Flexor Digitorum Brevis

The flexor digitorum brevis is a short, thick muscle located in the sole of foot, right under the plantar aponeurosis (deep fascia). It originates by a short strong tendon from the medial tubercle of the calcaneum bone and the plantar aponeurosis. Then it extends forwards, with the muscular belly ending up in four tendons, which are lodged in the synovial canal with the flexor digitorum longus tendons. Right in the region of the proximal phalanges of the lateral four toes, each of the four flexor digitorum brevis tendons splits into two slips that are inserted into the base of the middle phalanges of these toes.

Action/Function

This plantar muscle flexes the middle phalanges of the lateral four toes, closing them tightly. Although it is not as dexterous and practical as the flexor muscles of fingers and hand, it is very useful for neurologists when performing the Babinski reflex test on adults to see if there is a neurological degeneration or damage of spinal cord motor fibers; when it does not contract and the toes remain extended and open, then it is a sign that there is damage to spinal cord.

Innervation

The flexor digitorum brevis is innervated by branches of the medial plantar nerve, which originates from L5, S1 roots.

Blood Supply

It is supplied by arterial branches of the lateral and medial plantar artery, which arise from the posterior tibial artery.

Below, image of plantar (sole) surface of human foot, showing the flexor digitorum brevis muscle

 

Palmar Interossei

The palmar interossei are three small, spindle-shaped muscles which lie on the interosseous spaces of metacarpal bones. The first one is located on the radial portion of palm; it arises from the ulnar side of second metacarpal bone (index finger) and it is inserted into the ulnar side of the metacarpophalangeal joint of index finger and its dorsal aponeurosis.

The second and third palmar inertossei muscles are located on the ulnar portion of hand. They originate from the fourth and fifth metacarpal bone, respectively, and are inserted into the radial side of the capsule of the metacarpophalangeal joints of the ring and little finger. Meanwhile, the first (thumb) and third metacarpal bone (middle finger) bear no palmar interossei muscles.

Action/Function

They flex the proximal phalanges of the index, ring, and little finger. They also extend their middle and distal phalanges.

Innervation

They are innervated by secondary branches of the ulnar nerve, whose root fibers spring from C8 andT1 of brachial plexus.

Blood Supply

These three small muscles receives oxygen-rich blood from branches of the deep palmar arch, which is a curving arterial branch communicating the radial and ulnar artery.

Below, picture of deep muscles of hand, showing the palmar interossei and the dorsal interossei muscles of right hand.

Insulin vs Glucagon

In the insulin vs glucagon comparison, we can say they are both hormones secreted by the endocrine pancreas. However, the similarity ends there, because they perform different metabolic functions. Although most people have only heard of or read about the former, because almost everybody knows that those patients who suffer from type II diabetes have too much insulin in their bloodstream, the latter role during time of fasting is extremely important.

The reason why almost no one has ever heard of glucagon is because our modern lifestyle has become contaminated by carbohydrates; too much carbs, which are the results from the development of modern agriculture; and modern lifestyle also implies a sedentary life. And you eat too much carbs and lead a sedentary life, your pancreas won’t secrete this hormone. To summarize, insulin vs glucagon means either gaining weight or losing weight; thus, the former means metabolic diseases, while glucagon paves the way for a healthy cellular respiration.

Insulin

This hormone is produced by the beta cells of the islets of Langerhans. Whenever you eat carbs, your glucose (sugar) levels in your bloodstream go up, and since it is bad for your body tissues, glucose has to be lowered to normal levels. So, insulin is secreted and pumped into your bloodstream. Then this hormone induces your body cells to take up more glucose out your blood, and the excess glucose molecules that are not used by your tissues cells are absorbed by the adipose cells and converted into triglycerides and stored as such in their cytoplasm, making you fat or gain weight.

But too much insulin is inflammatory to your body tissues as your body cells become resistant to it and they no longer pay attention to its presence. Thus, in time your glucose levels remain high, which is also inflammatory, meaning they both do damage to your body tissues. This is the case when somebody suffers from diabetes. The culprit behind it is called carbohydrates.

Glucagon

When you are fasting or when you are working out, your glucose levels in your bloodstream drop naturally without the intervention of insulin because you are not eating carbs and your muscle cells are using up a lot of glucose to produce ATP. As your sugar levels drop, glucagon is produced by the alpha cells of the islets of Langerhans of the pancreas and then released into your bloodstream, inducing the liver to break down glycogen into glucose (glycogen is stored in this organ and muscle cells as an energy reserve tank). But if you keep fasting or working out, you run out of glycogen too; if this is the case, your pancreas keep secreting glucagon, which activates an enzyme called lipase.

