Written by Franzgayle T. Husain

Reviewed by Dr. Reuben J C. Los Baños, Ph.D.

The word histology comes from the Greek word “histo,” which means tissue, and “logos,” which means study. Hence, medical histology refers to the study of the structure of tissues. It examines tissues, cells, and organs from a morphological and molecular standpoint.

Before we delve more into histology, let us first understand the concept of cells and tissues.

Cells and Tissue

The human body is consists of trillions of cells that work various functions. It serves as the fundamental unit of life and is essential for the survival of individuals. When a group of cells has the same structure and function, they form tissues.

Tissues play a significant role in various activities of your body. Different types perform distinct functions, including secretion, movement, and strength. Classification of tissue forms four groups– nervous, Muscle, epithelial, and connective tissue. Once they get damaged by different diseases, it will put your life at risk.

Histology is the opposite of gross anatomy because it focuses more on the cellular level. Medical professionals study the role and anatomy of tissues under the microscope. They examine how it interacts with your body systems and how diseases affect them.

History of Histology

The scientist Marie François Xavier Bichat first did the study of tissues. He was the one who used the term tissue in an anatomical sense. He discovered different weaves and textures in the body and named them layers of tissues.

Bichat was able to discover these during his dissection for his anatomical studies. Bichat then created a classification of these issues based on their distinct textures. His workings made him the father of modern histology and descriptive anatomy.

What is histology used for?

All multicellular organisms possess tissues and organ systems. Thus, scientists examine cells to understand concepts and answer questions in many fields.

Medicine

In medicine, it is vital to understand the normal to identify the abnormal. Using histology allows you to detect any abnormalities in your tissues. Whenever there is a disruption of your cells, it affects your body’s activities. This explains why medical professionals conduct histological tests to diagnose certain diseases.

Agriculture

Examining plants in histological viewpoints helps in identifying chemicals present in the soil. These hazardous chemicals can put your plants at risk. But with histology, you can prevent potential dangers from diseases. Additionally, this can aid in deploying the best control methods in the longer term.

Autopsies

Microscopic tissue examination helps in explaining the cause of death of some patients. This is applicable when macroscopic studies fail to provide specific diagnostic pathology. Microanatomy may disclose information about a person’s environment after they die.

How is histology performed?

In every laboratory work, a specific person works on certain procedures. A histotechnologist examines preserved sections and smears of tissues. They stain these samples and place them under a microscope.

Histotechnologists make sure that a tissue section is of good quality. This allows various interpretations of any microscopic cellular changes. They preserve and process the sample’s structures by following these steps:

1. Fixation. Histotechnologists fix the sample as soon as it arrives in the laboratory. They put it in a liquid fixing agent like formalin. The formaldehyde solution penetrates your specimen, resulting in chemical and physical changes. This helps in preserving the tissue and protecting it from the following stages.

After fixation, the histotechnologist will trim and place your sample in labeled cassettes. Generally, this stage is the crucial part of preparing histological sections. Once there is a delay of fixation, your specimen may become damaged.

2.       Dehydration

Melted paraffin wax is hydrophobic. Thus, it is essential to remove the water first from the specimen. To do this, soak your sample in an increased concentration of alcohol solution. In this way, you can avoid distortion of tissue and remove water and formalin.

3.       Clearing

After dehydration, the specimen is immediately transferred to an intermediate solvent like xylene. This type of solvent is soluble in both ethanol and paraffin wax. Using this will remove the amount of fat present, allowing wax infiltration.

In this stage, the solvent xylene replaces the ethanol in the specimen. But the molten paraffin wax will take its place once the tissue becomes embedded.

4.       Infiltration

Now that the tissue has cleared, a histology wax can infiltrate your specimen. Wax, like paraffin, is liquid at 60°C. Thus, you must let it cool to solidify and allow thin sectioning.

5.       Embedding

Embedding happens after infiltration with wax. You must put the tissue in a mold that contains molten wax. Placing resin on it creates a big solid tissue block. This can be clamped into a microtone and sectioned once it has changed.

In embedding, you must ensure that the specimen is in the correct orientation in a mold. Any errors may result in damaged elements during microtomy.

6.       Section-cutting

Histotechnologists can now trim your tissue specimen into thin sections. They can put it in a microscope slide. They use an instrument called microtome to perform section cutting. It must be in thin sections in the form of a ribbon.

Each routine has its required thickness of your tissue. Most specimens for routine hematoxylin and eosin (H&E) are 3-5 μm in thickness. Meanwhile, specimens for amyloid deposits must be at 8-12 μm.

After cutting, you must transfer these sections to a warm water bath to allow them to float on the surface. You can now pick them up and place them under a microscopic slide.

7.       Staining

Most of your cells appear colorless and transparent, so you must stain them to produce contrast. Using histochemical stain provides a more precise visualization of your specimen. It makes the structures and features of your tissues more visible and easier to examine.

How does histology help diagnose an injury or disease?

Understanding the normal anatomy of your tissues is one way of detecting infection. Healthcare providers interpret the changes that arise caused by diseases. Each condition generates distinct changes of characteristics in your tissue structure. Thus, a histological examination can provide information that helps diagnose illness injuries.

