NB12-1 - Biological Rhythms and DLA Flashcards
Describe the single and double neuron oscillator arrangements and how they work.
Single Neuron Oscillator - a neuron that, once stimulated, will fire APs in a particular rhythm for a period of time.
Two-Neuron Oscillator - the first cell, called the E cell, is an excitatory cell that receives constant excitatory input from another neuron. The E cell synapses on an inhibitory I Cell, stimulating it. The I cell will then inhibit the E cell. This leads to an “on and off” AP rhythm in the E cell. Refer to image
List the ways we need to know that neuronal assemblies can end up firing together in rhythm.
- Collective entrainment - after a bit of random firing, eventually a group of neurons will fire in rhythm
- Pacemaker - a single or group of pacemaker neurons will set the rhythm that other neurons will follow
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List the three major types of biological rhythms and provide examples for each.
Ultradian Rhythms - < 1 day to complete; respiration, HR
Circadian Rhythms - ~1 day to complete; sleep-wake cycle
Infradian Rhythm - >1 day to complete; menstrual cycle
Describe the basic set-up of a pacemaker system.
There is rythmic regulatory input (ie - sunlight) to a primary pacemaker (ie - suprachiasmatic nucleus), which then stimulates several secondary oscillators resulting in synchronized rythmic output from those tissues.
As it applies to respiratory rhythm pacemaker system, what structures provide the regulatory input? Where are these structures found? How are these structures regulated and what do they send this information to?
The structure responsible for providing the regulatory input to the primary respiratory rhythm pacemaker (pre-botzinger complex) is the apneustic center in the pontine respiratory group. It provides tonic excitatory input which is selectively inhibited by the pneumotaxic center, also in the PRG, which processes information relevant to breathing requirements from
What are the primary respiratory rhythm generators? Where are they found? What do they receive input from and what structures do they send their output do? What is the final result of their output?
- Pre-Botzinger Complex - found in the medulla. Receives inhibitory input from the Botzinger complex (during exhalation) and tonic stimulatory input from the apneustic center. It simultaneously stimulates the rostral VRG and inhibits the Botzinger complex to cause inhalation.
- Dorsal Respiratory Group (DRG) - found in the medulla. Receives stimulatory input form pulmonary stretch receptors and peripheral chemoreceptors. Stimulates the rostral ventral respiratory group (VRG) to cause inhalation
- Botzinger Complex - found in the medulla. Receives inhibitory input from the pre-botzinger (during inhalation) and stimulates the caudal VRG to cause expiration
Describe how stimulation of the rostral VRG causes inspiration?
Neurons from the rostral VRG stimulate the phrenic motor nucleus in the ventral horn at C3-C5.
Where are the chemoreceptors located that are principally responsible for sensing the O2 and CO2 levels?
Chemoreceptors in the carotid bodies primarily sense O2 while the chemoreceptors of the ventral medulla primarily sense CSF pH which is usually a direct indicator of plasma CO2 levels.
List and describe the abnormal respiratory rhythms we need to know and their causes.
- Cheyne-Stokes Respiration - periods of apnea followed by a perior of waxing and waning of respiratory depth. Caused by lesions in the forebrain, most notably the corticospinal and corticobulbar fibers.
- Hyperventilation - caused by midbrain lesions
- Apneusis (inspiratory cramps) - prolonged inspiratory plateaus of high lung volume followed by prolonged expiratory pauses with low long volume. Caused by pontine lesions
- Ataxic Breathing - randomly occurring large and small breaths alternating with prolonged periods of apnea. Caused by lower pontine and upper medullary lesions. Refer to image
Describe how body temp, melatonin, and cortisol levels change throughout a 24hr period.
Body temp and cortisol both reach their peak in the middle of a wake cycle and their trough in the middle of a sleep cycle.
Melatonin reaches its peak in the middle of a sleep cycle and its trough in the middle of a wake cycle
What is the technical term for sunlight when discussing circadian rhythms? What happens to the circadian rhythm in the absence of sunlight and why?
Sunlight is known as the zeitgeber in this context
Without the zeitgeber, the body still has its own free running rhythm. The problem is that it is about 24.5hrs in duration. This means that in the absence of sunlight a person would steadily go to bed about 30minutes later each night.
Describe the pathway that allows sunlight to control melatonin release.
- Light stimulates photosensitive ganglion cells in the retina (not rods or cones)
- Light signal is carried in the retino-hypothalamic tract fibers which synpase in and stimulate the suprachiasmatic nucleus (SCN) of the hypothalamus.
- Suprachiasmatic nuclei axons then synapse on and inhibit the paraventricular nucleus in the hypothalamus
- Paraventricular nuclei axons synapse in the intermediolateral cell column of the cervical spine
- Neurons from the intermediolateral cell column synapse in the superior cervical ganglion
- Neurons from the superior cervical ganglion synapse on and stimulate the pineal gland to release melatonin
- Therefore, when the SCN is stimulated, the pineal gland is not stimulated and melatonin secretion is inhibited.
What clock tissues besides the pineal gland will SCN fibers synapse on? What is the effect?
Cardiovascular clocks - control BP and thrombogenesis
Stomach/GI clocks - control glucose tolerance and lipid metabolism
Adrenal clocks - control glucocorticoid release
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