The receptive field of an individual sensory neuron is the particular region of the sensory space in which a stimulus will modify the firing of that neuron. This region can be a hair in the cochlea or a piece of skin, tongue or other part of an animal's body. Additionally, it can be the space surrounding an animal, such as an area of auditory space, fixed in a reference system based on the ears but that moves with the animal as it moves, or in a fixed location in space, independent of the animal's location. Receptive fields have been identified for neurons of the auditory system, the somatosensory system, the visual system; the term receptive field was first used by Sherrington to describe the area of skin from which a scratch reflex could be elicited in a dog. According to Alonso and Chen it was Hartline who applied the term to single neurons, in this case from the retina of a frog; the concept of receptive fields can be extended further up the nervous system. For example, the receptive field of a ganglion cell in the retina of the eye is composed of input from all of the photoreceptors which synapse with it, a group of ganglion cells in turn forms the receptive field for a cell in the brain.
This process is called convergence. The auditory system processes the temporal and spectral characteristics of sound waves, so the receptive fields of neurons in the auditory system are modeled as spectro-temporal patterns that cause the firing rate of the neuron to modulate with the auditory stimulus. Auditory receptive fields are modeled as spectro-temporal receptive fields, which are the specific pattern in the auditory domain that causes modulation of the firing rate of a neuron. Linear STRFs are created by first calculating a spectrogram of the acoustic stimulus, which determines the how the spectral density of the acoustic stimulus changes over time using the Short-time Fourier transform. Firing rate is modeled over time for the neuron using a peristimulus time histogram if combining over multiple repetitions of the acoustic stimulus. Linear regression is used to predict the firing rate of that neuron as a weighted sum of the spectrogram; the weights learned by the linear model are the STRF, represent the specific acoustic pattern that causes modulation in the firing rate of the neuron.
STRFs can be understood as the transfer function that maps an acoustic stimulus input to a firing rate response output. In the somatosensory system, receptive fields are regions of the skin or of internal organs; some types of mechanoreceptors have large receptive fields. Large receptive fields allow the cell to detect changes over a wider area, but lead to a less precise perception. Thus, the fingers, which require the ability to detect fine detail, have many, densely packed mechanoreceptors with small receptive fields, while the back and legs, for example, have fewer receptors with large receptive fields. Receptors with large receptive fields have a "hot spot", an area within the receptive field where stimulation produces the most intense response. Tactile-sense-related cortical neurons have receptive fields on the skin that can be modified by experience or by injury to sensory nerves resulting in changes in the field's size and position. In general these neurons have large receptive fields.
However, the neurons are able to discriminate fine detail due to patterns of excitation and inhibition relative to the field which leads to spatial resolution. R e c e p t i v e f i e l d = c e n t e r + s u r r o u n d In the visual system, receptive fields are volumes in visual space, they are smallest in the fovea where they can be a few minutes of arc like a dot on this page, to the whole page. For example, the receptive field of a single photoreceptor is a cone-shaped volume comprising all the visual directions in which light will alter the firing of that cell, its apex is located in the center of the lens and its base at infinity in visual space. Traditionally, visual receptive fields were portrayed in two dimensions, but these are slices, cut along the screen on which the researcher presented the stimulus, of the volume of space to which a particular cell will respond. In the case of binocular neurons in the visual cortex, receptive fields do not extend to optical infinity. Instead, they are restricted to a certain interval of distance from the animal, or from where the eyes are fixating.
The receptive field is identified as the region of the retina where the action of light alters the firing of the neuron. In retinal ganglion cells, this area of the retina would encompass all the photoreceptors, all the rods and cones from one eye that are connected to this particular ganglion cell via bipolar cells, horizontal cells, amacrine cells. In binocular neurons in the visual cortex, it is necessary to specify the corresponding area in both retinas. Although these can be mapped separately in each retina by shutting one or the other eye, the full influence on the neu
In physics, sound is a vibration that propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz is not perceptible by humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges. Acoustics is the interdisciplinary science that deals with the study of mechanical waves in gases and solids including vibration, sound and infrasound. A scientist who works in the field of acoustics is an acoustician, while someone working in the field of acoustical engineering may be called an acoustical engineer. An audio engineer, on the other hand, is concerned with the recording, manipulation and reproduction of sound. Applications of acoustics are found in all aspects of modern society, subdisciplines include aeroacoustics, audio signal processing, architectural acoustics, electro-acoustics, environmental noise, musical acoustics, noise control, speech, underwater acoustics, vibration.