Trapped in between your adipose (fat) cells, lipase triggers the release of triglycerides from your fat cells into your bloodstream, converting them into the smaller molecules of glycerol and fatty acids. These moles travel into the liver through the hepatic artery proper where they are metabolized into ketone bodies that are used as fuel by the cells mitochondria, replacing glucose.

To make it brief, glucagon makes your body burn the fat you have stored around your waist as you lose weight. And when you lose weight, it means that your body cell mitochondria are using ketone bodies (which derive from fat) as fuel instead of glucose. And when this happens, you have a healthy and more efficient cellular respiration. In other words, the possibilities for you to develop either type II diabetes and cancer are 0 (zero).

Insulin

Insulin is a hormone released by the beta cells of islets of Langerhans in the endocrine pancreas. Along with glucagon, it plays a key role in keeping normal sugar levels in the blood. When you eat too much carbs and your glucose level goes up, it lowers it by inducing the liver hepatocytes to convert the excess glucose into glycogen and molecules of triglyceride. The former is the body first energy reserve, while the latter are stored in adipose cells as the second fuel reserve.

Insulin is a protein polypeptide hormone, whose structural unit is a monomer, with a molecular weight of about 6,000. However, its molecular weight may increase to 12,000 or more due to the fact that the insulin molecule can combine different number of monomers, depending on varying conditions. Every monomer consists of 51 amino acids, which are organized into two peptide chains, A and B, joined together by two disulfide bridges.

When the pancreas does not produce enough insulin, then your sugar levels will shoot up and will remain in dangerous high levels. Insulin insufficiency is called diabetes. High levels of glucose is inflammatory and, in the long run, it damages the endothelial lining of arteries and arterioles. Thus, the function of insulin is essential for a normal energy metabolism and health.

Remember: sugar in the bloodstream is called glucose, which is monosaccharide. A monosaccharide is the simplest form of carbohydrates. Table sugar, on the other hand, is disaccharide, which is made up of glucose and fructose.

Ketolysis

Ketolysis is the degradation (the breaking down) of ketone bodies into simpler molecules to be employed as fuel in the production of ATP by the cell mitochondria. This metabolic pathway only takes place in the absence of glucose, during starvation or when the individual is on a ketogenic diet.

Metabolic process

The ketone body Beta-hydroxybutyrate is produced by the liver cell mitochondria from fatty acid, which in turn derives from the saturated fat we eat or from the adipose tissue we have as a store of energy in our body. Once this ketone body is released, it travels in the bloodstream and gets into our brain through the brain blood barrier. There, it gets into the nerve cell cytoplasms where it is degraded first into acetoacetate, through the intervention of ß-hydroxybutyrate Dehydrogenase enzyme, and then into acetoacetyl CoA thanks to the CoA Transferase (Thiophorase) enzyme. The CoA (coenzyme A) is added to acetoacetyl by the molecule succinyl CoA, which is an intermediate of the TCA cycle.

Finally, acetoacetyl CoA gets split into two molecules of acetyl CoA; this is done by the Thyolase enzyme. Each of the acetyl CoA can be used in the TCA cycle for the production of ATP (Adenine TriphosPhate), yielding 10 ATPs each.

Below, a complete diagram of ketolysis

 

Brown Fat vs White Fat

Brown fat vs white fat; which one reflects a healthy metabolic state? An which one is a sign of bad metabolism and future heart condition? People do know that there is an adipose tissue, but most of them do not know that there are two types: the brown and the white. The cells that make them up are in a different metabolic states and gives the human body two different shapes. One grows proportionately on our body, the other builds up around our waist, giving us a bulging belly.

The healthy fat

We can say that brown fat is a healthy kind of fat, for its adipose cells contain mitochondria, the cell organelles that produce ATP from either glucose or ketone bodies. So, this type of adipose cells are always providing us with heat as they are constantly burning fuel to produce ATP, the energy that we need. Thus, they are called thermogenic. So, these adipose cells do not bulge and swell up with triglycerides, for they do not store fuel but burn it constantly to manufacture ATP. Since, they provides us with heat, the immune system function also improves. Brown fat is related to our diet and lifestyle as it could be found in the body of the primitive hunters and shepherds community where they do not eat starches and sugar, but only animal fat and meat.

