Do you know which system of the body converts food into the nutrients? It is the digestive system (1, 2). These nutrients provide the energy we need to survive. It also processes solid waste, or stool, with the help of a bowel movement.
The organs of the digestive system are:
Rectum and anus.
The supporting organs are the pancreas, liver, and gall bladder. Let us see how these organs work together in our digestive system.
Are you aware that digestion starts before you even take a bite? In fact, the mouth is the beginning of the digestive tract? The salivary glands get active as we smell and see the food.
Function: Saliva mixes with the food and breaks it down. This helps nutrients to be absorbed. When we swallow, the tongue passes the food into your throat and your esophagus.
The esophagus is Located near the windpipe or trachea. The esophagus receives food from the mouth when we swallow it.
Function- Peristalsis, or series of muscular contractions, delivers food to the stomach. The esophageal sphincter prevents the contents of the stomach from flowing back into the esophagus.
The stomach is a hollow organ that holds food while mixed with stomach enzymes. These enzymes help in food breakdown.
Function- The stomach secretes acid and powerful enzymes that are responsible for the breakdown process. The contents are released into the small intestine.
The small intestine has three parts: the duodenum, jejunum, and ileum.
1. The duodenum is responsible for the continuous breaking-down process.
2. The jejunum and ileum are mainly responsible for the absorption of nutrients into the bloodstream.
Function- The small intestine breaks down food using pancreatic enzymes and bile from the liver. Pancreatic enzymes, water, bile, and mucus contribute to the change in the consistency: semisolid to liquid. The leftover-food residue then moves on to the large intestine, or colon.
The pancreas secretes enzymes into the duodenum. These digestive enzymes break down carbohydrates, fats, and protein. The pancreas also secretes insulin, passing it directly into the bloodstream.
The liver is the body’s “chemical factory.” It takes the intestine’s raw materials and makes all the various chemicals the body needs to function.
The liver has many functions; it absorbs nutrients from the small intestine. Bile from the liver helps in digesting fat and some vitamins.
The liver helps to detoxify potentially harmful chemicals. The liver breaks down the toxic drugs that can be further excreted.
The gallbladder stores and concentrates bile from the liver. The bile is then released into the duodenum. The bile helps absorb and digest fats.
Colon or large intestine
The large intestine (colon) is a 6-foot long muscular tube. The colon connects the small intestine to the rectum.
The colon is responsible for processing waste and emptying the bowels. The large intestine is made up of
the ascending colon,
the transverse colon,
the descending colon,
the sigmoid colon
The colon empties its contents into the rectum to begin elimination (a bowel movement).
The rectum is an 8-inch chamber. It connects the colon to the anus. The sphincters relax and the rectum contracts, disposing of its contents.
The anus is a 2-inch long canal and the last part of the digestive tract. The anus has the pelvic floor muscles and the two anal sphincters. The external sphincter holds the stool until reaching a toilet, where it then relaxes to release the contents.
Disclaimer and references
All the images used are under a creative common license.
Physiology is the study of the functioning of the human body. It is the above-mentioned systems that maintain a steady-state/ homeostasis or milieu-interieur as defined by the French physiologist Claude Bernard and American physiologist Walter Canon. Rudolph Virchow, (who gave the postulates of cell theory, that all cells arise from pre-existing cells and the cell is the basic structural and functional unit of life), popularized the cellular theory of disease.
According to it, all diseases have a cellular origin, and thus macroscopic changes and signs and symptoms are preceded by cellular and biochemical derangements in cells. According to him, therefore, pathology is an altered state of physiology that must be corrected. Failure to do so would lead to disease progression and death in some instances.
Body Composition and Water Distribution
The average human male weighs about 70 kg and a female weigh about 60 kg. The human body is composed of 60% water which amounts to 42 litres. The intracellular component is about 2/3rd which is 28 litres and the extracellular component is about 14 litres. The amount of blood in the human body is about 5 litres. It is composed of plasma (around 3 litres) and blood cells (red blood cells, white blood cells and platelets).
