The Brain Can Determine the Static Position of the Head Due to Sensors in the
Chapter 2: Somatosensory Systems
The somatosensory systems inform u.s. about objects in our external environs through touch (i.eastward., concrete contact with skin) and well-nigh the position and movement of our body parts (proprioception) through the stimulation of muscle and joints. The somatosensory systems also monitor the temperature of the body, external objects and environment, and provide information about painful, itchy and tickling stimuli. The sensory data processed by the somatosensory systems travels along dissimilar anatomical pathways depending on the information carried. For example, the posterior cavalcade-medial lemniscal pathway carries discriminative touch on and proprioceptive information from the body, and the chief sensory trigeminal pathway carries this data from the face up. Whereas, the spinothalamic pathways carry crude touch, hurting and temperature data from the body, and the spinal trigeminal pathway carries this information from the face.
This first series of capacity on somatosensory systems concentrates on the somatosensory systems that provide accurate data about the location and temporal features of stimuli and about sharp pain, tactile stimuli and the position and move of body parts. This chapter describes somatosensory stimuli, the sensations produced when they are applied, and the cutaneous, muscle, and joint receptors that are responsible for initiating the perceived somatic sensations. Subsequent chapters describe the pathways processing other pain, temperature, crude impact and visceral sensations.
2.1 Somatic Stimuli
Modality Specificity in the Somatosensory System. The somatosensory systems procedure information most, and represent, several modalities of somatic awareness (i.eastward., pain, temperature, touch, proprioception). Each of these modalities can be divided into sub-modalities, equally shown in Table 1 (due east.g., pain into abrupt, pricking, cutting hurting; tiresome, burning pain; and deep aching pain). Discriminative touch is also subdivided into touch, pressure level, flutter and vibration. Each of these sensations (i.e., sub-modalities) is represented by neurons that exhibit modality specificity. That is, when a somatosensory neuron is stimulated naturally (east.m., by pare warming) or artificially (e.one thousand., past electrical stimulation of the neuron), the sensation perceived is specific to the information commonly processed by the neuron (i.e., warm pare). Consequently, a "warm" somatosensory neuron will not respond to cooling of the skin or to a touch on stimulus that does not "warm" the peel. The somatosensory receptor and its fundamental connections determine the modality specificity of the neurons forming a somatosensory pathway.
| Table I | ||||
| Modality | Sub Modality | Sub-Sub Modality | Somatosensory Pathway (Trunk) | Somatosensory Pathway (Face) |
| Hurting | sharp cut hurting | Neospinothalamic | Spinal Trigeminal | |
| wearisome burning hurting | Paleospinothalamic | |||
| deep agonized pain | Archispinothalamic | |||
| Temperature | warm/hot | Paleospinothalamic | ||
| cool/cold | Neospinothalamic | |||
| Touch | crawling/tickle & rough touch | Paleospinothalamic | ||
| discriminative bear on | touch | Medial Lemniscal | Chief Sensory Trigeminal | |
| pressure | ||||
| flutter | ||||
| vibration | ||||
| Proprioception | Position: Static Forces | muscle length | ||
| muscle tension | ||||
| joint pressure level | ||||
| Motion: Dynamic Forces | muscle length | |||
| muscle tension | ||||
| articulation force per unit area | ||||
| joint angle | ||||
Tactile Stimuli. Tactile stimuli are external forces in physical contact with the skin that give rise to the sensations of touch, pressure, flutter, or vibration. Nosotros normally think of impact as involving minimal force on-or-by an object that produces very fiddling distortion of the peel. In dissimilarity, pressure involves a greater forcefulness that displaces the skin and underlying tissue. Fourth dimension varying tactile stimuli produce more complex sensations such as object movement or object palpitate (twenty to 50 Hz) or vibration (100 to 300 Hz). An initial clinical examination of discriminative impact often involves testing the vibratory sense by applying a 128 Hz tuning fork over a bony prominence.
