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Neuroscience and Head and Neck Anatomy > Hypothalamus > Flashcards

Hypothalamus Flashcards

1
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4
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In general, what is the function of the hypothalamus?

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To sample current status of both external and internal environment and make adjustments in order to maintain homeostasis

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5
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What are the 4 major functions of the hypothalamus?

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6
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What are the 3 ways in which the hypothalamus can communicate with the tissues/structures that it interacts with?

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7
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What are some important areas of the brain that send neuronal projections TO the hypothalamus?

A

Hippocampus

Amygdala

Septal area

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8
Q

What are some important ares of the brain that receive neuronal projections from the hypothalamus?

A

Cingulate gyrus

Prefrontal cortex

**NOTE: they do so indirectly via the thalamus**

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9
Q

The […] of the hypothalamus are important for memory.

A

Mamillary bodies

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10
Q

Neuronal projections from the mamillary bodies of the hypothalamus project where?

A

Anterior nucleus of thalamus –> cingulate gyrus (involved in short term memory)

Midbrain tegmentum (autonomic function)

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11
Q

Explain this diagram

A

Shows areas that receive efferent projections from the medial and lateral hypothalamus

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12
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13
Q

What is the median eminence?

A

A circumventricular organ (secretory)

The hypothalamus requires that some things that otherwise would not be able to cross the BBB are able to cross it in some places. The median eminence is such a place where certain compounds can cross and be sampled from the blood by the hypothalamus. It is also a place where they hypothalamus can secrete hormones into the capillaries to reach the pituitary.

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14
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What are parvocellular neurons of the hypothalamus?

A

They secrete “releasing hormones” into the median eminance, which then travel via capillary bed to anterior pituitary causing AP to release hormones that enter general circulation and act in an endocrine fashion on distant tissues.

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15
Q

What is the hypothalamic pituitary adrenal axis?

A

Neural inputs from the SCN or the cortex due to circadian rhythms or stress synapse on the paraventricular nucleus and stimulate parvocellular neurons in PVN to release CRH and AVP into median eminence. CRH and AVP enter capillary bed via median eminence and travel to anterior pituitary. There they act on cells to stimulate the release of ACTH into the blood stream. ACTH (among other things) causes adrenal glands to secrete cortisol, which feeds back onto the hypothalamus and anterior pituitary in a negative fashion, inhibiting its own production.

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16
Q

How does the body respond differently to short term stressors vs. prolonged stressors?

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17
Q

The adrenal cortex of the medulla secretes […] while the adrenal medulla secretes […]

A

Corticosteroids

Epinephrine and norepinephrine

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18
Q

What is the hypothalamic - pituitary - thyroid axis?

A

Parvocellular neurons in PVN and dorsomedial nuclei are stimulated to release TRH into median eminence. TRH enters capillary bed via median eminence and travel to anterior pituitary. There it acts on cells to stimulate the release of TSH into the blood stream. TSH causes thyroid to secrete T3 and T4 into blood to act on target tissues. T3 and T4 feed back onto the hypothalamus and anterior pituitary in a negative fashion, inhibiting their own production.

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19
Q

What is the hypothalamic - pituitary - gonad axis?

A

Parvocellular neurons in preoptic nucleus are stimulated to release Gonadotropin releasing hormone (GnRH) into median eminence. GnRH enters capillary bed via median eminence and travel to anterior pituitary. There it acts on cells to stimulate the release of luteinizing hormone (LH) and follicle stimulating hormone (FSH) into the blood stream.

  • In females: LH and FSH cause ovaries to secrete estrogen and progesterone into blood to act on target tissues. They both also feed back onto the hypothalamus and anterior pituitary in a mixed fashion, can be inhibitory or stimulatory depending on where the female is in her cycle.
  • In males: LH and FSH cause testes to release testosterone into blood to act on target tissues. Testosterone also feedsback onto anterior pituitary and hypothalamus to inhibit its own production.
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20
Q

What is the hypothalamic - pituitary - liver axis?

A

Parvocellular neurons in arcuate nucleus are stimulated to release growth hormone releasing hormone (GHRH) into median eminence. GHRH enters capillary bed via median eminence and travel to anterior pituitary. There it acts on cells to stimulate the release of somatostatin (SST) and growth hormone (GH) into the blood stream.

SST remains locally in pituitary and inhibits the release of GH. GH enters blood and stimulates release of IGF-1 from liver which promotes muscle and bone growth.

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21
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What role does the hypothalamus play in prolactin release?

A

Hypothalamus makes prolactin releasing factor (PRF) and thyroid releasing factor –> median eminence –> anterior pituitary –> release of prolactin –> act on target tissues (breast and ovaries)

Inhibited by dopamine

22
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What are magnocellular hypothalamic neurons?

A

These are neurons whose cell bodies are in the hypothalamus but whose axons project to the posterior pituitary directly via the infundibular stalk. Once in the posterior pituitary, they release hormones directly into the capillary beds of the posterior pituitary. As such, the molecules they secrete are NOT RELEASING FACTORS but are infact endocrine hormones because they travel through the bloodstream to reach their target tissues.

23
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True or false: The posterior pituitary secretes hormones directly.

A

FALSE - no hormones are made in the posterior pituitary. All hormones that are secreted from the posterior pituitary are made by magnocellular neurons in the hypothalamus that simply use the posterior pituitary as a projection site so they can gain access to blood supply.

