Decussation of Pyramids

The decussation of pyramids is the crossing over of pyramidal fibers to the opposite side on the anterior side of medulla oblongata. The pyramidal, or corticospinal, fibers are myelinated axons that spring from pyramidal neurons that lie in layer V of the primary motor cortex, which extends alongside and parallel to the central sulcus (Roland's fissure). They comprise about 80% of the pyramidal tract corticospinal fibers. The 20% of the fibers do not cross over.

As they run down through the brainstem, those fibers originating in the left cerebral hemisphere cortex run diagonally across the medulla ventral fissure, over to the right side of anterior aspect of this portion of brainstem. Meanwhile, the corticospinal fibers arising from the right cerebral cortex cross over to the left side of medulla anterior surface.

The decussation of pyramids takes place in lower half portion of anterior aspect of medulla. This anatomical feature makes it possible for the left cerebral hemisphere to control the right side of the body, and the right cerebral hemisphere to control the left side of the body.

Below, schematic image of decussation of pyramids on anterior aspect of medulla, with pons on top.

Left Cerebral Hemisphere

The left cerebral hemisphere is one of the two longitudinal cerebral halves of the human brain. Like its opposite on the right side, it is divided into four lobes; frontal, temporal, parietal, and occipital. The left cerebral hemisphere is connected to the right hemisphere through the corpus callosum.

The primary motor area (motor strip) of left cerebral hemisphere controls movement of the right side of the body. This is due to the fact that pyramidal nerve cell myelinated fibers cross over to the opposite side at the decussation of the pyramids on anterior side of the medulla oblongata. Depending on the severity, a stroke affecting the left cerebral hemisphere may result in functional loss or motor skill impairment of the right side of the body, and may also cause loss of speech.

Superior Function

Linear and analytical reasoning and language skills such as oral articulation of words and grammar comprehension are often lateralized to the left hemisphere of the brain, which contains the Broca's cortical area and the Wernicke's. Dyscalculia is a neurological syndrome associated with damage to the left temporo-parietal junction.

Below, image of left cerebral hemisphere; external, lateral side.

 

Weight and Size of Brain

Although the weight and size of brain differ from person to person, anthropologists and physicians estimate that the average weight of an adult male is 1,400 grams (1.4 kg), or 49.9 ounces, while the female brain weight is 1,300 grams, or 45 ounces. The average weight of the newborn is 400 grams, or 14.1 ounces, which is doubled at the end of the first and tripled at the end of the fourth year. However, in advanced senescence (old age) and in alcoholics, the cerebrum starts losing considerably weight, due to demyelinization, which means loss of myelin sheath in the cerebral fasciculi (bundles). This is because of a bad or toxic nerve cell respiration (production of ATP).

Body weight and cranial shape also affect the weight of the brain; for example, the cerebrum of people with a brachycephalic cranium weighs more than those with a dolichocephalic one. Finally, the weight of Homo sapiens brain also depends on the diet and lifestyle; eating meat, eggs, and saturated fat and spending time learning, studying and working out favor greatly the healthy development of the myelin sheath and the cerebral bundles.

Size and dimension

The average sagittal (occipitofrontal) diameter of the brain of an adult, male human being ranges from 16 to 17 cm (6.4 to 6.8 inches), while the maximum width in the parietal region averages 14 cm (5.6 inches). The maximum height can reach to 12.5 cm (5 inches). The cerebrum of dolicocephalic people is longer, but individuals with a mesocephalic and brachycephalic crania have wider brain than dolicocephalics, especially in the parietal region.

The average volume of  today's Homo sapiens' brain is 1,425 cm3 (cubic centimeters), with the volume being the space it occupies in a three-dimensional aspect. However, the primitive hunter brain volume averaged bigger than today's, with 1,600 cm3 for Homo sapiens neanderthalensis and 1,500 cm3 for Cro-magnon hunters. It says a lot about the diet and the motor and temporospatial functions stimulation that implied living in a harsh environment and having to fight for survival.

Phineas Gage Case

The Phineas Gage case was a horrible medical condition of frontal lobe damage. In September, 1848, Phineas Gage, foreman of a road construction gang, had an iron rod blown through his head, achieving immortality. But he did not become immortal in the usual way by going directly to his heavenly reward, for he survived. In fact, it was the details of his survival which constituted the basis for the very considerable amount of fame that came his way.

