Limbic System Flashcards
what does the limbic system do?
-Brings together components of the cerebral hemispheres and the diencephalon
-The limbic system is concerned with memory and with visceral and motor responses involved in defensive and reproductive behaviours
describe the limbic lobe
-Ring of grey matter on the medial aspect of the each hemisphere
–Parahippocampal and cingulate gyri
–Septal area
What does the limbic system include?
-Limbic lobe
–Hippocampus
–Dentate gyrus
–Amygdaloid body
–Hypothalamus
–Anterior thalamus
how does the hippocampus develop? and what does it come to occupy?
-by a process of continuing the expansion of the medial edge of the temporal lobe
-comes to occupy the floor of the temporal horn of the lateral ventricle
-In the mature brain the parahippocampal gyrus on the external surface is continuous with the concealed hippocampus
What is the alveus of the hippocampus
-layer of white matter on the ventricular surface
–Forms the fimbria
–Continues to the crux of the fornix
describe the surface of the dentate gyrus of the hippocampus
-surface is toothed
describe the subiculum of the hippocampus
Transition from 3 layered hippocampus to the six layered parahippocampus
what are the 3 main areas of the hippocampus?
-CA1 (cornu ammonis)
-CA1 is adjacent to the subiculum
-CA2
-CA3
-CA3 is near the dentate gyrus
What are the 3 layers of the hippocampal cortex?
-pyramidal cell layer (stratum pyamidale)
-molecular layer
-polymorphic layer (stratum oriens)
describe the pyramidal layer of the hippocampus
-Large pyramidal neurons
-Principle cells of the hippocampus
-Dendrites extend into the molecular layer
-Axons traverse the alveus and fimbria
-Branches are called the schaffer collaterals pass through the polymorphic layer
-Synapse with dendrites of other pyramidal cells in the molecular layer
describe the molecular layer of the hippocampus
-Interacting dendrites and axons
-Located in the centre of the hippocampus surrounding the hippocampal sulcus
describe the polymorphic layer of the hippocampus
-Similar to layer 6 of neocortex
-Located beneath the alveus and contains axons, dendrites and interneurons
what are the 3 layers of the dentate gyrus
-granule cell layer
-mossy fibres
-hilus
Describe the granule cell layer of the dentate gyrus
-Small neurons
-principle cells of the dentate gyrus
-Region of adult neurogenesis
describe the mossy fibres of the dentate gyrus
-Efferent fibres of the dentate gyrus
-Many branches that synapse with the principle cells in CA3 and CA2
describe the hilus layer of the dentate gyrus
-Contains the axons of the granule cells and interneurons
what are the main afferent connections of the hippocampus
-Cerebral cortex
-Septal area
-Contralateral hippocampus
-Various brainstem nuclei
describe the cortical afferent connections of the hippocampus
-Largest contingent of fibres is from the entorhinal cortex
-Follow two routes to the hippocampus
describe the perforant path
-From entorhinal cortex through the subiculum across the hippocampal sulcus to the dentate gyrus
describe the alvear path
-Traverses the subcortical white matter to end in the hippocampus
Describe the entorhinal cortex
-Part of the primary olfactory area
-Also receives association fibres from the neocortex of the temporal lobe
-Which in turn communicates with various sensory regions of neocortex
-Through these connections via the perforant and alvear paths the hippocampal formation is informed of all sensory information as well as higher brain functions
describe the connections of the contralateral hippocampus
-commissural fibres cross the midline at the hippocampal commissure
describe the septal area afferents
-Septal and basal forebrain cholinergic nuclei via the fimbria-fornix (cholinergic and GABAergic)
describe the afferent connections from brainstem to hippocampus
-Ventral tegmental area (dopamine)
-Locus coeruleus (noradrenalin)
-Raphe nuclei (serotonin)
describe the efferent connections of the hippocampus
-Connections through which the hippocampal formation receives information from the entorhinal area and neocortex are paralleled by reciprocal connections
-Descending projections to diencephalon and brainstem via the fimbria-fornix
describe the fornix
-Contains around 1 million myelinated axons
-Most from the subiculum rest from hippocampus or afferents to the hippocampal formation
-Efferent fibres first traverse the alveus on the way to the fimbria
-Fimbria continues to the crus of the fornix
-The crus curves around the thalamus and joins to form the body of the fornix
-Above the third ventricle the body of the fornix separates into the columns
-Columns innervate the septal area anterior hypothalamus substantia innominata, lateral dorsal thalamus and the mammillary bodies
what are the afferents to the circuit of papez
-Neocortex
-Thalamus
-Septal area
-Reticular formation:
–Raphe nuclei
–Ventral tegmental area
–Catacholamine nuclei
what are the efferents from the circuit of papez
-Neocortex
-Reticular formation:
– Raphe nuclei
– Ventral tegmental area
– Catacholamine nuclei
-Brainstem/spinal cord:
– Solitary nucleus
– Dorsal nucleus of the vagal nerve
– Autonomic nuclei of the spinal cord
what is the circuit of papez?
