The Nervous SystemThe Nervous SystemLectured by Bien Nillos, MDLectured by Bien Nillos, MD

Reference: Gray’s AnatomyReference: Gray’s Anatomy

The Nervous SystemThe Nervous System

• the most complicated and highly organized of the most complicated and highly organized of the various systems which make up the the various systems which make up the human body human body

• the mechanism concerned with the the mechanism concerned with the correlation and integration of various bodily correlation and integration of various bodily processes and the reactions and adjustments processes and the reactions and adjustments of the organism to its environment of the organism to its environment

• may be divided into two may be divided into two parts, parts, centralcentral and  and peripheral.peripheral.

CNSCNS

• The The central nervous systemcentral nervous system consists  consists of of the the encephalonencephalon or  or brain,brain, contained  contained within the cranium, and the within the cranium, and the medulla medulla spinalisspinalis or  or spinal cord,spinal cord, lodged in the  lodged in the vertebral canal; the two portions are vertebral canal; the two portions are continuous with one another at the continuous with one another at the level of the upper border of the atlas level of the upper border of the atlas vertebra. vertebra.

PNSPNS

• The The peripheral nervous systemperipheral nervous system consists of  consists of a series of nerves by which the central a series of nerves by which the central nervous system is connected with the various nervous system is connected with the various tissues of the body. For descriptive purposes tissues of the body. For descriptive purposes these nerves may be arranged in two these nerves may be arranged in two groups, groups, cerebrospinalcerebrospinal and  and sympathetic,sympathetic, th the arrangement, however, being an arbitrary e arrangement, however, being an arbitrary one, since the two groups are intimately one, since the two groups are intimately connected and closely intermingled.  connected and closely intermingled. 

• The The enteric nervous systementeric nervous system, a , a subsystem of the peripheral nervous subsystem of the peripheral nervous system, has the capacity, even when system, has the capacity, even when severed from the rest of the nervous severed from the rest of the nervous system through its primary system through its primary connection by the connection by the VagusVagus nerve nerve, to , to function independently in controlling function independently in controlling the gastrointestinal system the gastrointestinal system

The NeuronThe Neuron

•   The nervous tissues are composed The nervous tissues are composed of of nerve cellsnerve cells and their various processes,  and their various processes, together with a supporting tissue together with a supporting tissue called called neuroglia,neuroglia, which, however, is found  which, however, is found only in the brain and medulla spinalis. only in the brain and medulla spinalis. Certain long processes of the nerve cells are Certain long processes of the nerve cells are of special importance, and it is convenient of special importance, and it is convenient to consider them apart from the cells; they to consider them apart from the cells; they are known as are known as nerve fibers.nerve fibers.

• To the naked eye a difference is obvious To the naked eye a difference is obvious between certain portions of the brain between certain portions of the brain and medulla spinalis: the and medulla spinalis: the gray gray substancesubstance and the  and the white substance.white substance.  

• The gray substance is largely composed The gray substance is largely composed of nerve cells, while the white substance of nerve cells, while the white substance contains only their long processes, the contains only their long processes, the nerve fibers nerve fibers

• The nerve cells vary in shape and size, and The nerve cells vary in shape and size, and have one or more processes: have one or more processes:

(1) (1) Unipolar cells - Unipolar cells - found in the spinal found in the spinal ganglia; the single process, after a short ganglia; the single process, after a short course, divides in a T-shaped mannercourse, divides in a T-shaped manner

(2) (2) Bipolar cells-Bipolar cells- found in the spinal found in the spinal ganglia,  when the cells are in an ganglia,  when the cells are in an embryonic condition.  embryonic condition. 

(3) (3) Multipolar cells - Multipolar cells - which are pyramidal which are pyramidal or stellate in shape, and characterized by or stellate in shape, and characterized by their large size and by the numerous their large size and by the numerous processes which issue from them. processes which issue from them.

• Nerve fibers are found universally in Nerve fibers are found universally in the peripheral nerves and in the the peripheral nerves and in the white substance of the brain and white substance of the brain and medulla spinalis. medulla spinalis.

• They are of two kindsThey are of two kinds

1.1. medullatedmedullated or  or white fiberswhite fibers

2.2. non-medullatednon-medullated or  or gray fibers.gray fibers.

