biological rhythms

Question 1

rhythm

Answer 1

any process that varies through time

-has a constant period

Question 2

period

Answer 2

time interval

= length of time to complete one cycle

Question 3

frequency

Answer 3

number of completed cycles per unit of time

Question 4

cycle

Answer 4

repeating unit

Question 5

phase

Answer 5

any point in a cycle

Question 6

amplitude (strength/ intensity)

Answer 6

amount of change above or below the average value

Question 7

exogenous

Answer 7

factors outside of the organism

Question 8

endogenous

Answer 8

factors within the organism

Question 9

circadian rhythm

Answer 9

period around 24 hours a day (ex: sleep wake cycle, body temperature)

Question 10

ultradian rhythm

Answer 10

period less than 24 hours

ex: circatidal: 12.4 hours

Question 11

infradian rhythms

Answer 11

period greater than 24 hours, less than 1 year

• circanular: moon phases
• ovulatory cycle

Question 12

circannual rhythm

Answer 12

BR approximately 1 year

-ex: seasonal changes

Question 13

Zeitberger

Answer 13

environmental time cue/temporal synchronizer

• something in the environment the cues internal rhythm to synchronize with external cue
• most primary zeitberger is light

Question 14

free running

Answer 14

biological rhythms NOT synchronized by environmental cues

Question 15

entrainment

Answer 15

synchronization of endogenous rhythms with periodic cue in the environment

Question 16

reason for jet lag

Answer 16

MAJOR phase shift: quick adaptation of activity levels, but other rhythms/physiological rhythms/processes lead to a rapid phase shift

Question 17

biological blocks

Answer 17

internal timing mechanisms that are responsible for generating rhythms and allowing entrainment to take place

Question 18

arrhythmia

Answer 18

activity present but a lack of rhythm

-happens when SCN is lesioned

Question 19

restoration of SCN rhythm

Answer 19

SCN tissue transplants–> restoration in circadian functioning in SCN lesioned recipient so that the period of the recipient’s rhythm matches that of the donor, regardless of the original rhythm

Question 20

humoral output

Answer 20

diffusible signal responsible for LOCOMOTOR activity

• SCN transplant studies in hamsters
• SCN tissue transplanted into the brain of an arrhythmic, SCN lesioned hamster
• restored circadian rhythms but NOT endocrine function
• b/c no neural connectivity was re-established, hypothesized that rhythms in locomotor activity could be supported by diffusible SCN signal
• transplants sealed in semipermeable membrane

Question 21

neural output

Answer 21

mediates ENDOCRINE function

Question 22

eye pathway

Answer 22

light–> ganglion layer and inner retina to rods and cone photo receptors–> R’s and C’s send info to ganglion cells–> intrinsically photosensitive retinal ganglion cells contain melanospin–> encodes and transmits light information into the SCN via the RHT

Question 23

SCN: central vs. peripheral oscillators

Answer 23

SCN acts a central oscillator and coordinates/acts as a master clock for the peripheral oscillators
-peripheral oscillators have different phase relationships and the SCN makes sure that these rhythms are properly synchronized

Question 24

Estrogens and scalloping

Answer 24

on day of estrus, F hamsters in chronic dark conditions have an earlier onset of running behavior= phase advanced (rising levels of estrogens–> earlier onset of behavior)

scalloping can be eliminated via ovariectomy

but E replacement to OVX free running F rats–> decreased period of locomotor activity onset, suggesting direct effect of E on clock

Question 25

Glucocorticoids CR

Answer 25

cortisol: highest in morning just when you wake (if nocturnal, highest post wake prior to activity onset) corresponds with activity levels and locomotor activity

Question 26

gonadotropins

Answer 26

LH - patterns of LH release dependent on E feedback (+/-) and signals from SDN - LH surge is a product of estradiol signals from the ovaries AND a circadian signal from the SCN - SCN sends direct and indirect projections to GnRH system to appropriately time LH surge

Question 27

Swann and Turek: Splitting

Answer 27

constant light--> split in activity levels so that there are 2 distinct LH pulses - decreased period--> more LH pulses * SDN controls activity of hormones, and when activity splits, you get a double hormone pattern

Question 28

sex steroid hormones: estrogen and t CR

Answer 28

Estrogens: no CR testosterone: CR of T in males that persists under constant conditions

Question 29

Melatonin CR

Answer 29

=darkness hormone - same pattern of release for diurnal and nocturnal animals: high at night, low in day - light-dark cycle, NOT tied to activity levels - secreted ONLY at night - duration of melatonin secretion reflects lengths of photoperiod= day length

Question 30

pathway of melatonin release

Answer 30

light--> melanospin expressing retinal ganglion cells--> RHT--> SCN--> PVN--> multi synaptic pathway--> pineal-->melatonin enzymes that produce melatonin are inhibited when there is light

Question 31

type 1 seasonal breeder

Answer 31

driven by endogenous and exogenous signals ex: reproduction in Syrian golden hamsters (breed in spring/summer, respond favorably to light (day=long) so when days get short, use that cue to shut down reproduction (b/c you don't breed in winter b/c baby will be born in unfavorable conditions)

Question 32

type 2 seasonal breeder

Answer 32

truly endogenous, driven by circannual clocks; without external cues, rhythm persists (ex: ground squirrel)

Question 33

type 1 seasonal breeder syrian golden hamster example steps

Answer 33

1. decrease in mating behavior is happening in the fall to the point where they are at reproductive quiescence (complete cessation of reproductive activity) 2. photo refractory: will not respond to short day length--> increase in reproductive behaviors, happens end of winter/early spring 3. photorefractoriness STOPS after exposure to long days 4. photosensitivity: must be exposed to long days in order to show response to short days of fall and winter

Question 34

SCN as a clock and calendar: melatonin example

Answer 34

clock: day vs. night pattern of melatonin calendar: short day vs. long day pattern (seasonal)--> varies in duration **SCN controls the rhythm of sexual activity and physiology b/c of DURATION of melatonin secretion determines the biological response (gonads are smaller in the winter when melatonin duration is high, testes larger in summer when melatonin duration in low)

Question 35

variations in breeding practices among short and long day breeders: interpretation of melatonin signals and relation to fertility

Answer 35

melatonin signal encoded differently by short and long day breeders (short day= sheep, long=hamster) long days: eye--> RHT--> SCN--> pineal--> decrease M duration--> sheep will be anovulatory, hamster will be fertile short days: sheep will be ovulatory, hamster will be infertile

Question 36

hypothalamic interpretation of M will impact GnRH release, LH/FSH release, and release of ovarian/testicular hormones

Answer 36

if hypo interprets M as inhibitory -lower GnRH--> lower FSH/LH--> lower sex hormones if hypo interprets M as stimulatory -higher GnRH--> higher FSH/LH--> higher sex hormones short day breeder -high duration of M--> enhance GnRH... long day breeder -low duration of M--> enhance GnRH...

Question 37

estradiol, melatonin, long day and short day breeders, reproductive transitions

Answer 37

melatonin is altering estradiol feedback on AVPV and ARC - seasonal reproductive transitions are a result of changes in ability of estradiol to inhibit GnRH - Sheep: long days - -estradiol--> inhibit GnRH--> decreased LH/FSH--> blocking ovulation (E has higher levels during long days) Sheep during short days: estradiol concentrations go down, decreased negative feedback--> higher GnRH--> higher LH/FSH--> ovulation--> sex behavior

Question 38

seasonal changes in ARC kisspeptin cells and GNRH neurons

Answer 38

- breeding season: increase in number of kiss1 cells in caudate - and increase in % of GnRH cells with kiss 1 input