Reticular System Flashcards
sensory, motor, and autonomic functions
- sleep and wakefulness cycles
- consciousness
- and the regulation of emotional behavior.
reticular formation
represents a phylogenetically older region of the brain because it is found in the core of the brainstem of lower forms
reticular formation
- lateral third of the reticular formation contains small-sized cells
- receive afferent fibers from both neighboring regions of the brainstem as well as from distant structures
parvocellular regions
medial two thirds of the reticular formation contains different groups of large- sized cells
magnocellular regions
At least ___ distinct magnocellular regions in the pons and ___ large region in the medulla
two; one
produce serotonin that is distributed to wide regions of the brain and spinal cord
raphe nuclei
reticular formation receives inputs from ___ and ___ regions associated with sensory modalities as well as from structures associated with motor functions
brainstem; forebrain
pain and temperature signals are contained within the ___, which passes directly from the spinal cord to the contralateral ventral posterolateral nucleus of the thalamus
lateral spinothalamic tract
which sensory and other inputs to the reticular formation can modulate cortical neurons, cortical excitability, and states of consciousness
reticular activating system
received by a number of limbic structures (amygdala, hippocampal formation, and septal area)
secondary olfactory signals
receive significant inputs from two key regions associated with motor functions: the cerebellum and sensorimotor cortex
magnocellular nuclei
The reticular formation and ___ share reciprocal connections, which complete a circuit comprising feedback pathways between these two regions for the regulation of motor functions associated with each of these two structures
cerebellum
Cerebellar fibers that project to the reticular formation of the medulla and pons arise from the
fastigial nucleus
The fibers are both crossed and uncrossed and use the ___ (the pathway that passes just dorsal to the superior cerebellar peduncle).
uncinate fasciculus
terminate in the pons and medulla near cell groups that give rise to the reticulospinal tracts
corticoreticular fibers
influence both voluntary as well as reflex motor functions by acting on those neurons of the reticular formation that control extensor motoneuron activity
corticoreticular fibers
primary afferent fibers contained in cranial nerves
(CN) IX and X.
fibers arising from higher order autonomic integrative regions, which include the ___, as well as parts of the ___.
hypothalamus; limbic system
transmit both chemoreceptor and baroreceptor afferent signals to the brainstem.
glossopharyngeal and vagus nerves (CN IX and X)
signals arise from the aortic and carotid bodies
chemoreceptors
signals arise from the aortic arch and carotid sinus
baroreceptors
chemoreceptors and baroreceptors terminate in the
solitary nucleus
- Secondary neurons located in the solitary nucleus then project to the ___ and the ventrolateral medullary depressor areas located in the medullary reticular formation.
- this information is important for reflex regulation of blood pressure and respiration
nucleus ambiguus
of the brainstem reticular formation that provide basic mechanisms for the control of blood pressure, heart rate, and respiration
autonomic regions
These regions of hypothalamus project most heavily to the midbrain ___ and neighboring regions of the dorsal and lateral tegmental fields of the reticular formation
PAG
contains cells whose axons travel long distances
reticular formation
The reticular formation contains cells whose axons travel long distances. Some ascend to the ___, and others descend to the spinal cord or project to the ___
forebrain; cerebellum
efferent fibers that travel long distances arise from the ___ of the reticular formation, and those that travel only short distances as interneurons lie mainly in the ___ of the reticular formation.
medial two thirds; lateral third
The main dendritic branches of the neurons are oriented in a ___ perpendicular to the long axis of the brainstem
plane
Cells situated in the medial two thirds of the reticular formation of the medulla and pons give rise to ___ that travel for long distances in both directions
bifurcating axons
involve projections from the reticular formation to the intralaminar nuclei of the thalamus
first two mechanisms
involves direct projections from monoaminergic neurons of the reticular formation to the cerebral cortex
third mechanism
- low-frequency stimulation of nonspecific thalamic nuclei produces a distinctive cortical electrical pattern called a ___
- This response is characterized by a surface negative wave, which reaches a maximum amplitude rapidly and then slowly decreases in size.
