:
 Plasma volume : Plasma volume decreases by 10 % during sleep
 Cardiovascular system :
Heart rate : the heart rate reduces during sleep.It varies between 45
and 60 beats per minute (Bradycardia)
Blood pressure : Systolic blood pressure falls to about 90 to 110 mmHg.

20.  Lowest level of blood pressure is reached about 4th hour of sleep and
remains at this level till a short time before waking up.Then,the blood
pressure starts to rise. If sleep is disturbed by exciting dreams,the
pressure is elevated above 130mmHg.
3.Respiratory system: Rate and force of respiration are decreased.
Respiration becomes irregular
4.GIT(gastrointestinal tract)-salivary secretion decreases during sleep.
5.Excretion : formation of urine decreases and specific gravity of urine
increases.

21. 6.Sweat secretion –sweat secretion decreases during sleep.
7.Lacrimal secretion : decreases during sleep.
8. Muscle tone : tone in all muscles except ocular muscles decreases
significantly during sleep.This is called sleep paralysis.
9. Brain : brain is inactive during sleep.