11. Lecture 24, 25 Flashcards Preview

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1
Q

What is the retinohypothalamic tract?

A

SCN receives a selective input from the retina that is necessary and sufficient for photic entrainment of circadian rhythms

Slide 1 lecture 24

2
Q

Are retinal photoreceptors required for circadian photoreception?

A

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

3
Q

What does a pulse of light do to intrinsically sensitive retinal ganglion cells (ipRGC)?

A

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

4
Q

What is time compensated sun compass orientation?

A

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

5
Q

How does circadian rhythms control melanin production?

A

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

6
Q

Where do the neurons most critical for sleep and wake reside?

A

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

7
Q

What do neuromodulators do?

A

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

8
Q

What systems are active and inhibited during wake state and sleep state?

A

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

9
Q

What is orexin neurons role in the sleep wake cycle?

A

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

10
Q

What is advanced sleep phase syndrome (ASPS)?
What is delayed sleep phase syndrome (DSPS)?
What is non-24-hour sleep wake syndrome?

A

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

11
Q

Study the peripheral circadian clocks on slide 15-16 lecture 24

A

Okay

12
Q

What is astrocyctic control of SCN time keeping?

A

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

13
Q

What is astrocytic control of SCN time keeping?

A

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

14
Q

What does glutamergic signalling have to do with astrocytes control of time keeping?

A

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)

15
Q

What is the neuroendocrinology of fluid homeostasis?

Breakdown of incoming fluid and outgoing wastes

A

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

16
Q

Study the ion concentrations in different compartments on slide 3 lecture 25

A

Okay

17
Q

What is intracellular fluid, extracellular fluid, interstitial fluid, and plasma?

A

ICF- 2/3 of total body water volume, materials moving in and out must cross cell membrane

ECF- includes all fluid outside cells
1/3 body fluid volume
Consists of interstitial fluid and plasma

Interstitial fluid- lies between circulatory system and the cells
75% of ECF volume

Plasma- liquid matrix of blood, substances moving between plasma and interstitial fluid must cross the leaky exchange epithelium of capillaries

Slide 4 lecture 25
25% ECF volume

18
Q

What are the 4 steps that occurs when fluid leaves plasma?

A
  1. Fluid leaves plasma at arteriolar ends of capillaries because the outward force of hydrostatic pressure predominates
  2. Fluid returns to plasma at venue at ends of the capillaries because the inward force of colloid osmotic pressure predominates
  3. Hydrostatic pressure within interstitial spaces forces fluid into lymph capillaries
  4. Interstitial fluid is in equilibrium with transcellular and intracellular fluids

Slide 4 lecture 25

19
Q

What are increases of plasma osmolality of ~10mosmol/kg associated with?

A

Associated with feelings of headache, reduced levels of alertness and difficulty in concentrating

20
Q

What do larger perturbations (>10mosmol/kg) in plasma osmolality lead to?

A

Lead to lethargy, weakness, irritability, spasticity, confusion, coma, and seizures

Exceeding 80mosmol/kg leads to seizures and death

Can occur as a result of excessive voluntary drinking or compulsive drinking or from accidental over hydration in the hospital setting

21
Q

What is the blood brain barrier?

A

Diffusion barrier impedes influx of most compounds from blood to brain
Essential for maintaining a constant internal environment

Continuous right junctions link brain capillary endothelial cells

Slide 8 lecture 25

22
Q

What organs lack a blood brain barrier?

A

Circumventricular organs lack a blood brain barrier
Several restricted areas of brain are supplied by leaky capillaries so neurons there are directly exposed to blood solutes and macromolecules

Lack of blood brain barrier in the posterior pituitary is necessary to allow hormones that are released there to enter the general circulation

Slide 9 lecture 25

23
Q

What are the 3 nuclei in the hypothalamus and pituitary gland?

A

Supraoptic nuclei (to posterior pituitary)

Paraventricular nuclei (to posterior pituitary)

Nuclei sending axons to median eminence

Slide 10 lecture 25

24
Q

What does increased osmolality signal?

A

Signals arginine vasopressin secretion from the posterior pituitary

Normal plasma osmolality is ~290mOsm

Threshold for vasopressin release is ~280mOsm and rises steeply with increases in osmolality (as does thirst)

Slide 11 lecture 25