what is the reticular activating system (RAS)
reticular formation and other brainstem regions involved in mediating the the shift from sleep to waking
what does a transection of only ascending sensory pathways in the RAS do
no effect on sleep-wake states
what happens when the brainstem is transected at the spino-medullary junction
no effect on sleep-wake states
what happens when the mid brain is transected between the the inferior and superior colliculi
results in a perpetual sleep like state
what results from stimulation of the reticular formation in the midbrain
wakes sleeping animals
what is synchronized activity
- occurs when many neurons fire simultaneously, then simultaneously stop firing
- large voltage deflection in the EEG
- associated with non-waking states
what is desynchronized activity
- occurs when neurons in a given region do not fire in synchrony with many other neurons
- EEG trace looks largely flat
- Occurs during alert wakefulness
how are sleep states differentiated
- Certain rhythmic patterns in the EEG
- Presence or absence of eye movements
- degree of muscle tone
what is EEG
electroencephalography (EEG); extracranial recordings of neuronal activity
what is EOG
electrooculography (EOG); recordings of electrical signals from extraocular muscles of the eyes
what is EMG
electromyography (EMG); recordings of electrical signals from muscles
what are sleep wake states controlled by
- midbrain reticular formation, thalamus, and cerebral cortex
- neuromodulary centers
what are the anatomical substrates of the awake state
- MRF excites thalamic cells
- thalamic cells depolarize enough to fire in an ongoing way
- Ongoing thalamic input excites cortex, causing desynchronized EEG
what are the anatomical substrates of the onset of sleep state
- MRF firing slows
- thalamic cells fire in bursts that alternate with firing in the neocortex
- Slower frequency with deeper stages of sleep; in stage 4 sleep: 3-4 Hz, delta waves
what is the location of the reticular formation
runs longitudinally within the brainstem from the medulla to the upper midbrain
describe the reticular formation
- RF neurons span large territories within the brainstem
- Long dendrites run perpendicular to the neuroaxis
- Axons branch extensively along the neuroaxis
- Integrate input from and send output to many regions of the nervous system
what are the afferents of the RF
- spinoreticular tracts: visceral and somatic sensory input (ascending)
- motor signals from the cortex, superior colliculus, and the cerebellum (descending)
what are the efferents of the RF
- reticulospinal tracts: posture, visceral motor (descending)
- cerebellum, thalamus, intralaminar nuclei of the thalamus (ascending)
what are the cholinergic nuclei
- pedunulopontine tegmental nuclei (PPT)
- laterodorsal tegmental nuclei (LDT)
what is the function of the cholinergic nuclei
regulate sleep-wake states and attention
what are the dopaminergic nuclei
- substantia nigra pars compacta (SNc)
- Ventral tegmental area (VTA)
what is the nigrostriatal pathaway
SNc –> striatum
what is the mesolimbic pathway
VTA –> limbic structures
what is the mesocortical pathway
VTA –> prefrontal cortex
