In the lower medulla, axons carrying information originating from the upper body synapse onto neurons in the cuneate nucleus subdivision of the dorsal column nuclei, while axons from the lower body synapse onto neurons in the gracile nucleus.
#Where does the somatic nervous system carry signals to skin
Tactile sensory information gathered by the mechanoreceptors in the skin of the body enters the spinal cord through the dorsal roots and ascends ipsilaterally through the dorsal column to the lower medulla. The three receptors and their functions are: (1) muscle spindles that are found in striated muscles and provide information about changes in muscle length (2) Golgi tendon organs that are found in tendons and provide information about changes in muscle tension and (3) joint receptors that give signals when joint movements come close to range limits ( Proske and Gandevia, 2012). For proprioception, other types of mechanoreceptors provide information about the position of limbs and other body parts in space. Ruffini corpuscles are found in the next layer of skin, the dermis, and pacinian corpuscles are found deep in the dermis or even the subcutaneous layer. Meissner corpuscles are found in the tips of the dermal papillae, close to the skin surface.
For touch, the skin contains four morphologically different mechanoreceptor cells ( Zimmerman et al., 2014). Within the skin and muscle, specialized sensory receptor cells called mechanoreceptors typically encapsulate the afferent fibers used for touch and proprioception. These afferent fibers conduct the action potentials past the cell bodies in the ganglia until they reach their synaptic terminals in the target structures within the CNS. These afferent nerve fibers conduct the signal to cell bodies that reside within the dorsal root ganglia for the body or within the cranial nerve ganglia for the head. For both of these subsystems, somatic sensations begin from activity detected by specific receptors on afferent nerve fibers whose processes branch within skin or muscle. One important subsystem uses skin receptors to mediate the sensation of touch, and the other subsystem uses receptors in muscles, tendons, and joints to mediate proprioception – the ability to sense the position of our own limbs and body parts in space. The somatic sensory system mediates a number of sensations that are transduced by receptors in the skin or muscle. Liu-Ambrose, in Handbook of Clinical Neurology, 2016 Somatic sensory system: proprioception and touch
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