Sensory neuron
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Sensory neurons, also known as afferent neurons, are
The sensory information travels on the
Types and function
Sensory neurons in vertebrates are predominantly pseudounipolar or bipolar, and 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.
Smell
The sensory neurons involved in
Taste
Taste sensation is facilitated by specialized sensory neurons located in the taste buds of the tongue and other parts of the mouth and throat. These sensory neurons are responsible for detecting different taste qualities, such as sweet, sour, salty, bitter, and savory. When you eat or drink something, chemicals in the food or liquid interact with receptors on these sensory neurons, triggering signals that are sent to the brain. The brain then processes these signals and interprets them as specific taste sensations, allowing you to perceive and enjoy the flavors of the foods you consume. [6] When taste receptor cells are stimulated by the binding of these chemical compounds (tastants), it can lead to changes in the flow of ions, such as sodium (Na+), calcium (Ca2+), and potassium (K+), across the cell membrane. [7] In response to tastant binding, ion channels on the taste receptor cell membrane can open or close. This can lead to depolarization of the cell membrane, creating an electrical signal.
Similar to olfactory receptors, taste receptors (gustatory receptors) in taste buds interact with chemicals in food to produce an action potential.
Vision
Issues and decay of sensory neurons associated with vision lead to disorders such as:
- Macular degeneration – 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.[10]
- Glaucoma – loss of retinal ganglion cells which causes some loss of vision to blindness.[11]
- Diabetic retinopathy – poor blood sugar control due to diabetes damages the tiny blood vessels in the retina.[12]
Auditory
The auditory system is responsible for converting pressure waves generated by vibrating air molecules or sound into signals that can be interpreted by the brain.
This mechanoelectrical transduction is mediated with
Problems with sensory neurons associated with the auditory system leads to disorders such as:
- Auditory processing disorder – 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.[14]
- temporal lobes, again not allowing the brain to process auditory input correctly.[15]
Temperature
Thermoreceptors are sensory receptors, which respond to varying temperatures. While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that mammals have at least two distinct types of thermoreceptors.[16] The bulboid corpuscle, is a cutaneous receptor 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 or distortion.[17]
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.[18]
Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.
Problems with mechanoreceptors lead to disorders such as:
- Neuropathic pain - a severe pain condition resulting from a damaged sensory nerve [20]
- Hyperalgesia - an increased sensitivity to pain caused by sensory ion channel, TRPM8, which is typically responds to temperatures between 23 and 26 degrees, and provides the cooling sensation associated with menthol and icillin [20]
- Phantom limb syndrome - a sensory system disorder where pain or movement is experienced in a limb that does not exist [21]
Internal receptors
Internal receptors that respond to changes inside the body are known as interoceptors.[4]
Blood
The aortic bodies and carotid bodies contain clusters of glomus cells – peripheral chemoreceptors that detect changes in chemical properties in the blood such as oxygen concentration.[22] 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.[23][24] They are found in internal organs as well as on the surface of the body to "detect and protect".[24] Nociceptors detect different kinds of noxious stimuli indicating potential for damage, then initiate neural responses to withdraw from the stimulus.[24]
- Thermal nociceptors are activated by noxious heat or cold at various temperatures.[24]
- Mechanical nociceptors respond to excess pressure or mechanical deformation, such as a pinch.[24]
- 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 and Allium plants, which target the sensory neural receptor to produce acute pain and subsequent pain hypersensitivity.[25]
Connection with the central nervous system
Information coming from the sensory neurons in the head enters the central nervous system (CNS) through cranial nerves. Information from the sensory neurons below the head enters the spinal cord and passes towards the brain through the 31 spinal nerves.[26] 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
- Baroreceptors respond to pressure in blood vessels
- Chemoreceptors respond to chemical stimuli
- Electromagnetic radiation receptors respond to electromagnetic radiation[27]
- infrared radiation
- visible light
- ultraviolet radiation[citation needed]
- Electroreceptors 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
- mechanical stress or mechanical strain
- Nociceptors respond to damage, or threat of damage, to body tissues, leading (often but not always) to pain perception
- osmolarityof fluids (such as in the hypothalamus)
- Proprioceptorsprovide the sense of position
- Thermoreceptors respond to temperature, either heat, cold or both
Location
Sensory receptors can be classified by location:
- epidermis.[28]
- Muscle spindles 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:
- epidermis.
- Encapsulated receptors consist of the remaining types of cutaneous receptors. Encapsulation exists for specialized functioning.
Rate of adaptation
- A
- A phasic receptor is a sensory receptor that adapts rapidly to a stimulus. The response of the cell diminishes very quickly and then stops.[32] It does not provide information on the duration of the stimulus;[30] instead some of them convey information on rapid changes in stimulus intensity and rate.[31] An example of a phasic receptor is the Pacinian corpuscle.
