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Stress and the Brain > Homeostasis and Hypothalamus > Flashcards

Homeostasis and Hypothalamus Flashcards

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1
Q

Motivation?

A

1)
- Source of goal driven behavior
* Motives generally stem from needs and desires
2) Motivations may be conscious or unconscious
* Drives may stem from needs that are beyond conscious awareness

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2
Q

Drive-Reduction Theory

A
  • Behaviors are motivated by the drive to maintain biological homeostasis
  • When a biological need arises, we feel an internal tension (for instance, hunger).
  • The internal tension motivates a need to restore balance.
    4) Behavior is directed to fulfill the need
  • The goal is to get back to balance
  • So we eat when we’re hungry. Or find warmth when we’re cold.
    5) Many different drives
  • Survival: Hunger, thirst, warmth
  • Reproduction: Sex, Affection
  • Social: Affiliation, Approval, Self-Esteem
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3
Q

Homeostasis?

A
  • maintaining the body’s equilibrium
  • An organism’s ability to maintain the internal systems required to stay alive
    EX. : * Breathing to maintain oxygen levels
  • Eating to maintain energy and nutrient requirements
  • Maintaining proper levels of glucose for energy
  • Maintaining proper electrolytes for organ function
  • Urinating and defecating to rid body of waste
  • Immune activity to eliminate infectious agents
  • Maintaining proper body temp, blood pressure, water balance, etc…
    Homeostasis is a “balancing act” between many different system
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4
Q

Maslow’s Hierarchy of Needs

A
  • People have multiple sources of motivation * Biological, Social, Personal
  • Higher needs can only be satisfied if lower needs are met first * #1) Physiological needs (food, water)
  • Maintain homeostasis. Stay alive….
  • 2) Safety needs (shelter, survival)
  • 3) Social needs (love, friends, approval)
  • 4) Esteem needs (feelings of self-worth)
  • 5) Self-actualization (becoming our ideal self)
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5
Q

Hypothalamus function

A

Regulates the body’s homeostasis
* Allows brain to control hormones in the body
* Connected to pituitary and pineal glands
Hypothalamus regulates several biological drives:
* Hunger, Thirst, Sleep
* Body temp, blood pressure
* Sex desire
* Reward motivation
* Stress responses:
1) ”Fight or Flight” (sympathetic)
2) Metabolic change (HPA axis)

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6
Q

Hypothalamus and hunger

A

1) Hunger and body weight regulated by hypothalamus and pituitary
* Hypothalamus detects markers of the body’s energy stores * Levels of fats and sugars available for metabolism
* When energy stores are low…
Triggers release of the hormone ghrelin which motivates eating behavior
* When energy stores are high…
Triggers release of the hormone leptin which reduces appetite

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7
Q

Hypothalamus also regulates….

A

1) Basal metabolism
* How the body uses and burns calories
2) Set point
* Body’s naturally preferred weight range
3) Genetic differences also impact basal metabolism and set point
* Body shape, distribution of fat cells,

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8
Q

Hypothalamus and sexual drives

A

Sexual drives are regulated by the hypothalamus
1) In both males and females hypothalamus regulates GnRh
* Gonadotropin releasing hormone which regulates sex hormones
2) Regulates sex hormones
* Testosterone, estrogen, progesterone
* “Bonding” hormones like oxytocin as well
3) Regulates menstrual cycles in women
4) Involved in sexual desire
* Testosterone increases sexual desire in both men and women
5) Involved in sexual orientation
* Differences in hypothalamus between gay and straight men

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9
Q

A Hierarchy of Homeostatic Controls

A

1) Organs and their local reflexes
* Internal organs have built-in reflexes
2) Autonomic Nervous System and Endocrine System
* Two pathways for CNS to communicate with internal organs
3) Brainstem regulation
* Able to regulate outputs of the ANS
4) Hypothalamic regulation
* Can regulate brainstems control of ANS
* Can regulate endocrine system
5) Higher brain areas
* Regulation from areas involved in attention, memory, emotion
* May involve conscious and unconscious activity

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10
Q

Local reflex loops

A

Organs send/receive info to spinal cord creating reflex loops
* Organ and spinal cord can adapt organ functioning to local needs

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11
Q

Which organ detects glucose levels?

A

pancreas

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12
Q

Blood Glucose

A
  • Must regulate levels of glucose available to the body
  • Releases insulin when glucose levels are too high (extra glucose get stored)
  • Releases glucagon when glucose level are too low (to free up stored glucose)
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13
Q

Organs of Homeostatic Organization

A

1) Water regulation
* Proper hydration is needed to transport material throughout the body
* Kidneys monitor and regulate levels of water in the blood
* When water levels are low, kidney reduces amount of water in urine to keep the blood water levels higher
2) Thermoregulation
* Must regulate body temperature for optimal metabolism
* The biochemical reactions (like enzyme activity) impact by temperature
* When too hot, sweat glands activated to cool your body
* When too cold, muscles shiver to raise body temperature
* Getting “goosebumps” is an example of organ reflex

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14
Q

Why people are getting “goosebumps”?

