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.
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prepared by Janice Meeking, Mount Royal College
C H A P T E R 13
The Peripheral Nervous
System and Reflex Activity:
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Peripheral Nervous System (PNS)
• Sensory receptors
• Peripheral nerves and associated ganglia
• Motor endings
Trang 3Central nervous system (CNS) Peripheral nervous system (PNS)
Motor (efferent) division Sensory (afferent)
division
Somatic nervous system
Autonomic nervous system (ANS)
Sympathetic division
Parasympathetic division
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Sensory Receptors
environment (stimuli)
trigger nerve impulses
perception (interpretation of the meaning of the stimulus) occur in the brain
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Classification by Stimulus Type
• Mechanoreceptors—respond to touch, pressure,
vibration, stretch, and itch
Trang 7Classification by Location
• Respond to stimuli arising outside the body
• Receptors in the skin for touch, pressure,
pain, and temperature
• Most special sense organs
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Classification by Location
• Respond to stimuli arising in internal viscera
and blood vessels
• Sensitive to chemical changes, tissue
stretch, and temperature changes
Trang 9Classification by Location
• Respond to stretch in skeletal muscles,
tendons, joints, ligaments, and connective tissue coverings of bones and muscles
• Inform the brain of one’s movements
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Classification by Structural Complexity
• Vision, hearing, equilibrium, smell, and taste
(Chapter 15)
• Tactile sensations (touch, pressure, stretch,
vibration), temperature, pain, and muscle sense
• Unencapsulated (free) or encapsulated
dendritic endings
Trang 11Unencapsulated Dendritic Endings
• Cold receptors (10–40ºC); in superficial dermis
• Heat receptors (32–48ºC); in deeper dermis
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Unencapsulated Dendritic Endings
• Respond to:
• Pinching
• Chemicals from damaged tissue
• Temperatures outside the range of thermoreceptors
• Capsaicin
Trang 13Unencapsulated Dendritic Endings
• Tactile (Merkel) discs
• Hair follicle receptors
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Trang 15Encapsulated 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
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Trang 17From Sensation to Perception
perception
internal and external environment
those stimuli
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Sensory Integration
proprioceptors, and interoceptors
processed along the way
Trang 19Sensory Integration
systems:
1 Receptor level—the sensor receptors
2 Circuit level—ascending pathways
3 Perceptual level—neuronal circuits in the
cerebral cortex
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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
Trang 21Processing at the Receptor Level
• Stimulus energy is converted into a graded
potential called a receptor potential
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Processing at the Receptor Level
potential and generator potential are the same thing
stimulusreceptor/generator potential in afferent neuron
action potential at first node of Ranvier
Trang 23Processing at the Receptor Level
• In special sense organs:
stimulus receptor potential in receptor cell
release of neurotransmitter generator potential in first-order sensory neuron
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Adaptation of Sensory Receptors
presence of a constant stimulus
• Receptor membranes become less responsive
• Receptor potentials decline in frequency or
stop
Trang 25Adaptation of Sensory Receptors
beginning or end of a stimulus
• Examples: receptors for pressure, touch, and smell
• Examples: nociceptors and most
proprioceptors
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Processing at the Circuit Level
• Pathways of three neurons conduct sensory
impulses upward to the appropriate brain regions
• Conduct impulses from the thalamus to the
somatosensory cortex (perceptual level)
Trang 27Processing 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)
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Main Aspects of Sensory Perception
complex aspects and several stimulus
properties
submodalities of a sensation (e.g., sweet or sour tastes)
significant patterns in stimuli (e.g., the melody
in a piece of music)
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Receptor level
Circuit level
(processing in ascending pathways) Spinal cord
Cerebellum
Reticular formation
Pons
Muscle spindle
Free nerve endings (pain, cold, warmth)
Medulla
Perceptual level (processing in cortical sensory centers)
Motor cortex
Somatosensory cortex
Thalamus
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Perception of Pain
bradykinin
neurotransmitters glutamate and substance P
endogenous opioids
Trang 31Structure of a Nerve
peripheral axons enclosed by connective tissue
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Structure of a Nerve
• 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
Trang 33Blood vessels Fascicle
Epineurium Perineurium Endoneurium
Axon Myelin sheath
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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
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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
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Trang 38Copyright © 2010 Pearson Education, Inc. Figure 13.4 (2 of 4)
Schwann cell Macrophage Macrophages clean out the
dead axon distal
to the injury
2
Trang 39Aligning Schwann cells form regeneration tube
3
Axon sprouts,
or filaments, grow through a regeneration tube formed by
Schwann cells
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Schwann cell Site of new
myelin sheath formation
4
The axon regenerates and
a new myelin sheath forms
Single enlarging
axon filament