unit 8 Flashcards
cns stimulants
drugs that increase activity of the central nervous system and the body, that produce arousal and have sympathomimetic effects
- drugs that increase the rate of behavior
cns depressants
drugs that reduce activity of the central nervous system and the body to decrease arousal
- drugs that decrease the rate of behavior
behavioral arousal exists on a continuum
Over the course of time, physiological, behavioral and cognitive functions vary in level of arousal/intensity.
- An obvious example of change in arousal levels is the sleep/wake cycle.
- The fluctuations depend upon changes in neural activity at both the systems and cellular levels.
At a systems level, there are neural substrates that control rhythmic changes in level of arousal.
At a cellular level, neurotransmitters and drugs affecting these neurotransmitters act to change levels of activity and arousal.
Details :Organisms display a wide spectrum of frequencies in their rhythmic processes. The left side shows the various frequencies, and the right side shows the periods of selected examples. (Note: period = 1/frequency.)
The sine wave or sinusoid wave is a mathematical curve that describes a smooth repetitive oscillation.
circadian
entrained = 24 hours; free running = 24 +/- 2 hours (ex: daily temperature cycle)
ultraradian
period of <24 hours (ex: human basic rest activity cycle)
circatidal
based on tides; entrained = 12.4 hours, free running = 11-14 hours
infradian
period is a multiple of the circadian period (ex: menstrual cycle)
circalunar
based on moon; entrained = 29.5 days; free running = 26-32 days
seasonal running
seasonally dependent (ex: breeding season)
types of biological rhythms
High-frequency events include the electrical activity of the brain (EEG: electroencephalogram), heart rate (cardiac), rate of breathing (respiratory), and sleep-stage (rate of progression through different levels of sleep). These cycles are often referred to as ultradian rhythms (processes having periods much less than 24 hrs). Circadian rhythms are often arbitrarily defined as having periodicities between 20 and 28 hrs. Two examples of low-frequency cycles are the menstrual cycle of women and the seasonal (circannual) cycle of hibernation. Such long-period rhythms are referred to as infradian rhyth
body temperature circadian rhythm
- Almost every physiological or behavior response you can measure will show a rhythmic pattern.
- Body temperature change is an excellent example of a circadian rhythm.
when cycles get out of phase,
adverse effects may ensue
- For example, when the sleep-wake cycle is out of phase with the rhythms that are controlled by the circadian clock (e.g., during shift work or rapid travel across time zones disturbances, e.g., jet lag, may result.
geophysical determinants of circadian, seasonal and circannual rhythms
The earth’s yearly revolution about the sun and its daily rotation on its axis determine the light-dark patterns to which we are exposed. Seasonal changes occur because the earth’s axis of rotation is tilted with respect to its plane of revolution. In the northern hemisphere, the north pole is tilted toward the sun from March to September. Therefore, the northern hemisphere receives more sunlight per day than the southern hemisphere. Then from September to March, the southern hemisphere is tilted toward the sun and determines the seasons of spring and summer for that hemisphere.
Main Points:
- Many biological rhythms are related to the earth’s rotation on its axis (circadian rhythms 24 hr) and the earth’s revolution around the sun.
- Some rhythms are related to multiples of circadian rhythms.
- Some rhythms are related to other environmental stimuli such as tides and the lunar cycle.
recording the wheel-running activity of a hamster
how is the circadian rhythm studied?
(left) Methods of recording the wheel-running activity of a hamster. In the traditional method, each wheel rotation activates a sideways movement of a pen on a moving sheet of paper. When the 24-hour strips are arranged one under the other, the human eye can easily pick out rhythmic behavior in the daily patterns of activity. The 24-hour strips are often plotted so that the continuity of the rhythmic pattern can be visualized (lower left); on the first line, day 1 is plotted, and on the next line day 2, and so on. For more objective analyses, a digital record can be made. The amount of activity can then be plotted against time and analyzed statistically. Rodents may run for miles during a night, and a digital record may be necessary to distinguish between different amounts of activity. (right) An actogram demonstrating a light-dark entrained circadian rhythm and demonstrating the effects of removal of the light-dark cycle (i.e., removal of the Zeitgebers) to produce a free running rhythm.
- Zeitgeber = time giver
Main Points:
- Rodents have been used extensively in circadian rhythm research.
- Behavioral patterns associated with locomotor activity, eating, drinking, etc. are frequently used as dependent variables.
- Data are collected on paper or by computer and are presented as actograms.
entrainment
helps animals maintain an adaptive phase relationship with the environment as well as prevent drifting of a free running rhythm
- means to match a body cycle with an environmental cycle
- e.g matching of sleep/wake cycle with light/dark cycle
free running cycles are not
adjusted to an environmental cycle
the circadian system model
assumes that there is a central pacemaker that generates the oscillation in biological and physiological rhythms. A stimulatory input, namely light activating an input pathway, is used by the central pacemaker to entrain the rhythms. Drugs that affect circadian rhythms may act on any, or each, part of this system.
suprachiasmatic nucleus ablation results in loss of circadian rhythms
Evidence suggests that the suprachiasmatic nucleus is part of the central pacemaker. The suprachiasmatic nucleus is located in the hypothalamus right at the base of the brain. It is located just above (“supra”) the fiber crossings of the visual system called the optic chiasm.