• The The medullated fibersmedullated fibers form the  form the white part of the brain and medulla white part of the brain and medulla spinalis, and also the greater part of spinalis, and also the greater part of every cranial and spinal nerve, and every cranial and spinal nerve, and give to these structures their give to these structures their opaque, whiteopaque, white aspect. aspect.

• Most of the fibers of the sympathetic Most of the fibers of the sympathetic system, and some of the system, and some of the cerebrospinal, consist of cerebrospinal, consist of the the graygray or  or gelatinous nerve gelatinous nerve fibersfibers ( (fibers of Remakfibers of Remak) )

• axis-cylinderaxis-cylinder is the essential part of  is the essential part of the nerve fiber, and is always the nerve fiber, and is always present; the medullary sheath and present; the medullary sheath and the neurolemma are occasionally the neurolemma are occasionally absent, expecially at the origin and absent, expecially at the origin and termination of the nerve fiber termination of the nerve fiber

• The The medullary sheath,medullary sheath, or  or white white matter of Schwannmatter of Schwann, is regarded as , is regarded as being a fatty matter in a fluid state, being a fatty matter in a fluid state, which insulates and protects the which insulates and protects the essential part of the nerve—the axis-essential part of the nerve—the axis-cylinder.  cylinder. 

• The medullary sheath undergoes The medullary sheath undergoes interruptions in its continuity at regular interruptions in its continuity at regular intervals, giving to the fiber the intervals, giving to the fiber the appearance of constriction at these points: appearance of constriction at these points: these are known as the these are known as the nodes of Ranviernodes of Ranvier

• There may also be seen transverse lines There may also be seen transverse lines beyond the nodes termed beyond the nodes termed Frommann’s Frommann’s lineslines; the significance of these is not ; the significance of these is not understood.  understood. 

• oblique clefts may be seen in the oblique clefts may be seen in the medullary sheath, subdividing it into medullary sheath, subdividing it into irregular portions, which are irregular portions, which are termed termed medullary medullary segments,segments, or  or segments of Lantermannsegments of Lantermann

• The The neurolemmaneurolemma or  or primitive primitive sheathsheath presents the appearance of a  presents the appearance of a delicate, structureless membrane. delicate, structureless membrane. Here and there beneath it, and Here and there beneath it, and situated in depressions in the white situated in depressions in the white matter of Schwann, are nuclei matter of Schwann, are nuclei surrounded by a small amount of surrounded by a small amount of protoplasm protoplasm

Wallerian DegenerationWallerian Degeneration

• When nerve fibers are cut across, the When nerve fibers are cut across, the central ends of the fibers degenerate as central ends of the fibers degenerate as far as the first node of Ranvier; but the far as the first node of Ranvier; but the peripheral ends degenerate peripheral ends degenerate simultaneously throughout their whole simultaneously throughout their whole length. The axons break up into fragments length. The axons break up into fragments and become surrounded by drops of fatty and become surrounded by drops of fatty substance which are formed from the substance which are formed from the breaking down of the medullary sheath. breaking down of the medullary sheath. The nuclei of the primitive sheath The nuclei of the primitive sheath proliferate, and finally absorption of the proliferate, and finally absorption of the axons and fatty substance occurs axons and fatty substance occurs

• retrograde retrograde degenerationdegeneration

• Wallerian degeneration occurs after axonal injury in both Wallerian degeneration occurs after axonal injury in both the peripheral nervous system (PNS) and central Nervous the peripheral nervous system (PNS) and central Nervous System (CNS). It occurs in the axon stump distal to a site of System (CNS). It occurs in the axon stump distal to a site of injury and usually begins within 24-36 hours of a lesion. injury and usually begins within 24-36 hours of a lesion. Prior to degeneration distal axon stumps tend to remain Prior to degeneration distal axon stumps tend to remain electrically excitable. After injury, the axonal skeleton electrically excitable. After injury, the axonal skeleton disintegrates and the axonal membrane breaks apart.  disintegrates and the axonal membrane breaks apart. 

NeurogliaNeuroglia

• the peculiar ground substance in the peculiar ground substance in which are imbedded the true nervous which are imbedded the true nervous constituents of the brain and medulla constituents of the brain and medulla spinalis, consists of cells and fibers. spinalis, consists of cells and fibers.