24
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What are 2 important hormones that are secreted by magnocellular neurons?

A

Vasopression (ADH)

Oxytocin

25
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Describe the role of stress in the HPA axis.

A

Stimuli –> amygdala interprets stimuli as stressful –> activates PVN –> stimulates HPA axis to release cortisol –> cortisol feedsback directly to hypothalamus and anterior pituitary to shut off its production and also feedsback to hippocampus which then feedsback onto PVN to shut off HPA axis

26
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What role does the hippocampus play in the stress response?

A

In response to cortisol binding in hippocampus, it will attempt to inhibit the PVN to reduce cortisol production

27
Q

What are the 2 types of receptors that glucocorticoids can bind to?

A

Mineralocorticoid (high affinity, requires very little ligand to become activated, for moment to moment respones and circadian rhythm control)

Glucocorticoid (low affinity, requires more ligand to become activated, implicated in chronic stress response)

28
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What effect does chronic stress have on neurons in the hippocampus?

A

In certain region of hippocampus, has been shown to cause atrophy of dendrites on neurons leading to decreased inhibition of PVN by hippocampus

29
Q

What impact does leptin have on food intake?

A

Suppresses

30
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What impact does insulin have on food intake?

A

Suppresses

31
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What impact does ghrelin have on food intake?

A

Stimulates

32
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What cells produce leptin?

A

Adipocytes

33
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What cells produce ghrelin?

A

Cells that line stomach wall

34
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What is the impact of NPY on appetite?

A

Stimulates intake

35
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What is the impact of oxytocin and PYY on food intake?

A

Inhibits

36
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With regards to food intake hormones, what is a first and second order neuron?

A

First order neuron is in hypothalamus, has receptors for anorexogenic or orexogenic hormones.

Second order neuron is synapsed on by first order neuron and directs appropriate behaviors via higher order brain centers in response to the hormone

37
Q

Explain this diagram.

A
  • Ghrelin act on 1st order neurons in arcuate nucleus –> 1st order neurons release NPY onto other brain regions which will stimulate food intake. Ghrelin indirectly inhibits 1st order neurons in arcuate nucleus that secrete POMC.
  • Insulin and leptin in blood bind to receptors on 1st order neurons in arcuate nucleus –> 1st order neuron releases POMC onto higher brain regions which will inhibit food intake. These hormones also bind to receptors on 1st order neurons in arcuate nucleus that release NPY and inhibit these neurons.
  • Glucose inhbits 1st order neurons in hypothalamus that secrete NPY –> suppresses food intake
38
Q

Where are the 1st order neurons in the hypothalamus that are responding to appetite hormones?

A

Arcuate nucleus

39
Q

POMC is converted to […] which is released from 1st order neurons onto 2nd order neurons.

A

alpha melanocyte stimulating hormone

POMC is a pro-hormone –> is cleaved to aMSH

40
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Where are second order neurons in the hypothalamus involved in food intake?

A

Paraventricular nucleus

Lateral hypothalamus

Perifornical area

**NOTE - all 3 areas receive input from both types of 1st order neurons**

41
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Although the PVN and LH both receive input from 1st order neurons, they produce different physiological responses to these inputs. What does the PVN control vs. the LH?

A

PVN = endocrine and autonomic responses

LH = controls intake of food and behaviors that are needed for that to happen

42
Q

What are the 2 kinds of thirst?

What types of receptors mediate each type of thirst?

A
43
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Osmoreceptors are important in modulating thirst. Where are these receptors found in the hypothalamus?

A

Circumventricular organs

  • Organum vasculosum (in PVN)
  • Subfornical organ (Supraoptic nucleus)
44
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How is vasopressin (ADH) secretion regulated?

A
45
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How does the osmolality of blood impact the firing rate of magnocellular neurons in the PVN and SON?

A
46
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How are the PVN and SON related to the baroreceptor reflex?

A
47
Q

We have thermoreceptors in our skin to detect the temperature of our environment. Describe the internal mechanisms we have to detect internal temperature.

A

Preoptic area has thermoreceptors to detect temperature of blood in brain

48
Q

The […] of the hypothalamus controls heat loss and promotes heat dissipation directly when the skin or blood temperature is too high

A

Preoptic area

49
Q

When we are cold, the […] of the hypothalamus detects that the skin and / or blood temp is too cold but it can’t act directly to correct this circumstance. Instead it communicates with the […] of the hypothalamus, which acts to conserve/generate heat.

A

Preoptic area

Posterior hypothalamus

50
Q

True or false: a brain is not required to produce a fever in response to a pyrogen.

A

False - we need a brain to have a fever.

Fever is beneficial for boosting immune response and destroying infectious organisms

51
Q

How does the brain detect presence of pyrogens so it knows to respond by producing a fever?

A

Cytokines produced in periphery in response to the pyrogen circulate and are sampled in the blood by the organum vasculosum (CVO) in brain. Enothelial cells in the nearby preoptic area of hypothalamus make prostaglandins in response to cytokines from pyrogen, and prostaglandins tell the preoptic area to increase the core body temp to a new set point thus elevating the whole body temp.

52
Q

The posterior hypothalamus is involved in […]

A

Heat regulation

Neuroscience and Head and Neck Anatomy (40 decks)

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