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Sensory neurons, also known as afferent neurons, are
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. ...
s in the
nervous system
In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...
, that convert a specific type of
stimulus
A stimulus is something that causes a physiological response. It may refer to:
*Stimulation
**Stimulus (physiology), something external that influences an activity
**Stimulus (psychology), a concept in behaviorism and perception
*Stimulus (economi ...
, via their
receptors
Receptor may refer to:
*Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a n ...
, into
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s or
graded potential
Graded potentials are changes in membrane potential that vary in size, as opposed to being all-or-none. They include diverse potentials such as receptor potentials, electrotonic potentials, subthreshold membrane potential oscillations, slow-wave ...
s. This process is called
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 ...
. The
cell bodies of the sensory neurons are located in the
dorsal ganglia of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
.
The sensory information travels on the
afferent nerve fibers in a
sensory nerve
A sensory nerve, or afferent nerve, is a general anatomic term for a nerve which contains predominantly somatic afferent nerve fibers. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) fro ...
, to the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
via the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
. The stimulus can come from ''exteroreceptors'' outside the body, for example those that detect light and sound, or from ''interoreceptors'' inside the body, for example those that are responsive to
blood pressure or the
sense of body position.
Types and function
Different types of sensory neurons have different sensory receptors that respond to different kinds of stimuli. There are at least six external and two internal sensory receptors:
External receptors
External receptors that respond to stimuli from outside the body are called exteroreceptors.
Exteroreceptors include
olfactory receptor
Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give r ...
s (smell),
taste receptor
A taste receptor or tastant is a type of cellular receptor which facilitates the sensation of taste. When food or other substances enter the mouth, molecules interact with saliva and are bound to taste receptors in the oral cavity and other loc ...
s,
photoreceptors (vision),
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 (hearing),
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 ...
(temperature), and a number of different
mechanoreceptors (stretch, distortion).
Smell
The sensory neurons involved in
smell are called
olfactory sensory neurons. These neurons contain
receptor
Receptor may refer to:
* Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse
*Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
s, called
olfactory receptor
Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give r ...
s, that are activated by
odor molecules in the air. The molecules in the air are detected by enlarged
cilia and
microvilli. These sensory neurons produce action potentials. Their axons form the
olfactory nerve, and they synapse directly onto neurons in the cerebral cortex (olfactory bulb). They do not use the same route as other sensory systems, bypassing the brain stem and the thalamus. The neurons in the olfactory bulb that receive direct sensory nerve input, have connections to other parts of the olfactory system and many parts of the limbic system. 9.
Taste
Similar to
olfactory receptor
Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give r ...
s,
taste receptor
A taste receptor or tastant is a type of cellular receptor which facilitates the sensation of taste. When food or other substances enter the mouth, molecules interact with saliva and are bound to taste receptors in the oral cavity and other loc ...
s (gustatory receptors) in
taste bud
Taste buds contain the taste receptor cells, which are also known as gustatory cells. The taste receptors are located around the small structures known as papillae found on the upper surface of the tongue, soft palate, upper esophagus, the c ...
s interact with chemicals in food to produce an
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
.
Vision
Photoreceptor cells are capable of
phototransduction, a process which converts light (
electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...
) into electrical signals. These signals are refined and controlled by the interactions with other types of neurons in the retina. The five basic classes of neurons within the retina are
photoreceptor cells,
bipolar cells,
ganglion cells
{{stack,
A ganglion cell is a cell found in a ganglion. Examples of ganglion cells include:
* Retinal ganglion cell (RGC) found in the ganglion cell layer of the retina
* Cells that reside in the adrenal medulla, where they are involved in th ...
,
horizontal cells, and
amacrine cells. The basic circuitry of the retina incorporates a three-neuron chain consisting of the photoreceptor (either a
rod or
cone
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines con ...
), bipolar cell, and the ganglion cell. The first action potential occurs in the retinal ganglion cell. This pathway is the most direct way for transmitting visual information to the brain. There are three primary types of photoreceptors:
Cones
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines conn ...
are photoreceptors that respond significantly to
color
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...
