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Bear: Neuroscience: Exploring the Brain 3e

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1 Bear: Neuroscience: Exploring the Brain 3e
Chapter 12: The Somatic Sensory System Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

2 Introduction Somatic Sensation Enables body to feel, ache, chill
Sensitive to stimuli Responsible for feeling of touch and pain Somatic sensory system: Different from other systems Receptors: Distributed throughout Responds to different kinds of stimuli Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

3 Touch Types and layers of skin Hairy and glabrous (hairless)
Epidermis (outer) and dermis (inner) Functions of skin Protective function Prevents evaporation of body fluids Provides direct contact with world Mechanoreceptors Most somatosensory receptors are mechanoreceptors Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

4 Touch Mechanoreceptors (Cont’d) Pacinian corpuscles Ruffini's endings
Meissner's corpuscles Merkel's disks Krause end bulbs Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

5 Touch Mechanoreceptors (Cont’d) Åke Vallbo and colleagues
Slides 5 and 6 were switched – the flow is better this way and follows the text. Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

6 Touch Mechanoreceptors (Cont’d)
Receptive field size and adaptation rate Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

7 Touch Mechanoreceptors (Cont’d) Two-point discrimination
Importance of fingertips over elbow Primary Afferent Axons Aa, Ab, Ad, C C fibers mediate pain and temperature Ab mediates touch sensations Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

8 Touch The Spinal cord Spinal segments (30)- spinal nerves within 4 divisions of spinal cord Dermatomes- 1-to-1 correspondence with segments Shingles Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

9 Touch The Spinal cord (Cont’d) Sensory Organization of the spinal cord
Divisions Cervical (C) Thoracic (T) Lumbar (L) Sacral (S) Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

10 Touch Spinal cord (Cont’d) Sensory Organization of the spinal cord
Division of spinal gray matter: Dorsal horn; Intermediate zone; Ventral horn Myelinated Ab axons (touch-sensitive) Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

11 Touch Dorsal Column–Medial Lemniscal Pathway
Touch information ascends through dorsal column, dorsal nuclei, medial lemniscus, and ventral posterior nucleus to primary somatosensory cortex The Trigeminal Touch Pathway Trigeminal nerves Cranial nerves Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

12 Touch Somatosensory Cortex Primary Other areas Postcentral gyrus
Posterior Parietal Cortex Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

13 Touch Somatosensory Cortex (Cont’d)
Brodmann’s Area 3b (or S1): Primary somatosensory cortex Receives dense input from VP nucleus of the thalamus Neurons: Responsive to stimuli Lesions impair somatic sensations Electrical stimulation evokes sensory experiences Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

14 Touch Somatosensory Cortex Cortical Somatotopy Homunculus
Importance of mouth Tactile sensations: Important for speech Lips and tongue: Last line of defense Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

15 Touch Somatosensory Cortex (Cont’d) S1: Rat Vibrissae “Barrel cortex”
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

16 Touch Somatosensory Cortex (Cont’d) S1 – Owl monkey
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

17 Touch Somatosensory Cortex (Cont’d) Cortical Map Plasticity
Remove digits or overstimulate – examine somatotopy before and after Conclusions of experiments Reorganization of cortical maps Dynamic Adjust depending on the amount of sensory experience Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

18 Touch Somatosensory Cortex (Cont’d) The Posterior Parietal Cortex
Involved in somatic sensation, visual stimuli, and movement planning Agnosia Astereoagnosia Neglect syndrome Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

19 Pain Nociceptors Pain and nociception
Pain - feeling of sore, aching, throbbing Nociception - sensory process, provides signals that trigger pain Nociceptors: Transduction of Pain Bradykinin Mast cell activation: Release of histamine Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

20 Pain Nociception and the Transduction of Painful Stimuli (Cont’d)
Types of Nociceptors Polymodal nocireceptors, Mechanical nocireceptors, Thermal nocireceptors Hyperalgeia Primary and secondary hyperalgesia Bradykinin, prostaglandins, and substance P Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

21 Pain Primary Afferents and Spinal mechanisms
First pain and second pain Referred pain: Angina Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

22 Pain Ascending Pain Pathways
Differences between touch and pain pathway Nerve endings in the skin Diameter of axons Connections in spinal cord Touch – Ascends Ipsilaterally Pain – Ascends Contralaterally Removed last part and grouped onto next slide Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

23 Pain Ascending Pain Pathways (Cont’d) Spinothalamic Pain Pathway
Brown-Séquard Syndrome The Trigeminal Pain Pathway The Thalamus and the Cortex Touch and pain systems remain segregated Pain and temperature information sent to various cortical areas Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

24 Pain Ascending Pain Pathways (Cont’d)
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

25 Pain The Regulation of Pain Afferent Regulation Descending Regulation
The endogenuos opiates Opioids and endomorphins Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

26 Pain The Regulation of Pain (Cont’d) Descending regulation
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

27 Temperature Thermoreceptors “Hot” and “cold” receptors
Varying sensitivities Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

28 Temperature Thermoreceptors Hot and cold receptors
Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

29 Temperature The Temperature Pathway
Organization of temperature pathway Identical to pain pathway Cold receptors coupled to Ad and C Hot receptors coupled to C Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

30 Concluding Remarks Sensory systems exhibit similar organization and function Sensory types are segregated within the spinal cord and cerebral cortex Repeated theme Parallel processing of information Perception of object involves the seamless coordination of somatic sensory information Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

31 End of Presentation Neuroscience: Exploring the Brain, 3rd Ed, Bear, Connors, and Paradiso Copyright © 2007 Lippincott Williams & Wilkins

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