Olfactory Gustatory and Limbic system | Anatomy2Medicine
Olfactory Gustatory and Limbic system

Olfactory Gustatory and Limbic system

      • mediates the special visceral afferent (SVA) modality of smell via the olfactory nerve (CN I).
      • is the only sensory system that has no precortical relay in the thalamus.
      • projects to the thalamus, hypothalamus, amygdala, and hippocampal formation.
      • Olfactory pathway

 

  • Olfactory receptor cells

 

          • are chemoreceptors.
          • number 25 million on each side.
          • are replaced throughout life (they may regenerate).
          • are found in the nasal mucosa.
          • are first-order neurons in the olfactory pathway.
          • are unmyelinated bipolar neurons whose central processes are CN I.

 

  • have axons that enter the olfactory bulb and synapse in the olfactory glomeruli with mitral and tufted cells.
  • Olfactory bulb

 

          • lies on the cribriform plate of the ethmoid bone and receives the olfactory nerve.

 

  • contains mitral and tufted cells (second-order neurons) that project via the olfactory tract and the lateral olfactory stria to the primary olfactory cortex and the amygdaloid nucleus.
  • Olfactory tract

 

          • contains the anterior olfactory nucleus.
          • gives rise to the medial and lateral olfactory striae.
          • projects to the contralateral olfactory tract via the anterior commissure.

 

  • Lateral olfactory stria

 

          • projects to the primary olfactory cortex and the amygdaloid nucleus.

 

  • Primary olfactory cortex

 

          • overlies the uncus of the parahippocampal gyrus (area 34).
          • receives input from the lateral olfactory stria.
          • consists of prepiriform and periamygdaloid cortices.

 

  • projects to the mediodorsal nucleus of the thalamus via the amygdaloid nucleus to the hypothalamus and via the entorhinal cortex (area 28) to the hippocampal formation.
  • Mediodorsal nucleus of the thalamus

 

          • projects to the orbitofrontal cortex, where the conscious perception of smell takes place.
        • Pathways of the olfactory system : Summary
          • The olfactory nerve enters the olfactory bulb via the cribriform plate

 

  • Mitral and tufted cells of the olfactory bulb project via the lateral olfactory stria to the primary olfactory cortex (prepiriform and periamygdaloid cortices).

 

          • The primary olfactory cortex projects to the hypothalamus, thalamus, amygdaloid nucleus, and entorhinal area
      • Clinical Nueroanatomy
        • Anosmia, the loss of smell
          • occur as a result of a lesion of the olfactory nerve
          • anosmia is ipsilateral.
          • Olfactory nerves may be damaged by
            • fractures of the cribriform plate

 

  • meningitis
  • meningiomas
  • gliomas

 

            • by abscesses of the frontal lobes.

 

  • Olfactory hallucinations may be a consequence of lesions of the para hippocampal uncus.
  • Foster Kennedy syndrome

 

          • results from a meningioma of the olfactory groove

 

  • compresses the olfactory tract and the optic nerve.

 

          • results in ipsilateral anosmia, optic atrophy, and contralateral papilledema.

 

  • Fracture of the cribriform plate of the ethmoid bone may result in anosmia and cerebrospinal rhinorrhea.
  • Gustatory System

 

      • mediates the SVA modality of taste.
      • mediates gustation, which, like smell, is a chemical sense

 

  • Gustatory pathway
  • Taste receptor cells
  • are chemoreceptors.

 

          • are modified epithelial cells, not neurons.
          • are continuously being regenerated.

 

  • are located in the taste buds of the tongue, epiglottis, and palate.

 

          • Are innervated by
            • SVA fibers of the facial nerve(CNVII)
            • the glosso pharyngeal nerve (CNIX)

 

  • vagal nerve (CN X).
  • First-order neurons

 

          • are pseudounipolar ganglion cells in the
            • geniculate ganglion of CN VII,

 

  • petrosal ganglion of CN IX
  • nodose ganglion of CN X.

 

          • project centrally, via the solitary tract, to the solitary nucleus.

 

  • Solitary nucleus

 

          • receives taste input from the tongue and epiglottis.

 

  • projects ipsilaterally via the central tegmental tract to the ventral posteromedial (VPM) nucleus of the thalamus.
  • Parabrachial nucleus of the pons

 

          • receives taste input from the solitary nucleus.
          • projects taste input to the hypothalamus and amygdala.

 

  • Ventral posteromedial nucleus
  • projects to the gustatory cortex of the parietal operculum (area 43) and parainsular cortex.
  • Gustatory cortex of the insular area (area 43)

 

          • projects via the entorhinal cortex (area 28) to the hippocampal formation.

 

  • Taste perception

 

        • Taste buds on the tongue detect:
          • Sweetness at the apex of the tongue
          • Saltiness posterolateral to the apex of the tongue
          • Bitterness on the circumvallate papillae
          • Sourness on the anterior two-thirds of the dorsal surface of the tongue
      • Gustatory pathway : Summary
        • CN VII, CN IX, and CN X transmit taste (SVA) information from the anterior two-thirds of the tongue, the posterior third of the tongue, and the epiglottis to the solitary tract and nucleus
        • from the solitary nucleus via the central tegmental tract to the medial parabrachial nucleus; and to the VPM nucleus of the thalamus, hypothalamus, and amygdaloid complex

 

  • The gustatory cortex is located in the parietal operculum and in the parainsular cortex.

 

      • Ageusia (gustatory anesthesia, or lack of sense of taste)
        • is most commonly caused by heavy smoking.
        • is most frequently associated with
        • peripheral lesions of CN VII
          • Bell palsy
          • disease of the middle ear [chorda tympani]

 

  • CN IX