Reticular Formation Flashcards
reticular formation “evolutionary age” and general functions
- phylogenetically old part of brainstem
- has over 100 loosely distributed nuclei that functionally link higher brain centers with the spinal cord, maintain vegetative functions and regulate states of arousal and consciousness
describe the architecture of the reticular formation
-the cytoarchitecture consists of large and small cells intermixed with bundles of ascending and descending myelinated fibers
how are the dendrites of the reticular formation oriented with respect to the neuroaxis?
-perpendicular
Describe the general afferents of the reticular formation
- ascending sensory information both visceral and somatic
- descending motor signals from the cortex, superior colliculus, and cerebellum
the main efferents of the reticular formation include
- spinal cord controlling/modulating: postural control, visceral motor, and crude voluntary motor
- cranial nerve nuclei (eye movements)
- cerebellum
- and thalamus
the reticular formation gains access to widespread areas of cortex via the ____ nuclei through which it can regulate conscious state.
-intralaminar thalamic nuclei
How do monoamine neurons in the reticular formation project to the cortex?
-directly!! No need to go through the thalamus
let’s play a game:
Neurotransmitter, location, effect
serotinin
- raphe nuclei
- mood
let’s play a game:
Neurotransmitter, location, effect
norepinephrine
- locus coeruleus
- vigilance and attention
let’s play a game:
Neurotransmitter, location, effect
acetylcholine
- pedunculopontine/laterodorsal tegmentum –> sleep/wake cycles and behavioral salience
- basal forebrain–> attention and memory
let’s play a game:
Neurotransmitter, location, effect
histamine
- tuberomammillary hypothalamus
- alertness
let’s play a game:
Neurotransmitter, location, effect
Dopamine
- ventral tegmental area
- motivated behavior and cognition
peptide containing cells in the lateral hypothalamic area
- widespread projections to cortex and thalamus and regulate arousal
- orexin and melanin-concentrating hormone
Experimental Investigation of Conscious State:
during the 1930’s-50s, researchers performed different brainstem lesions. Describe their methods and some of their results
-if they lesioned ONLY major ascending sensory pathways, but NOT the reticular formation than sleep-wakefulness was not disrupted
—-BUT—–
IF they lesioned the reticular formation, but not ascending sensory pathways they produced a permanent coma
describe a way to waken a sleeping animal
-stimulate the midbrain reticular formation
Reticular Activating System
-nickname of the reticular formation since it is necessary for maintaining conscious awake states
EEG
electroencephalogram was developed by Hans Berger in the 1920’s
- electrodes are placed on scalp and grounding position like the ear
- EEG records waves of electrical activity conducted from the cortex through the head; these reflect the activation of the cortex by the thalamus
The EEG represents ___ activity. When groups of cells fire in a ___ manner, they produce a large amplitude electrical signals
- summed
- synchronized
EEG: alpha waves
- Stage 1
- a person at rest with eyes closed
- cortical activity is described as being moderately synchronized in slow, small amplitude a waves
Beta waves
- when a person is alert and concentrating on a task
- these waves are describes as lower amplitude waves that occur with a higher frequency. these reflect desynchronized firing
The first definitive EEG sign of sleep state is the ___
sleep spindle. This occurs in stage 2
describe stage 4 EEG patterns
-amplitude of synchronous EEG increases dramatically while the frequency declines
Delta sleep (slow wave)
- occurs in stage 4
- the sleep is deep and the body exhibits low BP, low HR, and slow respirations
AFTER an episode of slow-wave sleep
- the EEG reflects an awake pattern called rapid eye movement (REM)
- this is paradoxical sleep
describe the physiological events associated with REM sleep
- EMG will show muscle atonia
- EOG shows rapid eye twitches
- increased BP, HR, respiration, and the brain will consume more O2
** most dreaming occurs during REM :)
Animals and humans will die if __ sleep is prevented
REM
-within 12-16 days for humans
What are the causes of death in animals that have been deprived of sleep?
- autonomic and immune system failures
- disrupted weight control, body temp, and cardiovascular function and sepsis secondary to immunodeficiency
REM rebound
-since REM is the most crucial component of sleep a person who is deprived of REM sleep one night will spend double the time in REM the following night
Newer research indicates that sleep is necessary for
- optimum removal of brain metabolites and contaminant s
- this happens thanks to an increase in interstitial space and a greater perfusion of brain tissue by CSF
Through its diffuse projections to the intralaminar nuclei, the ____ RF is positioned to control conscious states
-mesencephalic
In the ALERT state, the excitatory projections of the MRF to the intralaminar nuclei cause thalamic and cortical activity to _____
-desynchronize
Under what conditions can the thalamus and cortex process meaningful sensory information
- alert state
- excitatory projections of the MRF to the intralaminar nuclei cause the thalamic and cortical activity to desynchronize
When a person enters sleep, cells of the ___ begin to slow down. A process which is facilitated by reducing sensory input. As the __ drive to the ___ circuitry falls below a certain threshold, the thalamic and cortical cells begin to fire in a ___, oscillatory manner
- mesencephalic RF (MRF)
- MRF
- thalamocortical
- synchronized
As a person falls asleep, the termination in the EEG peak is due to inhibition from the ___
-reticular thalamus
The onset of non-REM sleep is correlated with increased activity in the
- ventrolateral preoptic area of the hypothalamus
- these are GABA neurons
Stimulation of the VLPO induces ___ in animals
sleep
VLPO cells project to the:
- histamine cells in the tuberomammillary hypothalamus
- orexin neurons in the lateral hypothalamic area
- cholinergic cells in the PPT/LDT
- norepinephrine cells in the locus coeruleus
- serotonin cells in the raphe nuclei
lesions of the tuberomammillary hypothalamus histamine cells leads to
- somnolence
- this is why anti-histamine drugs can make one sleepy
Brainstem cholinergic cells are known to fire before EEG evidence of REM. This activation _____ the _____ and prevents rhythmic firing of thalamocortical circuits. This leads to the EEG becoming ____
- depolarized the thalamus
- desynchronized
Timing trigger
- talking about the REM timing trigger
- thought to lie at the midbrain-pons junction
What accounts for the muscle atonia during REM
-result of the inhibition of motor neurons
Describe the circuit for inhibition of motor neurons during REM
- Glutamate neurons in the sublaterodorsal nucleus of the pons are activated by cholinergic PPT/LDT. The SLD neurons project directly to the spinal cord and indirectly to glutamate neurons in the supraolivary medulla which also project to the spinal cord!
- the glutamate projections activate GABA/glycine interneurons in the spinal cord that then inhibit motor neurons
REM behavior disorders
- can occur from lesions in the pons or medulla which would release the motor inhibition during REM
- Humans with this lesion will act out their dream
Patients with narcolepsy have
- excessive daytime sleepiness suggesting REM intrusion into the wake cycle
- cataplexy (loss of muscle tone) suggestion intrusion of REM atonia into then wake cycle
- hypnagogic and hypnopompic hallucinations at sleep onset and offset, respectively
Sleep paralysis
- represents the inappropriate intrusion of cortical sensory processing and consciousness into the REM sleep state
- people suddenly become aware of muscle atonia and are unable to move despite sending urgent motor commands
a strain of Dobermans suffer from narcolepsy because of a mutation in the gene coding for
orexin receptor
