Lecture7_somatosensation_corrected - Somatosensation...

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Somatosensation
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Vision Hearing Olfaction Taste Somatosensation Vestibular Reflexes ( Stimulus→Response ) People Places Objects Events Sensory Perception State 1 State 2 State N Familiar stimuli & states Hunger Thirst Sleep Temp. Motivational Drives Muscles Actual Reward Habits ( State→Action ) Action 1 Action 2 Action N Behavioral Repertoire State→Value Decision Policy select Voluntary action plan Prediction Errors Expected Reward Schematic Diagram of Adaptive Behavioral Control
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On each side, a spinal nerve splits into two different root systems: Dorsal roots carry sensory information into the spinal cord from the body Ventral roots carry motor commands out of the spinal cord to the muscles Spinal Nerves The spinal cord is subdivided into 5 main segments: cervical, thoracic, lumbar, sacral, and coccygeal The spinal cord is protected by the bony vertebrae, and by the meninges There are 31 pairs of spinal nerves (they come in pairs because they innervate both sides of the body) Each pair of nerves relays information to and from different regions of the body
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The area of skin innervated by a single spinal nerve is called a dermatome There are five groups of somatosensory dermatomes: Cervical (8): Arms and back of head Thoracic (12): Back and stomach Lumbar (5): Lower back & front of legs Sacral (5): Buttocks and back of legs Coccygeal (1): pelvis & groin Facial somatosensatory information enters the brain through cranial (rather than spinal nerves) Spinal cord segments and dermatomes
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Somatosensory nerve endings in the skin are transducers Different kinds of receptors in the skin sense different kinds of touch stimuli by transducing different kinds of energy Different sensory axons carry different kinds of touch information (“labeled lines”) from specific body regions Transduction : the conversion of energy from one form into another. All sensory systems transduce some form of energy into action potentials .
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Three main types of somatosensory receptors Discriminative Touch: pressure, vibration, texture Sensed by mechanoreceptors in the skin Travels to brain via the dorsal column spinal pathway Proprioception: position of joints & limbs Sensed by mechanoreceptors (e.g., stretch receptors) in muscles & tendons Travels to brain via the dorsal column spinal pathway Pain and Temperature: tissue damage, heat, cold Sensed by chemoreceptors in the skin Travels to brain via the spinothalamic tract, also known as the anterolateral spinal pathway TRANSDUCTION OF MECHANICAL ENERGY TRANSDUCTION OF CHEMICAL/THERMAL ENERGY
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3 2 2 3 2 2 3 2 2 3 3 2 3 3 3 3 2 3 2 3 3 3 3 2 3 3 3 2 2 4 2 3 4 3 2 4 4 3 5 5 4 6 3 3 5 3 3 6 3 3 5 4 4 5 4 3 5 4 3 4 4 3 4 4 3 5 5 4 5 5 4 5 6 4 6 4 3 4 5 4 4 3 3 4 3 3 3 2 2 2 3 3 3 2 3 2 3 5 2 3 5 2 DRG Neurons TO SPINAL CORD Spike trains and neural firing rates Each DRG neuron fires sequences of action potentials called spike trains
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  • Fall '07
  • shaine
  • order neurons, drg neurons

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