28- Sleep

Question 1

what is an EEG?

Answer 1

electroencephalogram = measures electrical activity generated by the brain, brain rhythmicity

small voltage fluctuations are measured between pairs of electrodes = generate electric EEG signals

Question 2

what is the use of EEGs?

Answer 2

help diagnose certain neurological disorders - e.g. epilepsy

show that sleep and waking EEGs are distinctly different

Question 3

how are EEG signals measured and generated - method and equipment? neurone activity?

Answer 3

non-invasive electrodes placed on standard positions on the scalp - connected to amplifiers and a recording device. small voltage fluctuations between two paired electrodes measured = used to generate an EEG signal

depends on the synchronous firing activity of large numbers of neurons = summed post-synaptic activity of many neurons measured to generate electrical signal

synchronous activity is important - many small APs form individual neurons when fired at the same time will create a larger amplitude EEG electrical signal

if activity isn’t synchronised, decreased amplitude

Question 4

describe different EEG signals and patterns in different states of alertness

Answer 4

in waking states - many active neurons firing at different times, asynchronous activity. produces high frequency, low amplitude EEG signals = e.g. beta and alpha EEG signals

in non-waking states - few active neurons with a common, slow input, synchronous activity. produces low frequency, high amplitude EEG signals = e.g. theta and delta

Question 5

describe the Hz frequencies and associated alertness states of alpha, beta, theta and delta EEG signals

Answer 5

beta = 14-30 = awake, mental activity

alpha = 8-13Hz = awake but resting

theta = 4-7Hz = non-dreaming sleep, sometimes associated with waking states

delta = less than 4Hz = deep sleep

Question 6

name the two ways synchronous brain rhythm activity is generated

Answer 6

thalamic pacemaker
collective behaviour of cortical neurons

Question 7

describe the two ways synchronous brain rhythm activity generated

Answer 7

thalamic pacemaker
- thalamus has a collection of nuclei, contain neurons
- synaptic connections between excitatory and inhibitory neurons & neurons’ intrinsic properties force them to conform to a rhythm
- small group of thalamocortical neurons project rhythm to large number of cerebral cortical neurons

collective behaviour of cortical neurons
- excitatory and inhibitory interconnections of cortical neurons create coordinated synchronous activity
- activity remains localised or spreads to other brain regions, larger regions of the cortex

Question 8

function of brain rhythms?

Answer 8

unsure - hypothesised to be by-products of brain activity, unavoidable consequences of interconnected brain circuitry with no real function

Question 9

what is sleep?

Answer 9

a readily reversible state of reduced responsiveness to & interaction with the environment

Question 10

what are the three functional states of the brain?

Answer 10

waking, non-REM sleep and REM sleep

Question 11

describe the EEG pattern in the state of wakefulness?

Answer 11

high frequency, low amplitude

many active neurons, firing at different times with varying levels of activity - asynchronous activity

Question 12

describe features of non-REM sleep - EEG pattern, physiological changes and movement

Answer 12

EEG pattern = low freq, high amplitude

physiological changes = greater decrease in breathing, heart rate and brain energy consumption compared to REM. less of a core body temperature decrease

movement: occasional, involuntary, rarely dreaming

Question 13

describe features of REM sleep - EEG pattern, physiological changes and movement

Answer 13

EEG pattern = high frequency, low amplitude (similar to waking)

physiological changes = increase in brain energy consumption compared to waking state, balanced out by greater decrease in core body temp. irregular decrease in heart rate and breathing, less of a decrease compared to non-REM.

movement: immobile, muscle paralysis. vivid dreams.

Question 14

why do we sleep?

Answer 14

restoration - resting, recovering

adaptation - protection against predators, conserving energy

Question 15

describe the sleep cycle

Answer 15

EEG rhythms divided into four stages of sleep - depends on depth of sleep

starts with period of non-REM sleep, each cycle repeats every 90 minutes through varying deep states of non-REM to REM

Question 16

describe the neural mechanism of waking

Answer 16

increased brainstem activity and neuron firing of certain neurotransmitters:
- 5-HT = raphe nuclei
-noradrenaline = locus coeruleus
- histamine = midbrain
- orexin = lateral hypothalamus
- Ach = basal forebrain/ nucleus basalis

neurons synapse with thalamic and cerebral cortical neurons - increase excitatory activity, suppress rhythmic firing that occurs during sleeping

Question 17

describe the neural mechanism of sleep

Answer 17

decrease in brainstem activity and neuron firing rate, decrease in Ach, 5-HT and noradrenaline

pons Ach neurons increase firing = induce REM sleep, contribute to dreams, activates cerebral cortex

thalamic neuron rhythmic firing to cerebral cortex - contributes to emotional aspect of dreams

lack of excitatory brainstem activity = removes suppression on rhythmic thalamic and cerebral cortex firing present during sleep

sleep promoting factors - adenosine, nitric oxide, inflammatory factors and melatonin contribute

adenosine = released as NT - decreases heart rate, resp. rate, BP and smooth muscle tone. receptor antagonist (e.g. caffeine) promotes wakefulness.

nitric oxide = acts as vasodilator, decreases smooth muscle tone. suppresses activity of neurone that promote wakefulness.

inflammatory factors = cytokines and interleukins released by immune cells promote sleep to fight infection and conserve energy

melatonin = initiates and maintains sleep. rises during the evening, peaks in the early hours and falls before waking. used to treat insomnia.

Question 18

name the four sleep promoting factors

Answer 18

adenosine
nitric oxide
melatonin
inflammatory factors

Question 19

what is a circadian rhythm?

Answer 19

any rhythm within a period of approx. 24 hours, considered ‘biological brain clocks’

most physiological processes rise and fall with circadian rhythms - e.g. body temp, growth hormone, cortisol, sleep-wake/melatonin

Question 20

what is a zeitgeber? what is its significance in investigating biological brain clocks?

Answer 20

zeitgeber - environmental cues (e.g. light, dark, temperature) that indicate a time of day

for studies into biological brain clocks, need to be conducted in isolation away from zeitgebers to put individuals in a free-running state. see if biological brain clocks hold without environmental cues.

Question 21

what is the importance of the SCN (suprachiasmatic nucleus) in circadian rhythms?

Answer 21

SCN is located in the hypothalamus - gets innervation from retina, synchronises circadian rhythms with light-dark cycles

important for circadian rhythm and sleep-wake cycle even without zeitgebers

Question 22

mechanism of SCN?

Answer 22

each SCN neuron is a mini ‘brain clock’ with a 24hr pattern of activity

SCN clock genes produce a protein - sends feedback to SCN, decreases gene transcription and inhibits further protein production within 24 hours

SCN 24hr cycle is reset by light info. from the retina - cycle occurs every 24 hours

SCN influences other circadian rhythms in the body - e.g. core body temp, feeding, metabolism, autonomic nervous system