• Some of the cells are stellate in Some of the cells are stellate in shape shape

The Spinal CordThe Spinal Cord• forms the elongated, nearly cylindrical, part of forms the elongated, nearly cylindrical, part of

the central nervous system which occupies the the central nervous system which occupies the upper two-thirds of the vertebral canal. upper two-thirds of the vertebral canal.

• Its average length in the male is about 45 cm., in Its average length in the male is about 45 cm., in the female from 42 to 43 cm., while its weight the female from 42 to 43 cm., while its weight amounts to about 30 gms. amounts to about 30 gms.

• It extends from the level of the upper border of It extends from the level of the upper border of the atlas to that of the lower border of the first, or the atlas to that of the lower border of the first, or upper border of the second, lumbar vertebra. upper border of the second, lumbar vertebra.

• Above, it is continuous with the brain; below, it Above, it is continuous with the brain; below, it ends in a conical extremity, the ends in a conical extremity, the conus conus medullaris,medullaris, from the apex of which a delicate  from the apex of which a delicate filament, the filament, the filum terminale,filum terminale, descends as far  descends as far as the first segment of the coccyx as the first segment of the coccyx

• The Spinal Cord does not fill the part The Spinal Cord does not fill the part of the vertebral canal in which it lies; of the vertebral canal in which it lies; it is ensheathed by three protective it is ensheathed by three protective membranes, separated from each membranes, separated from each other by two concentric spaces:other by two concentric spaces:

1.1. dura materdura mater  2.2. arachnoidarachnoid3.3. pia materpia mater

Dura MaterDura Mater

• is a strong, fibrous membrane which forms a wide, is a strong, fibrous membrane which forms a wide, tubular sheath; tubular sheath;

• extends below the termination of the medulla extends below the termination of the medulla spinalis and ends in a pointed cul-de-sac at the spinalis and ends in a pointed cul-de-sac at the level of the lower border of the second sacral level of the lower border of the second sacral vertebra. vertebra.

• is separated from the wall of the vertebral canal by is separated from the wall of the vertebral canal by the the epidural cavity - epidural cavity - which contains a quantity of which contains a quantity of loose areolar tissue and a plexus of veins; loose areolar tissue and a plexus of veins;

• betweenbetween the dura mater and the subjacent the dura mater and the subjacent arachnoid is a capillary interval, the arachnoid is a capillary interval, the subdural subdural cavity - cavity - which contains a small quantity of fluid, which contains a small quantity of fluid, probably of the nature of lymph probably of the nature of lymph

ArachnoidArachnoid

• a thin, transparent sheath, separated from a thin, transparent sheath, separated from the pia mater by a comparatively wide the pia mater by a comparatively wide interval, the interval, the subarachnoid cavity,subarachnoid cavity, which  which is filled with cerebrospinal fluid.  is filled with cerebrospinal fluid. 

Pia MaterPia Mater

• closely invests the spinal cord and closely invests the spinal cord and sends delicate septa into its substance; sends delicate septa into its substance; a narrow band, the a narrow band, the ligamentum ligamentum denticulatum,denticulatum, extends along each of  extends along each of its lateral surfaces and is attached by a its lateral surfaces and is attached by a series of pointed processes to the inner series of pointed processes to the inner surface of the dura mater. surface of the dura mater.

Spinal NervesSpinal Nerves

• Thirty-one pairs of spinal nerves Thirty-one pairs of spinal nerves spring from the spinal cordspring from the spinal cord

• each nerve has an anterior (ventral), each nerve has an anterior (ventral), and a posterior (dorsal) root, the and a posterior (dorsal) root, the latter being distinguished by the latter being distinguished by the presence of an oval swelling, presence of an oval swelling, the the spinal ganglion,spinal ganglion, which contains  which contains numerous nerve cells numerous nerve cells

• The pairs of spinal nerves are grouped as The pairs of spinal nerves are grouped as follows: follows: cervical 8, thoracic 12, lumbar 5, sacral 5, cervical 8, thoracic 12, lumbar 5, sacral 5, coccygeal 1coccygeal 1

the spinal cord is divided into cervical, the spinal cord is divided into cervical, thoracic, lumbar and sacral regions, thoracic, lumbar and sacral regions, corresponding with the attachments of the corresponding with the attachments of the different groups of nerves. different groups of nerves.

The BrainThe Brain

• is contained within the cranium, and is contained within the cranium, and constitutes the upper, greatly expanded constitutes the upper, greatly expanded part of the central nervous system. part of the central nervous system.

