RETICULAR FORMATION

1. RETICULAR
FORMATION
DR.NILESH KATE.
M.D.
ASSOCIATE PROFESSOR,
DEPARTMENT OF PHYSIOLOGY,
ESIC MEDICAL COLLEGE,
GULBARGA.

2. OBJECTIVES
 Introduction.
 Location of Reticular Formation.
 Nuclei of Reticular Formation.(neuronal aggregates)
 Afferents and Efferent of Reticular Formation.
 Functions of Reticular formation.
 Ascending Reticular activating system.
 Descending Reticular activating system
 Role in sleep and wake fullness.
 Role in EEG and learning.
 Applied physiology.

3. INTRODUCTION

4. PHYSIOLOGICAL ANATOMY.
 Formed by neurons & processes
left over after well defined named
nuclei & pathways.
 Phylogenetically :- old system.
 Poorly defined
 Located in the brain stem.
 Comprises of medullary,
pontine,& midbrain RF.
 Poly synaptic
 Has both ascending and
descending components.

5. EXTENT OF RETICULAR FORMATION:
 The reticular
formation is situated
in brain stem, and
extends downwards
into spinal cord and
upwards up to
thalamus and sub
thalamus.

6. NEURONAL AGGREGATES.
RETICULAR NUCLEI.
The entire reticular
formation is broadly
arranged into three
columns:
 Median
 Medial and
 Lateral columns

7.  Position:- Lie next to middle line.
 Nuclei:- Collectively called nuclei of Raphe.
 Extension:- From the medulla up to the midbrain in
vertical sheets bilaterally
 Present in the Para median zone.
 Serotonergic neurons.
THE MEDIAN COLUMN

8.  Position:- lateral to the nuclei of median
column.
 Nuclei:- Collectively made up of large cells
mainly
 1. Giganto cellular nucleus.
 2. Pontine tegmental reticular nucleus.
 3. Cunei form and sub cuneiform nuclei.
THE MEDIAL COLUMN

9.  Position:- Lateral to the nuclei of medial
column.
 Nuclei:- Collectively made up of small cells
mainly
 Parvocellular cells:- Control mainly the
visceral functions.
 Extension:- From medulla to mid brain
THE LATERAL COLUMN

10. FUNCTIONAL NEURONAL AGGREGATES.
 Cardiac centers
 Respiratory centers.
 Vasomotor centers.
 Salivatory centers
 Chemoreceptors neurons.

11. RETICULAR PATHWAYS
 Connections
Afferent
connections.
Efferent
connections.
Descending
projections.
Ascending
projections.

12. AFFERENTS TO RETICULAR FORMATION
1. Spinal cord via the
spino reticular tract and via
collaterals from all
ascending tracts.
2. Brain stem afferents
from the cranial nerves .
(Including Vestibular)
3. Tectoreticular :- Tectum
(Superior and inferior
colliculi) conveying visual
and auditory impulses

13. AFFERENTS TO RETICULAR FORMATION
4 Cerebellum (cerebello reticular)
5. Basal ganglia directly and
indirectly
6. Neocortex – Cortico reticular
fibres from the motor, sensory
cortex, orbital, prefrontal, parietal
and temporal lobes, cingulate
gyrus and collaterals from the
corticofugal fibres.
7. Limbic lobe including the
amygdaloid, hippocampus.

14. EFFERENTS FROM RETICULAR FORMATION
 Efferent connections are:
1. To the spinal cord.
The descending reticulospinal
tracts (medial inhibitory and lateral
facilitatory) connect with the
anterior horn cells either directly or
through internuncial neurons.
 They also connect to the lateral
horn cells which are the cells of
origin of sympathetic nervous
system.
 2. To brain stem.
The reticulo bulbar fibres connect
to the cranial nerve motor nuclei.

15. EFFERENTS FROM RETICULAR FORMATION
3. To the Cerebellum
4. To the red nucleus,
substantia nigra and
tectum in the midbrain
5. To the thalamus, sub
thalamic nuclei and
hypothalamus
6. To the corpus striatum,
Neocortex and limbic
lobe indirectly through
the thalamus and
hypothalamus.

16. FUNCTIONAL COMPONENTS OF RETICULAR
FORMATION
 On the basis of functions,
Two systems namely:
 1. Ascending reticular
activating system
 2. Descending reticular
activating system.

17. ASCENDING RETICULAR ACTIVATING
SYSTEM
 It projects into cerebral cortex in
two ways
 1. Through Subthalamus and
 2. Through Thalamus
 Begins in lower part of brain
stem, extends upwards through
the Pons, midbrain, thalamus and
finally projects throughout the
cerebral cortex.

