Fifty Flashcards
What does the limbic lobe consist of? What does the limbic system consist of? What is its function?
The term limbic means a border and the limbic lobe consists essentially of the cingulate
gyrus and its anterior extension, the septal area, bordering the corpus callosum and the
parahippocampal gyrus bordering the rostral brainstem.
The term limbic system is an arbitrary and controversial term that includes numerous and
variable cortical and subcortical structures related to functions such as memory,
emotions, and reward. Two key structures in the limbic system are the hippocampus and
the amygdala (amygdaloid nucleus).
What does the hippocampus look like? Where is the located? What are its 3 parts? What is the most medial part of the parahippocampal gyrus?
The hippocampus resembles a sea horse about two inches in length deep to the posterior
part of the parahippocampal gyrus. It is divided into three parts: 1) the dentate gyrus,
2) the hippocampus proper, and 3) the subiculum, which is continuous with the
entorhinal area, the most medial part of the parahippocampal gyrus.
What is the entorhinal cortex and what is its function? What is the function of the papez circuit? From where does it arise? What are the steps of it?
Information of ongoing events from cortical sensory association areas converge in the entorhinal cortex which provides the chief input to the hippocampus.
From the hippocampus arises Papez circuit, a reverberating circuit that somehow triggers the consolidation of memory and learning.
Hippocampus=fornix=mamillary nuclei=mammilothalamic tract=anterior thalamic nuclei=cingulate gyrus=cingulum=entorhinal area
What is the hippocampus highly vulnerable to? What is it often involved with? What do bilateral lesions of the hippocampi or entorhinal areas result in? What is it? What do bilateral lesions of the mammilary bodies and/or medial parts of the thalamus result in? How might this occur? What are the two functions of the entorhinal area? Where does it project to? What are frequently the earliest changes in alzheimers? Abnormalities where might lead to epilepsy?
The hippocampus is highly vulnerable to ischemia and is often involved in Alzheimer’s disease and epilepsy. Bilateral lesions of the hippocampi or the entorhinal
areas (papez circuit) result in anterograde amnesia, a condition in which short term or working memory and long term or declarative memory are normal, but the ability to form new memories and learning is lost.
Bilateral lesions of the mamillary bodies and/or the anterior thalamic nuclei, medial thalamus, mammilothalamic tract, result in anterograde amnesia sometimes accompanied by confabulations. This is seen in Korsakoff’s syndrome which may occur in chronic alcoholics that develop a thiamin deficiency. Other parts of the brain may also become involved.
The entorhinal area is especially important because it not only serves as the chief input to the hippocampus but also serves as the chief output of the hippocampus by projecting to the parahippocampal cortex and, in turn, to widespread cortical association areas.
Abnormalities in the entorhinal area are frequently the earliest changes in Alzheimer’s disease. In addition, abnormalities in the entorhinal area or the hippocampus may result in epilepsy.
Where is the amygdala located? What are the 3 parts?
The amygdala or amygdaloid nucleus is deep to the anterior part of the parahippocampal gyrus in the region of the uncus.
Medial, Lateral, Central
Explain the pathway of olfaction. What projections result in appropriate responses to pleasant aromas or to unpleaseant odors?
Its medial part that includes the uncus is phylogenetically the oldest part of the amygdala and receives mainly olfactory input. Receptors in the olfactory mucosa are bipolar neurons whose axons form about 20 bundles of olfactory nerves that pierce the cribriform plate of the ethmoid bone and synapse in the overlying olfactory bulb. From the olfactory bulb impulses travel in the olfactory tract and then the lateral olfactory stria to the vicinity of the uncus and medial amygdala (primary olfactory cortex).
Projections from the medial amygdala to the hypothalamus elicit appropriate responses to pleasant aromas, e.g., appetite, salivation, or to unpleasant odors, e.g., nausea and/or vomiting.
What information does the lateral amygdala receive? From where? Describe the complete pathway involved.
The lateral amygdala receives information of past experiences from widespread cortical association areas that converge in the entorhinal area before entering the amygdala (FEAR).
Information from the lateral amygdala (basolateral) projects to the hypothalamus which then elicits the appropriate emotional responses via its connections with autonomic and somatic effector sites in the brainstem and spinal cord.
Describe other projections of the amygdala and further pathways of these projections. What is their function?
The amygdala also projects to the medial dorsal thalamic nucleus which in turn projects to the prefrontal cortex, especially the orbitofrontal cortex and the anterior
part of the cingulate gyrus (medial prefrontal) where the awareness of emotions reside.
What are anxiety disorders such as panic attacks and PTSD associated with? What do bilateral lesions of the amygdalae result in? Explain. What is temporal lobe epilepsy typically associated with?
Anxiety disorders such as panic attacks and post-traumatic stress disorder seem to be associated with activity in the amygdala and its circuitry.
Bilateral lesions of the amygdalae result in the Klüver-Bucy Syndrome which includes a profound loss of fear, a severe lack of emotional responsiveness, and an inability to recognize fearful or angry facial expressions.
Temporal lobe epilepsy is typically associated with an aura of a foul odor or a frightening sensation followed by a brief loss of consciousness during which there is a deja vu experience as well as tongue and lip movements.
Where is the accumbens nucleus located? Describe the pathway it is involved in. Input/output. Describe the input/output/pathway of the septal nuclei.
The accumbens nucleus is part of the ventral striatum and is located between the head of the caudate nucleus and the putamen in the vicinity of the anterior commissure. It is closely related to the septal nuclei. The accumbens is part of the “limbic loop” of the basal ganglia and as such receives input from the prefrontal cortex and projects to the ventral pallidum, which, in turn, projects to the prefrontal cortex via the medial dorsal thalamic nucleus. The accumbens nucleus also receives input from the amygdala.
The septal nuclei, which receive input chiefly from the amygdala, project to the midbrain reticular formation via paths through the hypothalamus and epithalamus, thus forming routes to reach brainstem effector sites.
What are the accumbens and septal nuclei associated with? Which projections play an important role in these phenomena?
The accumbens and septal nuclei are associated with reward mechanisms and pleasure.
Electrical stimulation in lower animals and man results in extreme gratification and evidence suggests that these structures are related to the euphoria associated with the use of psychostimulant drugs. Dopaminergic projections to these nuclei from the ventral tegmental area and serotonergic projections from the raphe nuclei play important roles in these phenomena.
Which areas of the cerebral cortex are strongly associated with limbic functions? What is their function?
Areas of the cerebral cortex strongly associated with limbic functions are the orbitofrontal cortex and the cingulate gyrus. The orbitofrontal cortex is associated with
social behavior which is seriously impaired following injuries such as the case of Pheneas Gage. The anterior part of the cingulate gyrus is an inhibitory control center
that elicits caution or second thoughts before taking possibly inappropriate actions.