You will develop brown fat if you get in the metabolic state of ketosis. And that only happens if you do not eat carbs, and when you eat only animal fat, meat, eggs, butter, nuts, that is to say the hunter's diet; which is the ketogenic diet. Today we see brown fat in babies, who are surrounded by pads-like brown fat all over their bodies, for they consume an enormous amount of saturated fat when they eat their mother's milk, which contains up to 50% fat. That is the main reason why babies do not shiver or shake when exposed to lower temperatures, for they are surrounded by brown fat, like the Inuit people's (Eskimos) body, at least until the 1980's when they were still pure hunters.

The unhealthy fat

Nowadays white fat is a symbol of sedentary life and junk food, such as starches, table sugar, fructose, in other words carbohydrates, which are massively provided to us by modern agriculture and the milling industry that produces refined flour. The adipose cells in this type of fat do not have mitochondria, so they do not produce ATP and heat. Their only function is to store triglycerides in great amount, getting stuffed and swollen with them.

White fat builds up mainly around our waists when glucose levels in our bloodstream go up beyond the normal limit. Since too much sugar in our blood is inflammatory, it has to be lowered. Thus, pancreas insulin make the cells in our body tissues convert the excess glucose into molecules of triglycerides, which are later absorbed by the adipose cells in the adipose tissue. Thus, white fat is related to coronary diseases, diabetes, and Alzheimer disease.

In the brown fat vs white fat comparison. It is clear that brown fat was the fat that covered the body of our ancestors. The hunters that lived during the last glacial period.

By Carlos B. Camacho (biological anthropologist)

Origin of Mitochondria

The origin of mitochondria goes back in time two billion years, when a cell engulfed another one. Yes, a mitochondrion is one pro-karyotic cell living in perfect symbiosis in an eukaryotic cell. This endosymbiotic relationship allowed the proliferation of multi-celled organisms.

Endosymbiotic origin of mitochondrion

In 1970, biologist Lynn Margulis published an endosymbiotic theory of the mitochondrion. About two billion years ago, a cell penetrated another cell and began living forever inside the cytoplasm of its host. This is the perfect symbiosis in biology which made possible the evolution of life on Earth, with single cells evolving into multicellular organisms. This is thanks to the capacity of the intruder cell (the mitochondrion) of consuming free available fuel stuff (pyruvate and acetyl CoA, which are the byproducts of glycolysis and ketolysis) in the cytoplasm, converting them into ATP. Thus, the new energy being produced in great amount influenced the host cell nucleus DNA to split in two, causing the cell to divide into two and proliferate.

As you know, the mitochondrion is an important eukaryotic cell organelle, which generates the vital energy needed by the cell in the form of ATP (Adenosine TriPhosphate) through what is known as cellular respiration. This is the reason, it is often referred to as the cell power plant. The word mitochondrion was first employed in 1898 by the German microbiologist Carl Benda, with “mitos” meaning thread, and “chondros” meaning granule. However, it had already been discovered in 1857 by the Swiss scientist Albert von Kolliker using an optical microscope.

How many mitochondria are there in a cell?

Depending on the type of cell and tissue, the number of mitochondria in their cytoplasm ranges from zero to thousands, with the red blood cells having none and a hepatocyte having more than two thousands.

This very reasonable and logic theory is based on the fact that the mitochondrion has its own DNA material as well as its own ribosomes and membranes that isolate it. When a mitochondrion has good health, that is when it runs efficiently producing enough ATP, its DNA will divide in two, splitting the mitochondrion into two mitochondria. This process is called mitochondrial bioneogenesis, which is only possible in the absence of deleterious free radicals. The more mitochondria in a cell, the more ATP per second there will be; in other words, the faster the metabolism will be.

Cell Chemical Reactions

The cell chemical reactions take place millions of times every second in our body tissue. In these reactions there are transport of material, production of energy, formation of structures, such as the molecules of proteins, and removal of wastes. This is what makes living things unique among all forms of matter, having the capacity to interact with the environment and manipulate matter and energy, with the help of enzymes, to transform them into useful products for growth and multiplication.

All cells take in essential substances, such as water, oxygen, and nutrients from their external environment. Inside the cells, these substances undergo chemical reactions of several types to break down substances, synthesize others, repair defective structures. These fast chemical processes also provide energy for these life-sustaining activities as well as others, such as reproduction, while surplus byproducts of these reactions are eliminated as wastes. The energy needed by eukaryotic cells to keep themselves alive and carry out many chemical reactions is known as ATP (Adenosine Triphosphate), which is produced from either glucose or ketone bodies during one of these reactions.