. In humans the three different types of cones correspond with a primary response to short wavelength (blue), medium wavelength (green), and long wavelength (yellow/red).
["eye, human." Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.] Rods are photoreceptors that are very sensitive to the intensity of light, allowing for vision in dim lighting. The concentrations and ratio of rods to cones is strongly correlated with whether an animal is
diurnal or
nocturnal. In humans, rods outnumber cones by approximately 20:1, while in nocturnal animals, such as the
tawny owl
The tawny owl (''Strix aluco''), also called the brown owl, is commonly found in woodlands across Europe to western Siberia, and has seven recognized subspecies. It is a stocky, medium-sized owl, whose underparts are pale with dark streaks, a ...
, the ratio is closer to 1000:1.
Retinal ganglion cells are involved in the
sympathetic response
The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the ...
. Of the ~1.3 million ganglion cells present in the retina, 1-2% are believed to be photosensitive.
Issues and decay of sensory neurons associated with vision lead to disorders such as:
*
Macular degeneration
Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, som ...
– degeneration of the central visual field due to either cellular debris or blood vessels accumulating between the retina and the choroid, thereby disturbing and/or destroying the complex interplay of neurons that are present there.
*
Glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
– loss of retinal ganglion cells which causes some loss of vision to blindness.
*
Diabetic retinopathy
Diabetic retinopathy (also known as diabetic eye disease), is a medical condition in which damage occurs to the retina due to diabetes mellitus. It is a leading cause of blindness in developed countries.
Diabetic retinopathy affects up to 80 perc ...
– poor blood sugar control due to diabetes damages the tiny blood vessels in the retina.
Auditory
The
auditory system is responsible for converting pressure waves generated by vibrating air molecules or
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'' b ...
into signals that can be interpreted by the brain.
This mechanoelectrical transduction is mediated with
hair cells
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. ...
within the ear. Depending on the movement, the hair cell can either hyperpolarize or depolarize. When the movement is towards the tallest
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 ...
, the Na
+ cation channels open allowing Na
+ to flow into cell and the resulting depolarization causes the Ca
++ channels to open, thus releasing its neurotransmitter into the afferent auditory nerve. There are two types of hair cells: inner and outer. The inner hair cells are the sensory receptors .
Problems with sensory neurons associated with the auditory system leads to disorders such as:
*
Auditory processing disorder
Auditory processing disorder (APD), rarely known as King-Kopetzky syndrome or auditory disability with normal hearing (ADN), is a neurodevelopmental disorder affecting the way the brain processes auditory information. Individuals with APD usually ...
– Auditory information in the brain is processed in an abnormal way. Patients with auditory processing disorder can usually gain the information normally, but their brain cannot process it properly, leading to hearing disability.
*
Auditory verbal agnosia
Auditory verbal agnosia (AVA), also known as pure word deafness, is the inability to comprehend speech. Individuals with this disorder lose the ability to understand language, repeat words, and write from dictation. Some patients with AVA describe ...
– Comprehension of speech is lost but hearing, speaking, reading, and writing ability is retained. This is caused by damage to the posterior superior
temporal lobes
The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe is involved in pro ...
, again not allowing the brain to process auditory input correctly.
Temperature
Thermoreceptors are sensory receptors, which respond to varying
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer.
Thermometers are calibrated in various Conversion of units of temperature, temp ...
s. While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that
mammals have at least two distinct types of thermoreceptors.
[Krantz, John. ]
Experiencing Sensation and Perception
''. Pearson Education, Limited, 2009. p. 12.3
The
bulboid corpuscle
The bulboid corpuscles (end-bulbs of Krause) are cutaneous receptors in the human body.
The end-bulbs of Krause were named after the German anatomist Wilhelm Krause (1833–1910).
Function
The end-bulbs of Krause were thought to be thermorecept ...
, is a
cutaneous receptor
A cutaneous receptor is the type of sensory receptor found in the skin ( the dermis or epidermis). They are a part of the somatosensory system. Cutaneous receptors include mechanoreceptors (pressure or distortion), nociceptors (pain), and thermore ...
a ''cold-sensitive'' receptor, that detects cold temperatures. The other type is a warmth-sensitive receptor.
