Limbic System Flashcards
- links a group of functionally related structures that are interposed between the cerebral cortex and the underlying diencephalon
- hippocampal formation, septal area, and amygdala
- prefrontal cortex and cingulate gyrus as components within this system
limbic system
- either directly or indirectly communicate with the hypothalamus or midbrain periaqueductal gray (PAG)
- modulate the functions normally attributed to the hypothalamus and/or midbrain
limbic structures
limbic structures receive inputs from at least two sources
- one or more sensory systems, either directly or indirectly through interneurons in the cerebral cortex
- brainstem monoaminergic fiber system
The hippocampal formation consists of the ___, ___, and __-
hippocampus; dentate gyrus; subicular cortex
The primary cell type within the hippocampus is the ___, which has both basal and apical dendrites
pyramidal cell
extend laterally and slightly in the direction of the ventricular surface
basal dendrites
extend away from the ventricular surface toward the dentate gyrus
apical dendrites
- superficial layer of the hippocampus
- fiber layer adjacent to the inferior horn of the lateral ventricle
alveus
situated adjacent to the inferior horn of the lateral ventricle, which contains axons of pyramidal cells that project out- side the hippocampus as well as hippocampal afferent fibers from the entorhinal cortex
external plexiform layer
contains basal dendrites and basket cells
stratum oriens
contains the pyramidal cells of the hippocampus
pyramidal cell layer
two layers that contain the apical dendrites of the pyramidal cells and hippocampal afferents from the entorhinal cortex
stratum radiatum and stratum lacunosum-moleculare
pyramidal cells of the hippocampus are arranged in a ___
C-shaped fashion
the pyramidal cells situated closest to the subiculum are referred to as the
CA1 field
pyramidal cells located within the hilus of the dentate gyrus
CA4 field
located between the CA1 and CA4 fields
CA2 & CA3 fields
- Collaterals of axons arising from CA3 pyramidal cells project back to the CA1 field
recurrent or schaffer collaterals
CA1 field, the pyramidal cells are highly susceptible to anoxia, especially during periods of temporal lobe epilepsy. This region is referred to as ___
Sommer’s sector
The dentate gyrus can also be thought of as a primitive three-layered cortical structure. It is multilayered, and the principal cell type is the ___
granule cell
axon of the granule cell, called a ___, makes synaptic contact with pyramidal cells in the CA3 region
mossy fiber
passes from the lateral entorhinal cortex into the molecular layer of the hippocampus
lateral perforant pathway
- medial pathway
- enters the alveus of the hippocampus after passing through the white matter adjoining the subiculum
medial perforant pathway
- passes rostral to the anterior commissure and supplies the septal area
- topographically organized in that fibers situated near the anterior pole of the hippocampal formation project to the lateral aspect of the lateral septal nucleus, whereas neurons situated more posteriorly in the hippocampal formation project to progressively more medial aspects of this nucleus
- arises from the hippocampus and subicular cortex
precommissural fornix
- innervates the anterior thalamic nucleus, mammillary bodies, and adjoining regions of the medial hypothalamus
- arises solely from the subicular cortex
postcommissural fornix
enable the hippocampal formation to communicate with widespread regions of neocortex, including areas that receive different modalities of sensory information
subicular and entorhinal cortex
- provides connections between the hippocampus on each side of the brain
- provide the structural basis by which seizures spread from the hippocampus on one side of the brain to the hippocampus on the other side, allowing for the formation of secondary epileptogenic foci on the side of the temporal lobe contralateral to the site where the primary focus is present
commissural component
hippocampal formation plays an important role in the control of ___ behavior
aggression and rage
activation of the part of the hippocampal formation closest to the amygdala facilitates ___, whereas activation of the portion closest to the septal pole ___ this form of aggression
predatory attack behavior; suppresses
- arises from the subiculum near the temporal pole of hippocampus and projects directly to the ventromedial region of the hypothalamus
- terminates in the region between suprachiasmatic and arcuate nuclei, which contain hypophysiotrophic hormones that control anterior pituitary function
medial corticohypothalamic tract
