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You are watching: Which receptors adapt most slowly or not at all?

Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. Second edition. Sunderland (MA): Sinauer Associates; 2001.

By covenant with the publisher, this book is available by the find feature, however cannot it is in browsed.

The committed sensory receptor in the cutaneous and subcutaneous tissues space dauntingly varied (Table 9.1). Lock include cost-free nerve endings in the skin, nerve endings associated with specializations the act together amplifiers or filters, and also sensory terminals connected with committed transducing cells that affect the finishing by virtue the synapse-like contacts. Based on function, this variety of receptors can be split into 3 groups: mechanoreceptors, nociceptors, and thermoceptors. On the basis of their morphology, the receptors near the body surface can also be split into free and also encapsulated types. Nociceptor and thermoceptor specializations are described as free nerve endings due to the fact that the unmyelinated terminal branches of these neurons ramify extensively in the upper regions of the dermis and epidermis; their role in pain and also temperature sensation is debated in chapter 10. Many other cutaneous receptors show some degree of encapsulation, i beg your pardon helps identify the nature that the stimuli come which they respond.


Despite your variety, all somatic sensory receptors job-related in essentially the same way: Stimuli applied to the skin deform or otherwise change the nerve endings, which in turn affects the ionic permeability that the receptor membrane. Changes in permeability generate a depolarizing existing in the nerve ending, thus producing a receptor (or generator) potential that triggers activity potentials, as described in Chapters 2 and also 3. This overall process, in i beg your pardon the energy of a economic stimulation is converted into an electric signal in the sensory neuron, is dubbed sensory transduction and is the vital first step in every sensory processing.

The high quality of a mechanosensory (or any kind of other) economic stimulation (i.e., what that represents and also where that is) is figured out by the properties of the pertinent receptors and the ar of their central targets (Figure 9.1). The quantity or toughness of the stimulus is conveyed through the price of activity potential discharge prompted by the receptor potential (although this partnership is nonlinear and often rather complex). Some receptors fire rapidly as soon as a stimulus is very first presented and then autumn silent in the visibility of ongoing stimulation (which is come say castle “adapt” to the stimulus), vice versa, others generate a continual discharge in the presence of an ongoing stimulus (Figure 9.2). The usefulness of having actually some receptor that it is adapted quickly and others that execute not is to carry out information around both the dynamic and also static features of a stimulus. Receptors that at first fire in the presence of a stimulus and also then end up being quiescent are particularly effective in send information around changes in the details the receptor reports; conversely, receptor that proceed to fire convey information about the persistence that a stimulus. Accordingly, somatic sensory receptors and also the neurons that offer rise to them are usually classified into rapidly or slowly adapting varieties (see Table 9.1). Rapidly adapting, or phasic, receptor respond maximally but briefly come stimuli; their response decreases if the economic stimulation is maintained. Conversely, progressively adapting, or tonic, receptors keep firing as long as the stimulus is present.

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Figure 9.1

General organization of the somatic sensory system. (A) Mechanosensory information about the body reaches the mind by method of a threeneuron relay (shown in red). The very first synapse is make by the terminals that the centrally projecting axons the dorsal source (more...)


Figure 9.2

Slowly adapting mechanoreceptors continue responding to a stimulus, whereas rapidly adapting receptors respond just at the beginning (and frequently the offset) the stimulation. These practical differences enable the mechanoreceptors to carry out information about (more...)

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By commitment with the publisher, this book is available by the find feature, yet cannot it is in browsed.