Brain Anatomy: Subarachnoid Spaces and Cisterns

Subarachnoid Spaces

• Triangular spaces are found in the sulci between the gyri, where the subarachnoid trabecular tissue is found.
• Subarachnoid cisternae are the wide intervals at the base of the brain.
• The largest of the subarachnoid cisterns is the Cerebellomedullary cistern (Cisterna magna).

Cisterns

• Pontine cistern is also known as Prepontine cistern or Cisterna pontis.
• Superior cistern is also known as Quadrigeminal cistern or Cistern of the great cerebral vein.
• Ambient cisterns are thin, sheet-like extensions of the superior cistern that extend laterally about the midbrain.
• Ambient cisterns connect to the Interpeduncular cistern.
• Interpeduncular cistern is located at the base of the brain, between the two temporal lobes of the brain.

Meninges

• Pia mater joins with the ependyma to form choroid plexuses, which produce cerebrospinal fluid.
• Pia mater attaches to the dura mater by the denticular ligaments through the arachnoid membrane in the spinal cord.

Brain Divisions

• The brain is divided into Forebrain (Prosencephalon), Midbrain (Mesencephalon), and Hindbrain (Rhombencephalon).
• The forebrain is subdivided into Telencephalon (Cerebrum) and Diencephalon.
• The hindbrain is subdivided into Metencephalon (pons and cerebellum) and Myelencephalon (medulla oblongata).
• The clinical divisions of the brain are Cerebrum (telencephalon, diencephalon), Cerebellum, and Brain stem (midbrain, pons, medulla oblongata).

Insula

• The insula lies on the floor of the lateral cerebral fossa.
• The pole of the insula is directed forwards and laterally towards the lateral sulcus.
• The Limen insulae is a circular sulcus that forms the posterior horn of the lateral ventricle.

Lateral Ventricle

• The inferior horn of the lateral ventricle is located in the temporal lobe.
• The components of the inferomedial wall of the inferior horn of the lateral ventricle are Collateral eminence, collateral sulcus, pes hippocampi, fimbria of the hippocampi, and choroid plexus.
• The superolateral wall of the inferior horn of the lateral ventricle is formed by Tapetum, tail of the caudate nucleus, and stria terminalis.
• The collateral trigone is located between the inferior and posterior horn of the lateral ventricle.

Basal Ganglia

• The lentiform nucleus is divided into Putamen (lateral portion) and Globus pallidus (medial portion).
• The head of the caudate nucleus is located anteriorly in the anterior horn of the lateral ventricle, forming its lateral wall.
• The body of the caudate nucleus is located above the thalamus, in the central part of the lateral ventricle.
• The tail of the caudate nucleus is located in the inferior horn of the lateral ventricle.
• The claustrum is located between the external and internal capsule.
• The amygdaloid body is located between the temporal pole of hemisphere and the inferior horn of lateral ventricle.

Corpus Striatum

• The corpus striatum is composed of the Lentiform nucleus and Caudate nucleus.
• The striatum is composed of the Caudate nucleus and Putamen.
• The pallidum is composed of the Globus pallidus.

Cortex

• The operculum is formed by the Temporal, parietal, and frontal lobes.
• The areas in the cortex are Motor area, Sensory area, Auditory area, Motor speech area, and Visual area.
• There are two auditory areas in the cortex: Primary auditory cortex (temporal lobe) and Auditory association cortex (temporal lobe).
• The sensory cortex is located in the Parietal lobe (Postcentral gyrus).
• The motor cortex is located in the Precentral gyrus in the Frontal lobe.

Rhinencephalon

• The Rhinencephalon is the oldest part of grey matter, located underneath the cerebellum.
• The Rhinencephalon is divided into Olfactory lobe (peripheral rhinencephalon) and Limbic lobe (central rhinencephalon).
• The components of the anterior part of the olfactory lobe are Olfactory bulb, olfactory tract, olfactory pyramid, medial and lateral olfactory striae.
• The middle part of the olfactory lobe terminates in the paraolfactory area (subcalosa), paraterminal gyrus, and septum lucidum.
• The intermediate part of the olfactory lobe terminates in the anterior perforated substance.
• The lateral part of the olfactory lobe terminates in the hippocampal gyrus in the uncus, passing through the limen of insula.

Fornix

• The body of the fornix is divided into two columnae fornicis at the beginning of the septum pellucidum.
• The columnae fornicis descend into the Hypothalamus, forming the anterior arch.
• The inferior part of the body of the fornix is divided into Part libera (free part) and Part tecta (hidden part) inside the hypothalamus.
• The fornix ends in the Mamillary body.

Ventricles

• The lateral ventricles are divided into four parts: Central part, Anterior horn, Posterior horn, and Inferior horn.
• The central part is located in the parietal lobe, above the thalamus, and beneath the corpus callosum.
• The anterior horn is located in the frontal lobe, continuous behind the interventricular foramen.
• The posterior horn is located in the occipital lobe.
• The inferior horn is located in the temporal lobe.

Other Structures

• The components of the commisure of telencephalon are Anterior commissura, Corpus callosum, and Fornix commissure.
• The central parts of the corpus callosum are Rostrum, Genu, Body (trunk), and Splenium.
• The lateral parts of the corpus callosum are Radiation (forceps minor and major).
• The origin of the fornix is the Fimbriae of the hippocampus.
• The fornix runs along the inferior margin of the inferior horn of the lateral ventricle.
• The body of the fornix is formed by the Crura fornicis running anteriorly and medially behind the corpus callosum.