The Third & Lateral Ventricles

The Third & Lateral Ventricles, and Limbic System

The Third Ventricle -median cleft between two thalami -cavity of diencephalon, except for area in front of interventricular foramen which is derived from median part of telencephalon -cavity is lined by ependyma.

Communications: -anterosuperiorly, on each side, communicates with lateral ventricle through interventricular foramen(or foramen of Monro). This foramen is bounded anteriorly by column of fornix & posteriorly by tubercle of thalamus -posteroinferiorly, in median plane communicates with 4th ventricle through cerebral aqueduct. Recesses: -are the extention of cavity & are: *suprapineal *pineal *infundibular *optic

Boundaries -Anterior Wall: Lamina terminalis, anterior commissure and anterior column of fornix.-the two columns of fornix diverge, pass downwards & backwards,& sink into lateral wall of 3rd ventricle to reach mamillary body. -Posterior Wall: Pineal body, posterior commissure(in the lower lamina of pineal stalk) & cerebral aqueduct. -Roof: formed by ependyma lining under surface of tela choroidea of 3rd ventricle. -At jx. of roof with anterior & lateral walls, there are interventricular foramina.

-Floor: formed by hypothalamic structures: Optic chiasm, tubercinerium, infundibulum, mamillary bodies, posterior perforated substance & tegmentum of midbrain. At jx. of floor with anterior wall, there is optic recess.

-Lateral Wall:-formed by medial surface of thalamus (posterosuperior part), hypothalamus(anteroinferior part) & hypothalmic sulcus which separates thalamus from hypothalmus extends from interventricular foramen to cerebral aqueduct. -interthalamic adhesion connects medial surface of two thalami -habenular stria lies at jx. Of roof and lateral vetricle & join posteriorly at habenular commissure -columns of fornix run downward & backward to reach mamillary bodies.-lies beneath lateral wall of ventricle.

The Lateral Ventricle -two irregular cavities situated one in each cerebral hemisphere -each lateral ventricle communicates with third ventricle through interventricular foramina. -each lateral ventricle consists of * central part * 3 horns( ant., post., & inf.)

Central Part: -extends from interventricular foramen in front of to the splenium of corpus callosum behind. -Boundaries * Roof: formed by undersurface of corpus callosum * Floor is formed (from lateral to medial side) by body of caudate nucleus, stria terminals, thalamostriate vein and lateral portion of upper surface of thalamus. *Medial wall: is formed by septum pellucidum & body of fornix.

Choroid Fissure: -line along which choroid plexus invaginates into central ventricle is called choroid fissure -c shaped slit in medial wall of cerebral hemisphere starts at interventricular foramen(above & in front) & passes around thalamus & cerebral peduncle to uncus. -convex margin is bounded by fornix( body and crus), fimbria & hippocampus. -concave margin is bounded by thalamus(sup. & post. surface), tail of caudate nucleus & stria terminalis -in central part of lateral ventricle, choroid fissure is narrow gap between edge of fornix & upper surface of thalamus. Gap invaginate by choroid plexus.

Anterior horn: -part of lateral ventricle which lies in front of interventricular foramen & extends into frontal lobe. -boundaries: *anterior: posterior surface of genu & rostrum of corpus callosum *roof: anterior part of trunk of corpus callosum *floor: head of caudate nucleus and upper surface of rostrum of corpus callosum *medial: septum pellucidum & column of fornix.

Posterior Horn: -part of lateral ventricle which lies behind splenium of corpus callosum & extends into occipital lobe -Boundaries: *floor & medial wall: bulb of posterior horn raised by forceps major & calcar avis raise by anterior part of calcarine sulcus *roof & lateral wall: Tapetum

Inferior horn: -largest horn of lateral ventricle begins a jx of central part with posterior horn of lateral ventricle & extends into temporal lobe. -Boundaries *Roof(and lateral wall): chiefly tapetum, tail of caudate nucleus, stria terminalis & amygdaloid body *Floor: collateral eminence raise by collateral sulcus & hippcampus medially

Introduction:

Limbic System

-parts of human brain controlling behavioral patterns such as aggression, rage, emotion, housing, mating etc constitute limbic system Constituent Parts: -olfactory nerves, bulb tract, striae & trigone -anterior perforated substance -pyriform lobe, consisting of uncus, anterior part of parahippocampal gyrus. -posterior part of parahippocampal & cingulate gyrus. -hippocampal formation, including hippocampus, dentate gyrus, indusium griseum & longitudinal striae -amygdaloid nuclei -septal region -fornix, stria terminalis, stria habenularis, anterior commissure

Functions: -controls food habits necessary for survival -controls sex behaviour necessary for survival of species -controls emotional behaviour expressed in form of joy & sorrow, fear, fight & friendship, & liking & disliking

Following are terms with their components related to limbic system: -Rhinencephalon: comprises of *olfactory mucosa *olfactory bulb *olfactory tract-3 roots 1)medial root ends in subcallosal or parolfactory gyrus 2)intermediate root ends in anterior perforated substance & diagonal band of Broca. 3)lateral olfactory root ends in pyriform lobe(uncus, anterior part of parahippocampal gyrus, cortex region of limen insulae, dorsomedial part of amygdaloid nucleus.

-limbic lobe: subcallosal gyrus, cingulate gyrus & parahippocampal gyrus. -hippocampal formation: hippocampus, dentate gyrus, part of parahippocampal gyrus -limbic system: limbic lobe, hippocampal formation, amygdaloid nucleus, hypothlamus, anterior nucleus of thalamus -connecting pathways: alveus,fimbria, fornix, mamillothalamic tract, stria terminalis -papez circuit: hippocampal formation, fornix, mamillary body, cingulate gyrus.

Clinical Anatomy -Hippocampal-amygdala complex is related to memory of recent events. Lesion of this complex are associated with a loss of memory for recent events only. General intelligence remains unaltered. -Destructions of olfactory nerves result n loss of sense of smell(anosmia). Tumor such as meningioma in the floor of the anterior cranial fossa may press the olfactory bulb or tract. -Lesion that affects uncus & amygdaloid body may cause uncinate fits characterised by imaginary disagreeable odour, by movement of lips & tongue, and often by dreamy state.