Histopathology, a branch of histology, tackles tissues affected by diseases. Damage of cells and inflammation reactions indicates signs of viral infection. Pathologists look for any changes in your cells that might explain your conditions.

Your tissues contain evidence of a pathological process. Interpreting it provides crucial information for your diagnosis and treatment of your disease. Although some changes are vague, there are others that are obvious.

Cancer is a known disease that results from mutations in your cells’ genes. Histopathologists examine your cells from suspicious lumps in your body. They perform a biopsy to provide information about the type of cancer you might have. It is also one way to determine whether your cancer is malignant or benign.

You must remember that histopathology results are only one piece of the puzzle. Pathologists perform laboratory procedures to identify the virus and confirm the diagnosis. These procedures include immunohistochemistry (IHC), serology, and molecular biology.

What is the difference between cytology and histology?

Cytology and histology both study human cells and tissues. But they differ when it comes to the scope of their study. The former focuses on the structure of a single cell or a small group of cells found in body fluids. While the latter investigates the entire section of human tissue.

Cytology or otherwise known as cytopathology, examines your cells for diagnostic purposes. Medical professionals like pathologists observe any abnormalities in your cells. Hence, they use cytology tests to analyze cells for diagnosis. This explains why cytology is used for screening and diagnosing cancer.

Generally, there are two branches of cytology–exfoliative cytology and intervention cytology.

Exfoliative Cytology

Exfoliative cytology is when a pathologist examines cells shed by your body or scraped from the surface of your epithelial tissue. Smears that have been spontaneously shed or manually removed from epithelial and mucous surfaces may contain these exfoliated cells.

These are some exfoliative cytology that deals with manual tissue brushing.

• Gynecological samples
• Gastrointestinal tract samples
• Skin or mucus samples

There are three examples of exfoliative cytology that involve collecting tissues or fluids that your body sheds. These are:

• Respiratory samples
• Urinary samples
• Discharge or secretion samples

Intervention Cytology

Medical professionals intervene with your body to get cells for cytology tests. This means that they will perform procedures that involve piercing your skin to get samples of your cells. Hence why its name is “Intervention Cytology.”

Fine needle aspiration (FNA) is the most used method of intervention cytology. The FNA is helpful for evident lesions. A medical professional injects a needle into the lesion or on the area that draws out a fluid. They may do a fine-needle aspiration in the following parts of your body:

• subcutaneous soft tissue tumors
• thyroid
• lymph nodes,
• salivary glands
• breast.

What is the role of histology in medicine?

Tissues act as building blocks of your body. It forms your organs as it works together. Thus, histology will help you understand and predict the activities of your organs. This is important in the field of medicine, especially for diagnosing diseases. Medical students can also get a better knowledge of cellular biology.

Studying how these cells work provides different insights into the development of complex organs and your organ systems. The information you gain allows you to monitor how your body reacts when certain diseases or treatments affect you.

Diseases occur when there is a rupture of your cells due to infection. Some disorders involving infected connective tissue include lupus and rheumatoid arthritis. They arise when your collagen and elastin become swollen. This then caused harm to the proteins and body parts they connect.

Medical professionals use histology to study the development of these diseases. Observing their progress helps them to identify suitable treatments. This is also one way of comparing the efficacy of different medications and lifestyle choices on your body.

Furthermore, histological studies contribute to the advancement of medical science. Researchers use tissues to test discoveries and verify theories about drug medication. As for medical students, this widens their knowledge of cellular biology and pathology.

Is medical histology hard?

In research conducted by Garcia et al. (2019), they found that undergraduate biology students find it hard to study histology. The nature of the topic and its terminology made it difficult for them to comprehend. But for P. del Rio-Hortega (1933), histology is an exotic meal where you become addicted as you taste it repeatedly.

Medical schools integrate histology into their curriculum to provide information about biological tissues, animal growth, physiology, and tissue diseases. It also continues to deliver different findings in clinical medicine and advanced research.

Unfortunately, medical students find this complex due to insufficient time and attention. Students suggest that teachers should base their teaching on practical tasks. They must also add anatomy subjects and make histology education more engaging.

Learning histology is challenging, but constant reading will make you appreciate it more. One cannot know medicine well if they have no rich perspective on the tissue-level organization.

References

García, M., Victory, N., Navarro-Sempere, A., & Segovia, Y. (2019). Students’ Views on Difficulties in Learning Histology. Anatomical sciences education, 12(5), 541–549. https://doi.org/10.1002/ase.1838

Sorenson, R. L (2008). Atlas of Human Histology: A Guide to Microscopic Structure of Cells, Tissues, and Organs. Retrieved from https://histologyguide.com/about-us/sorenson-atlas-of-human-histology- chapters-1-and-14.pdf

Hussein IH, Raad M, Safa R, Jurjus R, and Jurjus A (2015). Once Upon a Microscopic Slide: The Story of Histology. J Cytol Histol 6:377. doi:10.4172/2157-7099.1000377