It seems that Phineas Gage had poured a charge of powder into a hole in a rock, prior to a routine blasting operation. The usual procedure was then for an assistant to cover the powder with sand. For some reason this had not been done, and Gage neglected to check on the matter. Instead, supposing the sand covering to be in place, he dropped a heavy tamping iron into the hole. The result was catastrophic: the iron rod struck upon rock, made a spark, ignited the powder inside the hole, and took off for the stratosphere. On its way the rod, which was nearly 4 feet long, passed cleanly through Phineas' brain, entering high in his left cheek and coming out from the top of his head, causing frontal lobe damage.

Phineas Gage was stunned for about an hour, after which, with some assistance, he was able to walk off to see a surgeon, talking on the way about the hole in his head. Eventually he recovered from the infection that developed in the wound and lived for another twelve years. Scientists verified the story by actual examination of the damaged brain. It was found that not only the left frontal lobe had been severely damaged, but the damage had spread to the right frontal lobe as well.

Gage's surprising survival of such a spectacular injury was followed by equally surprising aftereffects. The aftereffects were remarkable precisely because of their nonspectacular nature. For Gage could still displayed no loss of memory and he was still able to perform his job. For a man with such extensive damage of the very portion of the cerebrum which had long been believed to be the seat of the higher intellectual processes, Gage displayed a disproportionately small decrease in his mental capacities. Yet, there were some changes in Phineas Gage, though, but they were of quite a different nature from what what would have been predicted by the then prevailing theories.

The Phineas Gage case proved that there is is a stark change in human personality as composed and rational behavior is strongly affected when there is a massive damage to the frontal lobe. However, it seems there is no memory loss. Thus, it shows that the frontal lobe plays an important role in inhibiting and modulating behavior and mental impulses to successfully adapt to the environment. This part of the cerebral cortex also has to do with an insight and deep empathic understanding of other people and their circumstances.

Before the accident Phineas Gage had been considerate, efficient, and well-balanced. Afterward he was fitful and irreverent, indulging frequently in gross profanity and manifesting little consideration for others. He had become obstinate yet capricious and vacillating. With these new traits Gage could no longer be trusted to supervise others. In fact, he showed little inclination toward work of any kind, but instead chose to travel around, making a living by exhibiting himself and his tamping iron.

Association Fibers in the Brain

The association fibers in the brain link up the different cortical areas with one another. In human beings, they are very complex and work as the inner wiring, integrating every part of the cerebral cortex into one operating whole. Thus, the frontal lobe is connected to all the other lobes. These fibers get together to form fasciculi, which are thick bundles consisting of billions of myelinated neuron axons.

These association fibers in the brain vary considerably in length and thickness, making up the white matter of the cerebrum. Therefore, short and long association fibers can be distinguished in the cerebrum. The short association fibers provide connections within a cerebral lobe or from one gyrus, or convolution, to the next.

The shortest fibers connect adjacent cortical parts; they reenter the cortex after running just a short distance through the white matter; thus, the layer of arcuate fibers lies immediately beneath the cortex. On the other hand, the long association fibers connect different cerebral lobes and form compact bundles, each one called fasciculus, that can be recognized with the naked eye.

Long association fibers

The superior longitudinal fasciculus lying dorsolaterally to the putamen is a strong association bundle between frontal lobe and occipital lobe with fibers branching to the parietal lobe and temporal lobe. The inferior occipitofrontal fasciculus passes through the ventral part of the extreme capsule from the frontal lobe to the occipital lobe.

The inferior longitudinal fasciculus extends between occipital lobe and temporal lobe. The uncinate fasciculus connects the temporal cortex with the frontal cortex; its ventral part provides a connection between the entorhinal area and the orbital area of the frontal lobe.

The arcuate fasciculus, which is unique in humans, connects the two language areas, with the fibers projecting from the Wernicke's area on the back of the temporal lobe to the Brocca's area in the back of the 3rd frontal gyrus; this fiber bundle makes a big arch. Other fiber bundles are the vertical occipital fasciculus and the orbitofrontal fasciculus.

Below, schematic drawing exhibiting the association fibers that link up the different parts of the cerebral cortex. Number 5 and 4 represent the superior longitudinal fasciculus; # 6- the inferior occipitofrontal fasciculus; #7- inferior longitudianal fasciculus; # 8- uncinate fasciculus, which is made up of fronto-temporal myelinated fibers. # 1 and 2 are short association fibers, or intergyral fasciculi.

