C6 - Organ of olfaction, rhinencephalon, limbic system

Question 1

Which terms should be included in rhinencephalon?

Answer 1

• Rhinencephalon:
  
  • Lateral rhinal sulcus
  • Rostral comissure
  • Septal region (septum)
  • Lobus piriformis
    
    • Amugdaloid nucleus (amygdala)
  • Hippocampus
    
    • Fimbra
    • Fornx
  • Cortex:
    
    • Paleocortex
      
      • Septum
      • Lobus piriformis
    • Archicortex
      
      • Hippocampus
• Olfactory pathway:
  
  • Olfactory nerves
  • Bulbus olfactorius
    
    • Pedunculus olfactorius
  • Tractus olfactorius lateralis (to lobus piriformis & hippocampus)
  • Tractus olfactorius medialis (to septal region)
  • Tractus olfactorius intermedium (to rostral commissure)

Question 2

Which terms should be included in limbic system?

Answer 2

• Outer cortical rim:
  
  • ​Septal region
  • Cingulate gyrus
  • Parahippocampal gyrus
  • Lobus piriformis
• Deep telencephalic structures:
  
  • ​Amygdaloid nucleus (amygdala)
  • Accumbens nucleus
  • Hippocampus
    
    • Fimbra
    • Fornix
• Diencephalic structures:
  
  • ​Habenular nucleus
    
    • Stria habenularis
  • Thalamus (rostral thalamus)
  • Hypothalamus
  • Mamillary nucleus (body)
• Mesencephalic structures:
  
  • ​Interpeduncular nucleus
  • Midbrain reticular formation
• Pons structures:
  
  • ​Ventral tegmental nucleus
  • Locus ceruleus

Question 3

Organ of olfaction

Answer 3

• Location: in the nose
• Consists of a large area of olfactory mucosa in animals with a well developed sense of smell

Olfactory pathway:

• ​The pathway begins with primary afferent neurons that are the olfactory receptor cells
• Cell bodies of the olfactory neurons are located in the olfactory epithelium of mucosa covering ethmoturbinates (ethmoconchae) in the nasal cavity
• Axons of these receptor cells (neurons) collect into bundles that pass through the cribriform plate of the ethmoid bone as olfactory nerves
  
  • The nerves enter the bulbus olfactorius
• In the bulbus olfactorius, axons of olfactory nerves synapse in glomeruli (spherical ramifications) formed by dendrites of mitral cells (projection neurons)
• Axons of mitral cells form three olfactory tracts:
  
  • ​Tractus olfactorius lateralis:
    
    • ​Goes to lobus piriformis and hippocamus
  • ​Tractus olfactorius intermedia:
    
    • ​Deep tract
    • COveys axost to bulbus olfactorius via the rostral commissura (commissre of the rhinencephalon)
  • ​Tractus olfactorius medialis:
    
    • ​Coveys fibers to septal region → limbic system

Question 4

Rhinencephalon

Answer 4

• Also called the small brain or olfactory brain

Olfactory pathway

• The olfactory pathway begins with special afferent neurons in the olfactory mucosa
• Bundels of neuros constitute the n. olfactorius (I) and passes through the cribiform plate of os temporale in the olfactory bulb
• Bulbus olfactorius forms the most rostral part of the rhinencephalon
  
  • ​Location: fossa ethmoidalis
• Continues caudally to pedunculus olfactorius which bifucates into:
  
  • Tractus olfactorius lateralis
  • Tractus olfactoriusm medialis
• The tractus olfactorius medialis et lateralis borders trigonum olfactorium
• Olfactory area = trigonum olfactorium + substantia perforata rostralis
• Larger tractus olfactorius lateralis continues caudally to join the lobus piriformis
  
  • ​Medially, it is continued with hippocampus
  • Detatches fibers to amygdala

Question 5

Limbic system

Answer 5

• A collection of brain structures involved in emotional behavior
• Consists of:
  
  • Cortical components​
    
    • ​Forms ring at medial surface of cerebral hemisphere:
      
      • Cingulate gyri
      • Piriform lobe
      • Hippocampus
  • Subcortical components
    
    • ​Includes components of:
      
      • Diencephalon:
        
        • ​Habenula
        • Hypothalamus
        • Thalamus
      • Mesencephalon:
        
        • ​Interpeduncular nuclei
        • Tegmental nuclei
      • Amygdala body
• It receives olfactory input from the lobus piriformis which triggers emotions such as fear, aggression and apparent pleasure. It also efffects thirst, hunger and sexual behavior
• Closely related to formatio reticularis (interconnected nuclei of brainstem)
• Septum telencephali (pellucidum)​
  
  • ​Thin septum between fornix and corpus callosum
  • Forms part of medial wall of the lateral ventricle