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By the end of this section, you will be able to:
  • Identify the general and special senses in humans
  • Describe three important steps in sensory perception
  • Explain the concept of just-noticeable difference in sensory perception

Senses provide information about the body and its environment. Humans have five special senses: olfaction (smell), gustation (taste), equilibrium (balance and body position), vision, and hearing. Additionally, we possess general senses, also called somatosensation, which respond to stimuli like temperature, pain, pressure, and vibration. Vestibular sensation , which is an organism’s sense of spatial orientation and balance, proprioception    (position of bones, joints, and muscles), and the sense of limb position that is used to track kinesthesia    (limb movement) are part of somatosensation. Although the sensory systems associated with these senses are very different, all share a common function: to convert a stimulus (such as light, or sound, or the position of the body) into an electrical signal in the nervous system. This process is called sensory transduction    .

There are two broad types of cellular systems that perform sensory transduction. In one, a neuron works with a sensory receptor    , a cell, or cell process that is specialized to engage with and detect a specific stimulus. Stimulation of the sensory receptor activates the associated afferent neuron, which carries information about the stimulus to the central nervous system. In the second type of sensory transduction, a sensory nerve ending responds to a stimulus in the internal or external environment: this neuron constitutes the sensory receptor. Free nerve endings can be stimulated by several different stimuli, thus showing little receptor specificity. For example, pain receptors in your gums and teeth may be stimulated by temperature changes, chemical stimulation, or pressure.

Reception

The first step in sensation is reception    , which is the activation of sensory receptors by stimuli such as mechanical stimuli (being bent or squished, for example), chemicals, or temperature. The receptor can then respond to the stimuli. The region in space in which a given sensory receptor can respond to a stimulus, be it far away or in contact with the body, is that receptor’s receptive field . Think for a moment about the differences in receptive fields for the different senses. For the sense of touch, a stimulus must come into contact with body. For the sense of hearing, a stimulus can be a moderate distance away (some baleen whale sounds can propagate for many kilometers). For vision, a stimulus can be very far away; for example, the visual system perceives light from stars at enormous distances.

Transduction

The most fundamental function of a sensory system is the translation of a sensory signal to an electrical signal in the nervous system. This takes place at the sensory receptor, and the change in electrical potential that is produced is called the receptor potential    . How is sensory input, such as pressure on the skin, changed to a receptor potential? In this example, a type of receptor called a mechanoreceptor    (as shown in [link] ) possesses specialized membranes that respond to pressure. Disturbance of these dendrites by compressing them or bending them opens gated ion channels in the plasma membrane of the sensory neuron, changing its electrical potential. Recall that in the nervous system, a positive change of a neuron’s electrical potential (also called the membrane potential), depolarizes the neuron. Receptor potentials are graded potentials: the magnitude of these graded (receptor) potentials varies with the strength of the stimulus. If the magnitude of depolarization is sufficient (that is, if membrane potential reaches a threshold), the neuron will fire an action potential. In most cases, the correct stimulus impinging on a sensory receptor will drive membrane potential in a positive direction, although for some receptors, such as those in the visual system, this is not always the case.

Questions & Answers

name the gas that diffuses into the plants leaves on a bright, sunny day
Tuhemwe Reply
explain why this gas diffuses into the plant's leaves
Tuhemwe
name two gases that diffuses out of the plant's leaves on a bright sunny day
Tuhemwe
what is ecosystem
Rondy Reply
why does a car move yet it is not a living thing?
Sserujja
what is the reason of swelling due to fracture
Ejaz Reply
how do animals reproduce
Kelvin Reply
be specific because there are so many types of animals and how they reproduce are different
Sheillah
yeah
Chinwendu
what happens when you sneeze
Asuquo Reply
The sneeze center sends out a signal to tightly close your throat, eyes and mouth. Your chest muscles contract and compress your lungs while your throat muscles relax. All of that means air, saliva and mucus is forced out of your nose and mouth. AAAAAHHHH-CHOOOO.
Hassan
how are you
Ayouba
hy
Ejaz
hii
Ishitha
hello
mahesha
Hello
Madu
Am fine
Abavon
how far
Abavon
hello
Sheillah
with why
Sheillah
with what
Sheillah
I have a question plzz
Sheillah
what is globsl warming
Rondy
Global warming is the overall rise in temperature of the Earth itself which is caused by multiple factors. Such factors include: greenhouse gases, the burning of fossil fuels and other forms of human activity.
Maryam
It's overall effects are known as climate change.
Maryam
thanks
Rondy
good
Haider
No problem.
Maryam
Thank you.
Maryam
what is creatinine?
Haider
Creatinine is a waste product produced in the body during muscle metabolism. This waste product is expelled from the body through urine. Here is it's formula:  C4H7N3O
Maryam
Formula: C4H7N3O
Maryam
ok
Haider
ok
Stephen
Outline the process of cell in the body interms of it's function.
Aliruku Reply
what communication method used mainly by plants
Jerda Reply
what is biology
james Reply
Biology is the study of life
Omoloju
define nerve impulse
Karlin Reply
A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulsesare mostly electrical signals along the dendrites to produce a nerve impulse or action potential. The action potential is the result of ions moving in and out of the cell.
Sam
What is the Molecular Biology?
Service Reply
The branch of biology that deals with the structure and function of the macromolecules (e.g. proteins and nucleic acids) essential to life.
Sam
what is botany
Sillah
Description Description Botany, also called plant science, plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field.
Sam
what is the difference between mitosis and meiosis?
Fatima Reply
what is an element
Saidu Reply
Element is any one of the simplest chemical substances that cannot be decomposed in a chemical reaction.
Lucky
an element is a substance that cannot be broken down into any other substance
Akosua
explain why only one sperm fertilisers the ovum
Frazzy Reply
its because other sperms are destroyed on the way
Nasib
A test tube is full of a colourless gas that puts a lighted wooden splint.what gas is this?
Jerda
what is cell
Dau Reply
Cell is the smallest unit of life
Yodit
cell refers of the basic, structural and function unit of an organism
jacob
smallest functional unit of an organism
Nasib
is the smallest basic unit of life
Tuhemwe
Is a basic unit of life
James
It's the basic, structural and functional unit of life/living organisms
Ese
explain for me for ecological factors affecting each of aquatic and terrestrial habitats
Ikeh Reply
Temperature, high humidity
Afriyie
50%
Yodit
temperature,light intensity,Co2
Nasib

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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