Proprioceptive Stimuli. i Proprioceptive stimuli are internal forces that are generated by the position or motility of a torso part. Static forces on the joints, muscles and tendons, which maintain limb position confronting the strength of gravity, indicate the position of a limb. The motion of a limb is indicated by dynamic changes in the forces applied to muscles, tendons and joints. An initial clinical test of proprioception oft involves testing the position sense by having the patient, with eyes closed, bear on one finger with another after the target finger has been moved.
Proprioception is disquisitional for maintaining posture and balance. Somatosensory proprioceptive cues are combined with vestibular proprioceptive cues and visual cues to command motor responses to changes in body/head position. During a clinical exam, the Romberg test requires the patient to maintain residue while standing with feet together and eyes closed. It tests whether the proprioceptive components are working properly when the visual cues are missing and proprioceptive cues are the major sources of information.
Sharp Cut Hurting Stimuli. Painful (nociceptive) stimuli are tissue-dissentious sources of energy that may be external or internal to the torso surface. Precipitous, cutting hurting is the sensation elicited on initial contact with the painful stimulus. The sensation of dull, called-for pain may follow as a consequence of tissue inflammation. An initial clinical exam of the pain sense often involves testing sharp, cutting pain sensitivity by request the patient, who has her/his eyes closed, what they feel when pricked with a pin. Pain mechanisms and pathways are described in detail in afterwards chapters.
2.2 Introduction to Peripheral Organization of Somatosensory Systems
Peripheral Somatosensory Neurons. The cell bodies of the start-society (1°) somatosensory afferent neurons2 are located in posterior root or cranial root ganglia (i.e., are part of the peripheral nervous system, Figure 2.one). The 1° afferents are pseudounipolar cells. The cell body gives rise to a single process that divides to course a peripheral axon and a key axon. The peripheral axon travels to and ends in the skin, muscle, tendon or joint and the fundamental axon travels to and ends in the central nervous arrangement.
Somatosensory Receptor Organ. The receptors of most sensory systems are located in specialized sensory receptor organs (e.g., the photoreceptors in the middle and the auditory and vestibular hair cells in the inner ear) or within a restricted part of the trunk (eastward.m., the gustatory modality buds in the oral fissure and the olfactory receptors in the olfactory mucosa of the olfactory organ). For the tactile component of the somatosensory system, the pare covering the entire body, caput and face functions equally the touch receptor organ, whereas joint tissues, muscles and tendons act as the proprioception receptor organs. These sensory receptor organs "house" the somatosensory receptors and deliver the somatosensory stimuli to the receptors.
Sensory Receptors. Specialized sensory receptor cells (eastward.g., the photoreceptors of the eye) are located in specialized receptor organs, produce receptor potentials, contain synaptic specializations, and release neural transmitters (Figure ii.2). Specialized sensory receptors may be modified neurons (e.k., the photoreceptors and olfactory receptors) or modified epithelial cells (e.g., taste receptors and the auditory and vestibular pilus cells).
| Effigy 2.1 | Effigy 2.two |
In that location is only i blazon of sensory receptor cell in the somatosensory organisation, the Merkel cells, and they are found simply in skin. The vast bulk of somatosensory receptors are not specialized receptor cells. That is, they are formed by the endings of the somatosensory 1° afferent peripheral axon and next tissue (Figure 2.3). At that place is no synaptic specialization or neurotransmitter within the adjacent tissue. The adjacent tissue too does not generate receptor potentials.
| Figure 2.three | ||
| (B) Nearly somatosensory receptors are not specialized receptor cells and are formed by the terminal endings of the somatosensory i° afferents. It is the i° afferent terminal that produces a generator potential (1) which, in turn, initiates action potentials (2 & three) in the ane° afferent axon. The 1° afferent releases neurotransmitter on two° afferents in the central nervous system. The 2° afferent generates action potentials (four) in response to the transmitter by the i° afferent. |
Instead of catastrophe on specialized receptors, most peripheral axons of somatosensory 1° afferents travel to skin, muscle or joint, branch near their concluding sites, and end in the pare (Figure 2.four), muscle, tendon or articulation tissue.