going downwards is the circuit
-Entorhinal cortex area of the parahippocampal gyrus
-VIA Perforant and alvear pathway
-Hippocampal formation
-VIA Fimbria-fornix
-Mammilary body
-VIA Mammilothalamic fasciculus
- Anterior thalamic nuclei
-VIA Internal capsule
-Cingulate gyrus
-VIA Cingulum
-Entorhinal cortex
what is the circuit of papez for?
Ring of interconnected nuclei involved in emotion and emotional expression
describe the amygdaloid body
-Several nuclei situated between the anterior end of the temporal horn of the lateral ventricle and the ventral surface of the lentiform nucleus
-Corticomedial group:
–Dorsomedial division of the amygdaloid body, blends in with the cortex of the uncus
–Afferent fibres come from the olfactory bulb
- Ventrolateral division:
– Basolateral
– Central: - No input from olfactory bulb
- Connect with the corticomedial group and entorhinal cortex
- Included in the limbic system
what are the reciprocal connections with cortex from basolateral amygdala
-Frontal
–Temporal
–Cingulate gyrus
what are the subcortical connections of basolateral amygdala
– Thalamus – intralaminar nuclei
– Catecholamine nuclei
– Raphe nuclei – serotonin
– Parabrachial nuclei – substance P
– Ventral tegmental area - dopamine
– Basal forebrain nuclei – acetylcholine
what are the afferents of central nuclei of amygdala
-Receives afferents from the corticomedial and basolateral nuclei
what are the reciprocal connections with cortex of central nuclei of amygdala
– Prefrontal
– Temporal
– Anterior cingulate gyrus
what are the efferent connections of central nuclei of amygdala
-Septal area, preoptic area, anterior hypothalamus
– Via the stria terminalis
- Vagus nerve and the solitary nucleus
– Via the medial forebrain bundle - Nucleus accumbens and the dorsomedial nucleus of the thalamus
–Via the ventral amygdalofugal pathway
describe the habenular nuclei connections
-Habenular nuclei
–Via the stria medullaris thalami
-Habenula innervates the interpeduncular nucleus
–Via the habenulointerpeduncular tract
-Habenular nuclei also receive afferents from globus pallidus providing a pathway by which the
neocortex can influence autonomic function
What are the functions of the amygdaloid body?
-Central and basolateral nuclei are chiefly responsible for the behavioural and emotional functions of the limbic system
-Emotion – activities of the brain evoked by incentives for survival
-strong affective reactions such as:
–Fear and anger
–Sexual behaviour
-Electrical stimulation of the amygdala:
–Increased heart rate and respiration
–Suppression of salivation
–Pupillary dilation
–Changes in facial expression
-Therefore, the amygdala may give rise to the automatic and somatic accompaniments of fear and anxiety
