Download Reticular Formation

Reticular Formation
Dr. Sam David
Reticular Formation
 Consists of neurons within the central core of
the brainstem
 Multi-neuronal, polysynaptic pathway
 Receives input from almost all sensory
system (except the dorsal column pathway)
 Has efferent connections, either direct or
indirect, with all levels of the CNS
 Hence has multiple functions and affects
Motor, Sensory, Autonomic functions and
responsiveness of the cortex
Reticular Formation
5 groups of Nuclei in the MEDULLA:
Lateral reticular nucleus
Paramedian reticular nucleus
Ventral reticular nucleus
Magnocellular reticular nucleus
Parvicellular reticular nucleus
Caudal Medulla Oblongata
Lat. RN: discrete, well defined. Located
near lateral surface from caudal medulla to
mid olivary nucleus level.
Paramedian RN: adjacent to midline. Entire
length of medulla.
Ventral RN: caudal 1/2 of
medulla. Has small and large
neurons.
Midbrain
Pons
Medulla
Paramedian Reticular Nucleus
Ventral Reticular Nucleus
Lateral Reticular Nucleus
Rostral Medulla Oblongata
Magnocellular RN: contains
very large neurons
Parvicellular RN: contains small
neurons. Located immediately lateral
to magnocellular nucleus. From midolivary level to rostral limit of medulla.
Magnocellular Reticular
Nucleus
Parvicellular Reticular
Nucleus
Paramedian Reticular Nucleus
Ventral Reticular Nucleus
Lateral Reticular Nucleus
Pons
Caudal Pontine RN: extension of
magnocellular nucleus
Rostral Pontine RN: lacks large
neurons
Parvicellular RN: Located in
lateral tegmentum. Extension of
Parvicellular nucleus in medulla
Rostral Pontine
Reticular Nucleus
Caudal Pontine
Reticular Nucleus
Magnocellular Reticular
Nucleus
Ventral Reticular Nucleus
Parvicellular Reticular
Nucleus
Paramedian Reticular
Nucleus
Lateral Reticular Nucleus
Midbrain
Mesencephalic RN: Consists of scattered cells in
area bounded by tectum, Red nucleus and
ascending lemniscus.
Mesencephalic Reticular
Nucleus
Rostral Pontine
Reticular Nucleus
Caudal Pontine
Reticular Nucleus
Parvicellular Reticular Nucleus
Magnocellular Reticular
Nucleus
Ventral Reticular Nucleus
Paramedian Reticular
Nucleus
Lateral Reticular Nucleus
Functional Organization
Connections with the Cerebellum
Red Nucleus
Lateral Reticular
Nucleus
Spinoreticular tract
Collaterals from Spinal
lemniscus
Functional Organization
Connections with the Cerebellum
Red Nucleus
Lateral Reticular
Nucleus
Spinoreticular tract
Collaterals from Spinal
lemniscus
ICP
Cerebellum
Functional Organization
Connections with the Cerebellum
Paramedian reticular
nucleus
Cerebellum
Connections with the Spinal Cord
Motor areas of Cerebral
Cortex
Red Nucleus
Substantia nigra
Medial areas of RF
Cerebellum
Medulla & Pons
SPINAL CORD
Terminates directly or indirectly
on  and  motor neurons
Visceral functional connections -1
 Regulates visceral functions through
connections with nuclei of Autonomic outflow
 Regulates respiration through connections with
motor neurons in Phrenic nucleus and thoracic
spinal cord.
 Reticular formation neurons involved in
Respiratory & Cardiovascular control are
intermingled.
Visceral functional connections -2
 Maximal Inspiratory response evoked by
Magnocellular Ret. Nu. in Medulla
 Maximal Expiratory response evoked by
Parvicellular Ret. Nu. in Medulla
 Normal respiratory rhythm controlled by
Pontine RF (Pneumotactic centre).
Visceral functional connections -3
 Ventral & Magnocellular reticular nuclei have
depressor effects on Heart rate and Blood
pressure
 Lateral reticular nucleus in Medulla has
opposite effects on heart rate and blood
pressure.
Ascending Reticular Activating System
Cortical input
Medial reticular areas send
collaterals that synapse with other
reticular neurons. Via this repetition
of relays (polysynaptic), axons reach
the diencephalon ending in
Hypothalamus and Thalamus
(Intralaminar nuclei, and Nucleus of
the midline)
Intralaminar nuclei send fibers to
other thalamic nuclei that then
project to widespread areas of the
cerebral cortex including nonspecific association areas and areas
involved in emotions.
Olfactory input
(mesencephalic RF)
Superior Colliculus
(retinal input)
Vestibular & Cochlear Nuclei
Nucleus of Spinal Tract of V
Solitary Nucleus
Spinal Lemniscus
Spinoreticular Tract (magnocellular RF,
Rostral pontine RF)
Functions of the Ascending
Reticular Activating System
 Relatively non-specific
 Sensory modalities are merged in a polysynaptic
pathway
 Only provides a vague awareness of any particular
sensory modality
 Results in cortical stimulation with profound effects on:
levels of Consciousness and Alerting reactions to
sensory stimuli
Functions of the Ascending
Reticular Activating System
 When the cortex is stimulated by the ARAS during
sleep: EEG activity of the cortex changes from sleep
pattern to waking state
 When the cortex is stimulated by the ARAS while
awake: Sharpens attentiveness and creates optimal
conditions for the perception of other sensory data
conveyed via more direct pathways.
 Damage to RF results in COMA
Simultaneously recorded surface EEG, EEG 1.2 mm into the
cortex in a lightly anesthetized cat. Stimulation of the midbrain
reticular formation (MRF) at 300 Hz at the bar produced an
alerting response. (Reproduced, with permission, from Steriade
M, Amzica F, Contreras D: Synchronization of fast (30–40 Hz)
spontaneous cortical rhythms during brain activation. J Neurosci
1996;16:392.)
In situ hybridization images show matched coronal brain sections of the
lateral hypothalamus hybridized with a 33P-labeled antisense riboprobe for
orexin (a neurpeptide).
Chemelli RM, et al., (1999) Narcolepsy in orexin knockout mice: molecular genetics
of sleep regulation. Cell 98:437-451
(E) EEG/EMG recording during a typical narcoleptic episode. The EEG shows that
the start of this episode corresponds to two high-amplitude spindling epochs,
marked with arrows, associated with phasic EMG activity as muscle tone declines at
the onset of attack. The star marks the onset of observable immobility.
Chemelli RM, et al., (1999) Narcolepsy in orexin knockout mice: molecular genetics
of sleep regulation. Cell 98:437-451
Functions of the Ascending
Reticular Activating System
 General anesthetics are thought to suppress
transmission through the RF
 Cutaneous stimuli and olfactory stimuli are especially
important in maintaining Consciousness
 While visual and auditory stimuli are important in
levels of alertness and attention