Objectives Describe the development of meninges. Describe the development of brain vesicles from the neural tube. Describe the development of the different parts of brain. Describe the development of brain ventricles and choroid plexuses Describe the development of the cranial nerves and their ganglia. Describe the congenital anomalies of brain and spinal cord.

Meninges: The meningeal layers originate from: Paraxial mesenchyme in the trunk and caudal regions of the head. Neural crest in regions rostral to the mesencephalon. The meninges may be divided in development into the pachymeninx (dura mater) and leptomeninges (arachnoid mater, subarachnoid space with arachnoid cells and fibres, and pia mater). All meningeal layers are derived from loose mesenchyme which surrounds the developing neural tube, termed primary meninx.

Rhombencephalon:Hindbrain Rhombencephalon consists of the myelencephalon, most caudal of the brain vesicles,and metencephalon, which extends from the pontine flexure to rhombencephalic isthmus.

Myelencephalon: It is brain vesicle that gives rise to medulla oblongata. It differs from the spinal cord in that its lateral walls are everted. Alar and basal plates separated by sulcus limitans can be clearly distinguished

The basal plate, similar to that of spinal cord contains motor nuclei. These nuclei are divided into three groups: (1) Somatic efferent. (2) Special visceral efferent. (3) General visceral. Somatic efferent group continues rostrally into mesencephalon as somatic efferent motor column. In myelencephalon, it includes neurons of hypoglossal (XII) nerve. In the metencephalon and the mesencephalon, the column contains neurons of abducens (VI),trochlear (IV), and oculomotor(III) nerves.

Special visceral efferent group extends into the metencephalon, forming special visceral efferent motor column. Its motor neurons supply striated muscles of pharyngeal arches. In myelencephalon, the column is represented by neurons of accessory (XI),vagus (X), and glossopharyngeal (IX) nerves. The general visceral efferent group contains motor neurons that supply involuntary musculature of the respiratory tract, intestinal tract, and heart.

The alar plate contains three groups of sensory relay nuclei: (1)Somatic afferent (general sensory) receives sensations of pain, temperature, and touch from pharynx by way of glossopharyngeal nerve (IX). (2) Special afferent receives from taste buds of tongue, palate, oropharynx, epiglottis and from vestibulocochlear nerve (VIII) for hearing and balance. (3) General visceral afferent, group receives interoceptive information from respiratory gastrointestinal tract and heart by vagus nerve (X).

Roof plate of myelencephalon consists of a single layer of ependymal cells covered by pia mater The two combined are known as tela choroidea. Proliferation of vascular mesenchyme forms sac-like invaginations that project into the underlying ventricular cavity and form the choroid plexus, which produces cerebrospinal fluid.

Metencephalon: Similar to myelencephalon it is characterized by basal and alar plates. Two new components form: (1) Cerebellum, a coordination center for posture and movement. (2) Pons, the pathway for nerve fibers between spinal cord, cerebral and cerebellar cortices. Basal plate of metencephalon contains three groups ofmotor neurons: (1) Somatic efferent, which gives rise to the nucleus of the abducens nerve. (2) Special visceral efferent containing nuclei of the trigeminal and facial nerves. (3) General visceral efferent, with axons that supply the submandibular and sublingual glands.

Marginal layer of basal plates of metencephalon makes a bridge for nerve fibers connecting cerebral cortex and cerebellar cortex with the spinal cord.Hence, this portion of the metencephalon is known as pons (bridge). In addition to nerve fibers, pons contains pontine nuclei, which originate in the alar plates of metencephalon and myelencephalon. Alar plates of the metencephalon contain three groups of sensory nuclei: (1) Somatic afferent which contains neuronsof the trigeminal nerve. (2) Special afferent. (3) General visceral afferent.

Cerebellum Dorsolateral parts of alar plates bend and form rhombic lips which join and form the cerebellar plate. In a 12-week embryo, this plate shows a small midline vermis, and two lateral hemispheres. A transverse fissure soon separates the nodule from vermis and lateral flocculus from hemispheres. This flocculonodular lobe is phylogenetically the most primitive part of the cerebellum.

Initially cerebellar plate consists of neuroepithelial, mantle, and marginal layers. Cells formed by the neuroepithelium migrate to surface of the cerebellum to form external granular layer. In the sixth month of development external granular layer gives rise to various cell types. These cells migrate toward the differentiating Purkinjecells and give rise to granule cells.

