All you need to know about neurons What neurons look like Types How do they carry a message? Synapses Neurons are responsible for carrying information throughout the human body. Using electrical and chemical signals, they help coordinate all of the necessary functions of life. In this article, we explain what neurons are and how they work. In short, our nervous systems detect what is going on around us and inside of us; they decide how we should act, alter the state of internal organs (heart rate changes, for instance), and allows us to think about and remember what is going on. To do this, it relies on a sophisticated network — neurons. It has been estimated that there are around 86 billionTrusted Source neurons in the brain; to reach this huge target, a developing fetus must create around 250,000 neurons per minuteTrusted Each neuron is connected to another 1,000 neurons, creating an incredibly complex network of communication. Neurons are considered the basic units of the nervous system. Because they are Neurons, sometimes called nerve cells, make up around 10 percent of the brain; the rest consists of glial cells and astrocytes that support and nourish neurons. What do neurons look like? Diagram of a neuron. Neurons can only be seen using a microscope and can be split into three parts: Soma (cell body) — this portion of the neuron receives information. It contains the cell’s nucleus. Dendrites — these thin filaments carry information from other neurons to the soma. They are the “input” part of the cell. Axon — this long projection carries information from the soma and sends it off to other cells. This is the “output” part of the cell. It normally ends with a number of synapses connecting to the dendrites of other neurons. Both dendrites and axons are sometimes referred to as nerve fibers. Axons vary in length a great deal. Some can be tiny, whereas others can be over 1 meter long. The longest axon is called the dorsal root ganglionTrusted Source (DRG), a cluster of nerve cell bodies that carries information from the skin to the brain. Some of the axons in the DRG travel from the toes to the brain stem — up to 2 meters in a tall person. Types of neurons Neurons can be split into types in different ways, for instance, by connection or function. Connection Efferent neurons — these take messages from the central nervous system (brain and spinal cord) and deliver them to cells in other parts of the body. Afferent neurons — take messages from the rest of the body and deliver them to the central nervous system (CNS). Interneurons — these relay messages between neurons in the CNS. Function Sensory — carry signals from the senses to the CNS. Relay — carry signals from one place to another within the CNS. Motor — carry signals from the CNS to muscles. How do neurons carry a message? Neurons carry messages via action potentials. If a neuron receives a large number of inputs from other neurons, these signals add up until they exceed a particular threshold. Once this threshold is exceeded, the neuron is triggered to send an impulse along its axon — this is called an action potential. An action potential is created by the movement of electrically charged atoms (ions) across the axon’s membrane. Neurons at rest are more negatively charged than the fluid that surrounds them; this is referred to as the membrane potential. It is usually -70 millivolts (mV). When the cell body of a nerve receives enough signals to trigger it to fire, a portion of the axon nearest the cell body depolarizes — the membrane potential quickly rises and then falls (in about 1,000th of a second). This change triggers depolarization in the section of the axon next to it, and so on, until the rise and fall in charge has passed along the entire length of the axon. After each section has fired, it enters a brief state of hyperpolarization, where its threshold is lowered, meaning it is less likely to be triggered again immediately. Most often, it is potassium (K+) and sodium (Na+) ions that generate the action potential. Ions move in and out of the axons through voltage-gated ion channels and pumps. This is the process in brief: Na+ channels open allowing Na+ to flood into the cell, making it more positive. Once the cell reaches a certain charge, K+ channels open, allowing K+ to flow out of the cell. Na+ channels then shut but K+ channels remain open allowing the positive charge to leave the cell. The membrane potential plunges. As the membrane potential returns to its resting state, the K+ channels shut. Finally, the sodium/potassium pump transports Na+ out of the cell and K+ back into the cell ready for the next action potential. Action potentials are described as “all or nothing” because they are always the same size. The strength of a stimulus is transmitted using frequency. For instance, if a stimulus is weak, the neuron will fire less often, and for a strong signal, it will fire more frequently. Myelin Myelinated axon compared with demyelinated axon. Image credit: Dr Jana Most axons are covered by a white, waxy substance called myelin. This coating insulates nerves and increases the speed at which impulses travel. Myelin is created by Schwann cells in the peripheral nervous system and oligodendrocytes