Hypothalamus Flashcards
What 3 functions does the hypothalamus regulate in concern to homestasis?
- Autonomic
- Endocrine
- Behavior
From what parts of the body does the hypothalamus receive sensory signals?
- All parts (vision, olifactory, somatosensory, etc….)
How does the hypothalamus use the sensory signals it receives to assess homeostasis?
Compares levels with set biological check points
How many hormones does the hypothalamus release?
8
How can the hypothalamus control blood pressure and electrolyte balance with behavior?
- Drinking water
- Intake of salt
How can the hypothalamus regulate body temperature through the ANS?
Shivering
How can the hypothalamus control energy metabolism?
- Feeding
- Digestion
- Metabolic rate
How can the hypothalamus control reproduction?
Behavior: Sexual drive
Hormones: Pregnanct, lactation, etc
If the hypothalamus receives information from the periphery about an imbalance that can be solved hormonally, how does it get that message to peripheral glands?
- Hypothalamus produce releasing or inhibiting factors
- These factors are secreted into a portal system into the pituitary gland
- Adenohypophysis produces and stores secondary releasing factors
- Secondary releasing factors reach the peripheral glands which promote their own hormones for systemic circulation
What are the only 2 hormones not produced via the adenohypophyseal system?
- Oxytocin
- Antidiruetic hormone
By what type of system are oxytocin and ADH released to systemic circulation?
Neurohypophyseal system
Describe the release of oxytocin and ADH by neurohypophyseal systems?
- Hypothalamus produces the hormones
- Hormones travel by axoplasmic flow via the hypohypophseal tract to the neurophypophysis in the posterior pituitary gland
- When needed, action potentials cause the release of the hormone into systemic circulation
Which portion of the ANS do posterior aspects of the hypothalamus correspond to?
Sympathetic nervous system
Which portion of the ANS do anterior aspects of the hypothalamus correspond to?
Parasympathetic nervous system
Which portion of the hypothalamus inhibits the other portion of the hypothalamus?
Anterior inhibits posterior
By what tract does the hypothalamus reach the frontal lobe and limbic system, affecting behavior?
Mammilothalamic tract
What structure separates the medial and lateral groups of the hypothalamus?
The columns of the fornix
How do the medial and lateral nuclei of the hypothalamus correspond to one another?
They serve the opposite functions.
For example)
Arousal vs Sleep
Rage vs Docility
etc..
What are the 3 portions of the medial nuclear group?
Anterior
Middle
Posterior
What is an important nucleus in the anterior medial group related to biological rhythms?
- Suprachiasmatic nucleus (drives circadian rhythms)
What is the hypothesis for hypothalamic regulation of body fat and food consumption called?
Lipostatic hypothesis
Describe the lipstatic hypothesis.
- Body weight has a stable baseline (if animal is starved, it gains back weight after it is fed, and vice versa)
- Leptin regulates body mass, decreases appetite, and increases energy expenditure
- When leptin is depleted, the adaptive responses to fight starvation are activated
Is the lateral hypothalamus or the ventromedial hypothalamus responsible for feeding drive? Which is responsible for inhibition?
Drive: Lateral hypothalamus
Inhibition: Ventromedial hypothalamus
What are 2 ways to stimulate eating?
- Excite feeding center
- Damage/ disinhibit inhibitory center
How does the arcuate nucleus respond to elevated leptin levels?
- Release alpha-MSH and CART peptides, which diminish appetite
Where is the arcuate nucleus located?
On the base of the 3rd ventricle
What 3 areas does the arcuate nucleus project to to inhibit appetite?
- Paraventricular nucleus
- Intermediolateral gray matter of spinal cord
- Lateral hypothalamus
What effect do decreased leptin levels have on the arcuate neurons?
Release NPY and AgRP, which increase appetite through the 3 methods
Which ANS is stimulated when leptin is low?
Parasympathetic to stimulate feeding
How do the orexigenic (feeding peptides) increase appetite?
Inhibit secretion of TSH and ACTH
How long do hormonal processes of the hypothalamus take to have effect?
Days/ weeks
What peptide neurotransmitter informs the cortex about leptin levels?
MCH
What behavior affects the motivation to eat?
- When you ate your last meal
- How big it was
Describe the interplay between the desire for food (orexigenic signals), food consumption, and hormonal/ chemical satiety signals.
- Food consumption begins when orexigenic signals are greatest,
- Food consumption continues slightly after satiety signals have begun to climb, and they climb even higher after food consumption has commenced
- Satiety signals then drop as orexigenic signals begin to climb again
(Dr. A says eat, and then WAIT before seconds to allow you satiety signals to catch up)
What are the 3 phases of appetite, eating, disgestion, and satiety?
- Cepahlic
- Gastric
- Substrate
What are 3 signals of satiety?
- Gastric distension
- Cholecystokinin
- Insulin
What is the “liking” conception of why we eat?
Hedonic
What is the “wanting” conception of why we eat?
Drive reduction
What is the “electrical stimulation” conception of why we eat?
Sites of electrical stimulation related to hunger drive
What neurotransmitter was found in the axons found to be related to hunger in the ventral tegmental area of the forebrain?
Dopamine!
