Neurophysiology: Neuron Division and Brain Metabolism
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Questions and Answers

What percentage of body weight does the brain comprise?

  • 4%
  • 1%
  • 2% (correct)
  • 3%

    • What happens to brain cells if there is an interruption in blood or oxygen?

  • They adapt to anaerobic metabolism
  • They die within 4 to 6 minutes (correct)
  • They become dormant
  • They regenerate

    • How long can brain cells function without oxygen?

  • 10 seconds (correct)
  • 10 minutes
  • 30 seconds
  • 1 minute

    • What is the major fuel source for the brain?

    <p>Glucose</p> Signup and view all the answers

    What are the three major divisions of the brain based on embryologic origin?

    <p>Forebrain, Midbrain, and Hindbrain</p> Signup and view all the answers

    What is the consistency of the brain?

    <p>Soft and custard-like</p> Signup and view all the answers

    What happens in case of cardiac arrest?

    <p>Unconsciousness with cardiac arrest</p> Signup and view all the answers

    What makes up the brain stem?

    <p>Midbrain, Pons, and Medulla</p> Signup and view all the answers

    What is the primary cause of lesions in the central nervous system in Multiple Sclerosis?

    <p>Breakdown of the blood brain barrier during viral infection</p> Signup and view all the answers

    What is the name of the disease that is characterized by demyelination of the ventral spinal roots?

    <p>Guillian-Barre Syndrome</p> Signup and view all the answers

    What percentage of patients with Guillian-Barre Syndrome will achieve a spontaneous recovery?

    <p>80-90%</p> Signup and view all the answers

    What is the term for the hard, demyelinated or sclerotic patches throughout the white matter of the central nervous system?

    <p>Lesions</p> Signup and view all the answers

    What is the primary mechanism of injury in Multiple Sclerosis?

    <p>Demyelination of axons</p> Signup and view all the answers

    What is the term for the immune cells that enter the brain and colonize it during viral infection in Multiple Sclerosis?

    <p>B-cell lymphocytes</p> Signup and view all the answers

    What is the term for the progressive ascending muscle weakness of the limbs in Guillian-Barre Syndrome?

    <p>Flaccid paralysis</p> Signup and view all the answers

    What is the primary function of the brain, spinal cord, and peripheral nervous system that can be impaired due to injury?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of supporting cells in the nervous system?

    <p>To provide structure, support, and nutrition for neurons</p> Signup and view all the answers

    What is the term for the cell body of a neuron?

    <p>Soma</p> Signup and view all the answers

    Where are the neuronal cell bodies located in the CNS?

    <p>In groups called nuclei</p> Signup and view all the answers

    What is the function of the dendrites in a neuron?

    <p>To carry nerve impulses towards the cell body</p> Signup and view all the answers

    What is the term for the connections between neurons?

    <p>Synapses</p> Signup and view all the answers

    How many axons does a typical neuron have?

    <p>One axon</p> Signup and view all the answers

    What is the purpose of the axon in a neuron?

    <p>To carry impulses away from the cell body</p> Signup and view all the answers

    Where are the neuronal cell bodies located in the PNS?

    <p>In groups called ganglia</p> Signup and view all the answers

    Which of the following is a characteristic of brain tissue?

    <p>It can be compressed, contused, and destroyed</p> Signup and view all the answers

    What is the primary function of the Blood-Brain Barrier?

    <p>To permit the passage of essential substances into the brain</p> Signup and view all the answers

    What is a characteristic of cerebral capillaries at birth?

    <p>They are more permeable than in adulthood</p> Signup and view all the answers

    What is the primary reason why lipid-soluble compounds can easily enter the brain?

    <p>Because they are highly lipid-soluble</p> Signup and view all the answers

    What is the primary function of the Circle of Willis?

    <p>To provide a backup system for blood flow in case of disruption</p> Signup and view all the answers

    What is the approximate percentage of cardiac output that is dedicated to cerebral blood flow?

    <p>1/6</p> Signup and view all the answers

    What is the primary mechanism controlling cerebral blood flow?

    <p>Autoregulation</p> Signup and view all the answers

    What is the effect of increased carbon dioxide concentration on cerebral blood flow?

    <p>It increases cerebral blood flow</p> Signup and view all the answers

    What is the primary reason for increased cerebral blood flow in response to decreased oxygen concentration?

    <p>To wash out the accumulated lactic acid and other acidic materials</p> Signup and view all the answers

    What is the effect of increased hydrogen ion concentration on neural activity?

