The hypothalamus is an area of the brain responsible for the control of the body’s autonomic nervous system, as well as the regulation of various vitally important biological processes, such as body temperature, blood pressure, thirst, hunger, the sleep-wake cycle, important aspects of parenting and attachment behaviors, fatigue, etc.
By receiving signals from the nervous system, the diencephalon interprets the signals which are later received by the pituitary gland (which controls the endocrine system). While the thalamus sends and receives signals to and from the brain and body, the hypothalamus sends signals to the pituitary gland and results in the excretion of hormones.
Anatomy and Structure of the Hypothalamus
The hypothalamus is the brain structure located below the thalamus. Along with the thalamus, it’s part of the bigger brain structure known as the diencephalon.
The diencephalon is located at the upper end of the brainstem and is also known as the betweenbrain or interbrain. This part of the brain also helps control various vital functions of the body which are also supported by the hypothalamus.
From an anatomical point of view, the hypothalamus comprises the floor of the third ventricle, i.e. one of the four void spaces through which the cerebral fluid flows).
Structural Relations of the Hypothalamus
In the para-sagittal plane, the thalamus is divided into three regions:
- Supraoptic (anterior) hypothalamic region – This hypothalamic area comprises of the following nuclei: preoptic nucleus, medial preoptic nucleus, supraoptic nucleus, paraventricular nucleus, anterior hypothalamic nucleus, suprachiasmatic nucleus, lateral nucleus.
- Tuberal (middle) hypothalamic region – It contains the following nuclei: a part of the preoptic nucleus, part of the suprachiasmatic nucleus, the lateral nucleus, tuberomammillary nucleus, the lateral tubular nuclei, and the lateral area of the hypothalamus.
- Mammillary (posterior) hypothalamic region – This hypothalamic area comprises of the following nuclei: part of the lateral nucleus, part of the suprachiasmatic nucleus, anterior nucleus, paraventricular nucleus, dorsomedial nucleus, ventromedial nucleus, infundibular nucleus, and the posterior nucleus of the hypothalamus.
Types of Hypothalamic Nuclei
The roles played by all the nuclei in the hypothalamus are not fully known. However, some roles have been identified:
- The preoptic nucleus of the hypothalamus – This nucleus comprises neurons that are sensitive to subtle changes in temperature. Hence, it’s responsible for thermoregulation. Its neurons receive stimulation from the thermoreceptors in the skin, the mucous membranes, as well as the hypothalamus.
- The paraventricular nucleus of the hypothalamus – This nucleus comprises a group of neurons sensitive to stress and other physiological changes. It is responsible for the autonomic responses, as well as the regulation of metabolism, growth, reproduction, and the immune system.
- The supraoptic nucleus of the hypothalamus – This nucleus comprises bundles of magnocellular neurosecretory cells. The neurons of this hypothalamic nucleus are responsible for the production of the hormone vasopressin (the antidiuretic hormone), as well as the hormone oxytocin.
- The anterior nucleus of the hypothalamus – This nucleus is responsible for the functions of the circadian rhythm of the human body, as well as the regulation of temperature. Damage or a lesion in this area of the hypothalamus can result in hypothermia.
- The dorsomedial nucleus of the hypothalamus – This nucleus is responsible for the regulation of various physiological circadian rhythms, as well as feeding, drinking, and body-weight regulation.
- The ventromedial nucleus of the hypothalamus – The ventromedial nucleus is responsible for feelings of fullness after eating. Damage to this area causes overeating.
- The lateral nucleus of the hypothalamus – This nucleus comprises the primary orexinergic nucleus within the hypothalamus. It has a main role in the regulation and control of energy balance, as well as the regulation of food consummation.
- The arcuate nucleus of the hypothalamus – This nucleus contains various types of neurons which aids the regulation of homeostasis. The articulate nucleus of the hypothalamus supports various physiological functions, such as eating, metabolism, fertility, and regulation of the cardiovascular system of the human body. It also inhibits lactation by inhibiting the release of prolactin.
- The mammillary nucleus of the hypothalamus – This nucleus is responsible for the recollective memory and the transmission of electrical impulses.
- The posterior nucleus of the hypothalamus – This nucleus is responsible for the regulation of blood pressure elevation and for thermoregulation of the body.
- The parasympathetic vagal nucleus of the hypothalamus – This nucleus is responsible for the production of hormones that regulate the autonomic responses and functions of the central nervous system.
What Is the Function of the Hypothalamus?
Functions of the hypothalamus include the monitoring and regulation of vital internal conditions such as:
- nutrient levels
- water-salt balance
- blood flow
- the sleep-wake cycle
- body temperature
- daily physiological cycles
- appetite
- sexual behavior
- emotional responses
- secretion of gonadotropin-releasing hormones
- production of antidiuretic hormone
- inhibition of prolactin release
To Which Stimuli Does the Hypothalamus Respond?
Since the hypothalamus initiates, regulates, and controls a plethora of functions (such as feelings, processes, or actions), it reacts to a great variety of stimuli.
Some of the stimuli the hypothalamus is responsive to are generated internally, while some are external, such as:
- Light stimuli
- Smell or olfactory stimuli (like pheromones)
- Autonomic inputs
- Steroids and steroid hormones
- Nerve impulses from the heart, the stomach, and the reproductive tract
- Hormonal and other signals (like leptin, ghrelin, angiotensin, insulin, pituitary hormones, glucose, osmolarity of blood), etc.
- Emotional stress
- Microbes and their effects on body temperature
From Which Brain Structures Does the Hypothalamus Receive Signals?
