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UIUC MCB 402 - Neuro 3 Somatosensory

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MCB 402Systems and Integrative Physiology• Nien-Pei Tsai, Ph.D.• Erik Nelson, Ph.D.http://www.life.illinois.edu/mcb/402/Neurophysiology• Lecture 1: Introduction, Overview of Nervous System, and Cellular Physiology• Lecture 2: Autonomic nervous system• Lecture 3: Somatosensory system• Lecture 4: Special senses I: Smell, Taste and Hearing • Lecture 5: Special senses II: Vision• Lecture 6: Motor system• Lecture 7: Higher functions of the nervous system• Lecture 8: Development and aging in neurophysiologyThalamus processes almost all sensory information going to the cortex.Thalamushttp://www.changepain-emodules.comSensory Modalities• General senses:  Somatic senses (from the body)touch, pressure, vibration, itch, warm/cold, etc., Visceral senses (from the organs)pressure, pain, stretch, hunger, warm/cold, etc., Special senses: taste, vision, hearing, smell, etc.,How does it work?Example: Somatic ReflexesAfferent: brings information in to the nervous system from sensory receptorsEfferent: carries information out of the nervous system to cause muscle contraction or gland secretion• First-order neurons: impulses from somatic receptors to the brain stem or spinal cord.• Second-order neurons: impulses from the brain stem and spinal cord to the thalamus.• Third-order neurons: impulses from the thalamusto the primary somatosensory area of the cortex on the same side.Sensory PathwaysConstazo, Physiology 5thSensory PathwaysDorsal column system and Anterolateral systemConstazo, Physiology 5thSensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.Sensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.Free nerve endings are used to detect pain, temperature, tickle, itch and some touch.Sensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.Encapsulated nerve endings are used to detect pressure, vibration and some touch.Sensory ReceptorsConnective tissueCopyright © 2014 John Wiley & Sons, Inc.Sensory receptors for some special senses include gustatory receptor cells in taste buds, photoreceptors in the retina of the eye and hair cells in the inner ear for hearing.Sensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.Sensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.• Receptors may also be grouped based on location of the receptors and the origin of the stimuli that activate them.• Exteroreceptors include: hearing, vision, smell, taste, touch, pressure, vibration and pain.• Interoreceptors monitor the body’s internal environment.• Proprioceptors provide information about body position, muscle length and tension and the position and movement of joints.Sensory Receptors• Two types of proprioceptors are muscle spindles and tendon organs. Muscle spindles: in skeletal muscles monitor their length and are involved in stretch reflexes. • Tendon organs: at the junction of a tendon and a muscle protect muscles and tendons from damage due to overstretching.ProprioceptorsSensory ReceptorsCopyright © 2014 John Wiley & Sons, Inc.Somatosensory ReceptorsMechanoreceptors are used to detect touch, pressure, vibration etc. in skin and stretching of blood vessels and internal organs.Copyright © 2014 John Wiley & Sons, Inc.Somatosensory ReceptorsThermoreceptors are used to detect changes in temperatures.Constazo, Physiology 5thSomatosensory ReceptorsNociceptors are used to detect painful stimuli or tissue damage. (the receptors for pain)• Tissues irritation or injury releases chemicals such as prostaglandins, kininsand K+ that stimulate nociceptors.• Pain may persist even after stimulus is removed because those chemicals linger.Pain• There are two types of pain: fast and slow. Fast pain (acute, sharp or pricking) perceived within 0.1 second. • Slow pain (chronic, burning, aching or throbbing) is perceived a second or more after the stimulus.http://reference.medscape.com/features/slideshow/pain-managementA-beta fiberC fiberPain• Superficial somatic pain: arising from skin receptors. • Deep somatic pain: skeletal muscles, joints, tendons and fascia.• Stimulation of pain sensors in visceral organs is visceral pain. This type of pain usually presents in or just deep to the skin that overlies the stimulated organ.Referred Pain The sites on the skin are innervated by nerves arising from the same spinal cord segments as those innervating the visceral organsCopyright © 2014 John Wiley & Sons, Inc.Summary• General senses vs Special senses• Sensory pathway 1st, 2nd, 3rdorders Dorsal column system and Anterolateral system• Sensory receptors Three types of nerve endings based on microscopic structure Three types of receptors based on stimulus detected• Pain Fast pain vs Slow pain; Referred


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UIUC MCB 402 - Neuro 3 Somatosensory

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