14. Temperature and Thirst PDF

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Temperature and ThirstThe Science of Motivation:understanding behavioural causation“Behavior is shaped and maintained by its consequences ““Mentalistic terms associated with reinforcers and with the states in which reinforcers are effective make it difficult to spot functional relations”. - (B.Skinn...

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Temperature and Thirst The Science of Motivation: understanding behavioural causation “Behavior is shaped and maintained by its consequences “ “Mentalistic terms associated with reinforcers and with the states in which reinforcers are effective make it difficult to spot functional relations”. - (B.F. Skinner, About Behaviorism, 1947)

Thorndike’s Law of Readiness -

Learning is motivated by an internal state.

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Carl Hull (1884 -1952) proposed that a reinforcer supports learning because it alleviates an internal state of deprivation -

e.g., food is reinforcing to an organism if and because it alleviates hunger state

Drive reduction theories -

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Emphasis on Homeostasis -

Physiological systems at equilibrium by constantly adjusting to change.

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There is some sort of optimal level of hunger or temperature or water level. Imbalance in homeostasis creates ‘arousal’ that initiates action.

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The goal is to decrease the ‘arousal’

Minimise difference between the optimum ‘set-point’ and ‘actual point’ -

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‘Actual point’ should be close to the ‘set point’. (set point = ideal homeostasis state)

Walter B Cannon 1871-1945 studied wounded soldiers during the war (how to treat state of shock when losing blood ‘acutely’)

Homeostasis and negative feedback Walter cannon 1871-1945 -

Early ideas about motivation applied the idea of negative feedback developed in physical systems (like thermostats) to behaviour

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Negative feedback = a process whereby the effect produced by an action serves to diminish or terminate that action. -

An action that produces the opposite reaction. (temp is hot -> u turn off the heater, the temp gets cold, now u have to turn it back on?)

Components of a homeostatic system 1. System variable: a. variable controlled by systems (e.g., temp, hydration, nutrients) 2. Set-point a.

the desired level of a variable

3. Sensor a.

a mechanism for measuring the variable

4. Effector system a. behavioural /physiological mechanism(s) to change variable and restore homeostasis (ex. Thermometer or like drinking water)

The principles of Homeostasis A number of physiological variables must be maintained within narrow limits for the body to function: -

Temperature

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Hydration - Drinking

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Nutrients - Feeding

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Humans (and all other endotherms) generate heat by metabolism

Regulation of body temperature -

Sensors -

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we can regulate our body temperature/produce our own heat

Cells in the Preoptic Area of the Hypothalamus -

we have thermal sensors throughout our periphery

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Optic area = the place below the optc track (where it crosses)

The Hypothalamus -

Sensse brain temperature

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controls physiological & behavioural responses to regulate temperature

Too Cold Response to Cold – effector systems -

Metabolism of brown fat (in babies) -

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Fat that produces heat w/ mitochondria

Increased thyroid activity -

(increases metabolism to produce heat

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Constriction of cutaneous blood vessels

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Shivering of muscles

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Reduces the area in which water will eva

Too Hot

Response to Heat – effector systems: -

Accelerated respiration -

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Perspiration -

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Helps lose water Lose water

Dilation of cutaneous vessel -

Evaporation => loose water

Homeostasis and temperature control

Homeostasis and temperature control Thirst and homeostasis -

As water is lost, cellular processes become inefficient and eventually excessive water loss is fatal (systems shut down)

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Fluid loss through evaporation, respiration (H2O), urine and sweating (H2O + salt)

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2/3 of body water is inside cells, the remaining 1/3 is extracellular -

Direct water loss occurs primarily from this extracellular compartment

Intracellular and intravascular (plasma) fluid volume and composition must be kept precise limits (0.19%) -

Extracellular fluid consists mainly of water and salts (esp. Sodium chloride) Intracellular – relative concentration solutes between intracellular and interstitial compartments (isotonic)

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Compartments are separated by semipermeable membranes that water can pass through (back and forth) -

Salt cant pass back and forth cause the molecule is too big so it need salt channels to do so

Osmometric thirst/cellular dehydration: Isotonic -> 0.19% set point for perfect level of salt/water ratio aka hydrated. Hypertonic -> too much salt (relative to …)

Hypotonic -> too little salt (relative to …) 1. If u lose water from intravascular plasma (from bloodstream) a. U have higher concentration of salt than set point (aka its hypertonic to solution b) 2. Now you attract water through semipermeable membranes from interstitial (between cells) a. Water goes from interstitial (between cells) to intravascular (blood plasma). 3. If interstitial (between cells) becomes hypertonic, it takes in water from intracellular (inside cells) a. THis is bad bc cells don't function w/o hydration. -

Microinjection of small amounts of NaCl into certain brain areas (like intracellular) stimulates drinking (proportional to amount of salt injected )(Gilman, 1937 )

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The increase in salt % (due to water loss) = osmotic imbalance between the extra- and the intra- cellular compartments -

Changes in osmolarity are monitored by cells (osmoreceptors) in -> Organum Vasculosum of the Lamina Terminalis (OVLT) at the base of the brain

Hypovolemic thirst -

Loss of extracellular fluid (ECL) levels can induce thirst in the absence of osmotic (salt) changes (bleeding or sweating)

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The thirst stimulus arises from 2 systems which measure blood pressure

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In the kidneys

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In the heart

This combined information stimulated brain sites which leads to drinking

!!! Angiotensin and drinking -

Hypovolemia (aka low blood pressure -> therefore low water pressure) causes the release of the enzyme renin from the kidneys -

Renin converts a blood borne molecule angiotensinogen into a hormone called angiotensin 1 and 2

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If you lose blood volume cause ur sweating a lot (water and salt loss), renin will release from kidneys and convert angiotensinogen to angiotensin 1 and 2.

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Hormone -> Angiotensin 1 and 2 does: to retain water and salt + gain more water and salt. -

Stimulates pituitary and kidneys

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Increase blood pressure by vasoconstriction

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Salt appetite

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Water appetite

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To release hormone to conserve salt and water

Stimulates drinking by binding on receptors in the Subfornical organ (SFO)

Receptors that regulate drink and behavior)

Optogenetically interrogating motivational (SFA) circuits: -

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Atria of heart contain neurons that detect stretch (baroreceptors)

encourage sodium into the cell

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Volume of return blood through veins detected by baroreceptors

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Information from baroreceptors to nucleus of the solitary tract

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Information to median preoptic area

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They are not thirsty at all, then when the light is turned on, they run to the water and drink it straight away -

They drink even more if they were just naturally thirsty (VERY strong water appetite)

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Atrial baroreceptor

Light gated salt channels => Making neurons in rat brains react to light to

Specifically drinking (not eating) so must be making them thirsty

Volumetric thirst = hypovolemic thirst

The Homeostatic negative feedback thirst control system

Thirst as a homeostatic motivation 3 routes that lead to drinking behaviour System variable: Hydration 1. Set-point: optimal fluid balance (a number of ‘blood pressure’) 2. Sensors: osmoreceptors in OVLT of brain, baroreceptors in heart and kidneys 3. Effector: Drinking, salt appetite & water conservation measures...