Open University. (n.d). Functions of tissues. Retrieved

from https://www.open.edu/openlearn/mod/oucontent/view.php?id=65376&section=1

Elliot, M. Miller, K. Pins, M. and Watson, Mark. (2004). What is a tissue? Retrieved

from https://www.roswellpark.org/sites/default/files/What_is_Tissue amp Why_is_it_Important.pdf

Wood, R. (1996). Sustainable agriculture: the role of plant pathology. Canadian Journal of Plant Pathology, 18(2), 141–144. https://doi.org/10.1080/07060669609500638

Lane, A. Buckley, G. McLaughlin, K. Whitehous, L. Knapp, S. and Cotoia, A. (2018). Histology. Retrieved from https://biologydictionary.net/histology/

Helmenstine, A. (2019). What Histology Is and How It’s Used. Retrieved

from https://www.thoughtco.com/histology-definition-and-introduction-4150176

Cleveland Clinic Organization. (2021). Cytology. Retrieved

from https://my.clevelandclinic.org/health/diagnostics/21714-cytology

Bruce-Gregorios, J. B. H., & Faldas, M. (2017). Histopathologic Techniques. Independently published.

Brown, R. (n.d). Histopathology. Retrieved from https://www.rcpath.org/discover-pathology/news/fact- sheets/histopathology.html

The Open University. (2016). Introduction to histopathology. Retrieved from https://www.open.edu/openlearn/mod/oucontent/view.php?printable=1&id=2312

Written by Elijah Dave M. Cordova

Reviewed by Dr. Reuben J C. Los Baños, Ph.D.

Neurotransmitters allow brain cells to communicate with each other. They enable the transfer of information across gaps among neurons. Among the major neurotransmitters in the CNS are acetylcholine and catecholamines. Serotonin and GABA (γ-aminobutyric acid) complete the list.

Before we go into each of them, let us first classify neurotransmitters.

1. Excitatory. They cause neuron firing of an action potential to a receiving neuron.
2. Inhibitory. It is the opposite of excitatory action. It inhibits the firing of action potentials across synapses.
3. Neurohormones. Neurons synthesize and secrete them into the bloodstream. Oxytocin and vasopressin are examples.
4. Neuromodulators. They influence other neurotransmitters and affect several neurons at once.

Acetylcholine (Ach) is a neuromodulator that affects your attention and memory. It also impacts how you learn things through integration. Ach cells originate in your brainstem and midbrain. They then travel to every area of the CNS through synapses.

In the Peripheral Nervous System (PNS), Ach is an excitatory neurotransmitter. Neuromuscular junctions often use Ach to send signals between your nerves and muscles. For example, acetylcholine signals parasympathetic smooth muscle movement.

Choline acetyltransferase catalyzes the production of acetylcholine. It separates the acetyl part of acetyl coenzyme A (acetyl-CoA). It then joins this acetyl part to choline to form the product.

Catecholamines are neurohormones crucial to maintaining homeostasis in your body. Your adrenal glands on top of your kidneys produce them. Dopamine is a catecholamine. So, too, are norepinephrine (NE) (i.e., noradrenaline (NA)) and epinephrine (adrenaline) catecholamines.

Dopamine is a neuromodulator across many brain regions. One of its main functions is in the prediction and learning of rewards. Axons of your midbrain house dopamine.

L-amino acid decarboxylase (i.e., DOPA decarboxylase) synthesizes dopamine from L-Dopa. It is a precursor chemical. This same enzyme also facilitates the synthesis of histamine and serotonin, another neurotransmitter.

Dopamine β-hydroxylase synthesizes noradrenaline from dopamine. Its cells originate from your brainstem. Its main function is regulating the sympathetic nervous system. It helps regulate your body systems based on specific situations.

You can think of it as what regulates your arousal to specific situations. In times of stress, norepinephrine increases your alertness or wakefulness. It is so that you can respond in a proper manner and ensure your survival.

Epinephrine is the hormonal equal to norepinephrine. They work together to form your “fight or flight” response which you need to survive.

During stress, norepinephrine constricts your blood vessels to raise your blood pressure. Meanwhile, epinephrine forces your heart to contract with much greater strength. Its actions increase blood pressure and cardiac output.

Your body releases noradrenaline to your blood circulation at a low dose. Your body releases adrenaline in stressful moments alone.

Serotonin uses the amino acid L-tryptophan in its synthesis. Hence, it is also known as 5- hydroxytryptamine (5-HT). Most of it is in the raphe nucleus of your brain stem. Serotonin also cannot pass through your blood-brain barrier. It performs its functions in your brain alone.

Serotonin, like dopamine, is a neuromodulator. Unlike adrenaline and noradrenaline, it does not have a specific function. Instead, it affects many brain regions and body systems in consequence. Serotonin affects your mood, sleep, circadian rhythms, and body temperature, among others.

GABA is a derivative of glutamate (glutamic acid), a non-essential amino acid. It is the main inhibitory neurotransmitter of your brain. This means it inhibits the transmission of messages along neural pathways. It makes sure that your brain does not send random messages.

