Identify the general and also special senses in humansDescribe three crucial steps in sensory perceptionExplain the concept of just-noticeable difference in sensory perception

Senses carry out information about the body and also its environment. People have 5 special senses: olfaction (smell), gustation (taste), equilibrium (balance and body position), vision, and also hearing. Additionally, us possess basic senses, additionally called somatosensation, i beg your pardon respond come stimuli like temperature, pain, pressure, and also vibration. Vestibular sensation, which is an organism’s feeling of spatial orientation and balance, proprioception (position of bones, joints, and muscles), and also the feeling of limb place that is supplied to track kinesthesia (limb movement) are part of somatosensation. Back the sensory systems linked with these senses are really different, all share a common function: to convert a stimulus (such together light, or sound, or the position of the body) right into an electric signal in the worried system. This procedure is called sensory transduction.

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There space two broad varieties of cellular equipment that carry out sensory transduction. In one, a neuron works v a sensory receptor, a cell, or cell process that is specialized to engage with and also detect a specific stimulus. Stimulation the the sensory receptor activates the linked afferent neuron, i m sorry carries information around the economic stimulation to the central nervous system. In the second type of sensory transduction, a sensory nerve ending responds come a economic stimulation in the internal or external environment: this neuron constitutes the sensory receptor. Totally free nerve endings deserve to be engendered by several different stimuli, for this reason showing little receptor specificity. Because that example, pain receptors in her gums and also teeth may be created by temperature changes, chemistry stimulation, or pressure.


, which is the activation of sensory receptor by stimuli such together mechanical stimuli (being bend or squished, because that example), chemicals, or temperature. The receptor can then respond come the stimuli. The an ar in space in i m sorry a given sensory receptor can respond come a stimulus, it is in it far away or in call with the body, is the receptor’s receptive field. Think because that a moment about the differences in receptive areas for the various senses. For the sense of touch, a stimulus need to come into call with body. For the feeling of hearing, a stimulus deserve to be a moderate street away (some baleen whale sounds can propagate for countless kilometers). Because that vision, a stimulus can be very far away; because that example, the visual mechanism perceives irradiate from stars at massive distances.


Figure 17.2) possesses specialized membranes that respond come pressure. Disturbance of this dendrites through compressing castle or bending them opens up gated ion channels in the plasma membrane of the sensory neuron, an altering its electrical potential. Recall that in the nervous system, a positive adjust of a neuron’s electrical potential (also called the membrane potential), depolarizes the neuron. Receptor potentials room graded potentials: the magnitude of this graded (receptor) potentials varies v the strength of the stimulus. If the size of depolarization is sufficient (that is, if membrane potential will a threshold), the neuron will certainly fire an action potential. In most cases, the exactly stimulus impinging on a sensory receptor will drive membrane potential in a optimistic direction, although for part receptors, such as those in the visual system, this is not constantly the case.

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Figure 17.2. (a) Mechanosensitive ion channels are gated ion channels that answers to mechanical deformation that the plasma membrane. A mechanosensitive channel is associated to the plasma membrane and the cytoskeleton by hair-like tethers. When pressure causes the extracellular procession to move, the channel opens, permitting ions to go into or leave the cell. (b) Stereocilia in the human ear are connected to mechanosensitive ion channels. When a sound causes the stereocilia come move, mechanosensitive ion channels transduce the signal to the cochlear nerve.

Sensory receptor for different senses are very different from every other, and also they are committed according to the kind of stimulus they sense: they have actually receptor specificity. Because that example, touch receptors, light receptors, and sound receptors space each set off by different stimuli. Touch receptors are not perceptible to light or sound; they are sensitive only to touch or pressure. However, stimuli may be linked at higher levels in the brain, as happens with olfaction, contributing to our sense of taste.


Four facets of sensory info are encoded by sensory systems: the type of stimulus, the place of the economic stimulation in the receptive field, the term of the stimulus, and also the family member intensity the the stimulus. Thus, activity potentials transmitted end a sensory receptor’s afferent axons encode one form of stimulus, and this distinction of the senses is preserved in various other sensory circuits. Because that example, auditory receptors transmit signal over their own committed system, and also electrical task in the axons that the listening receptors will be construed by the mind as an auditory stimulus—a sound.

The strongness of a economic stimulation is often encoded in the rate of action potentials produced by the sensory receptor. Thus, an extreme stimulus will develop a more rapid train of action potentials, and also reducing the stimulus will an in similar way slow the rate of production of action potentials. A second way in i beg your pardon intensity is encoded is through the number of receptors activated. An intense stimulus might initiate activity potentials in a large number of nearby receptors, while a much less intense stimulus could stimulate under receptors. Integration the sensory information begins as quickly as the information is received in the CNS, and the brain will further process incoming signals.


Perception is one individual’s interpretation of a sensation. Return perception counts on the activation that sensory receptors, tardy happens not at the level that the sensory receptor, but at higher levels in the nervous system, in the brain. The mind distinguishes sensory stimuli through a sensory pathway: action potentials indigenous sensory receptors travel along neurons the are dedicated to a particular stimulus. This neurons are devoted to that details stimulus and also synapse with certain neurons in the brain or spinal cord.

all sensory signals, other than those native the olfactory system, space transmitted though the main nervous system and also are routed come the thalamus and also to the appropriate an ar of the cortex. Recall that the thalamus is a structure in the forebrain that serves together a clearinghouse and relay station for sensory (as well as motor) signals. When the sensory signal exit the thalamus, that is performed to the details area of the cortex (Figure 17.3) committed to processing that certain sense.

exactly how are neural signal interpreted? interpretation of sensory signals between individuals of the same types is mainly similar, owing to the inherited similarity of your nervous systems; however, there space some separation, personal, instance differences. A great example of this is individual tolerances come a painful stimulus, such together dental pain, which absolutely differ.

