Layayoga: The Definitive Guide to the Chakras and Kundalini (84 page)

The filum terminale consists of the pia mater, some nerve cells and fibres, and the dural and arachnoidal sheaths. The filum terminale internum is more or less the miniature spinal cord, as all the elements present in the spinal cord are also found there. The central canal which lies within the upper part of the filum terminale internum (a distance of about 5 or 6 cm, superiorly) contains the grey matter around it. However, the neurogenic tissue begins to decrease gradually in the filum terminale, as it descends and there is a gradual shrinking of its tissues.

The Central Canal

There is a very narrow canal, called the central canal (the canalis centralis medullae spinalis), which is situated centrally in the grey matter of the spinal cord. It arises from the fourth ventricle of the hindbrain at the level of about the middle of the medulla oblongata, and descends through the lower half of the medulla oblongata to the upper end of the spinal cord at the level of the upper border of the atlas. From here the canal proceeds downwards to the conus medullaris, where it becomes dilated to form the terminal ventricle. The canal then passes into the filum terminale for about 5 or 6 cm where it ends. It forms the neural part of the filum terminale. It is lined with ciliated ependymal cells and is filled with cerebrospinal fluid.

The Brain (Encephalon)

The brain is divided into three main parts: hindbrain (rhombencephalon), consisting of the medulla oblongata, pons and cerebellum; mid-brain (mesencephalon) consisting of the tectum, cerebral peduncles, and tegmentum; and fore-brain (prosencephalon), consisting of the end-brain (telencephalon) and interbrain (diencephalon).

The brain stem is formed by the medulla oblongata, pons, and midbrain. In other words, the brain stem comprises practically all the parts, except the cerebellum and cerebrum.

The Medulla Oblongata

The medulla oblongata is a conical body, about 2.5 cm long. It is continuous with the upper end of the spinal cord at the level of the foramen magnum, and extends upwards to the lower margin of the pons. The medulla oblongata is divided into right and left halves by the anterior median fissure. Two bundles of nerve fibres, which arise from the cerebrum, descend through the crura cerebri and the pons to the anterior surface of the medulla oblongata to form the pyramids, lying on each side of the anterior median fissure. Most of the fibres of the pyramids decussate in the inferior part of the medulla oblongata to form the lateral corticospinal tract, and the rest descend without crossing, and form the anterior corticospinal tracts. They are called the pyramidal tracts. These tracts extend to the spinal cord. The communication between the medulla oblongata and the spinal cord with the cerebellum is via two bundles of fibres, termed the interior cerebellar peduncles, which arise from the medulla oblongata.

The Pons

The pons is the superior part of the hindbrain and is situated in front of the cerebellum. Its lower border is connected with the upper border of the medulla oblongata. It presents a broad convex ridge on its ventral surface, which separates it from the midbrain above, and the medulla oblongata below. The ridge is composed of transverse bundles of nerve fibres, and the pontine nuclei. These nerve-fibre bundles collect posteriorly, on each side, to form the middle cerebellar peduncle, which connects with the cerebellar cortex. This anterior ridge forms the basilar part of the pons. Two large bundles of nerve fibres, termed the crura cerebri, descend from the ventral surface of the midbrain to the basilar part of the pons where they form the longitudinal fascicles. Most of these fibres end in the pontine nuclei, and the rest pass as the pyramids from the lower border of the pons to the medulla oblongata. The dorsal part of the pons is continuous inferiorly with the medulla oblongata, and superiorly with the midbrain.

The cerebellum is situated in the posterior cranial fossa, dorsally to the medulla oblongata and pons. It consists of two hemispheres.

The Midbrain

The midbrain is the short, thick necklike structure which connects the hindbrain on one side, and the forebrain on the other. It consists of the cerebral peduncles, including the tegmentum, and the tectum.

Each half of the ventral part of the midbrain extends superiorly to the corresponding half of the forebrain, and is called the cerebral peduncle The ventral part of the cerebral peduncle is called the crus cerebri. The crus cerebri is a broad bundle of nerve fibres, which arises in the corresponding cerebral hemisphere, and descends to the pons and medulla oblongata.

