(Lesson-8)

• We can recognize three classes of

  environmental stimuli:

  1.)Mechanical forces – stimulate mechanoreceptors

  2) Chemicals – stimulate chemoreceptors

  3) Electromagnetic Energy – stimulate a variety of receptors, including photoreceptors
• ➢ Exteroceptors – are receptors that sense stimuli that arise in the external environment
• Interoceptors – sense stimuli that arise from within the body. These internal receptors

  detect stimuli related to muscle length and tension, limb position, pain, blood

  chemistry, blood volume and pressure, and body temperature.
• Sensory receptor cells

  • typically specialized to detect a single type of stimulus
  • work via mechanisms that are broadly similar to those used by cells to detect chemical signals
  • various stimuli types convert them into changes in membrane potential
• Classes of Environmental Stimuli

  Mechanical Forces

  Chemicals

  Electromagnetic Energy
• Mechanical Forces - stimulates mechanoreceptors
• Electromagnetic Energy - Stimulates a variety of receptor including photoreceptor
• Chemicals - stimulate chemoreceptors
• Four-Step Process of Information to CNS

  • Stimulus
  • Transduction
  • Transmission
  • interpretation
• Stimulus - physical stimulus impinges/affects on a sensory neuron or accessory structure
• Transduction - the stimulus energy is used to produce electrochemical nerve impulses in the dendrites of the sensory neuron
• Transmission - the axon of the sensory neuron conduct action potential energy afferent pathway to the CNS
• Interpretiation - the brain creates a sensory perception from electrochemical event produced by afferent stimulation
• Example of Mechanical Force Environmental Stimuli

  • Pressure
  • Gravity
  • Inertia
  • Sound
  • Touch
  • Vibration
• Example of Chemical Environment Stimuli

  • Taste
  • Smell
  • Humidity
• Example of Electromagnetic Energy Environmental Stimuli

  • Light
  • Heat
  • Electric
  • Magnetism
• Exteroceptor Sensory Transduction

  
  

  Stimulus - Taste

  Receptor - Taste Bud Cells

  Location - Mouth, Skin of Fish

  Structure - Epithelial Cells with Microvilli
• Exteroceptor Sensory Transduction

  
  

  Stimulus - Smell

  Receptor - Olfactory Neuron

  Location - Nasal Passage

  Structure - Ciliated Neuron
• Exteroceptor Sensory Transduction

  
  

  Stimulus - Vision

  Receptor - Rod & Cones Cells

  Location - Retina of the Eye

  Structure - Array of photosensitive pigments
• Interoreceptor Sensory Transduction

  
  

  Stimulus - Temperature

  Receptor - Hot & Cold Receptors

  Location - Skin, Hypothalamus

  Structure - Free Nerve Ending
• Interoreceptor Sensory Transduction

  
  

  Stimulus - Pain

  Receptor - Nociceptor

  Location - Throughout the Body

  Structure - Free Nerve Ending
• Interoreceptor Sensory Transduction

  
  

  Stimulus - Blood Pressure

  Receptor - Baroreceptor

  Location - Arterial Branches

  Structure - Nerve Ending over thin part of Arterial Wall
• Sensory Transduction

  Sensory cells respond to stimuli because they possess stimulus-gated ion channels in their membranes.
• A depolarization that occurs in a sensory receptor upon stimulation is referred to as a receptor potential.
• Cutaneous receptors – receptors of the skin that respond to stimuli at the

  border between the external and internal environments. Respond to heat, cold, pain, touch, and pressure
• Thermoreceptors – naked dendritic endings of sensory neurons that are

  sensitive to changes in temperature: cold & warm
• Nociceptors – the receptors that transmit impulses that are perceived by the brain as pain (stimulus that causes or is about to cause tissue damage)
• Mechanoreceptors – contain sensory cells with ion channels that are sensitive to a mechanical force applied to the membrane.
• Proprioceptors – sensory receptors that provide information about the relative position or movement of the animal’s body parts.
• Blood Pressure - is monitored at two

  main sites in the body. One is the

  carotid sinus, an enlargement of

  the left and right internal carotid

  arteries, which supply blood to the

  brain. The other is the aortic arch,

  the portion of the aorta very close to

  its emergence from the heart.
• Baroreceptors – highly branched

  network of afferent neurons at the

  walls of the blood vessels which

  detect tension in the walls.
• Chemoreceptors – sensory cells that contain membrane proteins that can bind to particular chemicals in the extracellular fluid.
• Taste buds—collections of

  chemosensitive epithelial cells

  associated with afferent

  neurons—mediate the sense of

  taste in vertebrates
• four kinds of taste buds

  salty,

  sweet,

  sour,

  bitter,

  and umami
• Cupula – gelatinous membrane
• Statocyst – sensory structure in which most invertebrates orient themselves; consists of ciliated hair cells with the

  cilia embedded in a gelatinous membrane containing crystals of calcium carbonate (statoliths).