Chapter 10a Sensory Physiology 2013 Pearson Education Inc About This Chapter General properties of sensory systems Somatic senses Chemoreception smell and taste The ear hearing The ear equilibrium The eye and vision 2013 Pearson Education Inc Table 10 1 1 Information Processing by the Sensory Division 1 of 2 Table 10 1 2 Information Processing by the Sensory Division 2 of 2 Sensory Pathways Stimulus as physical energy sensory receptor Receptor acts as a transducer Intracellular signal usually change in membrane potential Stimulus threshold action potential to CNS Integration in CNS cerebral cortex or acted on subconsciously 2013 Pearson Education Inc Figure 10 1a 1 of 3 Simple receptors are neurons with free nerve endings They may have myelinated or unmyelinated axons Stimulus Free nerve endings Unmyelinated axon Cell body Figure 10 1b 2 of 3 Complex neural receptors have nerve endings enclosed in connective tissue capsules This illustration shows a Pacinian corpuscle which senses touch Stimulus Enclosed nerve ending Layers of connective tissue Myelinated axon Cell body Figure 10 1c 3 of 3 Most special senses receptors are cells that release neurotransmitter onto sensory neurons initiating an action potential The cell illustrated is a hair cell found in the ear Stimulus Specialized receptor cell hair cell Synaptic vesicles Synapse Myelinated axon Cell body of sensory neuron Table 10 2 Types of Sensory Receptors Sensory Transduction Stimulus energy converted into information processed by CNS Ion channels or second messengers initiate membrane Adequate stimulus Form of energy to which a receptor potential change is most responsive Threshold Minimum stimulus Receptor potential Change in sensory receptor membrane potential 2013 Pearson Education Inc Figure 10 2a 1 of 2 Convergence creates large receptive fields The receptive fields of three primary sensory neurons overlap to form one large secondary receptive field Compass with points separated by 20 mm Skin surface Primary sensory neurons Secondary sensory neurons Convergence of primary neurons allows simultaneous subthreshold stimuli to sum at the secondary sensory neuron and initiate an action potential Two stimuli that fall within the same secondary receptive field are perceived as a single point because only one signal goes to the brain Therefore there is no two point discrimination Figure 10 2b 2 of 2 Small receptive fields are found in more sensitive areas When fewer neurons converge secondary receptive fields are much smaller Compass with points separated by 20 mm Skin surface Primary sensory neurons Secondary sensory neurons The two stimuli activate separate pathways to the brain The two points are perceived as distinct stimuli and hence there is two point discrimination Integration by CNS Sensory information Spinal cord to brain by ascending pathways Directly to brain stem via cranial nerves Visceral reflexes integrated in brain stem or spinal cord usually do not reach conscious perception knee jerk effect Perceptual threshold level of stimulus necessary to be aware of particular sensation Each major division of the brain processes one or more types of sensory information 2013 Pearson Education Inc Figure 10 3 SENSORY PATHWAYS IN THE BRAIN Most pathways pass through the thalamus on their way to the cerebral cortex Primary somatic sensory cortex Auditory cortex Visual cortex Gustatory cortex Olfactory cortex Olfactory bulb Olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex Most sensory pathways project to the thalamus The thalamus modifies and relays information to cortical centers Equilibrium pathways project primarily to the cerebellum FIGURE QUESTION Which sensory pathways shown do not synapse in the thalamus Nose Thalamus Sound Cerebellum Brain stem Equilibrium Eye Tongue Somatic senses Figure 10 3 Most pathways pass through the thalamus on their way to the cerebral cortex Gustatory cortex Olfactory cortex Olfactory bulb Olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex Slide 1 Primary somatic sensory cortex Auditory cortex Visual cortex Nose Thalamus Sound Cerebellum Brain stem Equilibrium Eye Tongue 2013 Pearson Education Inc Somatic senses Figure 10 3 Most pathways pass through the thalamus on their way to the cerebral cortex Gustatory cortex Olfactory cortex Olfactory bulb Olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex Most sensory pathways project to the thalamus The thalamus modifies and relays information to cortical centers Nose Thalamus Sound Cerebellum Brain stem Equilibrium Eye Tongue Slide 2 Primary somatic sensory cortex Auditory cortex Visual cortex 2013 Pearson Education Inc Somatic senses Figure 10 3 Most pathways pass through the thalamus on their way to the cerebral cortex Gustatory cortex Olfactory cortex Olfactory bulb Slide 3 Primary somatic sensory cortex Auditory cortex Visual cortex Olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex Most sensory pathways project to the thalamus The thalamus modifies and relays information to cortical centers Equilibrium pathways project primarily to the cerebellum Nose Thalamus Sound Cerebellum Brain stem Equilibrium Eye Tongue 2013 Pearson Education Inc Somatic senses Properties of Stimulus Modality Indicated by where Sensory neurons are activated Neurons terminate in brain Each receptor type is most sensitive to a particular modality of stimulus Labeled line coding 1 1 association of receptor with sensation 2013 Pearson Education Inc Properties of Stimulus Location According to which receptive fields are activated Auditory information is an exception Sensitive to different frequencies and timing Increases contrast between activated receptive fields Lateral inhibition and inactive neighbors Population coding Multiple receptors functioning together 2013 Pearson Education Inc Figure 10 4 The Brain Uses Timing Differences to Localize Sound Source of sound Sound takes longer to reach right ear Left Signals coming from the left reach the brain first Right Top view of head Figure 10 5 LATERAL INHIBITION Lateral inhibition enhances contrast and makes a stimulus easier to perceive The responses of primary sensory neurons A B and C are proportional to the intensity of the stimulus in each receptor field Secondary sensory neuron B inhibits secondary neurons A and C creating greater contrast between B and