21 - Hypothalamus Flashcards
What is the main function of the hypothalamus?
Homeostasis
Definition - maintenance of the body’s internal environment within normal physiological parameters
How does the hypothalamus accomplish this?
Via interconnections with areas of the brain related to emotions, sleep/wakening, hormones and autonomic activity
What else is the hypothalamus responsible for?
Monitoring…
- Blood glucose levels
- Blood osmolarity
- Body temperature
- Various hormone levels
What are the four boundaries of the hypothalamus?
Superior- hypothalamic sulcus
Anterior- lamina terminalis
Posterior- midbrain (interpeduncular fossa)
Inferior- optic chiasma, tuber cinereum, mammillary bodies
What two zones of the thalamus are there?
Medial and lateral zones
What are the zones divided by?
Fornix
Where are nuclei embedded in the hypothalamus?
In the wall of the third ventricles
What is the major blood supply to the hypothalamus?
Perforating branches of the circle of Willis
Which systems does the hypothalamus function to connect?
. Hypothalamus is the nodal point interconnecting structures relating to autonomic, endocrine, emotional and somatic functions.
There are five major inputs into the hypothalamus. What are they?
1 - Cerebrum 2 - Limbic system 3 - Retina 4 - Brainstem and spinal cord 5 - Intrinsic neurons
What does the cerebrum input into the hypothalamus?
Thoughts and decisions
What does the limbic system input into the hypothalamus?
It organizes appropriate behavioral responses that are associated with basic drives, feelings and motivation
What does the retina input into the hypothalamus?
Light information
What does the brainstem and spinal cord input into the hypothalamus?
Information from the viscera
What do the intrinsic neurons input into the hypothalamus?
They monitor blood temperature, osmolarity, hormone levels and glucose concentrations
What are the two major outputs of the hypothalamus?
1 - Brainstem and spinal cord
2 - Pituitary
What does the hypothalamus contribute to the brainstem and spinal cord
The hypothalamus influences the viscera via the brainstem and spinal cord by contributing autonomic messages to…
- CN VII (facial)
- CN IX (glossopharyngeal)
- CN X - Vagus
- Spinal nerves T1-T2
- Spinal nerves S2-S4
What does the hypothalamus contribute to the pituitary gland?
The hypothalamus sends signals to the pituitary gland in order to produce secretions (hormones and releasing factors)
What are the major nuclei of the hypothalamus?
- Anterior
- Arcuate
- Lateral
- Mamillary
- Medial preoptic
- Ventromedial
- Paraventricular
- Posterior
- Preoptic
- Supraoptic
- Suprachiasmic
We will only focus on a few of these, so don’t worry about knowing all the names and functions, just the ones included later in these note cards
How are the nuclei named?
Either based on their location or their shape
Describe the role of the hypothalamus as the “internal clock”
A hypothalamic nucleus serves as the “master clock” of the brain coordinating cyclic mechanisms such as sleep/wakefulness, temperature levels and hormonal release synchronized to circadian (24 hours) changes in light levels.
Which nucleus is responsible for this?
Suprachiasmatic
What characteristic of the suprachiasmatic nuclei makes it equipped for this role?
It has many melatonin receptors
What input does the suprachiasmatic nuclei receive?
The suprachiasmatic nuclei receives light information from the retinohypothalamic tract
What else influences the “internal clock”?
The pineal gland, which also receives light information, produces melatonin which then synchronizes the clock to a 24 hour cycle influencing sleep/wakefulness cycles through connections to reticular activating system in the brainstem
Describe how the hypothalamus plays a role in emotions, memory and learning
Structures of the limbic system have extensive interconnections with the hypothalamus. Limbic system evaluates incoming sensations for threats to survival, opportunities to mate, generates “feelings” of pleasure, fear, rage and associates them with memories. Limbic system organizes behavioral responses.
* Hypothalamus organizes visceral responses through autonomic nervous system: elevated/depressed heart rate, sweating, flushing/blanching, hormonal synthesis and release.*
What are the five main structures of the limbic system?
- Septal area
- Amygdala
- Hippocampal formation
- Anterior thalamic nucleus
- Cingulate gyrus (cortex)
What is the septal area responsible for?
Pleasure and reward, feelings of well being
What is the amygdala responsible for?
Basic drives (fear, rage, sex drive)
What is the hippocampal formation responsible for?
Short term memory and the conversion of short term memory into long term memory (consolidation)
What is the anterior thalamic nucleus responsible for?
It is the limbic system relay nucleus
What is the cingulate gyrus of the cortex responsible for?
Emotional “feelings” that are brought to consciousness
What nucleus is responsible for receiving signals from the limbic system regarding learning, memory and emotion?