Feedback System- Negative Feedback Loop
There are two main types of feedback which ensure that the body is continuously functioning which is normal physiology. A negative feedback and a positive feedback control mechanism regulate the functioning of body processes. In negative feedback, the response produced reduces the original stimulus. For example, the hypothalamus-pituitary-target organ axis. The pituitary is the master endocrine gland of the body. It controls all other endocrine organs with respect to their secretions. However, the pituitary is itself under the control of the hypothalamus. Considering the release of thyroxine hormone from the thyroid gland, the negative feedback loop becomes clear. The hypothalamus releases Thyroid Hormone Releasing Hormone (TRH). It acts on the pituitary to secrete Thyroid Stimulating Hormone or TSH. The TSH acts on the thyroid gland to stimulate the release of T3 and T4 hormones from the gland. However, increasing levels of the hormones have an inhibitory effect on the hypothalamus and the pituitary gland. They inhibit further release of TRH and TSH and thus maintain the circulating levels of T3 and T4.
Positive Feedback Loop:
Positive feedback loops, on the other hand, have a response that increases/stimulus, which increases the first incentive. Childbirth or parturition is a classic example of positive feedback. At the time of childbirth, the uterine muscles contract in response to oxytocin. When the head of the baby is engaged, it stretches the cervical opening. This stimulates the uterine muscles to contract further and push the baby downwards.
This leads to a positive loop of further dilatation and further uterine contractions, which continues until the baby is finally delivered. Blood clotting is another example of positive and negative feedback loops occurring together. When bleeding occurs, there is a release of clotting factors which lead to a coagulation cascade. This cascade continues and amplifies until the bleeding is controlled, which is positive feedback. This leads to the control of bleeding, which leads to the integrity of the vascular system. Thus, bleeding leads to further control of bleeding and coagulation, which is, therefore, an example of negative feedback.
Functions of Various Body Systems
The neuroendocrine system is the main seat of control and coordination. The neurons are the basic units of the nervous system. It can be broadly divided into the central nervous system (the brain, spinal cord, and central nerves) and a peripheral nervous system which is comprised of peripheral nerves (afferent- to the organ and efferent-away from the organ). Thus, a receptor-integrator-effector system is established. A large number of reflexes such as pain reflexes exist to protect ourselves from potentially harmful stimuli.
For example, on touching a hot object, we impulsively remove our hand away from the object. This is executed at the level of spinal cord and is thus protective in nature. Also included are the special senses of touch, smell, taste, vision and hearing. These specialised senses help us to communicate with our external environment effectively.
Circulatory, Excretory and Digestive Systems
The circulatory system ensures a constant dynamic blood flow, while ensuring supply of essential substrates and nutrients to body tissues. At the same time, they also collect harmful waste products and help in their removal.
The excretory system including kidneys, filters the blood of waste products of metabolism and thus helps in clearing the blood of unwanted harmful substances.
The digestive system is primarily concerned with energy production and metabolism. They ensure that complex food substances are broken down into simple soluble forms that are absorbed and assimilated in the body tissues. They are used for generating energy in the form of ATP which powers our daily life activities. The undigested and unabsorbed substances are egested out of the body.
The immune system is of particular importance and deserves special mention. The immune system responses are broadly divided into primary and secondary responses. Primary immunity or the innate immunity is the defense powers already in an individual by virtue of its original genetic makeup. It does not require prior exposure to an external agent. This is responsible for the acute signs of inflammation seen. For example, in the case of an ant-bite, the surrounding region is red, warm and tender to touch along with being swollen. The primary cells of this response are the neutrophils.
The secondary immune response or acquired immune response is specific and results in the production of antibodies against the invading pathogen. It has a lag period and is primarily mediated by the lymphocytes and macrophages. The primary lymphoid organs include the bone marrow and the thymus, for the production of B lymphocytes (which produce antibodies) and T lymphocytes which produce T-lymphocytes or cytotoxic cells.
Reproductive System and Development Phases
The reproductive system is primarily concerned with the perpetuation of life. The ability to reproduce is one of the fundamental characteristics of living organisms. Thus, the testis and ovaries produce male and female gametes respectively. During coitus or copulation, these gametes fuse with each other to form the zygote. The zygote is implanted in the lining of the uterus and grows into successive stages of embryo and fetus until delivery at 9 months of pregnancy. From birth onwards, various milestones have been defined.
Up to the first month after birth, the child is called a neonate. Up to one year of age, it is termed as an infant. A child is up to 14-16 years of age. The next few years are considered to be teenage years. The later stage is adulthood and finally old age (beyond 65 years) and death. They are further subdivided, for example as:
A working knowledge of anatomical terms is essential in order to know the descriptions in anatomy. It will help us to better understand the positions of various body parts in relation to each other and reference points.
