Chapter 4: How do Neurons use Electrical signals to Transmit Information? (Non MCQ Questions)

Question 1

What is Epilepsy? What drug is given to treat it? How prevalent is it? What 3 symptoms does it have at onset?

Answer 1

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”

2. 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
3. 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.

Question 2

What 3 questions was Descartes interested in that scientists still grapple with today?

Answer 2

1. How do our nerves detect a sensory stimulus and inform the brain about it?
2. How does the brain decide what response should be made?
3. How does the brain command muscles to move to produce a behavioral response?

Question 3

What is Electrical stimulation?

Answer 3

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

Question 4

What is Electricity?

Answer 4

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.

Question 5

What is an Electron?

Answer 5

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.

Question 6

What Electrical potential or electrical charge?

Answer 6

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.

Question 7

What is an Electroencephalogram/EEG?

Answer 7

electroencephalogram (eeG) graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons.

Question 8

What is a Voltmeter?

Answer 8

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.

Question 9

Who discovered that the flow of information in the nervous system was too slow to be conducted by electricity?

Answer 9

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.

Question 10

What was Julius Bernstein idea?

Answer 10

Bernstein’s idea was that waves of chemical change travel along an axon to deliver a neuron’s message.

Question 11

What is an Oscilloscope?

Answer 11

Device that serves as a sensitive voltmeter by measuring the flow of electrons to measure voltages.

Question 12

Why can’t we measure the electrical recording of a human neuron directly.

Answer 12

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

Question 13

What is the name of the species of squid that have giant axons?

Answer 13

Loligo Vulgaris

Question 14

What is a Microelectrode?

Answer 14

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

Question 15

What was the signficance of Hodgkin and Hukey’s recording of a Squid’s axon?

Answer 15

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.

Question 16

What are the extracellular fluids of a Neuron filled with?

Answer 16

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.

Question 17

What are positively and negatively charged ions called?

Answer 17

Positively charged ions are called cations, and negatively charged ions, including protein molecules, are called anions.

Question 18

What are the three factors that influence the movement f anions and cations into and out of cells?

Answer 18

Three factors influence the movement of anions and cations into and out of cells: diffusion, concentration gradient, and charge.

Question 19

What is Diffusion?

Answer 19

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

Question 20

What is concentration gradient?

Answer 20

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.

Question 21

What is a Voltage Gradient?

Answer 21

difference in charge between two regions that allows a flow of current if the two regions are connected

Question 22

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.

Answer 22

(1) Stimulation

(2) Recording

Question 23

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)

Answer 23

(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.

Question 24

The electrical activity of neuronal axons entails the diffusion of ions. ions may move down a(n) and down a(n) .

Answer 24

(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.

Question 25

in what three ways does the semipermeable cell membrane affect the movement of ions in the nervous system?

Answer 25

(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.

Question 26

What is resting potential?

Answer 26

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.

Question 27

What four charged particles take part in producing the resting potential?

Answer 27

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?

Question 28

What is Graded potential?

Answer 28

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.

Question 29

What is Hyperpolarization and depolarization?

Answer 29

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.

Question 30

Where does Hyperpolarization and Depolarization take place? What channels underlie it?

Answer 30

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.

Question 31

What channels have a role in Hyperpolarization?

Answer 31

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.

Question 32

What channels have a role in Depolarization?

Answer 32

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.

Question 33

Why are Puttlefish so dangerous?

Answer 33

The secrete Tetrodotoxin which impedes the electrical activity of Neurons.

Question 34

What is an Action Potential?

Answer 34

large, brief reversal in the polarity of an axon. An action potential is a brief but larger reversal in the polarity of an axon’s membrane that lasts about 1 millisecond Electrical stimulation of the cell membrane at resting potential produces localized graded potentials on the axon. The voltage across the membrane suddenly reverses, making the intracellular side positive relative to the extracellular side, and then it abruptly reverses again to restore the resting potential. Because the duration of the action potential is brief, many action potentials can occur within a second, as illustrated in Figure 4-14B and C, where the time scales are compressed.

Question 35

When do Action Potentials occur?

