Chapter 13 Part A

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ksales23
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98344
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Chapter 13 Part A
Updated:
2011-08-25 06:15:57
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Anatomy Physiology
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The Peripheral Nervous System and Reflex Activity
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  1. All neural structures outside the brain
    sensory receptors
    peripheral nerves and associated ganglia
    motor endings
    Peripheral Nervous System
  2. survival depends upon sensation and perception
    sensation: the awareness of changes in the internal and external environment
    Perception: the conscious interpretation of those stimuli
    From Sensation to Perception
  3. Input comes from exteroceptors, proprioceptors, and interoceptors
    Input is relayed toward the head, but is processed along the way
    Sensory Integration
  4. 1. Receptors level - the sensor receptors
    2. Circut level- ascending pathways
    3. Perceptual level- neuronal circuits in the cerebral cortex
    Levels of neural integration in sensory systems
  5. Receptors have specificity for stimulus energy
    Stimulus must be applied in a receptive field
    Transduction occurs
    stimulus energy is converted into a graded potential called a receptor potential
    Processing at the Receptor Level
  6. stimulus
    Receptor/generator potential in afferent neuron
    action potential at first node of Ranvier
    In general sense receptors, the receptor potential and generator potential are the same thing
  7. Stimulus
    receptor potential in receptor cell
    release of neurontransmitter
    generator potential in first-order sensory neuron
    action potentials (if threshold is reached)
    • Processing at the Receptor Level
    • in special sense organs
  8. Adaptation is a change in sensitivity in the presence of a constant stimulus

    Receptor membranes become less responsive

    Receptor potentials decline in frequency or stop
    Phasic (fast-adapting) receptors signal the begining or end of a stimulus
    eg: receptors for pressure, touch and smell

    Tonic receptors adapt slowly or not at all
    eg: nociceptors and most proprioceptors
    Adaptation of Sensory Receptors
  9. 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)
    Processing at the Circuit Level
  10. -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 stimulus (studied by the 2point
    discrimination test)
    Processing at the Perceptual Level
  11. Feature abstraction : identification of more complex aspects and several stimulus properties
    Quality discrimination : the ability to identify submodalities of a sensation (eg: sweet or sour taste)
    Pattern recognition : recognition o familliar or significant patterns in stimuli (eg: the melody in a piece of music)
    Main Aspects of Sensory Perception
  12. Specialised 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
    Sensory Receptors
  13. Based on:
    Stimulus type
    Location
    Structural complexity
    Classification of Receptors
  14. mechanoreceptors : respond to touch, pressure, vibration, stretch, and itch
    Thermoreceptors: sensitive to changes in temperature
    Photoreceptors: respond to light energy (re: retina)
    Chemoreceptors: respond to chemicals (smell, taste, changes in blood chemistry)
    Nociceptors: sensitive to pain-causing stimuli (eg: extreme heat or cold, excessive pressure, inflammatory chemicals)
    Classifacation by stimulus type
  15. 1. Exteroceptors: resond to stimuli arising outside the body. Receptors in the skin for touch, pressure, pain, an temperature...most special sense organs
    2. Interceptors (viseroceptors): respond to stimuli arising in internal viscera and blood vessels. Sensitive to chemical changes, tissue stretch, and temperature changes.
    3. Proprioceptors: Respond to stetch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles. Inform the brain of one's movements.
    Classification by location
  16. 1. Complex receptors (special sense organs) : Vision, hearing, equilibrium, smell, and taste
    2. Simple receptors for general sense: tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense. Unencapsulated (free) or encapsulated dendritic endings.
    Classification by structural complexity
  17. Thermoreceptors
    cold receptors (10-40*C); in superficial dermis
    heat receptors (32-48*C); in deeper dermis
    Nociceptors
    respond to: pinching
    chemicals from damaged tissue
    temperatures outside the range of
    thermoreceptors
    capsaicin
    Light touch receptors
    tactile (Merkel) discs
    hair folicle receptors
  18. 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 kinestethitec receptors - stretch in articular
    capsules
    Encapsulated Dendritic Endings

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