W10: Hypothalamic Function

Question 1

Functions of the hypothalamus

Answer 1

Homeostasis and survival (detects changes from a set-point = part of neuronal function)
Controlling motivated behaviours (when organisms do things for a particular reason e.g., eating cos hungry)
Loads: control of CVS, blood composition/volume, food/water intake, temp control, circadian rhythms (sleep), reproductive behaviour, emotional behaviour.

Question 2

How rare is hypothalamic dysfunction?

Answer 2

Physical brain injury - rare due to the central anatomical position. It is bilateral since it straddles the midline and thus damage on one side can to some degree be counteracted by the remaining side.

Question 3

What might happen in hypothalamic dysfunction?

Answer 3

E.g., in tumour growth or disruption to blood supply:
Diverse symptoms
Progressive changes, symptoms gradually become worse or acquire new ones
Location - also means if there is a problem it is difficult to operate on to remove a tumour e.g.

Question 4

How does the hypothalamus control so many functions?

Answer 4

It has many influences: ANS, endocrine (pituitary), behaviour.
Can integrate all of the somatic and autonomic activity to produce a response.

Question 5

How does the hypothalamus integrate everything?

Answer 5

It has many inputs

Question 6

What are the sensory inputs from the internal environment to the hypothalamus?

Answer 6

Sensory inputs from monitoring of internal environment - sensory receptors within the hypothalamus and receptors throughout the viscera which can influence the hypothalamus via inputs coming from the brainstem (e.g., BP). Associated with homeostasis.

Question 7

How do we get from processing the inputs to getting a change in the body?

Answer 7

The neural outputs

Question 8

What are the outputs of the hypothalamus?

Answer 8

Pituitary - hypothalamo-pituitary axis in relation to hormones
Brainstem - e.g., control the ANS and coordination of behaviour
Other regions of higher brain e.g. limbic - controlling emotions - which influences behaviour

Question 9

Internal structure of the hypothalamus

Answer 9

Contains many nuclei

Regions: anterior posterior axis, medial lateral axis

Question 10

Anatomical (nuclei) boundaries of the hypothalamus

Answer 10

PO - peri optic area (right at front)

MB - mammillary bodies (right at back)

Question 11

What is the tuberal region?

Answer 11

A mid region in the hypothalamus in which many of the nuclei reside

Question 12

What are the zones of the medial-lateral axis from inside to outside (most medial to the ventricle to furthest)?

Answer 12

Periventricular zone, medial zone, lateral zone

Question 13

What nuclei are found in the periventricular zone?

Answer 13

SCN - supra-chiasmatic nucleus = important in determining circadian rhythms
Arcuate nucleus = feeding
Paraventricular nucleus (spans periventricular zone and medial zone)

Question 14

What nuclei are found in the medial zone?

Answer 14

Paraventricular nuclei = role in pituitary control and feeding

Question 15

What nuclei are found in the lateral zone?

Answer 15

Lateral hypothalamic area = feeding

Supraoptic nuclei = release hormones from post. pituitary

Question 16

Which nuclei control the ANS and how?

Answer 16

Paraventricular nuclei
Sends outputs down to the brainstem, where interacting with various brainstem nuclei we can get control of the autonomic (sympathetic and parasympathetic) nervous system. Because their preganglionic neurones have their origins up in the brainstem.

Question 17

Evidence of the role of the hypothalamus in ANS control

Answer 17

If hypothalamus is stimulated or lesioned, it can induce changes in blood pressure and heart rate, and other ANS functions.

Question 18

How is the hypothalamus connected to the endocrine system - anterior pituitary?

Answer 18

Indirectly to the anterior pituitary: in hypothalamus are cell bodies of neurones in the PVN (and others, they are parvocellular (small)). They extend short axons which can release hypophysiotropic hormones into the local capillary bed within the stalk. Travel to the anterior pituitary gland glands, which secrete (or inhibits) the hormones to various parts of the body.

Question 19

How is the hypothalamus involved in behavioural control?

Answer 19

‘Motivated’ by wants/likes/needs to produce a reward.