Mechanoreceptors
Mechanoreceptors are sensory receptors which respond to mechanical forces, such as
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
or
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signa ...
.
Specialized sensory receptor cells called mechanoreceptors often encapsulate afferent fibers to help tune the afferent fibers to the different types of somatic stimulation. Mechanoreceptors also help lower thresholds for action potential generation in afferent fibers and thus make them more likely to fire in the presence of sensory stimulation.
Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.
Proprioceptors
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
are another type of mechanoreceptors which literally means "receptors for self". These receptors provide spatial information about limbs and other body parts.
Nociceptors are responsible for processing pain and temperature changes. The burning pain and irritation experienced after eating a chili pepper (due to its main ingredient, capsaicin), the cold sensation experienced after ingesting a chemical such as menthol or icillin, as well as the common sensation of pain are all a result of neurons with these receptors.
Problems with mechanoreceptors lead to disorders such as:
*
Neuropathic pain
Neuropathic pain is pain caused by damage or disease affecting the somatosensory system. Neuropathic pain may be associated with abnormal sensations called dysesthesia or pain from normally non-painful stimuli (allodynia). It may have continuous ...
- a severe pain condition resulting from a damaged sensory nerve
*
Hyperalgesia
Hyperalgesia ( or ; 'hyper' from Greek ὑπέρ (huper, “over”), '-algesia' from Greek algos, ἄλγος (pain)) is an abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can ...
- an increased sensitivity to pain caused by sensory ion channel,
TRPM8
Transient receptor potential cation channel subfamily M (melastatin) member 8 (TRPM8), also known as the cold and menthol receptor 1 (CMR1), is a protein that in humans is encoded by the ''TRPM8'' gene. The TRPM8 channel is the primary molecular ...
, which is typically responds to temperatures between 23 and 26 degrees, and provides the cooling sensation associated with menthol and icillin
*
Phantom limb syndrome - a sensory system disorder where pain or movement is experienced in a limb that does not exist
Internal receptors
Internal receptors that respond to changes inside the body are known as interoceptors.
Blood
The
aortic bodies and
carotid bodies contain clusters of
glomus cell
Glomus cells are the cell type mainly located in the carotid bodies and aortic bodies. Glomus type I cells are peripheral chemoreceptors which sense the oxygen, carbon dioxide and pH levels of the blood. When there is a decrease in the blood's p ...
s –
peripheral chemoreceptors Peripheral chemoreceptors (of the carotid and aortic bodies) are so named because they are sensory extensions of the peripheral nervous system into blood vessels where they detect changes in chemical concentrations. As transducers of patterns of va ...
that detect changes in chemical properties in the blood such as
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
concentration. These receptors are
polymodal responding to a number of different stimuli.
Nociceptors
Nociceptors respond to potentially damaging stimuli by sending signals to the spinal cord and brain. This process, called
nociception, usually causes the perception of
pain.
They are found in internal organs as well as on the surface of the body to "detect and protect".
[ Nociceptors detect different kinds of noxious stimuli indicating potential for damage, then initiate neural responses to withdraw from the stimulus.][
* ''Thermal'' nociceptors are activated by noxious heat or cold at various temperatures.][
* ''Mechanical'' nociceptors respond to excess pressure or mechanical deformation, such as a pinch.][
* ''Chemical'' nociceptors respond to a wide variety of chemicals, some of which signal a response. They are involved in the detection of some spices in food, such as the pungent ingredients in ]Brassica
''Brassica'' () is a genus of plants in the cabbage and mustard family ( Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, or mustard plants. Crops from this genus are sometimes called ''cole c ...
and Allium
''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, D ...
plants, which target the sensory neural receptor to produce acute pain and subsequent pain hypersensitivity.
Connection with the central nervous system
Information coming from the sensory neurons in the head enters the central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
(CNS) through cranial nerves
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
. Information from the sensory neurons below the head enters the spinal cord and passes towards the brain through the 31 spinal nerves. The sensory information traveling through the spinal cord follows well-defined pathways. The nervous system codes the differences among the sensations in terms of which cells are active.
