Group C nerve fiber - AbsoluteAstronomy.com

Location

C fibers are found in the peripheral nerves

Peripheral nervous system

The peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...

of the somatic sensory system

Somatosensory system

The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...

. They are afferent

Afferent

Afferent is an anatomical term with the following meanings:*Conveying towards a center, for example the afferent arterioles conveying blood towards the Bowman's capsule in the Kidney. Opposite to Efferent.*Something that so conducts, see Afferent nerve fiber...

fibers, conveying input signals from the periphery

Peripheral nervous system

to the central nervous system.

Structure

C fibres are unmyelinated

Myelin

Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system. Myelin is an outgrowth of a type of glial cell. The production of the myelin sheath is called myelination...

unlike most other fibers in the nervous system. This lack of myelination is the cause of their slow conduction velocity

Nerve conduction study

A nerve conduction study is a test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body.Nerve conduction velocity is a common measurement made during this test...

, which is on the order of no more than 2 . C fibers are on average 0.2-1.5 μm

Micrometre

A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

in diameter. The other main classification of nociceptors is Aδ fibers. These fibers have axons that are larger (1-5 μm), in diameter, are myelinated, and have a higher conduction velocity, which is on the order of about 20 m/s.

Remak bundles

C fiber axons are grouped together into what is known as Remak bundles. These occur when an unmyelinated Schwann cell

Schwann cell

Schwann cells or neurolemmocytes are the principal glia of the peripheral nervous system . Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle...

bundles the axons close together by surrounding them. The Schwann cell keeps them from touching each other by squeezing its cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

between the axons. The condition of Remak bundles varies with age. The number of C fiber axons in each Remak bundle varies with location. For example in a rat model, large bundles of greater than 20 axons are found exiting the L5 dorsal root ganglion

Dorsal root ganglion

In anatomy and neuroscience, a dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.-Unique unipolar structure:...

, while smaller bundles of average 3 axons are found in distal nerve segments. Multiple neurons contribute axons to the Remak bundle with an average ratio of about 2 axons contributed per bundle. The cross sectional area of a Remak bundle is proportional to the number of axons found inside it. Remak bundles in the distal peripheral nerve are clustered with other Remak bundles. The Remak Schwann cells have been shown to be electrochemically responsive to action potentials

Action potential

In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...

of the axons contained within them.

In experiments where nerve injury is caused but nearby C fibers remain intact, increased spontaneous activity in the C fibers is observed. This phenomenon supports the theory that damaged nerve fibers may release factors that alter the function of neighboring undamaged fibers. Study of Remak bundles has important implications in nerve regeneration after sustaining injury. Currently, recovery of distal C fiber function takes months and may still only regain incomplete function. This may result in abnormal sensory function or neuropathic pain. Remak bundles are thought to release certain trophic factors that promote the regeneration of the damaged axons.

Pathway

C fibers synapse to second-order projection neurons in the spinal cord at the upper laminae of the dorsal horn in the substantia gelatinosa

Substantia gelatinosa of Rolando

The apex of the posterior horn of the gray matter of the spinal cord is capped by a V-shaped or crescentic mass of translucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando , which contains both neuroglia cells, and small nerve cells...

. The second-order projection neurons are of the wide dynamic range (WDR) type, which receive input from both nociceptive terminals as well as myelinated A-type fibers. There are three types of second order projection neurons in the spinothalamic tract

Spinothalamic tract

The spinothalamic tract is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and crude touch...

: wide dynamic range (WDR), high threshold (HT), and low threshold (LT). These classifications are based on their responses to mechanical stimuli. The second-order neurons ascend to the brain stem

Brain stem

In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...

and thalamus

Thalamus

The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...

in the ventrolateral

Anatomical terms of location

Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...

, or anterolateral

Anatomical terms of location

, quadrant of the contralateral

Anatomical terms of location

half of the spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

, forming the spinothalamic tract. The spinothalamic tract is the main pathway associated with pain and temperature perception, which immediately crosses the spinal cord laterally. This crossover feature is clinically important because it allows for identification of the location of injury.

Function

Because of their higher conduction velocity, Aδ fibers are responsible for the sensation of a sharp first pain

Pain

Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...

. They respond to a weaker intensity of stimulus. C fibers respond to stimuli which have stronger intensities and are the ones to account for the slow, dull, longer-lasting, second pain.

