ch 19 book notes

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University of Toronto Scarborough
Janelle Leboutillier

Chapter 19 Notes EEG is the classical way for recording brain rhythms in the cerebral cortex EEG measures voltages generated by currents that flow during synaptic excitation of the dendrites of many pyramidal neurons in the cerebral cortex. The amplitude of an EEG depends on how synchronous the activity of the underlying neurons An alternative way to record the rhythms of the cerebral cortex is with magnetoencephalography (MEG). It is better than EEG when localizing the sources of neural activity in the brain, particularly when they are deep in the brain. EEG and MEG can record rapid fluctuations of neural activity, unlike fmri or Pet Eeg and meg measure direct neuronal activity, while fmri and mri measure blood flow or metabolism EEG can be classified differently according to frequency range: Beta rythms: fastest, 15-30 Hz, and signal an activated cortex Alpha rythms: 8-13 Hz, associated with quiet, waking states Theta rythms: 4-7 Hz and occur during some sleep states Delta rythms: quiet, slow, <4 Hz, often large in amplitude and signify deep sleep, like stage 3 and 4 sleep Gamma rhythms 30 – 90 Hz Amplitude is higher during resting states such as sleep because of greater synchrony, while lower in other states such as alertness because of processing neurons working. The activity of a large set of neurons will produce synchronized oscillations in one of two fundamental ways: 1. They take all their cues from a central block or pacemaker i.e. band leader 2. They may share or distribute the timing function among themselves by mutually exciting or inhibiting one another i.e jam session In the mammalian brain, the thalamus is a powerful pacemaker in that it can generate action potential discharges. How do the thalamic neurons oscillate? They have a particular set of voltage gated ion channels that allow each cell to generate self sustaining discharge patterns even when there is no external input to the cell Synaptic connections between excitatory and inhibitory thalamic neurons force each individual neuron to conform to the rythym of the group These coordinated rythms are then passed on to the cortex by thalamocortical axons, which excite cortical neurons Seizures are the most extreme form of synchoronous brain activity. Generalized seizure: involves the entire cortex of both hemispheres Partial seizure: involves only a circumscribed area of the cortex Seizures are accompanied by very large EEG patterns Epilepsy: repeated seizures Several mutations of genes that encode fot sodium channel proteins, for example, have been linked to rare forms of epilepsy. The channels stay open for too long. Another group of mutations impairs synaptic inhibition mediated by GABA. Drugs that block GABA receptors are convulsants (case seizures), while those that suppress seizures anti-convulsants. In generalized seizure, because all cortical neurons participate, behavior is are completely disrupted by tonic (constant) or clonic (ryhtmic) activity, or by both in sequence, so called tonic-clonic seizure. Absence seizures occur in childhood and consist of less than 30 sec of generalized 3 Hz EEG waves accompanied by unconsciousness. The motor signs of an absence seizure are fluttering eyelids or a twitching mouth. Partial seizure can be instructive: If in a sensory area, they can trigger an abnormal sensation, or aura, such as an odd smell or sparkling lights. Can cause déjà vu, and hallucinations, impair memory e.t.c Sleep is a readily reversible state of reduced responsiveness to, and interaction with, the environment.  REM sleep, Rapid Eye Movement, is when your EEG looks more awake than asleep, your body (except for your eye and respiratory muscles) is immobilized, and you conjure up the vivid, detailed illusions of dreams. REM sleep is dreaming sleep. Dominated by sympathetic activity  Non-REM sleep, also called slow wave sleep, is dominated by large, slow EEG rhythms. The brain does not generate complex dreams during this stage. Body is capable of movement during this period. Other body functions decreases, but digestive processes increase. Dominated by non-sympathetic activity.  Oxygen consumption of the brain is higher in REM sleep than when the brain is awake.  The paralysis that happens during REM sleep is atonia  Look @ table on pg 595 
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