| Effigy 2.iv |
All the peripheral terminal branches of a ane° somatosensory axon stop in a specific type of tissue (e.g., peel) and not in multiple types of tissue (i.east., not in skin and muscle). All the peripheral terminal branches of a 1° axon form only 1 type of somatosensory receptor.
| Figure 2.5 |
Many of the 1° somatosensory afferent terminals are enveloped in a connective tissue capsule along with surrounding muscle, tendon or cutaneous cells, or end on hair follicles. The hair follicles and the encapsulated tissue side by side to the 1° afferent terminals (i.eastward., skin, musculus, tendon, and joint tissues) contain no synaptic specializations and practice not generate receptor potentials or release neural transmitters. The complex of encapsulated tissue and afferent endings and the complex of hair follicle and afferent endings play a role in the receptor transduction process, and each complex is considered to form a "somatosensory receptor". Many other 1° somatosensory axons branch and finish in skin, muscle, or joint as free nerve endings. These endings are bare of myelin, are not encapsulated and are not associated with a specific type of tissue.
The sensitivity of the receptors to specific stimuli (e.1000., affect verses muscle stretch) is adamant by the location of the receptor and by the not-neural tissue surrounding the 1° afferent final (Figure two.6).
| Figure 2.half-dozen |
2.three Sensory Transduction
The Adequate Stimulus. The adequate somatosensory stimulus (i.e., the stimulus to which a somatosensory neuron is about sensitive) is either a mechanical forcefulness, a temperature change, tissue damage, or a chemic action. The discriminative touch and proprioceptive systems are most sensitive to mechanical forcefulness. Consequently, their sensory receptors are of the mechanoreceptor category.
Sensory Transduction. The non-neural tissue surrounding the peripheral ending of the somatosensory ane° afferent helps concentrate and deliver the stimulus (e.g., mechanical forcefulness) onto the 1° afferent terminal membrane. Somatosensory mechanoreceptors function to transduce the applied mechanical force into an electrical potential alter in the 1° afferent neuron.
The mechanoreceptor 1° afferent terminal membrane contains ion channels that respond to mechanical baloney by increasing sodium and potassium conductance (i.e., the channels are stress gated). Generator potentials are produced as sodium and potassium flow downwards their electrochemical gradients to depolarize the terminal ending (see Figure 2.3B). In almost cases, the magnitude and duration of the generator potentials are related to the applied mechanical force: the greater the mechanical strength, the greater is the depolarization, and the longer the mechanical force is applied, the longer the terminal remains depolarized (Figure 2.7). Terminals that do not sustain the depolarization for the duration of the mechanical baloney are called apace adapting. Terminals that sustain the depolarization with minimal decrease in amplitude for the duration of a stimulus are chosen slowly adapting.
| Figure 2.7 |
The generator potential spreads passively forth the 1° terminal fiber to the axon trigger zone - that part of the one° afferent axon containing voltage-sensitive sodium and potassium channels (meet Figure 2.3B). If the depolarization reaches threshold at these voltage-sensitive sites, action potentials are generated by the 1° afferent peripheral axon. When the activity potentials reach the central terminals of the 1° afferent, they initiate the release neurotransmitters on ii° afferents within spinal cord or brain stem nuclei. If, as in the example in Effigy 2.8, the generator potential is slowly adapting, the i° afferent produces a sustained discharge of action potentials that continue for the elapsing of the stimulus.
| Figure 2.8 |
If the generator potential is rapidly adapting (Effigy ii.ix), the 1° afferent produces a transient, short flare-up of activeness potentials and falls silent fifty-fifty in the continued presence of the stimulus.
| Effigy two.ix |
The rapidly adapting receptors produce generator potentials and activity potential discharges that follow the time-varying waveform of pressure changes produced by a vibrating stimulus (Figure 2.10, left console). In contrast, the slowing adapting receptors produce generator potentials and action potential discharges that are sustained and unable to mimic the time-varying design of the stimulus (Effigy 2.x, correct panel). Consequently, the responses of rapidly adapting one° afferents are best suited for representing fourth dimension varying (eastward.1000., vibrating or moving) stimuli, whereas slowly adapting ane° afferents better represent static stimuli (due east.g., sustained pressure).
