1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 13 The Peripheral Nervous System and Reflex Activity: Part A

2. Copyright © 2010 Pearson Education, Inc. Closing last weeks Muscle Practical M / W April 26 and 28 Same format, 50 muscle ID Final Exam Monday, May 3rd 10:30am–12:30pm Counts twice (¼) = 25% of final grade 100 questions, same format as other exams ½ new material, ½ old

3. Copyright © 2010 Pearson Education, Inc. Figure 13.1 Central nervous system (CNS)Peripheral nervous system (PNS) Motor (efferent) divisionSensory (afferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division

4. Copyright © 2010 Pearson Education, Inc. Sensory Receptors Specialized to respond to changes in their environment (stimuli) Activation results in graded potentials that trigger nerve impulses Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

5. Copyright © 2010 Pearson Education, Inc. Classification of Receptors Based on: Stimulus type Location Structural complexity

6. Copyright © 2010 Pearson Education, Inc. Classification by Stimulus Type Mechanoreceptors — respond to touch, pressure, vibration, stretch, and itch Thermoreceptors — sensitive to changes in temperature Photoreceptors — respond to light energy (e.g., retina) Chemoreceptors — respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors — sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)

7. Copyright © 2010 Pearson Education, Inc. Classification by Location 1.Exteroceptors Respond to stimuli arising outside the body Receptors in the skin for touch, pressure, pain, and temperature Most special sense organs

8. Copyright © 2010 Pearson Education, Inc. Classification by Location 2.Interoceptors (visceroceptors) Respond to stimuli arising in internal viscera and blood vessels Sensitive to chemical changes, tissue stretch, and temperature changes

9. Copyright © 2010 Pearson Education, Inc. Classification by Location 3.Proprioceptors Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Inform the brain of one’s movements

10. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendritic Endings Thermoreceptors Cold receptors (10–40ºC); in superficial dermis Heat receptors (32–48ºC); in deeper dermis

11. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendritic Endings Nociceptors Respond to: Pinching Chemicals from damaged tissue Temperatures outside the range of thermoreceptors Capsaicin

12. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendritic Endings Light touch receptors Tactile (Merkel) discs Hair follicle receptors

13. Copyright © 2010 Pearson Education, Inc. Table 13.1

14. Copyright © 2010 Pearson Education, Inc. Encapsulated Dendritic Endings All are mechanoreceptors Meissner’s (tactile) corpuscles — discriminative touch Pacinian (lamellated) corpuscles — deep pressure and vibration Ruffini endings — deep continuous pressure Muscle spindles — muscle stretch Golgi tendon organs — stretch in tendons Joint kinesthetic receptors — stretch in articular capsules

15. Copyright © 2010 Pearson Education, Inc. Table 13.1

16. Copyright © 2010 Pearson Education, Inc. Figure 13.2 1 2 3 Receptor level (sensory reception and transmission to CNS) Circuit level (processing in ascending pathways) Spinal cord Cerebellum Reticular formation Pons Muscle spindle Joint kinesthetic receptor Free nerve endings (pain, cold, warmth) Medulla Perceptual level (processing in cortical sensory centers) Motor cortex Somatosensory cortex Thalamus

17. Copyright © 2010 Pearson Education, Inc. Processing at the Receptor Level Receptors have specificity for stimulus energy Stimulus must be applied in a receptive field Transduction occurs Stimulus energy is converted into a graded potential called a receptor potential

18. Copyright © 2010 Pearson Education, Inc. Processing at the Receptor Level In general sense receptors, the receptor potential and generator potential are the same thing stimulus  receptor/generator potential in afferent neuron  action potential at first node of Ranvier

19. Copyright © 2010 Pearson Education, Inc. Processing at the Receptor Level In special sense organs: stimulus  receptor potential in receptor cell  release of neurotransmitter  generator potential in first-order sensory neuron  action potentials (if threshold is reached)

20. Copyright © 2010 Pearson Education, Inc. Adaptation of Sensory Receptors Adaptation is a change in sensitivity in the presence of a constant stimulus Receptor membranes become less responsive Receptor potentials decline in frequency or stop

21. Copyright © 2010 Pearson Education, Inc. Adaptation of Sensory Receptors Phasic (fast-adapting) receptors signal the beginning or end of a stimulus Examples: receptors for pressure, touch, and smell Tonic receptors adapt slowly or not at all Examples: nociceptors and most proprioceptors

22. Copyright © 2010 Pearson Education, Inc. Processing at the Perceptual Level Identification of the sensation depends on the specific location of the target neurons in the sensory cortex Aspects of sensory perception: Perceptual detection—ability to detect a stimulus (requires summation of impulses) Magnitude estimation—intensity is coded in the frequency of impulses Spatial discrimination—identifying the site or pattern of the stimulus (studied by the two-point discrimination test)

23. Copyright © 2010 Pearson Education, Inc. Main Aspects of Sensory Perception Feature abstraction—identification of more complex aspects and several stimulus properties Quality discrimination—the ability to identify submodalities of a sensation (e.g., sweet or sour tastes) Pattern recognition—recognition of familiar or significant patterns in stimuli (e.g., the melody in a piece of music)

24. Copyright © 2010 Pearson Education, Inc. Perception of Pain Warns of actual or impending tissue damage Stimuli include extreme pressure and temperature, histamine, K +, ATP, acids, and bradykinin Impulses travel on fibers that release neurotransmitters glutamate and substance P Some pain impulses are blocked by inhibitory endogenous opioids

25. Copyright © 2010 Pearson Education, Inc. Structure of a Nerve Connective tissue coverings include: Endoneurium — loose connective tissue that encloses axons and their myelin sheaths Perineurium — coarse connective tissue that bundles fibers into fascicles Epineurium — tough fibrous sheath around a nerve

26. Copyright © 2010 Pearson Education, Inc. Figure 13.3b Blood vessels Fascicle Epineurium Perineurium Endoneurium Axon Myelin sheath (b)

27. Copyright © 2010 Pearson Education, Inc. Classification of Nerves Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Types of fibers in mixed nerves: Somatic afferent and somatic efferent Visceral afferent and visceral efferent Peripheral nerves classified as cranial or spinal nerves

28. Copyright © 2010 Pearson Education, Inc. Ganglia Contain neuron cell bodies associated with nerves Dorsal root ganglia (sensory, somatic) (Chapter 12) Autonomic ganglia (motor, visceral) (Chapter 14)

29. Copyright © 2010 Pearson Education, Inc. Regeneration of Nerve Fibers Mature neurons are amitotic If the soma of a damaged nerve is intact, axon will regenerate Involves coordinated activity among: Macrophages — remove debris Schwann cells — form regeneration tube and secrete growth factors Axons — regenerate damaged part CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration

30. Copyright © 2010 Pearson Education, Inc. Figure 13.4 (1 of 4) Endoneurium Droplets of myelin Fragmented axon Schwann cells Site of nerve damage The axon becomes fragmented at the injury site. Wallerian degeneration occurs distal to injury. 1

31. Copyright © 2010 Pearson Education, Inc. Figure 13.4 (2 of 4) Schwann cellMacrophage Macrophages clean out the dead axon distal to the injury. 2

32. Copyright © 2010 Pearson Education, Inc. Figure 13.4 (3 of 4) Fine axon sprouts or filaments Aligning Schwann cells form regeneration tube 3 Axon sprouts, or filaments, grow through a regeneration tube formed by Schwann cells.

33. Copyright © 2010 Pearson Education, Inc. Figure 13.4 (4 of 4) Schwann cell Site of new myelin sheath formation 4 The axon regenerates and a new myelin sheath forms. Single enlarging axon filament