BIOL 2301 LEC 19

• Sensation


  Conscious awareness of incoming sensory information

  
• Sensation can only occur if the sensory input has reached the cerebral cortex

  
• Receptors


  Respond to a stimuli and initiate sensory input to the CNS

  
• Receptors range in complexity
• Stimuli


  Changes in the sensory information that our receptors detect

  
• Transducers


  Change energy from one form to the next
• Receptors


  • Establish and maintain a resting membrane potential across their plasma membrane
  • Contain modality-gated channels in their plasma membranes
• General senses


  • Somatic sensory receptor
  • Visceral sensory receptor

  
• Special senses


  • Gustation
  • Olfaction
  • Audition
  • Vision
  • Equilibrium

  
• Sensory receptors by stimulus origin


  • Exteroceptors
  • Interoceptors
  • Somatic sensory receptors

  
• General sensory receptors by modality


  • Thermoreceptors
  • Chemoreceptors
  • Mechanoreceptors
  • Baroreceptors
  • Osmoreceptors
  • Proprioceptors
  • Nociceptors

  
• Sensory receptors by structure


  • Encapsulated
  • Unencapsulated
  • Sensory cells coupled to neurons
  • Neurons with peripheral processes

  
• Tonic receptors


  Respond continuously to stimuli at a constant rate
• Phasic receptors


  Detect new stimuli or changes in the state of the detected stimulus

  
• Receptive field


  The area through which a stimulus is detected
• Receptor potential


  Graded potential generated when a stimulus meets the threshold to activate the receptor

  
• Adaptation


  Ability of a sensory receptor to become less sensitive in the continued presence of a stimulus

  
• Coding signal intensity


  • Graded potentials reflect duration and magnitude of a stimulus
  • Action potential frequency represents stimulus intensity

  
• Recruitment


  Strong stimuli activate more sensory units
• Lateral inhibition


  Fully stimulated cells inhibit partially stimulated neighboring sensory cells

  
• Tactile receptors


  • Unencapsulated
  • Encapsulated
• Tactile sensation


  • Touch
  • Pressure
  • Vibrations
• Unencapsulated tactile receptors


  • Free nerve endings
  • Root hair plexuses
  • Tactile Discs (Merkel discs)

  
• Free nerve endings & root hair plexus


  • Terminal branches of dendrites
  • Slow to rapidly adapting
  • Polymodal
• Merkel (or tactile) cells


  • Tonic receptors
  • Detect fine touch
  • Distinguish texture and shapes of objects
• Encapsulated tactile receptors


  • Meissner's corpuscles
  • Ruffini corpuscles
  • Krause's corpuscles
  • Pacinian corpuscles
• Meissner's corpuscles


  • Phasic receptors
  • Detect light touch and vibrations
• Ruffini corpuscles


  • Tonic receptors
  • Detect skin distortion and continuous deep pressure
• Krause's corpuscles


  • Detect light pressure and temperature
• Pacinian corpuscles


  • Rapidly adapting
  • Detect deep pressure and high frequency vibration
• Thermoreceptors


  Detect changes in temperature
• Nociceptors


  Subtype of free nerve endings that respond to cellular damage, noxious chemicals, and cellular signals

  
• Pain


  • Fast pain
  • Slow pain
  • Acute pain
  • Chronic pain
  • Visceral pain
• Referred pain


  Perception of sensory nerve signals of the viscera in dermatomes of the skin

  
• Pain pathways


  1. First order neuron

  2. Second order neuron

  3. Thalamus

  4. Insular cortex

  5. Anterior cingulate cortex

  6. Somatosensory cortex
• Pain nerve fibers


  • Aα
  • Aδ
  • C
• Modulation of the pain pathway


  • Pain fibers can produce excitatory or inhibitory influences
  • Descending inhibitory neurons originate in the brain
  • Analgesics modify the perception of pain
  • Anesthetics block the generation and conduction of action potentials
  • Endogenous opiates modulate pain