Reflexes

6 Key excerpts on "Reflexes"

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  eBook - PDF

  Discovering Psychology

  The Science of Mind

  • John Cacioppo, Laura Freberg(Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Jane Burton/Dorling Kindersley/Getty Images Chapter 8 | THE ADAPTIVE MIND Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. HOW DO ANIMALS USE Reflexes, INSTINCTS, AND LEARNING TO RESPOND TO THEIR ENVIRONMENTS? 277 Reflexes are inevitable, involuntary responses to stimuli. In casual conversa-tions, we sometimes attri-bute a baseball player’s high batting average or our ability to step on the brake in time to avoid an automobile acci-dent to great Reflexes, but in fact, these examples involve learned behaviors that have become fast and automatic as a result of lots of practice. Nobody is born knowing how to hit baseballs or use the brakes of a car, so these behaviors do not meet our definition of a reflex. In humans, most Reflexes are controlled by nervous system circuits located in the spinal cord and brainstem, described in Chapter 4. Your physician checks one of these Reflexes by tapping your knee with a hammer. The tap stretches your leg muscles, and the stretch is sensed by neurons in the spinal cord. Motor neurons in the spinal cord tell your thigh muscle to contract to compensate for the stretching, and your foot kicks out. No experience with knee-tapping is necessary to produce this behavior, nor can you voluntarily prevent it. By the time your brain realizes your knee was tapped, you have already reacted. Other Reflexes pull our bodies away from painful stimuli, such as when we step on a tack or piece of glass or touch a hot stove, turn our heads in the direction of loud sounds, and help us stand up-right and walk.

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  Cognition

  • Arnold Lewis Glass(Author)
  • 2016(Publication Date)
  • Cambridge University Press

    (Publisher)

  The neural mechanisms of Reflexes formed the basis of the enhanced neural mechanisms that made cognition possible. 1.2 1.1 Reflexes 3 Most neurons communicate with the adjacent neuron by releasing a chemical signal called a neurotransmitter, which floats across the synapse and is taken up by the next neuron and stimulates it. (Some interneurons communicate by generating an electrical charge in the gap between them, but their function is not well understood: (Apostolides and Trussell, 2013.) Many Reflexes respond to stimulation from the environment. For example (as the great physiologist Ivan Pavlov discovered), placing a small amount of meat in a dog’s mouth caus- es it to salivate, which begins the process of digesting the meat. The pupillary light reflex varies the size of the pupil so that the right amount of light for vision enters the eye. The accommodation reflex varies the shape of the eyeball so that the image projected on the retina is not blurred. In addition to regulating purely life functions through simple actions, Reflexes evolved to perform increasingly complex actions in response to stimuli in the ani- mal’s environment. Reflexes are also called unconditioned responses, because of a mistranslation from Rus- sian. Pavlov described Reflexes as unconditional because the same stimulus always caused the same response regardless of other conditions; “unconditional” was mistranslated as “un- conditioned.” The same mistranslation has been extended to the stimulus of the reflex, which is called the unconditioned stimulus. In many texts, stimulus and response are simply referred to by the initials US and UR. Motor neurons are response neurons that initiate muscle contraction or relaxation, pro- ducing body movement. For example, blowing a puff of air in someone’s eye causes it to blink, thus protecting the eye from harm. The sea snail In the simplest creatures that have Reflexes, the Reflexes are the only kinds of actions that the creature performs.

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  eBook - ePub

  The Brain and the Nervous System

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  reflexus , “reflection”) was introduced into biology by 19th-century English neurologist Marshall Hall, who fashioned the word because he thought of the muscles as reflecting a stimulus much as a wall reflects a ball thrown against it. By reflex, Hall meant the automatic response of a muscle or several muscles to a stimulus that excites an afferent nerve. The term is now used to describe an action that is an inborn central nervous system activity, not involving consciousness, in which a particular stimulus, by exciting an afferent nerve, produces a stereotyped, immediate response of muscle or gland.

  The anatomical pathway of a reflex is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more interneurons within the central nervous system, and an efferent (motor, secretory, or secreto-motor) nerve. Most Reflexes have several synapses in the reflex arc. The stretch reflex is exceptional in that, with no interneuron in the arc, it has only one synapse between the afferent nerve fibre and the motor neuron. The flexor reflex, which removes a limb from a noxious stimulus, has a minimum of two interneurons and three synapses.

  Probably the best-known reflex is the pupillary light reflex. If a light is flashed near one eye, the pupils of both eyes contract. Light is the stimulus; impulses reach the brain via the optic nerve; and the response is conveyed to the pupillary musculature by autonomic nerves that supply the eye. Another reflex involving the eye is known as the lacrimal reflex. When something irritates the conjunctiva or cornea of the eye, the lacrimal reflex causes nerve impulses to pass along the fifth cranial nerve (trigeminal) and reach the midbrain. The efferent limb of this reflex arc is autonomic and mainly parasympathetic. These nerve fibres stimulate the lacrimal glands of the orbit, causing the outpouring of tears. Other Reflexes of the midbrain and medulla oblongata are the cough and sneeze Reflexes. The cough reflex is caused by an irritant in the trachea and the sneeze reflex by one in the nose. In both, the reflex response involves many muscles; this includes a temporary lapse of respiration in order to expel the irritant.

