Physical stimuli, such as pressure and vibration, as well as the sensation of sound and body position balance , are interpreted through a mechanoreceptor. Another physical stimulus that has its own type of receptor is temperature, which is sensed through a thermoreceptor that is either sensitive to temperatures above heat or below cold normal body temperature.
Ask anyone what the senses are, and they are likely to list the five major senses—taste, smell, touch, hearing, and sight. However, these are not all of the senses. The most obvious omission from this list is balance. Also, what is referred to simply as touch can be further subdivided into pressure, vibration, stretch, and hair-follicle position, on the basis of the type of mechanoreceptors that perceive these touch sensations.
Other overlooked senses include temperature perception by thermoreceptors and pain perception by nociceptors. Within the realm of physiology, senses can be classified as either general or special.
A general sense is one that is distributed throughout the body and has receptor cells within the structures of other organs.
Mechanoreceptors in the skin, muscles, or the walls of blood vessels are examples of this type. General senses often contribute to the sense of touch, as described above, or to proprioception body position and kinesthesia body movement , or to a visceral sense , which is most important to autonomic functions.
A special sense discussed in Chapter 15 is one that has a specific organ devoted to it, namely the eye, inner ear, tongue, or nose. Each of the senses is referred to as a sensory modality. Modality refers to the way that information is encoded into a perception. The main sensory modalities can be described on the basis of how each stimulus is transduced and perceived. The chemical senses include taste and smell.
The general sense that is usually referred to as touch includes chemical sensation in the form of nociception, or pain. Pressure, vibration, muscle stretch, and the movement of hair by an external stimulus, are all sensed by mechanoreceptors and perceived as touch or proprioception.
Hearing and balance are also sensed by mechanoreceptors. Finally, vision involves the activation of photoreceptors.
Listing all the different sensory modalities, which can number as many as 17, involves separating the five major senses into more specific categories, or submodalities , of the larger sense. An individual sensory modality represents the sensation of a specific type of stimulus. For example, the general sense of touch, which is known as somatosensation , can be separated into light pressure, deep pressure, vibration, itch, pain, temperature, or hair movement.
In this chapter we will discuss the general senses which include pain, temperature, touch, pressure, vibration and proprioception.
We will discuss the special senses, which include smell, taste, vision, hearing and the vestibular system, in chapter Somatosensation is considered a general sense, as opposed to the submodalities discussed in this section. Somatosensation is the group of sensory modalities that are associated with touch and limb position.
These modalities include pressure, vibration, light touch, tickle, itch, temperature, pain, proprioception, and kinesthesia. Most of those affected suffer from joint damage and frequent fractures to bones in their feet and hands; some end up in wheelchairs even before they reach puberty Minde et al. It turns out pain—generally—serves us well. Living without a sense of touch sounds less attractive than being free of pain—touch is a source of pleasure and essential to how we feel.
Losing the sense of touch has severe implications—something patient G. Pain is an unpleasant experience that involves both physical and psychological components. Feeling pain is quite adaptive because it makes us aware of an injury, and it motivates us to remove ourselves from the cause of that injury.
In addition, pain also makes us less likely to suffer additional injury because we will be gentler with our injured body parts.
Generally speaking, pain can be considered to be neuropathic or inflammatory in nature. Pain that signals some type of tissue damage is known as inflammatory pain. In some situations, pain results from damage to neurons of either the peripheral or central nervous system. As a result, pain signals that are sent to the brain get exaggerated. This type of pain is known as neuropathic pain.
Multiple treatment options for pain relief range from relaxation therapy to the use of analgesic medications to deep brain stimulation. Some individuals are born without the ability to feel pain. This very rare genetic disorder is known as congenital insensitivity to pain or congenital analgesia. While those with congenital analgesia can detect differences in temperature and pressure, they cannot experience pain. As a result, they often suffer significant injuries.
Young children have serious mouth and tongue injuries because they have bitten themselves repeatedly. Not surprisingly, individuals suffering from this disorder have much shorter life expectancies due to their injuries and secondary infections of injured sites U.
