Neuroscience Exam 3

Homeostasis

Process by which the body achieves a stable, balanced internal environment. Occurs through the maintenance of optimal set points at which a given physiological system functions best.

Set Zone

The range within which a physiological system can function. Within this set zone, homeostasis will always try to return the system to the set point.

Negative Feedback

Homeostasis counteracts whatever is causing physiological system to deviate from the set point by doing the opposite to return to the set point again.

Thermoregulation

Process by which the body maintains an ideal temperature. For mammals, body temperature is maintained through metabolism. Partly behavioral, when the temperature outside the body is too cold, you can take action to prevent heat loss.

Preoptic Area (POA)

Part of the hypothalamus that takes care of the physiological responses that raise body temperature in response to cold. Also causes hypovolemic thirst and osmotic thirst.

Shivering

Heat generated through metabolic burn required for motion.

Constriction of Blood Vessels

Reduced blood flow makes sin and fat more effective as insulation.

Lateral Hypothalamus

Crucial for behavioral regulation of temperature, such as seeking out sources of heat, increasing surface area of the body that gets heat exposure.

Osmotic Thirst

When fluid levels drop, salt concentrations in the fluid between your cells increase. This thirst is triggered by an upswing in salt levels via urination or salt consumption.

Hypovolemic Thirst

Decrease in the volume of bodily fluids, such as blood (which is mostly water). This kind of thirst is triggered even if salt concentrations do not change (caused by sweating).

Osmosensory Neurons

Located in circumventricular organs, detect changes in concentration of salt in CSF of ventricular system. Too much salt, shrink. Too little salt, swell.

Osmosis

-Diffusion of solvent molecules across a permeable membrane. Changes in salt will cause cells to shrink or expand via osmosis as water passes through membranes.
-Shrinking opens mechanically-gated ion channels in membranes of osmosensory neurons. Causes a generator potential that makes the osmosensory neuron more likely to fire an action potential.
-Swelling closes mechanically gated ion channels.

Baroreceptors

Located in blood vessels of kidney and the heart, monitor changes in blood volume. Causes hypovolemic thirst. POA triggers physiological response by causing the release of the hormone vasopressin from the pituitary gland. Among other things, tells the kidney to retain water.

Essential Nutrients

Chemicals required for the normal maintenance and function of the body, and those that the body cannot manufacture and must be obtained from diet. Includes glucose, omega-3, and certain vitamins and minerals.

Glucose

Primary sugar that the body uses for energy. When glucose levels in the blood rise, the hormone insulin allows glucose to enter muscles.

Glycogen

Short-term storage of glucose.

Glucagon

Hormone that converts glycogen back into glucose.

Adipose Tissue (Fat)

Long term storage of glucose if the body has more glucose than is needed in the short-term. Decreases in glycogen cause the body to convert fats back into glucose.

Insulin

Released into the blood by the pancreas when you eat. Binds to a receptor on the surface of muscle and liver cells and allows glucose to enter cells in the body. Brain is the exception, brain does not require insulin to allow glucose to enter neurons.

Diabetes

A disease that results from a failure of insulin to allow glucose to be taken into cells. Type-I occurs when pancreas stops making insulin. Type-II occurs when cells no longer respond to insulin.

Basal Metabolism

The majority of energy consumption, your level of energy use when you are at rest. Energy goes to heat production, maintenance of ion gradients (especially in the brain), and life-sustaining cellular processes.

Metabolic Adaptation

Basal metabolism will decrease when energy intake decreases. Increases in basal metabolism in response to increases in energy intake do not tend to occur as rapidly, or to the same degree.

Hunger and Satiety

Hormones interact with hypothalamus to produce hunger (the motivational drive to eat) and satiety (the feeling of being full/absence of hunger).

Arcuate Nucleus

Part of the hypothalamus that monitors the level of various hunger and satiety-relevant hormones, which can activate either POMC or NPY neurons.

POMC Neurons

Signal satiety when activated, inhibiting hunger.

NPY Neurons

Signal hunger when activated, promoting feeding.

Ghrelin

Released from digestive organs in the absence of food in the gut. Levels drop off after eating. High levels activate NPY neurons and thus stimulate hunger. Primary hunger hormone.

Insulin (Hunger & Satiety)

Released from pancreas in response to food. High levels inhibit NPY neurons, reducing hunger. POMC neurons become disinhibited when NPY neurons turn off, increasing satiety.

Leptin

Released from fat cells. The amount circulating is proportional to body fat levels, thus providing info about long-term energy reserves. High levels both inhibits NPY neurons and activates POMC neurons, reducing hunger and promoting satiety. Primary satiety hormone.

Hedonic Feeding

Eating for pleasure rather than energy purposes. Controlled by the nucleus accumbens (NAcc), part of the basal ganglia involved in motivation. Expresses the mu-opioid receptor, which is activated by endogenous opioid NTs.

Circadian Rhythm

Fluctuations that occur over a roughly 24-hour period. Controls sleep and wakefulness, hormonal concentrations in the blood, and feeding.

Zeitgebers

External environmental cues that signal something about the time of day to the internal clock. For human beings, an important zeitgeber is a phase shift in light, such as the rapid increase in light levels that occurs when the sun comes up.

Free-Running Circadian Clock

Without zeitgebers, the clock will cycle once every 25 hours. Causes periods of sleep to drift in time.

Suprachiasmatic Nucleus (SCN)

Part of the hypothalamus that contains the circadian clock. Gets direct input from a population of light detecting retinal ganglion cells that carry info about phase shifts in light levels. SCN sends info to many places, such as to the pineal gland that regulates melatonin.

Clock, Cycle, Period, and Cryptochrome

SCN neurons make two proteins, clock and cycle. They form a dimer, which activates two genes: period and cryptochrome. Two proteins result (also called period and cryptochrome). These also form a dimer, which inhibits the clock/cycle dimer, thus preventing it from activating period and cryptochrome genes. Period/cryptochrome dimer slowly breaks down, releasing the clock/cycle dimer from inhibition. Process takes ~24 hours and is the molecular basis of the circadian rhythm. Glutamate released from specialized retinal ganglion cells onto SCN neurons mimics the effects of clock/cycle, thus syncing the molecular clock with daylight.

Waking Brain Waves

Being awake is characterized by EEG activity that is desynchronized across the cortex (synchronized waking activity usually only occurs during seizures). Waking brain waves tend to be high frequency and low-amplitude.

Non-REM Sleep

Divided into three phases with distinct brain-wave patterns. First phase is similar to being awake with slightly lower frequency. Second phase is imbetween first and third phase, lower frequency and slightly higher amplitude. Third phase is slow-wave sleep, involves high amplitude low frequency brain waves and (non-seizure) synchronization of activity across the cortex.

REM Sleep

Brain wave activity similar to awake, due to dreaming. Involves rapid, darting movement of the eyes. Complete loss of muscle tension.

Typical Sleep Stages

80% non-REM, 20% REM. Sleeper moves in and out of REM in a repeating cycle. REM takes up a greater portion of sleep as night progresses. Deepest phase of non-REM sleep, slow-wave sleep, tends to occur earlier in the night. Thought to be the most restful and restorative.

Functions of Sleep

You sleep more and have higher proportion of REM sleep when you’re younger. Growth hormones tend to be released during slow-wave sleep. Memory processes recalling the day before occur during slow-wave sleep, promoting memory storage. CSF washes brain during sleep, clearing metabolites.

Mechanism of Sleep