C fibers are considered polymodal because they can respond to thermal, mechanical, and chemical stimuli. C fibers respond to all kinds of physiological changes in the body. For example, they can respond to hypoxia

Hypoxia (medical)

Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...

, hypoglycemia

Hypoglycemia

Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...

, hypo-osmolarity, the presence of muscle metabolic products, and even light or sensitive touch. C fiber receptors include:

C fiber nociceptors
- responsible for the second, burning pain
C fiber warming specific receptors
- responsible for warmth
ultra-slow histamine-selective C fibers
- responsible for itch
tactile C fibers
- sensual touch
C mechano- and metabo- receptors in muscles or joints
- responsible for muscle exercise, burn and cramp

This variation of input signals calls for a variety of cells of the cortex

Cerebral cortex

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

in lamina 1 to have different modality-selectiveness and morphologies. These varying neurons are responsible for the different feelings we perceive in our body and can be classified by their responses to ranges of stimuli. The brain uses the integration of these signals to maintain homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

in the body whether it is temperature related or pain related.

Vanilloid Receptor

The vanilloid receptor (VR-1, TRPV1) is a receptor

Sensory receptor

In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism...

that is found on the free nerve endings of both C and Aδ fibers that responds to elevated levels of heat (>43°C) and the chemical capsaicin

Capsaicin

Capsaicin 2CHCH=CH4CONHCH2C6H3-4--3- ) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact...

. Capsaicin activates C fibers by opening a ligand

Ligand

In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

-gated ion channel

Ion channel

Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...

and causing an action potential to occur. Because this receptor responds to both capsaicin and heat, chili peppers are sensed as hot. VR-1 is also able to respond to extracellular

Extracellular

In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...

acidification and can integrate simultaneous exposure to all three sensory stimuli. VR1 is essential for the inflammatory sensitization to noxious thermal stimuli. A second type of receptor, a vanilloid-like receptor

TRPV2

Transient receptor potential cation channel subfamily V member 2 is a protein that in humans is encoded by the TRPV2 gene.- Function :This gene encodes an ion channel that is activated by high temperatures above 52 °C. The protein may be involved in transduction of high-temperature heat responses...

(TRPV2,VRL-1), has a higher threshold of activation regarding heat of about 52°C and also responds to capsaicin and low pH. Both types of receptors are transmembrane receptors that are closed during resting conditions. When open, these receptors allow for an influx of sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

and calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

which initiates an action potential across the fibers. Both receptors are part of a larger family of receptors called transient receptor potential

Transient receptor potential

Transient receptor potential channels are a group of ion channels located mostly on the plasma membrane of numerous human and animal cell types. There are about 28 TRP channels that share some structural similarity to each other...

(TRP) receptors. If damage to these heat transducer receptors occurs, the result can be chronic neuropathic pain caused by lowering the heat pain threshold for their phosphorylation

Phosphorylation

Phosphorylation is the addition of a phosphate group to a protein or other organic molecule. Phosphorylation activates or deactivates many protein enzymes....

Role in Neuropathic Pain

Activation of nociceptors is not necessary to cause the sensation of pain. Damage or injury to nerve fibers that normally respond to innocuous stimuli like light touch may lower their activation threshold needed to respond; this change causes the organism to feel intense pain from the lightest of touch. Neuropathic pain syndromes are caused by lesions or diseases of the parts of the nervous system that normally signal pain. There are four main classes:

peripheral focal and multifocal nerve lesions
- traumatic, ischemic
  Ischemia
  In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
  
  or inflammatory
peripheral generalized polyneuropathies
Polyneuropathy
Polyneuropathy is a neurological disorder that occurs when many peripheral nerves throughout the body malfunction simultaneously. It may be acute and appear without warning, or chronic and develop gradually over a longer period of time. Many polyneuropathies have both motor and sensory...
- toxic, metabolic
  Metabolism
  Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
  
  , hereditary
  Heredity
  Heredity is the passing of traits to offspring . This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent cell or organism. Through heredity, variations exhibited by individuals can accumulate and cause some species to evolve...
  
  or inflammatory
CNS
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

lesions
- stroke
  Stroke
  A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
  
  , multiple sclerosis
  Multiple sclerosis
  Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
  
  , spinal cord injury
complex neuropathic disorders
- complex regional pain syndromes
  Complex regional pain syndrome
  Complex regional pain syndrome is a chronic progressive disease characterized by severe pain, swelling and changes in the skin. It often affects an arm or a leg and may spread to another part of the body.Though treatment is often unsatisfactory, early multimodal therapy can cause dramatic...
  