They describe the relative structures or locations in the body. These are with reference to the normal anatomical position of the body in which the body is erect with arms by the side and the palms facing forwards.
Superior: Towards the head end of the body e.g.: Upper limbs are superior to the lower limbs or the nose is superior to the mouth. It is also termed as rostral.
Inferior: Away from the head (not necessarily towards the feet). The neck is inferior to the head. It is also referred to as caudal (caudal meaning tail-end)
Anterior: It is also referred to as the front-facing part. For e.g. the torso is the anterior part of the body. It is also referred to as ventral.
Posterior: It is the backside. For e.g. the calf muscles are on the posterior aspect.
Medial: Towards the midline of the body or towards a sagittal plane (example, the thumb is medial to the little finger in the anatomical position).
Lateral: Away from the midline of the body (for example, the little toe is located at the lateral side of the foot).
Median: It refers to a midline structure, which is generally solitary or single. The thyroid is in the median plane.
Proximal: Towards or nearest the trunk or the point of origin of a part (example, the humerus bone is proximal to the bones of the forearm).
Distal: Away from or farthest from the trunk or the point of origin of a part (The wrist is distal to the forearm).
Planes of the Body
They divide the body into halves, right and left, upper and lower, anterior and posterior.
Coronal Plane (Frontal Plane) – A vertical plane that runs from side to side; It divides the body or its parts into anterior and posterior portions.
Sagittal Plane (Lateral Plane) – A vertical plane running from front to back; divides the body or any of its parts into the right and left sides.
Axial Plane (Transverse Plane) – A horizontal plane; divides the body or any of its parts into upper and lower parts or a superior and inferior part.
Median plane – It is the midsagittal plane of the body; It divides the body or its parts into right and left halves.
Introduction to Human Body: Human Body Organization, Organ Systems and Anatomy Overview
The Human Body:
The human body is the result of millions of years of evolution. Keeping in line with the ‘Theory of Natural Selection’, as envisaged by Charles Darwin, it has evolved with time.
Some organs have been reduced to a vestige (the appendix for one was used for digesting cellulose rich fibers. With the discovery of fire and consequent changes in eating habits, it no longer serves its purpose). Others have developed varied degree of specializations. The human thumb, for example, is freely apposable and the human hand is specialized for grasping, and other dexterous movements.
The erect posture which man acquired has emancipated his upper limbs while the lower limbs became specialized for weight-bearing and support. As a result, the upper limb has more mobility at the cost of stability while the lower limb is less mobile in exchange for increased stability.
Human Body Organization:
The current era man or Homo sapiens is a bipedal animal which has an enormous thinking capacity, courtesy, a well-developed frontal cortex, which is the seat of knowledge and creative thought processes. Like all living organisms, the human body is made of cells.
Cells constitute the basic structural and functional unit of life. Cells comprise od a cell membrane which enclose the cytoplasm or the cellular matrix which has various organelles for its functions. At an elemental level though, the cell is composed of hydrogen, nitrogen, carbon, oxygen and other trace elements. These elements interacted with each other to form the cell, the first living organism. Over time, these cells coalesced to form various organisms.
The longest cells in the human body are the axons which run from the brain and spinal cord to distal most organs and vice-versa. The axons of these neurons can be as long as 1metre, but due to their smaller diameters (in the range of micrometres or 10-6 m, they are seen only under a microscope with appropriate stains). The body is composed of nearly 30 trillion cells, a majority of which are RBCs, which carry oxygen to the tissues. These cells are arranged into tissues. A tissue is a group of cells performing the same function (for e.g. nervous tissue, connective tissue, vascular tissue, etc).
These tissues combine to form organs. The individual cells or tissues do not have any fundamental properties of their own in an organ. It is only when they interact with each other via various signalling pathways, that they function as an organ.
For example, the liver has a connective tissue matrix, it has vessels which carry blood to and from it, specialised Kupffer cells (modified macrophages or those cells which kill invading microbes), and a system of ducts to carry bile to the small intestine. Thus, as an organ, the liver is composed of a diverse set of tissues, which ensures that it functions optimally. The organs combine together to form organ systems.
Each organ system is specialised in its own right. However, they are inextricably linked to each other for their normal functioning. The organ systems include, but are not limited to, the nervous system, the integumentary system (skin and appendages), cardiovascular system, respiratory system, nervous system, endocrine system, the reproductive system and the excretory system.
A system-wise composition includes:
Nervous System- The Brain, spinal cord and the nerves.
