Thursday 28 March 2024

All about the central nervous system

 The central nervous system consists of the brain and spinal cord. The central nervous system controls thought, movement, and emotion, as well as breathing, heart rate, hormones, and body temperature.

The central nervous system (CNS) is referred to as “central” because it combines information from the entire body and coordinates activity across the whole organism.

This article briefly overviews the CNS. It looks 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

Here are some key points about the central nervous system. More detail and supporting information are in the main article.

  • The CNS consists of the brain and spinal cord.
  • The brain is the most complex organ in the body and uses 20% of the total oxygen we breathe.
  • The brain consists of an estimated 100 billion neurons connected to thousands more.
  • The brain can be divided into four main lobes: temporal, parietal, occipital, and frontal.

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 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.

Now we will look at some of the parts of the CNS in more detail, starting with 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% 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.

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.

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.

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.

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.

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.

Source - Medical News Today


Wednesday 27 March 2024

Where are the kidneys located, what do they do, and what do they look like?

 The kidneys are a pair of bean-shaped organs located below the rib cage, one on each side of the spine. The kidneys help remove waste products from the body, maintain balanced electrolyte levels, and regulate blood pressure.

The kidneys are some of the most important organs in the body. The ancient Egyptians left only the brain and kidneys in position before embalming a body, inferring that they held a higher value than other organs.

In this article, we look at the structure and function of the kidneys, the diseases that affect them, and how to keep them healthy.

The positioningTrusted Source of the kidneys is just below the rib cage, with one on each side of the spine. The right kidney is generally slightly lower than the left kidney to make space for the liver.

The kidneys are two bean-shaped organs that are roughly the size of a fist. A tough, fibrous renal capsule surrounds each kidney and provides support for the soft tissue inside. Beyond that, two layers of fat serve as further protection. The adrenal glands lie on top of the kidneys.

Inside the kidneys are a number of pyramid-shaped lobes. Each consists of an outer renal cortex and an inner renal medulla. Nephrons flow between these sections. Each nephron includes a filter, called the glomerulus, and a tubule. The glomerulus filters blood, which enters the kidneys through the renal arteries and leaves through the renal veins. The kidneys are relatively small organs, but they receive 20–25%Trusted Source of the heart’s output.

The tubule returns necessary substances to the blood and removes waste that then becomes urine. The kidneys excrete urine through the ureter, a tube that leads to the bladder.

What does a kidney look like?

Each kidney is approximately 3 centimeters (cm) thick, 6 cm wide, and 12 cm long. In males, the average weightTrusted Source of the kidneys is roughly 129 grams (g) for the right one and 137 g for the left. In females, the average weightTrusted Source of these organs is 108 g for the right kidney and 116 g for the left kidney.

Waste excretion

Reabsorption of nutrients 

The kidneys reabsorbTrusted Source nutrients from the blood using tubules and transport them to where they will best support health. They also reabsorb other products to help maintain homeostasis. Reabsorbed products include:

Maintaining pH

Osmolality regulation

Regulating blood pressure

Secretion of active compounds

The kidneys release several important compounds, including:

  • Erythropoietin: This controls erythropoiesis, which is the production of red blood cells. The liver also produces erythropoietin, but the kidneys are its main producers in adults.
  • Renin: This enzyme helps manage the expansion of arteries and the volumes of blood plasma, lymph, and interstitial fluid. Lymph is a fluid that contains white blood cells, which support immune activity, and interstitial fluid is the main component of extracellular fluid.
  • Calcitriol: This is the hormonally active metabolite of vitamin D. It increases both the amount of calcium that the intestines can absorb and the reabsorption of phosphate in the kidney.

A range of diseases can affect the kidneys. Environmental or medical factors may lead to kidney disease, and they can cause functional and structural problems from birth in some people.

Diabetic nephropathy

In people with diabetic nephropathy, damage occurs to the capillaries of the kidney as a result of long-term diabetes. The symptoms may not become apparent until years after the damage starts to develop. They can include:

  • fluid buildup
  • sleep difficulty
  • poor appetite
  • upset stomach
  • weakness
  • difficulty concentrating

Kidney stones

Stones can form as a solid buildup of minerals in the kidneys.

They can cause intense pain and might affect kidney function if they block the ureter.

Kidney infections

Kidney infections tend to result from bacteria in the bladder that transfer to the kidneys.

The symptoms can include lower back pain, painful urination, and, sometimes, fever. Changes in the urine may include the presence of blood, cloudiness, and an unusual odor.

Kidney infections are more commonTrusted Source in females than in males and more likely to affect those who are pregnant. The infection often responds well to antibiotics.

Renal failure

In people with renal failure, the kidneys become unable to filter out waste products from the blood effectively.

If an injury or another factor, such as the overuse of medication, causes kidney failure, the condition may be reversible with treatment.

If the cause is a disease, however, kidney failure often does not have a full cure.

Kidney hydronephrosis

Hydronephrosis means “water on the kidney.”

It usually occurs when an obstruction prevents urine from leaving the kidney, causing intense pain.

In time, untreated hydronephrosis can put pressure on a person’s kidneys and may result in kidney damage.

