Time varying tactile stimuli produce more complex sensations such as object movement or object flutter (20 to 50 Hz) or vibration (100 to 300 Hz).
#FREE NERVE ENDINGS FUNCTION SKIN#
In contrast, pressure involves a greater force that displaces the skin and underlying tissue. We normally think of touch as involving minimal force on-or-by an object that produces very little distortion of the skin. Tactile stimuli are external forces in physical contact with the skin that give rise to the sensations of touch, pressure, flutter, or vibration. The Sensory Modalities Represented by the Somatosensory Systems
The somatosensory receptor and its central connections determine the modality specificity of the neurons forming a somatosensory pathway. Consequently, a "warm" somatosensory neuron will not respond to cooling of the skin or to a touch stimulus that does not "warm" the skin. That is, when a somatosensory neuron is stimulated naturally (e.g., by skin warming) or artificially (e.g., by electrical stimulation of the neuron), the sensation perceived is specific to the information normally processed by the neuron (i.e., warm skin). Each of these sensations (i.e., sub-modalities) is represented by neurons that exhibit modality specificity. Discriminative touch is also subdivided into touch, pressure, flutter and vibration. Each of these modalities can be divided into sub-modalities, as shown in Table 1 (e.g., pain into sharp, pricking, cutting pain dull, burning pain and deep aching pain). The somatosensory systems process information about, and represent, several modalities of somatic sensation (i.e., pain, temperature, touch, proprioception). Modality Specificity in the Somatosensory System. Subsequent chapters describe the pathways processing other pain, temperature, crude touch and visceral sensations. 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.
#FREE NERVE ENDINGS FUNCTION SERIES#
This first series of chapters on somatosensory systems concentrates on the somatosensory systems that provide accurate information about the location and temporal features of stimuli and about sharp pain, tactile stimuli and the position and movement of body parts.
Whereas, the spinothalamic pathways carry crude touch, pain and temperature information from the body, and the spinal trigeminal pathway carries this information from the face. For example, the posterior column-medial lemniscal pathway carries discriminative touch and proprioceptive information from the body, and the main sensory trigeminal pathway carries this information from the face. The sensory information processed by the somatosensory systems travels along different anatomical pathways depending on the information carried. The somatosensory systems also monitor the temperature of the body, external objects and environment, and provide information about painful, itchy and tickling stimuli. The somatosensory systems inform us about objects in our external environment through touch (i.e., physical contact with skin) and about the position and movement of our body parts (proprioception) through the stimulation of muscle and joints.
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