Functions of BSRF
BSRF is a neuronal network extending the length of the medulla, pons, midbrain and then projects into thalamus and hypothalamus. Caudally it is continuous with the internuncial neurons of the spinal cord.
The efferent fibres of the reticular formation are organised into ascending and descending reticular formation.
The ascending reticular formation projects into other areas of brain, including brain stem, cerebrum and cerebellum; the descending reticular formation projects into the spinal cord.
The BSRF regulates the sensory, motor and the endocrine functions.
It is constituted by very small to very large sized sensory and motor neurons. The small neurons form multiple connections within the reticular formation.
Ascending reticular formation
Ascending reticular formation alters the consciousness through the sensory inputs from the auditory, visual, olfactory, tactile, pain and proprioceptive sensory systems. It regulates the neuronal activity within the brain and contributes to wakefulness. It controls the activity of the cerebral cortex, hippocampus, basal ganglia and cerebellum and it is referred to as behavioral arousal.
Ascending Reticular Activating System (ARAS) of the BSRF is involved in alertness/ wakefulness of the animal. They receive sensory information from all sensory receptors and also have inputs from the brainstem, cerebellum and cerebral cortex. These sensory inputs activate the RAS neurons and this in turn activates wide areas of the cerebral cortex. Reduction in the activity of the RAS can lead to sedation, sleep and coma.
Descending reticular formation
Ascending reticular formation influences the motor activities such as flexor and extensor reflexes and decerebrated rigidity. It alters the activity of the alpha and gamma motor systems through reticulospinal tract. It also contains centres that inhibit spinal motor neurons.
The reticular formation contains the centres that promote wakefulness (midbrain RAS). Through pontine raphe nuclei it promotes sleep.
Other functions of BSRF are – Respiratory control, cardiovascular, micturition, emesis, rumination, deglutition, mastication control etc.
ROLE OF RETICULAR FORMATION
Ascending projections to the BSRF to cortex involves in maintenance of cortical excitability and consciousness.
Wakefulness depend on an adequate impulse from BSRF through the Ascending Reticular Activating System( ARAS) and Diffuse Thalamo Cortical Projection System( DTPS)
Neuro humoral theory suggests the involvement of noradrenaline and serotonin in sleep- wakefulness rhythm.
Noradrenaline from nerve endings of medullary cells have positive influence on ARAS and maintain wakefulness. It also responsive for phasic events of sleep like rapid eye movement( REM).
Serotonin produced by the midbrain raphe nucleus is a depressant acting on the BSRF and diminishes the ascending reticular drive, ultimately end up in sleep.
Acetyl choline balances the action of NE and serotonin in sleep – wakefulness rhythm.
Melatonin- pineal hormone causes sleep and act as a trigger switching the reticular system to act through other neurotransmitter .