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Somatosensory_Systems

Somatosensory_Systems - Somatosensory Systems Somatosensory...

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Somatosensory Systems
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Somatosensory Systems Cutaneous Senses 1. Touch 2. Temperature 3. Pain Information about body movement and position
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Generalizations Somatosensory systems are organized somatotopically (have a body map). Primary sensory neurons are located outside the CNS (in a ganglion). Information from one side crosses the midline to the contralateral thalamus and then to the contralateral somatosensory cortex.
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Skin Receptors Many types Separate into: 1. Touch/Pressure/Vibration 2. Pain and Temperature For the body, all neurons are dorsal root ganglion neurons. For the head and neck, info carried by cranial nerves.
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Skin Receptors • Corpuscles : Associated with skin vibrations and pressure 1. Meissner s corpuscles: low- frequency vibrations 2. Pacinian: high-frequency vibrations • Merkel s disks : light pressure Transduction occurs when stimulus bends membrane, resulting in opening of sodium channels.
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Skin Receptors Free nerve endings 1. Carry pain and temperature sensations. 2. Temperature is transduced by temperature-activated ion channels (with many different types “tuned” to different ranges of temperature). 3. Pain is transduced from different types of stimuli (mechanical and temperature) by specialized types of fibers (more later).
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Tactile Information From the Body • Dorsal Column Pathway : Fine, tactile discrimination • Spinothalamic Pathway : Pain, temperature, and light touch (more later)
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Tactile Information From the Body • Dorsal Column Pathway : Fine, tactile discrimination Axons of dorsal root ganglion sensory neurons (1st order neurons) send axons up the ipsilateral dorsal columns of the spinal cord to synapse onto neurons in the dorsal column nuclei of the medulla.
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