neuro: sleep Flashcards
what are brain rhythms?
-brain rhythms refer to distinct patterns of neuronal activity that are associated with specific patterns, sleep state and arousal
what is the electroencephalogram?
- it is a measurement of electrical activity generated by the brain and recorded by placing electrodes on the scalp.
-EEG is used to diagnose certain neurological disorders (seizures in epilepsy)
-it is non invasive.
what does the EEG measure?
-the electrical activity of one neurone would be too small.
-EEG measures a large number (1000) of similarly oriented neurons.
-requires synchronous activity across groups of cells
what does the amplitude of an EEG depend on?
-depends on how synchronous the activity of a group of cells is.
-when a group of cells are excited and synchronous the tiny signals sum to generate a large surface signal.
-timing is everything, as a similar amount of excitation could occur at irregular intervals and result in a small summed signal.
how are EEG rhythms categorised?
-they are categorised by their frequency range
-alpha and beta frequency ranges (high frequency, low amplitude) are associated with alertness and waking.
- beta- awake with mental activity
-alpha- awake and resting
-low frequency high amplitude- associated with non dreaming sleep.
- theta: sleeping
-delta: deep sleeping (even lower frequency and higher amplitude than theta)
how are synchronous brain rhythms generated?
- thalamic pacemaker bold text :the thalamus with its vast input to the cerebral cortex can act as a pacemaker.
-synaptic connections between excitatory and inhibitory thalamic neurones force each individual neuron to conform to the rhythm of the group - co-ordinates rhythms are then passed on to the cortex by thalamocortical axons.
-collective behaviour of the cortical neurones:
Some rhythms of the cerebral cortex don’t depend on a thalamic pacemaker but rely instead on collective interactions of cortical neurones themselves.
what are green functions of brain rhythms?
- a possible hypothesis is that the brain rhythms have no direct function, but instead are by-products
- brain circuits are strongly interconnected. With various forms of excitatory feedback , Rhythyms may be an unavoidable consequence.
- even If they serve no purpose, they provide us with a convenient window on the functional states of fhe brain (ex epilepsy)
what is sleep?
- sleep is a readily reversible state of reduced responsiveness to, and interaction with the environment.
what is non-rem sleep?
- non- rapid eye movement sleep.
-higher amplitudes ans lower frequencies
-body capable of involuntary movement, rarely accompanied by vivid, detailed dreams
“Idling brain in a moveable body”
what is REM sleep?
-body immobilised accompanied by vivid detailed dreams
- “an active hallucinating brain in a paralysed body”
explain the sleep cycle?
EEG rhythyms can be subdivided into 4 stages.
-each night begins with a period of Non REM sleep.
- sleep stages are then cycled throughout the night, repeating approximately every 90 minutes
- as the night progresses there is a shift from non REM sleep to REM sleep.
compare the physiological aspects of non REM and REM sleep
- Non rem sleep:
Temperature : 🔽
Heart rate : 🔽🔽
Breathing: 🔽🔽
Brain energy consumption: 🔽
REM sleep:
Temperature: 🔽🔽🔽
Heart rate: 🔽 (irregular)
Breathing: 🔽 (irregular)
Brain energy consumption: 🔼🔼🔼
why do we need to sleep?
- there is no single theory of the function of sleep, although most reasonable ideas fall into two categories
Restoration and adaptation.
Restoration: we sleep to rest and recover and to prepare to be awake again.
Adaptation: we sleep to protect ourselves and to conserve energy.
explain the neural mechanisms if wakefulness?
- during wakefulness there is an increase in brain stem activity.
-several sets of neurons increase rate of firing in anticipation of wakening and enhance the wake state (eg noradrenaline, Ach, 5-HT, histamine)
-increase in excitatory activity suppresses rhythmic forms of firing in the thalamus and cortex, present during sleep
neural mechanisms of sleep?
- during sleep there is a decrease in brain stem activity
- several sets of neurones decrease rate of firing during sleep (eg Ach, 5-HT, and noradrenaline)
- however, cholinergic neurones in PONS is shown to increase rate of firing to induce REM sleep, linked with dreaming.
-rhythmic forms of firing in the thalamus has been shown to block the flow of sensory information up to the cortex. - there are also other sleep promoting factors involved in promoting sleep.