in the CNS. There are small gaps in the myelin coating, called nodes of Ranvier. The action potential jumps from gap to gap, allowing the signal to move much quicker. Multiple sclerosis is caused by the slow breakdown of myelin. How synapses work Neurons are connected to each other and tissues so that they can communicate messages; however, they do not physically touch — there is always a gap between cells, called a synapse. Synapses can be electrical or chemical. In other words, the signal that is carried from the first nerve fiber (presynaptic neuron) to the next (postsynaptic neuron) is transmitted by an electrical signal or a chemical one. Chemical synapses Illustration of a synapse Image credit: U.S. National Institutes of Health Once a signal reaches a synapse, it triggers the release of chemicals (neurotransmitters) into the gap between the two neurons; this gap is called the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft and interacts with receptors on the membrane of the postsynaptic neuron, triggering a response. Chemical synapses are classified depending on the neurotransmitters they release: Glutamergic — releases glutamine. They are often excitatory, meaning that they are more likely to trigger an action potential. GABAergic — release GABA (gamma-Aminobutyric acid). They are often inhibitory, meaning that they reduce the chance that the postsynaptic neuron will fire. Cholinergic — release acetylcholine. These are found between motor neurons and muscle fibers (the neuromuscular junction). Adrenergic — release norepinephrine (adrenaline). Electrical synapses Electrical synapsesTrusted Source are less common but are found throughout the CNS. Channels called gap junctions attach the presynaptic and postsynaptic membranes. In gap junctions, the post- and presynaptic membranes are brought much closer together than in chemical synapses, meaning that they can pass electric current directly. Electrical synapses work much faster than chemical synapses, so they are found in places where quick actions are necessary, for instance in defensive reflexes. Chemical synapses can trigger complex reactions, but electrical synapses can only produce simple responses. However, unlike chemical synapses, they are bidirectional — information can flow in either direction. In a nutshell Neurons are one of the most fascinating types of cell in the human body. They are essential for every action that our body and brain carry out. It is the complexity of neuronal networks that gives us our personalities and our consciousness. They are responsible for the most basic of actions, and the most intricate. From automatic reflex actions to deep thoughts about the universe, neurons cover it all. Last medically reviewed on December 7, 2017 Neurology / Neuroscience How we reviewed this article: SOURCES Share this article Medically reviewed by Seunggu Han, M.D. — By Tim Newman on December 7, 2017 Latest news What do people experience at the border between life and death? Exercise restores brain insulin sensitivity, may protect against type 2 diabetes Researchers are trialing lab-grown blood transfusions: What to know Alzheimer’s disease: New biomarker identified, may lead to earlier diagnosis Alzheimer's: Could beer hop compounds help reduce toxic clumps? Was this article helpful? Yes No New way for gut neurons to communicate with the brain A new study reveals how neurons in the gut wall relay sensory information to the spinal cord and brain, which may influence mood and well-being. Research indicates that the way gut neurons communicate with the brain may have an effect on mood and well-being. The enteric nervous system (ENS) — sometimes referred to as the “second brain” — is the nervous system of the gut. It contains some 500 millionTrusted Source neurons and controls important reflexes, such as peristalsis, the contraction of muscles in the gut to enable digestion. It is also responsible for the secretion of digestive enzymes that help break down food. The ENS is also a critical part of the gut-brain axis, through which the gut communicates with the brain — and the vagus nerve is particularly essential for conveying information about the intestines to the brain. The gut-brain axis performs several functions. The majority of serotonin, a neurotransmitter associated with mood, is found in the gut, for example. In a new study published in the journal eNeuro, researchers from Flinders University, in Adelaide, Australia, have identified a new way that neurons in the gut wall can activate neurons that connect to those in the spinal cord. They found highly coordinated activity in the gut wall neurons, which they suggest is a powerful mechanism to transmit information about what is going on in the gut to the brain. The gut’s own nervous system The gut is unique among the internal organs, in that it has its very own nervous system. This has been a subject of interest for Nick Spencer, senior author of the new study and a professor at the university’s College of Medicine and Public Health. “The gut has its own nervous system, which can function independently of the brain or spinal cord. Understanding how the gut communicates and controls other organs in the body can lead to important