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Chapter 16
Sensory, Motor & Integrative Systems
Principles of Human Anatomy and Physiology, 11e
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INTRODUCTION
• The components of the brain interact to receive sensory
input, integrate and store the information, and transmit
motor responses.
• To accomplish the primary functions of the nervous system
there are neural pathways to transmit impulses from
receptors to the circuitry of the brain, which manipulates the
circuitry to form directives that are transmitted via neural
pathways to effectors as a response.
Principles of Human Anatomy and Physiology, 11e
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Sensory Modalities
• The classes of sensory modalities are general senses and
special senses.
– The general senses include both somatic and visceral
senses, which provide information about conditions
within internal organs.
– The special senses include the modalities of smell, taste,
vision, hearing, and equilibrium.
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Process of Sensation
• Sensory receptors demonstrate selectivity
– respond to only one type of stimuli
• Events occurring within a sensation
– stimulation of the receptor
– transduction (conversion) of stimulus
• vary in amplitude
– generation of impulses when potential reaches
threshold
– integration of sensory input by the CNS
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Sensory Receptors
• Receptor Structure may be simple or complex
– General Sensory Receptors (Somatic Receptors)
• no structural specializations in free nerve endings
that provide us with pain, tickle, itch, temperatures
• some structural specializations in receptors for
touch, pressure & vibration
– Special Sensory Receptors (Special Sense Receptors)
• very complex structures---vision, hearing, taste, &
smell
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Structural Classification of Receptors
• Free nerve endings
– bare dendrites
– pain, temperature, tickle, itch & light touch
• Encapsulated nerve endings
– dendrites enclosed in connective tissue capsule
– pressure, vibration & deep touch
• Separate sensory cells
– specialized cells that respond to stimuli
– vision, taste, hearing, balance
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Classification by Stimuli Detected
• Mechanoreceptors
– detect pressure or stretch
– touch, pressure, vibration, hearing, proprioception,
equilibrium & blood pressure
• Thermoreceptors detect temperature
• Nociceptors detect damage to tissues
• Photoreceptors detect light
• Chemoreceptors detect molecules
– taste, smell & changes in body fluid chemistry
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Classification by Location
• Exteroceptors
– near surface of body
– receive external stimuli
– hearing, vision, smell, taste, touch, pressure, pain,
vibration & temperature
• Interoceptors
– monitors internal environment (BV or viscera)
– not conscious except for pain or pressure
• Proprioceptors
– muscle, tendon, joint & internal ear
– senses body position & movement
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Adaptation of Sensory Receptors
• Change in sensitivity to long-lasting stimuli
– decrease in responsiveness of a receptor
• bad smells disappear
• very hot water starts to feel only warm
• Variability in tendency to adapt:
– Rapidly adapting receptors (smell, pressure, touch)
• specialized for detecting changes
– Slowly adapting receptors (pain, body position)
• nerve impulses continue as long as the stimulus
persists – Pain is not easily ignored.
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Itch and Tickle
• Itch and tickle receptors are free nerve endings.
– Tickle is the only sensation that you may not elicit on
yourself.
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Meissner’s Corpuscle
• Dendrites enclosed in CT in dermal papillae of hairless skin
• Discriminative touch & vibration-- rapidly adapting
• Generate impulses mainly at onset of a touch
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Hair Root Plexus
•Free nerve endings found around follicles, detects
movement of hair
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Merkel’s Disc
•
Flattened dendrites touching cells of stratum basale
•
Used in discriminative touch (25% of receptors in hands)
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Ruffini Corpuscle
• Found deep in dermis of skin
• Detect heavy touch, continuous touch, & pressure
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Pacinian Corpuscle
• Onion-like connective tissue capsule enclosing a dendrite
• Found in subcutaneous tissues & certain viscera
• Sensations of pressure or high-frequency vibration
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Referred Pain
• Visceral pain that is felt just deep to the skin overlying the stimulated
organ or in a surface area far from the organ.
• Skin area & organ are served by the same segment of the spinal cord.
– Heart attack is felt in skin along left arm since both are supplied by
spinal cord segment T1-T5
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Proprioceptive or Kinesthetic Sense
• Awareness of body position & movement
– walk or type without looking
– estimate weight of objects
• Proprioceptors adapt only slightly
• Sensory information is sent to cerebellum & cerebral
cortex
– signals project from muscle, tendon, joint capsules
& hair cells in the vestibular apparatus
– receptors discussed here include muscle spindles,
tendon organs (Golgi tendon organs), and joint
kinesthetic receptors (Figure 16.4).
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Muscle
Spindles
• Specialized intrafusal muscle fibers enclosed in a CT capsule and
innervated by gamma motor neurons
• Stretching of the muscle stretches the muscle spindles sending sensory
information back to the CNS
• Spindle sensory fiber monitor changes in muscle length
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Golgi Tendon Organs
• Found at junction of tendon & muscle
• Consists of an encapsulated bundle of collagen fibers laced with
sensory fibers
• When the tendon is overly stretched, sensory signals head for the
CNS & resulting in the muscle’s relaxation
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Joint Receptors
• Ruffini corpuscles
– found in joint capsule
– respond to pressure
• Pacinian corpuscles
– found in connective tissue around the joint
– respond to acceleration & deceleration of joints
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