  [CRPSs]

After a nerve lesion of either C fibers or Aδ fibers, they become abnormally sensitive and cause pathological

Pathology

Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....

spontaneous activity. This alteration of normal activity is explained by molecular and cellular changes of the primary afferent

Afferent

nociceptors in response to the nerve damage. The abnormal activity of the damaged nerves is associated with the increased presence of mRNA

Messenger RNA

Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...

for voltage-gated sodium channels. Irregular grouping of these channels in sites of the abnormal activity may be responsible for lowering the activation threshold, thus leading to hyperactivity.

Central Sensitization
Sensitization
Sensitization is an example of non-associative learning in which the progressive amplification of a response follows repeated administrations of a stimulus. An everyday example of this mechanism is the repeated tonic stimulation of peripheral nerves that will occur if a person rubs his arm...

After nerve damage or repeated stimulation, WDR (wide dynamic range) neurons experience a general increase in excitability. This hyper-excitability can be caused by an increased neuronal response to a noxious stimulus (hyperalgesia

Hyperalgesia

Hyperalgesia is an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves. Temporary increased sensitivity to pain also occurs as part of sickness behavior, the evolved response to infection.-Types:...

), a larger neuronal receptive field

Receptive field

The receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron. Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system....

, or spread of the hyper-excitability to other segments. This condition is maintained by C fibers. C fibers cause central sensitization of the dorsal horn in the spinal cord in response to their hyperactivity. The mechanism underlying this phenomenon involves the release of glutamate

Glutamic acid

Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...

by these pathologically sensitized C fibers. The glutamate interacts with the postsynaptic

Chemical synapse

Chemical synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands. Chemical synapses allow neurons to form circuits within the central nervous system. They are crucial to the biological computations that underlie...

NMDA receptors

NMDA receptor

The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....

, which aids the sensitization of the dorsal horn. Presynaptic

Chemical synapse

neuronal voltage-gated N-calcium channels are largely responsible for the release of this glutamate as well as the neuropeptide

Neuropeptide

Neuropeptides are small protein-like molecules used by neurons to communicate with each other. They are neuronal signaling molecules, influence the activity of the brain in specific ways and are thus involved in particular brain functions, like analgesia, reward, food intake, learning and...

, substance P

Substance P

In the field of neuroscience, substance P is a neuropeptide: an undecapeptide that functions as a neurotransmitter and as a neuromodulator. It belongs to the tachykinin neuropeptide family. Substance P and its closely related neuropeptide neurokinin A are produced from a polyprotein precursor...

. The expression of presynaptic

Chemical synapse

neuronal voltage-gated N-calcium channels increases after a nerve lesion or repeated stimulation. NMDA receptor

NMDA receptor

The NMDA receptor , a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function....

activation (by glutamate) enhances postsynaptic Nitric Oxide Synthase

Nitric oxide synthase

Nitric oxide synthases are a family of enzymes that catalyze the production of nitric oxide from L-arginine. NO is an important cellular signaling molecule, having a vital role in many biological processes...

. Nitric Oxide is thought to migrate back to the presynaptic membrane to enhance the expression of the voltage-gated N-calcium channels resulting in a pain wind-up

Pain wind-up

Pain wind-up is central pain sensitization caused by repeated painful stimulation of peripheral nerves at sufficient intensity to stimulate group C nerve fibers, leading to progressively increasing electrical response in the corresponding spinal posterior horn neurons...

phenomenon. This abnormal central sensitization cycle results in increased pain (hyperalgesia) and pain responses from previously non-noxious stimuli evoke a pain response (allodynia

Allodynia

Allodynia is a pain due to a stimulus which does not normally provoke pain. Temperature or physical stimuli can provoke allodynia, and it often occurs after injury to a site...

).

