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A BMS 381 - Developmental neurobiology > Hypothalamus structure and function > Flashcards

Hypothalamus structure and function Flashcards

1
Q

What is the function of the hypothalamus?

Why?

A

Maintain the stability of the internal environment (homeostasis)

So can survive long enough to reproduce and maintain the species

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2
Q

What is the hypothalamus connected to?

How?

A

Connected to MANY structures in the body

Via the portal capillaries

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3
Q

Where do the axons from the hypothalamus project?

A

Directly into specialised fenestrated capilaries

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4
Q

What does the hypothalamus exert control over to control homeostasis?

A

The autonomic nervous system and the endocrine (hormonal) system

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5
Q

What is physical homeostasis?

What does it control? (7)

A

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

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6
Q

What does energy balance include? (3)

A
  • Food intake
  • Digestion
  • Metabolic rate
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7
Q

Where is the circadian clock in the body?

A

In the hypothalamus

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8
Q

As well as PHYSICAL homeostasis, what else does the hypothalamus control?

A

Mental and behavioural homeostasis (emotion and motivation)

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9
Q

What are emotional responses important for?

Why?

A

Survival

Modulate the ANS to respond to threatening stimuli

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10
Q

How/why are emotional responses adaptive?

A
  • Evolution has selected for adaptive traits
  • More likely to survive and reproduce if prepared to deal with threat
  • Stress is beneficial - don’t freeze
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11
Q

What is the fight or flight response controlled through?

A

The hypothalamus pituitary adrenal axis

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12
Q

What behaviours does motivation underlie?

A

Feeding, sexual, survival, reproduction

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13
Q

What parts of the brain mediate emotion and motivation?

A

The hypothalamus and the limbic system

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14
Q

What does mental/behavioural homeostasis involve?(5)

A

1) Desires
2) Mood
3) Motivation
4) Trust
5) Reproductive/sexual behaviours

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15
Q

What is ‘allostasis’?

A

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
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16
Q

What is important about the cells of the hypothalamus?

How is this determined?

A

They have a LIFE-LONG plasticity –> important for survival

Determined by allostasis and the adaptive features of the hypothalamus

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17
Q

What is the disadvantage of a plastic system?

A

Fragile - knock on effects if ‘tip too far’

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18
Q

What are 4 clinical outcomes that can arise from a fault in the hypothalamic circuit?

A

1) Fever
2) Addiction
3) Anxiety
4) Obesity

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19
Q

How does FEVER arise from a fault in the hypothalamic circuit?

Normal situation?

A

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)
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20
Q

How does ADDICTION arise from a fault in the hypothalamic circuit?

What are the side effects?

A
  • 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
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21
Q

How does ANXIETY arise from a fault in the hypothalamic circuit?

A
  • 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
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22
Q

How does OBESITY arise from a fault in the hypothalamic circuit?

A
  • Feeding in part is controlled by the hypothalamus

- Interactions between HYPOTHALAMUS and LIMBIC REWARD CIRCUITY are important to feeding behaviour

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23
Q

How does the hypothalamus relate to the limbic system?

A

Hypothalamus is PART of the limbic system

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24
Q

What limits the hypothalamus anteriorly?

A

Optic Chiasm and anterior commissure

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25
Q

What limits the hypothalamus posteriorly?

A

Mammillary bodies

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26
Q

What is the hypothalamus made of?

A

Many nuclei containing clusters of neurons

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27
Q

What is the hypothalamus connected to ventrally?

A

The infundibulum: glial cell containing outgrowth

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28
Q

What sits above the infundibulum?

A

A random arrangement of neurons in nuclei

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29
Q

What are 7 parts of the hypothalamus?

A

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

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30
Q

Where does the suprachiasmatic nuclei lie?

A

Very anteriorly, close to the eyes

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31
Q

What is contained in the suprachiasmatic nuclei?

A

The circadian clock

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32
Q

What studies show the biological functions of particular neurons in particular nuclei of the hypothalamus?

A

1) Lesion studies

2) Genetic loss of function studies

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33
Q

What hormones is the STRESS RESPONSE mediated by?

A

Corticotropin releasing hormone in the PVN

SF1 neurons in the VMN

34
Q

What hormones is REPRODUCTION mediated by?

A

GnRH neurons in the Arc

DA neurons in the Arc

35
Q

What hormones is SLEEP mediated by?

A

GABA-ergic and hypocretin neurons in the lateral hypothalamus and the zona incerta

36
Q

What hormones is ELECTROLYTE BALANCE AND BLOOD PRESSURE mediated by?

A

AVP neurons in the PVN

37
Q

What hormones is ENERGY BALANCE mediated by?

A

Pomc and NYP neurons in the Arc

38
Q

What hormones is the CIRCADIAN CYCLE mediated by?

A

Neurons in the SCN

39
Q

How do pomc and NYP neurons interact?

A

Act AGAINST each other

40
Q

What is the central regulator of hormones in the body?

A

NOT the pituitary (pituitary is regulated by the HYPOTHALAMUS)

41
Q

What is a neurohormone?

A

A hormone made by a neuron

42
Q

How does the hypothalamus control the pituitary?

A

Releasing hormone released from the hypothalamus - via hypothalamic neurons –> release of these hormones from the pituitary gland

43
Q

Where are releasing hormones made?

A

By the neurons of the hypothalamus

44
Q

What is the structure of the anterior pituitary gland?

A

5 different cell types that make 5 different types of hormone

45
Q

What is physical homeostasis controlled by?

