Talks about the RAS in the brain of a human body

1. Reticular activating system

2. RETICULAR ACTIVATING SYSTEM
• Is an area of the brain (including the reticular
formation and its connections) responsible for
regulating arousal and sleep-wake transitions.
• It is one of the most important parts of the brain,
which controls many vital brain functions of
consciousness.
• Moruzzi and magoun first investigated the brain`s
sleep-wake mechanisms in 1949.
• It was later appreciated that the RAS is responsible
for many cognitive functions related to awareness.

3. Anatomical components
• The RAS is composed of several neuronal circuits connecting
the brainstem to the cortex.
• This pathway originates in the upper brainstem reticular core
and project through synaptic relays in the rostral intralaminar
and thalamic nuclei to the cerebral cortex.
• Several areas traditionally included in the RAS are;
1. Midbrain reticular formation
2. Mesencephalic nucleus (mesencephalon)
3. Thalamic intralaminar nucleus
4. Dorsal hypothalamus
5. tegmentum

4. Neurotransmitters
• The neuronal circuits of the RAS are modulated by complex
interactions between a few main neurotransmitter.
• The RAS contains both cholinergic and adrenergic
components , which exhibits synergy as well as competitive
actions to regulate thalamocortical activity and the
corresponding behavioral state
• The RAS functions are controlled by certain cholinergic
(related to acetylcholine) and adrenergic (related to
adrenaline) neurotransmitters.

5. RAS; location and structure
• The RAS connects the lower parts of the brain, which
is the brain stem, to the cerebral cortex through
various neural paths .
• The brain stem controls most of the involuntary
functions as well as reflexes of the body , while
cerebral cortex is the seat of consciousness and
thinking abilities.
• So, the RAS forms a link between these two different
regions.

6. RAS; Location & structure
• One is the ascending RAS (which has
connections with the cerebral cortex,
hypothalamus and thalamus) and the other is
the descending RAS (which is connected to the
cerebellum and many sensory nerves)
• A large part of the RAS consists of the brain
parts that are responsible for the survival
instincts.

7. Function
• Regulating sleep-wake transitions
• The main function of the RAS is to modify and potentiate thalamic
and cortical functions such that electroencephalogram(EEG)
desynchronization ensures.
• There are distinct differences in the brain`s electrical activity during
periods of wakefulness and sleep;
– Low voltage fast burst brain waves (EEG desynchronization) are associated with wakefulness and
REM sleep (which are electro physiologically identical)
– Large voltage slow waves are found during non-REM sleep.
• When thalamic relay neurons are in burst mode the EEG is
synchronized and when they are in tonic mode it is desynchronized.