One of the most remarkable examples of cell communication is the fight or flight response. When a threat occurs, cells communicate rapidly to elicit physiological responses that help the body handle extraordinary situations. The movie depicts just some of the communication and responses involved in the fight or flight response. Below is a detailed guide to events taking place in the movie.
|An environmental signal travelsinto the brain. In response,
the amygdala, a primitive structure in the brain, fires off
a nerve impulse to the hypothalamus (not shown). The
hypothalamus sends a chemical signal to another part of the
brain called the pituitary gland.
|In the pituitary gland, corticotrope cells release
adrenocorticotropic hormone (ACTH, green molecules) into the
|Simultaneously, nerve impulses travel from the hypothalamus
along the spinal cord to the adrenal gland (atop the kidneys).
Both the chemical signal (ACTH) and the nerve impulse
initiated in the hypothalamus travel to the adrenal gland.
|In the adrenal gland, the nerve impulse signals chromaffin
cells to release epinephrine (blue molecules, also known as
adrenaline) into the bloodstream. Epinephrine will travel to
many different cell types throughout the body.
|The ACTH (green) previously secreted by the pituitary gland
travels through the blood stream to cells in another area of the
|1:01 - 1:35
|The Cortisol Production Signaling Cascade:
|On the surface of an adrenal cell, the signaling
molecule ACTH (green, not drawn to scale) docks on a
MC2-R receptor (yellow), causing it to change shape.
|Inside the adrenal cell, the conformational change of
the receptor causes the G protein complex (pink, right) to
become activated and uncoupled. The G protein stimulates
adenylate cyclase (red, left) to convert ATP (the cell's
energy molecule) into cAMP (a signaling molecule, blue).
|cAMP activates Protein Kinase A (PKA) causing it to
release its catalytic subunits (only one is shown here
for simplicity). The catalytic PKA subunit travels to the
mitochondrial membrane and switches on a protein called
steroidogenic acute regulatory protein (StAR, not shown).
|StAR is responsible for mediating the complicated task of
importing cholesterol (yellow) into the mitochondrion.
|Inside the mitochondrion, enzymes convert the cholesterol
into 17-OH-pregnenolone. 17-OH-pregnenolone is released
from the mitochondrion and sent to the endoplasmic
reticulum, where it is converted into 11-deoxycortisol.
|This compound is then sent back to the mitochondrion
where it is finally transformed into the final product,
cortisol. Cortisolleaves the adrenal cell by freely
crossing the cell membrane, and it enters the bloodstream.
|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
|A view of epinephrine (blue) that was released earlier by
the adrenal gland. From here, the epinephrine will travel
to several cell types, eliciting different responses.
|1:45 - 2:20
|The Glycogenolysis Signaling Cascade:
|On the surface of a liver cell, epinephrine (blue, not
drawn to scale) binds to an alpha-1 adrenergic receptor
(yellow), causing it to change shape.
|Inside the liver cell, the conformational change of
the alpha-1 adrenergic receptor causes the G protein
complex to become activated and uncoupled. The G
protein (red, left) binds to phospholipase-C (center),
causing it to produce and release the signaling molecule
IP3 (pink, right).
|IP3 binds to receptors on the surface of the endoplasmic
reticulum (ER, green), stimulating the release of calcium
ions (red spheres).
|Calcium interacts with phosphorylase kinase (yellow),
stimulating it to release its associated molecules of
glycogen phosphorylase (orange).
|Glycogen phosphoryase breaks a glycogen molecule into
individual glucose subunits.
|The newly-formed glucose is transportedout of the
liver cell and it enters the bloodstream. This glucose will
provide an immediate source of energy for muscle cells
|Simultaneously, epinephrine (blue) travels through the
bloodstream to other cell types.
|In the skin, epinephrine binds to a receptor on an
erector pilli smooth muscle cell. This causes a signaling
cascade (similar to the glycogenolysis signaling cascade,
above) that contracts the muscle, raising the hair on the
surface of the skin.
|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
|In the lungs, epinephrine sets off a signaling cascade
(similar to the cortisol signaling cascade, described
above) that relaxes muscle cells surrounding the
bronchioles to enable increased respiration.
|Epinephrine can have opposite effects (contraction, or
relaxation) depending on the type of signaling machinery
presentin 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, epinephrine acts on the pacemaker cells, stimulating them to beat faster. As a result, energy and messenger molecules are circulated throughout the body at a faster rate.