Hypothalamic Circuit: Feedback and Regulation
By: Dr. Simon Spanswick, University of Calgary
In this activity you will examine the process of feedback loops and explore the role of the hypothalamus in hormone release and the generation of behavior.
After completing this activity, you should be able to:
This activity relates to the following principles of nervous system function:
A feedback loop allows for systematic control over the amount of hormone that is released into the body. The release of hormones can be modulated to meet changing environmental demands placed on the organism. This is an important homeostatic mechanism to ensure that the appropriate hormone level is maintained.
Let's look at how a feedback loop works, using the hypothalamus, which works to regulate hormone levels, as an example. Pay attention to the positive and negative symbols in the diagram, which indicate the direction of the feedback. (Positive feedback stimulates release, and negative feedback inhibits this process.)
Now let's consider a few case studies that show the feedback loop in action. Read the description beneath the figure and answer the questions about each case study.
Let's review the feedback loop process. Place the components of the hypothalamic feedback loop in the correct order, based on what you have just learned.
Stimulation studies reveal a role for the hypothalamus in many complicated goal-directed behaviors, including eating, drinking, digging, and fear, to give a just few examples.
Select each of the four nuclei — the ventromedial hypothalamus, the lateral hypothalamus, the periventricular region, and the medial hypothalamic region — to see what role it plays in the generation of these regulatory behaviors.
The ventromedial hypothalamus (VMH) contains cells that, when activated, signal the organism to stop eating. Early experiments determined that damage of the VMH interferes with this signal and results in a significant increase in body weight. In combination with cells in the arcuate nucleus (not shown), the VMH forms part of a system designed to inhibit the consumption of food.
When activated, the lateral hypothalamus elicits eating. Control of this phenomenon is also mediated by neuropeptide Y containing neurons in the arcuate nucleus (not shown). Fluctuating hormone levels (such as insulin) stimulate these neurons, ultimately resulting in eating behavior. Damage to this system results in aphagia, a failure or an unwillingness to eat.
An important requirement for normal bodily function is the maintenance of the appropriate level of solute concentration. Increases in solute concentration (salts, for example) result in osmotic thirst. The hypothalamus has receptors bordering the third ventricle that detect and relay information about solute concentration in order to maintain homeostasis.
Hypovolemic thirst is induced when there is a drop in the fluid volume in the body. This is mediated by midline hypothalamic neurons and stimulates drinking. In this case, the organism prefers salty fluids, as drinking water would decrease the solute concentration in the body.
The activity of the hypothalamus is controlled in a top-down manner via neural connections with a number of other brain structures. Cerebral inputs funnel through the hypothalamus, which sends axons to other brainstem structures, ultimately resulting in motivated behavior.
The organization of this system demonstrates several key principles of nervous system function, illustrated here by the process of milk production.
Which of the principles listed below do you think most apply to the body's feedback system?
Congratulations! You successfully completed the Hypothalamic Circuit: Feedback and Regulation activity! In this activity, you explored the function of the hypothalamus, its role in a feedback loop, its connection to other brain structures, and ultimately its importance in the generation of behavior.
Your instructor may now have you take a short quiz about this activity. Good luck!