Sound is defined as " Oscillation in pressure, particle displacement, particle velocity, etc. propagated in a medium with internal forces, or the superposition of such propagated oscillation. Auditory sensation evoked by the oscillation described in." Sound can be viewed as a wave motion in air or other elastic media. In this case, sound is a stimulus. Sound can be viewed as an excitation of the hearing mechanism that results in the perception of sound. In this case, sound is a sensation. Sound can propagate through a medium such as air and solids as longitudinal waves and as a transverse wave in solids; the sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium; as the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure and displacement of the medium vary in time.
At an instant in time, the pressure and displacement vary in space. Note that the particles of the medium do not travel with the sound wave; this is intuitively obvious for a solid, the same is true for liquids and gases. During propagation, waves can be refracted, or attenuated by the medium; the behavior of sound propagation is affected by three things: A complex relationship between the density and pressure of the medium. This relationship, affected by temperature, determines the speed of sound within the medium. Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction. If the sound and wind are moving in opposite directions, the speed of the sound wave will be decreased by the speed of the wind; the viscosity of the medium.
Medium viscosity determines the rate. For many media, such as air or water, attenuation due to viscosity is negligible; when sound is moving through a medium that does not have constant physical properties, it may be refracted. The mechanical vibrations that can be interpreted as sound can travel through all forms of matter: gases, liquids and plasmas; the matter that supports the sound is called the medium. Sound cannot travel through a vacuum. Sound is transmitted through gases and liquids as longitudinal waves called compression waves, it requires a medium to propagate. Through solids, however, it can be transmitted as transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves are waves of alternating shear stress at right angle to the direction of propagation. Sound waves may be "viewed" using parabolic objects that produce sound; the energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression or lateral displacement strain of the matter, the kinetic energy of the displacement velocity of particles of the medium.
Although there are many complexities relating to the transmission of sounds, at the point of reception, sound is dividable into two simple elements: pressure and time. These fundamental elements form the basis of all sound waves, they can be used to describe, in every sound we hear. In order to understand the sound more a complex wave such as the one shown in a blue background on the right of this text, is separated into its component parts, which are a combination of various sound wave frequencies. Sound waves are simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties: Frequency, or its inverse, wavelength Amplitude, sound pressure or Intensity Speed of sound DirectionSound, perceptible by humans has frequencies from abou
The hair follicle is a dynamic organ found in mammalian skin. It resides in the dermal layer of the skin and is made up of 20 different cell types, each with distinct functions; the hair follicle regulates hair growth via a complex interaction between hormones and immune cells. This complex interaction induces the hair follicle to produce different types of hair as seen on different parts of the body. For example, terminal hairs grow on the scalp and lanugo hairs are seen covering the bodies of fetuses in the uterus and in some new born babies; the process of hair growth occurs in distinct sequential stages. The first stage is called anagen and is the active growth phase, catagen is the resting stage, telogen is the regression of the hair follicle phase, exogen is the active shedding of hair phase and lastly kenogen is the phase between the empty hair follicle and the growth of new hair; the function of hair in humans has long been a subject of interest and continues to be an important topic in society, developmental biology and medicine.
Of all mammals, humans have the longest growth phase of scalp hair compared to hair growth on other parts of the body. For centuries, humans have ascribed esthetics to scalp hair styling and dressing and it is used to communicate social or cultural norms in societies. In addition to its role in defining human appearance, scalp hair provides protection from UV sun rays and is an insulator against extremes of hot and cold temperatures. Differences in the shape of the scalp hair follicle determine the observed ethnic differences in scalp hair appearance and texture. There are many human diseases in which abnormalities in hair appearance, texture or growth are early signs of local disease of the hair follicle or systemic illness. Well known diseases of the hair follicle include alopecia or hair loss, hirsutism or excess hair growth and lupus erythematosus; the position and distribution of hair follicles changes over the body. For example, the skin of the palms and soles do not have hair follicles whereas skin of the scalp, forearms and genitalia have abundant hair follicles.
