Lecture 7: Hypothalamus Flashcards Preview

Neuro I Exam 3 - Physiology > Lecture 7: Hypothalamus > Flashcards

Flashcards in Lecture 7: Hypothalamus Deck (47)
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1
Q

What happens to core temperature, thermal set point, and metabolic rate during sleep?

A
  • Sleep accompanied by lowering of the thermal set point
  • Metabolic rate reduces
  • Heat loss increases (vasodilation/sweat)
  • Core temperature decreases
2
Q

Exercise elevates what aspect of your body temperature?

A

Elevates core temperature

3
Q

High intensity, long-duration exercise raises _______.

A

Set-point

4
Q

Core temperature follows a circadian rhythm, when is it lowest and highest?

A
  • Lowest between 3-6 AM
  • Peaks between 3-6 PM
5
Q

What nucleus governs the circadian rhythm of core body temperature?

A

Suprachiasmatic nucleus of anterior hypothalamus

6
Q

During what reproductive phase do you see a 0.5 °C increase in body temperature?

A

Post-ovulatory phase

7
Q

During what reproductive phase do you see a 0.3-0.5 °C increase in body temperature?

A

Ovulation

8
Q

Cold temperature stimulate the release of what hormone, why?

A
  • TRH
  • Thyroxine increases cellular metabolic rate
9
Q

Which hormones increase cellular metabolic rate?

A
  • Thyroxine
  • Epinephrine
10
Q

What factors influence thermoregulation in newborns?

A
  • Large suface area:mass ratio (they lose heat better than adults!)
  • Do not readily sweat
  • Large deposits of brown adipose
  • Modest vasoconstriction of skin to reduce heat loss when needed
11
Q

What happens to thermosensation, heat dissipation, and metabolic rate as we age?

A
  • Progressive decline in thermosensation w/ older age
  • Reduced metabolic rate
  • Reduce metabolic potential w/ diminished muscle mass
  • Reduced ability to dissipate heat
12
Q

Thermoreceptors for hot and cold sensations are made up of what kind of fibers?

A
  • Heat = C-fiber
  • Cold = C-fiber and Aδ fibers
13
Q

What are the TRP channels for hot and cold sensation?

A

Cold = TRPA1 and TRPM8

Hot = TRPV1 (V = Vanilloid = capsaicin (hot peppers))

14
Q

What kind of thermoreceptors found on the skin, characteristics, and which are more abundant?

A
  • Warm or cold-sensitive (not both)
  • Often polymodal (i.e., temperature and touch sensitive)
  • Cold >> warm-sensitive receptors
  • Cues atmospheric changes (tells us about enviornmental conditions)
15
Q

What is the heat responsive portion of the hypothalamus and what is its function?

A
  • Anterior hypothalamic nucleus and preoptic nucleus
  • Heat loss behaviors
16
Q

What is the cool responsive portion of the hypothalamus and what is its function?

A
  • Posterior hypothalamus
  • Heat production behaviors
17
Q

How does temperature affect neurons of the hypothalamus and are there more heat or cold sensitive neurons?

A
  • Neurons are excited or inhibited by temperature
  • 3x more heat-sensitive (preoptic nuclei and anterior hypothalamic nuclei)
  • There are more heat-sensitive because protecting your brain from overheating is MOST important
18
Q

What are 3 ways we can generate heat?

A
  1. Shivering (dorsomedial posterior hypothalamus)
  2. Voluntary muscle activity (running, jumping, rubbing) via cortex
  3. Non-shivering thermogenesis (hormones, eating, brown adipose)
19
Q

What part of the hypothalamus induces shivering and how?

A

Dorsomedial posterior hypothalamus increases motorneuron excitation

20
Q

Brown adipose is abundant in who and what is it responsible for; stimulated by what part of the ANS?

A
  • High in infants; recent evidence shows existence in adults
  • Low efficiency hydrolysis of ATP = heat production
  • Sympathetics stimulation results in fatty acid metabolism
  • Is considered low efficiency, which means its producing lots of heat!
21
Q

What are the 4 ways to dissipate heat and how does each work?

A

1) Evaporation: insensible (respiratory) and sweat
2) Convection: dissipation through air
3) Conduction: dissipation through physical contact w/ an object
4) Radiation: infrared radiation transfers heat between objects NOT in physical contact

22
Q

Colder temperatures cause the hypothalamus to stimulate the release of what hormone and why?

A
  • Stimulate the release of thyroxin
  • Increases metabolic rate to generate heat production
  • Raises body temperature
23
Q

Hotter temperatures cause the hypothalamus to inhibit the release of what hormone and why?