The enzyme glutamic acid decarboxylase (GAD) synthesizes GABA from glutamic acid. It demands cofactor pyridoxal phosphate (derived from Vitamin B6) in its synthesis. As GABA increases in your brain, it inhibits the action of GAD. With this, it manages its own synthesis.

GABA-A and GABA-B are its two receptors. They act on both receiving and transmitting targets. They do this to fine-tune the responses of your CNS. GABA cells work through lateral inhibition. This mechanism ensures the highlighting of important information in your brain.

In essence, GABA blocks noise or irrelevant message transmission. GABA also promotes sleep but inhibits brain regions that promote awakening. Abnormalities in GABA contribute to anxiety disorders which unnecessary brain activity often causes.

What triggers neurotransmitter release?

You have now come to appreciate the role of neurotransmitters in your body. Now, we ask how they travel across synapses. The opening of voltage-gated calcium channels triggers the release of neurotransmitters. These neurotransmitters travel to your synapses.

Your brain cells have dendrites that receive information and axons that conduct information. A myelin sheath can protect your axons and speed up its message transmission. Degradation of this myelin sheath leads to multiple sclerosis. It leads to a lack of muscle control.

Nerve cells also have the soma or cell body. It contains all things your nerve cell needs. The information your dendrites receive may belong from the environment or other neurons. Most neurons have one axon and many dendrites. These are multipolar neurons.

Each axon terminates on the next neuron at a synapse. These synapses are less than a millionth of an inch apart. A synapse is a specialized structure for transferring information.

The tip of each axon is the axon terminal. This part of your neuron contains synaptic vesicles that house neurotransmitters. Meanwhile, the postsynaptic membrane of the target cell has receptors for those neurotransmitters.

Your axon terminal also contains voltage-gated calcium channels. An action potential travels from your dendrites to your axons. When an action potential reaches your axon terminal, it changes its membrane potential. This action potential also opens these voltage-gated calcium channels.

Now, calcium flows into your axon terminal through diffusion. This event increases the concentration of calcium in your axon terminal. This calcium causes the fusing of vesicle and axon terminal membrane proteins.

This fusion allows your neurotransmitters to communicate outside the neuron through the synapse. These neurotransmitters diffuse into the synapse and bind to target cell receptors. They fit the receptors like a key to a lock.

Three things affect this process.

The frequency of action potentials fired down your axon opens more calcium channels. More calcium would flow in the axon terminal. More synaptic vesicles would fuse with the membrane of your axons. Hence, more neurotransmitters would travel into the synapse.

The duration of action potentials fired down your axon means longer neurotransmitter release.

Third, the blockage of target cell receptors causes failure of message transmission. It can also show the presence of a disease. Myasthenia gravis is muscle weakness due to circulating antibodies that block acetylcholine receptors.

When the train of action potentials stops firing, your calcium channels will close. Calcium stops flowing into your axon. The fusion between your vesicles and axon membrane stops. Hence, there are no more neurotransmitters that travel down your synapses.

Where can you find vesicles of neurotransmitters?

Neurotransmitter vesicles are also known as synaptic vesicles. These vessels store neurotransmitters for transport across synapses. They are in the neuron region known as the axon hillock or axon terminal. This region is the release zone.

Synaptic vesicles contribute a great deal toward the transmission of neurotransmitters across neurons. They aid in facilitating the communication between the CNS and the rest of your body.

When an action potential travels down your axon terminal, it generates a set of reactions. This results in the release of neurotransmitters kept by your synaptic vesicles. These neurotransmitters travel through synapses to communicate with target cells.

Removal of neurotransmitters from the synapse entails either of the following:

1. Reuptake.

Here, uptake pumps take your neurotransmitters from the synapse. Then, your axon terminal membrane would close off. An example of this would be serotonin uptake pumps. Selective serotonin reuptake inhibitors (SSRIs) induce serotonin buildup in your body.

• Deactivating Enzymes.

These enzymes break down your neurotransmitters. An example of this would be acetylcholinesterase (AchE). It breaks down acetylcholine in your synapses. Inhibition of its action or production builds up acetylcholine in your synapse.

How does neurotransmission affect human behavior?

Everything psychological is biological. Our biological condition affects our ideas, impulses, and moods. Our neurons communicate with neurotransmitters. This communication leads to motion and emotion. They make us move and feel.

Endorphins make you feel good. They are like opium in that they associate with the control of pain and pleasure. Your systems would flood with endorphins after exercising or eating delicious food. Falling in love can make you feel good too.

Norepinephrine controls alertness and arousal as discussed in a previous section.

Glutamate, from which we derive GABA, is also a neurotransmitter. It helps manage memory. Having too much glutamate in your CNS could cause migraines or seizures. Hence, some people sensitive to glutamate avoid monosodium glutamate (MSG). It is an ingredient you can find in ramen.

Serotonin affects your feelings of hunger, your mood, and your sleep. We link depression to low amounts of serotonin. Some antidepressants like SSRIs treat depression by increasing serotonin levels in the brain.

Acetylcholine affects learning, memory, and muscle action. Deterioration of acetylcholine-producing neurons causes Alzheimer’s. It is a progressive neurological degradation due to brain degeneration.