breakthroughs for disease treatment.” – Prof. Nick Spencer In the new study, Prof. Spencer and colleagues focused on viscerofugal neurons, which are found in the gut wall and project to neurons in the spinal cord. They investigated how these neurons work using the mouse colon, which contracts in a cyclical pattern known as the colonic motor complex. Viscerofugal neurons are known to be active during this process, but exactly how has, until now, been unclear. Recording neurons as they fire The researchers recorded the electrical activity of the viscerofugal neurons. They found that the firing of these neurons was associated with changes in the activity of the smooth muscle of the colon. The neurons fired in a highly synchronized way, which was associated with the parallel activation of neurons in the spinal cord. This suggests that viscerofugal neurons relay activity from the nervous system of the gut to the sympathetic nervous system — in other words, the spinal cord and brain. “The new study has uncovered how viscerofugal neurons provide a pathway so our gut can ‘sense’ what is going on inside the gut wall, then relay this sensory information more dynamically than was previously assumed to other organs, like the spinal cord and brain, which influence our decisions, mood and general well-being,” explains Prof. Spencer. The activation of viscerofugal neurons has previously been thought to require changes in the circumference of the gut wall — by the gut filling up, for instance — but this study shows that the process does not require any such mechanical activity. Medical relevance These findings may also have clinical relevance, as a growing number of conditions have been associated with changes to the gut. “There is significant interest in how the gut communicates with the brain as a major unresolved issue because of growing evidence that many diseases may first start in the gut and then travel to the brain, an example of which is Parkinson’s disease,” explains Prof. Spencer. As the scientist highlights, there is a well-established connection between the gut and Parkinson’s disease. One study, for example, showed that men who experience constipation are over four timesTrusted Source more likely to develop the condition. There is also accumulating evidence to suggest an association between changes in the gut and autism, multiple sclerosis, dementia, and stroke, making studies like this essential in understanding and eventually treating diverse neurological conditions. Biology / BiochemistryGastroIntestinal / GastroenterologyNeurology / Neuroscience Share this article By Eleanor Bird, M.S. on August 9, 2020 — Fact checked by Mary Cooke, Ph.D. Latest news What do people experience at the border between life and death? Exercise restores brain insulin sensitivity, may protect against type 2 diabetes Researchers are trialing lab-grown blood transfusions: What to know Alzheimer’s disease: New biomarker identified, may lead to earlier diagnosis Alzheimer's: Could beer hop compounds help reduce toxic clumps? Was this article helpful? Yes No All about the central nervous system What is the CNS? Brain Spinal cord White and gray matter Central glial cells Cranial nerves CNS diseases The central nervous system consists of the brain and spinal cord. It is referred to as “central” because it combines information from the entire body and coordinates activity across the whole organism. This article gives a brief overview of the central nervous system (CNS). We will look at the types of cells involved, different regions within the brain, spinal circuitry, and how the CNS can be affected by disease and injury. Fast facts on the central nervous system The CNS consists of the brain and spinal cord. The brain is the most complex organ in the body and uses 20 percent of the total oxygen we breathe in. The brain consists of an estimated 100 billion neurons, with each connected to thousands more. The brain can be divided into four main lobes: temporal, parietal, occipital and frontal. What is the central nervous system? Qi Yang/Getty Images The CNS consists of the brain and spinal cord. The brain is protected by the skull (the cranial cavity) and the spinal cord travels from the back of the brain, down the center of the spine, stopping in the lumbar region of the lower back. The brain and spinal cord are both housed within a protective triple-layered membrane called the meninges. The central nervous system has been thoroughly studied by anatomists and physiologists, but it still holds many secrets; it controls our thoughts, movements, emotions, and desires. It also controls our breathing, heart rate, the release of some hormones, body temperature, and much more. The retina, optic nerve, olfactory nerves, and olfactory epithelium are sometimes considered to be part of the CNS alongside the brain and spinal cord. This is because they connect directly with brain tissue without intermediate nerve fibers. Below is a 3D map of the CMS. Click on it to interact and explore the model. Now we will look at some of the parts of the CNS in more detail, starting with the brain. The brain The brain is the most complex organ in the human body; the cerebral cortex (the outermost part of the brain