Test: Neuroanatomy - NEET PG MCQ

• Forceps major is the collection of commissural fibers in the splenium part of the corpus callosum, communicates somatosensory information between the two halves of the parietal lobe and the visual cortex at the occipital lobe.
• Uncinate fasciculus connects parts of the limbic system (hippocampus and amygdala in the temporal lobe) with frontal lobe structures such as the orbitofrontal cortex.
• Cingulum fibers project from the cingulate gyrus to the entorhinal cortex, allowing for communication between components of the limbic system.
• Superior longitudinal fasciculus connects the frontal, occipital, parietal, and temporal lobes on the same cerebral hemisphere.

Indusium griseum is a thin layer of gray matter in contact with the dorsal surface of the corpus callosum and continuous laterally with the gray matter of the cingulate gyrus.

This is a sagittal section of brain, the marker showing rostrum part of corpus callosum (a commissural fibers system connecting left and right cerebral hemispheres). The orbital regions of the frontal lobes are connected via the rostral fibers of corpus callosum.

The marked structure is formix, which is the major output (efferent) tract for hippocampus.

• It is identified by its relations: Superiorly-Septum pellucidum connected to corpus callosum; Inferiorly-Third ventricle (in the midline).
• Fornix is an important part of the limbic system. It is a C-shaped, structure, extends from the hippocampus to the mammillary bodies of the hypothalamus and the anterior nuclei of the thalamus.
• Transection of the fornix at the level of its body can lead to memory loss.

Projection fibres project from higher to lower centers (or vice versa) in CNS.

• Collection of axons are categorized on the basis of their course and connection into association fibers, projection fibers, and commissural fibers.
• Association fibers connect cortical regions within the same cerebral hemisphere of the brain e.g., arcuate fasciculus connecting Wernicke's area with Broca's area.
• Projection fibers project from higher to lower centers (or vice versa) in CNS e.g., internal capsule
• Commissural fibers are transverse fibers that interconnect similar regions in the left and right sides of CNS (cerebral hemisphere, brainstem, cerebellum, spinal cord) e.g., corpus callosum.
  

Tapetum (part of corpus callosum) are the axons that connect temporal lobes of the opposite cerebral hemispheres. Arcuate fasciculus has association fibres connecting Wernicke's sensory speech area with Broca's motor speech area.

• Fornix is the major efferent (not afferent) tract for hippocampus.
• Internal capsule has projection (not association) fibres connecting higher brain centres (like cerebrum) with lower centres (like brainstem and spinal cord).
• Details: White matter is constituted by the bundles of myelinated axons, which connect various gray matter areas and carry nerve impulses between neurons.
• Collection of axons are categorized on the basis of their course and connection into association fibres, projection fibers, and commissural fibers.
  • Association fibers connect cortical regions within the same cerebral hemisphere of the brain.
  • Projection fibers project from higher to lower centers (or vice versa) in CNS.
  • Commissural fibers are transverse fibers that interconnect similar regions in the left and right sides of CNS (cerebral hemisphere, brainstem, cerebellum, spinal cord).

Lamina terminalis represents the cephalic end of the primitive neural tube and corresponds with the site of closure of rostral (anterior) neuropore. It lies at the anterior boundary of third ventricle. 

• This clinical case is craniorachischisis, which is the most severe form of dysraphism. It occurs due to total failure of neural tube closure.
• Brain and spinal cord are exposed to the surrounding amniotic fluid, resulting in necrosis, degeneration or angioma-like formations.
• Entire neural tube remains open.
  

• The present case shows a cystic swelling in the lumbosacral region, filled with fluid and has visible neural tissue as well, indicative of meningomyelocele.
• In Myelomeningocele, the skin is intact, and the placode-containing remnants of nervous tissue is observed in the center of the lesion, which is filled with cerebrospinal fluid.

• Microglia are specialized macrophages (mesodermal in origin) capable of phagocytosis that protect neurons of the central nervous system.
  • They are derived from the earliest wave of mononuclear cells that originate in blood islands early in development and colonize the brain shortly after the neural precursors begin to differentiate.
  • They are self-renewing population and are distinct from macrophages and monocytes.
• Macroglia cells are derived from neuroectoderm and include: Astrocytes, oligodendrocytes, ependymal cells, Schwann cells.