In dopamine-depleted animals, what effect does it have on their hunger?
Animals enjoy food when they eat it, but do not have the motivation to seek it out
When do serotonin levels rise in relation to food?
When it is seen or smelled.
When do serotonin levels spike in relation to food?
During eating
When are serotonin levels low in relation to food?
After food has been absorbed
Why may antidepressant drugs be used to stimulate hunger?
SSRIs make more serotonin available
What 2 metabolic reasons may provide drinking motivation to the individual?
- Low blood volume
- Hypertonicity/ high concentration of substances in the blood
What hormone is released in response to a low blood volume?
ADH
What organ is responses to changes in blood volume? Why?
The Subfomical organ is responsive to changes in blood volume signal from the kidneys because it doesn’t have a blood brain barrier
Where are chemo/ mechanoreceptors that are sensitive to changes in blood volume/ pressure?
In the aortic arch
What is osmometric thirst?
Hypertonicity induced thirst
What organ is plays a role in osmometric thirst?
The OVLT
Where is the OVLT found?
- In the hypothalamus (lamina terminalis)
Does the OVLT have a blood brain barrier?
No
How does the OVLT stimulate thirst?
- Releases thirst stimulating hormones via magnocellular neurosecretory cells
What areas of the hypothalamus are related to thirst, and which inhibit thirst?
Lateral: Thirst
Medial: Inhibitory
What is diabetes insipidus?
- Not enough ADH is released in response to thirst
- Lateral areas are stimulate, but the fluid is secreted through urine
What temperature does the hypothalamus try to keep the body?
98.6 F, 37 C
Where are the neurons for temperature homeostasis located in the hypothalamus?
Clustered anteriorly
Where are the humoral and visceromotor responses to body temperature homeostasis located?
medial preoptic area
Where are the neurons for somatic motor (behavioral) responses located for temperature homeostasis?
Lateral hypothalamus
What is the visceromotor response to a fall in temperature?
Goosebumps
What is the involuntary somatic motor response to a fall in temperature?
- Shivering
- Seeking warmth
What is the humoral response to rises in temperature?
- TSH release slowed
What is the ANS response to thirst?
Sympathetic activity
What is the ANS response to decreasing body temperature? Increase?
Decrease: Parasympathetic activity
Increase: Sympathetic activity
What is sleep?
- Easily reversible state of reduced responsiveness to, and reaction with environment
What area in the thalamus can “switch” an individual from wakefulness to sleep? How is this accomplished?
- Pre-optic area
- Inhibits brain stem and other area neurons that maintain arousal
What area controls is influenced by light-dark cycles in relation to sleep?
- Suprachiasmatic nucleus
What types of brain waves are exhibited by a wakeful individual? What is the frequency?
Alpha waves
- 8 - 12 Hz
Beta waves
- 12 - 30 Hz
How long is one sleep cycle?
90 minutes
What percent of sleep in spent in: Stage 1: Stage 2: Stage 3: Stage 4: Stage 5:
Stage 1: 4 - 5 % Stage 2: 45 - 55 % Stage 3: 4 - 6 % Stage 4: 12 - 15 % Stage 5: 20 - 25 %
Which stage of sleep contains REM?
Stage 5
What is the lightest stage of sleep?
Stage 1
At what stage does deep sleep begin?
Stage 3
What stage contains theta waves with sleep spindles (rapid frequency waves) and K complexes (high amplitude spikes)?
Stage 2
What stage contains high amplitude, synchronus delta waves?
Stage 4
What stage contains synchronus theta waves?
Stage 1
What stage displays similar brain activity to an awake individual?
Stage 5
Why is REM termed paradoxal sleep?
Deepest sleep, but brain looks like it is awake
What chemicals inhibit REM sleep?
NE and serotonin in brain stem
What chemical promotes REM sleep?
ACh in brain stem
What area of the hypothalamus “turns on” REM sleep?
Pre-optic
What portion of the hypothalamus inhibits REM sleep? (what chemical also)
Lateral hypothalamus (orexin)
What condition is precipitated by an inability to control orexin?
Narcolepsy
What related condition affects 70 % of people with narcolepsy?
Cataplexy:
- Transient episode of loss of muscle tone with full concious awareness
What stages of sleep become shorter as you progress through each 90 minute progression?
Stages 2 - 4
What is meant by synchronous?
- High amplitude, but low frequency
How are sleep stages progressed in terms of synchrocy?
Each stages becomes more synchronus
What is meant by desynchronous?
Low amplitude, but high frequency
What are 4 indications that the body is in a very deep sleep during REM sleep?
- Profound muscle relaxation
- Alterations in BP
- Altered pulse rate
- Altered respiration
How is the sensory thalamus altered in an awake vs asleep state?
Awake: Facilitated
Asleep: Inhibited
How is the reticular nucleus altered in an awake vs asleep state?
Awake: Inhibited
Asleep: Facilitated
How are thalamocortical neurons altered in an awake vs asleep state?
Awake: Active
Asleep: Slow rhythm
How is EEG altered in an awake vs asleep state?
Awake: Desynchronous
Asleep: Synchronus
How is the ACh system altered in awake vs asleep state?
Awake: Active
Asleep: Inactive, except for tegmental area in BS
