Sensory Systems Part II. Sarah L. Chollar University of California, Riverside

Transcription

1 Sensory Systems Part II Sarah L. Chollar University of California, Riverside

2 Somatosensory System Specialized Sensory Receptors: Mechanoreceptors Dermatomes Sensory Pathways Pain Somatotopic Map of the Cortex Phantom Pain

3 Mechanoreceptors Site of signal transduction for tactile (touch) information Kalat, Biological Psychology 9 th Edition (2007)

4 Dermatomes Represent areas of the body surface Alphanumeric designation represents the level of the spinal cord that sensory information enters the CNS Kalat, Biological Psychology 9 th Edition (2007)

5 Somatosensory Pathways

6 Pain Pathways and nuclei involved in processing pain Gate Theory Non-pain stimuli can affect the perception of pain Kalat, Biological Psychology 9 th Edition (2007)

7 Pain and Neurotransmission: Endorphins and Substance P Noiciceptive stimuli can trigger the release of Substance P which plays a role in perception of pain Activation through the spinothalamic tract triggers the release of endorphins (endogenous morphines) Enkephalin inhibits the release of Substance P and reduces the perception of pain Kalat, Biological Psychology 9 th Edition (2007)

8 Somatosensory Homunculus Somatosensory system is organized like a distorted map of the body surface Specializations exist Larger representations for hands and face

9 Somatotopy: Specialists /cimg/ gif Catania et al.,

10 Phantom Pain Phantom pain and sensation commonly occur following amputation of peripheral nerve damage Kalat, Biological Psychology 9 th Edition (2007)

11 Phantom Pain A map of the phantom hand is located on the shoulder and face of a man who was amputated Stimulating the face and shoulder in specific areas produced phantom sensations of individual fingers Phantom pain is associated with the extent of cortical reorganization Treatment Options Medications- generally ineffective Mirror box therapy Visualization Kalat, Biological Psychology 9 th Edition (2007)

12 Gustatory System Primary Tastes Gustatory Anatomy Receptor Distribution Gustatory Pathways Gustatory Disorders

13 Primary Tastes Primary Tastes Salty open ionotropic sodium channels Sweet close potassium channels Sour- close potassium channels Bitter release of calcium from internal stores Umami (savory)

14 Gustatory System Anatomy Kalat, Biological Psychology 9 th Edition (2007)

15 Distribution of Receptors No map of taste Each area of the tongue contains receptors for each of the primary tastes

16 Gustatory Processing Cranial nerves VII, X, XI Nucelus of the tractus solitarius (NTS) Medial lamniscus Thalamus VPM Primary gustatory cortex

17 Gustatory Processing Kalat, Biological Psychology 9 th Edition (2007)

18 Gustatory Disorders Aguesia: loss of the sense of taste. Hypogeusia: diminished sensitivity to taste. True loss of taste is rare, perceived loss of taste is often associated with a loss of smell May be triggered by medication, upper respiratory disorders, and sometimes associated with congenital chemosensory disorders

19 Olfactory System Olfactory Anatomy Olfactory Receptors Olfactory Bulb and Glomeruli Olfactory Processing Olfactory Disorders

20 Olfactory Anatomy Direct connection from receptors to olfactory bulb Olfactory receptors interact with many different odorants allowing us to perceive thousands of different odors with only a few hundred receptor types Kalat, Biological Psychology 9 th Edition (2007)

21 Olfactory Receptors Olfactory receptors are metabotropic G-protein coupled receptors Receptor turnover is about days this regeneration is unusual in the central nervous system Humans have hundreds of receptor types while many other animals have thousands Theories of Olfaction StericTheory Odor perception is related to chemical structure of odorant Lock-and-key mechanism VibrationalTheory Kalat, Biological Psychology 9 th Edition (2007)

22 Olfactory Receptors 1. Single receptors are activated by multiple odorants 2. A single odorant typically activates multiple receptors 3. Different odorants are recognized by different combinations of receptors Coding (Leffingwell, 2002) Receptors: labeled-line code Olfactory Bulb: cross-fiber coding also called population coding

23 Olfactory Bulb and Glomeruli Information from receptor subtypes converge on glomeruli in the olfactory bulb Different odorants elicit different patterns of activation among glomeruli

24 Olfactory Processing Receptors Olfactory Bulb Piriform Cortex Projects to hypothalamus and limbic system Dorsomedial thalamus Orbitofrontal Cortex

25 Olfactory Disorders and Etiology Table 1. CAUSES of OLFACTORY LOSS ANOSMIA a complete loss of smell HYPOSMIA partial loss of smell HYPEROSMIA enhanced smell sensitivity DYSOSMIA distortion in odour perception (includes parosmia & phantosmia) PAROSMIA distortion of perception of external stimulus PHANTOSMIA smell perception with no external stimulus Aetiology Head injury Post URI Nasal/sinus disease Idiopathic-nasal Toxic exposure-nasal Multiple Congenital Age Idiopathic-oral Miscellaeous-oral Toxic exposure-oral % patients 19* 17* 16* SEIDEN, A.M. (1997). Taste and Smell Disorders.

26 Discussion Sensory systems allow us to receive information about the environment Several themes, organization, processing All systems communicate using the electrochemical language of the nervous system Understanding how these systems work allows for the design of new therapeutic techniques for sensory disorders

27 Sensory Systems Themes Organization Topographic Maps Layers and Columns Pathways and Circuits Specialized Sensory Receptors Processing Signal Transduction Coding of Sensory Information Serial and Parallel Processing

28 Sensory Receptors Rods and Cones Olfactory Receptors Gustatory Receptors Mechanoreceptors Topographical Maps Retinotopic Map Somatotopic map Tonotopic Map

29 Coding of Sensory Information Limitations of the Action Potential Types of Coding Labeled-line code Cross-fiber coding Rate code Time code Place code Volley coding Types of coding are often used in combination within a given sensory system