    <p>It greatly depresses neural activity</p> Signup and view all the answers

    Which of the following is a known risk factor for stroke?

    <p>Polycythemia</p> Signup and view all the answers

    What is the effect of cocaine on stroke risk?

    <p>It increases the risk of both ischemic and hemorrhagic strokes</p> Signup and view all the answers

    What is the primary cause of increased cerebral blood flow in response to acidosis?

    <p>To wash out the acidic materials and provide more oxygen</p> Signup and view all the answers

    What is the effect of alcohol consumption on stroke risk?

    <p>It contributes to stroke risk through multiple mechanisms</p> Signup and view all the answers

    What is the primary difference between ischemic and hemorrhagic strokes?

    <p>Ischemic strokes are caused by clots, while hemorrhagic strokes are caused by bleeding</p> Signup and view all the answers

    What is the effect of increased carbon dioxide on cerebral blood flow?

    <p>It increases cerebral blood flow</p> Signup and view all the answers

    What is the primary function of the liver in relation to ammonia?

    <p>To convert ammonia to urea which is then excreted by the kidneys</p> Signup and view all the answers

    What is the effect of ammonia accumulation on the brain?

    <p>It alters cerebral metabolism and interferes with neurotransmitter function</p> Signup and view all the answers

    What is the primary cause of renal failure in hepatorenal syndrome?

    <p>Decreased blood volume leading to decreased GFR and tubular necrosis</p> Signup and view all the answers

    What is the term for inflammation of the liver?

    <p>Hepatitis</p> Signup and view all the answers

    What is the effect of hepatorenal syndrome on blood volume?

    <p>It increases blood volume</p> Signup and view all the answers

    What is the consequence of liver failure on ammonia removal?

    <p>Ammonia accumulates in the brain</p> Signup and view all the answers

    What is the pathological consequence of ammonia accumulation in the brain?

    <p>All of the above</p> Signup and view all the answers

    What is the role of the liver in regulating renal function in hepatorenal syndrome?

    <p>The liver produces vasoconstrictive substances, causing renal vasoconstriction</p> Signup and view all the answers

    What is the primary route of transmission for Hepatitis A virus?

    <p>Fecal-oral route through contaminated food or water</p> Signup and view all the answers

    What is the duration of the incubation period for Hepatitis A virus?

    <p>2-4 weeks</p> Signup and view all the answers

    During which period is fecal shedding of Hepatitis A virus greatest?

    <p>10-14 days before onset of symptoms</p> Signup and view all the answers

    What is the approximate percentage of people in developed countries who have evidence of Hepatitis A infection by mid-adult life?

    <p>40-50%</p> Signup and view all the answers

    What is the typical duration of Hepatitis A disease?

    <p>4 months</p> Signup and view all the answers

    What is the primary cause of post-transfusion hepatitis?

    <p>Hepatitis C</p> Signup and view all the answers

    What is the primary site of replication for Hepatitis A virus?

    <p>Liver</p> Signup and view all the answers

    What is the most common cause of chronic liver disease, cirrhosis, and liver cancer worldwide?

    <p>Hepatitis C</p> Signup and view all the answers

    What is the outcome of Hepatitis A infection in terms of chronic disease?

    <p>It never leads to chronic hepatitis</p> Signup and view all the answers

    What is the significance of hepatitis D?

    <p>It is a defective RNA virus that requires HBV for replication</p> Signup and view all the answers

    What is the significance of anti-HAV antibodies in the blood?

    <p>It indicates past infection</p> Signup and view all the answers

    What is a distinguishing feature of hepatitis E?

    <p>It has a high mortality rate among pregnant women</p> Signup and view all the answers

    What is the significance of antibodies in hepatitis C?

    <p>They serve as markers of the disease</p> Signup and view all the answers

    What is the significance of hepatitis G?

    <p>Little is known about hepatitis G</p> Signup and view all the answers

    What is the primary reason why a vaccine for hepatitis C is difficult to develop?

    <p>There are many subtypes of the virus</p> Signup and view all the answers

    What is a common mode of transmission for hepatitis C?

    <p>Tattooing, acupuncture, and body piercing</p> Signup and view all the answers

    What is the life expectancy after the onset of symptoms in patients with cirrhosis?

    <p>8-10 years</p> Signup and view all the answers

    What is the cause of secondary biliary cirrhosis in children?

