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Lecture_8 - Lecture 8 •  SmartSite: –  Lecture...

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Unformatted text preview: Lecture 8 •  SmartSite: –  Lecture 8 Notes •  Announcements: –  None •  Review CNS •  Sensory Systems –  Somatosensory –  The Ear •  Reading (Recommended): –  Relevant por;ons of Chapter 6 REV: Nervous System Organiza;on •  2 Cell types –  Neurons (func;onal; 1012) –  Glia (support) •  2 Primary divisions –  Central nervous system (CNS) –  Peripheral nervous system (PNS) •  Afferent division (Input) •  Efferent division (Output) REV: Percep;on •  Conscious interpreta;on of external world derived from sensory input •  Sensory input does not give true reality percep;on. Why? •  We don’t perceive or encode everything –  Humans have receptors that detect only a limited number of exis;ng energy forms –  Informa;on channels in our brains are not high ­ fidelity recorders •  Transduc5on in not linear (1:1) –  Cerebral cortex further manipulates the data Peripheral Nervous System •  Consists of nerve fibers that carry informa;on between the CNS and other parts of the body •  Afferent division –  Sends informa;on from internal and external environment to CNS •  Visceral afferent •  Sensory afferent –  Incoming pathway for informa;on from internal viscera (organs in body cavi;es) –  Soma;c (body sense) sensa;on »  Sensa;on arising from body surface and propriocep;on –  Special senses »  Vision, hearing, ves;bular, taste, smell Receptors •  Structures at peripheral endings of afferent neurons •  Convert forms of s;mulus energy into electrical signals (ac;on poten;als) –  Process is called transduc;on •  Detect s;muli –  change detectable by the body only if AP produced –  Minimum threshold of energy required Types of Receptors  ­ Energy •  Form of energy transduced. –  Photoreceptors  ­ Responsive to visible wavelengths of light –  Mechanoreceptors  ­ Sensi;ve to mechanical energy –  Thermoreceptors  ­ Sensi;ve to heat and cold –  Osmoreceptors  ­ Detect changes in concentra;on of solutes in body fluids and resultant changes in osmo;c ac;vity –  Chemoreceptors  ­ Sensi;ve to specific chemicals •  Include receptors for smell and taste and receptors that detect O2 and CO2 concentra;ons in blood and chemical content of diges;ve tract –  Nociceptors  ­ Pain receptors that are sensi;ve to ;ssue damage or distor;on of ;ssue Types of Receptors  ­ Loca;on •  Source/Loca;on of informa;on sensed. –  Exteroreceptors –  Interoceptors –  Proprioceptors Receptors & Transduc;on •  Receptors may be: •  Transduc;on: –  Specialized ending of an afferent neuron –  Separate cell closely associated with peripheral ending of a neuron –  S;mulus alters receptor’s permeability which leads to graded receptor poten;al –  Usually causes nonselec;ve opening of all small ca;on channels –  This change in membrane permeability leads to the influx of Na+ ions producing receptor (generator) poten;als. –  The magnitude of the receptor poten;al represents the intensity of the s;mulus (this is a graded poten;al). –  A receptor poten;al of sufficient magnitude can produce a depolariza;on of Em, leading to an ac;on poten;al (if > threshold). –  This ac;on poten;al is propagated along an afferent fiber to the CNS. Receptor Types &Transduc;on Fig. 6 ­1, pg. 184 Receptor Adapta;on •  Receptor membrane poten;als return towards res;ng levels by the process of adapta;on •  2 basic types of receptors defined according to their speed of adapta;on –  Tonic receptors •  Do not adapt at all or adapt slowly •  Muscle stretch receptors, joint proprioceptors •  Rapidly adap;ng receptors •  Tac;le receptors in skin –  May adapt slowly or rapidly to sustained s;mula;on –  Phasic receptors Tonic Receptor (Steady ­State) Fig. 6 ­4a, pg. 186 Phasic Receptor (Rate of Change) Fig. 6 ­4b, pg. 186 Phasic vs. Tonic Receptor Receptors are Modality Specific Fig. 6 ­5, pg. 187 Receptors are Modality Specific Connective tissue layers Axon afferent neuron Somatosensory Touch ­Vibra5on Mechanoreceptor Pacinian corpuscle ...
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