Chapter 13 Flashcards
diurnal animal
organism that is active chiefly during daylight
circadian rhythm
Day–night rhythm.
metabolic syndrome
combination of medical disorders, including obesity and insulin abnormalities, that collectively increase the risk of developing cardiovascular disease and diabetes.
biological clock
neural system that times behavior.
biorhythm
inherent timing mechanism that controls or initiates various biological processes.
what processes cycle daily?
Not only does human waking and sleep behavior cycle daily, so also do pulse rate, blood pressure, body temperature, rate of cell division, blood-cell count, alertness, urine composition, metabolic rate, sexual drive, feeding behavior, and responsiveness to medications. The activity of nearly every cell in our bodies, including gene expression, also has a daily rhythm.
What do biological clocks help with?
allows an animal to anticipate events in advance and prepare for them both physiologically and cognitively. And unless external factors get in the way, a biological clock regulates feeding times, sleeping times, and metabolic activity so that they are appropriate to day–night cycles. Biological clocks also regulate gene expression in every cell in the body so that cells function in harmony.
period
time required to complete a cycle of activity.
circannual
yearly; migratory cycles of birds
circadian
Daily; human sleep–wake cycle
ultradian
Less than a day; human eating cycles
infradian
more than a day; human menstrual cycle
do humans have an endogenous biological clock?
yes, it governs sleep-wake behavior
given no external cues, will people stay on a 24 hour cycle?
more or less, but may range from 25-27
free-running rhythm
Rhythm of the body’s own devising in the absence of all external cues.
Zeitgeber
environmental event that entrains biological rhythms: a “time giver.”
entrain
Determine or modify the period of a biorhythm.
rule of thumb to explain the period of free-running rhythms in light or dark
animals expand and contract their sleep periods as the sleep-related period expands or contracts.
when are Zeitgebers effective?
both sunrise and sunset
how many times per day can clocks be adjusted?
morning light sets the biological clock by advancing it, and evening darkness sets the clock by retarding it.
light pollution
exposure to artifical light that changes activity patterns and so distrupts circadian rhythms.
jet lag
fatigue and disorientation resulting from rapid travel through time zones and exposure to a changed light–dark cycle.
problems associated with light pollution
a great deal of inconsistent behavior associated with accidents, daytime fatigue, alterations in emotional states, and obesity and diabetes.
suprachiasmatic nucleus (sCn)
master biological clock, located in the hypothalmus just above the optic chiasm.
retinohypothalamic tract
neural route formed by axons of photosensitive retinal ganglion cells from the retina to the suprachiasmatic nucleus; allows light to entrain the rhythmic activity of the scn
what other neural structures display clock-like activity besides the SCN?
intergeniculate leaflet; pineal gland
when are neurons of the SCN most active?
neurons in this region are more active during the light period of the cycle than during the dark period.
what can entrain the SCN?
a regular feeding schedule
how do SCN cells synchronize?
SCN cells connect one to another through inhibitory GABA synapses, and these connections allow them to act in synchrony. Their entrainment depends upon external inputs.
where does the retinohypothalamic tract begin?
This pathway begins with specialized retinal ganglion cells (RGCs) that contain the photosensitive pigment melanopsin. These melanopsin-containing, or photosensitive RGCs, receive light-related signals from the rods and cones and send that information to visual centers in the brain. However, pRGCs also can be activated directly by certain wavelengths of blue light in the absence of rods and cones.
retinal ganglion cells
distributed across the retina and, in hu- mans, make up between 1 and 3 percent of all RGCs. Their axons project to various regions in the brain, including the SCN, which they innervate bilaterally.
Melanopsin- containing ganglion cells
use glutamate as their primary neurotransmitter but also contain two cotransmitters, substance P and pituitary adenylate cyclase-activating polypeptide (PACAP).
how many parts make up the SCN?
two; more ventrally located core and a more dorsally located shell.
what activates the core cells of the SCN?
The retinohypothalamic tract
core neurons
are not rhythmic, but they entrain the shell neurons, which are rhythmic.
where does the SCN receive projections from?
These include the intergeniculate leaflet in the thalamus and the raphé nucleus, the nonspecific serotonergic ac- tivating system of the brainstem.
what entrains the SCN?
is usually entrained by morning and evening light, but it can also be entrained or disrupted by sudden changes in lighting, by arousal, by moving about, and by feeding.
what other pathways influence SCN?
The intergeniculate leaflet and the raphé nucleus are pathways through which other photic and nonphotic events influence the SCN rhythm
how many groups of circadian neurons are there?
2: M cells and E cells
M cells
control morning activity and need morning light for entrain- ment;
E cells
control evening activity and need darkness onset for entrainment
where are the “timing devices” located?
in each SCN neuron and in most other cells of the body as well.
chronotype
individual differences in circadian activity.
dimer
two proteins combined into one.
circadian rhythm feedback loop
in which proteins are first made and then combine. The combined protein, called a dimer for “two proteins,” inhibits the production of its component proteins. Then the dimer degrades and the process begins anew
what produces cellular rhythm?
the increase and decrease in protein synthesis
SCN and Slave Oscillator
light entrains the SCN, and the pacemaker in turn drives a number of “slave” oscillators. Each slave oscillator is responsible for the rhythmic occurrence of one activity. In other words, drinking, eating, body temperature, and sleeping are each produced by a separate slave oscillator.
How does the SCN clock entrain slave oscillators?
- SCN neurons send axonal connections to nuclei close by in the hypothalamus and thalamus. These nuclei in turn have extensive connections with other brain and body structures to which they pass on the entraining signal.
- The SCN connects with pituitary endocrine neurons to control the release of a wide range of hormones. These hormones circulate through the body to entrain many body tissues and organs.
- The SCN also sends indirect messages to autonomic neurons in the spinal cord to inhibit the pineal gland from producing the hormone melatonin, which influences daily and seasonal biorhythms.
what controls the release of melatonin?
The SCN controls the release of melatonin from the pineal gland so that it circulates during the dark phase of the circadian cycle, and it controls the release of glucocorticoids from the adrenal gland so that they circulate during the light phase of the circadian cycle.
what does melatonin do?
sleep-promoting actions and influences the parasympathetic rest and digest system.
what do glucocorticoids do?
mobilize glucose for cellular activity and can support arousal responses in the sympathetic system.
melatonin
hormone secreted by the pineal gland during the dark phase of the day– night cycle; influences daily and seasonal biorhythms.