Download 16. Limbic system2010-10-01 05:141.9 MB

Limbic system
-The word limbic means the structure
which lies on the medial rim of the
brain between the cerebral cortex and
the hypothalamus.
- The cingulate gyrus and
parahippocampal gyrus are in
continuity with one another around the
splenium of the corpus callosum
-The cingulate gyrus projects to the parahippocampal gyrus via the fibers
of the cingulum which are association
fibers connecting frontal ; parietal ;
parahippocampal gyrus and the
adjacent temporal gyri.
- The principal structures of the limbic
system are linked by a series of looped
connections ( The Papez circuit )
that project into the hypothalamus.
It includes the subcalosal , cingulate, and parahippocampal gyri, the hipocampal
formation, amygdaloid nucleus, the mammilary bodies and the anterior thalamic
nucleus.
The alveus, fimbria, fornex, mammilothalamic tract and stria teminalis form the
connecting
pathway.
conceive
Planned behaviour
Conveyed
refined
Information can reach supramodal status and meaning
-The powerful input to the limbic system is from the neocortical association
areas.
It appears important to:- Intellectual; judgmental; predictive faculties and the planning ( regulation behavior ).
- Memory, emotional aspects of behaviour and stereognosis ( size; form andtexture ) an appreciation of the body image and perceptuospatial function and drive .
- The storage of previous sensory experiences. Recall objects seen or music
- Entry of information to the limbic
system is either directly to amygdala
or indirectly to hippocampal
formation , via the entorhinal area .
- The limbic system , via the
hpothalamus and its connections
with the outflow of the autonomic
nervous system and its control of
the endocrine system ( pituitary
gland ) is able to influence emotional
behavior . Like reactions to fear ;
anger ; sexual behavior .
- It is able to influence motor
responses through projections to
nucleus accumbens , which forms a
part of the basal ganglia.
amygdaloid
Entorhinal area ( E A ) is the cranial extension
of the parahippocampal gyrus
Hippocampal Formation
- It consists of the hippocampus , the dentate gyrus and part of the
parahippocampal gyrus .
- The hippocampus is formed by an infolding of the inferomedial part of the
temporal lobe into the lateral ventricle.
- The dentate gyrus lies between the parahippocampal gyrus and the
hippocampus. Anteriorly, it continues into the uncus .
- The hipocampus is concerned with converting recent memory to long
term memory ( permits a link to previous experience ).
- The hippocampal formation receives afferents from the inferior temporal cortex
via the entorhinal area .
- It receives fibers from the contralateral entorhinal area and hippocampus via the
fornix and hipoocampal commissure which consists of transverse fibers linking
the posterior columns of the fornix on each side.
- The efferent fibers which converge on the ventricular surface of the
hippocampus are called fimbria.
They pass posteriorly then
superiorly to become continuous
with the crus of the fornix which
curves forward beneath the
splenium of corpus callosum.
- The fornix is the principal efferent pathway from the
hippocampus. It is C- shaped
fascicle of fibers that links the
hippocampus with the mammillary
body of the hypothalamus.
- The 2 crura unite in the middle line
to form the body which divides into
2 columns . These curve downwards
forming the anterior border of the
interventricular foramen then enter
the hypothalamus. Most fibers
terminate in the mammillary body .
- The mammillary body
projects to A. nuclear group
of the thalamus via the
mammillothalamic tract and
to the brain stem via the
mammillotegmental tract .
- The A. nuclei of the
thalamus have major
connections with the
cingulate gyrus .
Amygdala
- It lies near the anterior temporal pole, between the inferior horn of the lateral ventricle and the lentiform nucleus.
- It appears to provide an affective connotation to experience and social stimuli. - It receives afferents from the inferior temporal association cortex ; the olfactory
tract and the septum.
- It receives afferent catecholamine and serotonin-containing projections from
the brain stem in the medial forebrain bundle.
- The principal efferent ,project into the stria terminalis which runs in the
wall of the lateral ventricle following the curvature of the caudate nucleus,
to terminate in the hypothalamus.
- The ventral amygdalofugal path consists of a diffuse array of fibers
passing inferior to the lentiform nucleus through the A. perforating
substance to reach the hypothalamus).
Septum
- It lies beneath the rostral part of the corpus callosum.
- It interconnects with the amygdala. - It projects to the hypothalamus via the medial forebrain bundle .- It connects to the monoaminergic nuclei in the brain stem. It dose so via fibers that project to the habenular nuclei (epithalamus) of the diencephalon and
constitute the stria medullaris thalami .
The habenular nuclei project to the interpeduncular nuclei which project
to the brain stem as well as the hypothalamus.
Limbic lobe disorder
- Alcohol abuse, with deficiency of thiamine in diet , lead to capillary
haemorrhages in the limbic system .The patient falls into confusion and coma
( Wernicke’s encephalopathy)
- If partial recovery occur , there is failure to remember previous experience
( Retrograde amnesia ) . Or to learn new facts ( Anterograde amnesia –This state
is called Korsakoff’s psychosis .
- A similar amnesic syndrome occurs when bilateral, surgical temporal lobectomy
including the hippocampal formations .
- Temporal lobe lesion near the amygdala and hippocampi can lead to complex
experiences of smell , mood , and memory .
- Surgical ablation of the amygdala has eliminated uncontrollable rage reaction in
some psychotic patients .