    <p>All of the above</p> Signup and view all the answers

    What is the result of severe liver disease?

    <p>Post-necrotic cirrhosis</p> Signup and view all the answers

    What is the percentage of people with Hepatitis C who develop post-necrotic cirrhosis?

    <p>25%</p> Signup and view all the answers

    What is the diagnosis method for post-necrotic cirrhosis?

    <p>Needle biopsy</p> Signup and view all the answers

    What is a common cause of obstructive jaundice?

    <p>All of the above</p> Signup and view all the answers

    What is the clinical manifestation of post-necrotic cirrhosis?

    <p>All of the above</p> Signup and view all the answers

    What is the outcome of untreated post-necrotic cirrhosis?

    <p>Either A or B</p> Signup and view all the answers

    What is the primary mechanism of liver cell injury during hepatitis virus infection?

    <p>Immune responses against the viral antigen</p> Signup and view all the answers

    What is the consequence of inflammatory process in hepatitis?

    <p>Damage and obstruction of bile ducts</p> Signup and view all the answers

    During which phase of hepatitis is the infection highly transmissible?

    <p>Prodromal (pre-icteric)</p> Signup and view all the answers

    What is the characteristic of the Kupffer cells in hepatitis?

    <p>Hyperplasia and infiltration with phagocytic cells</p> Signup and view all the answers

    What is the consequence of cell injury promoted by cell-mediated immunity in hepatitis?

    <p>Hepatic cell necrosis</p> Signup and view all the answers

    What is the time period after which regeneration of hepatic cells begins in hepatitis?

    <p>48 hours</p> Signup and view all the answers

    What is the characteristic of the inflammatory process in hepatitis?

    <p>Acute inflammation</p> Signup and view all the answers

    What is the consequence of obstructive jaundice in hepatitis?

    <p>Cholestasis</p> Signup and view all the answers

    Study Notes

    Neuron Structure and Function

    • Mature neurons do not divide, which is important to consider when neurons are injured, as new neurons are not generated to replace those that have lost function through damage or death.
    • Neurons have three components: the soma (cell body), dendrites, and axons.
    • Dendrites are multiple branch extensions of the cell body that carry nerve impulses towards the cell body and receive stimulation from other nerves.
    • The soma is the cell body that synthesizes the components necessary to maintain the function of the axon and its terminals.
    • Axons are long, conductive projections from the cell body that carry impulses away from the cell body.

    Brain Metabolic Requirements

    • The brain comprises 2% of body weight but receives 15% of cardiac output and consumes 20% of oxygen.
    • The brain cannot store oxygen and cannot participate in anaerobic metabolism.
    • If there is an interruption in blood or oxygen, brain cells can function for around 10 seconds without oxygen, and unconsciousness occurs with cardiac arrest.
    • Death of brain cells occurs within 4-6 minutes without oxygen, and glucose is the major fuel source with no provision for storing glucose.

    Brain Structure and Divisions

    • The brain has three major divisions based on embryologic origin: forebrain, midbrain, and hindbrain.
    • The forebrain is formed by the two cerebral hemispheres, the midbrain is formed by the cerebral peduncles, and the hindbrain is formed by the cerebellum, pons, and medulla.
    • The midbrain, medulla, and pons make up the brain stem.
    • Supporting cells, also known as neuroglial cells, provide structure, support, and nutrition for neurons.

    Multiple Sclerosis and Guillain-Barré Syndrome

    • Multiple sclerosis is a demyelination disease, and the cause is unknown, although there appears to be a genetic tendency towards developing the disease.
    • Lesions are hard, demyelinated or sclerotic patches throughout the white matter of the CNS, and they can be seen in the optic nerve, periventricular white matter, brain stem, cerebellum, and spinal cord white matter.
    • Axons die with demyelination.
    • Guillain-Barré Syndrome is a peripheral nervous system disease that causes demyelination of the ventral spinal roots, and the cause is unknown.
    • The disease is characterized by progressive ascending muscle weakness of the limbs, producing a symmetric flaccid paralysis.

    Blood-Brain Barrier

    • The blood-brain barrier is a protective CNS mechanism that permits the passage of essential substances, such as water, proteins, and electrolytes.
    • The barrier is more permeable at birth than in adulthood and can be altered by acute cerebral lesions, such as trauma and infection.
    • The barrier prevents many drugs from entering the brain, including highly water-soluble compounds, but lipid-soluble molecules, such as alcohol, nicotine, and heroin, can cross with ease.