slow wave of 4–7 Hz
theta rhythm
Normally, a rat can learn to enter the correct arm of a Y-maze or the correct series of arms in a more com- plicated maze such as an eight-armed radial maze. Animals sustaining hippocampal lesions consistently fail to approach the correct arm of the maze and consistently make the same or similar kinds of errors
spatial learning (spatial memory)
individual hippocampal cells change their discharge patterns as the animal moves to different parts of the cage or when it is placed in differ- ent arms of a radial maze
cognitive map
- earliest reported disorders
- memory disorder in which the patient displays amnesia (memory loss) of both anterograde and retrograde memory
- patient experiences a great deal of difficulty in recalling events in the recent past and handling and retaining new information as well as remembering those events that took place in the distant past
- associated with the toxic effects of alcohol or from a vitamin B1 (thiamine) deficiency
Korsakoff’s syndrome
memory loss that occurs after hippocampal damage
Anterograde memory
refers to loss of memory that occurs before damage to the hippocampus
retrograde memory loss
pathway linking the hippocampal formation
Papez circuit
- Patients sustaining hippocampal lobectomies display perseveration of response tendencies and further display
- patient displays anterograde amnesia, but retrograde amnesia is less severe
- Such a patient may also have difficulty in reading, in that he is unable to remember a previously read line
short-term memory disorder
- hippocampal mechanism that has been proposed as a model for memory consolidation
- represents a change in synaptic strength as a manifestation of synaptic plasticity. LTP can be produced by stimulating fibers that make excitatory connections with hippocampal pyramidal cells
long-term potentiation (LTP)
- receives sensory afferent fibers from the medial olfactory stria, monoaminergic systems of the brainstem, hippocampal formation, amygdala, and feed- back signals from the lateral hypothalamus
- serves principally as a relay of the hippocampal formation to the hypothalamus
septal area
serve to modulate septal neuronal activity, as do the olfactory inputs
monoaminergic inputs
- The nuclei of the ___ have wide- spread projections that make synaptic connections with other parts of the limbic system
- project to olfactory, prefrontal, and anterior cingulate cortices as well as to the amygdala, mammillary bodies, habenular complex, and mediodorsal thalamic nucleus
diagonal band of Broca
feedback system to the hippocampal formation
septal area
- implicated in the control of functions normally attributable to the hypothalamus, such as aggression, rage, autonomic functions, self-stimulation, and drinking behavior
- lesions of the septal area in rats cause them to be highly irritable, aggressive, easily startled, and very difficult to handle
septal rage
stimulation of the septal area suppresses ___ secretion and adrenal activity in the rat
ACTH
lesions of the septal area facilitate ___ release
ACTH
region that integrates motor and motivational processes associated with the basal ganglia and limbic system, respectively
nucleus accumbens
major source of dopaminergic fibers to the limbic system and neocortex
ventral tegmentum
particular interest with respect to the development of Alzheimer’s disease
basal nucleus of Meynert
- the presence of neurofibrillary tangles
- extracellular deposition of the abnormal amyloid protein beta-amyloid cortex plaques in the cerebral cortex
- cell loss in the basal nucleus and reduced cholinergic content of cortical tissue
alzheimer’s disease
One approach to combating this disorder involves drug therapy. An example of this approach has been the use of the drug ___
Aricept
delay development of some of the symptoms of moderate and severe Alzheimer’s disease
Namenda (memantine)
amygdala contains a cortical mantle called the ___ that provides significant input to the amygdala and is, thus, functionally associated with it
pyriform lobe
includes mainly the cortical, medial, and medial aspect of the basal nuclei that lie within its dorsal and me- dial aspects
corticomedial group
includes the lateral, central, and lateral aspects of the basal nuclei
basolateral group
Communication from the amygdala to the hypothalamus can be achieved by direct or indirect pathways. Direct routes involve the ___ and ___
stria terminalis; ventral amygdalofugal pathway
___ arises mainly from the corticomedial group of nuclei, and a primary projection of these fibers is directed to the rostrocaudal extent of the preopticomedial hypothalamus.
