 |
| Halloween is a time when fear
is invited. The rush of
adrenaline in a controlled
environment is life-
affirming. Not much else to
comment on here,
except that he seems to have
excellent oral hygiene
for a chainsaw-wielding maniac.
|
Haunted houses are great examples of stimuli that induce the
fight or flight response. The name suggests that two mechanisms are fighting it out, but there is really only one
biologic pathway. Whether an animal tries to escape or tries to defend itself, its muscles and mind need to be ready.
In response to a threat, the brain triggers the release of epinephrine and cortisol from your adrenal glands into the blood. As a result,
your heart beats faster and stronger, your blood vessels dilate to move more
blood, and your lung vessels dilate to exchange more oxygen for carbon dioxide. Equally as important, your liver breaks down glycogen (a sugar storage molecule) to glucose
and dumps it into your bloodstream.
All these processes work together to increase your alertness
and increase the power of your muscles for a short time - like when mothers who lift cars off their small children. You are now ready to
respond to the threat; however, there is an exception – you may do nothing at
all.
One of the major control mechanisms of the fight or flight
response is the autonomic nervous system.
This is part of the peripheral nervous system (PNS, outside the brain and
spinal cord) and transmits information from the central nervous system to the
rest of the body. The autonomic system controls involuntary movements
and some of the functions of organs and organ systems.
Parts of the autonomic system acts like a teeter-totter, it's their relative balance that controls the outcomes.
In the fight or flight response, the sympathetic
system predominates and your heart rate increases and your blood vessels
dilate.
 |
The autonomic nervous system
is divided into sympathetic
and parasympathetic. Much of
the sympathetic innervation
comes from the thoracic and
lumbar regions, while most
parasympathetic innervation
is carried by the vagus nerve.
You can see that the two
systems have largely opposite effects.
|
Many people have had the experience of parasympathetic
domination coincident to a threat, for some folks it proceeds long enough to have an
observable result – they faint. The vagus nerve (a primarily parasympathetic
cranial nerve) controls much of this response, so it may be called the
vasovagal response. The parasympathetic-mediated reduction in blood oxygen and
glucose do not spare the brain - and when your brain is starved of oxygen and glucose, you pass out. Fighting or fleeing is difficult when you
are unconscious.
Lower animals will faint as well, but they have additional
defenses along these lines. Mammals, amphibians, insects and even fish can be
scared enough to fake death – ever hears of playin’ opossum?
There are overlapping mechanisms for feigned death, from tonic immobility (not moving) to thanatosis (thanat = death, and osis
= condition of, playing dead). When opossums employ thanatosis, they fall down,
stick their tongue out, and even emit a foul smelling odor from glands around their anus. One
study in crickets showed that those who feigned death the longest were more likely
to avoid being attacked, so this is definitely a survival adaptation – except for the opossums scared
by cars and decide to play dead in the street.
Feigned death deters predation, so being scared ain’t all
bad. Many predators won’t eat something that is already dead, so not moving
could protect them from attack. Another theory is the clot formation hypothesis; it contends that slowing the heart
and blood flow forces blood clots to form faster. This will reduce the amount of blood
lost during an attack, improving chances for survival.
New evidence is suggesting that even humans undergo tonic immobility. Post-traumatic
stress patients asked to relive their trauma show definite signs of tonic
immobility, although first they show signs of "attentive immobility," which is
more voluntary then the tonic form.
 |
I highly recommend this new
book for popular
biology and medicine
readers. Zoobiquity explores
a powerful reality. No disease--whether physical
or
psychiatric--is uniquely human. We have much to
learn from animal patients and from the doctors who
care for them. The impact on human medicine
will be significant.
|
In their book, Zoobiquity, What animals can teach us about health and the science of healing, Barabara
Natterson-Horowitz and Kathyrn Bowers talk about capture myopathy in animals. Small traps that limit movement, cause
pain, or are associated with loud noises can cause spontaneous death in
live-trapped animals. Several decades ago it was not unusual for 10% of trapped
animals to die. In birds, the death rate often rose to 50%! More humane methods of live
trapping have reduced the death rate, but point is made – these animals were
scared to death.
A human analogy of capture myopathy may have been
identified. People that have had a sudden emotional shock, perhaps the death of
a loved one, some other tragic occurrence, or crippling fear can undergo something that looks a
lot like a heart attack, even if they have no history of heart disease.
This sudden loss of heart rhythm has been called
broken-heart syndrome, but is more accurately termed stress cardiomyopathy (SCM). In these cases, the heart actually
changes shape! The part of the heart that pumps blood out to the body (left
ventricle) balloons out and loses the ability to pump efficiently. Dramatically
less efficient pumping leads to symptoms just like a heart attack.
 |
In the normal left ventricle
of the heart (left image), the muscle is
thick around the space (in
red) and contracts strongly. In SCM, the
space is ballooned at the
based (middle image) and the muscular wall
is thin, giving a weak
contraction. The change in shape can be seen in
the superimposed images on
the right, as is the octopus trap (tako-tsubo)
that the original Japanese
describers thought the lesion looked like,
hence the early name
takotsubo cardiomyopathy.
|
I was wondering if there was a link between SCM in humans
and capture myopathy in animals, so I asked Dr. Natterson-Horowitz. She told me that those
studies have not been done yet; we don’t know if there is a heart shape change
in captured animals. I think it would be hard to get approval for studies that would intentionally scare animals to death.
One interesting connection amongst fight or flight, capture
myopathy, and SCM is the catecholamine dump involved. Epinephrine and
norepinephrine control all three responses, and in humans they control even
more. Recent evidence shows that catecholamines mediate the production of fear
memories.
You remember fearful events more readily and more vividly as a survival adaptation. Strong memories help you to avoid dangerous situations in the future. In this way, your mind can affect how your body responds to a threat. We will see this again in just a bit.
You remember fearful events more readily and more vividly as a survival adaptation. Strong memories help you to avoid dangerous situations in the future. In this way, your mind can affect how your body responds to a threat. We will see this again in just a bit.
 |
All babies have an
exaggerated startle reflex until
they are several months old,
but in some cases it may
contribute to SIDS. An
exaggerated startle can lead to
apnea (temporary breathing
cessation) and this can be
compounded by a depressed
heart rate if the baby is
sleeping on its stomach.
Some clinicians also theorize
that swaddling may
contribute by exaggerating the startle
due to confinement stress,
but by far the greatest
association with SIDS is
stomach sleeping.
|
The startle reflex involves squinting to protect the eyes, raising the arms, hunching the body to protect the back of the neck, as well as inducing
the fight or flight response. With the loss of inhibitory signaling, the
signals that ramp up a startle response are unchecked and can lead to
uncontrolled beating of the heart (ventricular fibrillation, VF) and sudden
cardiac death.
Just as some cases of the fight or flight response going
too far, the startle can sometimes lead to VF. A recent study has shown that
the bigger the perceived threat, the bigger the startle reflex will be. Also, if
there is a fearful environment prior to the threat, then the startle will be
bigger. Once in a long while, it goes too far.
Similar to hyperekplexia, there is another condition that
could lead to VF and death in the environment of fear. Long QT syndrome can either be inherited or acquired later in life,
and affects the time between beats of the heart. In long QT, the interval is
variable and longer, and can lead to inefficient beating and VF.
 |
On echocardiogram tracings a
heartbeat has a certain shape, and
each point has a
corresponding name which is represented
by a letter.
If the time between the Q point and the T point
is too
long, the heart rhythm is subject to disintegrating
into chaos. In the 1990’s, the antihistamine Seldane was
taken off the market due to QT interaction when it was
given with the antibiotic erythromycin.
|
Long ago we
talked about premature burial. It would be easy to envision a person waking up
inside a coffin, and then dying from the fright of being buried alive! Does
this mean that you are putting yourself in peril every time you visit a haunted
house at Halloween? Probably not, remember that deaths from fright are
exceedingly rare. Maybe you could just feign death, and the horrible monster
will leave you alone.
For the next couple weeks - back to the science of flagella. Undulipodia are present in many phylums, except
for where they aren’t. On the other hand, some types of organisms don’t have
undulipodia - except for those that do.
Greek, R. (2012). Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing. By Barbara Natterson-Horowitz and Kathryn Bowers. Knopf Doubleday Publishing: New York, NY, USA, 2012; Hardback, 320 pp; $16.23; ISBN-10: 0307593487 Animals, 2 (4), 559-563 DOI: 10.3390/ani2040559
Volchan, E., Souza, G., Franklin, C., Norte, C., Rocha-Rego, V., Oliveira, J., David, I., Mendlowicz, M., Coutinho, E., Fiszman, A., Berger, W., Marques-Portella, C., & Figueira, I. (2011). Is there tonic immobility in humans? Biological evidence from victims of traumatic stress Biological Psychology, 88 (1), 13-19 DOI: 10.1016/j.biopsycho.2011.06.002
For more information or
classroom activities, see:
Fight or flight –
Autonomic nervous system –
Thantosis/tonic immobility –
Stress cardiomyopathy –
Hyperekplexia –
Long QT syndrome -
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