HP - C14Notes-The Somatic Nervous System (1).doc - Human Physiology Notes Chapter 14 – The Somatic Nervous System General Properties of Sensory

HP - C14Notes-The Somatic Nervous System (1).doc - Human...

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Human Physiology Notes Chapter 14 – The Somatic Nervous System General Properties of Sensory Systems Sensory receptors transduce (= change) environmental info into APs Each sensory receptor responds to a specific form (modality) of info like sound, light, pressure Types of Sensory Receptors o Simple receptors with free nerve endings o Receptors with ending enclosed in connective tissue o Specialized sensory receptors that release NT Functional Categories of Sensory Receptors o Chemoreceptors – activated by chemicals Tastebuds, olfactory epithelium Respond to oxygen levels, pH levels o Mechanoreceptors – respond to mechanical energy or deformation of their cell membrane Touch and pressure (baroreceptors) receptors Respond to pressure, cell stretch, vibration, acceleration, sound o Thermoreceptors - respond to temperature change o Photoreceptors – respond to light Sensory Receptor Responses o Receptors that respond to chemical, mechanical, thermal, or light energy will open ion channels that cause a change in membrane potential o Receptor Potentials o Sensory receptor equivalents to EPSPs Graded – amplitude is proportional to strength of tstimulus (not all-or-none) Light touch – small receptor potential Firm grip – large receptor potential Receptor potentials may initiate an AP that sends info to CNS o Tonic and Phasic receptors Tonic – respond at a constant rate as long as the stimulus is applied Slow adapting receptors Baroreceptors, irritant receptors, pain receptors Phasic – respond with a burst of activity but quickly reduce firing rate to constant stimulation (sensory adaptation) Rapidly adapting receptors Chemoreceptors for taste and smell Somatic Senses – touch, proprioception, temperature, nociception (pain and itch) Four somatosensory modalities o Touch - mechanoreceptors o Proprioreception – proprioceptors – signal positional information about the body o Temperature – thermoreceptors o Nociception – nociceptors signal pain Receptors for somatic senses located in skin and viscera Pathways for somatic perception project, cross midline, travel through thalamus to somatosensory cortex in post central gyrus Touch receptors - mechanoreceptors o Free nerve endings Respond to various touch and pressure stimuli Located around hair roots, under skin surface o Pacinian corpuscles Encapsulated (not free) in layers of connective tissue Detect vibration Located deep within skin Phasic so they can adapt quickly o Meissner’s corpuscles Encapsulated 1
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Detect flutter, stroking Located in superficial skin layers Phasic o Ruffini corpuscles Detect stretch of skin Located deep within skin Tonic o Merkel receptors Detect steady pressure and texture Superficial skin layers Tonic Temperature Receptors o Free nerve endings o Terminate in subcutaneous layers of skin o More cold receptors (respond to temps < 37 o C)
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  • Fall '16
  • Dusti Sloan

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