Physiology 2130 Lecture Notes - Lecture 26: Reticular Formation, Evoked Potential, Locus Coeruleus
1 May 2018
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Lecture 026: Consciousness, Evoked Potentials and Sleep
Consciousness
● Awareness of environment and oneself
● Content of consciousness
○ Memory, perception, attention
○ Depends on the cerebral cortex
● Level of consciousness
○ Awake, alert, asleep, coma
○ Depend on the brain stem
■ Rostral pons/caudal midbrain
● Old idea about consciousness: ascending reticular activating system
○ Pioneering experiments
■ Stimulate certain brain stem areas woke up sleep animals
■ Decerebrated (bilateral lesion) will lead to an unconscious animal (coma)
○ Also have descending system from the reticular system
■ Reticulospinal spinal axons send IPSP to alpha motor neurons to
proximal muscle
● Inhibits movements in REM sleep
● Modern view: conscious arousal system
○ Ascending arousal system
■ In the brainstem (rostral pons/caudal midbrain)
■ There are numbers of system of neurons that original in this area controls
consciousness
○ Noradrenergic System
■ Nucleus of origin: locus coeruleus
■ Sends axons to all areas of the brain (widespread connections)
● Cerebral cortex and the cerebellum
■ Uses norepinephrine
■ Alters membrane potentials
■ Produces a depolarization on the neurons of cerebral cortex
● Produces an “awake state”
● Closer to threshold, easier to activate
○ Serotonergic
■ Nucleus of origin: raphe nuclei
■ Failure to cause arousal in sudden infant death syndrome (SIDS)?
○ Dopaminergic
■ Widespread connections: cerebral cortex, limbic system
■ Involved in reward based learning, addition
○ Histaminergic
■ Antihistamines causes drowsiness
○ Cholinergic
■ Alzheimer’s disease
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○ All involved in “cooperative interplay” to achieve different levels of
consciousness
■ Different states of sleep, getting out of sleep into normal consciousnesses
Coma: the absence of consciousness
● Can result from:
○ Bilateral lesion of the cerebral cortex
■ From hypoxia, hematoma (blood clot push down on the cortex and cause
neuron hyperpolarization or death)
○ Bilateral lesion of the rosal brainstem
■ Decerebration
Locked-in Syndrome
● Stroke in the caudal pons
● Conscious (normal cognition)
○ Arousal neurons can go to all area of the cerebral hemispheres
● However,the motor pathways are blocked
○ thus there are no movements of the arms, leg or speech
● Can only blink (extraocular muscles) and move eyes
○ Cranial nerve III (oculomotor nerve) is still intact
○ One patient dicated memoir one letter at a time by blinking
Persistent Vegetative State
● Forebrain cortex damage (generated from hypoxia)
● Chronic
● Have partial
○ Can move eyelids, have saccades, swallow, moan
○ Have sleep-wake cycles
● However, there are no signs of consciousness
● But are some PVS Patients Conscious? (Adrian Owen)
○ Just can’t exhibit consciousness because they are paralyzes
○ Try to test with fMRI
○ Asked PVS patients with very specific Yes/No answers
■ YES: imagine playing tennis (active arm motor cortex)
■ NO: imagine walking through home (actives the hippocampal place area)
○ About 15% could answer by changing cortical blood flow (seen in fMRI)
Evoked Potentials
● Stimulate a nerve in a muscle -> creates AP that goes up the DC/ML -> ESPS in cortical
neurons -> summation of these electric potential is the evoked potential
● Where is the evoked potentials
○ Arms (20 ms) and leg (30 ms, further conduction time) -> somatosensory cortex
○ Visual flash (60 ms) -> visual cortex
■ Takes time because APs only begin to be generated in the ganglion
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Old idea about consciousness: ascending reticular activating system. Stimulate certain brain stem areas woke up sleep animals. Decerebrated (bilateral lesion) will lead to an unconscious animal (coma) Also have descending system from the reticular system. Reticulospinal spinal axons send ipsp to alpha motor neurons to proximal muscle. There are numbers of system of neurons that original in this area controls consciousness. Sends axons to all areas of the brain (widespread connections) Produces a depolarization on the neurons of cerebral cortex. All involved in cooperative interplay to achieve different levels of consciousness. Different states of sleep, getting out of sleep into normal consciousnesses. From hypoxia, hematoma (blood clot push down on the cortex and cause neuron hyperpolarization or death) Arousal neurons can go to all area of the cerebral hemispheres. However,the motor pathways are blocked thus there are no movements of the arms, leg or speech. Can only blink (extraocular muscles) and move eyes.