recruiting response
The behavioral response noted from such stimulation of the nonspecific thalamus is that the patient has a
drowsy apperance
- highly important because it serves to change excitability levels of the cortex so that they will become more receptive to other sensory inputs that reach the cerebral cortex through the classical ascending sensory pathways.
arousal
- cortical desynchronization
- enables the individual to respond in an appropriate way that generates conscious awareness of these stimuli
beta rhythm
- high spinal transection
- the cortical arousal pattern is retained
encéphale isolé preparation
- one produces a transection rostral to the trigeminal nerve
- the EEG pattern that results is characteristic of a sleeping animal.
cerveau isolé preparation
arise from different regions of the brainstem to supply the entire CNS, including the cerebral cortex, hypothalamus, and limbic system
monoaminergic neurons
give rise to serotonergic projections
raphe neurons
gives rise to noradrenergic projections
nucleus locus ceruleus
contains dopaminergic neurons that project to the entire forebrain with the exception of the neostriatum
ventral tegmental area
- fibers arising from the pons form the medial reticulospinal tract and issue from the ____ and ___
- pass in the ventral funiculus of the spinal cord
- facilitate both alpha and gamma motor neurons of extensors
nucleus reticularis pontis oralis and nucleus reticularis pontis caudalis
- fibers from the medulla arise from the ___, such as the nucleus gigantocellularis
- descend in the ventral funiculus as the lateral reticulospinal tract, where they also terminate on alpha and gamma motor neurons of extensors
magnocellular nuclei
the actions of the reticulospinal fibers serve to
modulate muscle tone, regulate posture, and participate in automatic reflex mechanisms involving the extensor musculature
if the inhibitory components of the reticulospinal pathways are disrupted by loss of corticoreticular inputs
spasticity
if the inputs from the cerebellum to the inhibitory zones of the reticular formation are disrupted
rigidity
located in the reticular formation and adjacent to the abducens nucleus and is chiefly responsible for the organization of horizontal eye movements
horizontal gaze center
most important controlling regions include the ___ and the ___for blood pressure because they receive inputs from primary and secondary autonomic afferents as well as from higher regulatory centers of the brain
solitary nucleus; caudal and rostral ventrolateral medulla
lesions of the reticular formation disrupt functions associated with the
hypothalamus and limbic system
administration of drugs that block one or more of the monoamine systems can affect ___ that are normally associated with the hypothalamus and limbic system
mood changes
- Most of nighttime sleep (approximately 75%) is not associated with rapid eye movements (REM)
- This activity is mediated mainly by ___
- These circuits are ultimately activated by the brainstem
thalamocortical circuits
- begins with brain wave (EEG) slowing and vertex waves or high voltage slow waves recorded from the vertex of the head, called drowsiness or stage 1 sleep
non -REM sleep
characterized by slowing of the EEG and clusters of 12 to 14 Hz rhythmic waves (“sleep spindles”) recorded in the central head region
- high-voltage, irregular, slow waves
stage 2
- characterized by high-voltage (75 V) slow waves of frequencies in the range of 2 Hz. Sleep is moderate to deep, and spindle activity declines
stage 3
characterized by more than 50% slow-wave activity.
stage 4
- as sleep ___, cortical neurons generate slow (delta frequency) waves.
deepens
most difficult stage to wake someone from
stage 4
sleep walking and talking are recorded from
stage 3 or 4 sleep
necessary for REM or “dreaming” sleep
pontine reticular formation
instrumental in the inhibition of muscle tone during REM sleep
pons
These waves serve as a marker for REM sleep in the cat but have never been demonstrated in humans
Ponto-geniculo-occipital waves
Two pontine reticular nuclei initiate REM sleep
pedunculopontine nucleus & lateral dorsal nucleus
- major norepinephrine cell group of the rostral pontine reticular formation
- provide the anatomical bases for the regulation of sensory functions of the cerebral cortex as well as cortical activation itself, which can affect REM sleep
locus ceruleus
destruction or pharmacological depletion of serotonin levels in the brain results in
long periods of wakefulness (insomnia)
- serotonin precursor
- restore normal states of slow-wave sleep.