  The first Reflexes develop in the womb. By seven and a half weeks after conception, the first reflex can be observed; stimulation around the mouth of the fetus causes the lips to be turned toward the stimulus. By birth, sucking and swallowing Reflexes are ready for use. Touching the baby’s lips induces sucking, and touching the back of its throat induces swallowing.

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  The Science of Signs and Symptoms

  In Relation to Modern Diagnosis and Treatment: A Textbook for General Practitioners of Medicine

  • Robert John Stewart McDowall(Author)
  • 2016(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  CHAPTER VII Reflexes Reflexes are movements which we make without any effort of will and, quite apart from their great physiological interest, their study is of the utmost value in the localization of nervous disease. Reflexes are amongst the most primitive movements of the body. They are primarily designed for protection, the maintenance of posture, the supply of food, and the adaptation of the animal to its environment. The axon reflex is the simplest form of reflex known, and is best exemplified by the fifth nerve, as shown by Ninian Bruce. If a blister is applied to the cheek a reddening of the skin results from dilatation of blood-vessels. This is not due to direct action on the blood-vessels, because, when the nerves supplying the part are cut, the dilatation is only obtained for a short time, and once the nerve has degenerated the reaction disappears entirely. Such section is not infrequently carried out in the treatment of obstinate neuralgia. As excision of the Gasserian ganglion does not affect the reaction, provided the nerves have not had time to degenerate, it must be assumed that the reflex depends entirely on the distal portion of the nervous connection. We know, however, that vaso-dilator nerve fibres pass out with the sensory nerves, and we may assume, then, that these have been stimulated and the impulse has passed over to the efferent vaso-dilators in the nerve trunk. The value of such a mechanism to the animal, for the protection of its skin, is obvious. The Lovén Reflexes, which are probably of the nature of axon Reflexes and are of importance in relation to the blood supply of organs in general, are referred to later. The spinal reflex, on the other hand, depends on the integrity of the reflex arc through the spinal cord. By means of such a reflex, sensory stimulation brings about a movement of voluntary muscle.

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  Biology as a natural science: The study of life in all its forms

  • Saket Kushwaha(Author)
  • 2023(Publication Date)
  • Delve Publishing

    (Publisher)

  To live, both internal and external changes must always be noticed and assessed. Since life on this planet evolved and the environment has become more complicated, organisms’ existence relied on their ability to adjust to changes in the circumstances. A swift response or reaction was one requirement for survival. Because chemical communication between cells was too sluggish for life, a mechanism emerged that allowed for rapid responsiveness. That system Nervous System, Sensory System and Immune System 195 was the nervous system, which is based on the practically instantaneous transmission of electrical impulses from one part of the body to another via specialized nerve cells known as neurons. There are two kinds of nervous systems: diffuse and concentrated. There is no brain in the diffuse system, which is seen in lower invertebrates, and neurons are dispersed all through the creature in a netlike arrangement. A part of the nervous system has a prominent role in planning information and guiding reactions in upper invertebrates and vertebrates’ centralized systems. This centralization is completed in vertebrates, who have a fully formed brain and spinal cord. Nerve fibers in the peripheral nervous system transport impulses from and to the brain and spine. Figure 7.1. Human Nervous System diagram. Source: Image by Wikimedia Commons 7.1.2. Sensory System Animals use their senses, also known as sensory reception or sense perception, to identify and react to events in their internal and external habitats. Animal senses are best explained due to the type of physical energy, or modalities, involved. Biology as a Natural Science: The Study of Life in all its Forms 196 The light senses (photoreception; i.e., vision), mechanical senses (mechanoreception; i.e., touch, balance, and hearing), chemical senses (chemoreception; i.e., taste and smell), and electric sense (electroreception) of some fish are the four primary modalities.

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  Techniques and Basic Experiments for the Study of Brain and Behavior

  • Jan Bures, Olga Burešová, Joseph P. Huston(Authors)
  • 2016(Publication Date)
  • Elsevier

    (Publisher)

  The reflex theory introduced by Descartes in the 17th century influenced all physiological and psychological thinking and remains the salient departure point of modern neurophysiology. The basic behavioral repertoire is firmly laid down in the predetermined neural connec-tions linking a definite response (unconditioned reaction — UR) to a particu-lar stimulus (unconditioned stimulus — US). These innate (unlearned, uncon-ditioned) reactions are supplemented by acquired (learned, conditioned) reactions to originally neutral stimuli, which, by repeated association with a US become conditioned stimuli (CS), i.e., signals of spatial and/or temporal closeness of the US (Pavlov, 1927). Whereas innate behaviors reflect genetically encoded response tendencies acquired over generations by the process of evolutionary selection, individu-ally acquired behavior is due to experiences recorded in the organism's mem-ory. A succession of external and/or internal events experienced by the ani-mal may induce a more or less lasting modification of the nervous system, accounting for the novel response to the previously ineffective stimuli. The underlying process called learning leads to storage of experiences in the form of memory traces (engrams), the revival of which influences the behavior of the animal. An experience no longer compatible with new environmental conditions is extinguished; an experience not called forth for a long time may be forgotten. The interaction between the organism and environment can assume differ-ent forms corresponding to separate behavioral entities. Whereas the respon-dent behavior consists of reactions triggered by discrete stimuli (e.g., noxious stimuli, food), the operant behavior can be considered to be generated by internal needs, and consists of emission of various responses, which may eventually induce the desired environmental change (e.g., availability of food).

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