Drugs
There are many drugs currently on the market that are used to manipulate or treat sensory system disorders. For instance, gabapentin 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.[20] Some drugs may be used to combat other health problems, but can have unintended side effects on the sensory system. Dysfunction in the hair cell mechanotransduction complex, along with the potential loss of specialized ribbon synapses, can lead to hair cell death, often caused by ototoxic drugs like aminoglycoside antibiotics poisoning the cochlea.[33] Through the use of these toxins, the K+ pumping hair cells cease their function. Thus, the energy generated by the endocochlear potential which drives the auditory signal transduction process is lost, leading to hearing loss.[34]
Neuroplasticity
Ever since scientists observed
Other animals
Hydrodynamic reception is a form of mechanoreception used in a range of animal species.
Additional images
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Illustration of Tactile Receptors in the Skin
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Illustration of Lamellated Corpuscle
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Illustration of Ruffini Corpuscle
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Illustration of Skin Merkel Cell
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Illustration of Tactile Corpuscle
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Illustration of Root Hair Plexus
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Illustration of Free Nerve Endings
See also
- Pseudounipolar neuron
- Neural coding
- Posterior column
- Receptive field
- Sensory system
- List of distinct cell types in the adult human body
- Sensory nerve
- Motor nerve
- Afferent nerve fiber
- Efferent nerve fiber
- Motor neuron
References
- ISBN 9781789080261.
- ISBN 978-0878936977.
- ^ Koop LK, Tadi P. Neuroanatomy, Sensory Nerves. 2022 Jul 25. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan–. PMID: 30969668.
- ^ ISBN 0805319409.
- ^ Breed, Michael D., and Moore, Janice. Encyclopedia of Animal Behavior . London: Elsevier, 2010. Print.
- ^ Vincis R, Fontanini A. Central taste anatomy and physiology. Handb Clin Neurol. 2019;164:187-204. doi: 10.1016/B978-0-444-63855-7.00012-5. PMID: 31604547; PMCID: PMC6989094.
- ^ Taruno A, Nomura K, Kusakizako T, Ma Z, Nureki O, Foskett JK. Taste transduction and channel synapses in taste buds. Pflugers Arch. 2021 Jan;473(1):3-13. doi: 10.1007/s00424-020-02464-4. Epub 2020 Sep 16. PMID: 32936320; PMCID: PMC9386877.
- ^ a b "eye, human." Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.
- PMID 17021323.
- OCLC 15695765.
- ^ "NIHSeniorHealth: Diabetic Retinopathy - Causes and Risk Factors". nihseniorhealth.gov. Archived from the original on 2017-01-14. Retrieved 2016-12-19.
- ISBN 978-0878936977.
- ^ "Auditory Processing Disorder (APD)" (PDF). British Society of Audiology APD Special Interest Group MRC Institute of Hearing Research.
- S2CID 25584363.
- ^ Krantz, John. Experiencing Sensation and Perception Archived 2017-11-17 at the Wayback Machine. Pearson Education, Limited, 2009. p. 12.3
- ISBN 978-0878936977.
- ISBN 978-0878936977.
- ^ PMID 16404144.
- PMID 10473458.
- ^ Satir, P. & Christensen, S.T. (2008) Structure and function of mammalian cilia. in Histochemistry and Cell Biology, Vol 129:6
- ^ Sherrington C. The Integrative Action of the Nervous System. Oxford: Oxford University Press; 1906.
- ^ PMID 29032407.
- PMID 32641835.
- ISBN 978-1111831004.
- ^ Michael J. Gregory. "Sensory Systems". Clinton Community College. Archived from the original on 2013-06-25. Retrieved 2013-06-06.
- ^ "Cutaneous receptor".
- ISBN 978-3-540-29678-2.
- ^ a b mentor.lscf.ucsb.edu/course/fall/eemb157/lecture/Lectures%2016,%2017%2018.ppt[dead link]
- ^ a b "Sensory Receptor Function". frank.mtsu.edu. Archived from the original on August 3, 2008.
- ISBN 978-0840068651. Retrieved 13 December 2017.
- ^ Wagner EL, Shin JB. Mechanisms of Hair Cell Damage and Repair. Trends Neurosci. 2019 Jun;42(6):414-424. doi: 10.1016/j.tins.2019.03.006. Epub 2019 Apr 13. PMID: 30992136; PMCID: PMC6556399.
- S2CID 8216716.
- ^ Schwartz and Begley 2002, p. 160; "Constraint-Induced Movement Therapy", excerpted from "A Rehab Revolution," Stroke Connection Magazine, September/October 2004. Print.
- OCLC 43344396.
External links
- Media related to Sensory neuron at Wikimedia Commons
- The major classes of somatic sensory receptors