Answer 35

An action potential occurs when a large concentration of, first, Na1 ions and, then, K1 ions crosses the membrane rapidly. The Depolarizing phase of the Action Potentials is due to the NA1 influx of and the hperpolarizing phase to K+ efflux. In short Na+ ions rush in and K+ plus ions rush out. Their combined flow underlies action potential. An action potential is triggered when the cell membrane is depolarized to about 250 millivolts. At this threshold potential, the membrane charge undergoes a remarkable further change with no additional stimulation. The relative voltage of the membrane drops to zero and then continues to depolarize until the charge on the inside of the membrane is as great as 130 millivolts—a total voltage change of 100 millivolts. Then the membrane potential reverses again, becoming slightly hyperpolarized—a reversal of a little more than 100 millivolts. After this second reversal, the membrane slowly returns to its resting potential at 270 millivolts.

Question 36

How many gates do Sodium and Potassium channels have?

Answer 36

Sodium channels have two gates and Potassium channels have one.

Question 37

What is Absolutely Refractory?

Answer 37

Refers to the state of an Axon in the repolarizing period during which a new action potential cannot be elicted (except with some exceptions) because gate 2 of sodium channels, which is not volatage sensitive, is closed.

Question 38

What is Reflective Refractory?

Answer 38

Refers to the state of an Axon in the later phases of an action potential during which increased electrical current is required to produce another action potential; a phase during which potassium channels are open.

Question 39

What is a Nerve Impulse?

Answer 39

Propagation of an action potential on an Axon. Each successive action potential gives birth to another down the length of the axon. A nerve impulse always maintains a constant size, and the action potential—the nerve’s “message”—arrives unchanged to every terminal of the nerve that receives it. Think of the voltage-sensitive channels along the axon as a series of dominoes. When one domino falls, it knocks over its neighbor, and so on down the line. There is no decrement in the size of the fall. The last domino travels exactly the same distance and falls just as hard as the first one did. Essentially, this “domino effect” happens when voltage-sensitive channels open. The opening of one channel produces a voltage change that triggers its neighbor to open, just as one domino knocks over the next. The channelopening response does not grow any weaker as it moves along the axon, and the last channel opens exactly like the first, just as the domino action stays constant to the end of the line.

Question 40

What determines Refractory Periods?

Answer 40

Refractory periods are determined by the position of the gates that mediate ion flow in the voltage sensitive channels. The refractory phase of the action potential has two practical uses for nerves conducting information. First, because of refractory periods, there is about a 5-millisecond limit on how frequently action potentials can occur. In other words, refractory periods limit the maximum rate of action potentials to about 200 per second. Variations in the sensitivity of voltage sensitive channels in different kinds of neurons likewise determine how frequently the neurons can fire. Second, although an action potential can travel in either direction on an axon, refractory periods prevent it from reversing direction and returning to the point from which it came. Thus, refractory periods create a single, discrete impulse that travels away from the point of initial stimulation. When an action potential begins at the cell body, it usually travels down the axon to the terminals.

Question 41

What is the Node of Ranvier?

Answer 41

The part of an Axon that is not covered by Myelin. Unmyelinated gaps on the axon between successive glial cells are richly endowed with voltage-sensitive channels. These tiny gaps in the myelin sheath, the nodes of Ranvier, are sufficiently close to one another that an action potential occurring at one node can trigger the opening of voltage-sensitive gates at an adjacent node.

Question 42

Why don't mammals have giant axons like Giant Squids?

Answer 42

For us mammals, with our many axons producing repertoires of complex behaviors, giant axons are out of the question. Our axons must be extremely slender because our complex behaviors require a great many of them. Our largest axons are only about 30 micrometers wide, so the speed with which they convey information should not be especially fast. And yet, like most vertebrate species, we humans are hardly sluggish creatures. We process information and generate responses with impressive speed.

Question 43

How do we process information and generate responses with impressive speed?