Mamillary bodies
What are the major interconnecting pathways between the hypothalamus and the limbic system?
Note - they are RECIPROCAL
- Fornix
- Mamillothalamic tract
- Mamillotegmental tract
- Stria terminalis and diagonal band
- Medial forebrain bundle
What is the fornix?
A C-shaped bundle of fibers (axons) in the brain that carries signals from the hippocampus to the mammillary bodies and then to the anterior nuclei of thalamus. The fornix is part of the limbic system.
What is the mamillothalamic tract?
A connection between the mamillary bodies of the hypothalamus and the anterior thalamiic nucleus of the thalamus
What is the mamillotegmental tract?
A connection between mamillary bodies of the hypothalamus and…
(1) the reticular formation of the brainstem
(2) cranial nerve nuclei
(3) autonomic segments of the spinal cord
What is the stria terminalis and diagonal band
Connections to the amygdala
What is the medial forebrain bundle
Connections to the septal area (nuclei) of the limbic system
Describe how the hypothalamus plays a role in autonomic control
The hypothalamus has been referred to as the “head (chief) ganglion” of the autonomic nervous system. The ANS is not truly autonomous in the sense of operating without coordination or higher level influences. The hypothalamus receives information from a variety of sources and provides visceral responses to thoughts, emotions and feedback information from the viscera
What input does the hypothalamus receive in order to contribute to autonomic control
The hypothalamus receives visceral information from internal organs such as pain, empty stomach, dryness in the mouth, and environmental information such as ambient temperature plus thoughts, emotions, and memories of events
Which two hypothalamus nuclei send out parasympathetics?
Two nuclei send out parasympathetics
- Preoptic nuclei
- Anterior nuclei
What parasympathetic responses is the hypothalamus responsible for?
- Pupillary constriction
- Increased salivation
- Decreased BP and HR
- Increased GI peristalsis
- Vasodilation
Which two hypothalamus nuclei send out sympathetics?
Two nuclei send out sympathetics
- Posterior nuclei
- Lateral nuclei
What sympathetic responses is the hypothalamus responsible for?
- Pupillary dilation
- Decreased salvation
- Increased HR and BP
- Decreased GI peristalsis
- Vasoconstriction
What is autonomic integration and how does the hypothalamus do this?
- Autonomic integration is the joining of fibers throughout the hypothalamus that all contribute to autonomics in the body
- Fibers from various nuclei converge on the paraventricular nucleus of the hypothalamus
- These fibers then continue via the dorsal longitudinal fasiculus and mammillotegmental tracts to the brain stem and spinal cord
What is the destination of these parasympathetic fibers?
- The parasympathetic nuclei
- Spinal nerve T1-L2
- Spinal nerve S2-4
Describe the role of the hypothalamus as an “internal thermostat”
The hypothalamus monitors blood temperature and works to maintain a constant internal homeostasis
What part of the “internal thermostat” is the anterior hypothalamus responsible for?
The anterior hypothalamus initiates heat loss
What nuclei of the anterior hypothalamus are responsible for initiating heat loss?
Two nuclei
- Preoptic nuclei
- Anterior nuclei
What visceral responses are initiated by the anterior hypothalamus for heat loss?
- Sweating
- Vasodilation
- Decreased muscular activity
What behavior responses are initiated by the anterior hypothalamus for heat loss?
- Seek a cooler environment
- Drink cold liquids
What part of the “internal thermostat” is the posterior hypothalamus responsible for?
The posterior hypothalamus activates heat conservation and heat production
What nuclei of the posterior hypothalamus are responsible for heat conservation and production?
Just one nuclei
- Posterior nuclei
What visceral responses are initiated by the posterior hypothalamus for heat conservation and production?
- Vasoconstriction
- Shivering
- TRH, which stimulates TSH, which stimulates TH, which increases metabolism
What behavioral responses are initiated by the posterior hypothalamus for heat conservation and production?
- Put on a sweater
- Throw another log on the fire
What is an antipyretic drug? How does this affect the hypothalamus? Example?
An antipyretic drug (or a fever-reducing drug) acts directly on the hypothalamus to cool the body temperature.
Example: Aspirin
Which two nuclei of the hypothalamus regulate food intake?
The lateral nucleus and the ventromedial nucleus
What effect does the lateral nucleus have on food intake?
Stimulation of the lateral nucleus induces eating
We call the lateral nucleus the “hunger” or the “feeding” center
What effect does the ventromedial nucleus have on food intake?
Stimulation of the ventromedial nucleus inhibits eating
We call the ventromedial nucleus the “satiety” center
Describe the role of the hypothalamus in monitoring blood parameters
The hypothalamus monitors blood parameters via intrinsic neurons. The hypothalamus is “triggered” by osmoreceptors, glucoreceptors and hormone changes.