Dopamine affects attention, emotion, and learning. It also impacts movement and pleasure. An excess of dopamine causes schizophrenia. It is a chronic psychiatric illness where you disassociate behavior, emotion, and thought. Excess dopamine also causes other addictive or impulsive behaviors.

Acetylcholine and dopamine neurotransmitters can be excitatory or inhibitory. It depends on the type of receptors they encounter.

Like neurotransmitters, hormones act on the brain. Some hormones are even identical to certain neurotransmitters. Hormones also affect our arousal, mood, and circadian rhythms. Besides this, they can impact physical growth and aid in sexual reproduction. They can also control your metabolism.

Neurotransmission occurs at high speeds. Hormones take their time and deliver slow communications through glands. Hence, hormones linger. This explains why it takes time to calm down after having a bout of severe stress or trauma.

Adrenaline works with noradrenaline for the fight or flight response.

Your endocrine and nervous systems work together to affect your behavior.

What neurotransmitter causes happiness?

Does happiness make you healthy? Does being healthy make you happy? We may go different ways here but we can agree that both are important. Hence, we now concern ourselves with what neurotransmitter causes happiness.

Seven neurotransmitters provide a general feeling of well-being. Adrenaline, dopamine and endocannabinoids are among them. So, too, do endorphin, GABA, oxytocin, and serotonin belong.

Adrenaline elicits an exhilarating feeling. It also creates a surge in energy. It makes you feel alive.

Dopamine drives behaviors driven by rewards and seeking pleasure. Several addictive drugs act on the dopamine system. These drugs block dopamine reuptake, leaving it in your synapses longer.

Endocannabinoids that include anandamide have similar effects to marijuana. They prevent anxiety and burnout. They contribute to the runner’s high you would get after sustained running.

Endorphins resemble opiates. They are painkillers in essence.

GABA creates a sense of calmness by inhibiting the firing of neurons. Benzodiazepines are anti-anxiety medications that work by increasing GABA.

Oxytocin is a neurohormone linked to feelings of intimacy and affection. Couples distant from each other for a long time have decreased oxytocin levels.

Serotonin affects your appetite, mood, social interaction, and performance. High serotonin levels mean increased self-esteem and feelings of worthiness.

Where is GABA neurotransmitter produced?

GABA is the brain’s main inhibitory neurotransmitter. It is also a major inhibitory neurotransmitter in the spinal cord. Glutamate decarboxylase uses Vitamin B6 (pyridoxine) to synthesize GABA from glutamate. GABA production happens in the brain and β-cells of the pancreas.

Several diseases exhibit GABA deficiencies:

1. Dystonia and spasticity.

Dystonia is involuntary muscle contraction. It causes repetitive and twisting motions. Spasticity refers to stiff muscles. A deficiency in GABA signaling can cause these two diseases.

• Hepatic encephalopathy.

It refers to impaired brain function due to advanced liver disease. Elevated ammonia levels can bind to a GABA complex and cause this disease.

• Huntington’s disease.

It is an inherited disease the causes the progressive degeneration of brain neurons. A lack of GABA exhibits this disease.

• Pyridoxine deficiency.

It is when your body does not have Vitamin B6 to produce GABA. Frequent seizures during infancy are common.

REFERENCES

Bergland, C. (2012). The Neurochemicals of Happiness. Psychology Today. https://www.psychologytoday.com/us/blog/the-athletes-way/201211/the-neurochemicals- happiness

Hank. (2014). The Chemical Mind: Crash Course Psychology #3 [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=W4N-7AlzK7s

Jensen, M. B. (2014). Neurotransmitter release | Nervous system physiology | NCLEX-RN | Khan Academy [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=Ac- Npt3vgCE

Pastore, R. (2020, May 7). What are the Main Neurotransmitters? PowerOnPowerOff. https://poweronpoweroff.com/blogs/guide/what-are-the-main-neurotransmitters

We hope and pray that everyone is okay in this time of great challenge. Just as the sun will continue to rise every day, humanity will always have the strength to continue even in times of great difficulty. Storms will come and go, but our faith will remain. Discovering God has always been a struggle, especially as a Ph.D. candidate trained to be skeptical about everything. Still, I have come to the conclusion that life is meaningless without God, and everything I must do in this world is to continue to know Him for it is the most worthwhile thing I can do in this world.

Written by Jean Mari A. Rojas

Edited and Reviewed by Dr. Reuben J C. Los Baños, Ph.D.

The term muscles came from the Latin word mus, which means “little mouse.” The naming of the term is because of how flexing muscles look like scurrying mice beneath the skin.

There are three types of muscles:

1. Skeletal muscles.
2. Smooth muscles.
3. Cardiac muscles.

Some muscles line the heart (cardiac muscles) and other hollow organs (smooth muscles). Both of these muscles have involuntary movement. 

Muscles make up most of our body mass, with 600 forces making up the entire muscular system. The muscular system combines with other body systems to achieve many functions.

The primary functions of the muscular system are contractibility and movement.