• In its early embryonic condition it In its early embryonic condition it consists of three hollow vesicles, termed consists of three hollow vesicles, termed the the hind-hind-brainbrain or  or rhombencephalon,rhombencephalon, the  the mid-mid-brainbrain or  or mesencephalon,mesencephalon, and  and the the fore-brainfore-brain or  or prosencephalonprosencephalon

• the wall of the the wall of the hind-brainhind-brain - form the medulla - form the medulla oblongata, the pons, and cerebellum, while its oblongata, the pons, and cerebellum, while its cavity is expanded to form the fourth ventricle cavity is expanded to form the fourth ventricle

• The The mid-brainmid-brain - forms the  - forms the cerebral cerebral aqueductaqueduct ( (aqueduct ofaqueduct of  SylviusSylvius), which serves as ), which serves as a tubular communication between the third and a tubular communication between the third and fourth ventricles; its walls are thickened to form fourth ventricles; its walls are thickened to form the corpora quadrigemina and cerebral peduncles the corpora quadrigemina and cerebral peduncles

• The The fore-brainfore-brain undergoes great modification: undergoes great modification: – anterior part or anterior part or telencephalontelencephalon expands laterally in the  expands laterally in the

form of two hollow vesicles, the cavities of which become form of two hollow vesicles, the cavities of which become the lateral ventricles, while the surrounding walls form the lateral ventricles, while the surrounding walls form the cerebral hemispheres and their commissures; the cerebral hemispheres and their commissures;

– the cavity of the posterior part or the cavity of the posterior part or diencephalondiencephalon forms  forms the greater part of the third ventricle, and from its walls the greater part of the third ventricle, and from its walls are developed most of the structures which bound that are developed most of the structures which bound that cavity cavity

The Medulla OblongataThe Medulla Oblongata

• extends from the lower margin of the extends from the lower margin of the pons to a plane passing transversely pons to a plane passing transversely below the pyramidal decussation and below the pyramidal decussation and above the first pair of cervical nerves; above the first pair of cervical nerves; this plane corresponds with the upper this plane corresponds with the upper border of the atlas behind, and the border of the atlas behind, and the middle of the odontoid process of the middle of the odontoid process of the axis in front; at this level the medulla axis in front; at this level the medulla oblongata is continuous with the spinal oblongata is continuous with the spinal cord cord

• medulla oblongata is pyramidal in medulla oblongata is pyramidal in shape, its broad extremity being shape, its broad extremity being directed upward toward the pons, while directed upward toward the pons, while its narrow, lower end is continuous with its narrow, lower end is continuous with the spinal cordthe spinal cord

• divided into a lower divided into a lower closed closed partpart containing the central canal, and an  containing the central canal, and an upper upper open partopen part corresponding with the  corresponding with the lower portion of the fourth ventricle lower portion of the fourth ventricle

•   The The anterior districtanterior district is named  is named the the pyramidpyramid ( (pyramis medullæ pyramis medullæ oblongatæoblongatæ) and lies between the ) and lies between the anterior median fissure and the anterior median fissure and the antero-lateral sulcus. antero-lateral sulcus. ItsIts upper end is  upper end is slightly constricted, and between it slightly constricted, and between it and the pons the fibers of the and the pons the fibers of the abducent nerve emerge; abducent nerve emerge;

• The two pyramids contain the motor fibers The two pyramids contain the motor fibers which pass from the brain to the medulla which pass from the brain to the medulla oblongata and spinal cord: oblongata and spinal cord: corticobulbar corticobulbar and corticospinal fibers and corticospinal fibers

• When these pyramidal fibers are traced When these pyramidal fibers are traced downward it is found that some two-thirds downward it is found that some two-thirds or more of them leave the pyramids in or more of them leave the pyramids in successive bundles, and decussate in the successive bundles, and decussate in the anterior median fissure, forming what is anterior median fissure, forming what is termed the termed the pyramidal decussationpyramidal decussation

• The The oliveolive is situated lateral to the  is situated lateral to the pyramid, from which it is separated pyramid, from which it is separated by the antero-lateral sulcus, and the by the antero-lateral sulcus, and the fibers of the hypoglossal nerve fibers of the hypoglossal nerve

PonsPons

• forepart of the hind-brain is situated in forepart of the hind-brain is situated in front of the cerebellum. From its superior front of the cerebellum. From its superior surface the cerebral peduncles emerge, surface the cerebral peduncles emerge, one on either side of the middle line. one on either side of the middle line.

