5. Rhinencephalon & the limbic system Flashcards
(45 cards)
2 functional divisions of the rhinencephalon
- Olfactory (paleopallium)
- Limbic (archipallium)
Components of the paleopallium - olfactory rhinencephalon (image slide 8-9)
- OLFACTORY BULB (source of olfactory neurons)
- OLFACTORY PEDUNCLE (has 2 olfactory tracts)
- PIRIFORM LOBE (with its lateral olfactory gyrus + parahippocampal gyrus)
Components of the limbic system (archipallium) - limbic rhinencephalon
TELENcephalon
* Hippocampus
* Cingulate gyrus
* Septal area
DIencephalon
* Hypothalamus
* Thalamus
* Epithalamus
MESencephalon
* Intercrural nucleus
* Reticular formation
3 histological divisions of the Rhinencephalon
- Molecular layer (I)
- Pyramidal layer (V)
- Multiform (VI)
3 roles of the olfactory rhinencephalon
- Localize FOOD
- Reflex secretion of DIGESTIVE ENZYMES
- Detect DANGER
What means ‘Macro- vs microsmatic’ species
- MACROsmatic: highly developed olfactory rhinencephalon -> dogs, bears, opossums
- MICROsmatic: poorly developed olfactory rhinencephalon -> primates
OLFACTORY NEURONS
1. Cell type?
2. Location (cell body + dendrites) ?
(slide 10)
- Bipolar
- Olfactory epithelium`
N.b. dendritic bulbs have little CILIA that project in the mucosal end of the epithelium in the nasal cavity
OLFACTORY NEURON - mechanism of signal trasduction by odorants?
- Odorant binds GPCR
- Activates adenylate cyclase
- Converts ATP -> cAMP
- cAMP activates Na channel
- Depolarization -> AP
2 rules broken by olfactory neurons
- Regenerate (replaced after 1 month)
- cell body elsewhere than DRG or CN ganglion
Are olfactory neurons myelinated?
No
In the olfactory bulb, olfactory neurons synapse with which cell types? (slide 10)
Brush and mitral cells (in the glomeruli of olfactory bulb)
Role of the olfactory peduncle
Contains axons (of the brush and mitral cells) connecting olfactory bulb with piriform lobe + limbic system. Axons are grouped into 2 olfactory tracts (lateral and medial)
Two targets of the LATERAL olfactory tract (slide 16)
- to olfactory TUBERCLE (nucleus between lateral and medial tracts) -> to PIRIFORM LOBE
- to LIMBIC SYSTEM (amygdala, entorhinal cortex, parahippocampal gyrus, hippocampus)
Two targets of the MEDIAL olfactory tract (slide 16)
- to CONTRALATERAL OLFACTORY BULB via rostral commissure
- to LIMBIC SYSTEM (septal nuclei -> medial forebrain bundle-> hypothalamus or reticular formation -> pS nuclei of CNVII, IX, X -> stimulate salivation + gastric secretions)
3 neurons of the olfactory pathways
- Olfactory neuron
- Olfactory bulb
- Variable depending on tract (lateral vs medial)
Describe the olfactory pathway
- OLFACTORY NEURON in olfactory epithelium (neuron 1)
- Joins other olfactory axons to form OLFACTORY NERVE (CNI)
- crosses cribriform plate
- Synapse with brush and mitral cells of the OLFACTORY BULB (neuron 2) just on top of cribriform plate
- Axons project caudally to form the OLFACTORY TRACTS of the olfactory peduncle
SUMMARY:
- Olfactory epithelium
- Olfactory neuron (CNI)
- Olfactory bulb
- Olfactory tracts (peduncle)
- Lateral tract = to olfactory tubercle -> piriform lobe OR limbic system
- Medial tract = to contralateral olfactory bulb OR limbic system
Do olfactory pathways have a thalamic relay?
No (thalamus evolved after)
Term for loss of smell
Anosmia
Effect of a lesion to
1. one olfactory bulb
2. two olfactory bulbs
3. Limbic sytem
- Unilateral anosmia
- Complete anosmia
- No effect on smell (but effect on emotional responses)
Most common causes of anosmia
- Severe rhinitis
- Head trauma
- Distemper
- Metronidazole
What are the constituents of the two cortical rings at the diencephalon-telencephalon junction (slide 23)
INNER RING:
- Amygdala
- Hippocampus
OUTER RING
- Cingulate gyrus
- Septal area
AMYGDALOID BODY
- Location
Rostral portion of piriform lobe
AMYGDALOID BODY
- Targets
- Septal area
- Hypothalamus
- Periaqueductal gray (mesencephalon)
via 2 projection pathways:
- Stria terminalis
- Diagonal band
AMYGDALOID BODY
- Function
Autonomic, endocrine, somatic responses associated with EMOTIONS
E.g. Respiration, circulation, dilation of the iris, gastric motility, micturition, piloerection, and the somatic expressions of fear, rage and aggression.