Excretory System- Pair of kidneys, ureters, bladder and urethra.
Reproductive system- Male and female gonads (testis and ovaries respectively), duct systems, accessory reproductive organs and the external genitalia in both sexes.
Endocrine System- The pituitary gland, thyroid, pancreas, parathyroid glands, ovaries, testis, etc.
Respiratory System- The external orifices, conducting pathways, lungs and the respiratory centres in the medulla.
Cardiovascular System- The heart, blood vessels and the blood components along with the cardiac centre in the medulla.
Digestive System- It includes the entire tube from the mouth to the anal canal comprising of the esophagus, stomach, small and large intestines, rectum and anus. It is also composed of accessory digestive organs such as the liver, gall bladder and the pancreas.
Integumentary System- The skin, hair, sweat and oil glands.
The nervous system and the endocrine system are responsible for controlling and coordinating various body activities. They ensure that the various processes which go on in the body are regulated. It is this regulation which helps the body to survive in various adverse conditions, which might otherwise have been unfavorable to life.
It is precisely because of this reason that human beings can be found in a diverse set of geographic and climactic conditions: From plains to hill-tops, freezing sub-zero polar areas to the scorching heats of dry deserts, from tribals in forests and islands to city dwellers in urban geographies.
The organ systems work in tandem to make a complete organism, the human being. These processes which help one survive are collectively referred to as life-sustaining processes (breathing, circulation, respiration, reproduction, etc) and the steady state I known as homeostasis. In medical terminology, homeostasis refers to a state of internal constancy despite changes in external surroundings.
Stated otherwise, homeostasis is the maintenance of near constant internal conditions to maintain the life in the wake of external changes. It is a set-point which exemplifies normal functioning. However, it is context specific, gender -specific and individualistic. Thus, we do not have a fixed value of normal values for various processes.
For example, though the normal blood pressure is stated as 120 mm (systolic) by 80 mm (diastolic) of Mercury, there is a normal range. The range for systolic blood pressure is 120-140 mm of Mercury, whereas the same for diastolic blood pressure is 80-90 mm of mercury. Similarly, though the average pulse (which is measured in the forearm radial artery and is an indicator of the heart rate) is taken as 72 beats per minute, the range of pulse is 60-100 beats per minute.
Disease- An outcome of disequilibrium:
Diseases refers to a disruption of homeostasis. There are multiple causes of the same. They may be the result of an insufficient blood supply, termed ischemia, leading to oxygen deprivation (hypoxia) and consequent cell death. They may also be due to infections which can be due to bacteria, viruses, fungi, parasites, etc. Or, they may result from physical and chemical injuries (burns, acids), irradiation, autoimmune diseases and hypersensitivity reactions.
Whatever the initial cause of insult, they lead to cellular injury. A prolonged, severe injury to a susceptible cell leads to cellular death and ultimately organ damage and system dysfunction which leads to signs and symptoms of a disease in a patient.
In the above-mentioned example, if the blood pressure is more than 140/90 mm of Hg, it is termed as hypertension. Hypertension, like most diseases, are multifactorial in origin. It will lead to thickening of heart walls, leading to inadequate pumping of blood to the rest of the critical organs, including the kidney, heart and brain.
Long-standing untreated hypertension can thus lead to chronic renal failure (kidneys), a heart attack or myocardial infarction (heart) or a paralytic attack/ stroke (brain). Similarly, a pulse below 60 is termed as bradycardia (brady-low) or above 100 is labelled as tachycardia (tachy-high) due to various pathologies.
The study of human body in Medicine is along the broad contours of the organ systems. An understanding of the normal functioning is essential before studying about the diseases and its treatments. It can be broadly divided into the three contours: Anatomy, Physiology and Biochemistry.
Anatomy is the structure of the human body as it is. It includes developmental anatomy (embryogenesis and genetics), gross anatomy (specialized subdivisions into the head, neck, upper limbs, thorax, abdomen, pelvis and lower limbs with respective muscles, organs and neuro-vascular structures) and microscopic anatomy (popularly referred to as histology).
The human body is made up of 206 bones which are divided into an axial skeleton comprised of 86 bones (inclusive of the skull bones and the vertebral column) and an appendicular skeleton (the four limbs consist of 120 bones in total, with each limb being composed of 30 bones). This subdivision is true for an adult human body. However, infants have a much larger number of bones, which fuse as the age progresses, resulting in 206 bones in an adult person.