A

Neurons in particular nuclei that act via neurohormones and neurotransmitters

46
Q

What are mental and behavioural homeostasis controlled by?

A

Neurons in particular nuclei that act via neurohormones and neuortransmitters

47
Q

What hormones is MOOD/AGRESSION mediated by?

A

SF1+ neurons in the VMN

48
Q

What hormones is TRUST mediated by?

A

Oxytocin+ neurons in the PVN

49
Q

Describe the hypothalamic circuitry

Why is this beneficial?

A

1) Discrete neurons in discrete nuclei - mediate different aspects of different responses/anticipatory behaviours
2) ALL hypothalamic nuclei/neurons form INTERLINKED circuits with each other - activity in one nuclei affects the activity in another

Beneficial:
- Optimised system so that all nuclei work together in an optimal way

50
Q

What does the hypothalamic circuitry mean for behaviour?

A

ONE behaviour can effect ANOTHER

51
Q

What is the disadvantage of the nuclei all being in circuits?

A

Disfunction in one system –> dysfunction in another

52
Q

What are the activities of the nuclei of the hypothalamus entrained to?

A

The circadian clock

53
Q

What are the 2 classes of PVN neurons?

A

Oxytocin+ and Vasopressin+

54
Q

Where do the neurons of the PVN project to in development?

How?

A

The BACK of the infundibulum

End feet of the neurons end on the fenestrated capillaries (portal capillaries)

55
Q

What does the back of the infundibulum become?

AKA?

A

The POSTERIOR pituitary gland

AKA: the neurohypophysis

56
Q

Where do the neurons of the PVN release hormones?

A

DIRECTLY into the vasculature

57
Q

What is an important feature of the infundibulum?

A

Highly vascularised

58
Q

How many neurons project to the median eminence?

Where from?

A

5 classes

From PVN and Arc

59
Q

What do the neurons projecting to the median eminence do?

What happens next?

A

Secrete regulatory hormones into the LOCAL PORTAL CIRCULATION that directly links to the ANTERIOR PITUITARY (not to the rest of the body)

1) Each neuron makes a DIFFERENT releasing hormone - released into the small capillary
2) Releasing hormone travels a small distance in the portal capillary and is released from the ENDOCRINE cell into the PITUITARY gland
3) Triggers the release of the complimentary hormone from the pituitary gland

60
Q

Which neurons from the PVN project directly to the posterior pituitary gland?

A

Oxytocin+ and Vasopressin+

–> hormones directly into blood stream

61
Q

Describe the hypothalamic-pituitary-adrenal axis example

A

1) Hypothalamic neuron (that makes CRH) –> medial eminece
2) CRH (corticotrophin release factor) released from end feet into the capillary gland –> travels short distance and encounters corticotroph
3) Corticotroph releases ATCH into bloodstream to the adrenal cortex

62
Q

What is a corticotroph?

A

Endocrine cell in the pituitary gland

Makes ACTH

63
Q

Wha does ACTH do in the adrenal cortex?

A

Regulates glucocorticoids and stress hormones (cortisol, corticosterone, adrenalin)

64
Q

What endocrine cell does gonadotophin releasing factor act on?

What does this cell make?

A

Acts on gonadotrophs

Makes LH and FSH

65
Q

Describe the hypothalamic-pituitary-thyroid axis example

A

Thyroid releasing hormone - releases TSH –> regulates thyroid by thyroid gland

66
Q

What controls ALL of the pituitary hormones?

A

The HYPOTHALAMUS

67
Q

Where does the hypothalamus lie?

A

In the ventral part of the brain- built on the 3rd ventricle

68
Q

What is the structure of the hypothalamus?

A

PATCHWORK of nuclei - don’t follow a set pattern

69
Q

Where do the key nuclei lie?

Examples?

A

Line the 3rd ventricle in the central hypothalamus

Nuclei that control energy and stress balance

70
Q

What is the ventral outgrowth in the embryo?

What does it give rise to?

A

Infundibulum

Gives rise to the median eminence and the posterior pituitary

71
Q

Where does the PVN sit?

A

At the TOP of the 3rd ventricle

72
Q

Where does the SCN sit?

A

At the bottom of the 3rd ventricle

73
Q

What lines the 3rd ventricle?

A

TANYCYTES line the VENTRAL 2/3

74
Q

What are tanycytes?

A

Specialised cells that line the ventral 2/3 of the ventricle and are subdivided into different categories depending on their position/projection

75
Q

What is the structure of a tanycyte?

A

Radial glial like - long basal projection

76
Q

Where do tanycytes project to?

77
Q

What is the function of tanycytes?

A

‘Gatekeepers’ - provide a direct link with the circulating systems/peripheral body:

  • Project directly to the MEDIAL EMINENCE (containing many portal capillaries)
  • Project directly to the Arc and VMN (brain)
78
Q

How does the brain communicate with the body?

A

Via axons that directly release neurohormones

79
Q

How does the body communicate with the brain?

A

Via TANCYCYTES - physically contact portal capillaries that feed information from the body

(Metabolites and hormones from the portal vasculature into the 3rd ventricle via CERTAIN tanycytes and back out via OTHER tanycytes)

80
Q

What are the 3 mechanisms in the hypothalamus that make its function analogous to servo-control systems?

A

1) H receives sensory information from the external body
2) Compares sensory information with optimum biological set points
3) Adjusts an array of autonomic, endocrine and behavioural responses aimed at maintaining homeostasis

A BMS 381 - Developmental neurobiology (17 decks)

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