CerebellumCerebellum

• constitutes the largest part of the constitutes the largest part of the hindbrain. It lies behind the pons and hindbrain. It lies behind the pons and medulla oblongata; between its central medulla oblongata; between its central portion and these structures is the portion and these structures is the cavity of the fourth ventricle. It rests on cavity of the fourth ventricle. It rests on the inferior occipital fossæ, while above the inferior occipital fossæ, while above it is the tentorium cerebelli, a fold of it is the tentorium cerebelli, a fold of dura mater which separates it from the dura mater which separates it from the tentorial surface of the cerebrum tentorial surface of the cerebrum

• The cerebellum consists of three The cerebellum consists of three parts, a median and two lateral, parts, a median and two lateral, which are continuous with each which are continuous with each other, and are substantially the same other, and are substantially the same in structure. The median portion is in structure. The median portion is constricted, and is called constricted, and is called the the vermis,vermis, from its annulated  from its annulated appearance which it owes to the appearance which it owes to the transverse ridges and furrows upon transverse ridges and furrows upon it; the lateral expanded portions are it; the lateral expanded portions are named the named the hemispheres.hemispheres.

Fourth VentricleFourth Ventricle

• cavity of the hind-brain, is situated in cavity of the hind-brain, is situated in front of the cerebellum and behind front of the cerebellum and behind the pons and upper half of the the pons and upper half of the medulla oblongata medulla oblongata

• It presents four It presents four angles,angles, and  and possesses a possesses a roofroof or dorsal wall,  or dorsal wall, a a floorfloor or ventral wall, and  or ventral wall, and lateral lateral boundariesboundaries

Cerebral PedunclesCerebral Peduncles

• two cylindrical masses situated at the base two cylindrical masses situated at the base of the brain, and largely hidden by the of the brain, and largely hidden by the temporal lobes of the cerebrum temporal lobes of the cerebrum

• The depressed area between the crura is The depressed area between the crura is termed the termed the interpeduncular fossa,interpeduncular fossa, and  and consists of a layer of grayish substance, consists of a layer of grayish substance, the the posterior perforated posterior perforated substance,substance, which is pierced by small  which is pierced by small apertures for the transmission of apertures for the transmission of bloodvessels bloodvessels

ThalamusThalamus

• two large ovoid masses, situated one two large ovoid masses, situated one on either side of the third ventricle on either side of the third ventricle and reaching for some distance and reaching for some distance behind that cavity. Each measures behind that cavity. Each measures about 4 cm. in length, and presents about 4 cm. in length, and presents two extremities, an anterior and a two extremities, an anterior and a posterior, and four surfaces, superior, posterior, and four surfaces, superior, inferior, medial, and lateral. inferior, medial, and lateral.

Optic ChiasmOptic Chiasm

• is a flattened, somewhat quadrilateral is a flattened, somewhat quadrilateral band of fibers, situated at the band of fibers, situated at the junction of the floor and anterior wall junction of the floor and anterior wall of the third ventricle. Most of its fibers of the third ventricle. Most of its fibers have their origins in the retina, and have their origins in the retina, and reach the chiasma through the optic reach the chiasma through the optic nerves, which are continuous with its nerves, which are continuous with its antero-lateral angles. In the chiasma, antero-lateral angles. In the chiasma, they undergo a partial decussation they undergo a partial decussation

Optic TractsOptic Tracts

• continued backward and lateralward continued backward and lateralward from the postero-lateral angles of the from the postero-lateral angles of the optic chiasma optic chiasma

Third VentricleThird Ventricle

• is a median cleft between the two is a median cleft between the two thalami. Behind, it communicates with thalami. Behind, it communicates with the fourth ventricle through the cerebral the fourth ventricle through the cerebral aqueduct, and in front with the lateral aqueduct, and in front with the lateral ventricles through the interventricular ventricles through the interventricular foramen. Somewhat triangular in shape, foramen. Somewhat triangular in shape, with the apex directed backward, it has with the apex directed backward, it has a a roof,roof, a  a floor,floor, an  an anterioranterior and  and a a posterior boundaryposterior boundary and a pair  and a pair of of lateral wallslateral walls

Cerebral HemispheresCerebral Hemispheres

• constitute the largest part of the constitute the largest part of the brain, and, when viewed together brain, and, when viewed together from above, assume the form of an from above, assume the form of an ovoid mass broader behind than in ovoid mass broader behind than in front, the greatest transverse front, the greatest transverse diameter corresponding with a line diameter corresponding with a line connecting the two parietal connecting the two parietal eminences.  eminences. 