Replacement therapy with 5-hydroxytryptophan
- EEG pattern characteristic of the awake state
paradoxical sleep
Lesions placed in the locus ceruleus or administration of the drug alpha methyldopa an suppress ___
paradoxical sleep
- show a clear-cut diurnal rhythm for light and darkness
- receive direct retinal inputs, and if the nucleus is destroyed, other rhythms, such as those for endocrine function and sleep–wakefulness cycles, are disrupted.
suprachiasmatic nucleus
- disabling form of somnolence
- individual experiences attacks of sleep at times and places where sleep does not normally occur
- individual may fall asleep in the car while driving or while giving a lecture
- display a sleep paralysis in which they remain awake at night, begin to hallucinate, and are unable to move
narcolepsy
- loss of muscle tone
cataplexy
- chronic inability to fall asleep in spite of appropriate opportunities to do so
- can either appear primarily as an abnormality in the sleep mechanism, or it can occur as a secondary phenomenon to a psychological or medical problem
insomnia
of insomnia is likely associated with pain, discomfort, or alcohol or drug abuse and is usually of short duration.
second form
- form of insomnia that occurs during non-REM sleep and is characterized by unusual autonomic and/or motor responses
- common in children than adults
- get up out of bed, put on his or her clothes in an awkward way, open doors, or even have something to eat. He or she usually obeys instructions to go back to bed.
somnambulism (sleepwalking)
- parasomnia that occurs mainly in children soon after falling asleep
- child awakens, is terrified, screams, and displays marked tachycardia and rapid respiration
- child remembers nothing of the event when he or she awakens in the morning.
night terrors
- patient complains of drawing pains in the calves and thighs, which may include creeping or crawling feelings
- temporarily relieved by movement of the legs
- associated with iron deficiency anemia
restless legs syndrome
- interruption of breathing
- decline in the oxygen content of the blood. The interruption of breathing leads to arousal from sleep or results in lighter stages of non-REM sleep in order for breathing to be maintained.
- show impaired performance in work-related functions and reduced intellectual capacity as well as excessive daytime sleepiness
- exacerbated in individuals who are obese because the added fatty tissue may further reduce the air passages
sleep apnea
- individual awakens very early or during the nighttime
- characteristic conditions of excessive guilt, depressed mood and appetite, and difficulties in concentrating on one’s work and remembering
depression
life- threatening event in the distant past of the individual reappears in his or her memory during the daytime or in the evening in dreams
posttraumatic stress disorder,
damage to the reticular formation of the pons or midbrain will produce ___ in most instances
coma
lesions of the midbrain reticular formation result in the
appearance of slow waves of large amplitude
lesions of the pons are frequently characterized by an alpha rhythm typically seen in a ___
normal drowsy person.
In the case of a pontine lesion, the patient lies quietly and displays a variety of autonomic and somatomotor reflexes as well as normal eye movements
coma vigil or akinetic mutism
Lesions involving the lower brainstem and possibly other regions such as cerebral cortex also produce a ___
loss of consciousness
provides a reliable and objective way of indicating the conscious state of an individual both at his initial examination as well as at later times
Glasgow Coma Scale
Central control of cardiovascular function is mediated primarily from the
Ventrolateral medulla
- gives rise to neurons that project to the intermediolateral cell column of the thoracolumbar spinal cord
- regulates sympathetic activity.