The skeletal framework is supported by muscles, numbering about 640 in an adult person. The number however varies due to anatomical variations in individuals. These muscles have two major functions.
The first is protection of internal organs of the body.
The second is execution of the motor response of the body (pushing, pulling, running, etc).
These skeletal muscles carry out voluntary activity, those which are under our will. Internal organs and viscera composed of smooth muscles which are involuntary in nature. They are not under our command and function with the help of the autonomic nervous system.
The heart is another specialized muscular organ. It is made of cardiac tissue. In anatomy, it shares the features of skeletal muscles. However, like smooth muscles it is involuntary in nature.
The body can also be divided into anatomically distinct compartments. They include the cranial cavity, the thoracic cavity and the abdominal cavity. The cranial cavity houses the brain.
The thoracic cavity has lungs and heart. The abdominal cavity has the stomach, liver, spleen, kidney and intestines, whereas the pelvic cavity (an extension of the abdominal cavity) houses the bladder, rectum and anal canal. In females it has the uterus and the ovaries.
In males, it houses the prostate and the various glands (Bulbourethral glands, seminal vesicles, etc). The thoracic cavity is separated from the abdominal cavity by a diaphragm which moves up and down with respiration.
The vascular system is broadly divided into the arteries, veins and capillaries. Arteries carry oxygenated blood from the heart to all the organs of the body. The veins carry de-oxygenated blood from the cells and tissues back to the heart.
Gaseous exchange occurs across capillaries. In the lungs, there is exchange of CO2 and O2. The superior and inferior vena-cava bring de-oxygenated blood from all the parts of the body to the heart. It is sent to the lungs for oxygenation by the pulmonary arteries.
Oxygen from the air is taken up in the pulmonary arteries which have divided to form pulmonary capillaries. These capillaries unite to form pulmonary veins which bring it to the heart. The aorta pumps the oxygenated blood to all the organs. Again, gaseous exchange takes place across capillaries at the level of organs and tissues. Oxygen is taken up by the cells and the waste products of metabolism and carbon-dioxide diffuse across into veins. Veins coalesce to form the superior and inferior vena cava and thus, the cycle is repeated.
The brain is one of the largest and most complex organs of the human body. It is the central organ of the nervous system and along with the spinal cord, it makes up the central nervous system.
The adult human brain contains about 95% of the neural tissue and weighs about 1.4 kilograms. The brain is contained and protected by the skull bones of the head and is suspended in cerebrospinal fluid and isolated from the bloodstream via the blood-brain barrier.
It is responsible for controlling almost all of the major activities performed by the body such as processing and relaying information received by the sensory organs, making decisions based on the bodily needs and controlling various organs to suit the same, and maintaining the basic body functions which are involuntary in nature.
Structural Organisation of the Brain and functions
On initial observation, we see that the brain is divided into two halves: Left and Right hemispheres.
Each hemisphere is divided into four lobes- frontal, temporal, parietal and occipital lobes.
Furthermore, there are six major divisions in the adult brain: medulla oblongata, the pons, mesencephalon, diencephalon, cerebellum, and the cerebrum (containing the two hemispheres).
The medulla oblongata, the Pons, and the mesencephalon are collectively referred to as the brain stem.
The brain stem contains important processing centers and also relays information to and from the cerebrum or cerebellum.
The cerebrum connects to the spinal cord via the brainstem and, the cerebellum is connected to the brainstem by pairs of tracts.
The cerebrum, brainstem, cerebellum, and spinal cord are covered by three membranes called meninges.
These membranes are the outer, tougher Dura mater; the middle arachnoid mater and the more delicate inner pia mater.
The space between arachnoid mater and pia mater is where we find cerebrospinal fluid.
The cerebrum is divided into the left and right hemispheres by a deep groove called the longitudinal fissure.
Each hemisphere is divided into four lobes as discussed above and each one has one or two specialized functions, although some of these functions might overlap.
The outer part of the cerebrum is the cerebral cortex and it is made up of grey matter arranged in layers that are folded to give a convoluted appearance that we usually see.
Beneath this cortex is the cerebral white matter.
The cerebral cortex
It is divided into two main functional areas – sensory cortex and motor cortex.
As the name suggests, the motor cortex sends axons down the motor neurons and the spinal cord to receive and transmit impulses pertaining to the motor functions.
The sensory cortex is responsible for obtaining and processing the sensory information received by the sensory nerves and regions of the brain such as the occipital lobe.