| Effigy 2.x |
ii.iv Somatosensory Receptor Types
| Effigy 2.xi |
Cutaneous Receptors
Some of the somatosensory receptors in peel (i.east., the cutaneous receptors) are classified as encapsulated receptors equally the 1° afferent final and surrounding cutaneous tissue are encapsulated past a thin sheath (Tabular array II). The encapsulated cutaneous receptors include Meissner corpuscles, Pacinian corpuscles and Ruffini corpuscles (Run across Figure 2.xi). Other cutaneous receptors are unencapsulated and include the hair follicle receptor (the 1° afferent ends on hair follicles) and the Merkel complex (the 1° afferent ends at the base of operations of a specialized receptor prison cell chosen the Merkel cell). The sensory receptors of the rough touch, pain and temperature senses are bare or free nervus endings. That is, they are unencapsulated, do not end on or near specialized tissue, and may be mechanoreceptors, nociceptors or thermoreceptors.
Every bit was noted earlier, the sensitivity (modality specificity) of the somatosensory receptor is adamant by its location and by the structure of the non-neural tissue surrounding the 1° afferent terminal. The following describes the most normally observed cutaneous receptors.
Meissner Corpuscle. The Meissner corpuscle is establish in glabrous (i.e., hairless) pare, within the dermal papillae (Figure ii.11). It consists of an elongated, encapsulated stack of flattened epithelial (laminar) cells with one° afferent terminal fibers interdigitated betwixt the cells (Figure 2.12).
| Figure 2.12 |
A force applied to non-hairy skin (Figure two.13) causes the laminar cells in the Meissner corpuscle to slide by 1 another, which distorts the membranes of the axon terminals located between these cells. If the force is maintained, the laminar cells remain in a stock-still, admitting, displaced position, and the shearing force on the axon terminals' membranes disappears. Consequently, the 1° afferent axons produce a transient, speedily adapting response to a sustained mechanical stimulus.
| Effigy 2.thirteen |
The Meissner 1° afferent discharges "follow" low frequency vibrating (30 -50 Hz) stimuli, which produces the sensation of "flutter" (Effigy two.10, left console). Considering a single one° afferent axon forms many, dispersed (3-4 mm) Meissner corpuscles, the 1° afferent can detect and point small movements across the peel. Stimulation of a sequence of Meissner corpuscles accept been described to produce the perception of localized move along the skin.
Consequently, Meissner corpuscles are considered to be the discriminative impact system's flutter and motion detecting receptors in non-hairy skin.
Pacinian Corpuscle. Pacinian corpuscles are found in subcutaneous tissue beneath the dermis (Effigy ii.9) and in the connective tissues of bone, the body wall and body cavity. Therefore, they tin exist cutaneous, proprioceptive or visceral receptors, depending on their location.
| Figure 2.14 |
The Pacinian corpuscle is football-shaped, encapsulated, and contains concentrically layered epithelial (laminar) cells (Effigy 2.fourteen). In cross section, the Pacinian corpuscle looks similar a slice of onion, with a unmarried 1° afferent concluding fiber located in its center. The outer layers of laminar cells contain fluid that is displaced when a force is applied on the corpuscle.
When a strength is first applied on the Pacinian corpuscle (Figure 2.xv), information technology initially displaces the laminar cells and distorts the axon terminal membrane. If the external force per unit area is maintained on the corpuscle, the displacement of fluid in the outer laminar cells dissipates the applied strength on the axon final. Consequently, a sustained forcefulness on the corpuscle is transformed into a transient forcefulness on the axon terminal, and the Pacinian corpuscle i° afferent produces a fast adapting response.
| Effigy 2.15 |
Pacinian corpuscles 1° afferent axons are most sensitive to vibrating stimuli (e.k., a tuning fork vibrating at 100 to 300 Hz, Effigy 2.10, left) and unresponsive to steady pressure. The sensation elicited when cutaneous Pacinian corpuscles are stimulated is of vibration or tickle.
Pacinian corpuscles in pare are considered to exist the vibration sensitive receptors of the discriminative bear upon system.