The lower left figure shows the locations of electrolytic lesions of the suprachiasmatic nucleus in a squirrel monkey. The lesions are just dorsal to the optic tracts.
Right: Double-plotted drinking record from a squirrel monkey before (A) and after (B, C) receiving a histologically verified total SCN lesion. The approximately 25-h drinking rhythm prelesion (A) persisted with a reduced amplitude for over 90 days postlesion (B) before finally decaying into arrhythmia (C).
projections of the SCN / subparaventricular zone complex and their likely functions
The SCN projects to many areas of the CNS including the sub paraventricular zone (SPVZ). Projections from the SCN and SPVZ influence many physiological and behavioral functions. For example, the projections from the SCN/SPVZ to the tuberal-posterior hypothalamic areas are implicated in controlling sleep-wake cycles. It isn’t necessary for you to know the specific projections and their associated functions but rather the principal that the SCN controls the rhythmicity of many functions via its influence on other brain structures.
circadian rhythms in mammalian cells are controlled by
a mechanism involving a molecular transcription-translation feedback loop
circadian rhythm in mammalian cells
The majority of the identified clock components are transcriptional activators or repressors that modulate Clock protein stability and nuclear translocation. A primary feedback loop, involves and BMAL1 whichheterodimerize in the cytoplasm to form a complex that translocate to the nucleus to initiate transcription of target genes such as PER and CRY. Negative feedback is achieved by PER:CRY heterodimers that inhibit the activity of the CLOCK:BMAL1 complex.
- The clock is located in each of the cells
continuum of states of behavioral arousal
- Over the course of time, physiological, behavioral and cognitive functions vary in level of arousal/intensity.
- The fluctuations depend upon changes in neural activity at both the systems and cellular levels.
- At a systems level, there are neural substrates that control rhythmic changes in level of arousal.
- At a cellular level, neurotransmitters and drugs affecting these neurotransmitters act to change levels of activity and arousal.
electroencephalographic recording and the psychological basis of the EEG
A) Cortical pyramidal cell showing an example of the momentary distribution of positive and negative charges at different points on the neuron. B) The arrangement of pyramidal cells across cortical sulci and gyri. C) The net result of the distribution of positive and negative charges across a region of cortex.
electroencephalographic recording and the physiological basis of the eeg
The brain wave patterns on the EEG are the net sum of the electrical activity from billions of cortical neurons.
Examples of human EEG records (3 upper traces) and a frequency analysis (lower trace) of the EEG records. The wave analysis, which has a separate peak for each frequency component, indicates that the frequencies most commonly present with eyes shut are 8-12/second (large peaks on the wave analysis).
arousal is associated with what wave forms?
low voltage high frequency
sleep is associated with what wave forms?
high voltage low frequency wave forms
electrophysiological correlates of waking and sleep stages
Characteristic EEG patterns seen during different stages of sleep in humans are shown here. The sharp wave called a vertex spike appears during stage 1 sleep. Brief periods of sleep spindles are characteristic of stage 2 sleep. Deeper stages of slow-wave sleep show progressively more large, slow delta waves. Note the similarity of activity during waking, stage 1 sleep, and rapid eye movement (REM) sleep.
properties of slow-wave and REM sleep
These are examples of different levels of activation of various physiological systems between slow-wave and REM sleep. These differences in physiological status are reflections of the differences in cortical arousal between the two states.
evidence for Bremer’s 1937 passive sensory theory of sleep
Sleep studies were important for helping determine how arousal works. Bremer proposed the first influential theory of the physiology of sleep. He hypothesized that sleep is caused by a reduction of sensory input to the forebrain. To test his hypothesis, he transected the neuraxis at the level between the superior and inferior colliculi to disconnect the forebrain from ascending sensory input. This produced a cat that appeared to be sleeping. The EEG produced almost continuous slow-wave sleep waveforms, hence, Bremer concluded that depriving the rostral brain produced sleep.
evidence for moruzzi and magoun’s active reticular-activating-system theory of sleep
Bremer’s “passive” theory of sleep was eventually replaced by the theory that sleep is actively regulated by an arousal mechanism in the reticular formation, i.e., by a reticular activating system.
In the late 1940’s Moruzzi and Magoun made small lesions in the core of the brain stem so that most of the classic ascending sensory pathways were left intact. Nevertheless, these animals displayed a sleep-like EEG pattern. Hence, they concluded that the reticular formation produced sleep through an active process.