There are many structures. Anatomically, the triad of hair follicle, sebaceous gland and arrector pili muscle make up the pilosebaceous unit. A hair follicle consists of: The papilla is a large structure at the base of the hair follicle; the papilla is made up of connective tissue and a capillary loop. Cell division in the papilla is either non-existent. Around the papilla is the hair matrix. A root sheath composed of an internal root sheath; the external root sheath appears empty with cuboid cells. The internal root sheath is composed of three layers, Henle's layer, Huxley's layer, an internal cuticle, continuous with the outermost layer of the hair fiber; the bulge is located in the outer root sheath at the insertion point of the arrector pili muscle. It houses several types of stem cells, which supply the entire hair follicle with new cells, take part in healing the epidermis after a wound. Stem cells express the marker LGR5+ in vivo. Other structures associated with the hair follicle include the cup in which the follicle grows known as the infundibulum, the arrector pili muscles, the sebaceous glands, the apocrine sweat glands.
Hair follicle receptors sense the position of the hair. Attached to the follicle is a tiny bundle of muscle fiber called the arrector pili; this muscle is responsible for causing the follicle lissis to become more perpendicular to the surface of the skin, causing the follicle to protrude above the surrounding skin and a pore encased with skin oil. This process results in goose bumps. Attached to the follicle is a sebaceous gland, which produces the oily or waxy substance sebum; the higher the density of the hair, the more sebaceous glands that are found. There are ethnic differences in several different hair characteristics; the differences in appearance and texture of hair are due to many factors: the position of the hair bulb relative to the hair follicle and shape of the dermal papilla, the curvature of the hair follicle. The scalp hair follicle in Caucasians is elliptical in shape and, produces straight or wavy hair, whereas the scalp hair follicle of people of African descent is more curvy, resulting in the growth of curled hair.
In utero, the epithelium and underlying mesenchyme interact to form hair follicles. A key aspect of hair loss with age is the aging of the hair follicle. Ordinarily, hair follicle renewal is maintained by the stem cells associated with each follicle. Aging of the hair follicle appears to be primed by a sustained cellular response to the DNA damage that accumulates in renewing stem cells during aging; this damage response involves the proteolysis of type XVII collagen by neutrophil elastase in response to the DNA damage in the hair follicle stem cells. Proteolysis of collagen leads to elimination of the damaged cells and to terminal hair follicle miniaturization. Hair grows in cycles of various phases: anagen is the growth phase; each phase has several morphologically and histologically distinguishable sub-phases. Prior to the start of cycling is a phase of follicular morphogenesis. There is a shedding phase, or exogen, independent of anagen and telogen in which one or several hairs that might arise from a single follicle exits.
Up to 90% of the hair follicles are in anagen phase, while 10–14% are in telogen and 1–2% in catagen. The cycle's length varies o
The Bulbous corpuscle or Ruffini ending or Ruffini corpuscle is a adapting mechanoreceptor located in the cutaneous tissue. More these detectors are located between the dermal papillae and the hypodermis, it is named after Angelo Ruffini. Ruffini corpuscles are enlarged dendritic endings with elongated capsules; this spindle-shaped receptor is sensitive to skin stretch, contributes to the kinesthetic sense of and control of finger position and movement. In particular they are at the highest density around the fingernails where they are believed to be useful for monitoring slippage of objects along the surface of the skin, allowing modulation of grip on an object. Ruffini corpuscles respond to sustained pressure and show little adaptation. Ruffinian endings are located in the deep layers of the skin, register mechanical deformation within joints, more angle change, with a specificity of up to 2.75 degrees, as well as continuous pressure states. They act as thermoreceptors that respond for a long time, so in case of deep burn there will be pain, as these receptors will be burned off.
Classically regarded as a thermoreceptor, the Ruffinian endings/corpuscle is not a thermoreceptor but is rather a mechanoreceptor. Paré M, Behets C, Cornu O. "Paucity of presumptive ruffini corpuscles in the index finger pad of humans". J Comp Neurol. 456: 260–6. Doi:10.1002/cne.10519. PMID 12528190
Free nerve ending
A free nerve ending or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. Afferent in this case means bringing information from the body's periphery toward the brain, they function as cutaneous nociceptors and are used by vertebrates to detect pain. Free nerve endings have no complex sensory structures, they are the most common type of nerve ending, are most found in the skin. They resemble the fine roots of a plant, they end in the stratum granulosum. FNEs surround hair follicles. Free nerve endings have different rates of adaptation, stimulus modalities, fiber types. Different types of FNE can be adapting, intermediate adapting, or adapting. A delta type II fibers are fast-adapting while A delta type I and C fibers are adapting. Free nerve endings can detect mechanical stimuli or danger. Thus, different free nerve endings work as thermoreceptors, cutaneous mechanoreceptors and nociceptors. In other words, they express polymodality; the majority of Aδ fibers and C fibers end as free nerve endings.
