1. Copyright © 2010 Pearson Education, Inc. Marieb Chapter 13 Part A PNS

2. Copyright © 2010 Pearson Education, Inc. Peripheral Nervous System (PNS) All neural structures outside the brain Sensory receptors Peripheral nerves and associated ganglia Motor endings

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 action potentials 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 Sensory Receptors Based on: Stimulus type Location Structural complexity

6. Copyright © 2010 Pearson Education, Inc. Classification by Structural Complexity 1.Complex receptors (special senses) Vision, hearing, equilibrium, smell, and taste (Chapter 15; we won’t cover these) More than one type of cell that work together 2.Simple receptors for general senses: Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sensation Unencapsulated (free) or encapsulated dendrites as sensors

7. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendrites Thermoreceptors Cold receptors (10–40ºC);more numerous, in superficial dermis Heat receptors (32–48ºC); in deeper dermis Also located in muscles, liver, hypothalamus, etc.

8. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendritic Endings Nociceptors ( PAIN receptors!) Respond to: Pinching/mechanical force Chemicals from damaged tissue (inflammation chemicals) Temperatures outside the range of thermoreceptors (extremes) Other chemicals [Capsaicin (hot pepper extract)] Located in skin, periosteum, joint capsules, tendons, meninges, blood vessel walls, etc.

9. Copyright © 2010 Pearson Education, Inc. Unencapsulated Dendrites Light touch receptors Tactile (Merkel) discs Hair follicle receptors

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

11. Copyright © 2010 Pearson Education, Inc. Encapsulated Dendrites All are mechanoreceptors Meissner’s (tactile) corpuscles— 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 (a proprioceptor)

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

13. 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)

14. 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 in this class

15. 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

16. 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 cerebellum and cortex of our position in space

17. Copyright © 2010 Pearson Education, Inc. From Sensation to Perception Survival depends upon sensation and perception Sensation: the awareness of changes in the internal and external environment Perception: the conscious interpretation of those stimuli

18. Copyright © 2010 Pearson Education, Inc. Sensory Integration Input comes from exteroceptors, proprioceptors, and interoceptors Input is relayed toward the head, but is processed along the way

19. Copyright © 2010 Pearson Education, Inc. Sensory Integration The signal can be processed and altered at three different levels: 1.Receptor level—the sensor receptors 2.Circuit level—ascending pathways 3.Perceptual level—neuronal circuits in the cerebral cortex

20. 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

21. Copyright © 2010 Pearson Education, Inc. Processing at the Receptor Level Stimulus energy is converted into a graded potential called a receptor potential (don’t pay attention to the term generator potential- only used with special senses) In general sense receptors, it works like this: stimulus  receptor potential in afferent neuron  action potential at first node of Ranvier

22. 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)

23. 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 So the receptor potentials decline in frequency or stop Why does this happen? Is it a good thing?

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

25. Copyright © 2010 Pearson Education, Inc. Adaptation - What Happens to Signaling?

26. Copyright © 2010 Pearson Education, Inc. Processing at the Circuit Level Ascending pathways of three neurons conduct sensory impulses to the appropriate brain regions First-order neurons Conduct impulses from the receptor level to the second-order neurons in the CNS Second-order neurons Transmit impulses to the thalamus or cerebellum Third-order neurons Conduct impulses from the thalamus to the somatosensory cortex (perceptual level)

27. 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

28. Copyright © 2010 Pearson Education, Inc. Perception of Pain Definition: an unpleasant sensory and emotional experience associated with actual or potential tissue damage Warns that you are “at the edge of a cliff!” Stimuli include: extreme pressure extreme temperature histamine, K +, ATP, acids, and bradykinin (chemicals released during inflammation) Some pain impulses are blocked by inhibitory endogenous opioids Is pain necessary?

29. Copyright © 2010 Pearson Education, Inc. Referred Pain Visceral pain afferent fibers travel along the same pathway as somatic pain fibers Referred Pain = pain stimuli arising in the viscera are perceived as somatic in origin Examples:

30. Copyright © 2010 Pearson Education, Inc. Referred Pain Heart Lungs and diaphragm Liver Stomach Kidneys Ovaries Small intestine Ureters Urinary bladder Colon Pancreas Liver Heart Appendix Gallbladder

31. Copyright © 2010 Pearson Education, Inc. Pain Does everyone have the same pain threshold? Does everyone have the same pain tolerance?

32. Copyright © 2010 Pearson Education, Inc. Pain Pain tolerance is influenced by many factors:

33. Copyright © 2010 Pearson Education, Inc. How Is Pain Processed?

34. Copyright © 2010 Pearson Education, Inc. Analgesia Defined as “ “ Major Analgesics Other agents that can act as pain relievers

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

36. Copyright © 2010 Pearson Education, Inc. Regeneration of Nerve Fibers Mature neurons can’t divide If the soma of a damaged nerve is intact, its axon will regenerate Involves coordinated activity among Macrophages Schwann cells Axons CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration (UGH!)