Pacinian corpuscle | |
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Details | |
Location | Skin |
Identifiers | |
Latin | corpusculum Pacinian |
MeSH | D010141 |
TH | H3.11.06.0.00009 |
FMA | 83604 |
Anatomical terms of microanatomy |
The Pacinian corpuscle (also lamellar corpuscle, or Vater-Pacini corpuscle) [1] is a low-threshold mechanoreceptor responsive to vibration or pressure, found in the skin and other internal organs. [2] In the skin it is one of the four main types of cutaneous receptors.
The corpuscles are present in skin notably on both surfaces of the hands and feet, arms, and neck. [3] Pacinian corpuscles are also found on bone periosteum, joint capsules, the pancreas and other internal organs, the breast, and genitals. [4]
Pacinian corpuscles are rapidly adapting mechanoreceptors. As phasic receptors they respond quickly but briefly to a stimulus with the response diminishing even when the stimulus is maintained. [5] They primarily respond to vibration, and deep pressure. They are especially sensitive to high-frequency vibrations. Groups of corpuscles sense pressure changes (such as on grasping or releasing an object). They are additionally crucially involved in proprioception. [1] The vibrational role may be used for detecting surface texture, such as rough and smooth.[ citation needed ]
Pacinian corpuscles are larger and fewer in number than Meissner's corpuscles, Merkel cells and Ruffini's corpuscles. [6] They may measure up to 2 mm in length, and nearly 1 mm in diameter. [7] They are oval, spherical, or irregularly coiled in shape. Larger ones are visible to the naked eye. [3] They have large receptive fields - as large as half of the palm. [7] In the skin, the corpuscles are situated deep within the dermis. [7]
Each corpuscle is associated with a myelinated axon; [3] these are some of the largest and fastest-conducting sensory axons arising from the skin. [7]
Towards the center of the corpuscle, the axon loses its sheaths, ending as with a slight bulge at the center of the corpuscle. This axon terminal issues brief projections of unknown functional significance into gaps between the surrounding innermost lamellae; large mitochondria and small vessels aggregate near these projections. [3]
The capsule consists of 20-70 concentrically-arranged connective tissue lamellae around the axon terminal at its center, forming a structure much like an onion. [7] The capsule consists of fibroblasts and fibrous connective tissue (mainly Type IV and Type II collagen network), separated by gelatinous material, more than 92% of which is water. [8] It presents a whorled pattern on micrographs.[ citation needed ]
If the corpuscle's capsule is experimentally removed, the divested axon terminal becomes slowly adapting. The capsule is therefore responsible for the corpuscle's selectivity for low-frequency stimuli. This is a result of the slippery lamellae sliding past each other when the corpuscle is structurally deformed by external pressure so that effects of sustained pressure are soon dissipated by the lamellae, abolishing deformation of the central axon terminal itself. [7] The capsule thus acts as a physiological high-pass filter. [3]
Pacinian corpuscles are rapidly adapting phasic receptors that detect gross pressure changes and vibrations in the skin. [5] Pacinian corpuscles have a large receptive field on the skin's surface with an especially sensitive center. [6]
The corpuscles are especially sensitive to vibrations, which they can sense even centimeters away. [6] Their optimal sensitivity is 250 Hz, and this is the frequency range generated upon fingertips by textures made of features smaller than 1 μm. [9] [10] Pacinian corpuscles respond when the skin is rapidly indented but not when the pressure is steady (due to the capsule). [6] It is thought that they respond to high-velocity changes in joint position. They have also been implicated in detecting the location of touch sensations on handheld tools. [11]
Pacinian corpuscles sense stimuli due to the deformation of their lamellae, which press on the membrane of the sensory neuron and causes it to bend or stretch. [12] When the lamellae are deformed, due to either application or release of pressure, a generator or receptor potential is created as it physically deforms the plasma membrane of axon terminal, making it "leak" different cations through mechanosensitive channels which initiates the receptor potential. This initial receptor potential is potentiated by voltage-activated ion channels present in the inner-coreof the corpuscle. Finally, the receptor potential is modulated to neural spikes or action potential with the help of opening of sodium ion channels present at the first Ranvier's Node of the axon. [13]
Due to generation of receptor potential in the receptive area of the neurite (especially near the heminode or half-node of the axon) the potential at the first Ranvier's node can reach certain threshold, triggering nerve impulses or action potentials at the first node of Ranvier. The first Ranvier's node of the myelinated section of the neurite is often found inside the capsule. This impulse is then transferred along the axon from node to node with the use of sodium channels and sodium/potassium pumps in the axon membrane.[ citation needed ]
Once the receptive area of the neurite is depolarized, it will depolarize the first node of Ranvier; however, as it is a rapidly adapting fibre, this does not carry on indefinitely, and the signal propagation ceases. This is a graded response, meaning that the greater the deformation, the greater the generator potential. This information is encoded in the frequency of impulses, since a bigger or faster deformation induces a higher impulse frequency. Action potentials are formed when the skin is rapidly distorted but not when pressure is continuous because of the mechanical filtering of the stimulus in the lamellar structure. The frequencies of the impulses decrease quickly and soon stop due to the relaxation of the inner layers of connective tissue that cover the nerve ending.[ citation needed ]
Pacinian corpuscles were the first cellular sensory receptor ever observed. They were first reported by German anatomist and botanist Abraham Vater and his student Johannes Gottlieb Lehmann in 1741, but ultimately named after Italian anatomist Filippo Pacini, who rediscovered them in 1835. [14] [15] John Shekleton, a curator of the Royal College of Surgeons in Ireland, also discovered them before Pacini, but his results were published later. [14] Similar to Pacinian corpuscles, Herbst corpuscles and Grandry corpuscles are found in bird species.[ citation needed ]
An axon or nerve fiber is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit information to different neurons, muscles, and glands. In certain sensory neurons, such as those for touch and warmth, the axons are called afferent nerve fibers and the electrical impulse travels along these from the periphery to the cell body and from the cell body to the spinal cord along another branch of the same axon. Axon dysfunction can be the cause of many inherited and acquired neurological disorders that affect both the peripheral and central neurons. Nerve fibers are classed into three types – group A nerve fibers, group B nerve fibers, and group C nerve fibers. Groups A and B are myelinated, and group C are unmyelinated. These groups include both sensory fibers and motor fibers. Another classification groups only the sensory fibers as Type I, Type II, Type III, and Type IV.