MacIver M, Tanelian D. "Free nerve ending terminal morphology is fiber-type-specific for A delta and C fibers innervating rabbit corneal epithelium". J Neurophysiol. 69: 1779–83. PMID 8509835. Gray's s233 Nociception: Transduction. From the University of Utah. Hada R. "". Shikwa Gakuho. 90: 161–80. PMID 2135092. Textbook in Medical Physiology And Pathophysiology: Essentials and clinical problems. Copenhagen Medical Publishers. 1999 - 2000 Cleland C, Hayward L, Rymer W. "Neural mechanisms underlying the clasp-knife reflex in the cat. II. Stretch-sensitive muscular-free nerve endings". J Neurophysiol. 64: 1319–30. PMID 2258749. Somatosensory System from Dr. Daley of North Carolina Wesleyan College
The rhesus macaque is one of the best-known species of Old World monkeys. It is listed as Least Concern in the IUCN Red List of Threatened Species in view of its wide distribution, presumed large population, its tolerance of a broad range of habitats. Native to South and Southeast Asia, rhesus macaque have the widest geographic ranges of any nonhuman primate, occupying a great diversity of altitudes and a great variety of habitats, from grasslands to arid and forested areas, but close to human settlements; the rhesus macaque is brown or grey in color and has a pink face, bereft of fur. Its tail is of medium length and averages between 22.9 cm. Adult males weigh about 7.7 kg. Females are smaller, averaging 5.3 kg in weight. Rhesus macaques have, on average, their ratio of arm length to leg length is 89%. They have a wide rib cage; the rhesus macaque has 32 teeth with a dental formula of bilophodont molars. The upper molars have four cusps: paracone, metacone and hypocone; the lower molars have four cusps: metaconid, protoconid and entoconid.
Rhesus macaques are native to India, Pakistan, Burma, Afghanistan, southern China, some neighboring areas. They have the widest geographic ranges of any nonhuman primate, occupying a great diversity of altitudes throughout Central and Southeast Asia. Inhabiting arid, open areas, rhesus macaques may be found in grasslands, in mountainous regions up to 2,500 m in elevation, they are regular swimmers. Babies as young as a few days old can swim, adults are known to swim over a half mile between islands, but are found drowned in small groups where their drinking waters lie. Rhesus macaques are noted for their tendency to move from rural to urban areas, coming to rely on handouts or refuse from humans, they adapt well to human presence, form larger troops in human-dominated landscapes than in forests. The southern and the northern distributional limits for rhesus and bonnet macaques currently run parallel to each other in the western part of India, are separated by a large gap in the center, converge on the eastern coast of the peninsula to form a distribution overlap zone.
This overlap region is characterized by the presence of mixed-species troops, with pure troops of both species sometimes occurring in close proximity to one another. The range extension of rhesus macaque – a natural process in some areas, a direct consequence of introduction by humans in other regions – poses grave implications for the endemic and declining populations of bonnet macaques in southern India; the Thai population is locally classified as endangered. There are about 1,000 troops at Wat Tham Pha Mak Ho, Tambon Si Songkhram, Wang Saphung district, Loei province; the name "rhesus" is reminiscent of the mythological king Rhesus of Thrace, a minor character in the Iliad. However, the French naturalist Jean-Baptiste Audebert, who applied the name to the species, stated: "it has no meaning". According to Zimmermann’s first description of 1780, the rhesus macaque is distributed in eastern Afghanistan, Bhutan, as far east as the Brahmaputra Valley in peninsular India and northern Pakistan.
Today, this is known as the Indian rhesus macaque M. m. mulatta, which includes the morphologically similar M. rhesus villosus, described by True in 1894, from Kashmir, M. m. mcmahoni, described by Pocock in 1932 from Kootai, Pakistan. Several Chinese subspecies of rhesus macaques were described between 1867 and 1917; the molecular differences identified among populations, are alone not consistent enough to conclusively define any subspecies. The Chinese subspecies can be divided as follows: M. m. mulatta is found in western and central China, in the south of Yunnan, southwest of Guangxi. M. m. tcheliensis, the north Chinese rhesus macaque, lives in the north of Henan, south of Shanxi, near Beijing. Some consider it as the most endangered subspecies. Others consider it synonymous with M. m. sanctijohannis, if not with M. m. mulatta. M. m. vestita, the Tibetan rhesus macaque, lives in the southeast of Tibet, northwest of Yunnan, including Yushu. M. m. littoralis, the south Chinese rhesus macaque, lives in Fujian, Anhui, Hunan, Guizhou, northwest of Guangdong, north of Guangxi, northeast of Yunnan, east of Sichuan, south of Shaanxi.
