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Bio Notes February 12

Bio Notes February 12 - Bio Notes CHAPTER 42 Sensory...

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Bio Notes February 12, 2009 CHAPTER 42 Sensory Receptors Classified by Location of Stimuli o Exteroceptors o Receive stimuli from outside environment How to determine the type of food source, friendly associations (pleasant or painful), hot or cold etc… o Interoceptors o Detect changes within the body o Changes in pH, body temp, chemical composition of blood, osmotic pressure o The person is unaware of messages sent to CNS until signal internal conditions E.g. thirst in diabetes insipidus Hyperglycemia- higher level of glucose in the blood- that changes the osmotic pressure in the body and the body has to rectify that Sensory Receptors Classified by Type of Energy Thermoreceptors : respond to heat and cold- o Receptors in antennae locate prey, or ticks identifying an endothermic prey o Mammals External: skin, tongue, ear, eye Changes in temp via receptors/nerve endings on body surface signal internal thermorecptors in hypothalamus Homeostatic mechanisms ensure constant internal body temperature Electroreceptors o Used by predatory fishes to detect prey Respond to electrical potential Electric fields from muscle activity of prey Feedback signals from electric organs (other animals) o Electromagnetic receptors Detect Earth’s magnetic field Some animals orient by magnetic fields Migratory animals (birds) navigate via magnetic fields Nociceptors o Pain receptors Free nerve endings (dendrites) of certain sensory neurons transmit signal Three types respond to extreme conditions o Strong tactile stimuli (1. mechanical) o Temperature extremes (2. thermal) o Certain chemicals (3. others) The release of neurotransmitters glutamate and substance P (enhances signal of glutamate ) enhances the signal via interneuron to the spinal cord, hypothalamus and finally the brain centers (pain
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awareness) Mechanoreceptors o Transduce mechanical energy Activated when they change shape (mechanical push or pull) Allow animals to feel, hear, maintain balance (head up, feet down) Operation of internal organs (presence food in stomach etc) o Include: Gravity (statocysts) In invertebrates: o Statocysts tilts in response to movement; correct abnormal orientation o Sensory hair cells bend one or more statoliths (granules of sand or calcium carbonate that change position as animal moves) o Receptor potentials and action potentials inform CNS of change in position Sensory (touch) Movement and tension (propriorectors, hair cells, and lateral line organs) In mammals: o Receptors in the skin (hair in a hair follicle) o Displacement of hair (motion) leads to movement of receptor in deeper hair follicle and receptor potential o Encapsulated endings- Merkel Discs (adapt slowly), Meissner (adapts quickly (action to impulse is quick but not sustained)), and Ruffini corpuscles (adapt slowly (helps adapt to pain)) o Pacinian Corpuscle responds to very deep touch and pressure caused by rapid movement of tissue; Action Potential ceases (e.g. surgery) Propriorectors
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