Neuro 14: Limbic System Flashcards
What are the 3 major olfactory epithelium?
- bipolar olfactory neurons
- sustentacular cells
- basal cells
–> you get progressive loss with age
organisation of olfactory system
- Olfactory neurones project into olfactory bulbs
- which synapse w/ 2nd order neurones (mitral cells)
- Forming an olfactory tract that travels to:
- Lateral + medial olfactory stria going to 2 places:
a) Piriform cortex of frontal lobe
b) Orbitofrontal cortex
o Connections to brainstem promote autonomic responses e.g. salivation when smell good food
Olfactory tract splits into :
- medial + lateral olfactory stria
most olfactory process takes place in the :
most olfactory process takes place in the :
a) piriform cortex
b) orbitofrontal cortex
–> connects to brainstem –> to cause autonomic responses
Define limbic system.
- the limbic system = rim or cortex adjacent to the corpus callous + diencephalon
what is the limbic system responsible for?
a) maintenance of homeostasis
b) agonistic behavior
c) sexual / reproductive behaviors
d) memory
How does the limbic system maintain homeostasis?
by:
- activation of visceral effector mechanisms
- modulation of pituitary hormone release
- initiation of feeding/drinking
- -> mainly hypothalamic function control
What are the 2 key parts of the limbic system?
and where are they found?
- amygdala
- hippocampus
found in the temporal lobe
What is the papez circuit?
- it is a neural circuit for the control of emotional expression
- amygdala + hippocampus = part of papez circuit
- cingulate cortex receives info from neocortex
- which passes it onto hippocampus via the cingulum bundle
- then passes through fornix –> into hypothalamus
- then there is projection to anterior nucleus of thalamus via MTT
- which projects back to cingulate cortex to perceive emotional experience
Where is the main afferent pathway of a hippocampus?
- perforant pathway
Where is the main efferent pathway of a hippocampus?
- fimbria/fornix
What is the function of the hippocampus?
- it is involved in memory + learning
What happens to the hippocampus in alzheimers disease?
- you get severe shrinking of the hippocampus
Where is the hippocampus located in?
- in the temporal lobe
- on the floor of lateral ventricles
the fornix lies immediate below the _____ _______
corpus callous
fibres of the fornix goes forwards –> and ends up in the _______ _____ at the base of the hypothalamus
fibres of the fornix goes forwards –> and ends up in the maxillary bodies at the base of the hypothalamus
note: hipocampus = penis shaped
-
What happens in cortical atrophy?
- there is a loss of neurons
- and ventricles = much larger than they should be
- there is hiding of the sulk
- frontotemporal = damaged more than alzheimer’s
What happens in early alzheimers
- hippocampus + entorhinal cortex = affected
- leads to short term memory problems
What happens in moderate alzheimers
- affects the parietal lobe
- dressing apraxia
What happens in late alzheimer’s
- affects the frontal lobe
- causes loss of executive skills
Where is amygdala located in?
- it is buried in the white matter of anterior temporal lobe
What are the main afferent connections of the amygdala?
- olfactory complex
- septum
- temporal neocortex
- hippocampus
- brainstem
What is the main efferent connections of the amygdala?
- stria terminalis
what is the main function of amygdala
- fear and anxiety
What is the Kluver - Bucy syndrome?
- syndrome due to bilateral lesions of the anterior temporal lobe
What are some symptoms of the Kluver-Bucy syndrome?
- hyperorality
- -> exploring things with mouth
- loss of fear
- visual agnosia
- ->can’t recognize objects
- hypersexuality
in humans: usually due too bilateral contusion of brain
What structures are associated with aggression?
- hypothalamus
- brainstem
- amygdala
( + serotonin )
What are the main afferent connections of the septal nuclei ?
- amygdala
- olfactory tract
- hippocampus
- brainstem
What is the main function of the septum ?
reinforcement + reward
DRUG dependence
mesolimbic pathway
mesolimbic pathway = dopaminergic pathway
- sits in midbrain
projects to cortex, nucleus accumbent + amygdala
via MFB
- dopaminergic neurones in VTN –> projects to nucleus accumbens
- stimulated in most recreational drugs
*VTN = ventral tegmental nucleus
clinical deficit of olfactory system can cause:
anosmia
What is the main part of emotional expression?
hypothalamus
What are the different mechanisms behind alzheimers?
- tau protein –> hyperphosphorylated –> causes tangle
note: recreational drugs
increases DA release in nucleus accumbens
–> stimulate midbrain neurones –> promote DA release / inhibit DA reuptake
overstimulation of mesolimbic pathway
can causes obsessive compulsive behavior
e.g gambling
Piriform cortex is found within the temporal lobe.
Explain the significance of this with regards to epileptic patients.
- Epilepsy = Often focussed in the temporal lobe
- ## so some people get prodromal aura –> smell just before seizure
what is the region of cortical representation of the limbic system?
- Cingulate cortex
What would you seen in a coronal CT head scan of a patient with alzheimer’s
- sulcus widens
- cortical atrophy
- ventricles are seen to be enlarged