Answer 43

Glial cells play a role in speeding nerve impulses in the vertebrate nervous system. Schwann cells in the human peripheral nervous system and oligodendroglia in the central nervous system wrap around each axon, forming the myelin that insulates it (Figure 4-20). Action potentials cannot occur where myelin is wrapped around an axon. For one thing, the myelin creates an insulating barrier to the flow of ionic current. For another, regions of an axon that lie under myelin have few channels through which ions can flow, and channels are essential to generating an action potential. But axons are not totally encased in myelin. Unmyelinated gaps on the axon between successive glial cells are richly endowed with voltage-sensitive channels. These tiny gaps in the myelin sheath, the nodes of Ranvier, are sufficiently close to one another that an action potential occurring at one node can trigger the opening of voltage-sensitive gates at an adjacent node. In this way, a relatively slow action potential jumps at the speed of light from node to node, as shown in Figure 4-21. This flow of energy is called saltatory conduction (from the Latin verb saltare, meaning “to dance”). Jumping from node to node speeds the rate at which an action potential can travel along an axon.

Question 44

Where can Action potentials not take place?

Answer 44

ction potentials cannot occur where myelin is wrapped around an axon. For one thing, the myelin creates an insulating barrier to the flow of ionic current. For another, regions of an axon that lie under myelin have few channels through which ions can flow, and channels are essential to generating an action potential. But axons are not totally encased in myelin. Unmyelinated gaps on the axon between successive glial cells are richly endowed with voltage-sensitive channels. These tiny gaps in the myelin sheath, the nodes of Ranvier, are sufficiently close to one another that an action potential occurring at one node can trigger the opening of voltage-sensitive gates at an adjacent node. In this way, a relatively slow action potential jumps at the speed of light from node to node, as shown in Figure 4-21. This flow of energy is called saltatory conduction (from the Latin verb saltare, meaning “to dance”). Jumping from node to node speeds the rate at which an action potential can travel along an axon.

Question 45

What is Saltatory Conduction?

Answer 45

Propagation of an Action Potential at succesive nodes of Ranvier; saltatory means jumping or dancing.

Question 46

How fast can nerve impulses travel in large mammalian axon nerves? How many second insulated and uninsulated?

Answer 46

On larger, myelinated mammalian axons, nerve impulses can travel at a rate as high as 120 meters per second. On smaller, uninsulated axons they travel only about 30 meters per second. Spectators at sporting events once performed a “wave” that traveled around a stadium. As one person rose, the adjacent person rose, producing the wave effect. This human wave is like conduction along an unmyelinated axon. Now think of how much faster the wave would complete its circuit around the field if only spectators in the corners rose to produce it, which is analogous to a nerve impulse that travels by jumping from one node of Ranvier to the next. The quick reactions that humans and other mammals are capable of are due in part to this saltatory conduction in their nervous systems.

Question 47

What is Excitatory postsynaptic potential?

Answer 47

brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to produce an action potential EPSPs are associated with the opening of sodium channels, which allows an influx of Na1 ions. IPSPs are associated with the opening of potassium channels, which allows an efflux of K1 ions (or with the opening of chloride channels, which allows an influx of Cl2 ions). Although the size of a graded potential is proportional to the intensity of the stimulation, an action potential is not produced on the motor neuron’s cell-body membrane even when an EPSP is strongly excitatory. The reason is simple: the cell-body membrane of most neurons does not contain voltage-sensitive channels. The stimulation must reach the axon hillock, the area of the cell where the axon begins. The hillock is rich in voltage-sensitive channels.

Question 48

The (1) results from the unequal distribution of (2) inside and outside the cell membrane.

Answer 48

(1) Resting Potentials | (2) Ions

Question 49

Because it is (1) the cell membrane prevents the efflux of large protein anions and pumps sodium ions out of the cell to maintain a slightly (2) charge in the intracellular fluid relative to the extracellular fluid.

Answer 49

(1) Semipermeable | (2) Negative

Question 50

For a graded potential to arise, an axon must be stimulated to the point that the transmembrane charge increases slightly to cause a(n) (1) or decreases slightly to cause a(n) (2) .

Answer 50

(1) Hyperpolarization | (2) Depolarization

Question 51

The voltage change associated with a(n (1)) is sufficiently large to stimulate adjacent parts of the axon membrane to the threshold for propagating it along the length of an axon as a(n) (2).

Answer 51

(1) Action Potential | (2) Nerve impulse

Question 52

briefly explain why nerve impulses travel faster on myelinated than on unmyelinated axons.