    Blood Supply and Regulation

    • The blood supply to the brain is provided by the two internal carotid arteries anteriorly and the vertebral arteries posteriorly.
    • The Circle of Willis is a communication network between the distal branches of the internal carotid and vertebral arteries.
    • Anastomosis of arteries provides continued circulation if blood flow through one of the main vessels is disrupted.
    • Regulation of cerebral blood flow is largely controlled by autoregulation, which maintains constant cerebral blood flow despite changes in systemic arterial pressure.

    Cerebral Blood Flow and Regulation

    • Cerebral blood flow is approximately 750ml/minute, which is about 1/6 of cardiac output.
    • Autoregulation is efficient within a range of MAP 60-140 mmHg.
    • Increases in carbon dioxide concentration and/or hydrogen ion concentration will increase cerebral blood flow, as will decreased oxygen concentration.
    • Acidosis will depress neuronal activity, and the increased blood flow is the body's attempt to "wash out" toxins.

    Cerebral Vascular Accident (Stroke)

    • A stroke is an acute focal deficit from a vascular disorder that injures brain tissue.
    • Known risk factors include age, heart disease, polycythemia, sickle cell, alcohol, and cocaine.
    • There are two main types of strokes: ischemic and hemorrhagic.
    • Ischemic strokes occur when there is a blockage in the blood vessels, while hemorrhagic strokes occur when there is a rupture of the blood vessels.

    Hepatic Encephalopathy

    • Ammonia is a by-product of protein metabolism and intestinal bacterial action that can accumulate and cause symptoms of hepatic encephalopathy.
    • In liver failure, ammonia is not converted to urea, leading to altered cerebral metabolism and interference with neurotransmitters.
    • Neurologic signs of hepatic encephalopathy include rigidity, hyperreflexia, and, rarely, seizures, and can lead to fatal coma.

    Hepatorenal Syndrome

    • Hepatorenal syndrome is a complication of advanced liver disease that refers to the occurrence of renal failure in association with advanced liver disease.
    • It can be caused by a sudden decrease in blood volume, which leads to decreased GFR and tubular necrosis.
    • The liver's inability to remove vasoconstrictive substances can also contribute to renal vasoconstriction.

    Hepatitis

    • Hepatitis refers to inflammation of the liver and can have various causes, including viral infections, reactions to drugs and toxins, and infectious disorders.
    • Hepatitis A is caused by a small RNA-containing virus and is transmitted through the fecal-oral route.

    Hepatitis A

    • The incubation period for Hepatitis A is 2-4 weeks, and individuals can be contagious for up to 2 weeks before the onset of symptoms.
    • The disease usually runs its course within approximately 4 months after exposure and does not cause a carrier state or chronic hepatitis.

    Hepatitis C

    • Hepatitis C is a single-strand RNA virus that is the most common blood-borne infection in the US.
    • It is a major concern, as even small amounts of blood during tattooing, acupuncture, and body piercing can facilitate transmission.
    • Chronic hepatitis occurs in 50-80% of cases, and it is the most common cause of chronic liver disease, cirrhosis, and liver cancer worldwide.

    Hepatitis D (Delta)

    • Hepatitis D is a defective RNA virus that cannot infect hepatocytes on its own and requires hepatitis B virus for replication.
    • It can convert mild HBV infection into severe, fulminant disease.

    Hepatitis E

    • Hepatitis E is common in developing countries and clinically resembles Hepatitis A.
    • It does not cause chronic or carrier states, but has a high mortality rate (20%) among pregnant women, leading to fulminant hepatitis.

    Pathophysiology of Hepatitis

    • Two mechanisms of liver injury with hepatitis virus are direct cellular injury and induction of immune responses against the viral antigen.
    • Hepatic cell necrosis, scarring, and Kupffer cell hyperplasia can occur, leading to fibrosis, cholestasis, and obstructive jaundice.

    Clinical Course of Hepatitis

    • The clinical course of hepatitis consists of four phases: incubation, prodromal, icteric, and post-necrotic.
    • The prodromal phase begins about 2 weeks after exposure and ends with the appearance of jaundice, accompanied by symptoms such as fatigue, nausea, and RUQ pain.
    • The post-necrotic phase can result in portal hypertension, ascites, bleeding varices, and encephalopathy.

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    Description

    Learn about the unique characteristics of mature neurons and the brain's high metabolic requirements, including its oxygen needs and response to interruptions.

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