Post on 23-Nov-2014
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