Answer 52

Nerve Impulses travel more rapidly on myelinated axons because of saltator conduction: action potentials leap between the nodes separating the glial cells that form the Axon's melin Sheath.

Question 53

What is a Neuron more than?

Answer 53

A microelectrode connected to an Axon. A neuron is more than just an axon connected to microelectrodes by some curious scientist who stimulates it with electrical current. A neuron has an extensive dendritic tree covered with spines, and through these dendritic spines, it can establish more than 50,000 connections to other neurons. Nerve impulses traveling to each of these synapses from other neurons bombard the receiving neuron with all manner of inputs. In addition, a neuron has a cell body between its dendritic tree and its axon, and this cell body, too, can receive connections from many other neurons.

Question 54

How many connections can a Neuron make with other Neurons?

Answer 54

50,000 connections.

Question 55

How does the neuron integrate it's enormous array of inputs into a nerve impulse?

Answer 55

Summation of ESPS's and IPSP's (this could be wrong)

Question 56

Who figured out how neurons integrates its enormous array imputs into a nerve impulse and how did he do it?

Answer 56

John C Eccles. He discovered Excitatory postsynaptic potentials and inhibitory postsynaptic potentials using an Oscilloscope. Conclusion: EPSPs increase the probability that an action potential will result. IPSPs decrease the probability that an action potential will result. To study the activity of motor neurons, Eccles inserted a microelectrode into the spinal cord of a vertebrate animal until the tip was located in or right beside a motor neuron’s cell body. He then placed stimulating electrodes on the axons of sensory nerve fibers entering the spinal cord. By teasing apart the fibers of the incoming sensory nerves, he was able to stimulate one fiber at a time. He recorded from the cell bodies of large motor neurons in the vertebrate spinal cord. He did so by refining the electrical stimulating and recording techniques developed for the study of squid axons (see Section 4-1). A spinal-cord motor neuron has an extensive dendritic tree with as many as 20 main branches that subdivide numerous times and are covered with dendritic spines. Motor neurons receive input from multiple sources, including the skin, joints, muscles, and brain.

Question 57

Why are Motor Neurons ideal for studying how a Neuron responds to diverse inputs?

Answer 57

The motor neuron, is the path by which the nervous system produces behavior. A spinal-cord motor neuron has an extensive dendritic tree with as many as 20 main branches that subdivide numerous times and are covered with dendritic spines. Motor neurons receive input from multiple sources, including the skin, joints, muscles, and brain.

Question 58

What determines if an Action potential results?

Answer 58

EPSPs (excitatory postsynaptic potential) increase the probability that an action potential will result. IPSPs (inhibitory postsynaptic potential) decrease the probability that an action potential will result.

Question 59

What is Myasthenia Graves?

Answer 59

In myasthenia gravis, the receptors of muscles are insensitive to the chemical messages passed from axon terminals. na+ and k+ ions do not move through the end-plate pore, and the muscle does not receive the signal to contract. as a result, the muscles do not respond to commands from motor neurons. Myasthenia gravis is rare, with a prevalence of 14/100,000, and the disorder is more common in women than in men. The age of onset is usually in the thirties or forties for women and after age 50 for men. in about 10 percent of cases, the condition is limited to the eye muscles, but, for the majority of patients, the condition gets worse. At the time when r. J. contracted the disease, about a third of myasthenia gravis patients died from the disease or from complications such as respiratory infections. a specialist suggested that r. J. undergo a treatment in which the thymus gland is removed. Within the next 5 years, all her symptoms gradually disappeared, and she remained symptom free thereafter. The thymus is an immune system gland that takes part in producing antibodies to foreign material and viruses that enter the body. in myasthenia gravis, the thymus may start to make antibodies to the end-plate receptors on muscles. Myasthenia gravis is one of nearly 80 autoimmune diseases, disorders in which the immune system makes antibodies to a person’s own body (rezania et al., 2011). others include neuromyalgia, multiple sclerosis, and diabetes. Contemporary treatments besides the removal of the thymus gland include drug treatments, such as those that increase the release of the chemical transmitter acetylcholine at muscle receptors. as a result, most myasthenia gravis conditions are controlled.

Question 60

What is an automimmune disease and how many of them are there?