Ruffini Corpuscle. The Ruffini corpuscles are plant deep in the skin (Figure 2.11), also as in articulation ligaments and joint capsules and can function equally cutaneous or proprioceptive receptors depending on their location. The Ruffini corpuscle (Figure 2.16) is cigar-shaped, encapsulated, and contains longitudinal strands of collagenous fibers that are continuous with the connective tissue of the skin or joint. Within the sheathing, the one° afferent fiber branches repeatedly and its branches are intertwined with the encapsulated collagenous fibers.
| Figure two.16 |
The Ruffini corpuscles are oriented with their long axes parallel to the surface of the pare and are most sensitive to skin stretch. Stretching the skin (Figure ii.17) stretches the collagen fibers within the Ruffini corpuscle, which compresses the axon terminals. As the collagen fibers remain stretched and the axon terminals remain compressed during the skin stretch, the Ruffini corpuscle's one° afferent axon produces a sustained slowly adapting discharge to maintained stimuli.
| Figure 2.17 |
Ruffini corpuscles in skin are considered to be skin stretch sensitive receptors of the discriminative touch system. They also piece of work with the proprioceptors in joints and muscles to point the position and move of body parts.
Pilus Follicle. The hair follicle receptor is an unencapsulated cutaneous receptor (Effigy ii.ten). The 1° afferent terminal axons spiral around the hair follicle base of operations or run parallel to the hair shaft forming a lattice-like pattern (Effigy two.18).
| Effigy 2.18 |
Most pilus follicle one° afferents are the fast-adapting blazon; displacement of the hair produces a transient discharge of activeness potentials at the onset of the displacement and a maintained displacement of the pilus often fails to produce a sustained discharge (Effigy ii.19). The pilus follicle afferents answer all-time to moving objects and signal the direction and velocity of the movement of a stimulus brushing against hairy pare.
| Figure 2.19 |
As Meissner corpuscles are absent from hairy skin, the hair follicle endings are considered to be the discriminative touch system'due south movement sensitive receptors in hairy peel.
Merkel Complex. The Merkel complex is found in both hairy and non-hairy skin and is located in the basal layer of the epidermis (Figure 2.11). The Merkel complex is unencapsulated and consists of a specialized receptor cell, the Merkel jail cell, and a ane° afferent terminal catastrophe, the Merkel deejayiii (Figure 2.20). Thick, curt, finger-like protrusions of the Merkel cell couple it tightly to the surrounding tissue. The Merkel jail cell is a modified epithelial cell, which contains synaptic vesicles that appear to release neuropeptides that modulate the activity of the i° afferent terminal. Each 1° afferent axon oftentimes innervates just a few Merkel cells in a discrete patch of peel (Effigy 2.18).
| Figure 2.20 |
A force practical to the skin overlying the Merkel cell distorts it (Figure 2.21), which stimulates its release of a neuropeptide at its synaptic junctions with the Merkel disk. Every bit the Merkel cell is mechanically coupled to the surrounding skin, it remains distorted for the elapsing of the force practical on the overlying peel. Consequently, the Merkel complex one° afferent axon responds to small forces applied to a discrete patch of skin with a slowly adapting, sustained discharge.
| Figure 2.21 |
Merkel cells are considered to be the fine tactile receptors of the discriminative affect organisation that provide cues used to localize tactile stimuli and to perceive the edges (shape or form) of objects.
Free Nervus Endings. Free nerve endings are found throughout the body, in skin (Effigy 2.11), muscles, tendons, joints, mucous membranes, cornea, body mesentery, the dura, the viscera, etc. The complimentary nerve endings in skin are stimulated past tissue-damaging (nociceptive) stimuli that produce the sensation of hurting or by cooling of the skin or the warming of skin or by touch on. Detect that although all cutaneous free nerve endings appear very similar morphologically, there are unlike functional types of free nerve endings, with each responding to specific types of cutaneous stimuli (e.g., nociceptive, cooling, warming or touch).