The intake, breaking down, and transformation of substances are called metabolism, which needs special enzymes that act as catalysts, causing and speeding all these cell chemical reactions that take place in the cell. The substances involved in the metabolism are elements, such as oxygen, and molecules, like water, salts, glucose, and ketone bodies. An element is a substance that cannot be broken down into simpler substances, for example oxygen, calcium, sodium, iron, etc, while molecules can be broken down and transformed, indeed, into simpler molecules or elements.

Brain Inferior Surface

The brain inferior surface is very irregular and contains a series of anatomical structures. These are the primitive parts in the evolution of Homo sapiens central nervous system. Although some of them are primitive, they are vital and essential for life. Looking at it with your naked eyes, you will notice the complex network of arterial blood vessels that supply the encephalon (all the CNS parts contained within the skull). On the other hand, the superior surface of the brain is regular, in a sense that it only includes the cerebral cortex, as it is convex like a dome.

Anatomical Description

The brain inferior surface lies on the sphenoid and inferior part of occipital bone. Not only do these bones have foramina (holes) for nerves, arteries, and spinal cord, but they also have irregular features, such as the sella turcica, on which the pituitary gland sits. But the three prominent features that make this aspect of the brain very irregular are the cerebellum, the brainstem, and the inferior portion of the temporal lobes, which curve around and extend towards the midline.

Below, you can see the inferior surface of brain. Every part is labeled and marked with arrows. There, you can see the allocortex, which include the paleocortex (rhinoncephalon: olfactory brain and olfactory bulb), the archicortex (hippocampus), and the parahippocampal girus. All these primitive structures are located on the inferior-posterior surface of the frontal lobes, and on inferior-medial surface of both temporal lobes.

At the center of the inferior aspect of encephalon, you can see a thick, cord-lice that extends downwards; it is the brainstem, which is made up of the midbrain, pons, and medulla oblongata. In front of the brainstem, there is the mammillary body, the tuber cinereum, the infundibulum, and the optic chiasma. In front of them, on the inferior frontal lobe, you can see the olfactory sulcus and the straight gyrus, lying medially. Finally, located behind the brainstem and bellow the cerebrum occipital lobe, there is the cerebellum, which is a massive structure of the encephalon, which functions a center of motor movement coordination.

 

Below, brain inferior surface, with the main arteries and cranial nerves labeled

 

Brain Longitudinal Fissure

The brain longitudinal fissure is the deepest groove of the cerebral cortex. It runs from front to back, dividing the cerebrum lengthwise into two encephalic halves; the left cerebral hemisphere, and the right hemisphere. However, this sulcus (groove) does not go all the way down as it ends up at the corpus callosum, which is the thick white bundle of myelinated fibers that connect them to one another.

The longitudinal fissure of the human brain measures between 3 and 5 cm deep. Inside it, there are the two cerebral cortex internal surfaces, one for each hemisphere. The internal (medial) surface, like the external surface of cortex, is characterized by a series of secondary grooves called sulcus (plural sulci), which mark off smaller structures called gyri (sing. gyrus), such as the cingulate gyrus which surrounds the corpus callosum.

The brain longitudinal fissure allow the partial entrance into the cerebrum by the three layers of the meninges; dura mater, arachnoid, and pia mater, and, with them, the cerebrospinal fluid.

Below, superior view of human brain and its two hemispheres divided by the longitudinal fissure.

 

Cerebral Cortex Structure

The cerebral cortex structure in the human being is composed of six layers of neurons and neuroglia cells. The Nissl silver impregnation of cell bodies in the early 20th century allowed scientists to make a histological division of the neocortex. It was done according to the dominant structure of each layer. Thus, the following layers were differentiated:

I - Molecular layer: it is the outermost layer, with relatively few nerve cells.

II - External granular layer: it is made up of mostly stellate neurons, with scattered small pyramidal nerve cells.

III - External pyramidal layer: it consists almost exclusively of small pyramidal neurons.

IV - Internal granular layer: it is formed by stellate and small pyramidal neurons.

V - Internal pyramidal layer: it is composed of large pyramidal neurons, which are known as Betz cells.

VI - Multiform layer: it is the innermost layer, which is made up of neurons of varied shapes and sizes.