 

Celiac Plexus

The celiac plexus, also called solar plexus, is an intertwined network of nerve fibers and ganglia, which is located throughout the upper abdominal region. It belongs to the autonomic nervous system and innervates both the viscera and the arteries of the abdominal cavity.

This network of nerves includes two celiac ganglia, which lie right above the celiac trunk (artery) on the anterior side of abdominal aorta, the superior mesenteric ganglion, which is located above the superior mesenteric artery at the point where it originates from the aorta, and the inferior mesenteric ganglion, situated also on anterior aspect of abdominal aorta, right above the inferior mesenteric artery.

The ganglia of the celiac plexus are interconnected with the ganglia of the sympathetic trunk, which are the two vertical chains of ganglia stringing along and parallel to the vertebral column, lying on both sides of it in two strands. The neurons of these ganglia send and receive afferent and efferent nerves to and from the spinal cord. Since they belong to the autonomic nervous system, the innervation of the smooth muscles of the viscera as well as the contraction and relaxation of the arteries walls, do not depends on our will; in other words, they are independent of the cerebral cortex.

Below, a diagram of the solar/celiac plexus. The schematic drawing is from an old Russian, State-printed encyclopedia on human anatomy.

 

Female Genital Anatomy

In the female genital anatomy, internal and external organs can be distinguished. The internal female genital organs consist of the ovary, the Fallopian tube, the uterus, the vagina, and the epoophoron. On the other hand, the external genital organs of women are the anatomical parts which lie exteriorly and can easily be observed, such as the vulva, clitoris, and the orifice of female urethra.

Internal Organs

Ovary– A paired almond-shaped organ lying on each side of the uterus. Not only did it produce the ova (egg cell) but it also releases the two feminine hormones: estrogen and progestorone. It is connected to the Fallopian tube through which the egg cell travels to the uterus.

Fallopian tube– A paired duct which stretches laterally from the uterus, with its lateral end curving downwards to partially surround the ovary. It is carries the female mature cell into the uterus to be fertilized.

Uterus– It is a hollow, pear-shaped muscular organ in which the ova get fertilized by the sperm cell, with the subsequent development of the embryo and fetus for nine months.

Vagina– A muscular genital canal, lined with mucous membrane, for the sexual intercourse between a female and the male and the birth of the fetus. Anatomically, it is the continuation of the uterus cervix. It is approximately 8 cm in length.

Epoophoron– A cluster of rudimentary tubules and ducts in the layers of the broad ligament of the uterus, near the mesosalpinx (below the Fallopian tube).

External Organs

Vulva– It  consists of the mons pubis, and the labia majora and minora, which are the outer and inner folds lying on each side of the orifice of the vagina.

Clitoris– A small, round erectile protrusion which ends up in the glans. It is highly sensitive and a source of pleasure when it is gently touched. It is the equivalent to the penis in male, originating from a phallic outgrowth, which is called the genital tubercle.

Female Urethra Orifice– It lies right above the orifice of the vagina.

Blood Supply

The internal genital organs (ovary, Fallopian tube, uterus, epoophoron, and ligaments) receive oxygenated blood from the ovarian artery (which arises straight from the abdominal aorta), from the uterine artery (which originates from the internal iliac), and from the vaginal artery (also from the internal iliac). Meanwhile, the external genital organs are supplied by branches of the internal pudendal artery, which springs from the internal iliac.

Below, a picture showing the female internal organs

Below, the female external genital organs

Taxonomy of Snakes

The taxonomy of snakes can be seen in the diagram below the page. As you can observe, all snakes belong to the kingdom: Animalia; Grade= Metazoan (multicellular animals); phylum= Chordate; subphylum= Vertebrate; class= Reptilia; subclass= Lepidosauria; order= Squamata; suborder= Serpentes (or Ophidia). The suborder Serpentes further divides into four large families= Elapidae (elapids), Viperidae (viperids), Colubridae (colubrids), and Boidae (boas/constrictors).

