reticular formation Flashcards
function of the reticular formation
- tasks involve nervous system as a whole
- functions are integrative
integrative functions of reticular formation include:
- sleep
- wakefulness
- alertness
- consciousness
- coordination of visceral functions (homeostasis)
- responses to pain/pain modulation
- body posture
- mental state
reticular formation defined as
gray matter that composes the core of the brain stem
- excluding cranial nerve nuclei and ascending and descending tracts)
reticular formation consists of
networks and branched neurons
reticular formation is
- related to many other parts of the nervous system
- the nuclei are not as clearly defined histologically
- phylogenetically old system
connections of the reticular formation
- afferent connections
- efferent connections
- reticular formation has integrative function
afferent connections to reticular formation
- all sensory systems (not specific)
- many other areas
efferent connections of reticular formation
very widespread
location of reticular formation
- near the center
- anterior to the ventricular system
- in the core of the brain stem
neuronal organization of the reticular formation
- large and small cells
- dendritic web of large cells = perpendicular to axis of brain stem
- projection neurons have long axons
- pathways are diffuse
- the cell bodies and axons are below the brainstem
axons of the neuronal projections of reticular formation
- ascend and descend
- have numerous collaterals
- make very large number of synaptic connections
general function of the reticular formation
- axons and dendrites pick up information
- ascending, descending tracts
- take general information from all kinds of places to the brain stem
the ascending axons has branches that go to
- PAG
- thalamus
- hypothalamus
the descending axons has branches that go to
- nucleus gracilis
- medulla
- etc.
configurations of the neurons of reticular formation
left: 2 neurons, opposite direction of movement, collateral extensions to communicate with each other
right: 1 neuron, with 2 branches that go up and down with collateral extension
serotonergic nuclei
raphe nucleus
- serotonin neurotransmitter
- project to thalamus, hypothalamus, basal ganglia, cortex, spinal cord, cerebellum
raphe nuclei
- in midline of medulla, pons, midbrain
- serotonergic
- efferent branches reach many parts of NS including spinal cord
locus ceruleus nuclei
- nucleus of noradrenergic pathways
- send to hippocampus, basal ganglia, cortex, cerebellum
- near mesencephalic V under superior cerebellar peduncle
- efferent branches reach many parts of the NS
dopaminergic pathways
- produce dopamine
- include substantia nigra and tegmental area
- project to insula, caudate and putamen, nucleus accumbens, hippocampus, cortex
electroencephalogram (EEG)
- sleep and consciousness
- record electrical acvitivy of the brain by picking up cortical activity
- filters out spikes
- left with synaptic activity of the brain
EEG waves
beta - wake brain (High freq. low volt)
alpha - close eyes and sit back (slow freq, higher volt)
theta - falling asleep (slow freq, high volt)
delta - deep sleep (slow waves, high amplitude)
EEG waves classified by
- frequency
- amplitude
- synchronized vs desynchronized
synchronized vs desynchronized
- waves start working together to increase synchronizaition for rhythm and higher frequency but low voltage
EEG waves during sleep
low frequency
high amplitude
synchronized
EEG waves during wakefulness
high frequency
low amplitude
REM sleep
- cycles of sleep
- episodes of desynchronization (4-5 times/night)
- rapid eye movements
sleep stages
REM = when you dream
how does reticular formation affect sleep and consciousness
- reticular activating system: projections to the thalamus which has many nuclei and activates the cortex
- thalamus > cortex
arousal
- reticular network receives collateral inputs form all ascending sensory pathways (typically sound)
coma
- lesions of reticular formation (upper brain stem) result in coma
- coma can also be the result of cortical damage
arousal nuclei include
- locus ceruleus
- raphe nuclei
sleep inducing system
- ascending arousal system originates in the pons
- sleep promoting neurons in hypothalamus inhibit arousal areas
- mutual inhibition produces a flip-flop switch
REM sleep system
wheredoes it stem from?
pontine reticular formation contains neurons that generate REM sleep
other uses of EEG
- detecting and localizing seizures
- identifying brain death
reticulospinal tracts have 2 types:
- medullary reticulospinal tract
- pontine reticulospinal tract
both located in anterior foniculus
reticulospinal tracts act:
- mainly on extensors
- mainly on gamma motor neurons
- controls sensitivity of spindles
gamma motor system
- gamma motor neuron goes to polar ends of spindles
- increase spindle stretch
- makes whole reflex more sensitive
intermediolateral cell column
- control of the autonomic nervous system and vital centers
- sympathetic part comes from this
- in lateral horn of grey matter
reticular formation sends signals down intermediolateral cell column and
influence sympathetic activity or autonomic activity in general
vital function
- respiration
- heart beat
cardiac and vascular centers
- cardiovascular:
- vasomotor center: vasoconstriction
- loacted in medulla
respiratory centers
- in pons and medulla
- lesions here can cause death
other autonomic centers of the medullary and pontine reticular formation
- swallowing
- vomiting
- gagging
- coughing
- sneezing
- shivering
- micturition
- crying
spinoreticular tract
- tract can project to reticular formation instead of VPL and go to large areas of cortex instead
- non-specific
pain modulation
- periacqueduct of grey is a source of descending pathway to RF in medulla (medial and lateral part)
- raphe nuclei send serotonin
- noradrenergic input to substantia gelatinosa
- (inhibit?) pain and temp signaling
reactions to noxious stimulus
- reflexes
- vocalization
- sweating
- pupillary dilation
- heart rate increase
- BP changes
- behavioral changes
mood disorders
monoamine hypothesis of depression
- noradrenergic, serotonergic, and dapaminergic send transmitters to nuclei that can indicate mood
