Chapter 1. Hypothalamic Circuit: Feedback and Regulation

1.0.1 Hypothalamic Circuit: Feedback and Regulation

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Hypothalamic Circuit: Feedback and Regulation
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Neuroscience in Action
hormones
regulatory substances, secreted by the brain and glands in the body, that influence development and body and brain function
homeostatic mechanism
Process that maintains critical body functions within a narrow, fixed range.
osmotic thirst
Thirst that results from a high concentration of dissolved chemicals, or solutes, in body fluids.
hypovolemic thirst
Thirst produced by a loss of overall fluid volume from the body.
Hypothalamus
Diencephalon structure that contains many nuclei associated with temperature regulation, eating, drinking, and sexual behavior.

Hypothalamic Circuit: Feedback and Regulation

By: Dr. Simon Spanswick, University of Calgary

1.1 Introduction

Introduction
Hypothalamic Circuit: Feedback and Regulation

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:

  • Describe a feedback loop
  • Describe the neural regulation of hormone release
  • Explain the role of the hypothalamus in the generation of behavior

This activity relates to the following principles of nervous system function:

  • Principle 4: The CNS Functions on Multiple Levels
  • Principle 6: Brain Systems Are Organized Hierarchically and in Parallel
  • Principle 10: The Nervous System Works by Juxtaposing Excitation and Inhibition

1.2 The Function of a Feedback Loop

The Function of a Feedback Loop
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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.)

1.3 Case Studies

Case Studies

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.

Question 1.1

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You would expect to observe a decrease in the level of hormones produced by her target organ. This could be resolved via hormone replacement therapy. Image
Your answer has been provisionally accepted. You'll get full credit for now, but your instructor may update your grade later after evaluating it.

Question 1.2

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You would expect to observe an increase in the level of pituitary hormones. This is because the target organs (in this case, the adrenal glands) are no longer providing inhibitory feedback to the hypothalamus. Image
Your answer has been provisionally accepted. You'll get full credit for now, but your instructor may update your grade later after evaluating it.

Question 1.3

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You would predict that the level of releasing hormones would be low, as the increased activity in the rest of the feedback loop serves to inhibit the hypothalamus. Image
Your answer has been provisionally accepted. You'll get full credit for now, but your instructor may update your grade later after evaluating it.

1.4 Reviewing the Feedback Loop

Reviewing the Feedback Loop

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.

Image

Question

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Correct.
Some of your answers are incorrect. Try again by changing your incorrect answers and resubmitting.
Incorrect.

1.5 How Does the Hypothalamus Produce Behavior?

How Does the Hypothalamus Produce Behavior?

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.

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1.6 Neural Regulation of the Hypothalamus

Neural Regulation of the Hypothalamus
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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.

Image

Which of the principles listed below do you think most apply to the body's feedback system?

  1. The nervous system produces movement in a perceptual world the brain constructs
  2. Neuroplasticity is the hallmark of nervous system functioning
  3. Many brain circuits are crossed
  4. The CNS functions on multiple levels
  5. The brain is symmetrical and asymmetrical
  6. Brain systems are organized hierarchically and in parallel
  7. Sensory and motor divisions permeate the nervous system
  8. The brain divides sensory input for object recognition and motor control
  9. Brain functions are localized and distributed
  10. The nervous system works by juxtaposing excitation and inhibition
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1.7 Summary

Summary

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!

Question

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Viewed final slide of activity