Role of the lateral hypothalamus (hunger center)
The lateral hypothalamus is responsible for perceiving the need for food and triggering appropriate behavior. Its neurons receive signals from an empty stomach, as well as humoral factors circulating in the "hungry blood".
Experiments by B.K. Anand and J. Brobeck clearly demonstrated the function of this area:
- Stimulation: irritation of the lateral regions in satiated animals causes them to start eating again, leading to hyperphagia (overeating).
- Destruction: bilateral damage to these areas in hungry animals causes aphagia — a complete refusal to eat, resulting in the animals dying of exhaustion even when food is available.
Excitation of the lateral hypothalamus also triggers ascending activating influences on the limbic-reticular complex and the cerebral cortex, forming the feeling of hunger and food motivation.
Ventromedial hypothalamus (satiety center)
The ventromedial nuclei of the hypothalamus are located close to the lateral nuclei and act as their functional antagonists.
Studies have revealed the following effects:
- Stimulation: electrical irritation leads to an immediate cessation of eating, even if the animal is very hungry.
- Destruction: bilateral destruction of this area deprives the animal of the feeling of satiety. As a result, bulimia ("wolfish hunger") and hyperphagia develop, logically leading to obesity.
Reciprocity of feeding centers
The functioning of the feeding center is based on the principle of reciprocity (mutual inhibition):
- Excitation of the "hunger center" causes inhibition of the "satiety center".
- Excitation of the "satiety center" suppresses the activity of the "hunger center".
However, this reciprocity is not absolute. During excitation of the lateral hypothalamus, a certain fraction of neurons in the ventromedial hypothalamus are activated in an anticipatory manner. This is a peculiar state of "anticipation" that prepares the system to receive signals from ingested food.
Briefly: answers to topical questions
Which specific CNS structures make up the feeding center at various levels?
The feeding center comprises neural elements located at various levels of the CNS, from the spinal cord to the cerebral cortex. Key divisions are located in the hypothalamus: the lateral hypothalamus ("hunger center") and the ventromedial hypothalamus ("satiety center"). Additionally, limbic-reticular structures, the cerebral cortex, and centers of the medulla oblongata (e.g., the vagus nerve nucleus, salivatory center) are involved in the functional feeding system.
What two phases is the physiological satiety process divided into?
The process of satiety is divided into two phases:
- Sensory satiety (primary) — a rapid process implemented on a neural basis upon irritation of the receptors of the oral cavity, esophagus, and stomach.
- Metabolic satiety (secondary, metabolic) — the final stage, occurring after food processing, its absorption into the blood, and the replenishment of metabolic needs and depots.
Through which neural pathways are afferent signals transmitted from an empty stomach to the hypothalamus?
Sources indicate that during hunger, afferent signals constantly flow from the empty stomach to the vagus nerve nuclei located in the medulla oblongata. The cause of this afferentation is tonic contraction of the stomach walls and irritation of its receptors. It is also noted that afferent signaling from the empty stomach is directed to the neurons of the lateral hypothalamus, although the specific further pathway from the vagus nerve nuclei to the hypothalamus is not detailed in the sources.
LH = Love to Hunger (Lateral = Hunger). VMH = Very Much Glutted (Ventromedial = Satiety).
Class and exam questions
Where are the main regions regulating hunger and satiety localized?
They are located in the hypothalamus: the lateral area is responsible for hunger, and the ventromedial area for satiety.
What happens upon destruction of the lateral hypothalamus?
A complete refusal to eat (aphagia) will occur, leading to exhaustion and death of the organism.
How is food motivation formed?
Excitation of the lateral hypothalamus is transmitted via ascending pathways to the cerebral cortex and limbic-reticular structures, creating a conscious feeling of hunger and prompting the search for food.
What else to study on this topic
- Afferent signaling from the gastrointestinal tract
- Humoral factors of "hungry blood"
- Connections of the feeding center with limbic-reticular structures
- Mechanisms of anticipatory excitation of the ventromedial hypothalamus
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