HOMEOSTASIS Flashcards
(31 cards)
What is homeostasis?
Maintenance of equilibrium by active regulation of internal states
Give some examples of what homeostasis does?
- cardiovascular function - blood pressure, heart rates
- body temp
- food and energy regulation
- find regulation
Why does multiple mechanism contol homeostasis?
Emphasis the importance to survival
Whats an example of homeostasis for energy conservation?
During sleep body temp decreases
Heart rate decrease
Respiration rate decrease
= energy conservation
What shows natural biological rhythms?
Circadian rhythms- daily cycle
Body temp, heart rates, respiration, sleep
Whats yearly cycle called?
Circannual rhythms
- hibernation, mateing behaviour and migration
What’s biorhythms linked to?
- light /dark cycle
- season = day length probably critical
How does light/ dark information affect body systems?
- circadian rhythm maintained in constant light - still follow a sleep-wake cycle for a while
- periodicity changed - cycle may shift
- suprachiasmatic nucleas lesion - caused. ->
- circadian rhythm abolished - it no longer follows a regular sleep schedule, hormones or temp
- no periodicity - not able to repeat the rhythms or cycle now
Where is the SCN found?
Located in hypothalamus, above the optic chasm
What do the cells in SCN show?
Oscillations of activity related to circadian rhythm and believed to form the
- biological clock
How does light information reach SCN?
Many non - mammalian species have photoreceptors outside the eye
Like reptiles have pineal gland is light sensitive
Describe the direct pathway from eyes to SCN?
- Light information is sent from the eye to the SCN (suprachiasmatic nucleus), which controls the body’s internal clock.
- The usual light detectors (rods and cones) do influence the SCN, but…
- Even without rods and cones, the SCN still receives light signals.
- ✅ This means there are other light-sensitive cells in the eye.
- These are called photoreceptive ganglion cells — they directly detect light and help control circadian rhythms, not vision.
What did Bremer state about passive onsent of sleep?
Surgically separated midbrain from forebrain in cats
• Animals remained permanently asleep
• Proposed that in the absence of sensory input the cortex became quiescent (i.e. sleep
Why did moruzzi and magnum do about passive onset of sleep?
• Electrical stimulation of the midbrain woke sleeping animals
• Lesions to this area caused persistent sleep
How does sleep ensue?
Activating system in the midbrain, which activates the cortex
• Lack of tonic activating influence of midbrain causes
cortical neurones to cease firing, and sleep to ensue
What does EEG recording show?
Abundant neuronal activity in cortex duringsleep
What was the patterns like during sleeping and waking?
Waves of activity, indicitating synchronous firing of cortical neurons
Synchronising stimulus coming from sub orbitals areas
Midbrain’s reticular formation still seen as important
Describe slow wave sleep?
progressive decrease in spinal reflexes
• progressive reduction in heart rate and breathing rate
• reduced brain temperature and cerebral blood flow
• increased hormone secretion (e.g. growth hormone)
• synchronised cortical activity
Describe REM sleep ?
• spinal reflexes absent
• rapid eye movements behind closed eyelids
• increased body temperature and cerebral blood flow
• desynchronised cortical activity
• dream
What happens to brains activity during sleep?
Awake - low amplitude high frequency EEG
Light sleep - increasing amplitude decreasing frequency EEG
Deep sleep - high amplitude low frequency EEG
Which leads to rapid movement sleep = low amplitude highfrequency eeg
Explain neuronal circuitry controlling sleep?
Cortex kept awake by ascending activation from midbrain
5th input inhibits activating system areas
Therefore promotes sleep
Stimulation of area surrounding SCN indicates slow wave sleep
Mechanism unclear
Explain neurotransmitters of sleep?
Neurotransmitters
• 5HT - promotes slow wave sleep – inhibition of ‘activating system’
• Noradrenaline - ? inhibition of muscle tone during REM sleep
• Dopamine - general arousal
• Acetylcholine - induces REM sleep
What’s insomnia
Reduction or absence of sleep - transient or persistent
What’s hypersomnia
Excessive drowsiness and falling sleep