Answer 60

Automimmune disease is an illness resulting from the loss of the immune system ability to discriminate between foreign pathogens in the body and the body itself. 80 automimmune diseses such as myasthenia gravis, multiple sclerosis and diabetes

Question 61

What is inhibitory postsynaptic potential (iPsP)

Answer 61

inhibitory postsynaptic potential (iPsP) brief hyperpolarization of a neuron membrane in response to stimulation, making the neuron less likely to produce an action potential. EPSPs are associated with the opening of sodium channels, which allows an influx of Na1 ions. IPSPs are associated with the opening of potassium channels, which allows an efflux of K1 ions (or with the opening of chloride channels, which allows an influx of Cl2 ions). Although the size of a graded potential is proportional to the intensity of the stimulation, an action potential is not produced on the motor neuron’s cell-body membrane even when an EPSP is strongly excitatory. The reason is simple: the cell-body membrane of most neurons does not contain voltage-sensitive channels. The stimulation must reach the axon hillock, the area of the cell where the axon begins. The hillock is rich in voltage-sensitive channels.

Question 62

How long do EPsP and IPsPs last?

Answer 62

A few milliseconds. EPSPs are associated with the opening of sodium channels, which allows an influx of Na1 ions. IPSPs are associated with the opening of potassium channels, which allows an efflux of K1 ions (or with the opening of chloride channels, which allows an influx of Cl2 ions). Although the size of a graded potential is proportional to the intensity of the stimulation, an action potential is not produced on the motor neuron’s cell-body membrane even when an EPSP is strongly excitatory. The reason is simple: the cell-body membrane of most neurons does not contain voltage-sensitive channels. The stimulation must reach the axon hillock, the area of the cell where the axon begins. The hillock is rich in voltage-sensitive channels.

Question 63

How do incoming graded potentials interacts?

Answer 63

Temporal Summation and Spatial Summation explain how graded potentials interact. A neuron with thousands of inputs responds no differently from one with only a few inputs. It democratically sums all inputs that are close together in time and space. The cell-body membrane, therefore, always indicates the summed influences of multiple inputs. Because of this temporal and spatial summation, a neuron can be said to analyze its inputs before deciding what to do. The ultimate decision is made at the axon hillock, the region that initiates the action potential. Summation is a property of both EPSPs and IPSPs in any combination. The interactions between EPSPs and IPSPs make sense when you consider that the influx and the efflux of ions are being summed. The influx of sodium ions accompanying one EPSP is added to the influx of sodium ions accompanying a second EPSP if the two occur close together in time and space. If the two influxes of sodium ions are remote in time or in space or in both, no summation is possible. The same is true regarding effluxes of potassium ions. When they occur close together in time and space, they sum; when they are far apart in either or both of these ways, there is no summation. The patterns are identical for an EPSP and an IPSP. The influx of sodium ions associated with the EPSP is added to the efflux of potassium ions associated with the IPSP, and the difference between them is recorded as long as they are spatially and temporally close together. If, on the other hand, they are widely separated in time or in space or in both, they do not interact and there is no summation

Question 64

What is Temporal Summation?

Answer 64

Temporal summation: graded potentials that occur at approximately the same time on a membrane are summed.

Question 65

What is Spatial Summation?

Answer 65

Spatial summation: graded potentials that occur at approximately the same location and time on a membrane are summed.

Question 66

How do Dendrites collect information?

Answer 66

Dendrites collect information in the form of graded potentials (EPSPs and IPSPs), and the axon hillock initiates discrete action potentials that are delivered to other target cells via the axon. But exceptions to this picture of how a neuron works do exist. For example, some cells in the hippocampus can produce additional action potentials, called depolarizing potentials, when the cell would ordinarily be refractory. The function of depolarizing potentials is not fully understood.

Question 67

What is the function of depolarizing neurons?

Answer 67

The function of depolarizing potentials is not fully understood. Dendrites collect information in the form of graded potentials (EPSPs and IPSPs), and the axon hillock initiates discrete action potentials that are delivered to other target cells via the axon. But exceptions to this picture of how a neuron works do exist. For example, some cells in the hippocampus can produce additional action potentials, called depolarizing potentials, when the cell would ordinarily be refractory.

