Chapter 4: How do Neurons use Electrical signals to Transmit Information? (Non MCQ Questions) Flashcards
What is Epilepsy? What drug is given to treat it? How prevalent is it? What 3 symptoms does it have at onset?
Dilantin (diphenylhydantoin), an
anesthetic agent.
Epilepsy is the most common neurological disease worldwide: 1 person in 20 experiences an epileptic seizure in his or her lifetime.
synchronous stimuli can trigger a seizure; thus, a strobe light is often used in diagnosis. some epileptic seizures can be linked to a specific symptom, such as infection, trauma, tumor, or other damage to a part of the brain. others appear to arise spontaneously. Their cause is poorly understood.
Three symptoms are common to many kinds of epilepsy: 1. an aura, or warning, of an impending seizure, which may take the form of a sensation, such as an odor or sound, or may simply be a “feeling”
- abnormal movements such as repeated chewing or shaking; twitches that start in a limb and spread across the body; and in some cases, a total loss of muscle tone and postural support causes the person to collapse
- loss of consciousness and later unawareness that the seizure happened
if seizures occur repeatedly and cannot be controlled by drug treatment, surgery may be performed. The goal of surgery is to remove damaged or scarred tissue that serves as the focal point of a seizure. removing this small area prevents seizures from starting and spreading to other brain regions. The condition of epilepsy reveals that the brain is normally electrically active and that if this activity becomes abnormal, the consequences are severe.
What 3 questions was Descartes interested in that scientists still grapple with today?
- How do our nerves detect a sensory stimulus and inform the brain about it?
- How does the brain decide what response should be made?
- How does the brain command muscles to move to produce a behavioral response?
What is Electrical stimulation?
electrical stimulation is passage of an electrical current from the uninsulated tip of an electrode through tissue, resulting in changes in the electrical activity of the tissue.
It was discovered by Luigi Galvani
What is Electricity?
Electricity is the flow of electrons from a body that contains a higher charge (more electrons) to a body that contains a lower charge (fewer electrons). This electron flow can perform work, such as lighting an unlit bulb. if biological tissue contains an electrical charge, the charge can be recorded; if tissue is sensitive to an electrical charge, the tissue can be stimulated.
What is an Electron?
Electrons are the negatively charged particles of atom. Together, all of the electrons of an atom create a negative charge that balances the positive charge of the protons in the atomic nucleus. Electrons are extremely small compared to all of the other parts of the atom.
What Electrical potential or electrical charge?
This electrical potential, or electrical charge, is the ability to do work through the use of stored electrical energy.
Electrical charge is measured in volts, the difference in charge between the positive and the negative poles. The positive and negative poles in a battery, like the poles in each wall socket in your home, when not connected, have a voltage between the poles.
What is an Electroencephalogram/EEG?
electroencephalogram (eeG) graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons.
What is a Voltmeter?
Voltmeter is device that measures the flow and the strength of electrical voltage by recording the difference in electrical potential between two bodies.
Richard Caton was the first to use them as a type of EEG.
Richard Caton, a Scottish physician who lived in the early twentieth century, was the first to measure the electrical currents of the brain with a sensitive voltmeter, a device that measures the flow and the strength of electrical voltage by recording the difference in electrical potential between two bodies. Caton reported that, when he placed electrodes on the skull of a human subject, he could detect fluctuations in his voltmeter recordings. Today, this type of brain recording, the electroencephalogram (EEG), is a standard tool used to monitor sleep stages and record waking activity as well as to diagnose disruptions such as those that occur in epilepsy.
Who discovered that the flow of information in the nervous system was too slow to be conducted by electricity?
Hermann von Helmholtz, a nineteenth-century German scientist, stimulated a nerve leading to a muscle and measured the time the muscle took to contract. The nerve conducted information at the rate of only 30 to 40 meters per second, whereas electricity flows along a wire at the much faster speed of light (3 3 108 meters per second). The flow of information in the nervous system, then, is much too slow to be a flow of electricity. To explain the electrical signals of a neuron, Julius Bernstein suggested in 1886 that the chemistry of neurons produces an electrical charge. He also proposed that the charge can change and so act as a signal. Bernstein’s idea was that successive waves of electrical change constitute the message conveyed by the neuron.
What was Julius Bernstein idea?
Bernstein’s idea was that waves of chemical change travel along an axon to deliver a neuron’s message.
What is an Oscilloscope?
Device that serves as a sensitive voltmeter by measuring the flow of electrons to measure voltages.
Why can’t we measure the electrical recording of a human neuron directly.
