The reticular formation The reticular formation

Reticular Formation Reticular Formation   loosely arranged neuron cell bodies intermingled with bundles of axons  Various nuclei: 1) Nuclei of medullary reticular formation 2) Nuclei of pontine reticular formation 2) Nuclei of pontine reticular formation 3) Nuclei of midbrain reticular formation 3) Nuclei of midbrain reticular formation   It receives and integrates input from all regions of the central nervous system and processes a great deal of neural information. Diffused mass of neurons and nerve fibers forming an ill-defined meshwork of reticulum in the central portion of the brainstem.

THE RETICULAR FORMATION (cont.) RF is formed of large number of neurons present through the entire brainstem, it extends upward to the level of the thalamus and downward to be continuous with the interneurons of the spinal cord.

Locations of the reticular and vestibular nuclei in the brain stem

THE RETICULAR FORMATION (cont.) Afferent projection 1. All sensory pathways (general or special sensations) 2. Cerebral cortex 3. cerebellum 4. Basal ganglia(corpus striatum) 5. Vestibular nuclei, visual pathway 6. Thalamus, Subthalamus and Hypothalamic nuclei

THE RETICULAR FORMATION (cont.) Efferent projection: Efferent projection: 1. Reticulobulbar and reticulospinal tracts 2. descending pathway to sympathetic and parasympathetic outflow of ANS 3. cerebellum 4. Basal ganglia(corpus striatum) 5. Thalamus, Subthalamus and Hypothalamic nuclei

Connections of Reticular Formation Fig. 1 -Afferent connections of reticular formation Fig. 2 – Efferent connections of reticular formation

Ascending Reticular Activating System - ARAS the reticular activating system (RAS) is an area of the brain (including the reticular formation and its connections) responsible for regulating arousal and sleep- wake transitions. the reticular activating system (RAS) is an area of the brain (including the reticular formation and its connections) responsible for regulating arousal and sleep- wake transitions. Receives fibers from the sensory pathways via long ascending spinal tracts. Receives fibers from the sensory pathways via long ascending spinal tracts. Alertness, maintenance of attention and wakefulness. Alertness, maintenance of attention and wakefulness. Emotional reactions, important in learning processes. Emotional reactions, important in learning processes. Tumor or lesion – sleeping sickness or coma. Tumor or lesion – sleeping sickness or coma. Functional divisions of Reticular Formation Fig.3 – Brain section.

Functions 1. Control of skeletal muscles 2. Control of somatic and visceral sensations 3. Control of ANS 4. Influence the biologic clock 5. The reticular activating system 6. Control of endocrine nervous system

Vestibulospinal and reticulospinal tracts descending in the spinal cord to excite (solid lines) or inhibit (dashed lines) the anterior motor neurons that control the body’s axial musculature

Damage to RF persistent unconsciousness and even coma Damage to RF persistent unconsciousness and even coma

Sleep Sleep is defined as changed state of consciousness from which the person can be aroused by sensory or other stimuli, it is facilitated by reducing sensory input and by fatigue. Coma is unconsciousness from which the person cannot be aroused.