Hypothalamus and Temp Regulation Flashcards
Describe the location of the hypothalamus and of its key nuclei (those with functions discussed in detail).
The hypothalamus is a small, wedge-shaped region that forms the ventral-most part of the the diencephalon, specifically the floor of the third ventricle and much of the walls.
Describe the role of the autonomic nervous system in homeostasis and emotional responses
Homeostasis: the ANS provides crucial input to the integrated responses capable of maintaining body temperature, body weight, and water balance.
Emotional responses: the ANS is responsible for control on unconscious physical responses to stress/emotion such as blushing, dry mouth, sweating, GI reactions and fainting.
Describe the neuroendocrine function of the hypothalamus:How does it control the anterior pituitary? Specify its role in posterior pituitary hormone secretion.
Posterior pituitary: HT regulates production of vasopressin and oxytocin by the hypothalamic supraoptic nuclei (SON) and paraventricular nuclei (PVN). These hormones are then transported down axons to the posterior pituitary and released into general circulation
Anterior pituitary: HT synthesizes and releases hormones into hypothalamo-pituitary portal circulation that regulate release of hormones from the anterior pituitary. This portal system carries these hormones directly to the endocrine cells of the anterior pituitary w/o being diluted by general circulation. HT hormones then regulate the release of anterior pituitary hormones. Anterior pituitary hormones then regulate the release of hormones from most peripheral endocrine organs
List the endocrine responses initiated by the hypothalamus
for maintenance of water balance
Somatic: Thirst (motivated behavior) = Increased drinking or Decreased drinking
Achieved by swallowing fluids
Endocrine: Increase or decrease of vasopressin from posterior pituitary
List the autonomic responses initiated by the hypothalamus
for maintenance of body temperature
Heat PRODUCTION
Autonomic: Non-shivering Thermogenesis
Somatic: Increase exercise or increase shivering
Endocrine: Thyroxin
Heat LOSS
Autonomic: heat flow to skin, sweating
Endocrine: Aldosterone (promotes Na+ reabsorption, more dilute sweat and decreased tonicity of sweat, making you more thirsty faster and preventing dehydration)
List the somatic motor responses initiated by the hypothalamus for maintenance of body weight
Automonic: Hunger reflects changes in GI motility (increase or decrease in digestion processes)
Somatic: Increase or decrease food acquisition (motivated behavior) by chewing and swallowing
Endocrine: Insulin/glucagon, Epinephrine
Define fever and pyrogens.
Fever: a regulated increase in body temperature
Pyrogen: fever producing agents which increase the “set-point” of the thermoregulatory system
Describe the changes in the hypothalamic mechanisms
regulating body temperature that result in fever and its associated symptoms.
Cytokines (IL-1, IL-6, TNF, interferon) released by immune cells act at a region of the hypothalamus called the OVLT (organumvasulosum of the lamina terminalis) that lacks a blood brain barrier. The OVLT then produces PGE2, which diffuses to the adjacent POAH (preoptic anterior hypothalamus) and decreases the activity of the thermoreceptors. This resets the hypothalamic temperature “set-point” to a higher level.
Thermoreceptors in the POAH generate action potentials at a frequency proportional to the local temperature. An increase in local temperature increases the firing rate and induces heat loss mechanisms. (A decrease in local temperature slows the firing rate of these cells.)
Fever-producing agents (via ↑ PGE2 production in the OVLT) increase the “set point” → creates a relative decrease in local brain temperature → leads to a decrease in firing rate of the thermoreceptors in the POAH.
This decrease in POAH neuron activity leads to activation of thermogenic responses (vasoconstriction, shivering etc.) identical to an actual fall in body temperature.
Describe the role of the hypothalamus in circadian rhythms.
Circadian rhythms are endogenous rhythms in biological parameters that are approximately 24 hours long. The primary circadian clock is located in the suprachiasmatic nucleus of the anterior hypothalamus. The SCN gets direct innervation from the retina: this provides information about the light/dark cycle and allows the endogenous rhythms to become trained to the light/dark cycle.
However, the SCN can generate these rhythms in the absence of a 24 hour light/dark cycle! However, the endogenous cycle runs slightly shorter than 24 hours. If you lesion the SCN, you obliterate the endogenous rhythm.
btw, circadian rhythms are not just important for sleeping- they are also related to body temp, water and food intake and activity
Describe the role of the hypothalamus in emotional and motivated responses
The hypothalamus is responsible for initiating the coordinated autonomic and behavioral responses that constitute emotional expression, but higher CNS areas are responsible for modulating emotional expression such that it is appropriate for the situation.
Hypothalamic control of emotional expression involves integration of somatic, autonomic, and endocrine responses
Projections too the limbic system, amygdala, hippocampus, etc
What is ‘sham rage’?
Its what happens when you overuse your shamwow.
Actually its a phenomenon observed when the hypothalamus is disconnected from higher brain areas, but the hypothalamic connections to the brainstem and spinal cord remain in tact.
This produces animals that are extremely aggressive and irritable.
Describe the location of the key nuclei (those with functions discussed in detail).
First of all, Location of the nuclei can best be appreciated by dividing the hypothalamus into 3 Anterior → Posterior regions using landmarks on the ventral surface of the brain:
* Anterior → above the optic chiasm (supraoptic) * Medial → above the pituitary (tuberal) * Posterior → above and including the mammillary bodies (mammillary)
Anterior region: Lateral preoptic nucleus, Medial preoptic nucleus, Suprachiasmatic nucelus
Medial: Dorsal, Dorsomedial, Lateral, Supraoptic, Ventromedial, Periventricular and Anterior nucleus
Posterior region: Posterior nucleus, Subthalamic nucleus, Lateral nucleus, Mammillary body
Describe the pathways connecting the hypothalamus with the autonomic motor systems
The ability of HT to regulate ANS is critical for its role in maintaining homeostasis and inducing emotional expression.
Efferent/afferent pathways from the hypothalamus to the ANS travel in the following tracts:
- Dorsal longitudinal fasiculus: to ANS nuclei in the brainstem reticular system
- Medial forebrain bundle: to brainstem reticular formation
- Mammillotegmental tract: from mammillary bodies to midbrain reticular formation (tegmentum)
In general, stimulation of the anterior hypothalamus increases PNS activity (or ↓ SNS actions) and stimulation of the posterior hypothalamus increases SNS activity.
Describe the pathways connecting the hypothalamus with the somatic motor system
The ability of HT to coordinate somatic motor activity leads to the organization of complex activities requiring both somatic and autonomic responses (vomiting, laughing, crying, facial expression). Also organizes motor activities required for homeostasis (chewing and swallowing).
HT neurons innervate neurons in the reticular formation of the brainstem near the motor nuclei of the cranial nerves. These somatic neurons in turn innervate skeletal muscle. Use same pathways as those used for the ANS
Describe the pathways connecting the hypothalamus with the endocrine system
*Posterior pituitary: HT regulates production of vasopressin and oxytocin by the hypothalamic supraoptic nuclei (SON) and paraventricular nuclei (PVN)
These hormones are then transported down axons to the posterior pituitary and released into general circulation
*Anterior pituitary: HT synthesizes and releases hormones into hypothalamo-pituitary portal circulation that regulate release of hormones from the anterior pituitary. This portal system carries these hormones directly to the endocrine cells of the anterior pituitary w/o being diluted by general circulation. HT hormones then regulate the release of anterior pituitary hormones. Anterior pituitary hormones then regulate the release of hormones from most peripheral endocrine organs
*****HT thus indirectly regulates most of the endocrine system.
