Class 4: Stress

Question 1

Define Stress.

Answer 1

The bodies response to internal or external pressure

Question 2

Define Stressor.

Answer 2

Stimuli that challenge the bodies homeostasis and cause activation of the stress response. (Physical or Psychological)

Question 3

Why would stress have evolved at all?

Answer 3

Stress for animals tend to be short-lived and caused in scenarios that are life or death so the overdrive is justified.

Question 4

What are the two things the stress response accomplishes?

Answer 4

1. Temporarily puts body and brain into ‘overdrive’ in order to deal with the stressor.
2. It suspends other functions so that it can conserve energy

Question 5

Who is the Godfather of Stress and what did he do?

Answer 5

Hans Selye, he described a reaction to stress called general adaptation syndrome (GAS) which proposed:

• the same general physiological reaction is mounted for all types of stressors
• physiologically there is no distinction between stressors (big or small)

Question 6

What is the three-stage model that the body goes through according to GAS?

Answer 6

General adaptation syndrome contains the phases:

1. Alarm Phase : Initiates fight or flight (SNS)
2. Resistance Phase : Physiological adaptions take place to help cope with prolonged stressors (HPA axis/Cortisol Release)
3. Exhaustion Phase : Physiological resources are depleted, diseases can begin to appear.

Question 7

What are the two separate pathways of the stress response?

Answer 7

1. Sympatho-adrenomedullary axis (SAM axis)

2. Hypothalamic-pituitary-adrenal axis (HPA axis)

Question 8

Describe the SAM axis of the stress response.

Answer 8

The Sympathomedullary pathway is the fast pathway which mediates the initial “alarm” phase of the stress response
-Activates the SNS which leads to release of epinephrine and norepinephrine

Question 9

Describe the HPA axis ‘pathway’ of the stress response and which phase it is responsible for

Answer 9

The slow pathway which mediates the “resistance” phase

Question 10

What are the two steps in SAM activation?

Answer 10

1. Neural circuits in the hypothalamus project to the spinal cord where they synapse and activate neurons of the SNS
2. SNS neurons project to the adrenal glands (i.e adrenal medulla, which releases catecholamines epi and nEpi)

Question 11

What are the Epi and nEpi (ligands) receptors called?

Answer 11

Adrenergic Receptors

Question 12

What are the three steps in HPA axis activation?

Answer 12

1. Hypothalamus releases corticotropin-releasing hormone (CRH) into anterior pituitary (AP)
2. CRH stimulates the AP to release adrenocorticotropic hormone (ACTH) into general circulation
3. ACTH stimulates the release of cortisol from the adrenal cortex

Question 13

During which phase of the stress response is cortisol released?

Answer 13

It is released during the resistance phase for adaptation.

Question 14

What are the two properties of cortisol?

Answer 14

1. Turns off stress response
2. Helps body adapt to continuing stressor by breaking down own tissue to produce energy and shutting off immune system, etc

Question 15

Where are the catecholamines and glucocorticoid receptors located?

Answer 15

The catecholamines (Epi and nEpi) and glucocorticoid (steroid cortisol) receptors are located throughout the body

Question 16

What does an activated steroid cortisol receptor in the hypothalamus (Glucocorticoid receptor GR) do?

Answer 16

It decreases the release of CRH

Question 17

What are 3 metabolic effects of Cortisol?

Answer 17

1. Decrease bone & connectivity tissue
2. Increase breakdown of lean body fat
3. Stimulation of liver to produce and release more glucose to increase blood sugar

Question 18

Under normal conditions, what part of the brain is in control?

Answer 18

The PFC has top-down control over lower brain areas (i.e the limbic system, basal ganglia, etc)

Question 19

Under stress conditions, what part of the brain is in control?

Answer 19

When stressed the PFC’s inhibitory projections to lower areas are shut down which allows the amygdala and basal ganglia to exert bottom-up control.

Question 20

How does stress “shut down” the the PFC?

Answer 20

When stressed DA and NE are released into the PFC by the brainstem activating their post-synaptic DA and NE receptors which in turn hyperpolarization of the PFC

Question 21

How does the Stress Response get shut down?

Answer 21

When cortisol level get too high the:

• hippocampus and hypothalamus work to reduce CRH
• anterior pituitary secretes less ACTH

Question 22

How does Chronic Stress ‘break’ the shutdown of the stress response?

Answer 22

Chronic cortisol release can lead to hippocampus less responsive to it causing to not know when to reduce cortisol levels