Basket and stellate cells are produced by proliferating cells in the cerebellar white matter. The cortex of the cerebellum, consisting of Purkinjecells, Golgi II neurons, and neurons produced by the external granular layer, reaches its defi nitive size after birth. The deep cerebellar nuclei, such as dentate nucleus, reach their final position before birth.

Mesencephalon (Midbrain): In mesencephalon each basal plate contains two groups of motor nuclei: (1) Somatic efferent represented by oculomotor and trochlear nerves. (2) General visceral efferent represented by nucleus of Edinger-Westphal. Marginal layer of each basal plate enlarges and forms crus cerebri. Alar plates of mesencephalon appear as two longitudinal elevations separated by a shallow midline depression. With further development, a transverse groove divides elevations into superior and inferior colliculi.

Prosencephalon (forebrain): It isconsists of telencephalon which forms cerebral hemispheres and diencephalon, which forms optic cup and stalk, pituitary, thalamus, hypothalamus, and epiphysis. Diencephalon: It develops from median portion of prosencephalon and consist of a roof plate and two alar plates but lack floor and basal plates.

Roof plate of diencephalon give rise to choroid plexus of the third ventricle. The most caudal part of roof plate develops into pineal body, or epiphysis.

Alar Plate, Thalamus, and Hypothalamus: Alar plates form lateral walls of diencephalon. Hypothalamic sulcus divides the plate into a dorsal region forming the thalamus and a ventral region forming the hypothalamus.

Cranial Nerves: By the fourth week of development, nuclei for all 12 cranial nerves are present. All except the olfactory (I) and optic (II) nerves arise from brainstem, and of these only the oculomotor (III) arises outside the region of the hindbrain.

Cranial NerveBrain RegionTypeInnervation Olfactory (I)TelencephalonSVANasal epithelium (smell) Optic (II)DiencephalonSSARetina (vision) Oculomotor (III)MesencephalonGSE Sup., inf., med. Rectus, inf. oblique, levator palpebrae sup. m. GVE (ciliary ganglion) sphincter pupillae, ciliary m. Trochlear (IV) Metencephalon (exits mesencephalon) GSESup. oblique m. Trigeminal (V)Metencephalon GSA (trigeminal ganglion) Skin, mouth, facial m., teeth, ant. two-thirds of tongue GVA (trigeminal ganglion) proprioception: skin, muscles, joints SVE (branchiomotor) M. of mastication, mylohyoid, ant. belly of digastric, tensor velipalatini, post. belly of digastric m.

Abducens (VI)MetencephalonGSELateral rectus m. Facial (VII)Metencephalon SVA (geniculate ganglion) Taste ant. two-thirds of tongue GSA (geniculate ganglion) Skin ext. auditory meatus GVA (geniculate ganglion) Ant. two-thirds of tongue SVE (branchiomotor) M. of facial expression, stapedius, stylohyoid, post. belly of digastric GVE Submandibular, sublingual, and lacrimal glands Vestibulocochlear (VIII) MetencephalonSSA (vestibular and spiral ganglia) Semicircular canals, utricle, saccule (balance) spiral organ of Corti (hearing)

Glossopharyngeal (IX) Myelencephalon SVA (inferior ganglion) Post. one-third of tongue (taste) GVA (superior ganglion) Parotid gland, carotid body and sinus, middle ear GSA (inferior ganglion) External ear SVE (branchiomotor)Stylopharyngeus GVE (otic ganglion)Parotid gland Vagus (X)Myelencephalon SVA (inferior ganglion) Palate and epiglottis (taste) GVA (superior ganglion) Base of tongue, pharynx, larynx, trachea, heart, esophagus, stomach, intestines GSA (superior ganglion) External auditory meatus SVE (branchiomotor) Constrictor m. pharynx, intrinsic m. larynx, sup. two-thirds esophagus GVE (ganglia at or near viscera) Trachea, bronchi, digestive tract, heart Spinal Accessory (XI)MyelencephalonSVE (branchiomotor)Sternocleidomastoid, trapezius m. Hypoglossal (XII)MyelencephalonGSEM. of tongue (except palatoglossus

Spina bifida Congenital Malformations Of CNS

Meningoencephalocele

Anencephaly Due to failure of closure of the rostral end of the neural tube. Failure of complete development of the brain, skull and scalp

Microcephaly

Congenital hydrocephalus Abnormal Accumulation of CSF inside the brain cavities

1) Spina bifida cystica 2) A-Spina bifida with meningocele

Myelocele: Myelocele: