Time to explore the
eye; not the senses, but rather something deeper. Class, today we’re going into
the tear ducts to explore how and why we cry.
-Miss. Frizzle
Heat pulsating, heart rate accelerating, chest tightening, throat
clenching, nose burning, eyes watering. “Don’t cry. Only babies cry,” you scold
yourself. A nearly silent sob seeps out—then the waterworks come like a dam
broken causing an uncontrollable flood. Many of us have been there…embarrassingly
crying over something we look back on (sometimes defensively) as “not a big
deal” and wonder why we cried about it. Whether it is the puppy and horse Budweiser commercial or the end of
Toy Story 3, or on a more serious
note at the loss of a loved one, some things just pull on our heart-strings more
than others. We also may be extremely stressed with
cortisol furiously pumping through our veins. Or we may have been
sleep deprived. The list goes on...
The act of crying is not just for sissies; tears serve a multitude of functions. There are three types of tears:
1.
Basal
tears act as a protective lubricant
by preventing desiccation so the eye and eyelids can move.
2.
Reflex
tears occur an involuntary response to an irritant such as the chemicals
released into the air from slicing those pesky onions. A signal is sent to the
brain which allows the tear duct response of releasing tears to clean the eye.
3.
Emotional
tears of sadness or joy can signal to others to elucidate our true feelings
and sincerity.
(aside from fake crying of course). The signal is one of need, appeasement, or
attachment. It shows our vulnerability and lets others know our emotions are
overwhelming us so much that they are literally flowing out of our body. Wait,
WHAT?!?
While reflex tears have been shown to be composed of mostly
water, emotional tears have high levels of adrenocorticotropic hormone (ACTH)
which is a hormone or chemical messenger that is linked to high stress
levels. So when a person consoling you says “let it all out,” there may be
some justification to this if we do indeed 'cry out' our stress, but little is
known about release theory.
But Miss. Frizzle,
where do tears come from? And why do we sometimes laugh when we’re happy?
Formation of Tears
The hypothalamus, important for bodily functions
like sleep regulation, appetite, and reproduction, is incapable of distinguishing
whether we are feeling happy, sad, overwhelmed, or stressed when it receives a
strong signal from the amygdala. The amygdala then activates the autonomic
nervous system (ANS), which results in involuntary body functions that we have
no conscious control over.
As you probably know, the ANS is composed of the sympathetic ("fight-or-flight") and parasympathetic ("rest-and-digest") sectors. In the sympathetic response, the hypothalamus activates the body during times of stress (e.g. release of glucose into the bloodstream, increased heart rate, etc.). The parasympathetic nervous system (PSNS), on the other hand, has a calming effect and is connected to our lacrimal glands, or tear ducts. When the neurotransmitter acetylcholine binds to receptors and activates the PSNS, one response is tear production. Additionally, the reason for a runny nose while crying is that tears flow through canals that drain into the nose. Here is a zoomed in view of the lacrimal gland:
As you probably know, the ANS is composed of the sympathetic ("fight-or-flight") and parasympathetic ("rest-and-digest") sectors. In the sympathetic response, the hypothalamus activates the body during times of stress (e.g. release of glucose into the bloodstream, increased heart rate, etc.). The parasympathetic nervous system (PSNS), on the other hand, has a calming effect and is connected to our lacrimal glands, or tear ducts. When the neurotransmitter acetylcholine binds to receptors and activates the PSNS, one response is tear production. Additionally, the reason for a runny nose while crying is that tears flow through canals that drain into the nose. Here is a zoomed in view of the lacrimal gland:
a. tear gland / lacrimal glandb. superior lacrimal punctum
c. superior lacrimal canal
d. tear sac / lacrimal sac
e. inferior lacrimal punctum
f. inferior lacrimal canal
g. nasolacrimal canal
Crying as
Communication
Who would have thought crying could actually sometimes
increase fitness rather than merely be a sign of weakness? The trade-off,
however, is that crying blurs our vision and often leaves us in an
unaggressive, helpless state. Conversely, tears of joy often during extreme
bouts of laughter act as social signals to strengthen bonds with people close
to us.
Males &
Females: A Disparity in Crying
Crying is a gendered activity; women generally cry more often than men. Social constructs deem women allowed to cry, especially during that time of the month, and deem men less masculine and mentally weak when they cry. Countless studies have shown that men and women perceive, process, express, and experience emotions differently. Of note, there is fMRI (functional Magnetic Resonance Imaging that uses strong magnetic fields and radio waves to form images of the body and brain) evidence that women’s neural hardwiring predisposes them to effectively process infant laughter and crying.
And what about those days when everything seems to set us off as if our eyes are leaky faucets (girls, you likely know what I’m talking about)? Blame it on the hormones! Increased crying could coincide with higher levels of the ovarian steroid hormones, progesterone and estradiol. These steroid sex hormones are implicated to exacerbate PD, or Premenstrual Distress associated with loneliness, crying, and skin blemishes. In a study conducted by Stoddard and colleagues, women who exercised moderately reported lower pain symptoms, and had lower peak estradiol and progesterone levels than did sedentary women—just another reason why exercise is so important.
WOW! Crying is way more complicated than I thought. Now I feel like I know a
lot more about different types of tears, hormonal and neuronal crying control, and even evolutionary reasons for crying. THANKS MISS. FRIZZLE!!