The cerebrum contains the ventricles where the cerebrospinal fluid is produced and circulated.
It is divided into three lobes – anterior lobe, posterior lobe, and the flocculonodular lobe.
The cerebellum rests at the back of the cranial cavity underneath the occipital lobes.
It is responsible for adjusting the motor activities on the basis of sensory information and memories of learned patterns of movement.
It lies below the cerebrum at the back of the skull.
The brainstem continues below in the body as the spinal cord protected by the vertebral column.
There are twelve pairs of cranial nerves, out of which ten arise from the brainstem.
The brainstem is involved in the regulation of many essential processes of the body such as breathing, controlling eye movement, balance, etc.
Many nerves that pass information to and from the cerebral cortex pass the brainstem thus making it one of the most important parts of the brain.
Fluids associated with the Brain
The neural tissue in the Central Nervous System has a vast blood supply, yet it is isolated from the general circulation by the blood–brain barrier (BBB).
BBB maintains a constant environment, for controlling and proper functioning of CNS neurons.
Cerebrospinal fluid (CSF) completely surrounds and bathes the exposed surfaces of the central nervous system.
CSF has several important functions, including supporting the brain, preventing contact of the delicate neural structures and the surrounding bones, transporting nutrients, chemical messages, and waste products in and out of the neural tissue.
Brain Injuries and Diseases
The brain is one of the most delicate organs is highly susceptible to injuries and diseases. These can ensue in many ways such as a traumatic brain injury resulting in a sports accident or a fall that may induce problems such as bleeding in the brain, compress the blood tissue or damage the blood supply.
Neurodegenerative diseases such as Alzheimer’s or Parkinson’s syndrome or dementia bring about progressive degeneration of the brain tissue and function.
Mental disorders such as depression, OCD, schizophrenia, etc deteriorate the functioning of the brain. Epileptic seizures due to abnormal electrical activity in the brain or a stroke as a result of decreased blood supply also have the tendency of altering the brain’s overall functionality.
Finally, brain death which results in total and irreversible loss of brain function and is usually characterized by coma, loss of reflexes, or apnoea.
The neural tissue contains two distinct cell types: neurons and neuroglia. Before knowing about these cells, lets first discuss briefly the Nervous System.
The nervous system is among the smallest of organ systems in terms of body weight and yet is the most complex and the most important one.
The nervous system includes all of the neural tissue in the body including the brain, the spinal cord, sensory organs, and the interconnecting nerves.
The nervous system along with the endocrine system controls and adjusts bodily functions.
The nervous system is divided into two parts: The central nervous system (CNS) containing the brain and the spinal cord, and the Peripheral nervous system (PNS) contains the peripheral nerves and neural tissue outside of CNS.
The central nervous system is responsible for the integration, processing, and coordination of the sensory and motor responses. It also involves higher functions such as memory, learning, intelligence, and emotion.
The CNS communicates with different parts of the body via the PNS by sending and receiving electrical impulses specific to the reaction needed. Afferent pathways bring in the sensory information to the CNS and the efferent pathways relay the motor information from the CNS to the other parts of the body.
Cells of the Central Nervous System
The neural tissue contains two distinct cell types: neurons, or the nerve cells, and neuroglia, the supporting cells.
The neurons are responsible for the transmission and processing of information in the nervous system. The neuroglia, supporting cells, isolate these neurons and provide a supporting framework, help maintain the intracellular environment and also act as phagocytes (cells that destroy bacteria and other pathogens).
Neuroglia is glial cells smaller than neurons, and they retain their ability to divide as opposed to neurons. Collectively, they account for nearly half the volume of the nervous system.
In the CNS, there are four distinct types of neuroglia – Astrocytes, Oligodendrites, Microglia, and Ependymal Cells. They perform a variety of functions including maintaining the blood-brain barrier, creating a 3D framework for the CNS, performing repairs in damaged neural tissues, guiding neuron development, providing structural stability, phagocytosis, neuron myelination, transport of cerebrospinal fluid (CSF) are to name a few.
Structurally, a neuron has a cell body called the soma. The cell body usually has several branching dendrites. Furthermore, the cell body is attached to an elongated axon that ends at one or more synaptic terminals. At each synaptic terminal, the neuron communicates with another cell.
The soma contains the organelles responsible for energy production and the biological synthesis of organic molecules. The neuronal nucleus is highly packed with mitochondria which generate ATP to meet the high energy demands of an active neuron.