The adequate stimulus is a property of a

sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...

that determines the type of energy to which a sensory receptor responds with the initiation of

sensory transduction In physiology, transduction is the translation of arriving stimulus into an action potential by a sensory receptor. It begins when stimulus changes the membrane potential of a receptor cell. A receptor cell converts the energy in a stimulus into ...

Sensory receptor Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...

are specialized to respond to certain types of stimuli. The adequate stimulus is the amount and type of energy required to stimulate a specific sensory organ. Many of the sensory stimuli are categorized by the mechanics by which they are able to function and their purpose. Sensory receptors that are present within the body typically are made to respond to a single stimulus. Sensory receptors are present all throughout the body, and they take a certain amount of a stimulus to trigger these receptors. The use of these sensory receptors allows the brain to interpret the signals to the body which allow a person to respond to the stimulus if the stimulus reaches a minimum threshold to signal the brain. The sensory receptors will activate the

system which will in turn send an electrical or chemical stimulus to a cell, and the cell will then respond with electrical signals to the brain which were produced from action potentials. The minuscule signals, which result from the stimuli, enter the cells must be amplified and turned into an sufficient signal that will be sent to the brain. A sensory receptor's adequate stimulus is determined by the signal transduction mechanisms and ion channels incorporated in the sensory receptor's plasma membrane. Adequate stimulus are often used in relation with

sensory threshold In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probabil ...

s and

absolute threshold In neuroscience and psychophysics, an absolute threshold was originally defined as the lowest level of a stimulus – light, sound, touch, etc. – that an organism could detect. Under the influence of signal detection theory, absolute threshol ...

s to describe the smallest amount of a stimulus needed to activate a feeling within the sensory organ.

Categorizations of receptors

They are categorized through the stimuli to which they respond. Adequate stimulus are also often categorized based on their purpose and locations within the body. The following are the categorizations of receptors within the body: *

Visual The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight ...

– These are found in the visual organs of species and are responsive to stimuli such as light and often consist of light sensitive molecules that enable certain species to have the ability to see the world in with they live. * Olfaction – These types of receptor sense are activated in order to sense the external molecules that enter the nasal organ and attach to the receptors which will interpret the stimuli and send the signal containing information about the stimuli to the brain. * Auditory – These types of receptors are often found within the organs used to hear and are responsive to vibrations within the surrounding areas, and they often allow their owners to understand information about sound waves traveling through the aid. *

Vestibular The Vestibular (from pt, vestíbulo, "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazilian university, universities to select the students extrance exam, admitted. The Vestibular usua ...

– These types of receptors are usually found within organs used to hear, and they aid in the detection of movement that surrounds the creature using it. * Gustatory – These sensory receptors are present within the mouth and are responsive to the molecular stimuli that enter the mouth. The receptors in the mouth typically fall into two of the following categories: receptors that are responsive to specific chemicals and receptors that are responsive to particles such as hydrogen ions, which are charged. * Tactile – These types of receptors are normally present within the skin and are able to respond to stimulation such as heat, pressure, and movement

Classes

There are several different types of stimuli to which adequate stimuli respond. The following are examples of stimuli to which receptors may: *

Light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

– When the adequate stimulus of a sensory receptor is light, the sensory receptors contain pigment molecules whose shape is transformed by light, and the changes in these molecules activate ion channels which initiate

. *

Sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by ...

– When the adequate stimulus of a sensory receptor is sound, the sensory receptors are

hair cell Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment ...

s (

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

s). These hair cells contain

stereocilia Stereocilia (or stereovilli or villi) are non-motile apical cell modifications. They are distinct from cilia and microvilli, but are closely related to microvilli. They form single "finger-like" projections that may be branched, with normal cell ...

, which when bent, trigger the opening of ion channels. Thus hair cells transform the pressure waves of the sound into receptor potentials to initiate

Sensory receptors

Sensory receptors are the ends of nerves within the body that respond to stimuli. There are many different types of sensory receptors that each respond to stimuli that they are uniquely fitted to res Types of sensory receptors include the following: *

Nociceptor A nociceptor ("pain receptor" from Latin ''nocere'' 'to harm or hurt') is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sens ...

– These are stimulus that are responsive to the stimuli that signal potential damage to the body. * Photoreceptors – These are receptors that are responsive to light that enters the eye and produces the visual stimuli that many animals use to function. *

Mechanoreceptors A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, a ...

– These are receptors that are responsive to physical stimulation such as movement, vibration, and stress. *

Thermoreceptors A thermoreceptor is a non-specialised sense receptor, or more accurately the receptive portion of a sensory neuron, that codes absolute and relative changes in temperature, primarily within the innocuous range. In the mammalian peripheral nervous s ...

– These are types of receptors that are present within the skin and monitor any changes in the skins temperature

Classic examples of absolute threshold

In 1962, Eugene Galanter, a psychologist, tested stimuli till people were able to feel them approximately 50% of the time, then used the following as examples of absolute threshold: *

– On a clear, dark night a candle can be seen from approximately 30 miles away. *

Olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, i ...

– A person can smell a single drop of perfume after it has diffused into 3 rooms. * Auditory – In a silent area, a person can hear a watch tick from approximately 20 feet. *

– A person is able to tell of a tilt that when on a clock face is seen to be less than half a minute. * Gustatory – A person can taste a single teaspoon of sugar which is diluted in 2 gallons of water. * Tactile – A person can feel a fly's wing dropped from 3 feet above them falling onto their cheek. Through these conditions, Galanter was able to show that human's sensory organs are often more sensitive than originally thought.

Notes

References

{{DEFAULTSORT:Adequate Stimulus Neurophysiology