Too small. Most humans and animal neurons are too small to measure there charge directly.on the order of 1 to 20 micrometers in diameter, too small to be seen by the eye and too small on which to perform experiments easily. The British zoologist J. Z. Young, when dissecting the North Atlantic squid, Loligo vulgaris, noticed that it has giant axons, as much as a millimeter (1000 micrometers) in diameter
What is the name of the species of squid that have giant axons?
Loligo Vulgaris
What is a Microelectrode?
The final ingredient needed to measure a neuron’s electrical activity is an electrode small enough to place on or into an axon—a microelectrode.
Microelectrodes can deliver an electrical current to a single neuron or record from it.
One way to make a microelectrode is to etch the tip of a piece of thin wire to a fine point of about 1 micrometer in size and insulate the rest of the wire. The tip is placed on or into the neuron.
Microelectrodes are used to record from an axon in a number of different ways. Placing the tip of a microelectrode on an axon provides an extracellular measure of the electrical current from a very small part of the axon. If a second microelectrode is used as the reference, one tip can be placed on the surface of the axon and the other inserted into the axon. This technique provides a measure of voltage across the cell membrane
What was the signficance of Hodgkin and Hukey’s recording of a Squid’s axon?
They explained the nerve impulse as changes in ion concentration across the cell membrane.
Using the giant axon of the squid, an oscilloscope, and microelectrodes, Hodgkin and Huxley recorded the electrical voltage on an axon’s membrane and explained the nerve impulse as changes in ion concentration across the cell membrane. The basis of this electrical activity is the movement of intracellular and extracellular ions, which carry positive and negative charges.
What are the extracellular fluids of a Neuron filled with?
The intracellular and extracellular fluids of a neuron are filled with various ions, including positively charged Na1 (sodium) and K1 (potassium) ions and negatively charged Cl2 (chloride) ions.
These fluids also contain numerous negatively charged protein molecules (A2 for short).
Positively charged ions are called cations, and negatively charged ions, including protein molecules, are called anions.
Three factors influence the movement of anions and cations into and out of cells: diffusion, concentration gradient, and charge.
What are positively and negatively charged ions called?
Positively charged ions are called cations, and negatively charged ions, including protein molecules, are called anions.
What are the three factors that influence the movement f anions and cations into and out of cells?
Three factors influence the movement of anions and cations into and out of cells: diffusion, concentration gradient, and charge.
What is Diffusion?
The movement of ions from an area of higher concentration to an area of lower concentration through random motion.
Because molecules move constantly, they spontaneously tend to spread out from where they are more concentrated to where they are less concentrated. This spreading out is diffusion. Requiring no work, diffusion results from the random motion of molecules as they move and bounce off one another to gradually disperse in a solution. When diffusion is complete, a dynamic equilibrium, with an equal number of molecules everywhere, is created
What is concentration gradient?
Differences in concentration of a substance among regions of a container that allow the substance to diffuse from an area of higher concentration to an area of lower concentration.
Concentration gradient describes the relative concentration of a substance in space or in a solution.
when you drop a little ink into a beaker of water, the dye starts out concentrated at the site of contact and then diffuses. The ink spreads out from a point of higher concentration to points of lower concentration until it is equally distributed, and all the water in the beaker is the same color. A similar process takes place when a salt solution is put into water. The salt concentration is initially high in the location where it enters the water, but it then diffuses from that location until its ions are in equilibrium. You are familiar with other kinds of gradients. A car parked on a hill will roll down the grade if the car is taken out of gear, a skier will slide down a mountain, and a dropped ball falls to the ground. Because ions carry an electrical charge and like charges repel one another, ion movement can be described either by a concentration gradient, the difference in the number of ions between two regions, or by a voltage gradient, the difference in charge between two regions.
What is a Voltage Gradient?
difference in charge between two regions that allows a flow of current if the two regions are connected
Experimental results obtained over hundreds of years from electrical (1) and, more recently, from electrical (2)implicated electrical activity in the nervous system’s flow of information.
(1) Stimulation
(2) Recording
by the mid-twentieth century, scientists solved three technical problems in measuring the changes in electrical charge that travel like a wave along an axon’s membrane: (1), (2) and (3)
(1) How to record from the giant axons of the North Atlantic Squid
(2) How to use an Oscilloscope to measure small changes in voltage
(3) How to craft microelectrodes small enough to place on or in an axon.
The electrical activity of neuronal axons entails the diffusion of ions. ions may move down a(n) and down a(n) .
(1) Concentration gradient, from an area of relatively high concentration to an area of lower concentration.
