Sleep & Circadian Rhythms Flashcards
What are Brain Rhythms?
Refer to distinct patterns of neuronal activity that are associated with specific behaviours, arousal level and sleep rate
List some environmental rhythms
The earth has a rhythmic environment that can vary with the seasons
- Temperature
- Precipitation
- Daylight
What must an animal do in order to survive and compete efficiently?
- In order to compete effectively and survive, an animals behaviour must oscillate with its environment
- The brain has evolved a variety of systems for thymine control such as sleep/wake cycle
What does an electroencephalogram (EEG) do?
It’s a measurement of electrical activity generated by the brain and recorded from the scalp
What does an electroencephalogram involve?
- Involves non invasive electrodes placed on standard positions on the head
- Connected to amplifiers and a recording device
Briefly describe how an electroencephalogram works (PART 1)
- EEG measures the combined activity of a large number (1000s) of similarly orientated neurons
- Requires synchronous activity across groups of cells
- EEG reflects summed post synaptic activity of large cell ensembles
Briefly describe how an electroencephalogram works (PART 2)
- The amplitude of an EEG signal depends upon 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
- However, timing is everything, the same amount excitation can occur at irregular intervals and result in a small summed signal
How can the EEG rhythms be categorised?
By their frequency range:
- A high frequency low amplitude associated with alertness and waking
- A low frequency high amplitude aaaociated with non dreaming sleep
What is the electroencephalogram used for today?
Primarily used to help diagnose certain neurological disorders (Seizures in epilepsy)
What are the 2 types of synchronous base rhythms?
- Pacemaker: Synchronous rhythms can be led by a central clock or pacemaker (e.g. thalamus)
- Collective behaviour: Synchronous rhythms can arise from the collective behaviour of cortical neurons themselves
Describe the thalamic pacemakers
- The thalamus can act as a pacemaker with its vast input to the cerebral cortex
- Synaptic connections between excitatory and inhibitory thalamic neurons force each individual neurons to conform to the rhythm of the group
- Co-ordinated rhythms are then passed to the cortex by thalamuocrotical axons
- Therefore a relatively small group of centralised thalamic neurons can compel a much larger group of cortical neurons
Describe the collective behaviour of cortical neurons
- Some rhythms of the cerebral cortex do not depend on a thalamic pacemaker
- Instes they rely on collective interactions of cortical neurons themselves
- Excitatory and inhibitory interconnections of neurons result in a coordinated synchronous pattern of activity
- This can remain localised or spread to encompass larger regions of the cerebral cortex
What are the functions of brain rhythms?
- One hypothesis is that most brain rhythms have no direct function but are by products instead
- Brain rhythms are strongly interconnected with various forms of excitatory feedback
- Rhythms must be an unavoidable consequence of such circuitry
- However even if brain rhythms don’t have a function, they provide us with a convenient window on the functional states of the brain
Define sleep
A readily reversible state of reduced responsiveness and interaction with the environment
Do we really need sleep?
- Prolonged sleep deprivation can be devastating to proper functioning
- However we can starve off sleep but not for long
- Longest record without sleep was 264.4 hours by Randy Gardner
- Sleep is be universal amongst all animals