Interstitial nephritis

A reaction to medications or infection can cause inflammation of the nephrons.

The treatment usually involves addressing the cause of inflammation or changing a course of medication.

Kidney tumor

These tumors can be benign or malignant. Benign cancers do not spread or attack tissue, but malignant cancers can be aggressive.

The most common malignant kidney cancer is renal cell carcinoma.

Nephrotic syndrome

When damage to the kidney affects its function, this causes protein levels in the urine to increase. This effect leads to a protein shortage throughout the body, which draws water into the tissues. The symptoms of nephrotic syndrome can includeTrusted Source:

  • puffy eyes
  • increased cholesterol levels
  • weight gain
  • fatigue
  • loss of appetite

Lower back pain and changes in urination, especially on one side, may be signs of kidney problems.

Some common causes of kidney damage may include:

  • Analgesics: Using pain medication over a long period might result in chronic analgesic nephritis. Examples include aspirin, acetaminophen, and nonsteroidal anti-inflammatory drugs (NSAIDs).
  • IgA nephropathy: Also known as Berger disease, this occurs when immunoglobin A (IgA) antibodies build up in the kidney. IgA forms a vital part of the immune system, but a buildup can be harmful. The disease progresses slowly, sometimes taking as long as 20 yearsTrusted Source to develop. The symptoms include abdominal pain, a rash, and arthritis. It can result in kidney failure.
  • Lithium: Doctors prescribe lithium to treat schizophrenia and bipolar disorder. However, lithium might cause nephropathyTrusted Source with long-term use. Close medical supervision can help a person avoid the negative effects of lithium.
  • Chemotherapy agents: The most common type of kidney issue in people with cancer is acute kidney injury. This might be due to the intense vomiting and diarrhea that are common side effects of chemotherapy.
  • Alcohol: Alcohol alters the kidneys’ ability to filter the blood. It also dehydrates the body, making it harder for the kidneys to redress internal balances, and increases blood pressure, which can also hinder the kidneys.

In the case of severe kidney damage, dialysis might be an option. Doctors only use this treatment for end stage kidney failure involving the loss of 85–90% of kidney function. Kidney dialysis aims to complete some of the functions of a healthy kidney. These include:

  • removing waste, excess salt, and water
  • maintaining the correct levels of chemicals in the blood, including sodium, bicarbonate, and potassium
  • maintaining blood pressure

The two most common types of kidney dialysis are:

Hemodialysis

An artificial kidney, or hemodialyzerTrusted Source, removes waste, additional fluids, and chemicals. The treating doctor makes an entry point in the body by connecting an artery and a vein under the skin to create a larger blood vessel.

Blood travels into the hemodialyzer, receives treatment, and then returns to the body. This process usually takes place three or four times a week.

Peritoneal dialysis

The doctor inserts a sterile cleansing solution into the abdominal cavity around the intestine. This is the peritoneum, and a protective membrane surrounds it.

In continuous peritoneal dialysis, the fluid drains through a catheter. The individual discards these fluids four or five times a day. In automated peritoneal dialysis, the fluid also drains through a catheter, and the exchanges usually occur throughout the night while the person sleeps.

The following are suggestionsTrusted Source for keeping the kidneys healthy and helping avoid kidney disease:

  • Eating a balanced diet: Many kidney problems result from high blood pressure and diabetes. As a result, maintaining a nutritious, well-balanced diet can prevent several common causes of kidney disease. The National Heart, Lung, and Blood Institute recommends the DASH dietTrusted Source for maintaining healthy blood pressure.
  • Getting enough exercise: Exercising for 30 minutes every day can reduce the risk of high blood pressure and obesity, both of which put pressure on kidney health.
  • Drinking plenty of water: Fluid intake, especially of water, is important. Many factors can affect how much water people should drink, but about 4–6 glasses per day can help improve and maintain kidney health.
  • Taking supplements: Be careful when taking supplements, as not all dietary supplements and vitamins are beneficial. Some can harm the kidneys if a person takes too many.
  • Limiting salt: Limit sodium intake to a maximum of 2,300 milligrams (mg)Trusted Source of sodium, and ideally 1,500 mgTrusted Source, each day.
  • Moderating alcohol: Consuming more than one drink per day for females and two per day for males can harm the kidneys and impair renal function.
  • Avoiding smoking: Tobacco smoke restricts blood vessels. Without an adequate blood supply, the kidneys will not be able to complete their normal work.
  • Taking over-the-counter (OTC) medications: A drug is not harmless simply because a person does not need a prescription to get it. Overusing OTC drugs, such as ibuprofen and naproxen, can damage the kidneys.
  • Screening for health conditions: Anyone with high blood pressure or diabetes should consider discussing regular kidney screening with a doctor to help spot any possible health issues.
  • Managing diabetes and heart disease: Following a doctor’s recommendations for managing these conditions can help protect the kidneys in the long term.
  • Taking steps to get quality sleep and control stress: The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends getting 7–8 hours of sleepTrusted Source each night and seeking out activities to reduce stress.

Keeping the kidneys in full working order is essential for overall health.

Source - Medical News Today