A
  • Inhibits thyroxin release
  • Decreases metabolic rate
  • Reduces heat production (lower body temp)
24
Q

When the core temperature increases (Tb >Tset-point) what occurs within the body?

A

Decreased heat production:

- Apathy (not activating skeletal muscle as much)

  • Anorexia (decrease in eating behaviors)

Increased heat loss:

- Vasodilation (more blood sent to skin = more heat lost)

- Evaporative heat loss (sweat)

- Insensible heat loss (panting)

25
Q

When the core temperature decreases (Tb < Tset-point) what occurs within the body?

A
  • Increased heat production: shivering and non-shivering thermogenesis
  • Decrease heat loss: vasoconstriction, decrease evaporative heat loss
26
Q

What stimulates the epithelial cells to secrete their fluid for the process of sweating, what are the components of this fluid, and what produces the primary secretion?

A
  • Cholinergic SYMPATHETIC fibers stimulate the epithelial cells
  • Secretory portion produces the primary secretion
  • Similar to plasma (lacks proteins)
  • Mainly water, Na+ and Cl-
27
Q

The postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it releases what NT to what receptor?

A

ACh (cholinergic) to act on a muscarinic receptor (mAChR)

28
Q

What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during low sweat rates?

A
  1. Fluid flow is slow
  2. Lots of reabsorption
  3. Osmotic pressure in duct is low
  4. Most water gets reabsorbed; but the sweat will be high in Na+
29
Q

What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during high sweat rates?

A
  1. Fluid flow is fast
  2. Less reabsorption
  3. Osmotic pressure higher in duct
  4. Less water is reabsorbed, so the sweat is very dilute (lots of water and little Na+)
30
Q

Acclimatization to hot enviornments takes how long and what occurs?

A
  • 1 to 6 weeks exposure to hot weather
  • Increase sweating capacity
31
Q

How does aldosterone affect the primary secretion of sweat and what does it help do?

A
  • Decreases NaCl content in the primary secretion
  • Helps conserve body salt
32
Q

Fever is a controlled increase in what aspect of body temperature?

A

Controlled increase in the hypothalamic set-point

33
Q

What contributes to the increased set-point during a fever?

A
  • Pyrogens like IL-1β
  • Induction of Prostaglandin E2 (major player)
  • Hypothalamic lesions can also lead to increased set-point
34
Q

What occurs to the set-point and body temperature during hyperthermia and hypothermia?

A
  • Set-point remains normal
  • Uncontrolled changes in body temperature
  • Enviornmental stresses excees body’s ability to regulate temperature
35
Q

The hypothalamus has reciprocal connections with what nucleus?

A

Nucleus tractus solitarius

36
Q

What part of the hypothalamus is crucial for sleep induction and what NT does it use?

A
  • Ventrolateral preoptic nucleus (VLPO)
  • GABAergic and inhibits arousal systems
37
Q

How is the lateral hypothalamus involved with sleep?

A
  • Arousal from sleep
  • Release of Orexin an excitatory neuropeptide
38
Q

Narcolepsy is caused by loss of?

A

Orexin from lateral hypothalamus

39
Q

How is the posterior hypothalamus involved in sleep; causes release of what NT from where?

A
  • Controls arousal from sleep, along with the lateral hypothalamus
  • Stimulation of brain arousal systems
  • Production of histamine from tuberomammillary nucleus
40
Q

How many stages of Non-REM sleep and how long is a sleep cycle?

A
  • 3 stages
  • Sleep cycle = 90-120 min.
41
Q

What is the location in the hypothalamus of the central thermoreceptors?

A

Pre-optic and superoptic region of hypothalamus

42
Q

The TRP channels that are thermoreceptors do what when activated?

A
  • Open and allows Na or Ca2+ influx
  • Activation triggers depolarization
43
Q

Why are there visceral thermoreceptors in the gut; what temperature do they detect?

A
  • Detect CORE temperature
  • Food ingested may change body temperature
  • Tells hypothalamus about any possible threats!
44
Q

What are 3 components of non-shivering thermogenesis?

A

1) Hormonal influence: thyroxin and epinephrine
2) Increases food intake: increase metabolism
3) Brown adipose tissue: low efficiency hydrolysis of ATP = lots of heat production

45
Q

Brown adipose tissue used for non-shivering thermogenesis requires activation by?

A

Sympathetics

46
Q

What are the 2 types of evaporative heat loss?

A
  1. Insensible (respiratory)
  2. Sweating (controlled)
47
Q

The primary secretion during sweating is high in what; what occurs as it moves into the duct of the sweat gland?

A
  • Primary secretion is high in water, sodium and chloride; lacks proteins; similar to plasma
  • Water. sodium and chloride are reabsorbed (taken back to the blood) in the duct of the sweat gland