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Mechanoreceptors are a type of sensory receptor that responds to mechanical pressure, distortion, or displacement of tissue. They are located on sensory neurons that convert mechanical pressure into electrical signals that are sent to the central nervous system. Cutaneous mechanoreceptors are present in the skin and respond to mechanical stimuli resulting from physical interaction, including pressure and vibration. Muscle spindles, a type of mechanoreceptor, can detect muscle tension and provide information about muscle length and the degree to which they are being stretched. They are found in most striated (skeletal) muscles and consist of specialized intrafusal muscle fibers surrounded by a capsule of connective tissue. The most sensitive mechanoreceptors in humans are the hair cells in the cochlea of the inner ear, which transduce sound for the brain.
| Characteristics | Values |
|---|---|
| Definition | A mechanoreceptor is a sensory receptor that responds to mechanical pressure or distortion |
| Location | Mechanoreceptors are located on sensory neurons |
| Function | They convert mechanical pressure into electrical signals that are sent to the central nervous system |
| Types | Cutaneous mechanoreceptors, muscle spindles, SA mechanoreceptors, QA mechanoreceptors, periodontal mechanoreceptors, baroreceptors, cardiopulmonary receptors, slowly adapting type 1 (SA1) mechanoreceptors, hair follicle receptors, hair cells, type 1 and type 2 mechanoreceptors |
| Sensitivity | Very sensitive to changes in stimulation |
| Stimulus | Stimuli include touch, pressure, stretching, sound waves, and motion |
| Adaptation | Mechanoreceptors can be categorised by their rate of adaptation, i.e. how quickly they return to a normal pulse rate after receiving a stimulus. Those that adapt quickly are called "phasic", while those that are slow to adapt are called "tonic". |
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What You'll Learn
Muscle spindles
Primary type Ia sensory fibres (large diameter) spiral around all intrafusal muscle fibres, ending near the middle of each fibre. Secondary type II sensory fibres (medium diameter) end adjacent to the central regions of the static bag and chain fibres. These fibres send information by stretch-sensitive mechanically-gated ion channels of the axons. The sensory innervation of the muscle spindle arises from both group Ia and group II afferent fibres, which differ in their axonal conduction velocity.
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Golgi tendon organs
The Golgi tendon organ (GTO) is a proprioceptor or sensory receptor that senses changes in muscle tension. GTOs are located in the musculotendinous junctions, or the interface between a muscle and its tendon. GTOs are nearly as common in most muscles as muscle spindles.
The GTO is a fusiform receptor enclosed within a thin perineural capsule containing packed tendinous collagen, with several muscle fibres attached to one pole. The collagen fascicles are attached to muscle fibres at one end and merge with the tendon of the muscle at the other. Each capsule is about 1 mm long, has a diameter of about 0.1 mm, and is perforated by one or more afferent type Ib sensory nerve fibres.
The GTO is named after Italian physician Camillo Golgi, who discovered it and made several other contributions to the study of the nervous system.
GTOs are activated by stretch or active contraction of a muscle and that transmit information about muscle tension. When the muscle generates force, the sensory terminals are compressed, deforming the terminals of the Ib afferent axon, opening stretch-sensitive cation channels. As a result, the Ib axon is depolarized and fires nerve impulses that are propagated to the spinal cord. If there is too much muscle tension, the GTO will inhibit the muscle from creating any force, thus protecting the muscle from injury.
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Mechanoreceptor activation
Mechanoreceptors are a type of somatosensory receptor that relays extracellular stimulus to intracellular signal transduction through mechanically gated ion channels. They are located on sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system (CNS). Mechanoreceptors can detect a wide range of mechanical stimuli from both the external and internal environments. External stimuli include touch, pressure, stretching, sound waves, and motion, while internal stimuli include muscle length and hollow organ distension.
There are four major categories of tactile mechanoreceptors: Merkel's disks, Meissner's corpuscles, Ruffini endings, and Pacinian corpuscles. Merkel's disks, or Merkel cells, are slowly adapting type 1 (SA1) mechanoreceptors that detect sustained pressure and underlie the perception of form and roughness on the skin. They are found in areas of the body with less tactile acuity, such as the fingertips and lips, and have small discrete receptive fields. Meissner's corpuscles are involved in skin movement and object handling detection, and their primary stimulation is through dynamic deformation. They are rapidly adapting type 1 (RA) mechanoreceptors that underlie the perception of light touch and adapt rapidly to changes in texture.
Ruffini endings, or Ruffini corpuscles, are slowly adapting type 2 (SA2) mechanoreceptors that detect tension deep in the skin and fascia and respond to skin stretch. They account for 20% of the receptors in the human hand and have large receptive fields. Pacinian corpuscles, or Lamellar corpuscles, are deformation or pressure receptors located in the skin and various internal organs. They sense vibrations and detect fine textures, such as rapid vibrations of about 200-300 Hz.
