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why do pupils dilate when skin is pinched

a reflected action or movement; the sum total of any particular automatic response mediated by the nervous system. A reflex is built into the nervous system and does not need the intervention of conscious thought to take effect. is an example of the simplest type of reflex. When the knee is tapped, the nerve that receives this stimulus sends an impulse to the spinal cord, where it is relayed to a motor nerve. This causes the quadriceps muscle at the front of the thigh to contract and jerk the leg up. This reflex, or simple reflex, involves only two nerves and one synapse. The leg begins to jerk up while the brain is just becoming aware of the tap. Other simple reflexes, the
stretch reflexes, help the body maintain its balance. Every time a muscle is stretched, it reacts with a reflex impulse to contract. As a person reaches or leans, the skeletal muscles tense and tighten, tending to hold him and keep him from falling. Even in standing still, the stretch reflexes in the skeletal muscles make many tiny adjustments to keep the body erect. The hot stove reflex is more complex, calling into play many different muscles. Before the hand is pulled away, an impulse must go from the sensory nerve endings in the skin to a center in the spinal cord, from there to a motor center, and then out along the motor nerves to shoulder, arm, and hand muscles.

Trunk and leg muscles respond to support the body in its sudden change of position, and the head and eyes turn to look at the cause of the injury. All this happens while the person is becoming aware of the burning sensation. A reflex that protects the body from injury, as this one does, is called a nociceptive reflex. Sneezing, coughing, and gagging are similar reflexes in response to foreign bodies in the nose and throat, and the wink reflex helps protect the eyes from injury. A conditioned reflex is one acquired as the result of experience. When an action is done repeatedly the nervous system becomes familiar with the situation and learns to react automatically, and a new reflex is built into the system. Walking, running, and typewriting are examples of activities that require large numbers of complex muscle coordinations that have become automatic. Are the eyes the windows to intelligence? In, Georgia psychologists Jason S. Tsukahara and colleagues report that there s a positive correlation between pupil size and cognitive ability. It s well known that our pupil size varies over time due to changes in both and cognitive effort. As Tsukahara et al. put it Starting in the 1960s it became apparent to psychologists that the size of the pupil is related to more than just the amount of light entering the eyes.

Pupil size also reflects internal mental processes. For instance, in a simple memory span task, changes in memory load, dilating with each new item held in memory and constricting as each item is subsequently recalled. However, Tsukahara et al. are saying that there s relationship between pupil size and cognitive ability across individuals. Here s the key figure showing the correlation between baseline (resting) and fluid intelligence ( ) in n=331 volunteers. Fluid intelligence is thought to be a major component of IQ. As you can see, the association is present in each of the three ethnic groups studied: In additional experiments, Tsukahara et al. show that baseline pupil size is a reliable measure, staying more or less constant within the same individual over repeated test sessions (r 0. 7); and that the correlation with intelligence can t be explained by some confounding variables such as age, gender, or nicotine and caffeine consumption. Now, when I first saw this paper, I was sure there had to be something wrong with Tsukahara et al. s methods. Indeed, you might say I rolled my eyes, because it seemed too good to be true that a measure as simple as pupil size would correlate with something as nebulous as IQ. But after reading the paper, I actually haven t been able to spot any flaws although perhaps my readers will.

Assuming the association is real, what is the cause of it? Tsukahara et al. speculate that the neurotransmitter Although we did not obtain any direct neural measures of brain function, neuroscience research has shown a close association of pupil size with activity in the locus coeruleus-norepinephrine system. [In the brain, norepinephrine] modulates the gain of target neurons to be more sensitive to incoming signals (both excitatory and inhibitory) this modulation of neural gain has an effect on the strength of functional connectivity throughout the brain. In other words, maybe people with higher trait norepinephrine signalling have both larger pupils and more efficient neural information processing as a result. I must admit that this seems rather too simplistic to me, but again, I can t really point to anything wrong with this logic specifically. Tsukahara JS, Harrison TL, Engle RW (2016). The relationship between baseline pupil size and intelligence. Cognitive Psychology, 91, 109-123 PMID:

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