Free nervus endings are considered to be the somatosensory receptors for hurting, temperature and crude impact.
| Table Ii Cutaneous Receptors | ||||
| Receptor | Type | Sensation | Signals | Accommodation |
| Meissner corpuscle | Encapsulated & layered | Impact: Flutter & Motility | Frequency/Velocity & Management | Rapid |
| Pacinian corpuscle | Encapsulated & layered | Affect: Vibration | Frequency: 100-300 Hz | Rapid |
| Ruffini corpuscle | Encapsulated collagen | Touch: Skin Stretch | Direction & Force | Slow |
| Hair follicle | Unencapsulated | Touch: Motility | Management & Velocity | Rapid |
| Merkel circuitous | Specialized epithelial cell | Touch, Pressure, Class | Location & Magnitude | Dull |
| Complimentary Nervus Ending | Unencapsulated | Pain, Touch, or Temperature | Tissue impairment, Contact, or Temperature change | Depends on information carried |
two.5 Proprioceptive Receptors
Proprioceptors are located in muscles, tendons, joint ligaments and in articulation capsules. There are no specialized sensory receptor cells for body proprioception4. In skeletal (striated) muscle, there are two types of encapsulated proprioceptors, muscle spindles and Golgi tendon organs (Effigy ii.22), also as numerous complimentary nerve endings. Within the joints, at that place are encapsulated endings similar to those in skin, as well every bit numerous free nerve endings.
| Effigy 2.22 |
Muscle Spindles. Musculus spindles are found in almost all striated muscles. A musculus spindle is encapsulated and consists of small-scale muscle fibers, called intrafusal musculus fibers, and afferent and efferent nerve terminals (Figure two.23).
| Figure ii.23 |
Intrafusal muscles are found exclusively in musculus spindle receptors and are distributed throughout the body among the ordinary extrafusal musculus fibers of skeletal muscles. The intrafusal fibers are fastened to the larger, surrounding extrafusal muscle fibers. They are oriented in parallel with the extrafusal fibers but do not contribute directly to muscle force when they contract considering of their small size.
There are two types of afferent terminals in the muscle spindle (Figure ii.23). The annulospiral endings wrap effectually the fundamental region of the intrafusal fibers, whereas the bloom-spray endings terminate predominantly in more polar regions (away from the central area) of the intrafusal fibers. The one° afferents forming the annulospiral endings are called the primary muscle spindle afferents, whereas those forming the flower-spray endings are called the secondary muscle spindle afferents.
In addition to afferent terminals, the terminals (motor endplates) of gamma motor neurons end on intrafusal muscle fibers. They will be described in detail in the capacity covering motor systems.
In summary, the musculus spindles are proprioceptors specialized to monitor musculus length (stretch) and signal the rate of change in muscle length by changing the belch rate of afferent action potentials. Muscle spindles are most numerous in muscles that carry out fine movements, such every bit the extraocular muscles and the intrinsic muscles of the hand. In that location are fewer spindles in large muscles that command gross movements of the body (eastward.thou., the muscles of the dorsum).
| Figure 2.24 |
Golgi Tendon Organs. Golgi tendon organs are establish in the tendons of striated extrafusal muscles near the muscle-tendon junction (Figure two.22). Golgi tendon organs resemble Ruffini corpuscles. For instance, they are encapsulated and contain intertwining collagen bundles, which are continuous with the muscle tendon, and fine branches of afferent fibers that weave between the collagen bundles (Effigy ii.24). They are functionally "in series" with striated muscle.
The Golgi tendon organ collagen fibers are continuous with the extrafusal muscle at one stop and with the musculus tendon at its contrary end. Consequently, the mechanical strength on the organ is maximal when the extrafusal muscles contract, shorten, and increase the tension on the tendon. When the muscles contract, the one° afferent terminals are compressed and remain compressed as long as the muscle remains contracted. The Golgi tendon organ 1° afferent response to sustained isometric muscle contraction is slowly adapting, and the 1° afferent generates action potentials as long every bit the tension is maintained. The responses of the Golgi tendon organ 1° afferent axon is maximal when the contracted muscle bears a load, eastward.chiliad., when lifting a heavy object.
