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42 Cards in this Set

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What detects temperature
on the body surface?
Somatosensory receptors.

Located all over body with lesser number in mouth and nasal cavity.
What receptors are responsible for the regulation of body temperature?
Central Thermoreceptors
Where are the Central Thermoreceptors located?
Central Thermoreceptors are located in the Hypothalamus and spinal cord.

Important for regulation of body temperature.
What are the most numerous type of Thermoreceptors?
Cold receptros are 3-10 times more numerous than warm receptors.
Where is temperature sensitivity the highest?

The lowest?
Temp sensitivity is highest on the glabrous skin of the hand.

It is lowest on the back and back of legs.
How do warm and cold receptors respond to changes in temperature?
2 ways receptors respond:

1. A TONIC component - where firiing rate may increase or decrease depending on the initial temperature.

2. A PHASIC component
- will always increase in response to changes in temperature
Are the direct physical effects of temperature thought to be the cause of the change in firing rate?
NO!

Direct physical effects (thermal exapansion, contraction, etc) arenot thought to be the cause of the receptor's firing rate.

Firing is thought to be due to changes in the receptors METABOLIC RATE.
Cold receptors are innervated by:
Small, Myelinated, a-delta fibers.
Describe the Phasic firing of COLD receptors.
The PHASIC firing of COLD receptors will always INCREASE in response to decreasing temperature.
Cold receptors that increase firing at temperatures above 45°C make up the phenomenon known as the:
Paradoxical cold response.
Define: Paradoxical Cold Response
Cold receptors that increase firing at temperatures above 45°C make up the phenomenon known as the:
Warm receptors are innervated by:
Unmyelinated C-fibers innervate WARM receptors.

(myelinated, a-delta are for COLD)
Which temperature receptors are distinct from warm and cold receptors?
Thermal Pain Receptors
At what temperatures do Thermal Pain Receptors begin firing?
COLD Pain = 15 Celsius

HEAT Pain = 45 Celsius
How adept are humans at localizing thermal stimuli?
POOR!!

The location of a hot or cold object is determined by touch receptors, not thermal receptors.
What ultimately controls body temperature?
HYPOTHALAMUS!

Controls body heat through autonomic contro of heat loss/production.
What is extremely important in the ability of the body to lose heat to the surroundings?
SKIN TEMP
When Skin Temp > Surroundings = _____

When Skin Temp < Surroundings = _____
When Skin Temp > Surroundings = Body Loses Heat

When Skin Temp < Surroundings = Body Gains Heat
Is there a truly normal body temperature?
No. The core temperature of healthy individuals ranges from 97 to 99 F.
Why must the body dissipate heat?
Without dissipation, the resting body temperature rises ~1 C/hour

(~10 C/hour during exercise)

Irreversible damages occurs at ~42 C.
Resting individuals would live about FIVE HOURS without heat dissipation.
What part of the Hypothalamus participates in increasing heat production and in heat conservation?
The POSTERIOR Hypothalamus

HOW?
- Constriction of Blood Vessels
- Shivering
What are the two mechanisms the Posterior Hypothalamus uses to conserve body heat?
1. Constriction of Blood Vessels

2. Shivering
A bilateral lesion of the Posterior Hypothalamus results in:
Poikilothermia - inability to regulate one's own body temperature
At what body temperature does irreversible damage begin to take place?
Irreversible damage beings to occur around 42C.
How long can a resting adult live without heat dissipation?
About 5 hours.
What are the steps and structures involved in shivering?
1. Cold signals from the skin and spinal cord --->

2. Dorsomedial part of the POSTERIOR HYPOTHALAMUS normally inhibited by head signals is activated by the cold signals. --->

3. Info sent to ANTERIOR HORN MOTOR Neurons in Spinal Cord --->

4. Muscle tone in INCREASED
How does “Chemical Thermogenesis” occur?
Circulating norepinephrine and epinephrine in the blood raise the rate of metabolism of the cells.
What is the amount of heat produced by "Chemical Thermogenesis" proportional to?
It is proportional to the amount of BROWN FAT present in body.
Chemical Thermogenesis and Shivering are two adaptations considered part of the:
Sympathetic Nervous System
Which hormone is able to increase cell metabolism?
Thyroid Hormone!
Can thyroid hormone help you adjust to a quick drop in the surrounding temperature?
No, thyroid hormone requires several weeks of cold exposure to be fully activated
What is the “set point” determined at the hypothalamus by integrating thermal inputs?
The "set point" is the core temperature where no thermoregulatory effector activity is required.

Similar to setting the temperature in your house.
What brain structure participates in body heat reduction?
ANTERIOR Hypothalamus
A lesion in the Anterior Hypothalamus will result in:
HYPERTHERMIA
What are (4) ways the body can increase heat dissipation?
1. Vasodilation
2. Cholinergic activation of sweat glands
3. Inhibition of heat producing mechanisms
4. Behavioral modifications (!! Most important !!)
Fever is defined as:
Fever: Body temperature outside the normally considered range
2 causes of fever are:
1. Brain abnormalities
2. Toxic substances that effect the temperature regulation centers of the brain.

When exposed to Pyrogens (proteins, breakdown products of proteins, toxins, bacterial toxins) the hypothalamus induces fever by endogenous production of PROSTAGLANDINS.

Pyrogens elevate the thermal "set point"

Asprin inhibits prostaglandin synthesis.
How does asprin reduce fever?
Asprin inhibits prostaglandin synthesis.
How can the Hypothalamus induce fever?
Fever is induced by endogenous production of prostaglandins
What effect do pyrogens have on the brain?
Pyrogens elevate the set point of the Hypothalamus.

When pyrogens are removed, the hypothalamic set point is quickly reset to a new, lower level.
Why would you still feel cold even as your body temperature is rising above its normal level?
The body is trying to reach a new, pyrogen-induced set point that is higher than normal.
Is fever an uncontrolled runaway condition?
No, fever is a controlled function of the body to re-regulate its temperature about a new elevated set point.