Complex and varied.

Question 20

Role of the hypothalamus in food intake

Answer 20

Energy comes from glucose - needed by the brain
Constant demand of glucose needed by the brain but intermittent supply due to not eating all the time
Thus storage system is needed
If the set point is disrupted, can cause starvation or obesity.
Intake regulation is complex.
E.g., in multiple sclerosis or neurodegenerative disease, it may be accompanied by changes in food intake regulation.

Question 21

Short term regulation of food intake

Answer 21

Hypothalamus contains receptors which are sampling levels of glucose in the blood and signals originating in the digestive system e.g., ghrelin
So there is an immediate ability to get input about the peripheral state - mechanoreceptors in the gut and glucose receptors in liver

Question 22

Long term regulation of food intake

Answer 22

Glycogen stores

Fat stores. Hypothalamus gets info on the size of these fat stores by an intermediate hormone = leptin.

Question 23

How does leptin signal to the hypothalamus to cause change in feeding behaviour?

Answer 23

As fat stores peripherally increase, the adipose sites gradually produce more leptin. Leptin can have an action on the arcuate nucleus.
The activity within neurones of the arcuate nucleus cause neurones that send their axons to the lateral hypothalamic area and the paraventricular nucleus to become activated.
So PVN is able to control the ANS and pituitary to change levels of endocrine activity.

Question 24

What happens if there are lesions within the paraventricular nucleus?

Answer 24

Uncontrolled feeding, so the signal from leptin is not converted into changes in activity. Can cause obesity.

Question 25

What happens if there is a lesion of the lateral hypothalamic area?

Answer 25

Reduction in intake/ eating ceases, reducing stores and causing starvation.

Question 26

What does the lateral hypothalamic area actually do?

Answer 26

Responsible for the motivation to search for food. When hungry it is more likely you will go and seek food. So it is able to signal widespread throughout the cortex since this controls behaviour.

Question 27

Summary of how hypothalamus controls feeding

Answer 27

Hypothalamus is able to affect pit hormones which might impact on metabolic rate, so if there is an excess of store, and leptin levels rise, we can by adjustment of metabolic rate, restore normal body weight.
This effect can be brought about by autonomic activity being altered too.
If leptin levels rise, the areas of the hypothalamus can act to make us less motivated to seek out food, returning to normal body weight.
Behavioural can also affect feeding behaviour.

Question 28

How can the hypothalamus detect temperature?

Answer 28

Hypothalamic thermoreceptors

Question 29

Role of hypothalamus in fever

Answer 29

Sometimes body temp does not stay within the normal range and a change in set point occurs, e.g. in pyrexia (fever), body temp is hotter than normal. In response to this the set-point might raise higher and hence the fever.

Question 30

How does the hypothalamus control normal temperature?

Answer 30

Integrated response needed:

• ANS can control vasomotor changes in the skin
• endocrine systems can change level of metabolism to release energy or less release e.g., depending on climate
• behavioural change - shivering, panting, seek warmth/shade etc

Question 31

What is the integrated response of the hypothalamus in reproductive behaviour

Answer 31

ANS has a role in activity of sex organs
Endocrine systems important in puberty and reproductive cycling (menstrual cycle)
Behavioural systems can cause courtship

Question 32

What are the sensory inputs from the external environment to the hypothalamus?

Answer 32

Sensory inputs from outside the body, e.g., originating in the olfactory system or in the retina. Also information from other parts of the brain = limbic regions (collection of brain areas that have a major impact on emotional state) and hippocampus (memory). External inputs.

Question 33

How is the hypothalamus connected to endocrine control - posterior pituitary?

Answer 33

Directly to the posterior pituitary: neurones with cell bodies up in hypothalamus - PVN and SO (have large cell bodies and are known as magnocellular cells). These extend their axons all the way down through the pituitary stalk, and release their neurohormones directly into the capillary bed of the post. pit, e.g., oxytocin and ADH.

Question 34

What areas of the brain suppress and promote food intake?

Answer 34

PVN suppresses food intake

Lateral hypothalamic nucleus promotes food intake