The Golgi tendon organ is a proprioceptor that monitors and signals muscle contraction against a force (muscle tension), whereas the muscle spindle is a proprioceptor that monitors and signals muscle stretch (musculus length).
Joint Receptors. Joint receptors are found within the connective tissue, capsule and ligaments of joints (Effigy 2.25). The encapsulated endings resemble the Ruffini and Pacinian corpuscles and the Golgi tendon organs.
| Figure 2.25 |
The articulation ane° afferents respond to changes in the angle, direction, and velocity of motion in a joint. The responses are predominantly rapidly adapting with few articulation 1° afferents signaling the resting (static) position of the joint. Information technology has been suggested that information from muscles, tendons, skin and joints are combined to provide estimates of joint position and motion. For example, when the hip joint is replaced — removing all joint receptors — the ability to detect the position of the thigh relative to the pelvis is not lost.
Gratis Nervus Endings. As mentioned higher up, free nerve endings of ane° afferents are abundant in muscles, tendons, joints, and ligaments. These gratuitous nerve endings are considered to be the somatosensory receptors for pain resulting from musculus, tendon, joint, or ligament damage and are non considered to be part of the proprioceptive system.
| Table Three | ||||
| Receptor | Type | Sensation | Signals | Adaptation |
| Muscle Spindle | Encapsulated annulospiral and flower spray endings | Muscle stretch | Muscle length & velocity | Rapid initial transient and slow sustained |
| Muscle: Golgi Tendon Organ | Encapsulated collagen | Muscle tension | Muscle contraction | Dull |
| Joint: Pacinian | Encapsulated & layered | Joint Movement | Direction & velocity | Rapid |
| Joint: Ruffini | Encapsulated collagen | Joint pressure | Pressure & Bending | Deadening |
| Joint: Golgi Organ | Encapsulated collagen | Joint torque | Twisting force | Slow |
2.vi Summary
In this chapter, you accept learned nigh somatosensory stimuli and the receptors of 3 components of the somatosensory systems. These three components provide accurate data most the location, shape, texture, and movement of tactile stimuli, (discriminative touch), the position and movement of torso parts (proprioception) and the application and location of painful stimuli (nociception). Tactile and proprioceptive stimuli are the mechanical forces produced when peel contacts external objects (discriminative touch), limbs oppose the force of gravity (body position) and muscles contract and trunk parts move. Painful stimuli are tissue-damaging forces. The sensations produced are those of touch, force per unit area, flutter, and vibration/move (discriminative touch), body position and motion (proprioception), and precipitous cutting pain. The discriminative bear upon receptors are encapsulated 1° afferent terminals (Meissner, Pacinian and Ruffini corpuscles), hair follicle endings and Merkel complexes in skin. The proprioceptive receptors in muscle are likewise encapsulated and include the muscle spindle and Golgi tendon organ. The joint receptors are similar to the encapsulated endings in skin and tendon and are found in the joint capsule and ligaments. The sharp cutting nociceptors are gratis nerve endings.
Although it is convenient to subdivide somatosensory receptors and pathways for didactic, clinical and enquiry purposes, it is important to keep in listen that most somatosensory stimuli act simultaneously and in varying degrees on all somatosensory receptors in the body part stimulated. For example, placing a heavy, cold object in an outstretched hand produces tactile, thermal, and proprioceptive sensations that allow us to appreciate the presence (touch, pressure), temperature, and weight of the object and provide proprioceptive information for finger, wrist and arm adjustments then we exercise not drib the object.
Test Your Knowledge
Brand the best match between the receptor blazon and the awareness elicited when the receptor is stimulated.
- Golgi tendon organ
- A
- B
- C
- D
- E
A. Fine affect
B. Vibration
C. Flutter
D. Muscle tension
E. Musculus length
A. Fine bear on This is an INCORRECT friction match.
B. Vibration
C. Palpitate
D. Muscle tension
E. Musculus length
A. Fine touch
B. Vibration This is an Incorrect lucifer.
C. Flutter
D. Musculus tension
East. Muscle length
A. Fine touch
B. Vibration
C. Flutter This is an INCORRECT lucifer.
D. Musculus tension
E. Muscle length
A. Fine impact
B. Vibration
C. Flutter
D. Muscle tension This is the Right lucifer!
Golgi tendon organs are stimulated during musculus tension (contraction against a force), whereas the musculus spindles are stimulated during musculus stretch.
