Hypothalamus Flashcards
What is the function of the hypothalamus?
Homeostasis and survivalby maintaining the set point of parameters. Involved in motivated behaviour.
It influences the ANS, endocrine system and behaviour by integrating all three.
The hypothalamus integrates somatic and autonomic responses. Give examples of functions under hypothalamic control.
CVS Blood compostion and volume Food and water intake Temperature control Circadian rhythms Reproductive behaviour Emotional behaviour
What supplies input into the hypothalamus?
Internal: Sensory receptors
External: Limbic regions, olfactory regions, retina, hippocampus
Where are the receptors located for homeostatic control?
Lie in hypothalamus or in circumventricular organs e.g. viscera
What outputs arise from the hypothalamus?
To pituitary for hormones
To brainstem for ANS control and coordinated behaviour
To limbic for emotion and coordinated behaviour
What do the external input areas provide information about or for?
Limbic = emotional state
Olfactory region = Influences motivated behaviour
Retina = Light to SCN
Hippocampus = memory
What is the structure of the hypothalamus?
Subdivided into regions that contain many nuclei. Has a heterogenous 3D structure. The nuclei work together to integrate ANS, endocrine and behaviour
What can be identified along the anterior-posterior axis of the hypothalamus?
Anteriorly: Preoptic area near optic chiasm. Contains SCN and nuclei concerned with set points of homeostasis.
Posteriorly: Contains mamillary bodies
What are mamillary bodies?
A collection of neurons involved in emotional processing. 1 located in each hemisphere.
What causes Korsokoff’s syndrome?
Disruption of mamillary body.
What can be identified along the medial-lateral axis of the hypothalamus?
3 zones located around the 3rd ventricle:
- Periventricular zone
- Medial zone
- Lateral zone
What is within the periventricular zone of the hypothalamus?
A thin area containing SCN and the arcuate nucleus which is sealing off the bottom of the 3rd ventricle
What is the arcuate nucleus involved in?
Feeding and anterior pituitary regulation
What is within the medial zone of the hypothalamus? What is its function?
Paraventricular nuclei that release hormones to the posterior pituitary and involve feeding.
What is within the lateral zone of the hypothalamus? What is its function?
Contains the lateral hypothalamic area for feeding and supraoptic nuclei which releases hormones to posterior pituitary.
Where is ANS input received from?
Exteroreceptors and interoreceptors (homeostasis)
Where is ANS output sent to?
Paraventricular nuclei and onto the brainstem nuclei for origin of preganglionic sym and parasym fibres for control.
Give an example of the types of ANS functions the hypothalamus influences?
HR and BP
How is the hypothalamus connected to the pituitary for endocrine control?
Indirectly connected to anterior pituitary via parvocellular neurosecretory cells which pass down the pituitary stalk and terminate on the capillary bed, releasing NT into blood of anterior pituitary. Releases hypophysiotropic hormones - GnRH, TRH etc that cause release of the anterior hormones into the body.
Directly connected to the posterior pituitary via magnocellular neurosecretory cells that terminate and release NT into the capillaries directly. Releases the neurohormones oxytocin and ADH that are produced in the hypothalamus.
How is food intake regulated short term and long term? What happens if the regulation is disrupted?
Body continuously demands glucose, but we only provide intermittent supply so it must be stored. A disruption in glucose intake leads to starvation or obesity.
Short term regulation:
- Hypothalamic inputs from mechanoreceptors in gut and glucose receptors in the liver.
- Hypothalamic glucose and ghrelin receptors for daily intake
Long term regulation:
Body weight is regulated through adipose tissue. Adipose tissue release leptin which acts on the hypothalamus to increase satiety and reduce intake and increase metabolism (ANS to liver, pituitary hormones)
Which hypothalamic nuclei are involved in food intake?
Arcuate - Has high leptin R density to detect adipose volume
Paraventricular nucleus - Controls ANS and signals to pituitary
Lateral hypothalamic area - Causes motivation to search for food and projects across cortex
What does a lesion in the paraventricular nucleus result in?
Unwanted feeding = obesity
What does a lesion in the lateral hypothalamic area cause?
Cessation of eating = starvation.
Linked to cancer and MS
Which nuclei/receptors are involved in temperature control?
Hypothalamic thermoreceptors - Change set point temporarily during fever
Anterior hypothalamic nuclei - For heat dissipation of excess
Posterior hypothalamic nucleu - For heat rentention
How do ANS, endocrine and behaviour all influence temperature control?
ANS for vasomotor changes in skin.
Endocrine increases/decreases metabolism for long term heat production and acclimatising.
Behavioural for shivering or seeking warmth/shade
How does the hypothalamus control reproductive behaviour?
Integrates endocrine for puberty and cycles, ANS for sexual organs and behavioural for courtship
What is sexual dimorphism?
Anatomical differences between males and females particularly in the preoptic area (sex hormone R lies within) resulting in differences in reproductive behaviour.
Why is a brain injury to the hypothalamus rare?
Due to location. Located bilaterally so if one is damaged the other takes over. Location makes it inoperable due to access.
Why is a tumour hard to identify in the hypothalamus?
Presents with diverse symptoms that are progressive.
