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Transcript
Chapter 15
Neural Integration I:
Sensory Pathways and the Somatic Nervous
System
© 2012 Pearson Education, Inc.
Sensory Receptors
Detect info about external/internal environment
• 3 classifications of sensory receptors:
• Interoceptors: monitor internal environment
• Exteroceptors: monitor external environment
• Proprioceptors: monitor position of muscles/joints
• Stimulus translated to AP  CNS = transduction
© 2012 Pearson Education, Inc.
Simple vs. Complex Receptors
Simple receptors
Complex receptors
• dendrites of sensory neurons
• Found in sense organs
• Branching tips of dendrites =
free nerve endings
• Example: eye’s visual
receptors
• Not protected by accessory
structures
• Protected by accessory cells
and CT
• Little specificity (i.e.: free
nerve endings respond to
stimulus caused by
chemicals, pressure,
temperature or trauma)
• Specific (i.e.: receptors cells
in eye are protected by
accessory structures and
CT, usually only stimulus
reaches these cells is light)
© 2012 Pearson Education, Inc.
Tonic vs. Phasic Receptors
Tonic
Phasic
• Always active
• Normally inactive
• A.k.a slow-adapting
receptors: little change in
receptor activity over time
• Provide info about intensity
and rate of change of
stimulus
• Indicates background level
of stimulation
• A.k.a. fast-adapting
receptors: respond strongly
at first, activity declines
© 2012 Pearson Education, Inc.
• Receptor specificity: receptors sensitive to specific stimuli
•
Examples:
• Touch receptors sensitive to pressure, not chemical stimuli
• Taste receptors sensitive to chemicals, not pressure stimuli
• Sensation: arriving information from receptors via AP
• Perception: conscious awareness of sensation
Receptive
field 1
Receptive field: area
monitored by single
receptor
Larger field=harder to
localize stimulus
© 2012 Pearson Education, Inc.
Receptive
field 2
Interpretation of Sensory Information
• Sensory neurons relay info from receptor to specific cortex areas
• Link between receptor and cortical neuron = labeled line
• Axons of labeled line carry info about 1 type of stimulus (modality)
• Sensory coding = translation of complex sensory info into meaningful
patterns of AP
• CNS interprets modality based on labeled line
• Cannot tell difference between true/false sensation
• i.e.: rub eyes = mechanical stimulus causes visual of flashes of
lights; any activity along optic nerve travels to visual cortex = visual
perception
© 2012 Pearson Education, Inc.
Nociceptors
• Tonic
• Locations:
• superficial portions of skin
• Joint capsules
• Periosteum
• Walls of BVs
• Detects: pain
• Myelinated Type A fibers: fast or prickling pain (i.e.: injection
or deep cut)
• Type C fibers: slow or burning/aching pain
© 2012 Pearson Education, Inc.
Thermoreceptors
• Phasic
• Free nerve endings in dermis, skeletal muscles, liver and
hypothalamus
• More cold than warm
• Carried along same pathway as pain sensations
• Info sent to
• Thalamus
• reticular formation of midbrain
• Primary sensory cortex
© 2012 Pearson Education, Inc.
Mechanoreceptors
• Stimulus caused by distortion of plasma membranes
• Three classes:
• Tactile (touch, pressure, vibration)
• Baroreceptors (pressure changes in BVs)
• Proprioceptors (position of joints/skeletal muscles)
© 2012 Pearson Education, Inc.
Types of Tactile Receptors
•Phasic
•Respond rapidly
•Best at detecting initial
contact and subsequent
movement
•Tonic; small receptive fields
•Located between epidermal
cells
•Sensitive to touch/pressure
© 2012 Pearson Education, Inc.
•Tonic; small
receptive fields
•Extremely
sensitive
•Found in stratum
basale
Types of Tactile Receptors
•Aka: Meissner’s
•Phasic
•Locations: eyelids, lips, fingertips, nipples,
external genitalia
•Fine touch/pressure or low frequency
vibrations
•Tonic
•Located in
dermis
•pressure
© 2012 Pearson Education, Inc.
•Phasic
•Deep pressure
•Provides somatic and
visceral sensory info
Chemoreceptors
• Only respond to water or lipid soluble substances dissolved in
body fluids
• Info sent to brain stem (i.e. respiratory and cardiovascular
centers), not cortex
• Located in:
• carotid and aortic bodies
• monitor pH, CO2 and O2 levels
© 2012 Pearson Education, Inc.