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Figure 17.3. In humans, through the exemption of olfaction, all sensory signals space routed native the (a) thalamus come (b) last processing areas in the cortex that the brain. (credit b: modification of job-related by Polina Tishina) Scientific technique Connection

Just-Noticeable Difference

It is easy to differentiate between a one-pound bag of rice and also a two-pound bag the rice. Over there is a one-pound difference, and one bag is twice as heavy as the other. However, would it it is in as basic to differentiate in between a 20- and also a 21-pound bag?

Question: What is the the smallest detectible load difference in between a one-pound bag of rice and also a bigger bag? What is the the smallest detectible difference between a 20-pound bag and also a larger bag? In both cases, at what weights space the differences detected? This the smallest detectible distinction in stimuli is recognized as the just-noticeable distinction (JND).

Background: study background literary works on JND and on Weber’s Law, a summary of a proposed mathematical relationship between the in its entirety magnitude of the stimulus and the JND. You will be testing JND of various weights that rice in bags. Choose a practically increment that is to be stepped v while testing. Because that example, you could pick 10 percent increments between one and two pounds (1.1, 1.2, 1.3, 1.4, and also so on) or 20 percent increments (1.2, 1.4, 1.6, and 1.8).

Hypothesis: develop a hypothesis about JND in terms of percent of the entirety weight being tested (such together “the JND in between the two small bags and also between the two big bags is proportionally the same,” or “. . . Is not proportionally the same.”) So, because that the an initial hypothesis, if the JND in between the one-pound bag and also a larger bag is 0.2 pounds (that is, 20 percent; 1.0 lb feels the very same as 1.1 pounds, however 1.0 lb feels much less than 1.2 pounds), then the JND in between the 20-pound bag and also a larger bag will likewise be 20 percent. (So, 20 pounds feels the very same as 22 pounds or 23 pounds, yet 20 pounds feels much less than 24 pounds.)

Test the hypothesis: Enlist 24 participants, and also split them into two teams of 12. To set up the demonstration, assuming a 10 percent increment was selected, have the an initial group be the one-pound group. Together a counter-balancing measure against a organized error, however, six of the an initial group will certainly compare one pound to two pounds, and also step down in weight (1.0 to 2.0, 1.0 come 1.9, and also so on.), while the other six will step up (1.0 to 1.1, 1.0 come 1.2, and also so on). Use the very same principle to the 20-pound group (20 to 40, 20 come 38, and also so on, and also 20 to 22, 20 come 24, and so on). Provided the large difference in between 20 and also 40 pounds, you might wish to usage 30 pounds together your larger weight. In any kind of case, use 2 weights the are conveniently detectable as different.

Record the observations: record the data in a table comparable to the table below. For the one-pound and also 20-pound teams (base weights) record a plus sign (+) for each participant the detects a difference in between the base weight and also the step weight. Record a minus authorize (-) because that each participant the finds no difference. If one-tenth measures were not used, then change the procedures in the “Step Weight” columns with the step you space using.


Table 17.1. Results the JND testing (+ = difference; – = no difference)Step WeightOne pound20 poundsStep Weight
1.122
1.224
1.326
1.428
1.530
1.632
1.734
1.836
1.938
2.040

Analyze the data/report the results: What action weight did every participants find to it is in equal v one-pound base weight? What about the 20-pound group?

Draw a conclusion: did the data support the hypothesis? are the final weights proportionally the same? If not, why not? execute the findings adhere come Weber’s Law? Weber’s regulation states the the concept that a just-noticeable difference in a economic stimulation is proportional come the magnitude of the initial stimulus.

 Summary

A sensory activation occurs once a physical or chemical stimulus is processed into a neural signal (sensory transduction) by a sensory receptor. Late is one individual interpretation of a sensation and also is a brain function. Humans have special senses: olfaction, gustation, equilibrium, and also hearing, add to the general senses of somatosensation.

Sensory receptors are either dedicated cells associated with sensory neurons or the committed ends of sensory neurons that are a part of the peripheral nervous system, and also they are offered to obtain information about the atmosphere (internal or external). Each sensory receptor is modified for the type of stimulus it detects. For example, neither gustatory receptors no one auditory receptors are sensitive come light. Every sensory receptor is responsive come stimuli within a specific an ar in space, which is recognized as that receptor’s receptive field. The most fundamental function that a sensory mechanism is the translate into of a sensory signal to an electric signal in the worried system.

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every sensory signals, other than those from the olfactory system, enter the main nervous system and are routed come the thalamus. When the sensory signal exit the thalamus, the is conducted to the specific area that the cortex devoted to processing that particular sense.


Exercises

Which that the following statements around mechanoreceptors is false?Pacini corpuscles are uncovered in both glabrous and also hairy skin.Merkel’s disks are plentiful on the fingertips and also lips.Ruffini endings are encapsulated mechanoreceptors.Meissner’s corpuscles extend into the reduced dermis.Where walk perception occur?spinal cordcerebral cortexreceptorsthalamusIf a who cold receptor no longer transform cold stimuli into sensory signals, the person has actually a problem with the process of ________.receptiontransmissionperceptiontransductionAfter somatosensory transduction, the sensory signal travels with the brain as a(n) _____ signal.electricalpressureopticalthermal

Answers