• Neuroepithelial cells are neuroectodermal in origin and are found in the ventricular zone of the neural tube. These are the ‘stem cells’ which differentiate further into neurons, astrocytes and other glial cells.
• Most glia are derived from ectodermal tissue (neural tube and crest). The exception is microglia, which are derived from hemopoietic stem cells (mesenchymal in origin).

• Neural tube develops into brain and spinal cord.
• Brain: Forebrain (Prosencephalon); Midbrain (Mesencephalon); Hindbrain (Rhombencephalon)

• Hypoglossal nucleus is a pure motor nucleus derived from the anterior basal plate of neural tube.
• Posterior alar plate gives sensory (not motor) nuclei.

Initially, corpus callosum forms a small bundle in the lamina terminalis and later extends first anteriorly and then posteriorly, arching over the thin roof of the diencephalon. It connects the nonolfactory areas of the right and the left cerebral cortices.

During the development of the corpus callosum, the dorsal part of the genu and the corpus form first. Subsequently, the anterior part of the genu and then the splenium arise. The rostrum is the last part to be formed.

• Neuronal migration disorders (NMDs) do not include porencephaly.
• Under neuronal migration disorders are Lissencephaly, Microgyria, Schizencephaly.
• Lissencephaly, which literally means smooth brain, is a rare brain formation disorder caused by defective neuronal migration during the 12th to 24th weeks of gestation, resulting in a lack of development of brain folds (gyri) and grooves (sulci).
• Terms such as ‘agyria’ (no gyri) or ‘pachygyria’ (broad gyri) are used to describe the appearance of the surface of the brain.
• Microgyria is a neuronal migration disorder, a developmental anomaly of the brain characterized by development of numerous small convolutions (microgyri), presenting with mental retardation. It is present in a number of specific neurological diseases, notably multiple sclerosis and Fukuyama congenital muscular dystrophy, a specific disease cause by mutation in the Fukutin gene.
• Alternate names for the condition are polygyria and micropolygyria.
• Schizencephaly is a neuron migration disorder leading to clefts in the brain, which extend from the CSF cavity (ventricles) and reach till the surface of brain. It is characterized by abnormal continuity of gray matter tissue extending from the ependyma lining of the cerebral ventricles to the pial surface of the cerebral hemisphere surface.

• CSF moves out of fourth ventricle into the subarachnoid space (not the other way around).
• Aqueductal stenosis dilates the proximal ventricles 1, 2 and 3 (not 4th).

• The anterior horn of the lateral ventricle lies anterior to its central part, the two being separated by an imaginary vertical line drawn at the level of the interventricular foramen.
• Anterior horn is closed anteriorly by the genu and rostrum of the corpus callosum.

Occipital (posterior) horn of lateral ventricle reaches posterior extent of the occipital lobe.

Floor of third ventricle has infundibular recess, which extends into the pituitary stalk (not anterior pituitary).

• Oculomotor nerve is not in the floor of 3rd ventricle, it passes under the floor, within the interpeduncular fossa.
• The anterior part of the floor of the third ventricle is formed mainly by hypothalamic structures.
• Immediately behind the optic chiasma lies the thin infundibular recess, which extends into the pituitary stalk.
• Behind this recess, the tuber cinereum and the mammillary bodies form the floor of the ventricle.

• Vagal triangle is seen at the floor of the fourth ventricle raised by vagal nucleus underneath.
• Floor of 4th ventricle has areas related to Abducent (6), vestibular (8), vagus (10), hypoglossal (12) nuclei.

• Facial nucleus is not present in the floor of the fourth ventricle.
• Facial colliculus is raised due to the axons of facial nerve winding around the abducent nucleus.

A group of nerve cells (gray matter) containing melanin pigment constitute the substantia ferruginea, at the floor of fourth ventricle.

• Facial colliculus is raised due to the axons of facial nerve winding around the abducent nucleus.
• It is the facial nerve axons (not the abducent nucleus) that raises the elevation called facial colliculus.