and the largest part by volume) contains an estimated 15–33 billion neurons, each of which is connected to thousands of other neurons. In total, around 100 billion neurons and 1,000 billion glial (support) cells make up the human brain. Our brain uses around 20 percent of our body’s total energy. The brain is the central control module of the body and coordinates activity. From physical motion to the secretion of hormones, the creation of memories, and the sensation of emotion. To carry out these functions, some sections of the brain have dedicated roles. However, many higher functions — reasoning, problem-solving, creativity — involve different areas working together in networks. The brain is roughly split into four lobes: Temporal lobe (green): important for processing sensory input and assigning it emotional meaning. It is also involved in laying down long-term memories. Some aspects of language perception are also housed here. Occipital lobe (purple): visual processing region of the brain, housing the visual cortex. Parietal lobe (yellow): the parietal lobe integrates sensory information including touch, spatial awareness, and navigation. Touch stimulation from the skin is ultimately sent to the parietal lobe. It also plays a part in language processing. Frontal lobe (pink): positioned at the front of the brain, the frontal lobe contains the majority of dopamine-sensitive neurons and is involved in attention, reward, short-term memory, motivation, and planning. Brain regions Next, we will look at some specific brain regions in a little more detail: Basal ganglia: involved in the control of voluntary motor movements, procedural learning, and decisions about which motor activities to carry out. Diseases that affect this area include Parkinson’s disease and Huntington’s disease. Cerebellum: mostly involved in precise motor control, but also in language and attention. If the cerebellum is damaged, the primary symptom is disrupted motor control, known as ataxia. Broca’s area: this small area on the left side of the brain (sometimes on the right in left-handed individuals) is important in language processing. When damaged, an individual finds it difficult to speak but can still understand speech. Stuttering is sometimes associatedTrusted Source with an underactive Broca’s area. Corpus callosum: a broad band of nerve fibers that join the left and right hemispheres. It is the largest white matter structure in the brain and allows the two hemispheres to communicate. Dyslexic children have smaller corpus callosums; left-handed people, ambidextrous people, and musicians typically have larger ones. Medulla oblongata: extending below the skull, it is involved in involuntary functions, such as vomiting, breathing, sneezing, and maintaining the correct blood pressure. Hypothalamus: sitting just above the brain stem and roughly the size of an almond, the hypothalamus secretes a number of neurohormones and influences body temperature control, thirst, and hunger. Thalamus: positioned in the center of the brain, the thalamus receives sensory and motor input and relays it to the rest of the cerebral cortex. It is involved in the regulation of consciousness, sleep, awareness, and alertness. Amygdala: two almond-shaped nuclei deep within the temporal lobe. They are involved in decision-making, memory, and emotional responses; particularly negative emotions. Spinal cord The spinal cord, running almost the full length of the back, carries information between the brain and body, but also carries out other tasks. From the brainstem, where the spinal cord meets the brain, 31 spinal nerves enter the cord. Along its length, it connects with the nerves of the peripheral nervous system (PNS) that run in from the skin, muscles, and joints. Motor commands from the brain travel from the spine to the muscles and sensory information travels from the sensory tissues — such as the skin — toward the spinal cord and finally up to the brain. The spinal cord contains circuits that control certain reflexive responses, such as the involuntary movement your arm might make if your finger was to touch a flame. The circuits within the spine can also generate more complex movements such as walking. Even without input from the brain, the spinal nerves can coordinate all of the muscles necessary to walk. For instance, if the brain of a cat is separated from its spine so that its brain has no contact with its body, it will start spontaneously walking when placed on a treadmill. The brain is only requiredTrusted Source to stop and start the process, or make changes if, for instance, an object appears in your path. White and gray matter The CNS can be roughly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area housing tracts of white matter. Both types of tissue contain glial cells, which protect and support neurons. White matter mostly consists of axons (nerve projections) and oligodendrocytes — a type of glial cell — whereas gray matter consists predominantly of neurons. Central glial cells Also called neuroglia, glial cells are often called support cells for neurons. In the brain, they outnumber nerve cells 10 to 1. Without glial cells, developing nerves often lose their way and struggle to form functioning