Classification
Adequate stimulus
A sensory receptor's adequate stimulus is the stimulus modality for which it possesses the adequate 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 ...
apparatus. Adequate stimulus can be used to classify sensory receptors:
* Baroreceptors respond to pressure in blood vessels
* Chemoreceptor
A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...
s respond to chemical stimuli
* Electromagnetic radiation receptors respond to electromagnetic radiation
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) li ...
** Infrared receptors respond to infrared radiation
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
** Photoreceptors respond to visible 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 ...
** Ultraviolet receptors respond to ultraviolet radiation
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...
* Electroreceptor
Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
s respond to electric fields
** Ampullae of Lorenzini respond to electric fields, salinity, and to temperature, but function primarily as electroreceptors
* Hydroreceptors respond to changes in humidity
* Magnetoreceptors respond to magnetic fields
* Mechanoreceptors respond to mechanical stress
In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...
or mechanical strain
* 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 ...
s respond to damage, or threat of damage, to body tissues, leading (often but not always) to pain perception
* Osmoreceptor
An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. Osmoreceptors can be found in several structures, including two of the circumventricular organs – ...
s respond to the osmolarity
Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L ...
of fluids (such as in the hypothalamus)
* Proprioceptor
Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense".
Proprioception is mediated by proprioceptors, mechanosensory neurons ...
s provide the sense of position
* Thermoreceptors respond to temperature, either heat, cold or both
Location
Sensory receptors can be classified by location:
* Cutaneous receptor
A cutaneous receptor is the type of sensory receptor found in the skin ( the dermis or epidermis). They are a part of the somatosensory system. Cutaneous receptors include mechanoreceptors (pressure or distortion), nociceptors (pain), and thermore ...
s are sensory receptors found in the dermis or epidermis.
* Muscle spindle
Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...
s contain mechanoreceptors that detect stretch in muscles.
Morphology
Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology:
* Free nerve endings
A free nerve ending (FNE) or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. ''Afferent'' in this case means bringing information from the body's periphery toward the brain. They function as cu ...
characterize the 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 ...
s and thermoreceptors and are called thus because the terminal branches of the neuron are unmyelinated and spread throughout the dermis and epidermis.
* Encapsulated receptors consist of the remaining types of cutaneous receptors. Encapsulation exists for specialized functioning.
Rate of adaptation
* A tonic receptor is a sensory receptor that adapts slowly to a stimulus and continues to produce action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s over the duration of the stimulus.[mentor.lscf.ucsb.edu/course/fall/eemb157/lecture/Lectures%2016,%2017%2018.ppt ] In this way it conveys information about the duration of the stimulus. Some tonic receptors are permanently active and indicate a background level. Examples of such tonic receptors are pain receptors
Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, ...
, joint capsule
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.muscle spindle
Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...
.
* A phasic receptor is a sensory receptor that adapts rapidly to a stimulus. The response of the cell diminishes very quickly and then stops. It does not provide information on the duration of the stimulus; instead some of them convey information on rapid changes in stimulus intensity and rate. An example of a phasic receptor is the Pacinian corpuscle
Pacinian corpuscle or lamellar corpuscle or Vater-Pacini corpuscle; is one of the four major types of mechanoreceptors (specialized nerve ending with adventitious tissue for mechanical sensation) found in mammalian skin. This type of mechanorece ...
.
Drugs
There are many drugs currently on the market that are used to manipulate or treat sensory system disorders. For instance, Gabapentin
Gabapentin, sold under the brand name Neurontin among others, is an anticonvulsant medication primarily used to treat partial seizures and neuropathic pain. It is a first-line medication for the treatment of neuropathic pain caused by diabeti ...
is a drug that is used to treat neuropathic pain by interacting with one of the voltage-dependent calcium channels present on non-receptive neurons. Some drugs may be used to combat other health problems, but can have unintended side effects on the sensory system. Ototoxic
Ototoxicity is the property of being toxic to the ear (''oto-''), specifically the cochlea or auditory nerve and sometimes the vestibular system, for example, as a side effect of a drug. The effects of ototoxicity can be reversible and temporary, ...
drugs are drugs which affect the cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory or ...
through the use of a toxin like aminoglycoside
Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer ...
antibiotics, which poison hair cells. Through the use of these toxins, the K+ pumping hair cells cease their function. Thus, the energy generated by the endocochlear potential The endocochlear potential (EP; also called endolymphatic potential) is the positive voltage of 80-100mV seen in the cochlear endolymphatic spaces. Within the cochlea the EP varies in the magnitude all along its length. When a sound is presented, th ...
which drives the auditory signal transduction process is lost, leading to hearing loss.