The central nervous system transmits the electrical signals received from the sensory stimuli directly to the hypothalamus. It has neuronal connections with the following brain structures:
- brainstem
- reticular system
- autonomic zones
- limbic forebrain
- amygdala
- septum
- diagonal band of Broca
- olfactory bulbs
- cerebral cortex
The Role of the Hypothalamus in the Secretion and Regulation of Hormones
The hypothalamus basically controls all glands of the endocrine system in the human body, which means that it directly controls and regulates the next list of functions:
- blood pressure;
- Body temperature;
- metabolism (thirst, hunger, satiety);
- memory;
- pupillary dilation;
- shivering;
- circadian rhythms;
- sweating;
- urinary bladder contraction;
- decreased heart rate;
- decreased blood pressure;
- adrenaline levels.
Hence, the hypothalamus is responsible for the secretion and regulation of the following hormones:
- Thyrotropin-releasing hormone (Prolactin-releasing hormone)
- Prolactin-releasing hormone
- Corticotropin-releasing hormone
- Dopamine (Prolactin-inhibiting hormone)
- Growth hormone-releasing hormone, or Somatocrinin
- Growth-hormone-inhibiting hormone, or Somatostatin
- Oxytocin
- Vasopressin (an antidiuretic hormone)
- Luteinizing hormone R.H.
- Follicle Stimulating Hormone Releasing Factor
What Happens When the Hypothalamus Is Damaged?
The function of the hypothalamus can be affected by severe head trauma, infections, tumors of the brain, radiation, or even drastic weight loss.
All of the aforementioned leads to disorders of the thermoregulation of the body, eating disorders (such as bulimia and anorexia nervosa), disruption of the circadian cycles (insomnia, for instance), as well as hypothalamic disease.
What Are the Symptoms of a Damaged Hypothalamus?
The list of symptoms of a damaged hypothalamus includes the following:
Hypothalamic Disease
The hypothalamic disease occurs as a result of physical head trauma that affects the brain. It disturbs most of the regular hypothalamic functions in the brain.
The symptoms of this neurological condition can manifest as:
- problems with eating
- sleeping disorders
- unusually high/low blood pressure
- fluctuations in body temperature
- unintentional weight gain/loss
- sudden changes in appetite
- insomnia
- infertility
- delayed onset of puberty
- stunted growth
- excessive dehydration
- frequent urination.
Anorexia Nervosa
This is a complex neurologically-psychiatric disease, caused by a functional disturbance of the hypothalamus. Typical for this disease is for the affected individual to avoid food to the degree of aversion.
This abnormality in the behavior and disorder in the feeding patterns appears when there is a problem in the synaptic transmission of the electrical impulses in any of the dedicated brain regions responsible for the regulation and control of feeding, such as the thalamus.
By evoking a ‘mixed-signal’, the hypothalamic hormones orexins and ghrelin, as well as serotonin and dopamine, play a significant role in the pathogenesis of eating disorders. In turn, this leads to dysfunction of the hypothalamic regulatory pathways.
Hypothermia
The hypothalamus is involved in the thermoregulation of the human body. If there is a disturbance is some of the neuron pathways of the central nervous system that relay the information about the body’s temperature, it may impair the mechanisms in the hypothalamus responsible for this function.
There are 3 stages of the hypothermia:
- The first stage includes symptoms like shivering and reduced circulation.
- The second stage notes the weakening of the pulse and the heart-rate, slow breathing, lack of coordination, irritability, confusion, and sleepiness.
- The symptoms of the third stage of hypothermia show disruption and extreme weakness in breathing, and fading pulse. The affected individual may lose consciousness at this advanced stage.
Insomnia
The weakened neural connections between the thalamus and hypothalamus result in disturbance of the circadian rhythms of the body, especially the sleep patterns. Insomnia, in particular, is a sleep disorder characterized by difficulty in falling asleep.
Fun Facts
Did you know?
- Even when we sleep, our brain never stops working! It stays awake to control and manage all the bodily systems, such as breathing, digestion, body movements, heartbeat rate, blood pressure, etc.
- The name of this brain structure comes from the Ancient Greek words ὑπό, meaning “under”, and θάλαμος, meaning “chamber”.
- Even though the brain is one of the most tender organs in the human body, and it controls the sensory processes, it feels no pain. This is due to the lack of nerves in its construction.
- The hypothalamus is such a small brain structure, that merely 1% of the entire weight of the brain goes to it.
- Serotonin and dopamine are the so-called happiness and motivation hormones, respectively. Their levels increase significantly during physical training, such as aerobics and sports, as these activities lower the levels of cortisol, i.e. the stress hormone. Actually, apart from learning, physical exercising is the best thing we can do for both our brain and our body.
- The urgent medical condition hypothermia occurs when the body loses heat faster than it can produce it, i.e. when the body temperature drops dangerously fast and below normal.
- Homeostasis in the human body is the tendency of its structures for maintaining a constant balance and ultimate conditions of bodily functions and processes.
- The mammillary bodies of the hypothalamus are a part of the limbic system, located at the end of the front arches of the fornix. They are directly connected to the brain, participate in the formation of memory, and aid the transmission of the electrical impulses to the thalamus.
- Damage or lesion to the lateral nucleus of the hypothalamus can lead to extremes of starvation such as anorexia nervosa.
- Oxytocin is a hormone that has a significant role in the process of childbirth and lactation, but also in the ability of an individual to experience compassion and social bonding.