(2) Voltage gradient, from an area of relatively high charge to an area of lower charge.
in what three ways does the semipermeable cell membrane affect the movement of ions in the nervous system?
(1) Ion channels in cell membrans may open to either facilate ion movement,
(2) close to impede ion movement or
(3) pump ions across the membrane.
What is resting potential?
Resting potential: Electrical charge across the cell membrane in the absence of stimulation; a store of potential energy produced by a greater negative charge on the intracellular side relative to the extracellular side.
We might use the term “potential” in the same way to talk about the financial potential of someone who has money in the bank—the person can spend the money at some future time. The resting potential, then, is a store of energy that can be used at a later time. Most of your body’s cells have a resting potential, but it is not identical on every axon. A resting potential can vary from 240 to 290 millivolts on axons of different animal species. The exact potential on an axon does not influence the neuron’s ability to participate in generating brain activity.
What four charged particles take part in producing the resting potential?
Four charged particles take part in producing the resting potential: ions of sodium (Na+) and potassium (K+), chloride ions (Cl-), and large protein molecules (A_).
These are the cations and anions defined in Section 4-1. These charged particles are distributed unequally across the axon’s membrane, with more protein anions and K1 ions in the intracellular fluid and more Cl2 and Na1 ions in the extracellular fluid. How do the unequal concentrations arise and how does each contribute to the resting potential?
What is Graded potential?
The small voltage fluctuation across the cell membrane
small voltage fluctuation in the cell membrane restricted to the vicinity on the axon where ion concentrations change to cause a brief increase (hyperpolarization) or decrease (depolarization) in electrical charge across the cell membrane.
The resting potential provides an energy store that can be used somewhat like the water in a dam, where small amounts can be released by opening gates for irrigation or to generate electricity. If the concentration of any of the ions across the unstimulated cell membrane changes, the membrane voltage changes. Conditions under which ion concentrations across the cell membrane change produce graded potentials, small voltage fluctuations that are restricted to the vicinity on the axon where ion concentrations change. Just as a small wave produced by dropping a stone into the middle of a large, smooth pond decays before traveling very far, graded potentials produced on a cell membrane decay before traveling very far. But an isolated axon will not undergo a spontaneous change in charge. For a graded potential to arise, an axon must somehow be stimulated. Stimulating an axon electrically through a microelectrode mimics the way in which membrane voltage changes to produce a graded potential in the living cell. If the voltage applied to the inside of the membrane is negative, the membrane potential increases in negative charge by a few millivolts.
What is Hyperpolarization and depolarization?
Part of graded potential. Hyperpolarization is due to an efflux of potassium (K+) making the extracellular side of the membrane more positive. The increase in charge across a membrane, usually due to the inward flow of chloride or sodium ions or the outward flow of potassium ions
Depolarization is due to an influnce of NA+ (sodium) through Na+ channels. It the decrease in electrical charge across a membrane usually due to inward flow of sodium ions.
Where does Hyperpolarization and Depolarization take place? What channels underlie it?
Hyperpolarization and depolarization typically take place on the soma (cell-body) membrane and on the dendrites of neurons. These areas contain channels that can open and close, causing the membrane potential to change as illustrated in Figure 4-13.
Three channels—for potassium, chloride, and sodium ions—underlie graded potentials: 1. Potassium channels For the membrane to become hyperpolarized, its extracellular side must become more positive, which can be accomplished with an efflux of K1 ions. But if potassium channels are ordinarily open, how can a greater-than-normal efflux of K1 ions take place? Apparently, even though potassium channels are open, some resistance remains to the outward flow of K1 ions. Reducing this resistance enables hyperpolarization. 2. Chloride channels The membrane can also become hyperpolarized if there is an influx of Cl2 ions. Even though chloride ions can pass through the membrane, more ions remain on the outside than on the inside, so a decreased resistance to Cl2 flow can result in brief increases of Cl2 inside the cell. 3. Sodium channels Depolarization can be produced by an influx of sodium ions and is produced by the opening of normally closed gated sodium channels.
What channels have a role in Hyperpolarization?
Potassium channels.Evidence that potassium channels have a role in hyperpolarization comes from the fact that the chemical tetraethylammonium (TEA), which blocks potassium channels, also blocks hyperpolarization.
What channels have a role in Depolarization?
Sodium channels.The involvement of sodium channels in depolarization is indicated by the fact that the chemical tetrodotoxin, which blocks sodium channels, also blocks depolarization.
Why are Puttlefish so dangerous?
The secrete Tetrodotoxin which impedes the electrical activity of Neurons.