Neuroplasticity
Ever since scientists observed cortical remapping in the brain of Taub's Silver Spring monkeys, there has been a large amount of research into sensory system plasticity. Huge strides have been made in treating disorders of the sensory system. Techniques such as constraint-induced movement therapy
Constraint-induced movement therapy (CI, CIT, or CIMT) is a form of rehabilitation therapy that improves upper extremity function in stroke and other central nervous system damage patients by increasing the use of their affected upper limb. developed by Taub have helped patients with paralyzed limbs regain use of their limbs by forcing the sensory system to grow new neural pathway
In neuroanatomy, a neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable neurotransmission (the sending of a signal from one region of the nervous system to an ...
s. Phantom limb syndrome is a sensory system disorder in which amputees perceive that their amputated limb still exists and they may still be experiencing pain in it. The mirror box
Mirror therapy (MT) or mirror visual feedback (MVF) is a therapy for pain or disability that affects one side of the patient more than the other side. It was invented by Vilayanur S. Ramachandran to treat post-amputation patients who had phantom ...
developed by V.S. Ramachandran, has enabled patients with phantom limb syndrome to relieve the perception of paralyzed or painful phantom limbs. It is a simple device which uses a mirror in a box to create an illusion in which the sensory system perceives that it is seeing two hands instead of one, therefore allowing the sensory system to control the "phantom limb". By doing this, the sensory system can gradually get acclimated to the amputated limb, and thus alleviate this syndrome.
Other animals
Hydrodynamic reception is a form of mechanoreception used in a range of animal species.
Additional images
File:Blausen 0809 Skin TactileReceptors.png, Illustration of Tactile Receptors in the Skin
File:Blausen 0804 Skin LamellatedCorpuscle.png, Illustration of Lamellated Corpuscle
File:Blausen 0807 Skin RuffiniCorpuscle.png, Illustration of Ruffini Corpuscle
File:Blausen 0805 Skin MerkelCell.png, Illustration of Skin Merkel Cell
File:Blausen 0808 Skin TactileCorpuscle.png, Illustration of Tactile Corpuscle
File:Blausen 0806 Skin RootHairPlexus.png, Illustration of Root Hair Plexus
File:Blausen 0803 Skin FreeNerveEndings.png, Illustration of Free Nerve Endings
See also
* Sensory nerve
A sensory nerve, or afferent nerve, is a general anatomic term for a nerve which contains predominantly somatic afferent nerve fibers. Afferent nerve fibers in a sensory nerve carry sensory information toward the central nervous system (CNS) fro ...
* Pseudounipolar neuron
A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches. A single process arises from the cell body and then divides into an axon and a dendrite. ...
* Efferent nerve
Efferent nerve fibers refer to axonal projections that ''exit'' a particular region; as opposed to Afferent nerve fiber, afferent projections that ''arrive'' at the region. These terms have a slightly different meaning in the context of the per ...
* Neural coding
Neural coding (or Neural representation) is a neuroscience field concerned with characterising the hypothetical relationship between the stimulus and the individual or ensemble neuronal responses and the relationship among the electrical activit ...
* Posterior column
Posterior may refer to:
* Posterior (anatomy), the end of an organism opposite to its head
** Buttocks, as a euphemism
* Posterior horn (disambiguation)
* Posterior probability
The posterior probability is a type of conditional probability that r ...
* Receptive field
The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms.
Complexity of the receptive field ranges from the unidimensional chemical structure of o ...
* Sensory system
The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved i ...
References
External links
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The major classes of somatic sensory receptors
{{Somatosensory system
Afferent neurons
Human cells
Sensory receptors
Receptor cells