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) Soma;c Nervous System Autonomic Nervous System 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: Specialized ending of an afferent neuron Separate cell synap;cally 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. Transduc;on: Receptor Types &Transduc;on Fig. 6-1, pg. 184 Ac;on Poten;al Firing Rate Propor;onal to S;mulus Intens;y Fig. 6-3, pg. 186 Fig. 6-3, p. 186 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 ...
View Full Document
- Spring '08