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RETICULAR FORMATION,

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Reticular Formation

Various nuclei: 1) Nuclei of medullary reticularformation

2) Nuclei of pontine reticular formation

3) Nuclei of midbrain reticularformation

within the meshes of this reticulum are located functionally associated nervous

structures which are vestibular nucleus, red nucleus and subthalamic nucleus.

Situated: - Downwards into spinal cord- U wards u to thalamus and subthalamus

Diffused mass of neurons and nerve fibers forming an ill-definedmeshwork of reticulum in the central portion of the brainstem.

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RETICULAR FORMATION AFFERENT & EFFERENTCONNECTIONS OF RETICULAR FORMATION

ReticularFormation

ReticularFormation

Cerebellum

RedNucleus

Thalamus,Hypothalamus

SC

CortexSubstancia Nigra

Tectum

EFFERENT CONNECTION TOTHE RETICULAR FORMATION

AFFERENT CONNECTION TOTHE RETICULAR FORMATION

Cortex

Thalamus

CorpusStriatum

Cerebellum

SC

SensoryPathways

(Touch, pain,

temperature,kinesthesticsensation)

Optic, auditoryolfactory andtastepathways

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Reticular neurons are classified into:

- sensory neurons

- Motor neurons

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Sensory neuron Motor neurons

Small in size Large in size

Large in number Small in number

Receive impulses from;Lemniscal pathways in brain

stem (medial, lateral,trigeminaland spinal lemnsci)

Olfactory pathway-vestibular

apparatus-cerebral cortex-cerebellum-hypothalamus

Receive impulse from sensoryneurons.

They are 2 types:

Facilitatory reticular formation(FRF)

Inhibitory reticularformation(IRF)

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reticular formation Divided into two branches

ASCENDING RETICULARACTIVATION SYSTEM

DESCENDING RETICULARACTIVATION SYSTEM

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DESCENDING RETICULAR ACTIVATION SYSTEM - DRAS

INHIBITORY (gives origin to

crossed lateral reticulospinal tract.)

Smoothness and accuracy ofvoluntary movements;

Reflex movements;

Regulates muscle tone;

Maintenance of posture;

FACILITATORY (gives origin tothe uncrossed medial

reticulospinal tract )

maintains the muscle tone;

Facilitates autonomic

functions;

Activates ARAS.

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ASCENDING RETICULAR ACTIVATION SYSTEM -ARAS

Receives fibers from the

sensory pathways via longascending spinal tracts.

Extends upward as reticularactivating system (RAS) that

relays in non specificthalamic nuclei (intralaminarand midline nuclei) thenthalamic radiation arises

toward the cerebral cortex.This pathway is calledreticulo-thalamocorticalpathway

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Ascending Reticular Activating System - ARAS

Functions:

Alertness, maintenance of attention and wakefulness.

Emotional reactions, important in learning processes.

It controls the ability to filter out information from external sourcesand focus on one particular fact, detail or thought .

It is responsible for providing an integrated (cardiovascular,respiratory and motor) response to external stimuli.

The Reticular Activating System is the attention center in the brain.It is the key to "turning on your brain," and also seems to be thecenter of motivation.

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Factors affecting activity of RAS

Factors increasing the activityof RAS

Impulses from sensory,motorpathways.

Stress

Sympathomimetic drugs

Caffeine

Thyroid hormone

Factors decreasing the activityof RAS

Decreased sensory input

Impulses from sleep centers

Anesthetic drugs

Tumor that destroy thissystem

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