Stress While escaping from Fire

Fight and Flight Response

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What is the stimulus ?

- What is the stimulus ?

A biologic stimulus is any external change in the environment that can be detected by an organism. The ability to respond to a stimulus is called irritability and is a necessary condition for life.

- The stimulus in this case is seeing the fire.

Our journey through the body

We will begin our journey through the body from the eyes of a person who is running away from a fire. When our body senses danger it responds by creating a fight or flight response. We will look at all the steps in this response.


Sensory Nerves in the eye sends information to the brain(the amygdala). The amygdala sends a electric message to the hypothalamus. the hypothalamus will do two things, the first is transmit a chemical signal to the pituitary gland which will release another chemical (ACTH) into the bloodstream. The second thing is transmit a nerve signal down the spinal cord. The chemical messenger (ACTH) and nerve impulse will travel to the same place, the adrenal gland.


First the Polarization of the neuron's membrane which are Sodium is on the outside, and potassium is on the inside. Being polarized means that the electrical charge on the outside of the membrane is positive while the electrical charge on the inside of the membrane is negative. The outside of the cell contains excess sodium ions (Na+); the inside of the cell contains excess potassium ions (K+). (Ions are atoms of an element with a positive or negative charge).

if cell membranes allow ions to cross the Na+ and K+ in fact, move back and forth across the membrane. However, Mother Nature thought of everything. There are Na+/K+ pumps on the membrane that pump the Na+ back outside and the K+ back inside. The charge of an ion inhibits membrane permeability (that is, makes it difficult for other things to cross the membrane).


Then the Resting potential gives the neuron a break. When the neuron is inactive and polarized, it's said to be at its resting potential.

Then the Action potential is created by Sodium ions move inside the membrane. The gated ion channels on the resting neuron's membrane open suddenly and allow the Na+ that was on the outside of the membrane to go rushing into the cell. Well, after more positive ions go charging inside the membrane, the inside becomes positive, as well; polarization is removed and the threshold is reached. After the stimulus goes above the threshold level, more gated ion channels open and allow more Na+ inside the cell. This causes complete depolarization of the neuron and an action potential is created.

After the inside of the cell becomes flooded with Na+, the gated ion channels on the inside of the membrane open to allow the K+ to move to the outside of the membrane. With K+ moving to the outside, the membrane's repolarization restores electrical balance, although it's opposite of the initial polarized membrane that had Na+ on the outside and K+ on the inside. Just after the K+ gates open, the Na+ gates close; otherwise, the membrane couldn't repolarize. So when the K+ gates finally close, the neuron has slightly more K+ on the outside than it has Na+ on the inside. This causes the membrane potential to drop slightly lower than the resting potential, and the membrane is said to be hyperpolarized because it has a greater potential. After the impulse has traveled through the neuron, the action potential is over, and the cell membrane returns to normal (that is, the resting potential).

Then the Refractory period occur when the Na+ and K+ are returned to their original sides: Na+ on the outside and K+ on the inside.

In resting potential and action potential a gap called a synapse or synaptic cleft separates the axon of one neuron and the dendrites of the next neuron. Neurons don't touch. The signal must traverse the synapse to continue on its path through the nervous system. Electrical conduction carries an impulse across synapses in the brain, but in other parts of the body, impulses are carried across synapses when these chemical changes occur (Calcium gates open, Releasing a neurotransmitter, The neurotransmitter binds with receptors on the neuron and lastly excitation or inhibition of the membrane occurs.)


The ACTH reaches the endocrine gland and it result in many other chemical reactions happening that will lead to the release of the stress hormone called cortisol. At the same time Nerve signals activate the release of epinephrine into the bloodstream which will interact with various target cells.

Cortisol will travel through the bloodstream to several cell types. It will initiate signaling cascades in these cells resulting in an increase in blood pressure, an increase in blood sugar levels, and suppression of the immune system.

Epinephrin travels through the blood to the liver then the liver will release sugar into the blood. The newly-formed glucose is transported out of the liver cell and it enters the bloodstream. This glucose will provide an immediate source of energy for muscle cells.

In the skin,

epinephrine binds to a receptor on an erector pilli smooth muscle cell. This causes a signaling cascade that contracts the muscle. Epinephrine also contracts specific types of muscle cells below the surface of the skin, causing beads of perspiration and raised hairs at the surface.

On the surface of sweat glands,

epinephrine binds to Alpha-1 adrenergic receptors, triggering a signaling cascade that contracts the gland, squeezing sweat to the skin's surface.

In the lungs,

epinephrine binds to receptors on smooth muscle cells wrapped around the bronchioles. This causes the muscles to relax, dilating the bronchioles and allowing more oxygen into the blood (to enable increased respiration).


Epinephrine can have opposite effects (contraction, or relaxation) depending on the type of signaling machinery present in the cell. Docking on alpha-1 adrenergic receptors on the erector pilli muscle causes contraction, while docking on beta-2 adrenergic receptors on bronchiole muscle cells cause relaxation.

In the heart,

At the sino-atrial node of the heart, epinephrine stimulates pace maker cells to beat faster. This increases the rate at which other chemical signals, glucose and oxygen are circulated to the cells that need them. As a result, energy and messenger molecules are circulated throughout the body at a faster rate.

Done By:

Nada Alhatheli - Fatima Yousef - Rowdha Sembakh