5. Rhinencephalon & the limbic system Flashcards
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.
HIPPOCAMPAL FORMATION
- Location
- Deep in the PARAHIPPOCAMPAL GYRUS
- Forms the medial wall of the temporal horn of the lateral ventricle
HIPPOCAMPAL FORMATION
- 3 continuous components (slide 26)
- HIPPOCAMPUS (seahorse shape, connects cingulate gyrus to hypothalamus)
- DENTATE GYRUS
- SUBICULUM
HIPPOCAMPAL FORMATION
- Where is the hippocampus?
- Caudal to piriform lobe
- Dorsal to caudal thalamus (adjacent to LGN)
- Covered by parahippocampal gyrus
HIPPOCAMPAL FORMATION
- What is the fornix? (slide 28)
- Fibers from hippocampus + subiculum, coursing below the corpus callosum.
- Has a fimbria + crus
- 2 cruras meet at the hippocampal commissure
- Most fibers project ventrally to mammillary bodies, some to septum
HIPPOCAMPAL FORMATION
- Functions
- Learning & memory (short term memory)
- Spatial orientation
- Emotions (aggressive behaviors)
CINGULATE GYRUS
- Location
- Dorsal to corpus callosum
- Conuous with septal area (rostrally) and parahippocampal gyrus (caudally)
CINGULATE GYRUS
- What is the cingulum?
- White matter (corona radiata) of the cingulate gyrus
made of longitudinal association fibers
CINGUALTE GYRUS
- Function
- Suppressive effect on visceral functions regulated by hippocampus
- Key role in aggressive behavior
SEPTAL AREA
- 2 constituents
- Location
- Septal nuclei
- Subcallosal area
Ventral to genu of corpus callosum
SEPTAL AREA
- Afferents & efferents
A: medial olfactory tract
E: various limbic system structure
(hippocampus, amygdala, habenular nucleus, hypothalamus)
HABENULAR NUCLEUS
- Location
- Rostral to pineal body (lunettes)
- Dorsal to 3rd ventricle
Part of epithalamus
HABENULAR NUCLEUS
- Afferents & efferents
A: SEPTAL AREA (via habenularis thalamus) - septum des lunettes
E: INTERCRURAL NUCLEUS (via habenulointercrural tract)
ROSTRAL THALAMIC NUCLEUS
- Afferents & efferents
A: MAMMILARY BODY (via mammilothalamic tract)
E: adjacent CINGULATE GYRUS + neopallium
MAMILLARY BODIES
- Location (paired)
- Ventral surface of hypothalamus
- Caudal to infundibulum
MAMMILARY BODIES
- Connections?
- HIPPOCAMPUS (via fornix)
- ROSTRAL THALAMIC NUCLEUS (mamillothalamic tract)
- TEGMENTUM (midbrain) + visceral motor nuclei (medulla) via mamillotegmental tract
- INTERCRURAL nucleus (via mammillary peduncle)
INTERCRURAL NUCLEUS
- Location
- Ventral surface of midbrain
- Between two crus
INTERCRURAL NUCLEUS
- Afferents & efferents
A:
- Habenular nucleus (habenulointercrural tract)
- Mammillary body (mammillary peduncle)
E: Brainstem reticular formation
Rabies virion will cause Negri bodies (cytoplasmic inclusion) especially in which neurons?
Hippocampal neurons
4 components of the PAPEZ CIRCUIT
- Hippocampal formation
- Mammillary body
- Thalamus
- Cingulate gyrus
Role of the PAPEZ CIRCUIT
Regulates emotions and behaviors, via connections with amygdala and septa nuclei
Clinical correlations - slides 37…