18. DESCENDING RETICULAR SYSTEM
 Functionally, descending
reticular system is
divided into two
subdivisions namely
i) Descending
inhibitory reticular
projection
ii) Descending
facilitatory reticular
projection

19. FUNCTIONS OF RETICULAR FORMATION
 Role in Sleep and Wakefulness cycle.
 Responsible for the alerting responses to emotion and to
muscular work.
 Controls muscle tone .
 Influences Endocrine Secretion
 Role in visceral function .
 Influences circadian rhythm.
 Influences EEG And LEARNING.
 Modulates afferent transmission
 Influences Autonomic nervous system.

20. ROLE IN SLEEP AND WAKEFULNESS
RAS :- Strong facilitatory drive to
central neurons
 Input through trigeminal
lemniscus and visuoauditory
tracts.
 Experimental evidence
 A section at the upper border
of the spinal cord separating
the entire brain - electrical
activity of the cortex showed a
desynchronized pattern,
indicating that the animal is
awake.

21. ROLE IN SLEEP AND WAKE FULLNESS
 A section above the
superior colliculi
separating the entire
brainstem. Electrical
activity of the cortex
showed, synchronized
pattern indicating that the
animal is in sleep.
 C) Extensive lesion of the
ARAS produces
Sleep

23. ROLE IN MUSCLE TONE
 Mainly the Descending
reticular formation has a
role in regulating the
muscle tone and hence
maintenance posture and
equilibrium
 Muscle tone is maintained
by facilitatory and
inhibitory reticular
formation

24. ROLE IN MUSCLE TONE:
 These two divisions act
through γ motor neurons
and there by modulate the
muscle tone. FRF
increases the muscle tone
of antigravity muscles. IRF
decreases.
 Normally there is a balance
between the activities of
the FRF and the IRF.

25. ENDOCRINE CONTROL - THROUGH HYPOTHALAMUS
A) Stress :-
Stimulate the reticular formation,
which in turn can active
hypothalamus through the CNS.
So, an increased release of CRF,
which while acting on the anterior
pituitary releases ACTH. This
increases cortisol secretion.
B) There is increased secretion of
catecholamine and Gastric HCL
secretion
C) stimulates TSH secretion through
the hypothalamus.
D) Cause release of gonadotrophins.

26. ROLE IN VISCERAL FUNCTION
 Visceral function like gastric
secretion, GIT motility, heart rate,
BP, Respiration, Salivation,
Vomiting, etc., are influenced by
various centers located in the RF
of the medulla.
 These are VMC, CIC, respiratory
centre, vomiting centre, salivary
nuclei, etc., the effects are
modified mainly through
autonomic nervous system.

27. CIRCADIAN RHYTHM
 Reticular activating
system influences
sleep and
wakefulness
 Thereby Regulates
Circadian rhythm

28. ROLE IN EEG AND LEARNING
 Activation of the entire cerebral
cortex .
 The EEG pattern obtained in this
state is desynchronized 18 –
30Hz.
 The animal is wakeful, alert and
the learning is facilitated
 Inactivation of the reticular
formation leads to
 Synchronized EEG pattern.
 Produce sleep hence animal
cannot learn.

29. AROUSAL FROM THE CORTEX
 The RAS can also be activated
from the cortex, the most
effective parts being the
 Orbital part of the frontal
lobe, superior temporal gyrus
and
 The cingulate gyrus (and
to some extent the sensory
motor cortex).
 This may be responsible for
the alerting responses to
emotion and to muscular
work.

30. MODULATION OF SENSORY INPUT
 Impulse modulation:-
 Impulses in the sensory receptor of their
transmission can be modulated by
reticular formation.
 It has been shown that stimulation of the
bulbar reticular formation inhibits
transmission at the first synapse of the
ascending sensory tracts.
 Selective attention
 It is also well known that when
one’s attention is intensely fixed
on one object or task, other
sensory impressions are less
effective .

31. NEUROTRANSMITTERS OF RETICULAR
FORMATION
 Large cholinergic neuron.:- project to cortex via
thalamus.
 Small adrenergic neurons:- via Intralaminar nuclei
of thalamus.
 Noradrenergic neurons.:- To cerebellum.
 Dopaminergic neurons :- To Basal ganglia
 Serotonergic neurons:- Project to Thalamus,
Cerebral cortex, Hypothalamus & Limbic structure.

32. APPLIED PHYSIOLOGY.
 Drugs Excite Reticular Formation:
 Alerting and arousal :-Sympathomimetic drugs (eg.,
adrenaline, nor adrenaline, amphetamine).
 Acetylcholine also increases cortical activity.
 Increased CO2, rise of BP also increase the excitability of
the RAS.
 Drugs Inhibits Reticular Formation:
 General anesthetics, sedatives eg., barbiturates diminish
RAS activity

33. AT THE END OF THE CLASS YOU CAN FIND
REASONS FOR
 Many prerequisites for sleep.
 Selective attention.
 Circadian rhythm.
 Sleep and wakefulness cycle.
 Action of different sedatives & hypnotics.
 Ways of Arousal from sleep.

34. Thank you