Limbic System Flashcards
Components of limbic system
. Hippocampal formation . Amygdala . Septal nuclei . Cingulate cortex . Entorhinal cortex . Perihinal cortex . Parahippocampal cortex
Hippocampus location
. Temporal lobe of each cerebral cortex
. Med. to inf. Horn of lat. ventricle
Structures and processes w/in hippocampus
. Subiculum
. Hippocampus proper
. Dentate gyrus
. Hippocampus proper and senate gyrus form 2 interlocking Cs
Hippocampus cortex
. 3 layers instead of 6 (paleocortex)
. Superficial molecular layer
. Deep polymorphic layer
. Structures are inside-out cortex so the molecular layer is on he side and the polymorphic layer is on the outside
. Middle layer: pyramidal cell layer in hippocampus, granule layer in dentate gyrus
CA3
. Area of hippocampus proper that is append by dentate gyrus
Alveus
. Polymorphic layer of hippocampus
. Equivalent to white matter of neocortex
Subiculum
, transition layer from hippocampus to the parahippocampal gyrus (6 layered cortex)
. Changes gradually from 3 to 6 layers
A major flow of info through the hippocampus comes from the ___
. Entorhinal cortex
Functions of hippocampus
. Lying down new memories
. Neural activity can modify synaptic strength in certain areas of hippocampus
. Modified synaptic strength (long-term potentiation) may be storage mechanism for memory
Reasoning behind hippocampus. Helping with memory formation
. Bilateral lesions of hippocampus cause impairment of recent memory w/ only mild behavioral changes
. Memory for remote events is unaffected ASD well as general intelligence, but person can’t learn new facts
. Anterograde amnesia occurs
. Korsakoff’s syndrome destroys mammillary bodies and have issues forming new memories
Fornix
. Major structures into and out of hippocampus
. Contains efferent and afferent fibers
Fornix pathway
. Begins as alveus (myelinated aff/efferents)
. Fibers travel post. And aggregate med. to form fimbria of fornix
. Fimbria thickness as it moves post. And splits off from hippocampus forming crura of each hippocampus
. 2 crura come together and form hippocampal commissure providing paths for hippocampi to communicate
. After hippocampal commissure the single fiber bundle is the fornix
. Continues as arc to ant. Commissure
Anterior commissure in relation to hippocampus
. Where fornix splits into 3 columns going to different structures
. Some fibers split before ant. Commissure (precommissural fornix)
. Some pass through to contralat. Hippocampus as second path for communication w/ each other
. Some split after the ant. Commissure (Post commissural fornix)
Precommissural fornix
. Split just before the ant. Commissure
. Goes to septal nuclei, ventral striatum, and the cingulate cortex
Postcommissural fornix
. Goes to mammillary bodies of hypothalamus and ant. Nuclei of thalamus
Amygdala
. Integrative center for emotions, emotional behavior, and motivation
. Collection of small nuclei in mediodorsal portion of temporal lobe
. Ant. And dorsal to tip of inf. Horn of lat. ventricle
. Deep to uncus (periamygdaloid cortex), ant. To hippocampal formation
. Pathways w/ afferent and efferent fibers
. Receives input from all senses and visceral inputs
Visceral inputs to amygdala come from ___
. Hypothalamus
. Septal area
. Orbital cortex
. Parabranchial nucleus
Auditory, visual and somatosensory info comes from ___
Temporal and ant. Cingulate cortices
Major output pathways of amygdala
. Ant. Olfactory nucleus . Ant. Perforated substance . Piriform cortex . Orbitofrontal cortex . Ant. Cingulate cortex . Hypothalamus . Septal nucleus . Ventral striatum
Projections from ventral striatum is important in ____
. Links in a basal ganglia important for Stimulus-response assoc. learning
Ventral amygdalofugal pathway
. Connects hypothalamus and septal nucleus
. Amygdala’s major connection is to hypothalamus and septal nucleus through stria terminalis
. Important bc it is link where motivation and drive can influence responses
. Link where responses are learned and where associative learning takes place