The muscular system’s primary function is contractibility. With this unique function, muscles are now responsible for almost all body movement. An exception to this is cilia, flagellum on sperm cells, and activity of some white cells.  

A combination of skeletal muscles, joints, and bones produces visible motions. These actions include walking and running.

• It helps in creating a quick response to our environment.

• Skeletal muscles also generate more subtle movements. These movements include facial expressions, eye movements, eating, and breathing.

Smooth and cardiac muscles work together to ease movement in the blood vessels and heart.   

• They work together to maintain blood pressure and circulate blood to the parts of the body.

Other functions of the muscular system include:

1. Maintain posture and body position. It helps keep the body upright, erect, and in the correct position when standing or sitting.

2. Skeletal muscles also help in stabilizing joints. Muscle tendons stretch over joints and contribute to their stability.

3. Muscle activity generates heat as a byproduct. This byproduct is essential in maintaining average body temperature. Almost 85% of the heat generated is from muscle contraction. When it is cold, our muscular system will increase movement to increase heat production. This movement is shivering. Blood vessels, lined with smooth muscles, also contract to maintain body heat.

Other functions: Organ protection, vision, urination, digestion, and respiration.

How are muscles made in the body?

Myogenesis is the production of muscle tissue from stem cells. It gets produced in the mesoderm during embryonic development. Myoblasts fuse into multinucleated fibers termed myotubes to create muscle fibers. Suppose adequate fibroblast growth factor (FGF) is available during early embryonic development. The myoblasts multiply.

Muscle formation comes with three stages:

1. Myoblasts fuse into multinucleated fibers termed myotubes to create muscle fibers.

In early embryonic development, these myoblasts proliferate. But only if enough fibroblast growth factor (FGF) is present. When the FGF runs out, the myoblasts stop division.

It also secretes fibronectin onto its extracellular matrix.

2. Myoblasts align into the myotubes.

3. Cell fusion itself.

Calcium ions are critical for development. Myocyte Enhance Factors (MEFs) that promote myogenesis. Serum Response Factor (SRF) plays a central role during myogenesis. It requires the SRF to express striated alpha-actin genes. The expression gets regulated by the androgen receptor.

It means its steroids can control myogenesis.

Muscular hypertrophy refers to the expansion and development of muscle cells. It refers to a muscle size expansion that occurs as a result of training. Toning or improving muscular definition by lifting weights during exercises increases hypertrophy.

There are three Mechanisms for developing muscular hypertrophy:

1. MECHANICAL TENSION

It uses heavy load and performs exercises through a full range of motion. It considers the time the muscle spends under tension provided by the external load (barbell, dumbbell, etc.). The more time spent with the haul, the more mechanical tension gets produced.

But, tension alone won’t result in maximal muscle growth. It has to go into a full range of motion.

2. MUSCULAR DAMAGE

DOMs (Delayed Onset of Muscle Soreness) result from micro-tearing of the muscle due to damage. It gets sustained during resistance training, coming from eccentric and concentric contractions.

The initiation of muscular injury stimulates mTOR pathways, which then trigger protein synthesis. It is here that the rebuilding of the damaged muscle begins.

3. METABOLIC STRESS

‘the burn’ or ‘the pump’ repetitions. It is getting into higher repetitions and taking short breaks intervals. It creates a continuous contracting and relaxing of the muscles. It results in a blood pooling effect that makes muscular (cell) swelling. It causes a restriction in blood supply to the muscle and a shortage of oxygenated blood. It results in less oxygen to feed the body during contractions.

It causes a massive build-up of metabolites such as lactate and hydrogen ions. The anabolic impact of the metabolic stress put on the muscles leads to molecular signaling. It also increases the body’s hormonal response.

Why is protein essential for muscle?

The human body consists of about 5 to 6 kilograms of muscle protein. Protein is the building block of our muscular system.

Your body requires protein to stay healthy. Its general function is to:

• Proteins are components of blood and it carries energy and oxygen throughout your body
• Help create antibodies that fight off infections and illnesses
• Help keep cells healthy and make new ones.

Strength training activity stimulates the process of muscle protein synthesis (MPS). But, it gets enabled when you eat protein. Eating the right amounts of protein will help maintain muscle mass and muscle growth.

The amino acid leucine is abundant in “fast-digesting” proteins. It aids in the stimulation of MPS. Slow digesting proteins, such as those found in eggs and milk may help in slowing down the MPS process.

Eating reasonable amounts of protein help increase muscular strength and mass. So in trying to gain muscles and be active, make sure always to have enough protein. Also, keeping the protein intake high will prevent muscle loss during the weight loss attempts.

Best sources of protein:

High-quality sources of protein include:

•  Fish, Poultry, Beef, or pork
• Tofu
• Eggs
• Dairy products

Plant-based sources include:

• Nuts
• Seeds
• Legumes, like beans, peas, or lentils
• Grains, like wheat, rice, or corn

What is the largest muscle of the body?

The gluteus maximus is the largest and heaviest muscle in the human body.  It is the gluteal muscles’ most superficial muscle. It makes it the enormous muscle at the hip, representing 16% of the total cross-sectional area. 