A

1) Getting “goosebumps” when you’re cold is a homeostatic reflex
2) Pilomotor reflex
* Tiny muscles attached to hair follicles contract in response to the cold
* An evolutionary leftover. For mammals with fur, the hair standing up may trap warm air around the body
3) The pilomotor reflex can also be triggered by activation sympathetic nervous system
4) Some individuals can consciously initiate having goosebumps

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15
Q

Common facts (misunderstandings) about the spinal cord

A

1) Spinal cord doesn’t run through middle of the spine
* Runs through a space at the back of the backbone (Vertebral foramen)
2) Spinal cord does not run all the way down to the bottom of the spine
* Spinal cord ends at the lumbar area
3) The center of the spinal cord is filled with grey matter (cell bodies) and surrounded by white matter (axons, nerves)

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16
Q

Somatic vs Autonomic Nervous System

A

Somatic:
1) Conscious and Voluntary
2) “Skeletal Nervous System”
3) Sensory and Motor neurons:
* Sensory nerves send info to CNS (spinal cord and brain)
* Motor nerves from CNS directly connects to a specific set of muscle fibers
Autonomic:
1) Unconscious and involuntary
2) Sympathetic and Parasympathetic:
* Also has sensory and motor nerves
* Sensory info from internal organs sent to brainstem. Remains unconscious
* Chain of two motor neurons (preganglionic, postganglionic)
* Axons are not well myelinated. Conducts signals slowly.

17
Q

Somatic vs. Autonomic Nervous System

A

Somatic Nervous System - motor neuron directly connects to muscle.
Autonomic Nervous System – motor neuron connects to a ganglia. Ganglia “relays” signal to the muscle

18
Q

Autonomic Nervous System function

A

1) Responsible for monitoring the internal organs and regulating their activity
2) Innervates (supply with nerves) cardiac muscle, smooth muscle, and glands
* Note that internal organs often contain “smooth muscle”
* Stomach, intestines, bladder, blood vessels, kidneys, etc
3) Regulates metabolic functions and physiology
* Heart rate, respiration, blood pressure, digestion, urination, glucose storage/use, body temperature, etc.
4) Autonomic nervous system contains sensory and motor neurons (like the somatic nervous system)

19
Q

Autonomic Nervous System Control? What are the 3 main divisions?

A

1) The ANS regulates internal organs
* The organs send signals to the ANS thru sensory nerves and hormones
* The ANS responds with motor nerves and hormones to alter activity of the internal organs
2) Three Main Divisions:
* Sympathetic Nervous System (“Fight or Flight”)
* Parasympathetic Nervous System (“Rest and digest”)
* Enteric Nervous System (“food and feces”):
1. Semi-autonomous system involved in digestion.
2. Some debate over whether it’s part of the autonomic system or digestive system

20
Q

what is Negative Feedback Loop?

A

A system of regulation where product of a reaction reduces the
occurrence of the reaction.
* The output of the system inhibits the system.
Negative feedback loops can be used to maintain a set-point
e.g. If the thermostat is set to 75 degrees
* The heater turn on when the room is too cold (make more heat).
* The heater turns off when the room gets too hot (make less heat).

21
Q

Negative Feedback Loops : Regulation of blood pressure

A

1) If blood pressure is too high…
* Baroreceptors fire more —-> cardiac output decreases & blood vessels dilate —-> blood pressure decreases
2) If blood pressure is too low
* Baroreceptors fire less —-> cardiac output increases & blood vessels constrict —-> blood pressure increases

22
Q

Would you ever want a positive feedback loop? Its benefit?

A

Positive feedback loops
* The product of a reaction encourages more of the reaction
* Positive feedback are useful if we want to amplify a reaction
Examples:
1) Blood clotting
* Platelets release clotting factors that attract more platelets
2) Lactation
* Breastfeeding increases milk production. Milk supply increases with more
breastfeeding.
3) Childbirth
* Oxytocin causes contractions. Contractions cause the release of oxytocin. Increasing the strength of contractions (to push the baby out)

23
Q

Why panic can make you pee?

A

1) The fight or flight should inhibit urination
* Sympathetic nervous system closes sphincter and relaxes bladder walls (to hold more urine)
* Parasympathetic nervous system opens sphincter and constricts bladder walls (to release)
2) But, a disorganized fear response (panic) may activate BOTH the sympathetic and parasympathetic systems
* They are two separate systems that mostly act to counter each other.
* So… a large sympathetic response prepares a large parasympathetic counter response
* Alternating signals to the different bladder muscles could lead to increased bladder pressure … and once the threshold is crossed … maybe difficult to stop.

