5/28- Limbic System Flashcards
(37 cards)
What is the most common type of epilepsy?
Medial temporal lobe seizure
Flowchart outlining fit of limbic system into the rest of the brain?
Input from:
- Cerebral cortex (sensory)
- Reticular formation
Outputs to:
- Cerebral cortex (association and motor)
- Hypothalamus
Basically tells you what’s most important with everything coming into the brain
Where is the limbic system (broadly)?
Top/middle of prefrontal brain
Major limbic system components and their functions (one word/phrase)?
Prefrontal cortex: conscience
Basal forebrain: relay system (like thalamus for rest of nervous system)
Hippocampus: memory center
Amygdala: emotions/fear
Large connections between limbic system components (what they are and what they connect)?
Uncinate fasciculus: medial and temporal lobes
Cingulate fasiculus: temporal and frontal lobes (via cingulate gyrus)
Medial forebrain bundle: many connections to hypothalamus
What is the prefrontal cortex (PFC)- characteristics/job?
Connects to what via what?
- Large relative size in humans compared to other primates/mammals
- Emotional parts: orbitofrontal and ventromedial cortex (dorsolateral is more rational thought)
- “Conscience”- powerful inhibition of lower hypothalamic-mediated aggression (superego)
- Connected via the uncinate fasciculus to medial temporal structures
Ex) Prefrontal lobotomy effects
Ex) Phineas Gage
Why was the prefrontal lobotomy performed? Effects?
- Wide variety of conditions from schizophrenia to chronic pain syndromes
(“Ice-pick lobotomy” also became popular through orbitofrontal cortex)
- Resulted in emotionally-stunted individuals; couldn’t express emotion
(Replaced by anti-psychotic medications)
What happened to Phineas Gage?
- Knocked out his orbitofrontal cortex with a tamping rod through his cheek/eye
- Remained conscious, but significant change in personality
- Became rude, very disinhibited, couldn’t hold a job (not inhibiting lower functions of hypothalamus)
Nuclei in basal forebrain?
- Nucleus accumbens
- Substantia innominata (involves basal nucleus of Meynert)
- Septal area (near septum pallucidum)
- Diagonal band of Broca
More posterior nuclei in basal forebrain?
- Septal area continued
- Stria terminalis and bed nuclei
- Diagonal band of Broca (now separated by anterior commissure)
Septal area connects most to what?
Septal area has many hippocampal connections
Afferent fibers: from hippocampus to medial/lateral septal areas
Efferent fibers: to diagonal band of Broca to hippocampus and back
Other septal area connections?
- To prefrontal cortex
Via medial forebrain bundle:
- To hypothalamus
- To mammillary bodies
- To medial thalamus
Function of septal area?
- Relay station between hippocampus and hypothalamus
- Modulates function of both of these
- Electrical stimulation modulates aggressive behavior and elicits drinking behavior
- Lesions cause “septal rage” (uninhibited lower structures/hypothalamus)
Nucleus accumbens connections?
Afferent: receives large dopaminergic projection from ventrotegmental area (VTA) in the mesolimbic pathway
Efferent:
- Projections back to VTA
- Substantia innominata
- Substantia nigra
Functions of nucleus accumbens?
- Integrates sequencing of motor responses associated with emotion and rewards
- Implicated in addiction (e.g. cocaine induces release of dopamine into this region)
– e.g. mice would hit reward level over food, reproduction, etc…
What is the substantia innominata? Connections?
Aka “perforated substance” b/c many blood vessels
- Relay nucleus form amygdala to lateral hypothalamus
- Also contains Nucleus Basalis of Meynert
- Cholinergic nucleus that projects to widespread areas of cortex and limbic system
Functions of substantia innominata?
- Arousal and memory
(Loss in Alzheimer’s disease and some in Parkinson’s)
Where is the hippocampal formation located?
Temporal lobe
Three divisions of the hippocampal formation?
- Subicular cortex/subiculum
- Hippocampus (CA regions, esp CA3 and CA1)- Archicortex
- Dentate gyrus (mossy fiber cells as opposed to pyramidal)
Two basic pathways in hippocampus
Both enter via entorrhinal cortex:
- Perforant pathway- through subiculum to dentate gyrus (projections back to CA 3 and 1 and back out entorrhinal path)
- Alvear pathway- forms fornix going to other regions of limbic system and cortex
What are the Schaffer collaterals?
Connection between CA3 and CA1 region; underly memory
What process sets memory storage?
Long term potentiation (e.g. CA3 input to CA1 neuron)
- Brief high frequency stimulation results in strong and long term potention of an otherwise weak signal
- Input without tetanus will not receive LTP
Biochemical process at play in long term potentiation (LTP)?
- Strong depolarization removes Mg2+ ion block of the NMDA receptor
- Glutamate binds and allows Ca to enter the post-synaptic neuron
- Ca acts as a 2nd messenger to activate kinases which can potentiate existing AMPA receptors and recruit new AMPA receptors to the synapse
What is the Papez Circuit?
- Efferent projections from hippocampus through fornix to post-commissural fornix down to mammillary bodies
- Mamillary bodies send projections through mammillothalamic tract to anterior nucleus of thalamus
- Ant. nucleus of thalamus sends projections to cingulate gyrus
- Then from cingulate gyrus back through entorrhinal cortex back to hippocampus
Mnemonic: “He Man Ate a Cat”
