Hypothalamus structure and function Flashcards
What is the function of the hypothalamus?
Why?
Maintain the stability of the internal environment (homeostasis)
So can survive long enough to reproduce and maintain the species
What is the hypothalamus connected to?
How?
Connected to MANY structures in the body
Via the portal capillaries
Where do the axons from the hypothalamus project?
Directly into specialised fenestrated capilaries
What does the hypothalamus exert control over to control homeostasis?
The autonomic nervous system and the endocrine (hormonal) system
What is physical homeostasis?
What does it control? (7)
Maintenance of healthy individual and species
Controls:
1) Body Temperature
2) Stress response
3) Reproduction
4) Sleep
5) Electrolyte balance and blood pressure
6) Energy balance
7) Circadian cycle
What does energy balance include? (3)
- Food intake
- Digestion
- Metabolic rate
Where is the circadian clock in the body?
In the hypothalamus
As well as PHYSICAL homeostasis, what else does the hypothalamus control?
Mental and behavioural homeostasis (emotion and motivation)
What are emotional responses important for?
Why?
Survival
Modulate the ANS to respond to threatening stimuli
How/why are emotional responses adaptive?
- Evolution has selected for adaptive traits
- More likely to survive and reproduce if prepared to deal with threat
- Stress is beneficial - don’t freeze
What is the fight or flight response controlled through?
The hypothalamus pituitary adrenal axis
What behaviours does motivation underlie?
Feeding, sexual, survival, reproduction
What parts of the brain mediate emotion and motivation?
The hypothalamus and the limbic system
What does mental/behavioural homeostasis involve?(5)
1) Desires
2) Mood
3) Motivation
4) Trust
5) Reproductive/sexual behaviours
What is ‘allostasis’?
The ability of the hypothalamus to re-set optimal set points:
- Change of set point as the needs of the body change (eg. get older, pregnant)
- Adaptation of the hypothalamus in an anticipatory manner
What is important about the cells of the hypothalamus?
How is this determined?
They have a LIFE-LONG plasticity –> important for survival
Determined by allostasis and the adaptive features of the hypothalamus
What is the disadvantage of a plastic system?
Fragile - knock on effects if ‘tip too far’
What are 4 clinical outcomes that can arise from a fault in the hypothalamic circuit?
1) Fever
2) Addiction
3) Anxiety
4) Obesity
How does FEVER arise from a fault in the hypothalamic circuit?
Normal situation?
Circuit not functioning properly
Normally:
- Hypothalamus regulates core body temp
- Detects changes in temperature and modulates the ANS to RETAIN or DISSIPATE heat (sweat/hair stand up)
How does ADDICTION arise from a fault in the hypothalamic circuit?
What are the side effects?
- Many recreational drugs work through hypothalamic neuronal pathways involved in REWARD and MOTIVATED behaviour in the LIMBIC SYSTEM
Knock on effect on all hypothalamic features:
- Sleep
- Energy balance
- Reproduction
How does ANXIETY arise from a fault in the hypothalamic circuit?
- Many anxiety disorders (eg. panic and post-traumatic stress) have physiological symptoms mediated by the LIMBIC SYSTEM and the AUTONOMIC NERVOUS SYSTEM
- Evidence that severe stress from genetics is due to a dysfunction in the hypothalamus
How does OBESITY arise from a fault in the hypothalamic circuit?
- Feeding in part is controlled by the hypothalamus
- Interactions between HYPOTHALAMUS and LIMBIC REWARD CIRCUITY are important to feeding behaviour
How does the hypothalamus relate to the limbic system?
Hypothalamus is PART of the limbic system
What limits the hypothalamus anteriorly?
Optic Chiasm and anterior commissure
What limits the hypothalamus posteriorly?
Mammillary bodies
What is the hypothalamus made of?
Many nuclei containing clusters of neurons
What is the hypothalamus connected to ventrally?
The infundibulum: glial cell containing outgrowth
What sits above the infundibulum?
A random arrangement of neurons in nuclei
What are 7 parts of the hypothalamus?
1) Paraventricular nucleus
2) Suprachiasmatic nucleus
3) Infundibulum/Pituitary
4) Dorsomedial hypothalamic nucleus
5) Ventromedial hypothalamic nucleus
6) Arcuate nucleus
7) Lateral hypothalamic area/lateral level
Where does the suprachiasmatic nuclei lie?
Very anteriorly, close to the eyes
What is contained in the suprachiasmatic nuclei?
The circadian clock
What studies show the biological functions of particular neurons in particular nuclei of the hypothalamus?
1) Lesion studies
2) Genetic loss of function studies