Stria terminalis
. Efferents to Septum and hypothalamus
. Similar to fornix of hippocampus
. Connects only to subcortical structures
. 2 amygdala can communicate w/ each other through this or the ant. Commissure
Amygdala functions
. Intense emotion
Urbach-Wiethe disease
. Causes lesions of the amygdala from Ca deposits
. If occurs early in life patients can not discriminate emotion in facial expressions but their ability to identify faces remains
Amygdala lesion affect on emotion
. Flat affect, placid
Septal area
. Brain region that includes both cortical and subcortical nuclei
. Septal nuclei lie rostral to ant. Commissure and preoptic area near the base of the septum pellucidum
. Functions as pleasure center
. Stimulate provides primary reinforcement for drive related to food or sex
. Lesions result in alterations in sexual or foraging behavior
Afferents to septal nuclei
. From hippocampal formation via the fornix (precommissural fibers)
. From amygdala via stria terminalis
Efferents from septal nuclei
. To the lat. hypothalamus and midbrain tegmentum via med. forebrain bundle (MFB)
. To hippocampus via fornix
Prefrontal cortex
. Assoc. cortex of frontal lone rostral to motor cortices (areas 9-12)
. Connected to limbic system and assoc. cortices via reciprocal connections to dorsomed. Thalamus nucleus, amygdala, hippocampal formation, brainstem nuclei
. Function: determine affective reactions to present situations not he basis of past experienced
. Judgement and foresight
Cingulate gyrus
.prominent gyrus on medial surface of cerebral hemisphere
. Receive inputs from prefrontal cortex and projects to the hippocampal formation via cingulum bundle
. Heavily connected w/ thalamus (ant. Nuclei) which is connected to hippocampal formation via fornix and hypothalamus via mamillothalamic tract
Cingulate gyrus functions
. Ant. Cingulate responds to physical pain
. Causes alterations in respiration and circulation (dec.), altered gut stuff (dec.), and pupillary dilation
. Causes inhibition of ongoing movements during pain stimulus
. Effects mediated through connections w/ hippocampal formation, hypothalamus and amygdala
Anterior nucleus of thalamus
. Receives inputs from hypothalamus via mammilothalamic tract and from the hippocampus via fornix
. Projects to cingulate gyrus
Dorsomedial nucleus of thalamus
. Receives amygdaloid inputs and inputs from prefrontal cortex
. Projects back to prefrontal cortex
Substantia innominata
. Basal forebrain structure
. Contains basal nucleus of Meynert
. Scattered groups of large cholinergic neurons
. Projects throughout neocortex, mostly prefrontal cortex
. Provides link btw limbic system and neocortex
. Shows marked cel loss in Alzheimer’s
Nucleus accumbens
. Area where caudate and putamen are continuous ventrally
. Special area functionally; highly connected w/ limbic system
. Has modulators role in regulating motivationally based motor behaviors
. Acts ass primary brain interface btw motivational state and motor behavior
. Par of brain circuit translates motivation into action
. Part of mesocorticolimbic dopaminergic system
. Plays role in mediating additions to drugs (acute reinforcing effects and motivational aspects fo drug withdrawal)
Paper circuit
. One of the major pathways of limbic system
. Involved in cortical control of learning and memory, emotion and social behavior
. Plays role in storing memory
General function of hypothalamus
. Influence on ANS
. Integrate autonomic and neuroendocrine system
. Higher nervous center for control of lower autonomic centers in brainstem and spinal cord
Suprachiasmatic hypothalamus function
. Sets circadian rhythm
Supraoptic/paraventricular hypothalamus
. Oxytocin and ADH synthesis/release
What part of hypothalamus has parasympathetic activity?
Anterior and medial hypothalamus
. Area inc. vagal and sacral autonomic activity
. Pupils constrict, dec. HR, inc. gut motility
Sympathetic activity is localized in what part fo hypothalamus?