ventrolateral medulla
primary properties of this region are associated with intellectual and affective functions
prefrontal cortex
Rapid eye movement (REM) sleep is believed to originate in the
Pons
Electrophysiological studies have indicated that rapid eye movement (REM) sleep originates in the ___
pontine reticular formation
contains cell bodies and axons associated with transmission of sensory information to higher regions, cranial nerve function, and descending fibers to the spinal cord
caudal medulla
associated with visceral processes, such as feeding, and contains ascending and descending fibers associated with limbic structures and monoaminergic systems
lateral hypothalamus
concerned with the transmission of impulses mainly to the frontal lobe
medial thalamus
A 72-year-old man was found unconscious in his home and was taken to the emergency room of the local hospital. After a few days, the patient remained in a coma, and the pattern on his electroencephalogram revealed mainly the presence of an alpha-like rhythm. In addition, the patient presented with normal eye movements and a variety of autonomic and somatomotor reflexes. On the basis of these observations as well as a magnetic resonance imaging scan, the neurologist concluded that the lesion was localized to the
pons
characteristic of a pontine lesion, which includes parts of the tegmentum but spares the dorsomedial region, which is associated with the control of horizontal eye movements
coma vigil
A middle-aged, male professor of neuroscience at a north- eastern medical school began to experience intermittent episodes of uncontrollable sleep, even while giving lectures to the first-year medical class. At the request of colleagues and students, it was suggested that he see a neurologist in the university hospital. The neurologic examination revealed temporary loss of muscle tone in the trunk and extremities, and in the sleep clinic, he experienced some hallucinations and tended to remain awake at night. The neurologist concluded that the patient was suffering from
narcolepsy
patient has frequent bouts of sleep during the day, an inability to sleep at night, and loss of muscle tone
narcolepsy
A 67-year-old woman complained to her ophthalmologist that she was experiencing double vision. After a thorough examination, the patient was given a neurologic examination. A magnetic resonance imaging scan revealed the presence of a small stroke. The most likely locus of the lesion was the
Dorsomedial pons
- the paramedian reticular formation of the caudal pons in the region of the abducens nucleus contains the ___
- serves to integrate cortical and vestibular inputs for the control of conjugate horizontal gaze. Damage to this region would result in loss of coordination of the eyes, causing double vision.
horizontal gaze center.
- Pain and temperature inputs to reticular formation
- affects cortical excitability and levels of consciousness
- also part of circuit for pain inhibition (through the PAG)
somatosensory signals from spinal cord
Provides multi-modal inputs associated with auditory, vestibular, and somatosensory sensations (from head region)
Cranial nerve nuclei
Provides multi-modal inputs associated with olfactory, visual, and auditory sensations to midbrain reticular formation
Secondary sensory pathways
Outputs from fastigial nucleus provide feedback signals to regions of medulla and pons associated with descending reticulospinal pathways
Cerebellum
Outputs from sensorimotor cortex regulate the activity of neurons in the pontine and medullary reticular formation whose axons form the reticulospinal pathways
cerebral cortex
provide baroreceptor and chemoreceptor signals to medullary and pontine reticular formation that mediate reflex regulation of blood pressure and respiration
CN IX and X
Descending outputs from limbic system and hypothalamus powerfully regulate autonomic functions associated with reticular formation
Limbic structures and hypothalamus
Reticular formation inputs to cerebral cortex regulate levels of cortical excitability related to many functions of cerebral cortex; examples include modulation of sensory perception, motor activity, and sleep and wakefulness
To thalamus and cerebral cortex
Descending pathways mediate inhibition of pain impulses at the level of the dorsal horn of spinal cord
To PAG
Reticulospinal fibers from pons facilitate extensor reflexes, whereas reticulospinal fibers from medulla inhibit extensor spinal reflexes; both descending fiber systems powerfully regulate postural reflexes
To spinal cord
Efferents to anterior and posterior lobes of cerebellum serve as part of a feedback circuit linking cerebellum with reticular formation; inputs from reticular formation provide continuous information to cerebellum concerning levels of excitability of reticular formation neurons that descend to spinal cord
To cerebellum
Horizontal gaze center of pons integrates cortical and vestibular inputs and controls horizontal movement of the eyes by its connections with CN VI and CN III
To CN VI and III
Solitary nucleus interactions with dorsal motor nucleus of CN X excites parasympathetic nervous system, whereas outputs from ventrolateral medulla to spinal cord mediate sympathetic activity; other descending fibers from reticular formation to spinal cord regulate respiration by acting upon neurons of the phrenic nerve
Autonomic Processes
