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Nociceptor
A nociceptor (; ) 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 sensation of pain to direct attention to the body part, so the threat can be mitigated; this process is called nociception. Terminology Nociception and pain are usually evoked only by pressures and temperatures that are potentially damaging to tissues. This barrier or threshold of pain, threshold contrasts with the more sensitive visual, auditory, olfactory, taste, and somatosensory responses to stimuli. The experience of pain is individualistic and can be suppressed by stress or exacerbated by anticipation. Simple activation of a nociceptor does not always lead to perceived pain, because the latter also depends on the frequency of the action potentials, integration of pre- and postsynaptic signals, and influences from higher or central processes. Scientific investigation Nociceptors were disc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nociception
In physiology, nociception , also nocioception; ) is the Somatosensory system, sensory nervous system's process of encoding Noxious stimulus, noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular signal, and recognize and characterize the signal to trigger an appropriate defensive response. In nociception, intense chemical (e.g., capsaicin present in chili pepper or cayenne pepper), mechanical (e.g., cutting, crushing), or thermal (heat and cold) stimulation of sensory neurons called nociceptors produces a signal that travels along a chain of nerve fibers to the brain. Nociception triggers a variety of physiological and behavioral responses to protect the organism against an aggression, and usually results in a subjective experience, or perception, of pain in Sentience, sentient beings. Detection of noxious stimuli Potentially damaging mechanical, thermal, and chemical stimuli are detecte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sensory Neuron
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 receptor potentials. This process is called sensory transduction. The cell bodies of the sensory neurons are located in the dorsal root ganglia of the spinal cord. The sensory information travels on the afferent nerve fibers in a sensory nerve, to the brain via the spinal cord. Spinal nerves transmit external sensations via sensory nerves to the brain through the spinal cord. 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 Sensory neurons in vertebrates are predominantly pseudounipolar or bipolar, and different types of sensory neurons have different sensory receptors that respond t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cornea
The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea Refraction, refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK. While the cornea contributes most of the eye's focusing power, its Focus (optics), focus is fixed. Accommodation (eye), Accommodation (the refocusing of light to better view near objects) is accomplished by changing the geometry of the lens. Medical terms related to the cornea often start with the prefix "''wikt:kerat-, kerat-''" from the Ancient Greek, Greek word κέρας, ''horn''. Structure The cornea has myelinated, unmyelinated nerve endings sensitive to touch, temperature and chemicals; a to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
A Delta Fiber
Group A nerve fibers are one of the three classes of nerve fiber as ''generally classified'' by Erlanger and Gasser. The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated. The other classification is a sensory grouping that uses the terms '' type Ia and type Ib'', '' type II'', ''type III'', and ''type IV'', sensory fibers. Types There are four subdivisions of group A nerve fibers: alpha (α) Aα; beta (β) Aβ; , gamma (γ) Aγ, and delta (δ) Aδ. These subdivisions have different amounts of myelination and axon thickness and therefore transmit signals at different speeds. Larger diameter axons and more myelin insulation lead to faster signal propagation. Group A nerves are found in both motor and sensory pathways. Different sensory receptors are innervated by different types of nerve fibers. Proprioceptors are innervated by type Ia, Ib and II ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cutaneous Nociceptor
A cutaneous receptor is a sensory receptor found in the skin that provides information about temperature, touch (including vibration and pain), spatial orientation,pressure (stretching or squeezing), and metabolic circumstances (including those induced by external chemical substances). The main four types of cutaneous receptors are tactile corpuscles, bulbous corpuscles, Pacinian corpuscles, and Merkel nerve endings, although the latter do not qualify as sensory corpuscles in the narrow sense. Types The sensory receptors in the skin are: *Mechanoreceptors **Bulbous corpuscles (skin stretch) ** Bulboid corpuscles (Cold) **Tactile corpuscles (changes in texture, slow vibrations) ** Pacinian corpuscles (deep pressure, fast vibrations) **Merkel nerve endings (sustained touch and pressure) **Free nerve endings *thermoreceptor *nociceptors *chemoreceptors Modalities With the above-mentioned receptor types the skin can sense the modalities touch, pressure, vibration, temperature and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nerve Conduction Velocity