. Lateral and posterior hypothalamus
. Activates thoracolumbar outflow
. Pupils dilate, inc. HR, bp, respiration, dec. gut motility
Thermoregulators in hypothalamus
. Temp control at 37 C w/ body temp lowest during sleep
. Neurons controlling this located in ant. Hypothalamus-preoptic region
. Inc. in core body temp activates anterior/preoptic regions of hypothalamus
. Dec. in core temp activates neurons in post. Region of hypothalamus
Changes that will promote heat loss
. Sweating
. Cutaneous vasodilation
. Behavior (turning on fan, removing clothes)
Changes that prevent/dec. heat production
. Dec. mm. Tone and activity
. Dec. secretion of thyroid hormone and E
. Dec. appetite
Lesions of anterior hypothalamus
May result in hyperthermia in hot environment or states of inc. metabolic activity
. 41 degrees: convulsions occur
. 43 degrees: death
Changes that prevent/dec. heat loss
. Cutaneous vasoconstriction
. Behavioral changes
Changes that promote heat production
. Shivering and inc. muscle tone
. Inc. secretion of thyroid hormone and E
Lesions of posterior hypothalamus
. May result in hypothermia in cold environment
. Core body temp falls and confusion results
. At 28 degrees thermoregulation is lost and will continue to decline until death
Bilateral lesions of posterior hypothalamus
. Result in inability to regulate body temp. In any environment due to destruction of area involved in heat production/conservation and descending fibers from heat-dissipation areas in ant. Hypothalamus
Products of macrophages in response to infections that are considered to be endogenous pyrogens
. IL-1
. IL-6
. TNF-a
Interleukin-1
. Enters brain where BBB is lacking and stimulates neurons in pyrogenic zone in med. preoptic area
. Stimulates glial cels to produce cytokines and prostaglandins
PGE2 during fever
. Inc activity of cold-sensitive neurons and inhibitory warm-sensitive ones
. This inc. temp set point and body temp rises until new set point is reached
. Shivering cessation of sweating and vasoconstriction lead to inc. body temp
. Aspirin and NSAIDS inhibit PGE2 synthesis to slow fevers
Antipyretic area
. Includes septal nuclei
. Become active when body temp rises to limit magnitude of fever
. Neurons are sensitive to ADH
. ADH injections into this area counteract fever
Food intake centers
. 2 centers
. Influences by circulating blood glucose and other emotional cues
. No neural receptors for calories ingested
How is feeling of satiety triggered?
Combo of plasma glucose levels, GI distension, body temp., and levels of peptide hormones
Ventromedial nucleus of hypothalamus
. Satiety center
. Neurons respons to high glucose levels and signal sense of fullness
. CCK is satiety factor released by duodenum. And jejunum in response to high fat
. Stimulation inhibits food intake
Leptin
. Circulation levels proportional to adipose tissue
. Acts on receptor in lat. hypothalamus to counteract effects of neuropeptide y and anandamine (potent feeding sitmulants)
Lesions of ventromedial nucleus of hypothalamus
. Result in hyperphagia
. Compulsive overeating
. Result in obesity
Lateral hypothalamic nucleus
. Feeding center
. Neurons respond to low glucose levels
. Lesions result in impairment or abolishment of desire to eat and can lead to death by starvation
. Amphetamines inhibit food by enhancing NE and dopamine levels in this nucleus
Ghrelin
. Stimulates appetite
. Produced in stomach and upper SI in respose to weight loss
Thirst center
. Ant. And lat. regions of hypothalamus
. Tied to supraoptic/ADH system
. Stimulation causes consumption of large amounts of fluids
. Lesions result in reduction of fluid intake
. Water satiety center is tried to satiety center and are not usually exclusive functions
Hypothalamus in relation to emotions
. Feelings subjectively is only in cerebral cortex
. Emotional reactions and physical expressions of emotion are mediated through hypothalamic-autonomic connections
Preoptic region in relation to sexual activity
. Regulates release of gonadotropin hormones from ant. Lobe of pituitary
. Release is cyclical in females
. Release is topical w/ regular fluctuations in males
. Important in mounting/ male behaviors whereas ventromed. Nucleus does female behaviors like lordosis
. Identical in both sexes until just before birth when testosterone in males makes it larger
What part of brain evokes flight responses?
Lateral part of the anterior hypothalamus
Intense stimulation of ventromedial nucleus evokes ___
Hissing, snarling, baring of teethe and biting response
Stimulation of preoptic area ___
Evokes a pleasure able sensation while stimulating VM produces avoidance reaction
Waking center and sleeping center
. . Anterior hypothalamus/preoptic area
. Promotes sleep through synthesis of prostaglandin PGD2 and an awake center in posterior hypothalamus promotes waking through synthesis of PGE2
. Lesions of sleep center result in prolonged periods of wakefulness
. Lesions of wake center result in hypersomnolence (inclination to sleep all the time)