Hasson, O. 2009. Emotional tears as biological signals. Evolutionary Psychology 7:363-370.
Olney, N.T., M.S. Goodkind, C. Lomen-Hoerth, P.K. Whalen, C. A. Williamson, D.E. Holley, A. Verstaen, L.M. Brown, B.L. Miller, J. Kornak, R.W. Levenson, and H.J. Rosen. 2011. Behaviour, physiology and experience of pathological laughing and crying in amyotrophic lateral sclerosis. Brain 134:3458–3469.
Proverbio, A.M., A. Zani, and R. Adorni. 2008. Neural markers of a greater female responsiveness to social stimuli. BMC Neuroscience 9:56-65.
Romans, S.E. and R.F. Clarkson. 2008. Crying as a gendered indicator of depression. Journal of Nervous & Mental Disease 196:237-243.
Crying is a gendered activity; women generally cry more often than men. Social constructs deem women allowed to cry, especially during that time of the month, and deem men less masculine and mentally weak when they cry. Countless studies have shown that men and women perceive, process, express, and experience emotions differently. Of note, there is fMRI (functional Magnetic Resonance Imaging that uses strong magnetic fields and radio waves to form images of the body and brain) evidence that women’s neural hardwiring predisposes them to effectively process infant laughter and crying.
Other findings show that women are more empathetic, sensitive, and inclined to express their own emotions to conspecifics, or those of the same species. Furthermore, women often are better at understanding non-verbal indicators of emotions (e.g. facial expressions). Evolutionarily speaking, this motherly wiring is vital for parental care because it gives moms the edge when it comes to recognizing and then comforting their offspring or others in times of need.
And what about those days when everything seems to set us off as if our eyes are leaky faucets (girls, you likely know what I’m talking about)? Blame it on the hormones! Increased crying could coincide with higher levels of the ovarian steroid hormones, progesterone and estradiol. These steroid sex hormones are implicated to exacerbate PD, or Premenstrual Distress associated with loneliness, crying, and skin blemishes. In a study conducted by Stoddard and colleagues, women who exercised moderately reported lower pain symptoms, and had lower peak estradiol and progesterone levels than did sedentary women—just another reason why exercise is so important.
Case Study:
Pathological Laughing & Crying
Some people have a neurodegenerative disease called amyotrophic lateral sclerosis (ALS or Lou Gehrig's Disease named after the Yankees baseball player). ALS can involves pathological (caused by
disease; extreme
in a way that is not normal or that shows an illness or mental problem) laughing and crying due to a dramatic
disorder of voluntary emotion regulation. The terms in the acronym ALS can be broken down into “no muscle
nourishment”+ “at the sides ” (referring to areas in a person's spinal cord where portions of the motor neurons that
signal and control the muscles are located) + “hardening of tissue.” Simply, ALS is a motor neuron disease that is a disruption of brain systems involved in
generating and/or regulating emotions via neurological injury, yet the exact
mechanism is not fully understood. Symptoms include uncontrollable outbursts of
crying and/or laughing among other things such as increasing muscle weakness, especially
involving the arms and legs, speech, swallowing, or breathing. Muscles stop
receiving messages from motor neurons and begin to atrophy, or shrink.
Olney and colleagues studied patients with pathological laughing and crying due to ALS and
those with ALS but no pathological laughing or crying. They quantified emotion
with self-reported emotions, video recordings of facial reactivity, and
peripheral physiological responses (skin conductance, heart rate, and somatic
activity). These outbursts were shown to be much more normal than
often portrayed in previous literature, although the ability to stop during an
episode is sometimes inhibited. Can you imagine the embarrassment you would
experience if you could not help laughing at a funeral? How terrible! They proposed that this disorder may be
due to dysfunction in frontal neural systems that support voluntary regulation
of emotion.
In sum, we cry for many reasons. There is more research to be done on how we cry, especially on how stress influences crying behavior. Thanks for reading!
In sum, we cry for many reasons. There is more research to be done on how we cry, especially on how stress influences crying behavior. Thanks for reading!
References
ALS Association.
2010. http://www.alsa.org/about-als/what-is-als.html Hasson, O. 2009. Emotional tears as biological signals. Evolutionary Psychology 7:363-370.
Olney, N.T., M.S. Goodkind, C. Lomen-Hoerth, P.K. Whalen, C. A. Williamson, D.E. Holley, A. Verstaen, L.M. Brown, B.L. Miller, J. Kornak, R.W. Levenson, and H.J. Rosen. 2011. Behaviour, physiology and experience of pathological laughing and crying in amyotrophic lateral sclerosis. Brain 134:3458–3469.
Proverbio, A.M., A. Zani, and R. Adorni. 2008. Neural markers of a greater female responsiveness to social stimuli. BMC Neuroscience 9:56-65.
Romans, S.E. and R.F. Clarkson. 2008. Crying as a gendered indicator of depression. Journal of Nervous & Mental Disease 196:237-243.
Searby, A. and J. Pierre. 2005. The double vocal
signature of crested penguins: is the identity coding system of rockhopper
penguins Eudyptes chrysocome due to
phylogeny or ecology? Journal of Avian Biology 36:449-460.
Stoddard, J.L., C.W. Dent, L. Shames,
and L. Bernstein. 2007. Exercise training effects on premenstrual distress and
ovarian steroid hormones. European Journal of Applied Physiology 99:27–37.
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