Gluteal muscles:

• Gluteus Maximus
• Gluteus Medius
• Gluteus Minimus

The origins of the gluteus maximus are:

• Posterior gluteal line of the ilium;
• The posterior surface of the lower part of the sacrum;
• Side of the coccyx;
• Aponeurosis of erector spinae;
• Sacrotuberous ligament;
• Gluteal aponeurosis;
• Attaches to thoracolumbar and its associated raphe

The insertions of the gluteus maximus are:

• The enormous proximal part inserts into the Iliotibial tract. It forms the majority of the fibers.
• The other fibers insert into the linea aspera of the femur.

• The aponeurosis joins to the femur’s gluteal tuberosity.

Because of its large size, Gluteus Maximus can exert a lot of force. As one of the muscles stretching the hip joint, it also helps maintain an erect posture. The Gluteus Maximus’ primary function is to extend and rotate the hip joint to the side. Upper fibers can abduct the hip while the lower fibers can adduct it.    

The Gluteus maximus and the hamstrings work in conjunction to produce different movements:

• Extending the trunk from a flexed position by pulling the pelvis backward;
• Bending forward;
• Superior fibers of the gluteus maximus extend the knee

Gluteus maximus has stability roles:

• Maintaining upright posture;
• Supporting of the lateral knee;
• Abducting of the medial longitudinal arch of the foot

Other functions include:

• self bracing mechanisms;
• supporting body weight while sitting;
• The quadriceps femoris can get weak or paralyzed. The gluteus maximus can get trained to produce functional knee extension.

A bruise to the gluteal region is the gluteal contusion. Some get anticoagulated or on blood thinners. Large amounts of bleeding can occur within and around the muscle. It can cause severe pain and swelling. Trauma causes the most gluteal injuries, either by fall or a direct hit to the area.

While a gluteal muscle strain occurs when a muscle or tendon gets stretched or in part torn. Overuse injuries are the leading cause of gluteal muscular strain. It can result in inflammation and damage to the muscular system.

The most common injuries experienced by athletes are gluteal tendinopathies. It stems from overtraining in squats and weightlifting. Inflammation of the hip and gluteus is a common running injury.

What is the smallest muscle in the body?

The stapedius muscle is the smallest in the human body, approximately 6 mm in length. Its location is in the middle ear’s tympanic cavity. It controls the vibration of the body’s smallest bone or known as the stirrup bone.

The origin of the stapedius: Pyramidal eminence of the tympanic cavity.

The insertion of the stapedius: Neck of stapes.

Although it is the tiniest skeletal muscle, the stapedius has a vital role in sound transmission and hearing. It’s the acoustic middle ear reflex’s effector component.

The sound threshold of a healthy person with normal hearing is around 85 dB. Vocalization-induced stapedius reflex reduces sound intensities. It reaches the inner ear by about 20 decibels.

The primary function of the stapedius is to protect the inner ear from loud noises. The facial nerve’s stapedial branch innervates the stapedius muscle. These autonomic fibers allow the muscle to take part in the auditory middle ear reflex. It protects the auditory system. 

Hyperacusis is a condition that causes normal sounds to get perceived as loud noises. This condition results from the paralysis of the stapedius. It allows wider oscillation of the stapes. It heightens the reaction of the auditory ossicles to sound vibrations, causing hyperacusis. 

Paralysis of the stapedius. It results when the nerve to the stapedius, a branch of the facial nerve, or its entirety, gets damaged. Example cases are Bell’s palsy, a unilateral paralysis of the facial nerve. Where the stapedius gets paralyzed, and hyperacusis may result.

Do muscles need oxygen?

Much like every other cell and organ of the body, the muscular system needs oxygen to function.

Oxygen gets carried via red blood cells, where it binds to a protein called hemoglobin. The heart pumps the red blood cells to the parts of the body. Afterward, the release of oxygen into the cells occurs. Oxygen then gets used for breaking down molecules.

Adenosine triphosphate (ATP) is fuel for the muscles. It is a molecule that is the primary energy source to keep our body functioning. Carbon Dioxide (CO2) and water (H2O) gets produced as a result.

Whether exercising or not, oxygen gets used to breaking down glucose. And glucose creates ATP. This process of breaking down glucose is aerobic metabolism, which requires oxygen.

Muscles need the energy to produce contractions. It gets derived from the ATP that is present.

When you exercise, your muscles consume more oxygen:

• Your heart rate and breathing rate rise, drawing more oxygen into the circulation. It results in the increased production of ATP;

• Increased heart rate and breathing to remove the amount of carbon dioxide generated 

Energy can also get produced by anaerobic metabolism, a process that does not need oxygen. When your body lacks oxygen or your other systems can’t get enough oxygen to your muscles, your body will go into anaerobic metabolism. The muscles will convert the glucose you have to into lactic acid. During an intense workout, this is when your performance begins to deteriorate. Deterioration and fatigue will make you feel weary.

Researchers from Sweden’s Karolinska Institute discovered about oxygen-sensitive enzyme FIH (Factor Inhibiting HIF). FIH’s role is crucial in transitioning from aerobic to anaerobic metabolism. According to the investigators, FIH will ensure that the muscles maintain aerobic metabolism for as long as possible. It will continue to be efficient in using oxygen before transitioning to anaerobic metabolism.