Other types of mechanoreceptors include hair cells, which are sensory receptors in the vestibular system of the inner ear and contribute to the auditory system and equilibrioception. Baroreceptors are a type of mechanoreceptor sensory neuron that is excited by the stretch of blood vessels. Juxtacapillary (J) receptors respond to events such as pulmonary edema, pulmonary emboli, pneumonia, and barotrauma. Muscle spindles are stretch receptors found in muscles that detect muscle tension and innervate via spinal neurons, which are important for the somatosensory system.
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Mechanoreceptor categories
Mechanoreceptors are a type of somatosensory receptor that responds to mechanical pressure or distortion. They are located on sensory neurons that convert mechanical pressure into electrical signals that are sent to the central nervous system (CNS). Mechanoreceptors can be categorized in several ways, including by the type of sensation they perceive, the rate of adaptation, and their morphology.
Sensation
Cutaneous mechanoreceptors respond to mechanical stimuli that result from physical interaction, including pressure, vibration, and stretching. They are located in the skin, like other cutaneous receptors. They can also be found in the tongue, where they play a role in haptic exploration and exteroceptive tactile perception of objects in the mouth.
Rate of Adaptation
Cutaneous mechanoreceptors can also be categorized based on their rates of adaptation. When a mechanoreceptor receives a stimulus, it begins to fire impulses or action potentials at an elevated frequency. The cell will eventually adapt to a constant stimulus, and the pulses will return to a normal rate. Receptors that adapt quickly are referred to as "phasic", while those that are slow to return to their normal firing rate are called "tonic".
Morphology
Cutaneous mechanoreceptors can also be categorized by their morphology, or structure. They can be either encapsulated or unencapsulated, and the free nerve endings are usually unencapsulated dendrites.
Types of Mechanoreceptors
There are four major categories of tactile mechanoreceptors: Merkel’s disks, Meissner’s corpuscles, Ruffini endings, and Pacinian corpuscles. Slowly adapting type 1 (SA1) mechanoreceptors, with Merkel corpuscle end-organs, detect sustained pressure and underlie the perception of form and roughness on the skin. Slowly adapting type 2 (SA2) mechanoreceptors, or Ruffini corpuscles, detect tension deep in the skin and respond to skin stretch. Rapidly adapting (RA) or Meissner corpuscles underlie the perception of light touch and adapt rapidly to changes in texture. Pacinian corpuscles detect rapid vibrations and produce transient responses, but have large receptive fields.
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Mechanoreceptor functions
Mechanoreceptors are a type of somatosensory receptor that responds to mechanical pressure or distortion. They are located on sensory neurons that convert mechanical pressure into electrical signals that are sent to the central nervous system. Mechanoreceptors are primary sensory structures that provide information about the mechanical features of the internal and external environments. They are present in the superficial as well as the deeper layers of skin and near bone.
There are four major categories of tactile mechanoreceptors: Merkel's Disks, Meissner's Corpuscles, Ruffini Endings, and Pacinian Corpuscles. The Slowly Adapting type 1 (SA1) mechanoreceptor, with the Merkel corpuscle end-organ (also known as Merkel discs), detects sustained pressure and underlies the perception of form and roughness on the skin. The Rapidly Adapting (RA) or Meissner corpuscle end-organ mechanoreceptor (also known as the tactile corpuscles) underlies the perception of light touch, such as a flutter or slip on the skin. It adapts rapidly to changes in texture (around 50 Hz vibrations).
The Slowly Adapting type 2 (SA2) mechanoreceptors, with the Ruffini corpuscle end-organ (also known as the bulbous corpuscles), detect tension deep in the skin and fascia and respond to skin stretch. They also produce sustained responses to static stimulation but have large receptive fields. The Pacinian corpuscle or Vater-Pacinian corpuscles or Lamellar corpuscles in the skin and fascia detect rapid vibrations of about 200-300 Hz.
Some other types of mechanoreceptors include hair cells, baroreceptors, and juxtacapillary (J) receptors. Hair cells are the most sensitive mechanoreceptors in humans and are found in the cochlea of the inner ear. They transduce sound for the brain. Baroreceptors are a type of mechanoreceptor sensory neuron that is excited by the stretch of blood vessels. Juxtacapillary (J) receptors respond to events such as pulmonary edema, pulmonary emboli, pneumonia, and barotrauma.
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Frequently asked questions
Mechanoreceptors are sensory receptors that respond to mechanical pressure or distortion. They are located on sensory neurons that convert mechanical pressure into electrical signals that are sent to the central nervous system.
Muscle spindles are a type of mechanoreceptor that can detect muscle tension and muscle length (the degree to which they are being stretched). They are found in most striated (skeletal) muscles and consist of specialised intrafusal muscle fibres surrounded by a capsule of connective tissue.
There are several types of mechanoreceptors in the human body, including Merkel discs, Meissner's corpuscles, Ruffini endings, Pacinian corpuscles, hair root plexuses, and muscle spindles.
