senses

Properties and Types of Sensory Receptors

  • Receptors: Structures specialized to detect stimuli; can be bare nerve endings or complex organs.
  • Info Types from Receptors:
    • Modality
    • Location
    • Intensity
    • Duration
  • Classifications:
    • By modality: thermoreceptors, photoreceptors, nociceptors, chemoreceptors, mechanoreceptors.
    • By origin: exteroceptors (external), interoceptors (internal), proprioceptors (body position).
    • By distribution: general senses (widely distributed) vs. special senses (complex organs in the head).

General Senses

  • Types of Somatosensory Receptors:
    • Unencapsulated: free nerve endings, tactile discs, and hair receptors.
    • Encapsulated: tactile corpuscles, end bulbs, bulbous corpuscles, lamellar corpuscles.
  • Projection Pathways: Signals travel via three neurons: first-order (to spinal cord/brain), second-order (decussate in CNS), third-order (to cortex).
  • Pain: Types include nociceptive (from tissue injury) and neuropathic (from nerve injury).
    • Fast pain (A-delta fibers), Slow pain (C fibers).
    • Referred Pain: Pain perceived at a location other than its origin.

Chemical Senses

  • Gustation (Taste):
    • Detected by taste buds, primarily on tongue.
    • Types: fungiform, foliate, vallate.
    • Pathways via cranial nerves—facial, glossopharyngeal, vagus.
  • Olfaction (Smell):
    • Detected by olfactory cells in the nasal cavity.
    • Pathways lead to olfactory bulb and primary olfactory cortex.

Hearing and Equilibrium

  • Hearing: Conduction of sound waves to the inner ear.
  • Anatomy: Outer ear (auricle, canal), middle ear (tympanic membrane, ossicles), inner ear (cochlea, vestibular apparatus).
  • Equilibrium: Detected by structures in the inner ear, responding to head orientation and motion.

Vision

  • Anatomy of the Eye:
    • Layers: fibrous outer (sclera, cornea), vascular middle (choroid, ciliary body, iris), inner (retina).
    • Optical Components: cornea, aqueous humor, lens.
  • Visual Process: Light is focused on the retina, causing a photochemical reaction.
  • Retina Components: Photoreceptor cells (rods/cones), bipolar cells, ganglion cells.
  • Visual Pathways: Processing in primary visual cortex, with dorsal (where) and ventral (what) pathways for interpretation.