13.2 Flashcards
The Suprachiasmatic Biological Clock
What part of the brain is known as the “master clock”?
The suprachiasmatic nucleus
What two other neural structures have a clocklike role in controlling behavior?
The intergeniculate leaflet and the pineal gland
How does the SCN receive information about light? (what tract)
Through the retinohypothalamic tract
The retinohypothalamic tract carries information about light changes to what kind of cells in the SCN?
Core cells
Signals from SCN core neurons entrains what other neuron in the SCN?
Shell neurons
SCN drives _________ and receives signals from other brain and body areas
Slave oscillators
What is the main excitatory neurotransmitter in the CNS?
Glutamate
Where is the core of the SCN located?
The ventral (front) part of the SCN
Where is the shell of the SCN located?
The dorsal (back) side of the SCN
What kind of neuron in the SCN is rhythmic?
Shell neurons
How do melanopsin-containing photosensitive RGCs excite cells in the SCN? (pathway and neurotransmitter(s))
They innervate the SCN bilaterally and are excited by glutamate, substance P, and PACAP
What is a nonphotic event?
Any stimulus independent of light that affects the endogenous circadian pacemaker
What structures carry information from nonphotic events to the SCN to influence its rhythm?
The intergeniculate leaflet and the raphe nucleus
What is evidence for suprachiasmatic cells being genetically programmed for rhythmicity?
Hamster who have suprachiasmatic lesion lose their free-running rhythm and it is regained with a transplant of suprachiasmatic cells
What is a dimer?
Two proteins combined into one
What is the feedback loop of the circadian rhythm?
Two proteins synthesized -> dimer -> inhibits genes that make the proteins -> dimer degrades -> process restarts;
Happens over the course of the day;
Transcription, translation, inhibition, decay
What happens if there is damage to the SCN?
Drinking, eating, sleeping, and wakefulness still occur but at inappropriate times
What is the organization of the circadian timing system?
Light information from RGCs -> entrains SCN pacemaker -> output to different slave oscillators -> drive different behaviors;
e.g. one slave oscillator controls time of eating, another controls rhythm of body temp, etc.
What is melatonin?
Hormone secreted by the pineal gland during the dark phase of the day-night cycle; influences daily and seasonal biorhythms
What are some pathways in which the SCN controls the rhythms in the body? (5 ways)
- SCN sends axonal connections to the hypothalamus and thalamus
- SCN connects with pituitary endocrine glands
- SCN sends indirect messages to autonomic neurons in the spinal cord to inhibit pineal gland from producing melatonin
- SCN cells themselves release hormones
- Controls release of glucocorticoids from the adrenal glands
What are glucocorticoids role in the sleep-wake cycle?
They mobilize glucose for cellular activity to support arousal responses in the sympathetic system;
promotes arousal activities during the light portions of the circadian cycle
How does the SCN affect gonads (in hamsters)?
The SCN tells the pineal gland not to produce melatonin during the light time and, when melatonin levels are low, gonads enlarge and are more interested in sexual behavior
What are chronotypes?
Time types; individual variations in circadian activity
What is a “lark” chronotype?
One who is early to bed and early to rise; energetic in the morning
What is an “owl” chronotype?
One who is late to bed and late to rise; energetic in the evening
Biological rhythms are timed by internal biological clocks. The master clock is the ________
Suprachiasmatic Nucleus (SCN)
Light cues entrain the SCN to control daily rhythms via the ______ tract, which receives information via ________ cells
Retinohypothalamic; melanopsin ganglion
Pacemaking produced by the SCN is a product of _______ cells, which activate slave oscillators via both _______ signals and _________ connections
shell; chemical; anatomical
Why should mealtimes occur at the same time of day each day?
Experimental evidence suggests that the circadian rhythm can put a time stamp on a behavioral event, rendering it easier to recall at the same time in the circadian cycle that it occurred in previously
