Limbic System Flashcards
What is the limbic system?
Includes the subcallosal area, cingulate gyrus, parahippocampal gyrus, unus, hippocampal formation and subcortical structures (hippocampus, amygdala and septal nuclei)
Interposed between the hypothalamus and neocortex
What are the functions of the limbic system?
Connections influence behavior, memory and pain perception
Bridge connecting endocrine, visceral, emotional and voluntary responses to the environment
Hypothalamus + limbic system = what?
Anatomical basis for emotional, drive related and motivated aspects of behavior
What is the hippocampal formation?
Curved sheet of cortex, important for learning and memory, folded into medial surface of temporal lobe
Consists of the subiculum, hippocampus proper (Ammon horn) and dentate gyrus
What is the afferent pathway of the hippocmapal formation?
Dentate gyrus —> CA3 —> CA1 —> subiculum
Describe the efferent pathway of the hippocampal formation
Fibers from cell bodies in the subiculum (CA2) and hippocampus proper (CA1) bundle into the fimbria -> fornix
Terminates in medial mammillary nucleus, ventromedial nucleus and anterior nucleus (dorsal thalamus)
Other projections: septal nuclei, frontal cortex, preoptic and anterior nuclei (hypothalamus) and nucleus accumbens
What is an uncal herniation?
Movement of the uncus (rostromedial edge of the temporal lobe) and possibly parahippocampal gyrus downward over the edge of the tentorium cerebelli (hemorrhagic lesion or tumor in the hemisphere)
Initially compresses the midbrain but if unchecked the damage ma extend into lower brainstem levels
What are the signs of an uncal herniation?
Dilated pupil and abnormal eye movements (CN III involvement) with double vision ipsilateral to the herniation
Weakness of the extremities (CST involvement) opposite to the dilated pupil
As it progresses respiration is affected, abnormal reflexes appear and there is a potentially rapid decline
What is Korsakoff’s syndrome?
Progressive degeneration of the mammillary bodies, hippocampal complex and dorsomedial thalamic nucleus
Impedes the retention of newly acquired memory, pts have severe difficulty learning new tasks and transforming short term into long term memory
Pts will confabulate, combine memories into a synthesized memory of an event that never occurred
Caused by a thiamine deficiency typically associated with chronic alcoholism
What is hippocampal amnesia?
Bilateral lesions of the hippocampi
Profound deficit in anterograde episodic memory (cannot learn new material), combined with spared procedural and working memory
Pts IQ and formal reasoning fairly normal
What is anosmia?
Loss of smell due to a viral infection of the olfactory mucosa, obstruction of the nasal passages, or may be congenital
Lesions due to shearing of CN1 or tumors in the floor of the anterior cranial fossa
Pts typically do not recover their sense of smell
What is phantosmia (olfactory hallucination)?
Distortion in a smell experience or the perception of a smell when no odor is present
Abnormal sequence of neuronal activity
Lesion of anterior/medial temporal lobe
Hippocampus, amygdala, or medial dorsal thalamic nuclei
Describe the structure and function of the amygdala
Structure that lies deep to the uncus just rostral to the hippocampus
Attaches emotional significance to a stimulus
Regulates visceral responses to emotional stimuli including pain
Emotional response to food, pleasant smells stimulate appetite and unpleasant smells suppress it
Involved with fear and reward
What are the afferents to the amygdala?
Sensory information from raphe nuclei, PAG, dorsal motor nucleus of X, nucleus solitarius and locus ceruleus
Input from the dorsomedial nucleus of the thalamus and info fro widespread cortical areas
Describe efferents from the amygdala
Includes the stria terminalis and ventral amygdalofugal pathways
Target hypothalamus, ventral striatum and septal nuceli (ST, VAF)
Cerebral cortex, including the frontal, prefrontal, cingulate and inferior temporal cortical areas