In neuroscience, nerve conduction velocity (CV) is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factors, which include age, sex, and various medical conditions. Studies allow for better diagnoses of various neuropathies, especially demyelinating diseases as these conditions result in reduced or non-existent conduction velocities. CV is an important aspect of nerve conduction studies. Normal conduction velocities Ultimately, conduction velocities are specific to each individual and depend largely on an axon's diameter and the degree to which that axon is myelinated, but the majority of 'normal' individuals fall within defined ranges. Nerve impulses are extremely slow compared to the speed of electricity, where the electric field can propagate with a speed on the order of 50–99% of the speed of light; however, it is very fast compared to the speed of blood flow, with some myelinated neuron ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Withdrawal Reflex
The withdrawal reflex (nociceptive flexion reflex or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli. The reflex rapidly coordinates the contractions of all the flexor muscles and the relaxations of the extensors in that limb causing sudden withdrawal from the potentially damaging stimulus. Spinal reflexes are often monosynaptic and are mediated by a simple reflex arc. A withdrawal reflex is mediated by a reflex arc, polysynaptic reflex resulting in the stimulation of many motor neurons in order to give a quick response. Example When a person touches a hot object and withdraws their hand from it without actively thinking about it, the heat stimulates Thermoreceptor, temperature and Nociceptor, pain receptors in the skin, triggering a sensory impulse that travels to the central nervous system. The sensory neuron then synapses with spinal interneuron, interneurons that connect to motor neurons. Some of these send motor impulses to the f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Afferent Nerve Fiber
Afferent nerve fibers are axons (nerve fibers) of sensory neurons that carry sensory information from sensory receptors to the central nervous system. Many afferent projections ''arrive'' at a particular brain region. In the peripheral nervous system, afferent nerve fibers are part of the sensory nervous system and arise from outside of the central nervous system. Sensory and mixed nerves contain afferent fibers. Structure Afferent neurons are pseudounipolar neurons that have a single process leaving the cell body dividing into two branches: the long one towards the sensory organ, and the short one toward the central nervous system (e.g. spinal cord). These cells do have sensory afferent dendrites, similar to those typically inherent in neurons. They have a smooth and rounded cell body located in the ganglia of the peripheral nervous system. Just outside the spinal cord, thousands of afferent neuronal cell bodies are aggregated in a swelling in the dorsal root known a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
C Fiber
Group C nerve fibers are one of three classes of nerve fiber in the central nervous system (CNS) and peripheral nervous system (PNS). The Group C fibers are unmyelinated and have a small diameter and low conduction velocity, whereas Groups A and B are myelinated. Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots (IV fiber). These fibers carry sensory information. Damage or injury to nerve fibers causes neuropathic pain. Capsaicin activates C fibre vanilloid receptors, providing the burning sensation associated with chili peppers. Structure and anatomy Location C fibers are one class of nerve fiber found in the nerves of the somatic sensory system. They are afferent fibers, conveying input signals from the periphery to the central nervous system. Structure C fibers are unmyelinated unlike most other fibers in the nervous system. This lack of myelination is the cause of their slow conduction velocit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pain
Pain is a distressing feeling often caused by intense or damaging Stimulus (physiology), stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sense, sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage." Pain motivates organisms to withdraw from damaging situations, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Congenital insensitivity to pain may result in reduced life expectancy. Most pain resolves once the noxious stimulus is removed and the body has healed, but it may persist despite removal of the stimulus and apparent healing of the body. Sometimes pain arises in the absence of any detectable stimulus, damage or disease. Pain is the most common reason for physician consultation in most developed countries. It is a major symptom in many medical conditions, and can interfere with a person's quality of life and general fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dorsal Root Ganglia
A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dorsal root ganglia. The axons of dorsal root ganglion neurons are known as afferents. In the peripheral nervous system, afferents refer to the axons that relay sensory information into the central nervous system (i.e. the brain and the spinal cord). Structure The neurons comprising the dorsal root ganglion are of the pseudo-unipolar type, meaning they have a cell body (soma) with two branches that act as a single axon, often referred to as a ''distal process'' and a ''proximal process''. Unlike the majority of neurons found in the central nervous system, an action potential in posterior root ganglion neuron may initiate in the ''distal process'' in the periphery, bypass the cell body, and continue to propagate along the ''proximal proces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
