Reticular formation

Various nuclei: 1) Nuclei of medullary reticular formation 2) Nuclei of pontine reticular formation 3) Nuclei of midbrain reticular

formation

• Situated: - Downwards into spinal cord - Upwards up to thalamus and subthalamus

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

Functional divisions of Reticular FormationAscending Reticular Activating System - ARAS

Receives fibers from the sensory pathways via long ascending spinal tracts.

Alertness, maintenance of attention and wakefulness.

Emotional reactions, important in learning processes.

Tumor or lession – sleeping sickness or coma.

Descending Reticular System

Inhibitory:- Smoothness and

accuracy of voluntary movements

- Reflex movements- Regulates muscle tone- Maintenance of posture- Control vegetative

functions

Facilitatory:- Mantains the

muscle tone- Facilitates

autonomic functions

- Activates ARAS

Reticular formation

• Afferents • Spinal cord----------spinothalamic

tract,spinoreticular tract,medial lemniscus• From cranial nerve nuclei---------

vestibular,acoustic and visual pathway

Reticular formation

• Cerebellum-------------cerebelloreticular• From

subthalamus,hypothalamus,thalamus,corpus striatum and limbic system

• From primary motor and primary sensory area

Connections of Reticular Formation

Afferent connections of reticular formation

Efferents

• Reticulospinal • Reticulobulbar• To sympathetic and parasympathetic outflow• To corpus striatum

Efferents

• Cerebellum• Red nucleus• Substantia nigra • Tectum• To thalamus• Subthalamus• Hypothalamus• Most regions of cerebral cortex

Efferent connections of reticular formation

Functions of reticular formation

• Control of skeletal muscles----------reticulospinal and reticulobulbar tracts influence alpha and gamma neurons

• Modulate muscle tone and reflex activity• Reciprocal inhibition• Maintenance of tone of antigravity muscles via

inner ear apparatus and vestibulospinal tract• Respiratory center controlling respiratory

muscles

Control of somatic and visceral sensation

• Central location --facilitatory or inhibitory influence---on ascending pathways to supraspinal levels

• Key role in gating mechanism for the control of pain perception

Control of autonomic nervous system

• Cortex,hypothalamus and other subcortical nuclei control ANS via Reticulospinal and Reticulobulbar tracts descending to sympathetic and parasympathetic outflow

•

Control of endocrine nervous system

• Directly or indirectly via hypothalamus through releasing or release inhibiting factors

• Influence on biological clock• Multiple afferent and efferent pathways to

hypothalamus can influence biological rhythms• Reticular activating system• All ascending sensory pathways to cerebral

cortex are channeled through reticular formation• Degree of wakefulness depends on the activity of

reticular activating system