In this chapter, you will learn to: Define peripheral nervous system and list its components; classify general sensory receptors by structure, stimulus detected, and body location; outline the events that lead to sensation and perception; describe receptor and generator potentials and sensory adaptation; describe the main aspects of sensory perception.
PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 13 The Peripheral Nervous System and Reflex Activity: Part A Copyright © 2010 Pearson Education, Inc Peripheral Nervous System (PNS) • All neural structures outside the brain • Sensory receptors • Peripheral nerves and associated ganglia • Motor endings Copyright © 2010 Pearson Education, Inc Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Copyright © 2010 Pearson Education, Inc Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Figure 13.1 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 Copyright © 2010 Pearson Education, Inc Classification of Receptors • Based on: • Stimulus type • Location • Structural complexity 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) Copyright © 2010 Pearson Education, Inc Classification by Location Exteroceptors • Respond to stimuli arising outside the body • Receptors in the skin for touch, pressure, pain, and temperature ã Most special sense organs Copyright â 2010 Pearson Education, Inc Classification by Location Interoceptors (visceroceptors) • Respond to stimuli arising in internal viscera and blood vessels • Sensitive to chemical changes, tissue stretch, and temperature changes Copyright © 2010 Pearson Education, Inc Classification by Location 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 Copyright © 2010 Pearson Education, Inc Classification by Structural Complexity Complex receptors (special sense organs) • Vision, hearing, equilibrium, smell, and taste (Chapter 15) Simple receptors for general senses: • Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense ã Unencapsulated (free) or encapsulated dendritic endings Copyright â 2010 Pearson Education, Inc Processing at the Circuit Level • Pathways of three neurons conduct sensory impulses upward 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) 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) 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) Copyright © 2010 Pearson Education, Inc Perceptual level (processing in cortical sensory centers) Motor cortex Somatosensory cortex Thalamus Reticular formation Pons Circuit level (processing in Spinal ascending pathways) cord Cerebellum Medulla Free nerve endings (pain, cold, warmth) Muscle spindle Receptor level (sensory reception Joint and transmission kinesthetic to CNS) receptor Copyright © 2010 Pearson Education, Inc Figure 13.2 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 Copyright © 2010 Pearson Education, Inc Structure of a Nerve • Cordlike organ of the PNS • Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue 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 Copyright © 2010 Pearson Education, Inc Endoneurium Axon Myelin sheath Perineurium Epineurium Fascicle Blood vessels (b) Copyright © 2010 Pearson Education, Inc Figure 13.3b 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 Copyright © 2010 Pearson Education, Inc Ganglia • Contain neuron cell bodies associated with nerves • Dorsal root ganglia (sensory, somatic) (Chapter 12) ã Autonomic ganglia (motor, visceral) (Chapter 14) Copyright â 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 Copyright © 2010 Pearson Education, Inc Endoneurium Schwann cells Droplets of myelin The axon becomes fragmented at the injury site Fragmented axon Site of nerve damage Copyright © 2010 Pearson Education, Inc Figure 13.4 (1 of 4) Schwann cell Copyright © 2010 Pearson Education, Inc Macrophage Macrophages clean out the dead axon distal to the injury Figure 13.4 (2 of 4) Aligning Schwann cells form regeneration tube Axon sprouts, or filaments, grow through a regeneration tube formed by Schwann cells Fine axon sprouts or filaments Copyright © 2010 Pearson Education, Inc Figure 13.4 (3 of 4) Schwann cell Site of new myelin sheath formation The axon regenerates and a new myelin sheath forms Single enlarging axon filament Copyright © 2010 Pearson Education, Inc Figure 13.4 (4 of 4) ... Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Copyright © 2010 Pearson Education, Inc Motor (efferent) division Somatic nervous system Autonomic nervous system. . .Peripheral Nervous System (PNS) • All neural structures outside the brain • Sensory receptors • Peripheral nerves and associated ganglia • Motor endings... at the Circuit Level • Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions • First-order neurons • Conduct impulses from the receptor level to the second-order