VPB 121: Veterinary Physiology - II (2+1)

FUNCTIONS OF BSRF

• It 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.
• The large size neurons are motor in function which bifurcate with one division extending upward to the thalamus or the basal regions of the diencephalon or the cerebrum.
• Nuclear mass
• Pre cerebellar reticular nuclei  ------>  projects to cerebellum.
• Non-cerebellar reticular nuclei:
  • Raphe nuclei: Inhibits the reticular activation system (RAS) and induces sleep.
  • Central group of nuclei  and
  • Lateral group of nuclei -These two nuclei contain respiratory and cardiac centres.    
• The brainstem reticular formation receives sensory input signals from all sensory systems–somesthetic, vestibular, visual, auditory, gustatory and olfactory sensory systems, through spino- reticular tract and also from the vestibular nuclei, cerebellum, and basal ganglia and motor area of the cerebral cortex.
• It integrates the sensory information within the CNS and controls the activities of both the motor neurons of skeletal muscles and the autonomic neurons (cardiovascular, respiratory and the G. I. tracts). The BSRF plays a key role in somatic and visceral motor control.
• The BSRF may either causes consciousness (wakefulness) by providing continuous stimulatory signals to the cortex or it  may induce  sleep by its inhibitory signals through raphe nucleus  to the ascending reticular activation system (ARAS).

Ascending reticular formation

• It 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

• It 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.