Longitudinal Cerebral Longitudinal Cerebral FissureFissure• contains a sickle-shaped process of dura contains a sickle-shaped process of dura

mater, the mater, the falx cerebri.falx cerebri. In front and  In front and behind, the fissure extends from the upper behind, the fissure extends from the upper to the under surfaces of the hemispheres to the under surfaces of the hemispheres and completely separates them, but its and completely separates them, but its middle portion separates them for only middle portion separates them for only about one-half of their vertical extent; for at about one-half of their vertical extent; for at this part they are connected across the this part they are connected across the middle line by a great central white middle line by a great central white commissure, the commissure, the corpus callosumcorpus callosum

Lateral Cerebral FissureLateral Cerebral Fissure

• fissure of Sylviusfissure of Sylvius

• is a well-marked cleft on the inferior is a well-marked cleft on the inferior and lateral surfaces of the and lateral surfaces of the hemisphere, and consists of a short hemisphere, and consists of a short stem which divides into three rami. stem which divides into three rami.

Central SulcusCentral Sulcus

• fissure of Rolandofissure of Rolando

• is situated about the middle of the lateral is situated about the middle of the lateral surface of the hemisphere, and begins in or surface of the hemisphere, and begins in or near the longitudinal cerebral fissure, a little near the longitudinal cerebral fissure, a little behind its mid-point. It runs sinuously behind its mid-point. It runs sinuously downward and forward, and ends a little downward and forward, and ends a little above the posterior ramus of the lateral above the posterior ramus of the lateral fissure, and about 2.5 cm. behind the fissure, and about 2.5 cm. behind the anterior ascending ramus of the same anterior ascending ramus of the same fissure fissure

Calcarine FissureCalcarine Fissure

• on the medial surface of the on the medial surface of the hemisphere. It begins near the hemisphere. It begins near the occipital pole in two converging rami, occipital pole in two converging rami, and runs forward to a point a little and runs forward to a point a little below the splenium of the corpus below the splenium of the corpus callosum, where it is joined at an callosum, where it is joined at an acute angle by the medial part of the acute angle by the medial part of the parietoöccipital fissure parietoöccipital fissure

Cingulate FissureCingulate Fissure

• on the medial surface of the hemisphere; it on the medial surface of the hemisphere; it begins below the anterior end of the corpus begins below the anterior end of the corpus callosum and runs upward and forward callosum and runs upward and forward nearly parallel to the rostrum of this body nearly parallel to the rostrum of this body and, curving in front of the genu, is and, curving in front of the genu, is continued backward above the corpus continued backward above the corpus callosum, and finally ascends to the supero-callosum, and finally ascends to the supero-medial border of the hemisphere a short medial border of the hemisphere a short distance behind the upper end of the distance behind the upper end of the central sulcus central sulcus

The Lobes of the The Lobes of the HemisphereHemisphere

• the the frontal,frontal, the  the parietal,parietal,the the tempotemporal,ral, the  the occipital,occipital, the  the limbic,limbic, and  and the the insula.insula.

Lateral VentriclesLateral Ventricles

• are irregular cavities situated in the are irregular cavities situated in the lower and medial parts of the cerebral lower and medial parts of the cerebral hemispheres, one on either side of the hemispheres, one on either side of the middle line. They are separated from middle line. They are separated from each other by a median vertical each other by a median vertical partition, the partition, the septum pellucidum,septum pellucidum, but  but communicate with the third ventricle communicate with the third ventricle and indirectly with each other through and indirectly with each other through the the interventricular forameninterventricular foramen

The Cranial NervesThe Cranial Nerves

END OF LECTUREEND OF LECTURE““The brain is like a muscle. When The brain is like a muscle. When

it is in use we feel very good. it is in use we feel very good. Understanding is joyous” - Understanding is joyous” - Carl Carl

Sagan Sagan