The dorsal part of the cerebral peduncle is called the tegmentum. It is composed of grey and of white matter. It is continuous inferiorly with the dorsal part of the pons, and superiorly with the hypothalamus. There is a thin layer of grey matter, called the substantia nigra between the crus cerebri and the tegmentum.

The tectum is that part of the midbrain which is posterior to the aqueduct. It consists of four small swellings, two on each side, the superior and inferior colliculi, which are composed of gray matter. Each superior colliculus is connected with the thalamus. The pineal body is situated between the superior colliculi.

The Interbrain (Diencephalon)

The interbrain is the inferior part of the fore-brain, lying above the midbrain. It consists of the thalamus, hypothalamus, metathalamus, and epithalamus. The thalamus forms the greater portion of the diencephalon. Medially, the two thalami are separated by the third ventricle. The thalamus consists of gray matter. It is the great sensory relay station and is interconnected with most parts of the cerebral cortex.

The Cerebrum

The upper part of the forebrain is the endbrain (telencephalon), or the cerebrum. The fundamental part of it is the paired cerebral hemispheres which form the largest part of the brain. There is a small unevaginated part under the large evaginated hemispheres, called the telencephalon medium.

The two cerebral hemispheres are almost separated from each other by the longitudinal cerebral fissure (fissura longitudinalis cerebri) in which is situated the falx cerebri. The surface of the hemispheres is convoluted. The elevations are called gyri. The gyri are separated from each other by grooves and fissures, called sulci. The interlobar sulci form lobes. There are four lobes in each hemisphere: the frontal lobe (lobus frontalis), parietal lobe (lobus parietalis), temporal lobe (lobus temporalis), and occipital lobe (lobusoccipitalis).

The convoluted surface of the hemispheres is covered by a layer of grey matter, consisting of nerve cells which are arranged in six strata. This cover of gray matter is called the cerebral cortex. Under this surface cortex lies the white matter. There is also the subcortical grey matter (basal ganglia) under the white matter. The white matter consists of the nerve fibres which are of three types: association fibres, which interconnect various parts of the same hemisphere; commissural fibres, which connect the parts of one hemisphere with those of the other; and projection fibres, which connect the cerebral cortex with other parts of the central nervous system. Of the commissural fibres, the corpus callosum is the most important. It is a thick, broad, arched body of nerve fibres, situated at the bottom of the longitudinal cerebral fissure. It connects one hemisphere with the other.

The Ventricular System of the Brain

The central canal of the spinal cord extends upwards through the foramen magnum into the inferior half of the medulla oblongata and opens into the fourth ventricle at about the level of the middle of the medulla oblongata. The fourth ventricle (ventriculus quartus) is the cavity of the hindbrain; it extends from the superior border of the pons to the middle of the medulla oblongata, and is situated in front of the cerebellum and behind the medulla oblongata and pons. Its superior end is narrow and is continuous with the cerebral aqueduct.

The cerebral aqueduct (aquaeductus cerebri) is an elongated narrow cavity, lying in the midbrain. It communicates with the third ventricle above. The third ventricle (ventriculus tertius) is a narrow cavity the greater part of which lies in the interbrain between the two thalami, and only a small part of it extends into the telencephalon medium, and the lamina terminalis is its rostral boundary. The third ventricle communicates with the lateral ventricles above through the two interventricular foramina. The lateral ventricles (ventriculi laterales) are two c-shaped cavities, situated one in each cerebral hemisphere, and communicate with the third ventricle.

The ventricles of the brain contain the cere brospinal fluid through which they are in continuation with the central canal of the spinal cord. The cerebrospinal fluid perhaps circulates around the brain and the spinal cord. The cerebrospinal fluid may serve to remove the metabolic waste products and to cleanse the nerve tissue.

The Blue Line

The blue line passes centrally through the filum terminale, spinal cord, and brain, as if it were the bisecting line, since these structures through which it passes show the bisectional pattern in their forms. The blue line, in reality, is the ‘one-dimensional’ line, indicating the boundary of the material aspect of the body, and beyond which, and extramaterially, lies the nadi-chakra (the non-material power-field), the central aspect of which is the sushumna nadi. The blue line also serves a practical purpose. It indicates certain borderland positions which have the greatest affinity with the chakras.