stria terminalis
arises mainly from the basolateral complex of amygdala, passes deep to the pyriform cortex, and supplies primarily the lateral hypothalamus and midbrain PAG
ventral amygdalofugal
hypersexuality, a change in dietary habits, a decrease in anxiety toward fear-producing objects, a tendency to orally explore and contact inedible objects, and visual agnosia
Klüver-Bucy syndrome
stimulation of the ___ has a powerful, facilitating effect on defensive rage behavior but has an equally potent suppression on predatory attack behavior
corticomedial amygdala
stimulation of the ___ has just the opposite effects on these forms of aggressive behavior.
basolateral region of amygdala
Stimulation of the ___ can induce ovulation, whereas transection of the ___ abolishes this response
corticomedial amygdala; stria terminalis
activation of the ___ facilitates growth hormone release, whereas the ___ inhibits growth hormone release
basolateral amygdala; corticomedial amygdala
experimental studies have identified circuits that include the amygdala in mediating conditioned fear responses in rodents to ___
auditory stimuli
difficulties in recognizing stimuli that one would normally characterize as fearful
Urbach-Wiethe disease
- unique in that it receives afferent fibers from all regions of the cerebral cortex
- receives inputs from all brainstem monoaminergic systems and limbic-related structures
prefrontal cortex
The anterior cingulate gyrus receives inputs from the following areas
- the anterior thalamic nucleus
- dopaminergic fibers
- diagonal band of Broca
Efferent fibers of the anterior cingulate gyrus project to the ___ and to the ___
mediodorsal thalamic nucleus; subicular cortex
associated with both emotional and intellectual processes
prefrontal cortex
- developed in 1936 by Egaz Moniz
- controlling human violence and manifestations of psychotic behavior that involved the undercutting of the afferent and efferent connections of the prefrontal cortex
prefrontal lobotomy
lesions of the ___ lead to an increase in feeding behavior, while stimulation of this region inhibits feeding
prefrontal cortex
inhibits respiratory movements, changes blood pressure, inhibits gastric motility, and raises the temperature of the extremities
electrical stimulation
- recorded at the scalp and sometimes from the surface of the brain during epilepsy surgery
- measures potential differences between two active electrodes on the scalp or between a scalp electrode and an inactive electrode, which is usually placed behind the ear
- measures the summation of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials from the scalp
- useful in other disorders, such as coma
EEG
- very slow, 1-Hz to 3-Hz, synchronous waves that occur under conditions of severe trauma to the brain
- occur normally for short periods during sleep
delta rhythm
paroxysmal events in which there is a significant change in the EEG that correlates with a change in behavior and/or consciousness
seizures
condition in which seizures are recurrent
epilepsy
time of the occurrence of the seizure
ictal period
time following the seizure
postictal period
time between seizures
interictal period
- Seizures can be classified into two basic types
partial or focal & generalized
seizure arises from specific regions of the brain and is limited to one hemisphere
partial or focal
seizures arise diffusely through- out the brain, causing a loss of consciousness
generalized
helps to define whether seizures arise from one or more specific areas or whether they develop diffusely
EEG
Partial seizures can be classified as either
simple partial or complex partial seizures
do not cause a change in consciousness, but the patient experiences various sensory and motor symptoms, usually not lasting more than 1 to 2 minutes
Simple partial seizures
- seizure activity begins locally over the cortex, causing either sensory or motor activity directly corresponding to the homunculus of either the sensory or motor cortex
- patient experiences a “march” of sensory or motor activity from muscle to muscle in the same order as the homunculus
Jacksonian March
speech difficulty that is a less severe form of aphasia
dysphasia
- simple partial seizures
- they provide a warning of the spread of the seizure, causing a complex partial seizure
aura
- most common type of seizure
- psychomotor seizures
- impairment or loss of consciousness
- patient may stare and not respond to commands
complex partial seizure
- arise diffusely from the cerebral cortex
- reveal epileptic activity diffusely
generalized seizures
- common type of generalized seizure is the generalized
- “convulsions,” involve a tonic phase or stiffening, followed by a clonic phase in which the extremities contract the agonistic and antagonistic muscles
tonic-clonic seizure
Prolonged seizure activity or the generation of two or more of these seizures in a row without regaining consciousness
status epilepticus
very brief (approximately 3–10 seconds long)
patient is unresponsive, commonly described as “daydreaming”
Absence seizures
very brief and characterized by a rapid muscle jerk accompanied by polyspike and wave complexes, which are also brief
Myoclonic seizures
found mainly in children with neurologic disorders, consist of a very brief complete loss of muscle tone
Atonic seizures,
- patient sits quietly and appears unaware of his surroundings during the time of the seizure (ICTAL PERIOD)
- patient may appear confused and experience auditory, olfactory, vertiginous, or even gustatory hallucinations
partial seizures
The postcommissural fornix arises from the
Subicular cortex
After a neurological examination, a 34-year-old man was diagnosed with temporal lobe epilepsy, the focus of which was estimated to be Sommer’s sector. This region is associated with the
CA1 hippocampal field
A 63-year-old man was transferred from a psychiatric clinic to the local hospital for a neurological examination because he showed signs of a Klüver-Bucy syndrome
Amygdala
placidity, hypersexuality, visual agnosia, oral tendencies, and loss of fear of objects that previously produced fear.
Klüver-Bucy syndrome
A 63-year-old woman was experiencing difficulties in a card-sorting test (as a measure of cognitive function), and failed to accurately perceive the vertical when seated in a tilted chair. A magnetic resonance imaging scan revealed the presence of a lesion in the
Prefrontal cortex
the patient will not vary her strategy for sorting cards even when asked to do so
card-sorting task
patient is placed in a tilted chair in the dark and asked to identify the true vertical, she is unable to do so, although normal individuals have little difficulty in doing so
perceptual task
A 78-year-old man was admitted to a neurological clinic because he was having memory difficulties. The diagnosis was that the patient was experiencing the early stages of Alzheimer’s disease. His disorder most likely involved loss of or damage to neurons in the
Basal nucleus of Meynert
Short-term memory processes, modulation of hypothalamic processes, in particular, emotional and endocrine functions
Hippocampal formation
Temporal lobe epilepsy, short-term memory disorders; aggressive and rage behavior, possible endocrine dysfunctions
Hippocampal formation
Modulates aggression and rage and other functions of the hypothalamus; also serves as a relay of hippocampal formation to hypothalamus
Septal area
Emotional disorders, including rage and aggression, and related functions of hypothalamus
septal area
Fear, regulation of aggression and rage, functions associated with hypothalamus, including feeding, endocrine and autonomic processes
Amygdala
Emotional disorders, e.g., aggression, rage, and loss of fear; disruption of other functions associated with hypothalamus, e.g., endocrine functions and eating disorders; temporal lobe epilepsy
Amygdala
Cognitive, autonomic, and emotional processes, including the control over aggression and rage
Prefrontal cortex
Loss of control over emotional processes, autonomic functions, flat personality, memory and intellectual deficits
Prefrontal cortex
Nucleus accumbens mediates mood states; basal nucleus of Meynert of substantia innominata is cholinergic and is believed to mediate memory functions of cerebral cortex
Basal forebrain: nucleus accumbens, substantia innominata
Dysfunctions of nucleus accumbens may be associated with addictive behavior; damage to basal nucleus of Meynert is associated with Alzheimer’s disease
Basal forebrain: nucleus accumbens, substantia innominata
