circadian rhythm

Question 1

calendar cells

Answer 1

cells responsible for long term time keeping

melatonin target cells

Question 2

how do calendar cells decode melatonin duration?

Answer 2

use a clock-gene based mechanism

Question 3

melatonin signal generator

Answer 3

LD cycle —> photoreceptors in the retina —> pineal glands which release melatonin or SCN circadian cell —> which go to other cell targets

Question 4

melatonin decoder in the pituitary gland

Answer 4

LD= short night = less melatonin signal time 
SD= long night and more melatonin signal time 

this melatonin signal goes to calendar cell —> lactotroph/PRL —> hair papilla, hepatocyte, luteal cell

Question 5

which receptors of calendar cells pick up melatonin?

Answer 5

MTI receptors

Question 6

long term changes in prolactin secretion in the pelage/moult cycle

Answer 6

prolonged SD results in the development of prolactin secretion and the reversion from white to agouti pelage

exposure to prolonged LD results in the initial refractory response that merges into the expression into the expression of circannual cycle; horn growth is suppressed during winter

Question 7

refractory period

Answer 7

insensitive phase to prolactin secretion

calendar cells have inhibition of prolactin secretion which occurs over a long time before it recovers

Question 8

two models of the photoperiod

Answer 8

amplitude model - changes in the amplitude of clock gene expression
phase control- based on relationships between proteins
proteins dimerise, meet in the nucleus and act on gene expression, chance of proteins meeting in the LD is lower, in SD chance of them meeting is higher and get higher gene transcription

Question 9

symptoms of jetlag

Answer 9

constipation- clock is coupled to digestive system
retrieving information- mental performance
retrograde amnesia

Question 10

zeitgeber

Answer 10

time giver- resetting stimulus that functions as a time cue

light

Question 11

molecular clockworks of circadian rhythms

Answer 11

positive elements = CLKC and BMAL
negative elements are PER and CRY

PER and CRY dimerise and inhibit the positive elements in the nucleus

negative elements undergo ubiquitination and phosphorylation to prevent further inhibition

Question 12

regulation of clockwork genes

Answer 12

CLOCK and BMAL dimerise and bind to the promoters of the dock controlled genes and induce the transcription of many genes including PER and CRY

PER and CRY dimerise and interact with CLKOCK and BMAL, initiating their degradation

Question 13

SCN

Answer 13

paired nuclei at the base of the hypothalamus just above the optic chiasm
r

Question 14

where does SCN receive input from?

Answer 14

retinohypothalamic tract

Question 15

projections from the SCN

Answer 15

PVN - relaying information to the periphery, ARC - feeding centres , LHA- behaviour

Question 16

retinohypothalamic pathway and non-visual photo info

Answer 16

cones and rods allow colour vision and shape
retinoganglionic cell- different photoreceptors called melatinopsin and send it to the hypothalamus and reset the clock
non-visual light input pathway, don’t use it to see

Question 17

San lesion

Answer 17

get random rhythms of sleep wake, feeding and temperatures

Question 18

disseminating temporal information

Answer 18

master clocks in the SCN in the anterior hypothalamus

feeds into PVN

PVN has bilateral communication, receives input and feedback

Question 19

central and peripheral clock coordination

Answer 19

light —> SCN —> PVN — IML —> SCG —> pineal gland

from SCN also to peripheral clock systems

Question 20

peripheral clock systems

Answer 20

all different hormones occur at different times of the day - sequential, internal master clock determines this to maintain homeostasis of sleep and metabolism

Question 21

body temperature and chronotype

Answer 21

not consistent across the day and night- temperature plunges during night time

Question 22

day and night difference in the effects of exercise

Answer 22

exercise later at night has a much more efficient glucose removal/uptake

insulin is similar between morning and evening, which needs to be there for glucose uptake

therefore glucose transporters may be regulated by the clock, even if high insulin doesn’t mean there will be glucose uptake if no transporters

Question 23

neurons in SCn

Answer 23

GABAergic neurons
= inhibitory
therefore a very strong inhibitory tone from the SCN which inhibits the PVN which usually occurs during the daytime. the inhibition is removed during the nighttime because there is no light coming in to stimulate the SCN

Question 24

connection between SCN and liver- glucose production

Answer 24

daytime-

SCN inhibits PVN which inhibits the liver and results in increased glucose during the day

Question 25

SCN and pancreas- feeding induced insulin release

Answer 25

SCN strong inhibitory tone during the day which regulates how much PVN can be stimulated but he VMH. At night you take away inhibition to VMH is dominated, which causes the rhythm to occur and stronger pancreatic output VMH produces glutamate in ultradian pulses so it continuously communicates with PVN during day and nighttime. but the SCN modulates this

Question 26

when does cortisol peak?

Answer 26

cortisol peaks immediately prior to the onset of activity --> end of night before we wake

Question 27

cortisol and HPA axis

Answer 27

rhythm is generated by the SCN signalling to the pVN, resulting in rhythmic corticotrophin-releasing hormone (CRH) secretion, but the adrenal gland has its own clock turn on light -- adrenal gland sees light ---> resetting queue- neuronal

Question 28

melatonin

Answer 28

rhythmic signals from the SCN to the pineal gland drive rhythmic melatonin release melatonin therapy is used for sleep disorders

Question 29

human circadian organisation

Answer 29

retina --> SCN ---> PVN ---> Intermediolateral column of spinal cord ---> superior cervical ganglion ---> pineal gland

Question 30

nighttime melatonin synthesis

Answer 30

have more stimulatory pathways from the SCN. gabaergic neurons are silent