Receptors Receptors Sensory receptors specialized cells or

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Receptors
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Receptors

• Sensory receptors specialized cells or cell
  process that monitors conditions in the body or
  the external environment
• Sensory information goes to the CNS and is called
  a SENSATION
• Conscious awareness of sensation is PERCEPTION

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General Senses

• Temperature
• Pain
• Touch
• Pressure
• Vibration
• Proprioception (body position)

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Special Senses

• Smell
• Taste
• Balance
• Hearing
• Vision

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Receptor Sensitivity

• Receptors are sensitive to specific stimuli
• Called receptor specificity
• Simplest receptors are dendrites of sensory
  neurons
• Free nerve endings
• Receptive field
• Larger the field the poorer the ability to
  localize a stimulus

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Sensory Processing

• Sensory information must be sent to the CNS for
  processing
• Arriving information is processed and interpreted
  by the CNS at both conscious and subconscious
  levels

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Sensory Limitations

• We do not have receptors for every possible
  stimulus
• Receptors have characteristic ranges of
  sensitivity
• CNS must interpret the stimulus. Our perception
  of the stimulus is also an interpretation and not
  always a reality

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General Senses

• Receptors for general senses are scattered
  through out the body
• EXTEROCEPTORS external environment
• INTEROCEPTORS conditions inside the body

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Nature of Stimulus

• 1. Nociceptor
• 2. Thermoreceptors
• 3. Mechanoreceptors
• 4. Chemoreceptors

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Nociceptors

• Pain receptors
• Superficial skin, joint capsules, bone, around
  walls of blood vessels
• Free nerve endings, large receptive fields
• Exact location pf painful sensation is often
  difficult to determine
• Three types of nociceptors
• Extremes of temperature
• Mechanical damage
• Dissolved chemicals from damaged cells

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Pain Fast and Slow

• Fast pain(prickling pain) deeps cuts
• Reach CNS very quickly primary sensory cortex
• Receives conscious attention
• Painful sensations stop only after the tissue
  damage has ended
• Slow pain(burning and aching pain) similar
  injuries as fast pain
• Sensation begins later and lasts longer
• Aware of the pain but have only a general idea of
  the area affected

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Thermoreceptors

• Found in the dermis, skeletal muscle, liver, and
  hypothalamus
• Free nerve endings
• Cold receptors are 3-4 times more numerous than
  warm receptors
• Temperature sensations carried along same
  pathways as pain sensation
• Thermoreceptors quickly adapt to stable
  temperature, very active when temperature is
  changing

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Mechanoreceptors

• Sensitive to stretch, compression, twisting.
• Three classes of mechanoreceptors
• Tactile receptors
• Baroreceptors(pressure changes in walls of blood
  vessels, urinary, digestive and reproductive
  systems)
• Proprioceptors(monitor the position of joints and
  muscles)

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Tactile Receptors

• Fine touch and pressure
• Receptors may be free nerve endings or
  encapsulated
• Encapsulated receptor examples are
• Tactile (Meissners) corpuscles for fine touch
• Lamellated (Pacinian) corpuscles for heavy
  pressure

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Encapsulated receptors
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Baroreceptors

• Stretch receptors that monitor changes in
  pressure
• Found in walls of blood vessels, and respiratory,
  digestive, and urinary organs
• Monitor blood pressure, help regulate cardiac
  function and blood flow
• Monitor degree of lung expansion
• Monitor visceral reflexes such as urination

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Baroreceptors
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Proprioceptors

• Monitor position of joints, the tension on
  tendons and ligaments, and the state of muscle
  contraction

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Chemoreceptors

• Specialized neurons that detect changes in the
  concentration of specific chemical or compounds
• Changes in pH or carbon dioxide are monitored

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Chemoreceptors