National Library of Medicine, Watch this video of a girl who feels no pain to learn more about congenital insensitivity to pain. When you step on a pin, this activates a host of mechanoreceptors, many of which are nociceptors. You may have noticed that the sensation changes over time. First you feel a sharp stab that propels you to remove your foot, and only then you feel a wave of more aching pain.
The sharp stab is signaled via fast-conducting A-fibers, which project to the somatosensory cortex. Al the other pains deep, visceral, burning, aching are carried via C fibers. Globulin B. Dopamine C. Arachnoid Acid D. Acetylcholine E. Dopamine is not released in response to noxious stimulation. Pricking pain B. Stimulation produced analgesia C. Referred pain D. Burning pain E. Sharp pain. C fibers transmit which type of pain?
C fibers carry the burning pain sensation. C fibers are A. The C fibers are unmyelinated fibers that carry burning pain. Bradykinins B.
Prostaglandins C. Histamine D. Dopamine E. Aspirin acts to block the formation of A. A delta fibers transmit primarily A. Pacinian corpuscles E. Meissner corpuscles. Only the free nerve endings are the receptors nociceptors that sense pain. Double pain sensation results from A. Deep pain C. Visceral pain D. Aching pain. A delta fibers transmit which type of pain to VPL? Burning pain B. Aching pain C. Somatic pain D. Pricking pain E. Visceral pain. Sharp pain, induced by a skin cut for example, is classified by A.
Discriminative touch is also subdivided into touch, pressure, flutter and vibration. Each of these sensations i. That is, when a somatosensory neuron is stimulated naturally e.
Consequently, a "warm" somatosensory neuron will not respond to cooling of the skin or to a touch stimulus that does not "warm" the skin. The somatosensory receptor and its central connections determine the modality specificity of the neurons forming a somatosensory pathway. 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.
We normally think of touch as involving minimal force on-or-by an object that produces very little distortion of the skin. In contrast, pressure involves a greater force that displaces the skin and underlying tissue. Time varying tactile stimuli produce more complex sensations such as object movement or object flutter 20 to 50 Hz or vibration to Hz.
An initial clinical examination of discriminative touch often involves testing the vibratory sense by applying a Hz tuning fork over a bony prominence. Proprioceptive Stimuli. Static forces on the joints, muscles and tendons, which maintain limb position against the force of gravity, indicate the position of a limb.
The movement of a limb is indicated by dynamic changes in the forces applied to muscles, tendons and joints. An initial clinical examination of proprioception often involves testing the position sense by having the patient, with eyes closed, touch one finger with another after the target finger has been moved. Proprioception is critical for maintaining posture and balance.
During a clinical examination, the Romberg test requires the patient to maintain balance 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 Cutting Pain Stimuli. Painful nociceptive stimuli are tissue-damaging sources of energy that may be external or internal to the body surface.
Sharp, cutting pain is the sensation elicited on initial contact with the painful stimulus. The sensation of dull, burning pain may follow as a consequence of tissue inflammation. Pain mechanisms and pathways are described in detail in later chapters. Peripheral Somatosensory Neurons.
The cell body gives rise to a single process that divides to form a peripheral axon and a central axon. The peripheral axon travels to and ends in the skin, muscle, tendon or joint and the central axon travels to and ends in the central nervous system.
Somatosensory Receptor Organ. The receptors of most sensory systems are located in specialized sensory receptor organs e. For the tactile component of the somatosensory system, the skin covering the entire body, head and face functions as 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 e. Specialized sensory receptors may be modified neurons e. Figure 2. The peripheral process is part of the peripheral nervous system PNS and terminates to form or end on a somatosensory receptor in skin, muscle or joint. The central process travels tso the central nervous system CNS where it terminates on a spinal cord or brain stem neuron.
These cells are specialized neurons A. There is only one type of sensory receptor cell in the somatosensory system, the Merkel cells , and they are found only in skin. The vast majority of somatosensory receptors are not specialized receptor cells.
There is no synaptic specialization or neurotransmitter within the adjacent tissue. The adjacent tissue also does not generate receptor potentials. Each terminal fiber forms, or ends on, a somatosensory receptor. 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". 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. The Adequate Stimulus. The adequate somatosensory stimulus i. The discriminative touch and proprioceptive systems are most sensitive to mechanical force.
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