hippocampus, limbic lobe, limbic system Flashcards
location of hippocampus
borders inferior horns of lateral ventricles
what is the hippocampus
cortical structure
what is the hippocampal formation
group of brain areas consisting of the dentate gyrus cornu ammonis (CA1, CA2, CA2) subiculum presubiculum parasubiculum entorhinal cortex
which 2 structures are 3 layered structures?
cornu ammonis + dentate gyrus
what does the intermediate layer of the 3 layered structure contain?
CA: pyramidal neurons
DG: granule neurons
what is the subiculum
zone of transition between hippocampus proper and parahippocampal cortex
what is the specificity of the subiculum
changes gradually from 3 layers to 6 layers
what is the specificity of the cornu ammonis?
it is divided into 3 regions and it contains pyramidal cells
what is the specificity of the dentate gyrus?
it contains granules
what is the intrinsic circuitry of the hippocampus?
it is a trisynaptic circuit
what is the alveus?
hippocampal equivalant of subcortical white matter
sort of shell
where is the alveus
under ependimal cells lining the ventricle
what does the alveus contain?
afferents + efferents from the hippocampus grouped in bundles called fimbriae of hippocampus at the superior surface of the hippocampus
what is the fornix
it is a prominent output pathway from the hippocampus
bundle of fibers connecting the hippocampus to the mamillary bodies
where does the fornix orgininate from?
originates from the alveus which in turn gives rise to fimbria
what happens when the hippocampus ends near the splenium ?
fimbia become detached bundles called crus or leg of fornix–> they then travel forward at the inferior edge of the septum pellucidum–>towards the monro foramen–> the fornix then turns inferiorly + posteriorly –> diverges into columns of fornix –> pass through hypothalamus towards mamillary bodies
what is the entorhinal cortex?
the principle source of input to the hippocampus
through its connections, hippocampus has access virtually to all types of sensory information
what is the papez circuit?
involved in memory and learning
related to post commissural fornix
What is the case of H.M. by Brenda Milne?
hipocampal formation, amygdala, part of multimodal association area of temporal cortex removed bilaterally
no seizures but anterograde amnesia: no recall of newly aquired info for more than a few minutes
what is the limbic system?
part of the CNS, controls emotional behaviour and emotional drive
what is the organisation of the limbic system ?
organized in 3 levels:
the hypothalamic level
the rhinencephallon level
the cortical level
what is the hypothalamic level?
oldest level repsonsible for self preservation, organises automatic responses in body related to viscera
what is the rhinencephalon level ?
it includes the olphactory system + amygdala
it helps with the comprehensive analysis of odors
where is the limbic system located
on both sides of the thalamus, just underneath the temporal lobe of the cerebrum
where is the limbic system located
on both sides of the thalamus, just underneath the temporal lobe of the cerebrum
where is the amygdala located?
in the temporal lobes
what is the limbic lobe ?
kind of border around the brain stem, most recent from evolutionary perspective
what are the boundaries of the hypothalamus ?
sup: hypothalamic sulcus which separates it from the thalamus
inf: optic chiasm, tuber cinerum and mammillary bodies
ant: lamina terminalis
post: tementum of bidbrain
med: 3rd ventricle
lat: internal capsule
what are the anterior regions of the hypothalamus responsible for ?
control of temp. + parasympathetic system
what are the posterior regions of the hypothalamus responsibl for ?
controling the sympathetic nervous system
what are the boundaries of the hypothalamus ?
sup: hypothalamic sulcus which separates it from the thalamus
inf: optic chiasm, tuber cinerum and mammillary bodies
ant: lamina terminalis
post: tementum of bidbrain
med: 3rd ventricle
lat: internal capsule
Which are the 3 main limbic afferents ?
the septal nuclei
hippocampus
amygdala
in the hippocampus, where do afferents pass?
they pass through the fornix and reach mamillary bodies
in the septal nuceli, where do afferents pass?
through the middle forbrain bundle which pass through the lateral portion of the hypothlamus and extend into the brainstem tegmentum
where are the septal nuclei located ?
adjacent to the septum pellucidum
where and what is the brainstem tegmentum ?
bidirectional bundle which also contains afferents form the brainstem to the hypothalamus and hypothalamic efferents
in the amygdala, where do afferents pass?
through the stria terminalis ( curved fiber bundle which acompanies the caudate nucleus)
under the lenticular nucleus directly reaching the hypothalamus
what are the 8 main hypothalamic functions ?
temp. reg control of autonomic centers control of rage and fear (mood) sexual arousal control of water intake control of food intake sleep wake cycle memory
how is the temperature regulated by the hypothalamus?
preoptic nucleus (anterior) contains thermosensitive neurons –> they respond to changes in core temp. of the body –> activity under influence of peripheral information coming from spinoreticular tract –> elevation of temperature correted by projections from posterior hypothalamus to sympathetic nervous system.
what controls rage and fear in the hypothalamus ?
lateral and ventromedial nuclei (tuberal region)
what parts of the hypothalamus controls water intake?
zona incerta
how does the hypothalamus control the sleep-wake cycle ?
via 2 pathways:
suprachiasmatic nucleus
tuberomammillary nucelus
how does the suprachiasmatic nucleus work?
tiny nucleus embeded in upper surface of optic chiasm receive direct impot from retina–> participates in setting normal cycle through connections with the pineal gland
how does the tuberomammillary nucleus work?
projects to cortex and brainstem–> activated during awake state by peptide OREXIN–> lesions cause hypersomnelance
how does the hypothalamus control memory?
Mammillary bodies belong to Paez circuit involving the hippocampus, fornix, mammillpthalamic tract
how does the hypothalamus control food intake ?
lateral + ventromedial nuclei constitute the appetite set point.
Lateral hypothalamic nuclei host feeding center –> stimulates eating
ventromedial inhibits uge to eat
how does the hypothalamus regulate sexual arousal?
medial part of
how does the hypothalamus regulate sexual arousal?
medial part of preoptic nucelus (anterior) shows high level of androgen receptors (males).
some neurons of ventromedial (tuberal) nucelus show high levels of estroge receptors (females)
where do all sensory afferents form retinal ganglion cells go to ?
suprachiasmatic nucleus
how do hypothalamic outputs largely reciprocate inputs?
same fiber bundles used
what are the 2 main efferent tracts?
mamillothalamic tract
mamillotegmental tract
what is the course of the mammillothalamic tracts?
from mammillary bodies to anterior nucleus of the thalamus
what is the course of the mammillotegmental tract?
branches from mammillothalamic tract + others reach bidbrain reticular formation
how is the hypothalamus directly responsive to physical stimulus?
hypothalamus contains intrinsic sensory neurons
there are direct projections from the cerebral cortex, what do they go through?
medial prefrontal cortex of frontal lobe insula throughmedial forbrain bundle
what is the medial forbrain bundle
fibers runnning longitudinally through lateral hypothalamus –> reach basal forbrain + brainstem tegmentum
what does the medial forbrain bundle do ?
it interconnects the hypothalamus with the basal forbrain + brainstem tegmentum
it conveys aminergic fibers from the brainstem to widespread cortical areas
what does the medial forbrain bundle do ?
it interconnects the hypothalamus with the basal forbrain + brainstem tegmentum
it conveys aminergic fibers from the brainstem to widespread cortical areas
what do the brainstem and the spinal chord do?
they convey visceral + somatic information relevant to the homeostatic role of the hypothalamus