The family Elapidae, in turn, comprises more than 30 genera, which include the mambas of Africa, the cobras of Southeast Asia, and the corals of America. On the other hand, there are more than six genera in the family Viperidae, of which the Bothrops and the Crotalus are the most important because they include a large number of venomous species, like the lancehead of South and Central America and the rattlesnakes, which are found throughout the American continent. Meanwhile, the Boidae family includes the boas, the anacondas of South America, and the pythons.

This is only a summary, since the taxonomy of snakes concerning families, genus, species, and subspecies is very complex as many herpetologists/serpentologists disagree with one another as to which taxonomical group a particular type of snake belongs to. Besides, it involves traveling to other countries and continents to study them and spending a lot of time and money.

Below, a diagram of the taxonomy of snakes

Families of Snakes

Four large families of snakes can clearly be distinguished, although they are harder to arrange and classify than other types of vertebrate. They are: elapids, vipers, colubrids, and the boas. They all belong to the order Squamata (scaled reptiles). This is the most objective and traditional classification of the different kinds of snakes today on planet Earth. Although there are authors and online encyclopedias which created other families of serpents, these are rare snakes as biologists are not sure weather these constitute new families as they have fundamental physical traits by which these slithering reptiles could well be classified within the aforesaid mentioned groups.

Elapids (Elapidae)

The snakes that belong to this family are the most dangerous of them all for the potency of their venom. They have two distinctive features by which they can be distinguished: 1) their pteroglyph fangs, which means that they are erect, grooved fangs located at the front of their mouth as they are curved but constantly erect, not folding back when they close their mouth; their lower jaw has a small hollow space on each side for them to be lodged. 2) Their lethal venom is neurotoxic, which means it affect the nervous system and nerve cells as the victim’s diaphragm and ribs muscles get paralyzed and he is not able to breathe. Cobras (Asia), mambas (Africa), Oxyuranus (taipans of Australia), and coral snakes (American continent and Europe) are the genera that make up this family.

Below, the most dreaded snake in the world; it is an elapid: a king cobra from Southeast Asia (from India to Vietnam)

Vipers (Viperidae)

This family of snakes are the most widely distributed in the world as they are found in all continents, except the Antarctica. They have hollow, retractable fangs and they have cytotoxic and hemotoxic venom, which means it destroys body tissues and red blood cells. This family include four genera: the Crotalus (pit vipers such as all the rattlesnakes ); the Bothrops (yarara and urutu from South and Central America); Azemiops (found in Asia); and Viperinae (viperines whose species are found in Europe, Asia, and Africa).

Below, a well-known species of vipers: a rattlesnake (sub-species: diamondback)

Colubrids (Colubridae)

This family includes more than 200 genera, which are wide-spread in the world, in all continents. Among them are garter snakes, king snakes, and water snakes. Most of them are not venomous as they are harmless, but there is an exception: the genus Boiga, whose members are venomous. However, their fangs are located backward and it is very difficult for them to bite well a large animal, such as humans, may be the fingers. The most well-known Boiga genus are the cat snake species, most of them inhabit the jungles of Southeast Asia.

Boas (Boidae)

All these snakes lack venom glands, neither do they have the typical pair of grooved or hollow fangs, with which other families of snakes inject their venom.  Although they are non-venomous, they do have a series of smaller curved fangs, with which they trap and hold firmly they prey when they swallow it. Other than that, their main characteristics are the fact that they are constrictors and big; they kill by constriction, winding around they prey’s body as they tighten their grip. As a matter of fact, the biggest snake in the world belong to this family, which is the Anaconda of South America. The green anaconda can be found in the jungles of Brazil, Venezuela, and Paraguay.

Other famous genus of this family are the Pythons. Although some biologists and wikipedia classify them as a different family, they really constitute just another genus the Boas family, as they are constrictors and non-venomous, and both can climb and swim well. Pythons inhabit the jungles of Africa and Asia.

By Carlos B. Camacho

Human Uterus

The human uterus is an unpaired hollow organ, which is composed of smooth muscles. It lies in the central portion of the cavity of the true pelvis, between the pubic symphysis and sacrum. This pear-shaped organ is an essential part of the feminine reproductive system, where the embryo and fetus develop and get nourished. Its upper portion is the widest part, while its lower section is narrowest part, which faces downwards and forwards. The top of the uterus is called the fundus, while the bottom is the cervix (neck), which fans out a little before continuing with the vagina.

