Homeostatis and Hypothalamus 3 Flashcards
What was the research that Cannon and Bard were doing?
They researched with “decerebrated” ( to surgically disconnect the cerebrum from lower brain area) cats.
What happened when the cortex was disconnected but the hypothalamus was intact?
able to sustain homeostais
able to land on feet
displayed “sham rage” (threat posture, hissing,)
Reactions were stereotyped and not at specific targets.
What happened when the hypothalamus was partially severed?
Sham rage partially displayed
Usually able to sustain homeostasis
What happened when hypothalamus was disconnected from brain stem?
No longer showed sham rage
difficult to keep the animal alive
What did this research experiment conclude on?
demonstrated that many complex functions are regulated automatically without input from higher brain areas.
What regulates stress hormone in the hypothalamus?
The paraventricular nucleus (PVN)
controls both sympathetic activation and HPA axis.
autonomic functions of the paraventricular nucleus (PVN)
dorsal and ventral projections from PVN.
projects to brain stem and spinal cord
regulates sympathetic and
endocrine functions of the paraventricular nucleus (PVN)
medial and lateral projections from PVN.
connects to pituitary
regulates the HPA axis.
What is cortisol used to maintain?
energy use
energy stores
cardiovascular functioning
Cortisol isn’t only for stress but increases to maintain stress responses.
How is cortisol regulated?
Regulated by multiple feedback systems
when cortisol levels get high, less cortisol is produced
Important regulate because too much cortisol can have negative effects.
How does cortisol travel in negative feedback loops?
Cortisol can pass through blood brain barrier
PVN detects cortisol with decreases CRF–> pituitary gland detects cortisol which decreases ACTH release.
What does the amygdala do for HPA activity?
Increases it.
What does the hippocampus do for HPA activity?
It can both decrease and increase HPA activity. BUT plays a major in role DECREASING HPA activity.
What happens when people have smaller hippocamupses?
less ability to inhibit HPA activation. They are more vulerable to developing PTSD after trauma.
Beta-endorphins.
An endogenous opioid
When the HPA axis is active, CRH from hypothalamus stimulates release of ACTH from pituitary. CRH also stimulates release of beta-endorphins.
Normal cortisol regulation
Cortisol is part of regular metabolism.
Circadian rhythm for cortisol productin
regulated by the sleep-wake cycle, influenced by hours of “daylight”
How does cortisol play a permissive and productive role
“Permissive”- normal levels of cortisol lets things happen.
Maintain regularly scheduled progress
“Productive”- high levels of cortisol makes things happen
“shift focuses to emergency tasks”
Certain metabolic functions get prioritized over others.
Circadian Rhythm of cortisol regulation?
Superchiasmatic nucleus (SCN) of hypothalamus. Receives visual info from thalamus. Day-night cycles detected form light exposure. SCN regulates daily activity of PVN. Relays info to PVN (feed- forward)
When does cortisol peak?
It peaks in the morning right as when you wake up.
When does it start decreasing?
Throughout the day and drops lowest when we sleep. drops cortisol helps you fall asleep.
Negative feedback loops with cortisol at the pituitary.
At the pituitary the detection of cortisol reduces ACTH
Negative feedback loops with cortisol at the hypothalamus.
Detection of cortisol in cerebrospinal fluid (third ventricle)
reduces activity of the medial PVN
What does the paraventricular nucleus of hypothalamus do?
Gets input form SCN.
Adjusts set point for cortisol throughout the day
uses negative feedback to maintain cortisol levels
Cortisol during stress?
stress decreases negative feedback loop. Increased cortisol should decrease production of CRF in the hypothalamus.
What are the two pathways of CRF neurons in PVN of hypothalamus.
Parvocelluar neurons of the PVN (CRF neurons) and Magnocellular neurons on the PVN (CRF-AVP neurons)
Parovoceullar neurons
smaller neurons in the paraventricular nucleus control normal levels of cortisol secretion
release CRF into pituitary –> pituitary releases ACTH
easily regulated by negative feedback loops
Magnocellular Neurons
Bigger neurons in the paraventricular nucleus
release CRF and Vassopression (AVP)
connections to pituitary to release ACTH
connections to brainstem (aminergic nuclei)
triggered by sympathetic activation
not easily regulated by negative feed back loops
What is a minor stressor?
A typical, short term stressor
Sympathetic activation of the HPA
SAM signals HPA
if stress is short-term, sympathetic turns off quickly
HPA regulation returns to “normal” circadian cycle
HPA return takes longer than SAM return to baseline
What is a major stressor?
Extreme or extended stressor
SAM and HPA may remain simultaneously active for extended time
effects of both are intensified
increase activation of CRF feedback system throughout brain
increased activation of Magnoceulllar (CRF-AVP) neurons of the PVN
PVN less responsive to negative feedback
more ACTH is released
HPA activity becomes less responsive to negative feedback
