Anatomy-Olfatory & Limbic Flashcards
What path is taken by the neurons that convey sense of smell?
1) Primary olfactory neuron -> Secondary mitral cell -> Lateral olfactory stria (goes to temporal lobe) or Medial olfactory stria (becomes the anterior white commissure)
Where do neurons projecting to the lateral olfactory stria project to?
Amygdala + Olfactory cortex (piriform cortex and entorhinal cortex) -> Dorsal medial (DM) thalamic nucleus -> Orbitofrontal cortex
Why do you sometimes lose your sense of smell (anosmia) in viral infections? What other conditions might be occurring if someone says food doesn’t fast the same anymore?
The virus kills the olfactory neurons. You can also lose olfactory neurons early on in neurodegenerative diseases (note the reduced cortical and amygdala response in the patients with Parkinson’s seen below)
A patient presents to your clinic complaining of anosia. He is 27 years old but still looks and talks like a little boy. MRI reveals small olfactory bulbs. What is causing his condition?
He has Kallmann Syndrome. This is from failure of LHRH neuroblasts to enter the olfactory bulb or hypothalamus, resulting in decreased sense of smell and lack of LH or FSH, causing delayed puberty.
What is the shopping list of components ascribed to the limbic system?
Limbic lobe: 1)subcallosal, 2)cingulate, 3)isthmus of cingulate & 4)parahippocampal gyrus. Subcortical: amygadala, 6) septal nuclei, 7) basal forebrain. 8) Anterior thalamus. 9)Mammillary bodies.
What structure in the limbic system is the crossroads between intellectual and emotional responses, involved in chronic pain syndromes, empathy and has reduced activity in schizophrenia?
Cingulate cortex. Note that this area is larger in females.
What are the three parts of the hippocampal formation?
1)Dentate gyrus 2)Subiculum 3) Hippocampal formation
How many layers are in the hippocampal formation?
1) Granule cells 2) Polymorphic layer 3) Molecular layer
How is declarative memory created?
Info is received in association cortex -> Organized in the entorhinal cortex -> processed in hippocampus (dentate-> proper-> subiculum-> fimbria) -> fornix -> mammary bodies -> septal nuclei -> anterior nucleus of thalamus -> and stored in the association cortex.
How is non-declarative memory created?
Connections between the cerebellum, basal ganglia and motor cortex are formed in motor learning.
How do memories form that we just cannot forget?
Every time you have to re-remember soothing it gets reinforced with new associations.
What symptoms would a patient have if you removed the entorhinal cortex in a patient?
Memory associated with the frontal cortex will be unaffected (working memory, nondeclarative memory). Formulation of new declarative memory would be impaired.
What region of the brain is primarily atrophied in Alzheimer’s disease?
Entorhinal cortex.
What is Papez circuit?
Cingulate cortex -> 1)CINGULUM -> hippocampus -> 2)FORNIX -> mammillary body -> 3)MAMMILLOTHALAMIC TRACT -> anterior nucleus of thalamus -> 4)INTERNAL CAPSULE -> cingulate cortex
A 44 year old man has anterograde amnesia, confabulations (holes in memory that are filled by false statements), hallucinations and lack of insight.
He has Korsakoff’s syndrome, a result of thiamine deficiency from alcoholism. This causes damage to the mammillary bodies and the thalamus (note dorsal medial nucleus damage in the thalamus) that impairs memory function.
What region of the brain is involved in pleasurable experiences that also results in impaired learning if it is lesioned?
Septal nuclei
Urbach-Wiethe Syndrome
Bilateral calcification of the amygdala that causes an inability to read negative emotions in others. They tend to have less fear of danger.
What is the function of this structure of the brain?
Note that it connects the caudate and the putamen, this is the nucleus accumbens. It is involved in pleasure, reward and addiction. Note the lit up nucleus accumbens seen below with cocaine addiction.
What cells are lost in Alzheimer’s disease that contributes to decreases in cholinergic neurons?
This is the basal forebrain. The cells indicated are the nucleus basalis of Meynert in the substantia innominata. These cells are involved in production of ACh.