M. m. brevicaudus referred to as Pithecus brevicaudus, lives on the Hainan Island and Wanshan Islands in Guangdong, the islands near Hong Kong. M. m. siamica, the Indochinese rhesus macaque, is distributed in Myanmar, in the north of Thailand and Vietnam, in Laos, in the Chinese provinces of Anhui, northwest Guangxi, Hubei, Hunan and eastern Sichuan, western and south-central Yunnan. Around the spring of 1938, a colony of rhesus macaques called "the Nazuris" was released in and around Silver Springs in Florida by a tour boat operator known locally as "Colonel Tooey" to enhance his "Jungle C
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell. Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine; the word "synapse" – from the Greek synapsis, meaning "conjunction", in turn from συνάπτεὶν – was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster's Textbook of Physiology. Sherrington struggled to find a good term that emphasized a union between two separate elements, the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall, a friend of Foster; some authors generalize the concept of the synapse to include the communication from a neuron to any other cell type, such as to a motor cell, although such non-neuronal contacts may be referred to as junctions. Synapses are essential to neuronal function: neurons are cells that are specialized to pass signals to individual target cells, synapses are the means by which they do so.
At a synapse, the plasma membrane of the signal-passing neuron comes into close apposition with the membrane of the target cell. Both the presynaptic and postsynaptic sites contain extensive arrays of a molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on an axon and the postsynaptic part is located on a dendrite or soma. Astrocytes exchange information with the synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission. Synapses are stabilized in position by synaptic adhesion molecules projecting from both the pre- and post-synaptic neuron and sticking together where they overlap. There are two fundamentally different types of synapses: In a chemical synapse, electrical activity in the presynaptic neuron is converted into the release of a chemical called a neurotransmitter that binds to receptors located in the plasma membrane of the postsynaptic cell; the neurotransmitter may initiate an electrical response or a secondary messenger pathway that may either excite or inhibit the postsynaptic neuron.
Chemical synapses can be classified according to the neurotransmitter released: glutamatergic, GABAergic and adrenergic. Because of the complexity of receptor signal transduction, chemical synapses can have complex effects on the postsynaptic cell. In an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by special channels called gap junctions or synaptic cleft that are capable of passing an electric current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell; the main advantage of an electrical synapse is the rapid transfer of signals from one cell to the next. Synaptic communication is distinct from an ephaptic coupling, in which communication between neurons occurs via indirect electric fields. An autapse is a chemical or electrical synapse that forms when the axon of one neuron synapses onto dendrites of the same neuron. Synapses can be classified by the type of cellular structures serving as the pre- and post-synaptic components.
The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses, however, a variety of other arrangements exist. These include but are not limited to axo-axonic, dendro-dendritic, axo-secretory, somato-dendritic, dendro-somatic, somato-somatic synapses; the axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. It is accepted that the synapse plays a role in the formation of memory; as neurotransmitters activate receptors across the synaptic cleft, the connection between the two neurons is strengthened when both neurons are active at the same time, as a result of the receptor's signaling mechanisms. The strength of two connected neural pathways is thought to result in the storage of information, resulting in memory; this process of synaptic strengthening is known as long-term potentiation. By altering the release of neurotransmitters, the plasticity of synapses can be controlled in the presynaptic cell.
The postsynaptic cell can be regulated by altering the number of its receptors. Changes in postsynaptic signaling are most associated with a N-methyl-d-aspartic acid receptor -dependent long-term potentiation and long-term depression due to the influx of calcium into the post-synaptic cell, which are the most analyzed forms of plasticity at excitatory synapses. For technical reasons, synaptic structure and function have been studied at unusually large model synapses, for example: Squid giant synapse Neuromuscular junction, a cholinergic synapse in vertebrates, glutamatergic in insects Ciliary calyx in the ciliary ganglion of chicks Calyx of Held in the brainstem Ribbon synapse in the retina Schaffer collateral synapse in the hippocampus The function of neurons depends upon cell polarity; the distinctive structure of nerve cells allows action potentials to travel directionally, for these signals to be received and carried on by post-synaptic neurons or received by effector cells. Nerve cells have long been used as models f