Special Senses and Thalamus

• Special senses are senses that have a specialized organ associated with them: smell (nose), vision (eye), hearing & balance (ear), taste (tongue)
• Auditory hair cells


  • Specialized cells of the cochlea that detect sounds
• Auditory pathway


  1. Auditory nerves

  2. Cochlear Nucleus

  3. Superior Olivary Nucleus

  4. Inferior Colliculus

  5. Medial Geniculate Nucleus

  6. Primary Auditory Cortex
• Ear


  • Houses the sense receptors for the auditory and vestibular systems
  • Directs sounds waves to the ear drum (tympanic membrane)
  • Anatomy: Outer, middle and inner ear
  • Eustachian tube equalizes pressure in middle ear
• Temporal bone


  • Houses the middle and inner ear
  • Pneumatised (air filled) portion is the mastoid process
  • Mastoid air cells are connected to the tympanic cavity
• Untreated middle ear infections

  Can cause mastoiditis- infection that affects the mastoid bone
• Entry to the central nervous system (CNS)

  1. Cochlea

  2. Auditory Nerve

  3. Cochlear Nucleus (Brainstem)

  4. Superior Olivary Nucleus (Brainstem)

  5. Inferior Colliculus (Brainstem)

  6. Medial Geniculate Nucleus (Thalamus)

  7. Primary Auditory Cortex (Cortex)
• Vestibular system


  • Function: Balance
  • Vestibular hair cells are specialized cells of the Semicircular canals and utricle that detect changes in rotational movements
• Vestibular pathway


  1. Vestibular apparatus

  2. Vestibulocochlear nerve

  3. Vestibular Nuclei

  4. Superior Colliculus

  5. Thalamus (VPM)

  6. Vestibular Cortex
• Vestibular apparatus


  • Crista ampullaris- senses angular acceleration and deceleration
  • Utricle: linear accelerations and head-tilts in horizontal plane
  • Saccule: linear accelerations and head tilts in vertical plane
• Gustatory system


  • Function: Taste
  • Taste receptors are specialized cells of the tongue that detect chemicals
  • Taste senses: sweet, bitter, salty, sour and umami
• Central Gustatory Pathway


  1. Tongue

  2. CN VII/CN IX

  3. Sensory ganglion

  4. Solitary Nucleus

  5. Thalamus (VPM)

  6. Gustatory Cortex
• Summary of sensory systems

  • Olfactory system
  • Visual system
  • Auditory system
  • Vestibular system
  • Gustatory system
• The thalamus is involved in the processing of sensory and motor signals, regulation of consciousness, sleep, and alertness
• Thalamic nuclei


  • Nuclei that transmit sensory information (except olfaction) to cerebral cortices
  • Nuclei that receive impulses from the cerebellum and basal ganglia and interface with motor cortices
  • Nuclei that are associated with limbic areas