E. Musculus length
A. Fine touch
B. Vibration
C. Flutter
D. Muscle tension
E. Muscle length This is an Incorrect friction match.
- Meissner corpuscle
- A
- B
- C
- D
- E
A. Fine touch on
B. Vibration
C. Flutter
D. Muscle contractions
E. Muscle length
A. Fine bear on This is an Wrong match.
B. Vibration
C. Palpitate
D. Muscle contractions
Due east. Muscle length
A. Fine touch
B. Vibration This is an INCORRECT match.
C. Palpitate
D. Muscle contractions
E. Muscle length
A. Fine bear on
B. Vibration
C. Flutter This is the CORRECT match!
Meissner corpuscle responds to time varying stimuli with frequency much below 100 cps.
D. Musculus contractions
E. Muscle length
A. Fine touch on
B. Vibration
C. Flutter
D. Muscle contractions This is an Wrong lucifer.
E. Musculus length
A. Fine touch
B. Vibration
C. Palpitate
D. Muscle contractions
E. Muscle length This is an Incorrect match.
- Merkel complex
- A
- B
- C
- D
- E
A. Fine touch
B. Vibration
C. Flutter
D. Musculus contractions
E. Musculus length
A. Fine bear upon This is the CORRECT match!
Merkel complex responds to localized, static tactile stimuli.
B. Vibration
C. Flutter
D. Muscle contractions
E. Musculus length
A. Fine touch
B. Vibration This is an Incorrect friction match.
C. Flutter
D. Musculus contractions
Due east. Muscle length
A. Fine touch on
B. Vibration
C. Flutter This is an Incorrect match.
D. Muscle contractions
Due east. Musculus length
A. Fine touch
B. Vibration
C. Flutter
D. Musculus contractions This is an INCORRECT match.
E. Muscle length
A. Fine touch on
B. Vibration
C. Flutter
D. Muscle contractions
E. Muscle length This is an INCORRECT match.
- Free nerve endings
- A
- B
- C
- D
- E
A. Fine touch
B. Vibration
C. Palpitate
D. Muscle contractions
E. Pain
A. Fine touch This is an Incorrect match.
B. Vibration
C. Flutter
D. Muscle contractions
E. Hurting
A. Fine touch
B. Vibration This is an INCORRECT match.
C. Palpitate
D. Muscle contractions
E. Pain
A. Fine bear upon
B. Vibration
C. Flutter This is an INCORRECT match.
D. Muscle contractions
Due east. Pain
A. Fine touch
B. Vibration
C. Flutter
D. Musculus contractions This is an Incorrect lucifer.
E. Pain
A. Fine touch
B. Vibration
C. Flutter
D. Muscle contractions
Eastward. Pain This is the CORRECT friction match!
- Pacinian corpuscle
- A
- B
- C
- D
- E
A. Fine touch
B. Vibration
C. Palpitate
D. Muscle contractions
E. Muscle length
A. Fine bear on This is an INCORRECT lucifer.
B. Vibration
C. Flutter
D. Muscle contractions
Eastward. Muscle length
A. Fine touch
B. Vibration This is the Right match!
Pacinian complex are most responsive to time varying stimuli with frequency between 100 to 300 cps.
C. Flutter
D. Muscle contractions
E. Muscle length
A. Fine touch
B. Vibration
C. Flutter This is an Wrong match.
D. Muscle contractions
Due east. Muscle length
A. Fine touch
B. Vibration
C. Flutter
D. Muscle contractions This is an Wrong match.
E. Muscle length
A. Fine touch
B. Vibration
C. Flutter
D. Muscle contractions
Eastward. Muscle length This is an Incorrect match.
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Source: https://nba.uth.tmc.edu/neuroscience/m/s2/chapter02.html
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