11. Lecture 24, 25 Flashcards
What is the retinohypothalamic tract?
SCN receives a selective input from the retina that is necessary and sufficient for photic entrainment of circadian rhythms
Slide 1 lecture 24
Are retinal photoreceptors required for circadian photoreception?
No, retinal photoreceptors not necessary for circadian photoreception
Opsin like pigment, melanopsin, is expressed in a small population of intrinsically photosensitive retinal ganglion cells (ipRGC) that respond directly to light
Retinal ganglion cells containing melanopsin innervate the SCN
Slide 2 lecture 24
What does a pulse of light do to intrinsically sensitive retinal ganglion cells (ipRGC)?
A pulse of light produces a burst of action potentials in ipRGCs
Graph on slide 3 lecture 24 shows photopigment spectral sensitivities of melanopsin containing ipRGCs compared to rods and 3 cone types
Slide 3 lecture 24
What is time compensated sun compass orientation?
Monarch butterflies use a time compensated sun compass to orient south during their fall migration
Butterfly circadian clock allows the butterflies to compensate for the movement of the sun
They are able to maintain a constant bearing in the southerly direction over the course of the day
Slide 4-5 lecture 24
How does circadian rhythms control melanin production?
Regulated by anatomical pathway from retina to the pineal gland
Photic input detected in retina by melanopsin containing neurons is relayed via retinohypothalamic tract to SCN
Paraventricular nucleus (PVN) receives GABAergic input from SCN
PVN neurons project to preganglionic sympathetic cell bodies that turn project axons to the superior cervical ganglion (SCG)
Norepinephrine released from terminals of SCG neurons in pineal gland stimulates melatonin production
Slides 6-7 Lecture 24
Where do the neurons most critical for sleep and wake reside?
They are part of the diffuse modulatory neurotransmitter systems that synapse directly on the entire thalamus, cerebral cortex, and many other brain regions
These systems act like switches or tuners of the forebrain, altering cortical excitability and gating the flow of sensory information to it
Slide 8 lecture 24
What do neuromodulators do?
Depolarizes thalamus neurons, increase their excitability, and suppress rhythmic forms of firing
May resemble what happens during transitions from non REM sleep to waking state
Slide 9 lecture 24
What systems are active and inhibited during wake state and sleep state?
During wake state, arousal systems are active and the vIPOA (major sleep promoting region) is inhibited
During sleep state, vIPOA is active and the arousal systems are inhibited
vIPOA and major wakefulness promoting regions are reciprocally connected
Slide 10 lecture 24
What is orexin neurons role in the sleep wake cycle?
Orexin neurons strongly excite neurons of the ACh, NE, 5HT, and histaminergic modulatory systems that promote wakefulness and inhibit sleep
Stabilize the sleep/waking flip-flop circuit in the waking state
Projections of the orexinergic neurons are excitatory and promote wakefulness
Slide 11-12 lecture 24
What is advanced sleep phase syndrome (ASPS)?
What is delayed sleep phase syndrome (DSPS)?
What is non-24-hour sleep wake syndrome?
ASPS- early morning wakening and inability to maintain wakefulness into the evening
Mutations in the Per2 gene
DSPS- late awakening and late bedtimes, inability to reset the clock to earlier times of day
Non 24 hour sleep wake syndrome- fail to entrain to the 24 hour day, frequent in blind people, free running period causes drift out of phase with the environment
Slide 13-14 lecture 24
Study the peripheral circadian clocks on slide 15-16 lecture 24
Okay
What is astrocyctic control of SCN time keeping?
Anti-phasic circadian cycles of neuronal and atrocytic activation, with [Ca]i levels peaking during circadian day and night
Anti-phasic circadian oscillations of neuronal [Ca]i and [Glu]e localized on neuronal cell membranes
Slide 17-18 lecture 24
What is astrocytic control of SCN time keeping?
Each SCN astrocyte is a minuscule clock that keeps time with a molecular cycle based on gene expression
When going into day astrocytes become quiescent and neurons depolarize
When going into night astrocytes become active and neurons hyperpolarize
Slide 19-21 lecture 24
What does glutamergic signalling have to do with astrocytes control of time keeping?
Glutamatergic signalling mediated astrocytic control of SCN time keeping
During circadian night, glutamate conc are high, driven by astrocytic release and reduced activity of glutamate transporters
During circadian daytime, clearance of extracellular glutamate by reduced astrocytic release and increased EAAT activity relieves GABAergic tone across the network, leading to depolarization and increased electrical firing across the suprachiasmatic nucleus (SCN)
What is the neuroendocrinology of fluid homeostasis?
Breakdown of incoming fluid and outgoing wastes
Incoming fluid- cerebrospinal fluid from subarachnoid space, between skull and brain, travels through a cavity surrounding an artery, propelled along by pulsing of blood flow. Fluid enters tiny channels that extend from cavity into astrocytes and then CSF Moves our of astrocytes and travels by convective flow thru brain tissue
Outgoing wastes- the fluid having picked up wastes from brain tissue is transported to the perivenous space, which surrounds a network of veins that drains blood from brain. In this cavity the fluid passes around larger veins that eventually reach the neck, wastes then move into the lymphatic system and eventually bloodstream
Slide 2 lecture 25