synapses. Glial cells are found in both the CNS and PNS but each system has different types. The following are brief descriptions of the CNS glial cell types: Astrocytes: these cells have numerous projections and anchor neurons to their blood supply. They also regulate the local environment by removing excess ions and recycling neurotransmitters. Oligodendrocytes: responsible for creating the myelin sheath — this thin layer coats nerve cells, allowing them to send signals quickly and efficiently. Ependymal cells: lining the spinal cord and the brain’s ventricles (fluid-filled spaces), these create and secrete cerebrospinal fluid (CSF) and keep it circulating using their whip-like cilia. Radial glia: act as scaffolding for new nerve cells during the creation of the embryo’s nervous system. Cranial nerves The cranial nerves are 12 pairs of nerves that arise directly from the brain and pass through holes in the skull rather than traveling along the spinal cord. These nerves collect and send information between the brain and parts of the body – mostly the neck and head. Of these 12 pairs, the olfactory and optic nerves arise from the forebrain and are considered part of the central nervous system: Olfactory nerves (cranial nerve I): transmit information about odors from the upper section of the nasal cavity to the olfactory bulbs on the base of the brain. Optic nerves (cranial nerve II): carry visual information from the retina to the primary visual nuclei of the brain. Each optic nerve consists of around 1.7 million nerve fibers. Central nervous system diseases Below are the major causes of disorders that affect the CNS: Trauma: depending on the site of the injury, symptoms can vary widely from paralysis to mood disorders. Infections: some micro-organisms and viruses can invade the CNS; these include fungi, such as cryptococcal meningitis; protozoa, including malaria; bacteria, as is the case with Hansen’s disease (leprosy), or viruses. Degeneration: in some cases, the spinal cord or brain can degenerate. One example is Parkinson’s disease which involves the gradual degeneration of dopamine-producing cells in the basal ganglia. Structural defects: the most common examples are birth defects; including anencephaly, where parts of the skull, brain, and scalp are missing at birth. Tumors: both cancerous and noncancerous tumors can impact parts of the central nervous system. Both types can cause damage and yield an array of symptoms depending on where they develop. Autoimmune disorders: in some cases, an individual’s immune system can mount an attack on healthy cells. For instance, acute disseminated encephalomyelitis is characterized by an immune response against the brain and spinal cord, attacking myelin (the nerves’ insulation) and, therefore, destroying white matter. Stroke: a stroke is an interruption of blood supply to the brain; the resulting lack of oxygen causes tissue to die in the affected area. Difference between the CNS and peripheral nervous system The term peripheral nervous system (PNS) refers to any part of the nervous system that lies outside of the brain and spinal cord. The CNS is separate from the peripheral nervous system, although the two systems are interconnected. There are a number of differences between the CNS and PNS; one difference is the size of the cells. The nerve axons of the CNS — the slender projections of nerve cells that carry impulses — are much shorter. PNS nerve axons can be up to 1 meter long (for instance, the nerve that activates the big toe) whereas, within the CNS, they are rarely longer than a few millimeters. Another major difference between the CNS and PNS involves regeneration (regrowth of cells). Much of the PNS has the ability to regenerate; if a nerve in your finger is severed, it can regrow. The CNS, however, does not have this ability. The components of the central nervous system are further split into a myriad of parts. Below, we will describe some of these sections in a little more detail. Last medically reviewed on December 21, 2017 Neurology / NeurosciencePsychology / Psychiatry How we reviewed this article: SOURCES Share this article Medically reviewed by Seunggu Han, M.D. — By Tim Newman — Updated on February 3, 2022 Latest news What do people experience at the border between life and death? Exercise restores brain insulin sensitivity, may protect against type 2 diabetes Researchers are trialing lab-grown blood transfusions: What to know Alzheimer’s disease: New biomarker identified, may lead to earlier diagnosis Alzheimer's: Could beer hop compounds help reduce toxic clumps? Was this article helpful? Yes No What are mitochondria? Structure DNA Functions Disease Aging Mitochondria are often referred to as the powerhouses of the cell. They help turn the energy we take from food into energy that the cell can use. But, there is more to mitochondria than energy production. Present in nearly all types of human cell, mitochondria are vital to our survival. They generate the majority of our adenosine triphosphate (ATP), the energy currency of the cell. Mitochondria are also involved in other tasks, such as signaling between cells and cell death, otherwise known as apoptosis. In this article, we will look at