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RETICULAR FORMATION DUHS

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					“RETICULAR FORMATION”
“LEARNING OBJECTIVES”
 • Reticular formation,
 • Location,
 • Function,
 • Somatic motor control,
 • CVS control,
 • Pain modulation,
 • Sleep and consciousness,
 • Habituation,
 • Sensory control,
 • Visceral control,
 • Reticular formation,
 • Nuclei,
 • Reticular neurons.
“RETICULAR FORMATION”
The reticular formation is a part of the
brain that is involved in actions such as,
 • Awaking/sleeping cycle,
 • Filtering incoming stimuli to
   discriminate irrelevant background
   stimuli.
 • It is essential for governing some of
   the basic functions of higher
   organisms.
 • Is one of the phylogenetically oldest
   portions of the brain.
 • The reticular formation is an
   apparently (but not actually) diffusely
   organised area that forms the central
   core of the brainstem.
The reticular formation is an apparently
(but not actually) diffusely organised
area that forms the central core of the
brainstem.
“LOCATION”
 • The reticular formation is a poorly-
   differentiated area of the brain stem.
 • Centered roughly in the pons.
 • The reticular formation is the core of
   the brainstem running through the
   mid-brain, pons and medulla.
 • The ascending reticular activating
   system connects to areas in the
   thalamus, hypothalamus, and cortex.
 • the descending reticular activating
   system connects to the cerebellum
   and sensory nerves.
“FUNCTIONS”
 • The reticular formation consists of
   more than 100 small neural
   networks,
 • with varied functions including the
   following:
 • Some motor neurons send their
   axons to the reticular formation
   nuclei.
 • Giving rise to the reticulospinal tracts
   of the spinal cord.
 • These tracts function in maintaining
   tone, balance, and posture--
   especially during body movements.




 •
“SOMATIC MOTOR CONTROL”
 • The reticular formation also relays
   eye and ear signals to the
   cerebellum so that the cerebellum
   can integrate visual, auditory, and
   vestibular stimuli in motor
   coordination.
 • Other motor nuclei include gaze
   centers, which enable the eyes to
   track and fixate objects.
 • central pattern generators, which
   produce rhythmic signals to the
   muscles of breathing and
   swallowing.
“CARDIOVASCULAR CONTROL”
 • The reticular formation includes the
   cardiac and vasomotor centers of
   the medulla oblongata
“PAIN MODULATION”
 • The reticular formation is one means
   by which pain signals from the lower
   body reach the cerebral cortex.
 • It is also the origin of the descending
   analgesic pathways.
 • The nerve fibers in these pathways
   act in the spinal cord to block the
   transmission of some pain signals to
   the brain.
“SLEEP AND CONSCIOUSNESS”
 • The reticular formation has
   projections to the thalamus and
   cerebral cortex that allow it to exert
   some control over which sensory
   signals reach the cerebrum and
   come to our conscious attention
 • It plays a central role in states of
   consciousness like alertness and
   sleep.
 • Injury to the reticular formation can
   result in irreversible coma.
“HABITUATION”
 • This is a process in which the brain
   learns to ignore repetitive,
  meaningless stimuli while remaining
  sensitive to others.
 • A good example of this is when a
   person can sleep through loud traffic
   in a large city, but is awakened
   promptly due to the sound of an
   alarm or crying baby.
 • Reticular formation nuclei that
   modulate activity of the cerebral
   cortex are called the reticular
   activating system or extrathalamic
   control modulatory system.
“SENSORY CONTROL”
 • Reticular neurons exert some control
   over activity in spinal reflex arcs.
• They can control over the access of
  sensory information to ascending
  pathways.
• Tonic inhibition of flexor reflexes
  originates in the reticular formation.
• The result that only noxious stimuli
  can normally evoke such a reflex.
• In addition, stimulation of certain
  regions of the medullary reticular
  formation causes inhibition of some
  sensory interneurons and tract cells
  in the spinal cord.
• This seems to be important in the
  regulation of pai perception.
 “VISCERAL CONTROL”
 • Centres controlling inspiration,
   expiration, and the normal rhythm
   of breathing have been identified
   physiologically in the medulla and
   pons.
 • Other centres controlling heart rate
   and blood pressure have been
   identified in the medullary reticular
   formation.
“RETICULAR FORMATION”
The reason it appears to be diffusely
organised is twofold:
 • Its pattern of connectivity is
   characterised by a great deal of
   convergence and divergence, so that
  a single cell may respond to several
  different sensory modalities or to
  stimuli applied practically anywhere
  on the body;
 • Although it is involved in several
   quite separate functions, the areas
   involved in these functions overlap
   considerably
“NUCLEI”
 • With the reticular formation, it is as
   though several nuclei had been
   scrambled together and dispersed
   along the brainstem.
 • Their constituent cells retained their
   original connections.
At most levels of the brainstem, the
reticular formation can be divided into
3 longitudinal zones arranged in a
medial to lateral sequence:
 • The raphe nuclei
 • The medial zone
 • And the lateral zone
“THE RAPHE NUCLEI”
 • These are thin plates of cells in and
   immediately adjacent to the sagittal
   plane.
 • Like the cells of the locus ceruleus,
   raphe neurons (G. raphe, seam) have
   exceedingly far-flung connections.
 • Serotonin is used as the
   neurotransmitter.
“THE MEDIAL ZONE”
 • This, alongside the midline raphe
   nuclei, contains a mixture of large
   and small neurons.
 • It is the source of most of the long
   ascending and descending
   projections from the reticular
   formation.
 • Some of the neurons in the medial
   zone of the rostral medullary
   reticular formation are so large that
   this area is referred to as the
   gigantocellular reticular nucleus.
“THE LATERAL ZONE”
 • This is particularly prominent in the
   rostral medulla and caudal pons.
It is primarily concerned with cranial
nerve reflexes and visceral functions
“THE RETICULAR NEURONS”
 • Many of these have extensive and
   complex axonal projections.
 • They may innervate multiple levels
   of the spinal cord or send numerous
   collaterals to the brainstem and
   diencephalon.
 • The generally do not send axons
   directly to the cerebral cortex,
   however.
   “THE RETICULAR NEURONS”
• Many of these have extensive and
  complex axonal projections.
• They may innervate multiple levels
  of the spinal cord or send numerous
  collaterals to the brainstem and
  diencephalon.
• The generally do not send axons
  directly to the cerebral cortex,
  however.
• A few may even have bifurcating
  axons that give rise to both
  ascending and descending
  connections.
• Reticular neurons have large fields of
  dendrites.
• The sometimes spread out in a plane
  perpendicular to the long axis of the
  brainstem.
• This allows them to receive synaptic
  inputs from ascending sensory
  pathways, descending cortical axons,
  and a variety of other sources.

				
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posted:8/29/2011
language:English
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