Central sensitization of the dorsal horn neurons that is evoked from C fiber activity is responsible for temporal

Time

Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

summation of “second pain” (TSSP). This event is called ‘windup’ and relies on a frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

greater or equal to 0.33Hz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

of the stimulus. Windup is associated with chronic pain

Chronic pain

Chronic pain has several different meanings in medicine. Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers being 3 months and 6 months since the initiation of pain, though some theorists and...

and central sensitization. This minimum frequency was determined experimentally by comparing healthy patient fMRI’s

Functional magnetic resonance imaging

Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...

when subjected to varying frequencies of heat pulses. The fMRI maps show common areas activated by the TSSP responses which include contralateral thalamus (THAL), S1, bilateral S2, anterior and posterior insula (INS), mid-anterior cingulate cortex

Cingulate cortex

The cingulate cortex is a part of the brain situated in the medial aspect of the cortex. It includes the cortex of the cingulate gyrus, which lies immediately above the corpus callosum, and the continuation of this in the cingulate sulcus...

(ACC), and supplemental motor areas (SMA). TSSP events are also associated with other regions of the brain that process functions such as somatosensory processing, pain perception and modulation, cognition

Cognition

In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...

, pre-motor activity in the cortex.

Treatment

Currently, the availability of drugs proven to treat neuropathic pain is limited and varies widely from patient to patient. Many developed drugs have either been discovered by accident or by observation. Some past treatments include opiates

Opiate

In medicine, the term opiate describes any of the narcotic opioid alkaloids found as natural products in the opium poppy plant.-Overview:Opiates are so named because they are constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy,...

like poppy

Poppy

A poppy is one of a group of a flowering plants in the poppy family, many of which are grown in gardens for their colorful flowers. Poppies are sometimes used for symbolic reasons, such as in remembrance of soldiers who have died during wartime....

extract, non-steroidal anti-inflammatory drugs like salicylic acid

Salicylic acid

Salicylic acid is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin...

, and cocaine

Cocaine

Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...

. Other recent treatments consist of antidepressants

Antidepressant

An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...

and anticonvulsants

Anticonvulsant

The anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...

, although no substantial research on the actual mechanism of these treatments has been performed. However, patients respond differently to these treatments possibly because of gender differences or genetic

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

backgrounds. Therefore, researchers have come to realize that no one drug or one class of drugs will reduce all pain. Research is now focusing on the underlying mechanisms involved in pain perception and how it can go wrong in order to develop an appropriate drug for patients afflicted with neuropathic pain.

Microneurography

Human microneurography or simply microneurography involves the insertion of metal microelectrodes into nerve fascicles. -Applications:Microneurography is used to study autonomic nervous system function. This is accomplished by recording muscle sympathetic nerve activity...

is a technique using metal electrodes

Electrode

An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

to observe neural traffic of both myelinated and unmyelinated axons in efferent

Efferent nerve

In the nervous system, efferent nerves, otherwise known as motor or effector neurons, carry nerve impulses away from the central nervous system to effectors such as muscles or glands...

and afferent neurons of the skin and muscle. This technique is particularly important in research involving C fibers. Single action potentials from unmyelinated axons can be observed. Recordings from efferent postganglionic

Postganglionic fibers

In the autonomic nervous system, fibers from the ganglion to the effector organ are called postganglionic fibers.-Neurotransmitters:The neurotransmitters used for postganglionic fibers differ:...

sympathetic C fibers of the muscles and skin yield important insights into the neural control autonomic

Autonomic nervous system

The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

effector organs like blood vessels

Blood vessel

The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...

and sweat gland

Sweat gland

Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:...

s. Readings of afferent discharges from C nociceptors identified by marking method have also proved as important tools to revealing the mechanisms underlying sensations such as itch

Itch

Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response...

.

Unfortunately, interpretation of the microneurographic readings can be difficult because axonal membrane potential can not be determined from this method. A supplemental method used to better understand these readings involves examining recordings of post-spike

Action potential

excitability and shifts in latency; these features are associated with changes in membrane potential of unmyelinated axons like C fibers. Moalem-Taylor et al. experimentally used chemical modulators with known effects on membrane potential to study the post-spike super-excitability of C fibers. The researchers found three resulting events. Chemical medulators can produce a combination of loss of super-excitability along with increased axonal excitability, indicating membrane depolarization

Depolarization

In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...

. Secondly, membrane hyperpolarization

Hyperpolarization

Hyperpolarization has several meanings:* Hyperpolarization occurs when the strength of the electric field across the width of a cell membrane increases...

can result from a blockade of axonal hyperpolarization-activated current. Lastly, a non-specific increase in surface charge and a change in the voltage-dependent activation of sodium channels results from the application of calcium.

Location

Structure

Remak bundles

Pathway

Function

Vanilloid Receptor

Role in Neuropathic Pain

Treatment

Microneurography

See also