how mitochondria work, what they look like, and explain what happens when they stop doing their job correctly. The structure of mitochondria A basic diagram of a mitochondrion Mitochondria are small, often between 0.75 and 3 micrometers and are not visible under the microscope unless they are stained. Unlike other organelles (miniature organs within the cell), they have two membranes, an outer one and an inner one. Each membrane has different functions. Mitochondria are split into different compartments or regions, each of which carries out distinct roles. Some of the major regions include the: Outer membrane: Small molecules can pass freely through the outer membrane. This outer portion includes proteins called porins, which form channels that allow proteins to cross. The outer membrane also hosts a number of enzymes with a wide variety of functions. Intermembrane space: This is the area between the inner and outer membranes. Inner membrane: This membrane holds proteins that have several roles. Because there are no porins in the inner membrane, it is impermeable to most molecules. Molecules can only cross the inner membrane in special membrane transporters. The inner membrane is where most ATP is created. Cristae: These are the folds of the inner membrane. They increase the surface area of the membrane, therefore increasing the space available for chemical reactions. Matrix: This is the space within the inner membrane. Containing hundreds of enzymes, it is important in the production of ATP. Mitochondrial DNA is housed here (see below). Different cell types have different numbers of mitochondria. For instance, mature red blood cells have none at all, whereas liver cells can have more than 2,000. Cells with a high demand for energy tend to have greater numbers of mitochondria. Around 40 percent of the cytoplasm in heart muscle cells is taken up by mitochondria. Although mitochondria are often drawn as oval-shaped organelles, they are constantly dividing (fission) and bonding together (fusion). So, in reality, these organelles are linked together in ever-changing networks. Also, in sperm cells, the mitochondria are spiraled in the midpiece and provide energy for tail motion. Mitochondrial DNA Although most of our DNA is kept in the nucleus of each cell, mitochondria have their own set of DNA. Interestingly, mitochondrial DNA (mtDNA) is more similar to bacterial DNA. The mtDNA holds the instructions for a number of proteinsTrusted Source and other cellular support equipment across 37 genes. The human genome stored in the nuclei of our cells contains around 3.3 billion base pairs, whereas mtDNA consists of less than 17,000Trusted Source. During reproduction, half of a child’s DNA comes from their father and half from their mother. However, the child always receives their mtDNA from their mother. Because of this, mtDNA has proven very useful for tracing genetic lines. For instance, mtDNA analyses have concluded that humans may have originated in Africa relatively recently, around 200,000 years ago, descended from a common ancestor, known as mitochondrial EveTrusted Source. What do mitochondria do? Mitochondria are important in a number of processes. Although the best-known role of mitochondria is energy production, they carry out other important tasks as well. In fact, only about 3 percent of the genes needed to make a mitochondrion go into its energy production equipment. The vast majority are involved in other jobs that are specific to the cell type where they are found. Below, we cover a few of the roles of the mitochondria: Producing energy ATP, a complex organic chemical found in all forms of life, is often referred to as the molecular unit of currency because it powers metabolic processes. Most ATP is produced in mitochondria through a series of reactions, known as the citric acid cycle or the Krebs cycle. Energy production mostly takes place on the folds or cristae of the inner membrane. Mitochondria convert chemical energy from the food we eat into an energy form that the cell can use. This process is called oxidative phosphorylation. The Krebs cycle produces a chemical called NADH. NADH is used by enzymes embedded in the cristae to produce ATP. In molecules of ATP, energy is stored in the form of chemical bonds. When these chemical bonds are broken, the energy can be used. Cell death Cell death, also called apoptosis, is an essential part of life. As cells become old or broken, they are cleared away and destroyed. Mitochondria help decide which cells are destroyed. Mitochondria release cytochrome C, which activates caspase, one of the chief enzymes involved in destroying cells during apoptosis. Because certain diseases, such as cancer, involve a breakdown in normal apoptosis, mitochondria are thought to play a role in the disease. Storing calcium Calcium is vital for a number of cellular processes. For instance, releasing calcium back into a cell can initiate the release of a neurotransmitter from a nerve cell or hormones from endocrine cells. Calcium is also necessary for muscle function, fertilization, and blood clotting, among other things. Because calcium is so critical, the cell regulates it tightly. Mitochondria play a part in this by quickly absorbing