Lecture 7: Hypothalamus Flashcards
What happens to core temperature, thermal set point, and metabolic rate during sleep?
- Sleep accompanied by lowering of the thermal set point
- Metabolic rate reduces
- Heat loss increases (vasodilation/sweat)
- Core temperature decreases
Exercise elevates what aspect of your body temperature?
Elevates core temperature
High intensity, long-duration exercise raises _______.
Set-point
Core temperature follows a circadian rhythm, when is it lowest and highest?
- Lowest between 3-6 AM
- Peaks between 3-6 PM
What nucleus governs the circadian rhythm of core body temperature?
Suprachiasmatic nucleus of anterior hypothalamus
During what reproductive phase do you see a 0.5 °C increase in body temperature?
Post-ovulatory phase
During what reproductive phase do you see a 0.3-0.5 °C increase in body temperature?
Ovulation
Cold temperature stimulate the release of what hormone, why?
- TRH
- Thyroxine increases cellular metabolic rate
Which hormones increase cellular metabolic rate?
- Thyroxine
- Epinephrine
What factors influence thermoregulation in newborns?
- 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
What happens to thermosensation, heat dissipation, and metabolic rate as we age?
- Progressive decline in thermosensation w/ older age
- Reduced metabolic rate
- Reduce metabolic potential w/ diminished muscle mass
- Reduced ability to dissipate heat
Thermoreceptors for hot and cold sensations are made up of what kind of fibers?
- Heat = C-fiber
- Cold = C-fiber and Aδ fibers
What are the TRP channels for hot and cold sensation?
Cold = TRPA1 and TRPM8
Hot = TRPV1 (V = Vanilloid = capsaicin (hot peppers))
What kind of thermoreceptors found on the skin, characteristics, and which are more abundant?
- 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)
What is the heat responsive portion of the hypothalamus and what is its function?
- Anterior hypothalamic nucleus and preoptic nucleus
- Heat loss behaviors
What is the cool responsive portion of the hypothalamus and what is its function?
- Posterior hypothalamus
- Heat production behaviors
How does temperature affect neurons of the hypothalamus and are there more heat or cold sensitive neurons?
- 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
What are 3 ways we can generate heat?
- Shivering (dorsomedial posterior hypothalamus)
- Voluntary muscle activity (running, jumping, rubbing) via cortex
- Non-shivering thermogenesis (hormones, eating, brown adipose)
What part of the hypothalamus induces shivering and how?
Dorsomedial posterior hypothalamus increases motorneuron excitation
Brown adipose is abundant in who and what is it responsible for; stimulated by what part of the ANS?
- 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!
What are the 4 ways to dissipate heat and how does each work?
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
Colder temperatures cause the hypothalamus to stimulate the release of what hormone and why?
- Stimulate the release of thyroxin
- Increases metabolic rate to generate heat production
- Raises body temperature
Hotter temperatures cause the hypothalamus to inhibit the release of what hormone and why?
- Inhibits thyroxin release
- Decreases metabolic rate
- Reduces heat production (lower body temp)
When the core temperature increases (Tb >Tset-point) what occurs within the body?
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)
When the core temperature decreases (Tb < Tset-point) what occurs within the body?
- Increased heat production: shivering and non-shivering thermogenesis
- Decrease heat loss: vasoconstriction, decrease evaporative heat loss
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?
- Cholinergic SYMPATHETIC fibers stimulate the epithelial cells
- Secretory portion produces the primary secretion
- Similar to plasma (lacks proteins)
- Mainly water, Na+ and Cl-
The postganglionic neuron for sweat gland innervation differs from other sympathetic postganglionic neurons in that it releases what NT to what receptor?
ACh (cholinergic) to act on a muscarinic receptor (mAChR)
What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during low sweat rates?
- Fluid flow is slow
- Lots of reabsorption
- Osmotic pressure in duct is low
- Most water gets reabsorbed; but the sweat will be high in Na+
What is fluid flow, reabsorption, osmotic pressure, and the reabsorption of water like during high sweat rates?
- Fluid flow is fast
- Less reabsorption
- Osmotic pressure higher in duct
- Less water is reabsorbed, so the sweat is very dilute (lots of water and little Na+)
Acclimatization to hot enviornments takes how long and what occurs?
- 1 to 6 weeks exposure to hot weather
- Increase sweating capacity
How does aldosterone affect the primary secretion of sweat and what does it help do?
- Decreases NaCl content in the primary secretion
- Helps conserve body salt
Fever is a controlled increase in what aspect of body temperature?
Controlled increase in the hypothalamic set-point
What contributes to the increased set-point during a fever?
- Pyrogens like IL-1β
- Induction of Prostaglandin E2 (major player)
- Hypothalamic lesions can also lead to increased set-point
What occurs to the set-point and body temperature during hyperthermia and hypothermia?
- Set-point remains normal
- Uncontrolled changes in body temperature
- Enviornmental stresses excees body’s ability to regulate temperature
The hypothalamus has reciprocal connections with what nucleus?
Nucleus tractus solitarius
What part of the hypothalamus is crucial for sleep induction and what NT does it use?
- Ventrolateral preoptic nucleus (VLPO)
- GABAergic and inhibits arousal systems
How is the lateral hypothalamus involved with sleep?
- Arousal from sleep
- Release of Orexin an excitatory neuropeptide
Narcolepsy is caused by loss of?
Orexin from lateral hypothalamus
How is the posterior hypothalamus involved in sleep; causes release of what NT from where?
- Controls arousal from sleep, along with the lateral hypothalamus
- Stimulation of brain arousal systems
- Production of histamine from tuberomammillary nucleus
How many stages of Non-REM sleep and how long is a sleep cycle?
- 3 stages
- Sleep cycle = 90-120 min.
What is the location in the hypothalamus of the central thermoreceptors?
Pre-optic and superoptic region of hypothalamus
The TRP channels that are thermoreceptors do what when activated?
- Open and allows Na or Ca2+ influx
- Activation triggers depolarization
Why are there visceral thermoreceptors in the gut; what temperature do they detect?
- Detect CORE temperature
- Food ingested may change body temperature
- Tells hypothalamus about any possible threats!
What are 3 components of non-shivering thermogenesis?
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
Brown adipose tissue used for non-shivering thermogenesis requires activation by?
Sympathetics
What are the 2 types of evaporative heat loss?
- Insensible (respiratory)
- Sweating (controlled)
The primary secretion during sweating is high in what; what occurs as it moves into the duct of the sweat gland?
- 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