The blue line starts centrally within the filum terminale at its inferior end, lying (according to our picture) at the level of the second segment of the coccyx. It then ascends centrally through the filum terminale to reach the caudal end of the central canal, lying about 5 or 6 cm down in the filum terminale internum from its superior end. The blue line then passes into the central canal at this point, and ascends centrally through the entire length of the central canal to the point where the central canal opens into the fourth ventricle, on a level with the middle of the medulla oblongata.

The blue line now passes centrally through the fourth ventricle, the cerebral aqueduct, and then the third ventricle, lying in the diencephalon. Thereafter the blue line passes through the rostral end of the third ventricle in its telencephalic part, the so-called telencephalon medium, to reach the lamina terminalis. From here it ascends through the anterior commissure, farnix, septum pellucidum, and corpus callosum. Finally, the blue line passes into the longitudinal, cerebral fissure which is situated between the two cerebral hemispheres, and reaches a central point of the cerebral cortex, above which lies the bregma.

The Course of the Sushumna

The blue line indicates indirectly the course of the sushumna nadi. The sushumna rises as the pranic radiation-line of deep red colour from the force-concentration centre, termed the kanda-mula. The kanda-mula is situated extra materially at a position which corresponds approximately to the point lying just below, but intimately connected with, the inferior end of the filum terminale. The sushumna starts from the central aspect of the kandamula. The kandamula is situated just below, but closely connected with, the starting point of the blue line. The sushumna ascends, as the blue line does, through the filum terminale, central canal, fourth ventricle, cerebral aqueduct, third ventricle, telencephalon medium, anterior commissure, farnix, septum pellucidum, corpus callosum and longitudinal cerebral fissure, and reaches a central point of the cerebral cortex. This is the superior end point of the sushumna. This terminal point of the sushumna has been technically termed the talu-mula, brahmarandhra, and dwadashanta.

The wajra nadi, which is situated within the sushumna as its second internal nadi, is vermilion red in colour, and arises from the same starting point as the sushumna (remaining within it), following the course of the blue line, and terminates where the sushumna ends. The chitrini is situated within the wajra as the third internal nadi, and is white in colour. It begins at the starting point of the wajra (and, consequently, of the sushumna) and proceeds upward along with the wajra, following the course of the blue line, and ends at the terminal point of the wajra and sushumna. The brahma nadi is situated within the chitrini. It starts from the muladhara, that is, a little above the starting point of the sushumna, or, more precisely, just above the inferior end of the blue line. The brahma nadi ascends along the chitrini (being within the chitrini), following the course of the blue line, and terminates at the superior end points of the chitrini, wajra, and sushumna. Therefore, the terminal points of all the four nadits are the same. These nadits have been clearly shown in the figure,
Plate 26
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Ida and Piṅgala

Kanda-mula is the power station from which the sushumna, ida and piṅgala have arisen as pranic radiation-lines. The kanda-mula is situated at an extra-material position just below the caudal end of the filum terminale, and under, but in contact with, the muladhara chakra. The sushumna starts from the central aspect of the kanda-mula and rises straight through the filum terminale, central canal and ventricles to the cerebral cortex where it ends. The sushumna, in its upward course, is spiraliform.

The ida originates from the left aspect of the kanda-mula and runs outside the vertebral column, and then ascends, remaining on the left side of it, and reaches the ajña chakra where it joins the sushumna. Similarly, the piṅgala starts from the right aspect of the kanda-mula, proceeds outside the vertebral column, and extends upward, remaining on the right of the vertebral column, and reaches the ajña when it joins the sushumna. So the positions of the ida and piṅgala in relation to the sushumna are: the sushumna assumes a central position and the ida is on its left side, and the piṅgala on its right side. The upper ends of the ida and piṅgala are in the ajña where they are in union with the sushumna. But the sushumna does not terminate here. It goes upwards to the cerebral cortex point and ends there.