Nerve tissue support cells (neuroglia), such as astrocytes and oligodendrocytes are found in every layer as they are inherent part of the cerebral cortex structure. Meanwhile, cortical areas that are concerned mainly with information processing are rich in granule (stellate) cells. The granular layers of these regions are also exceptionally thick. Areas, in which nerve impulses are transmitted out of the cortex (primary motor of frontal lobe) are distinguished by layers of large pyramidal neurons (Betz cells).

Image of layer III pyramidal neuron of pre-frontal cerebral cortex.

Cerebral Dominance and Language

Cerebral dominance and language are intimately related. Although the two cerebral hemispheres appear to be nearly symmetrical, the cerebral dominance of one half of the brain over the other is evident as it is where the language centers are located. The left cerebral hemisphere has a dominance over the right in 90% of people with regard to language comprehension and motor production (Wernicke's and Broca's areas respectively), with each having anatomical, chemical, and functional specializations.

Since the left cerebral hemisphere is highly specialized in language understanding, it is the side of the brain where the values or moral codes of a given culture is deeply internalized; thus, there is also a dominance of the left with regard to social adaptation; so, it has the cultural logic. We must remember that the left hemisphere deals with the somatosensory and motor functions of the right side of the body, and vice versa, due to the pyramid nerve crossing in the medulla oblongata.

Damage to the temporal region known as Wernicke’s area generally results in aphasias that are more closely related to comprehension—the individuals have difficulty understanding spoken or written language even though their hearing and vision are unimpaired. Although they may have fluent speech, their speech is incomprehensible. In contrast, damage to Broca’s area, the language area in the frontal cortex responsible for the articulation of speech, can cause expressive aphasias—the individuals have difficulty carrying out the coordinated respiratory and oral movements necessary for language even though they can move their lips and tongue. They understand spoken language and know what they want to say but have trouble forming words and putting them into grammatical order.

The potential for the development of language specific mechanisms in the left hemisphere is present at birth, but the assignment of language functions to specific brain areas is fairly flexible in the early years of life. Thus, for example, damage to the perisylvian area of the left hemisphere during infancy or early childhood causes temporary, minor language impairment, but similar damage acquired during adulthood typically causes permanent, devastating language deficits. By puberty, the transfer of language functions to the right hemisphere is less successful, and often language skills on this side are lost permanently.

Cerebral Hemispheres

The cerebral hemispheres are the two longitudinal halves into which the cerebrum is divided. The are separated from one another by the longitudinal fissure, which is deep, and run from front to back. However, they are also connected to one another by the corpus callosum. These anatomical halves are the left cerebral hemisphere and the right cerebral hemisphere.

The corpus callosum that join them is a thick bundle of white matter made up of myelinated axons connecting the left hemisphere cortex to the right hemisphere cortex. Each cerebral hemisphere controls one side of the body, but the motor controls are crossed: the right hemisphere controls the left side of the body, whereas the left hemisphere controls the muscular contractions of the right side of the body.

Differences and Function

Although the cerebral hemispheres are very similar in appearance, they differ in their function and the size of some structures. The left hemisphere is analytical, logical, and linear, whereas the right is wholistic, intuitive, creative and imaginative. But the most concrete evidence of hemispheric lateralization for one specific ability is language.

The major areas involved in language skills, Broca's area and Wernicke's area, are in the left hemisphere. Perceptual information from the eyes, ears, and rest of the body is sent to the opposite hemisphere, as motor impulses are sent out to the opposite side of the body; this is due to the crossing over of motor fibers at the pyramid of the medulla oblongata.

Below, a picture of the cerebral hemispheres and the longitudinal fissure. Superior view.

Right Cerebral Hemisphere

The right cerebral hemisphere is one of the two longitudinal halves into which the cerebrum is divided. Like the left, it is divided into four lobes: the frontal, temporal, parietal, and occipital. The right hemisphere motor strip controls the muscular movement of the left side of the body; that is to say that left-handed people are lateralized towards the right hemisphere.

The right cerebral hemisphere is connected to the left hemisphere through the corpus callosum, which is a band of white matter composed of myelinated fibers. The right hemisphere is linked to the basal ganglia and thalamus through myelinated axons which go from its frontal lobe to these regions.

The right cerebral hemisphere functions differently from the left, as it seems to have a complete different way of processing the data, or different approach to reality. It is wholistic, which means that the right hemisphere does not analyze incoming information, breaking it into parts, but synthesize it into one indivisible whole. It is also intuitive and imaginative.

The right cerebral hemisphere; external, lateral side. You can see the brainstem and the cerebellum below it.