Biological rhythms Flashcards
Name an efferent output of the suprachiasmatic nucleus and describe its role in the sleep-wake cycle (5 marks)
VLPO🡪
Project strongly to sub paraventricular nucleus
Contain inhibitory GABA-ergic neurones that innervate dorsalmedial nucleus of the hypothalamus.
GABA-ergic and Glutamatergic neurones in the dorsalmedial nucleus innervate the lateral hypothalamus
Suggests dorsalmedial nucleus promotes wakefulness during daytime.
Lateral hypothalamic area 🡪
Glutamatergic neurones innervate the lateral hypothalamic area
- the lateral hypothalamic area contains orexin and melanin-concentrating hormone. They are both seen as having antagonistic relationship with one another.
- orexin neurons: there are two types, orexin A and Orexin B. These peptides are implicated in the regulation of wakefulness and arousal and is actively release during the ‘awake’ period.
- MCH is also a peptide hormone. However, it is released during the ‘sleep’ period. It is also seen that an increased level of MCH seems to increase the total amount of time spent in both REM and NREM which in turn increases total sleep duration.
- These signalling systems also interconnect with the and feeding centres in the arcuate nucleus and may maintain the balance between sleep need and duration with hunger and food foraging.
Arcuate/ paraventricular nucleus🡪
arcuate neurons express a diverse mixture of neuromodulators that act within the arcuate nucleus and at projection targets such as the paraventricular nucleus of the hypothalamus (PVH), Ventral medial nucleus, and the lateral hypothalamic area (LHA). influence feeding behaviour to each nucleus.
Of these, GABA, neuropeptide Y, dynorphin, galanin, β-endorphin, and agouti-related protein stimulate feeding to the paraventricular nucleus.
whereas α-melanocyte-stimulating hormone, cocaine, and amphetamine-regulated transcript suppress feeding to the paraventricular nucleus.
And therefore, it is seen that the paraventricular area and the ventral medial nucleus of the hypothalamus regulates feeding activity, satiety and glucose homeostasis.
The paraventricular nucleus also has direct projections from the SC as seen.
Briefly explain the PER/CRY feedback mechanism and explain the importance of its role in the sleep-wake cycle. (6 marks)
CLOCK and BMAL1 heterodimerize.
They bind to an E-box (enhancer box)
They help promote the transcription of the genes Period (PER) and Cryptochrome (CRY)
These proteins are generally unstable and so bind to other proteins throughout the day.
One of these proteins is CKepsilon that phosphorylates PER at serine residues and allows it to heterodimerise with CRY. They then translocate back to the nucleus where they inhibit their own transcription. Over time the PER/CRY proteins break down and the cycle starts again.
Mutations of PER/CRY and their effects on sleep, show that clock genes directly regulate the timings of sleep onset and sleep duration.
Explain phase synchronisation and how this leads to long term potentiation (5 marks).
Phase synchronisation is when two neural oscillations have the same amplitude and phase angles and therefore are correlated. Evidence has shown that when a stimulus arrives during a peak of a hippocampal theta wave phase synchronisation, LTP is induced. Whereas, stimulation at the trough of oscillations induces LTD. Therefore, if a stimulus arrives at the appropriate time during theta phase synchronisation, it is encoded into long term memory. It has been theorised that gamma cycles code for new memories. Individual memories are stored by the spatial pattern of cells that fire within a given gamma cycle, which occurs within a theta phase. As different memories are activated in different gamma cycles, memory capacity is limited by the number of gamma cycles within a theta phase.