calcium ions and holding them until they are needed. Other roles for calcium in the cell include regulating cellular metabolism, steroid synthesis, and hormone signalingTrusted Source. Heat production When we are cold, we shiver to keep warm. But the body can also generate heat in other ways, one of which is by using a tissue called brown fat. During a process called proton leakTrusted Source, mitochondria can generate heat. This is known as non-shivering thermogenesis. Brown fat is found at its highest levels in babies, when we are more susceptible to cold, and slowly levels reduce as we age. Mitochondrial disease If mitochondria do not function correctly, it can cause a range of medical problems. The DNA within mitochondria is more susceptible to damage than the rest of the genome. This is because free radicals, which can cause damage to DNA, are produced during ATP synthesis. Also, mitochondria lack the same protective mechanisms found in the nucleus of the cell. However, the majority of mitochondrial diseases are due to mutations in nuclear DNA that affect products that end up in the mitochondria. These mutations can either be inherited or spontaneous. When mitochondria stop functioning, the cell they are in is starved of energy. So, depending on the type of cell, symptoms can vary widely. As a general rule, cells that need the largest amounts of energy, such as heart muscle cells and nerves, are affected the most by faulty mitochondria. The following passage comes from the United Mitochondrial Disease Foundation: “Because mitochondria perform so many different functions in different tissues, there are literally hundreds of different mitochondrial diseases. […] Because of the complex interplay between the hundreds of genes and cells that must cooperate to keep our metabolic machinery running smoothly, it is a hallmark of mitochondrial diseases that identical mtDNA mutations may not produce identical diseases.” Diseases that generate different symptoms but are due to the same mutation are referred to as genocopies. Conversely, diseases that have the same symptoms but are caused by mutations in different genes are called phenocopies. An example of a phenocopy is Leigh syndrome, which can be caused by several different mutations. Although symptoms of a mitochondrial disease vary greatly, they might include: loss of muscle coordination and weakness problems with vision or hearing learning disabilities heart, liver, or kidney disease gastrointestinal problems neurological problems, including dementia Other conditions that are thought to involve some level of mitochondrial dysfunction, include: Parkinson’s disease Alzheimer’s disease bipolar disorder schizophrenia chronic fatigue syndrome Huntington’s disease diabetes autism Mitochondria and aging Over recent years, researchers have investigated a link between mitochondria dysfunction and aging. There are a number of theories surrounding aging, and the mitochondrial free radical theory of aging has become popular over the last decade or so. The theory is that reactive oxygen species (ROS) are produced in mitochondria, as a byproduct of energy production. These highly charged particles damage DNA, fats, and proteins. Because of the damage caused by ROS, the functional parts of mitochondria are damaged. When the mitochondria can no longer function so well, more ROS are produced, worsening the damage further. Although correlations between mitochondrial activity and aging have been found, not all scientists have reached the same conclusions. Their exact role in the aging process is still unknown. In a nutshell Mitochondria are, quite possibly, the best-known organelle. And, although they are popularly referred to as the powerhouse of the cell, they carry out a wide range of actions that are much less known about. From calcium storage to heat generation, mitochondria are hugely important to our cells’ everyday functions. Last medically reviewed on February 8, 2018 Biology / Biochemistry How we reviewed this article: SOURCES Share this article Medically reviewed by Daniel Murrell, M.D. — By Tim Newman on February 8, 2018 Latest news What do people experience at the border between life and death? Exercise restores brain insulin sensitivity, may protect against type 2 diabetes Researchers are trialing lab-grown blood transfusions: What to know Alzheimer’s disease: New biomarker identified, may lead to earlier diagnosis Alzheimer's: Could beer hop compounds help reduce toxic clumps? Was this article helpful? Yes No RELATED COVERAGE What is a cell? Medically reviewed by Alana Biggers, M.D., MPH Our bodies contain trillions of cells. In this article, we explain what they are and what happens inside. We also describe some of the many types of… READ MORE Get our newsletter Keep up with the ever-changing world of medical science with new and emerging developments in health. Enter your email Your privacy is important to us About Us Contact Us Terms of Use Privacy Policy Privacy Settings Advertising Policy Health Topics Health Hubs Medical Affairs Content Integrity Newsletters © 2004-2022 Healthline Media UK Ltd, Brighton, UK, a Red Ventures Company. All rights reserved. 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