1 The f ollo wing descrip tion is based on lec ture no tes from Laszlo Zaborszky , from Rutgers Univ ersit y . 1 corpuscle Pacinian Hair receptor disks. corpuscle Ruffini’s R uffini c orpuscles and Merk el’s gland corpuscleSebaceous Dermisless) skin: Meissner c orpuscles,Meissner’s rec eptors in the glabrous (hair- the P acinian c orpuscles and the hairs. Enc apsulated rec eptors are endingreceptor Free nerveMerkel’s Septa the hair rec eptors at the roots of EpidermisEx amples for free rec eptors are be free rec eptors or enc apsulated. Papillary Ridges man skin: Mechanorec eptors c an Figure 1: R ec eptors in the hu- tanc e during the Hairy skinearly stages of Glabrous skinlif ting. In response to burst of ac tion po tentials when objec ts mo v e a small dis- objec ts are lif ted. These aff erents respond with a brief adap ting aff erents leads to adjustment of grip f orc e when Sensor y inf ormation from Meissner c orpuscles and rapidly Cutaneous receptors remo v ed. about muscle length, muscle tension, and joint angles. article, but some content has been The rec ep tors in muscles and joints pro vide inf ormation content has been changed in this fac e te xture (mechano rec eptors ),and pain (nocic eptors ). called Sensory Systems . None of the us about temperature (thermorec eptors ),pressure and sur- contains a chapter from a Wikibook c ep tors in the skin, the so called cutaneous rec ep tors, tell showcase page-based formatting. It and sensors in our muscles, tendons, and joints. The re- This is a sample document to Our somatosensor y system c onsists of sensors in the skin R OMIKIBOOKS F W 1 Anatomy of the Somatosensory System ----------------Page (0) Break---------------- 2 nocic ep tors are either high-threshold mechanorec ep tors Nocic ep tors hav e free ner v e endings. Func tionally , skin Nociceptors stretching of skin. R uffini c orpuscles respond to the lataral mo v ement or giv es a f eeling of vibration, while the slo wly adap ting Ac tivation of the rapidly adap ting P acinian c orpuscles up to se v eral sec onds in duration. tial indentation of skin, but also to sustained indentation ax ons, slo wly adap ting fibers respond no t only to the ini- man digits is reduc ed to 10/mm². Unlik e rapidly adap ting passage of time so that b y the age of 50,the densit y in hu- This inner vations densit y shrinks progressiv ely with the er glabrous surfac es, and at v er y lo w densit y in hair y skin. mouth (50/mm² of skin surfac e), at lo w er densit y in o th- are present at high densit y in the digits and around the rec ep tors mediating f orm perc ep tion, Merk el’ s rec ep tors f or f orm and te xture perc ep tion. As w ould be e xpec ted f or The slo wly adap ting Merk el’s rec eptors are responsible tivit y . of the role play ed b y somatosensor y neurons in mo tor ac- a rapid response to a tac tile stimulus is a clear indication refle xiv ely until the gripped objec t no longer mo v es. Such rapidly adap ting aff erent ac tivit y , muscle f orc e increases fibres. c entral portions of the intrafusal c oil around the non-c ontractile a sec ondary (group II) afferent a primary (group Ia) afferent and cle fibres. T he sensory endings of sisting of se v eral intrafusal mus- with its own motor supply c on- T he spindle is a stretch rec eptor and expanded schematic (right). nections in spinal c ord (middle ) in a muscle (left), neuronal c on- spindle showing t ypic al position Figure 2: Mammalian muscle F rom Wikibooks ----------------Page (1) Break---------------- 3 e v er the muscle is stretched, the intrafusal fibers are also intrafusal fibers are at tached to e xtrafusal fibers, so when- in c ontrast to the ordinar y extrafusal fibers .The ends of the third of the fibers. These fibers are called intrafusal fibers , small muscle fibers with a capsule surrounding the middle dles. The y are quite simple in principle, c onsisting of a f e w body are long, thin, stretch rec ep tors called muscle spin- Scat tered throughout virtually e v er y striated muscle in the Muscle Spindles with ref erred pain. poorly localiz ed, can be chronic and is of ten associated pain , arising from visc era, musculature and joints, is also outside margins. poorly localiz ed and poorly tolerated. The third or deep the table and Figure 3, intrude into the tiv e c omponent is called sec ond pain or burning pain ;it is bottom of the page. Wide content, lik e iz ed and easily tolerated. The much slo w er , highly aff ec- Also, figures are floated to the top/ called first pain or cutaneous pricking pain .It is w ell local- on whether the page is left or right). ted signal, which of ten has high spatial resolution, is margin ( on the left or right, depending used f or transmit ting these signals. The rapidly transmit- sidenotes are shown in the outside nents, c orresponding to diff erent t ypes of ner v e fibers Notice how figure captions and P ain signals can be separated into individual c ompo- non-no xious thermorec ep tors at high temperatures). ing (in c ontrast with the saturating responses display ed b y change their response rates as a linear func tion of warm- so respond to temperatures in the range of 40–60°C, and that depends on the degree of tissue def ormation. The y al- punc tures of the epithelium, with a response magnitude to no xious chemicals. These rec ep tors respond to minute only to intense mechanical stimuli, but also to heat and or polymodal rec eptors . P olymodal rec ep tors respond no t T able 1 field in fingers. tion” e.g. tapping with a pencil. large rec ep tiv e stretch” . Used f or joint position P acinian c orpuscle : “A diffuse vibra- Deep rec ep tor / R uffini’s c orpuscle : “A skin field Used f or rec ognizing te xture. edge or “ an X” in brail. small rec ep tiv e tec t an insec t or a ver y fine vibration. tial details, e.g. a round surfac e Surfac e rec ep tor /Hair rec eptor ,Meissner’s c orpuscle : De- Merk el’ s rec ep tor: Used f or spa- Rapidly adapting Slowly adapting Anatom y of the Somatosensory System ----------------Page (2) Break---------------- 4 t ype 4 joint rec ep tors are nocic ep tors. direc tion and speed of mo v ements). The free rec ep tors or ent charac teristics of joint func tion (position, mo v ements, and hav e been divided into f our groups. The y signal diff er- The joint rec ep tors are lo w -threshold mechanorec ep tors Joint receptors tivit y can be maintained at any giv en muscle length. late the sensitivit y of the muscle spindle so that this sensi- called gamma neurons . Gamma mo tor neurons can regu- plying the c ontrac tile portions of intrafusal fibers are publishing, see css4.pub . are called alpha motor neurons ,while the smaller ones sup- HTML and CSS for paper-based large mo tor neurons that supply e xtrafusal muscle fibers F or more e xamples of how to use Muscle spindles also rec eiv e a mo tor inner vation. The stretched and each sensor y ending fires impulses. cle is stretched, the c entral part of the intrafusal fiber is one or more sensor y endings applied to it. When the mus- f e w my ofilaments and is non-c ontrac tile, but it does hav e stretched. The c entral region of each intrafusal fiber has ments. A rrows indic ate ex citatory c onnections; filled circles inhibitory c onnections. Figure 3: Feedback loops for proprioc eptiv e signals for the perc eption and c ontrol of limb mov e- Gamma bias signal control Length Spindles feedback Velocity (primary muscle-spindel afferents)velocity Length error (primary muscle-spindel afferents)Length & Length (secondary muscle-spindel afferents) organs Muscle Load signal TendonMuscle force length Driving Muscle forces External neurons signalInter- Force feedback control Force (Golgi tendon organ) Force F rom Wikibooks ----------------Page (3) Break----------------