Describe osmoreceptors
Osmoreceptors detect blood concentration and osmolarity. The osmoreceptors send signals to the lateral hypothalamus (zona incerta) which stimulates water intake
Describe glucoreceptors
Glucoreceptors detect blood glucose levels. This affects the feeding and satiety centers of the hypothalamus.
Describe hormone changes
Changing hormone levels can trigger changes in hypothalamic releasing factors that are controlled by the anterior pituitary
Describe the role of the hypothalamus in influencing the posterior pituitary
The hypothalamus synthesizes and releases hormones of the posterior pituitary gland (the posterior part of the pituitary gland is called the neurohypophysis)
Which nuclei of the hypothalamus are involved in synthesizing and releasing hormones for the pituitary gland?
Two nuclei
- Supraoptic nuclei
- Paraventricular nuclei
Which pathway do the supraoptic and paraventricular nuclei utilize when influencing the posterior pituitary?
Hypothalamohypophyseal tract
AKA Supraopticohypophyseal tract
Which hormones does the hypothalamus synthesize and release to the pituitary gland?
- ADH (antidiuretic hormone) or vasopressin
- Oxytocin
How do intrinsic osmoreceptors trigger ADH production?
When intrinsic osmoreceptors sense dehydration, they trigger ADH synthesis in order to conserve water
What is a clinical effect of damage to the supraoptic or paraventricular nuclei of the hypothalamus?
Damage to this area of the hypothalamus can interrupt the synthesis of ADH, leading to copious urine formation and constant thirst.
What do we call this condition?
Diabetes insipidus
“tasteless diabetes”
How is diabetes insipidus different from diabetes mellitus?
Unlike diabetes mellitus, “flowing with honey,” blood and urine glucose levels are within the normal limits in diabetes insipidus
Describe the role of the hypothalamus in influencing the anterior pituitary
The hypothalamus produces releasing factors that stimulate or inhibit the release of hormones from the anterior pituitary
What nuclei of the hypothalamus are involved in the production of releasing factors that stimulate/inhibit the release of hormones from the anterior pituitary?
There are four nuclei (but just remember the two starred ones)
- Medial preoptic nuclei
- Preoptic nuclei
- Arcuate ***
- Periventricular ***
Which pathway does the hypothalamus utilize in order to influence the anterior pituitary?
- First via the tuberohypophysial tract (AKA tuberoinfundibular tract)
- Then via the vascular hypothalamo-hypophysial portal system
- This leads to the adenohypophysis of the anterior pituitary
What is the role of the hormones that the hypothalamus inhibits or stimulates in the anterior pituitary?
Hormones affecting…
- Body growth
- Thyroid secretion
- Gonadal function
- Adrenocortical secretion
- Mammary gland secretion
Describe the relationship between conscious thought and the hypothalamus
There are connections present between the frontal lobes and the hypothalamus, although these fibers are not well-defined as a pathway.
There are also direct and indirect pathways with the limbic system
What are examples of visceral responses to thoughts, feelings and emotions?
- Sweating and blanching
- Accelerated heart rate
- Constipation
- Increased or decreased frequency of urination when worried or scared (sympathetics)
- Sexual dysfunction when depressed (parasympathetics)
- Skipped or delayed menstruation with worry or depression (interruption of normal cycling of gonadotrophic hormones - hypothalamic releasing factors)
What are examples of somatic responses to conscious and unconscious thoughts (limbic system)
- Slouching and moving slowly when depressed
- Quick, agitated movements when stressed or anxious
Thoughts and emotions drive facial movements that are appropriate to those thoughts and emotions - sad, happy, frightened expressions
Describe how stoke victims are still able to move otherwise paralyzed muscles in an emotional response such as smiling
Example: smiling at a joke (a Duchenne smile or a “real” smile - not a fake one)
The muscles are only paralyzed for voluntary movement - the pyramidal pathway to them (corticonuclear pathway) is interrupted.
The pathway from the cerebrum to the hypothalamus takes a different route which is not well defined, but is not affected by the stroke.
Now we are going to go through the hypothalamus nuclei that you need to know the function of…
Just an FYI
Suprachiasmatic nuclei
Circadian cycles and the “internal clock”
Mammillary nuclei
Processing emotional information
Anterior and posterior nuclei
Regulating body temperature
Ventromedial and lateral nuclei
Satiety and feeding
Supraoptic and paraventricular nuclei
Produce hormones for the posterior pituitary
Preoptic, medial preoptic, arcuate and periventricular nuclei
Release or inhibit hormones from the anterior pituitary
In lecture he said to just know arcuate and periventricular for this function and bolded them in the handout/on the slides, FYI
