The central process of the sensory neuron enters the dorsal root of the spinal nerve or the sensory root of the cranial nerve, and passes to the spinal cord or brainstem, respectively. The central process of a pseudounipolar sensory neuron transmits the impulse toward the CNS. A synapse does not occur in the sensory ganglion, and the information detected in the periphery passes to the CNS without interruption. Pseudounipolar neurons possess only a single process that emerges from the ganglion cell body and branches into a central process and a peripheral process. The sensory neuron cell body for all somatosensory and visceral receptors is a pseudounipolar neuron located in the dorsal root sensory ganglia or the cranial sensory ganglia associated with CNs V, VII, IX, and X. The detection of somatic and visceral input from the environment occurs through specialized receptive nerve endings known as somatosensory receptors, which are formed by the peripheral axon of primary (afferent) sensory neurons ( ). General Properties of Somatosensory Receptors The special sensory pathways associated with vision, hearing, balance, smell, and taste are described in Chapter 15. The ascending somatosensory pathways of the body and the head are described in Chapters 12 and 15, respectively. Transmission of different somatosensory stimuli follows distinct anatomical sensory pathways to the cerebral cortex and cerebellum. This chapter introduces somatosensory stimuli and the types of cutaneous, muscle, joint, and visceral receptors that are responsible for detecting a perceived sensation. In comparison, sensory receptors that detect special sensory modalities such as light, smell, taste, and sound are modified neurons or specialized epithelial receptor cells, which exhibit restricted expression to the olfactory epithelium, the retina of the eye, the taste buds of the oral cavity, and the vestibulocochlear apparatus. Sensory receptors that detect sensations of pain, temperature, discriminative touch, pressure, visceral distention, and proprioception are known as somatosensory receptors and are broadly distributed within the skin, muscles, joint capsules, and viscera. Each type of receptor plays an integral role in collecting sensory input from the external and internal environment and transmitting the information to the central nervous system (CNS) for conscious and unconscious processing. Based on the type of stimulus to which the receptor responds, sensory receptors may be broadly classified as nociceptors, thermoreceptors, chemoreceptors, photoreceptors, and mechanoreceptors. The detection of sensory input occurs through specialized receptive nerve endings, known as sensory receptors, found at the terminal ends of afferent (sensory) peripheral nerve fibers. The body’s ability to adapt to its environment and maintain homeostasis depends on the transmission of sensory input by the peripheral nervous system (PNS).
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