24
Q

Components of the ANS

A

1) Descending nerve fibers from hypothalamus and brain stem

  • Descend through the intermediolateral cell column of the spinal cord
    2) Preganglionic nerve fibers
  • Extend from spinal cord to different autonomic ganglia
    3) Ganglia
  • Ganglia relay signals back and forth between internal organs and spinal cord
  • Densely packed and interconnected neurons allows ganglia to act as “mini-brains”
  • Ganglia involved in “local reflex loops”
    4) Postganglionic nerve fibers
  • Travel from the ganglia to their target organs
    5) Neuroeffector junctions
  • Place where the postganglionic nerves alter activity of the organ
  • Similar to synapse. Activity altered by neurotransmitter release
25
Q

Sympathetic vs. Parasympathetic Divisions

A

Sympathetic Nervous System:
* Also called the thoracolumbar division
* The nerves project from the middle of spine
* Thoracic region
* Sympathetic ganglia connected in a “sympathetic chain” * Sympathetic chain located next to spine
* Short preganglionic nerves
* Long postganglionic nerves
* Postganglionic nerves have many branches - Effects many organs.
Parasympathetic Nervous System:
* Also called the craniosacral division
* Nerves project from top and bottom of spine
* Cranial nerves and the sacral nerves
* Parasympathetic ganglia are not connected
* Parasympathetic ganglia located in the internal organs
* Long preganglionic nerves: Release acetylcholine
* Short postganglionic nerves: Release acetylcholine
* Postganglionic nerves have few branches: Effects are localized to specific organs

26
Q

Role of Hypothalamus

A

The Hypothalamus - major commander of autonomic nervous system.
1) Receives sensory inputs from the body
* Peripheral nervous system (somatic and autonomic)
2) Regulates activity of the brainstem and autonomic nervous system
* Direct control of sympathetic and parasympathetic systems
3) Controls endocrine function via the pituitary gland
* Also via the pineal gland
4) Can directly influence body posture and movement
* Able to trigger defensive reflexes
5) Receives regulatory inputs from higher brain areas
* Amygdala, hippocampus, sensory cortex, frontal lobes…

27
Q

Decerebrate?

A

Decerebrate – to surgically disconnect the cerebrum from lower brain areas (cut top part of brain from bottom)

28
Q

Early Research on Hypothalamus and Homeostasis (3 kinds)

A

A) Cortex disconnected, hypothalamus intact
- Able to sustain homeostasis
- Able to land on feet
- Displayed “sham rage”
1) Threat posture, hissing, attempts to bite and scratch.
2) Reaction was stereotyped. Not directed at a specific target.
B) Hypothalamus partially severed (keeps us alive and maintains balance)
- Sham rage partially displayed
- Usually able to sustain homeostasis
C) Hypothalamus disconnected from brain stem
- No longer showed sham rage
- Difficult to keep animal alive

29
Q

What are the Hypothalamic Nuclei and their functions?

A

1) Autonomic function
* Regulate the ANS
2) Endocrine function
* Control the release of hormones
3) Skeletal motor function
* Regulate posture and movement

30
Q

Paraventricular Nucleus (PVN)?

A

The Paraventricular Nucleus (PVN) of the Hypothalamus
* Regulates the stress response
* Controls both sympathetic activation and HPA axis

31
Q

2 Paths of Stress: Autonomic vs Endocrine functions of PVN?

A

Autonomic functions:
* Dorsal and ventral projections from PVN
* Projects to brain stem and spinal cord
* Regulates sympathetic/parasympathetic activity
Endocrine functions:
* Medial and lateral projections from PVN
* Connects to pituitary
* Regulates the HPA axis

32
Q

Functions of Cortisol

A

Cortisol is called a stress hormone, but is needed for normal homeostatic functioning (regulate all metabolic functions and reduces inflammation in the body)
* Has a wide range of effects
* Cortisol does not trigger a stress response. It regulates the stress response
* The presence of cortisol by itself should not be considered a sign of stress, but regulatory hormone even when not stressed

33
Q

HPA Axis (Endocrine regulation) cortisol

A

Cortisol used to regulate many systems:
* Energy use
* Energy stores
* Cardiovascular functioning
* Immune functioning
Normal daily cycles:
* Cortisol isn’t only involved in stress
* But increases beyond normal levels to maintain stress responses
Levels of cortisol regulated by multiple negative feedback systems:
* When cortisol levels get high, less cortisol is produced
* Important to regulate because too much cortisol can have negative effects

34
Q

Regulation of HPA

A

1) Negative Feedback Systems
* Cortisol can pass the blood brain barrier
* PVN detects cortisol (Decreases CRF release)
* Pituitary gland detects cortisol (Decreases ACTH release)
2) Amygdala
* Amygdala activation increases HPA activity
3) Hippocampus
* Can both increase and decrease HPA activity…
* But… plays a major role in decreasing HPA activity

35
Q

Another Stress Hormone Beta-Endorphin?

A
  • An endogenous opioid
  • When the HPA axis is active, CRH from hypothalamus stimulates release of ACTH from pituitary
  • But… CRH also stimulates the release of beta-endorphins
  • The endorphins have an analgesic (pain relieving) effect and may
    promote positive mood
  • Beta-endorphin maybe released in preparation for potential pain or injury

Stress and the Brain (20 decks)

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