A neuron, neurone, or nerve cell is an excitable cell that fires electric signals called action potentials across a neural network in the nervous system. Neurons communicate with other cells via synapses, which are specialized connections that commonly use minute amounts of chemical neurotransmitters to pass the electric signal from the presynaptic neuron to the target cell through the synaptic gap.
In neuroscience, saltatory conduction is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials. The uninsulated nodes of Ranvier are the only places along the axon where ions are exchanged across the axon membrane, regenerating the action potential between regions of the axon that are insulated by myelin, unlike electrical conduction in a simple circuit.
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 sensory receptor.
Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.
A cutaneous receptor is the type of sensory receptor found in the skin. They are a part of the somatosensory system. Cutaneous receptors include mechanoreceptors, nociceptors (pain), and thermoreceptors (temperature).
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.
The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway is the major sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception from the skin and joints. It transmits this information to the somatosensory cortex of the postcentral gyrus in the parietal lobe of the brain. The pathway receives information from sensory receptors throughout the body, and carries this in the gracile fasciculus and the cuneate fasciculus, tracts that make up the white matter dorsal columns of the spinal cord. At the level of the medulla oblongata, the fibers of the tracts decussate and are continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.
Tactile corpuscles or Meissner's corpuscles are a type of mechanoreceptor discovered by anatomist Georg Meissner (1829–1905) and Rudolf Wagner. This corpuscle is a type of nerve ending in the skin that is responsible for sensitivity to pressure. In particular, they have their highest sensitivity when sensing vibrations between 10 and 50 hertz. They are rapidly adaptive receptors. They are most concentrated in thick hairless skin, especially at the finger pads.
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.
In neuroscience and anatomy, nodes of Ranvier, also known as myelin-sheath gaps, occur along a myelinated axon where the axolemma is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction due to the manner in which the action potential seems to "jump" from one node to the next along the axon. This results in faster conduction of the action potential.
A dorsal root ganglion is a cluster of neurons 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 star-nosed mole is a small semiaquatic mole found in moist, low elevation areas in the northern parts of North America. It is the only extant member of the tribe Condylurini and genus Condylura, and it has more than 25,000 minute sensory receptors in touch organs, known as Eimer's organs, with which this hamster-sized mole feels its way around. With the help of its Eimer's organs, it may be perfectly poised to detect seismic wave vibrations.
Merkel nerve endings are mechanoreceptors situated in the basal epidermis as well as around the apical ends or some hair follicles. They are slowly adapting They have small receptive fields measuring some milimeters in diameter. Most are associated with fast-conducting large myelinated axons. A single afferent nerve fibre branches to innervate up to 90 such endings. Merkel nerve endings respond to light touch. They respond to sustained pressure, and are sensitive to edges of objects. Their exact functions remain controversial.
The tactile corpuscles of Grandry or Grandry corpuscles are mechanoreceptors found in the beak skin and oral mucosa of aquatic birds. They were first described by Grandry in 1869 in the bill skin of ducks and geese. Their general structure includes the flattened endings of an afferent nerve fiber sandwiched between two or more somewhat flattened sensory cells called Grandry cells, all surrounded by a layer of satellite cells and a partial capsule of collagen protein. Electrophysiological studies have shown that Grandry corpuscles function as rapidly adapting velocity detectors. In birds, Grandry and Merkel corpuscles share many morphological similarities, which has led to some confusion in the literature over their classification.
Cutaneous innervation refers to an area of the skin which is supplied by a specific cutaneous nerve.
Eimer's organs are organs for the sense of touch, shaped like bulbous papillae, formed from modified epidermis. First isolated by Theodor Eimer from the European mole in 1871, these organs are present in many moles, and are particularly dense on the star-nosed mole, which bears 25,000 of them on its unique tentacled snout. The organs are formed from a stack of epidermal cells, which is innervated by myelinated fibers from the dermis, which form terminal swellings just below the keratinized outer surface of the epidermis. They contain a complex of Merkel cell and neurite in the epidermis, and a lamellated corpuscle in the dermal connective tissue.
Pallesthesia, or vibratory sensation, is the ability to perceive vibration. This sensation, often conducted through skin and bone, is usually generated by mechanoreceptors such as Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an action potential in afferent nerves found in various layers of the skin and body. The afferent neuron travels to the spinal column and then to the brain where the information is processed. Damage to the peripheral nervous system or central nervous system can result in a decline or loss of pallesthesia.
The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. It has two subdivisions, one for the detection of mechanosensory information related to touch, and the other for the nociception detection of pain and temperature. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of body position and balance (proprioception).
The Golgi tendon organ (GTO) is a proprioceptor – a type of sensory receptor that senses changes in muscle tension. It lies at the interface between a muscle and its tendon known as the musculotendinous junction also known as the myotendinous junction. It provides the sensory component of the Golgi tendon reflex.