After exercising, your body will be in oxygen debt. It is necessary to refill debts and replenish the oxygen in your bloodstream. Cool-down exercises are essential for replenishing oxygen levels. Afterward, consume a protein-filled snack to replace your body’s glycogen storage.

Your body’s ATP levels get restored by combining oxygen and glycogen. It also aids the liver, kidneys, and muscles in the breakdown of lactic acid.

There are three types of muscles that you can find in the human body. They are the skeletal muscles, cardiac muscles, and smooth muscles. Skeletal muscles are voluntary muscles found in the bones. Smooth muscles, also called non-striated muscles, involve slow and involuntary movement. While cardiac muscles are involuntary striated muscles found in the heart.

REFERENCES:

B. (n.d.). Muscle Development | Boundless Anatomy and Physiology. Lumen Learning. Retrieved

November 18, 2021, from https://courses.lumenlearning.com/boundless-ap/chapter/muscle-development/

BSc, A. R. (2021, September 30). Orbicularis oculi. Kenhub. Retrieved November 18, 2021,

from https://www.kenhub.com/en/library/anatomy/orbicularis-oculi

Cooper, J. (2020, October 21). Benefits of Protein. WebMD. Retrieved November 18, 2021, from

https://www.webmd.com/diet/benefits-protein

E. (2017, December 22). Oxygen and Muscles. Expand a Lung. Retrieved November 18, 2021,

from https://expand-a-lung.com/oxygen-and-muscles/

Frothingham, S. (2019, April 26). What Is the Largest Muscle in the Body? Healthline. Retrieved

November 18, 2021, from https://www.healthline.com/health/largest-muscle-in-the-body

Gaillard, F. (2019, June 14). Stapedius muscle | Radiology Reference Article | Radiopaedia.org.

Radiopaedia. Retrieved November 18, 2021, from https://radiopaedia.org/articles/stapedius-muscle-1#:%7E:text=The%20stapedius%20muscle%20is%20the,cochlea%20via%20the%20oval%20window.

Grujičić, R., MD. (2021, September 30). Stapedius muscle. Kenhub. Retrieved November 18,

2021, from https://www.kenhub.com/en/library/anatomy/stapedius-muscle

Gunnars, K. B. (2019, March 8). 10 Science-Backed Reasons to Eat More Protein. Healthline.

Retrieved November 18, 2021, from https://www.healthline.com/nutrition/10-reasons-to-eat-more-protein#TOC_TITLE_HDR_10

Karolinska Institutet. (2018, April 3). How muscles regulate their oxygen consumption.

ScienceDaily. Retrieved November 18, 2021, from https://www.sciencedaily.com/releases/2018/04/180403124046.htm

Koshland, D. (2020, December 21). protein – The muscle proteins. Encyclopedia Britannica.

Retrieved November 18, 2021, from https://www.britannica.com/science/protein/The-muscle-proteins

Maldarelli, C., & Chodosh, S. (2021, October 4). Everything you’ve ever wanted to know about

muscles. Popular Science. Retrieved November 18, 2021, from https://www.popsci.com/build-muscle-faq-exercise-experts/

Marcin, A. (2020, May 1). What You Should Know About Building Muscle Mass and Tone.

Healthline. Retrieved November 18, 2021, from https://www.healthline.com/health/how-long-does-it-take-to-build-muscle#muscle-growth

N. (2018, May 31). What are the Main Functions of the Muscular System? New Mexico

Orthopaedic Associates, P.C. Retrieved November 18, 2021, from https://www.nmortho.com/what-are-the-main-functions-of-the-muscular-system/Patient, R. M. (2020, June 19). Orbicularis Oculi | Rehab My Patient. Rehabmypatient.Retrieved November 18, 2021, from https://www.rehabmypatient.com/face/orbicularis-oculi#:%7E:text=Injury%20to%20the%20orbicularis%20oculi,without%20the%20proper%20corrective%20lenses.

Panzo, K., & Los Baños, R. J. C. What is smooth muscle and its function?.https://getaprofessor.com/2024/05/29/what-is-smooth-muscle-and-its-function/

Physiopedia. (n.d.). Gluteus Maximus. Retrieved November 18, 2021, from

https://www.physio-pedia.com/Gluteus_Maximus

PowerDot. (n.d.). #32: Why Oxygenated Muscles Perform Better and Recover Faster.

PowerDot.Com. Retrieved November 18, 2021, from https://www.powerdot.com/blogs/training/oxygenated-muscles

W. (2019, September 27). Muscle Building: The 3 Mechanisms of Hypertrophy. ION Strength &

Conditioning. Retrieved November 18, 2021, from https://ioncardiff.com/the-3-mechanisms-of-hypertrophy/

Wedro, B. (2019, October 18). Gluteal Injury Treatment, Symptoms, Tests, Recovery, Prevention.

MedicineNet. Retrieved November 18, 2021, from https://www.medicinenet.com/gluteal_injury/article.htm