Size and Weight

The shape and size of the uterus change considerably during the different periods of life, particularly in connection with pregnancy. It measures approximately 7 cm in length in a nulliparous woman (who has never borne a child), and about 9 cm in length in a woman who has borne children. Meanwhile, the cavity of the uterus is about 6 cm in length. It is 5 cm wide at the level of the fundus at the top. Its weight varies from 30 to 100 g.

Structure

The wall of the uterus consists of three layers of tissues; the outer serous coat (perimetrium), the middle muscular coat (myometrium), and the inner mucous coat (endometrium). The perimetrium is a direct continuation of the serous coat of the urinary bladder, being fused with the myometrium for a long distance on the anterior and posterior surfaces, as well as on the fundus. The muscular coat, myometrium, is the thickest and strongest layer and it is composed of smooth muscle fibers with a mixture of connective tissue and elastic fibers.

The mucous coat of the uterus (endometrium) is fused with the muscular coat, forming the lining of the cavity. It consists of a single-layer columnar ciliated epithelium, containing tubular uterine glands. All three layers receive oxygenated blood from small branches from the uterine artery, which arises from the internal iliac.

Below, longitudinal section of human uterus.

Bulb of Vestibule

The bulb of vestibule consists of a mass of erectile tissue lying on either side of the vagina. It is a structure which is composed of two halves, right and left, which get fused together by means of a small and narrow intermediate part situated between the clitoris and the orifice of the urethra. Laterally and inferiorly, each half of the bulb is covered by the bulbospongiosus muscle.

Each of the two halves is a dense venous plexus (mass of blood vessels) whose elongated lateral portions are embedded in the base of the labia majora. Posteriorly, each half is also thicker than the anterior region, covering the greater vestibular gland. The bulb of the vestibule has a tunica albuginea investing the venous plexus, which is pierced by smooth muscle fibers and connective tissue bundles.

Each half of the bulb rests against the lateral (external) wall of the vagina, lying superficially to the triangular ligament. It corresponds to the bulb portions of the corpus spongiosum of the male. It receives oxygenated blood from a secondary branch of the internal pudendal artery.

Below, schematic drawing showing the bulb of vestibule of vagina and other external parts of the female reproductive organs

Broad Ligament of Uterus

The broad ligament of uterus is the broad fold of the peritoneum that holds up this female reproductive organ to the lateral wall of pelvis. It is formed by two peritoneal layers (anterior and posterior), extending laterally from both sides of the uterus. When it reaches the wall of the pelvis, these layers are continuous with the parietal peritoneum of the true pelvis. It is supplied by the uterine and ovarian artery.

Forming a septum across the pelvis, the broad ligament divides the cavity into an anterior and a posterior portion. The bladder, urethra, and vagina lie in the anterior portion, while the rectum lies in the posterior part. The anterior surface of the broad ligament faces forwards and downwards, with the posterior surface facing backwards and upwards. The posterior layer of the lateral part of the broad ligament gives rise to the mesovarium below the ampulla of the Fallopian tube. The ligament of the ovary is found on the posterior surface of the broad ligament.

At the base of the broad ligament of uterus, there are connective tissue bands that contain smooth fibers, forming the cardinal ligament on both sides of uterus. This ligament contributes to the fixation of the uterus and vagina. The Fallopian tube lies between the layers of the upper border of the broad ligament. The area of the broad ligament between the Fallopian tube and the mesovarium is called the mesosalpinx, which encloses the ovarian fimbria, the epoophoron, and the paraoophoron. The round ligament of the uterus can be seen on the anterior surface of the beginning of the broad ligament.

Below, drawing of the human female reproductive organs (posterior aspect), exhibiting the uterus, Fallopian tube, and the ovary being contained by the broad ligament of uterus.

Epoophoron

The epoophoron (parovarium) is a conglomerate of remnant tubules which lie in the lateral portion of the mesosalpinx among the peritoneal layers of the uterus broad ligament, between the Fallopian tube and the ovary.

The epoophoron consists of a fine network of tortuous, transverse tubules and longitudinal ducts. The tubules are blind and have no function as they are vestiges of the caudal part of the mesonephros (excretory organ), extending from the hilum of the ovary to the Fallopian tube. They open into the duct of the epoophoron, which is a remnant of the mesonephric duct.

Below, schematic picture of female reproductive organs, exhibiting the epoophoron, which is also called parovarium.