Question 68

The reverse movement of an action potential from the axon hillock into the dendritic field of a neuron is called (1)

Answer 68

Back propagation: reverse movement of an action potential into the dendritic field of a neuron; postulated to play a role in plastic changes that underlie learning. For example, back propagation may make the dendritic field refractory to incoming inputs, set the dendritic field to an electrically neutral baseline, or reinforce signals coming in to certain dendrites

Question 69

What do the many differences among neurons suggest?

Answer 69

The many differences among neurons suggest that the nervous system capitalizes on modifications of structure and function to produce adaptive behavior in each species. These variations do not exhaust the adaptability of neuronal mechanisms, because neuroscientists have engineered some of their own adaptions, as described in Research Focus 4-3, “Optogenetics and Light-Sensitive Channels,” on page 134.

Question 70

Graded potentials that decrease the charge on the cell membrane, moving it toward the threshold level, are called (1) because they increase the likelihood that an action potential will occur. Graded potentials that increase the charge on the cell membrane, moving it away from the threshold level, are called (2) because they decrease the likelihood that an action potential will result.

Answer 70

(1) Excitatory Postsynaptic potentials | (2) Inhibitory Postsynaptic potentials.

Question 71

Epsps and ipsps that occur close together in (1) and/or in (2) are summed. This is how a neuron (3) the information it receives from other neurons.

Answer 71

(1) Time (2) Space (3) Integrates

Question 72

The membrane of the (1) does not contain voltage-sensitive ion channels, but if summed inputs excite (2) the to a threshold level, action potentials are triggered and then propagated as they travel along the cell’s (3) as a nerve impulse.

Answer 72

(1) Cell body (2) Initial segment (3) Axon

Question 73

Explain what happens during back propagation

Answer 73

Some neurons have voltage sensitive channels on their dendrites that allow the reverse movement of an action potential into the neurons dendritic field.

Question 74

What is Optogenetics?

Answer 74

Optogenetics combines genetics and light to control targeted cells in living tissue. It's a transgenic technique. Introducing different light-sensitive channels into a species excites the organism’s movements with one light wavelength and inhibits them with another light wavelength.

Question 75

What is Optogenetics?

Answer 75

Optogenetics combines genetics and light to control targeted cells in living tissue. It's a transgenic technique. Introducing different light-sensitive channels into a species excites the organism’s movements with one light wavelength and inhibits them with another light wavelength. The movements of worms, fruit flies, and mice with genetically introduced light-sensitive channels have been controlled when their nervous-system cells have been illuminated with appropriate wavelengths of light. Using optogenetic techniques, light-sensitive channels can be incorporated into specific neural circuits so that only a subset of neurons is controlled by light stimulation. The promise is that investigating specific neuron populations can provide insight into brain disease, including conditions such as addictio

Question 76

Name two classes of light activated ion channels?

Answer 76

Channelrhodopsin-2. The Chr2 channel absorbs blue light and in doing so, opens briefly to allow the passage of cations, including sodium and potassium ions. These light-sensitive channels allow the passage of na+ and k+ ions when a cell is illuminated with blue light. The resulting depolarization excites the cell to generate action potentials. Halorhodopsin (nphr) is a light-driven ion pump, specific for chloride ions and found in phylogenetically ancient bacteria (archaea) known as halobacteria. when illuminated with green-yellow light, the halorhodopsin pumps Cl2 anions into the cell, hyperpolarizing it and so inhibiting its activity.

Question 77

What do Ion channels do in relation to the sensory systems?

Answer 77

In all our sensory systems, ion channels begin the process of information conduction

Question 78

What is a Stretch sensitive channel?

Answer 78

stretch-sensitive channel ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse. When these channels open, they allow an influx of Na1 ions sufficient to depolarize the dendrite to its threshold level. At threshold, the voltage-sensitive sodium and potassium channels are activated to open and initiate a nerve impulse that conveys touch information to your brain. Other kinds of sensory receptors have similar mechanisms for transducing (transforming) the energy of a sensory stimulus into nervous-system activity. When displaced, the hair receptors that provide information about hearing and balance likewise activate stretchsensitive channels. In the visual system, light particles strike chemicals in receptors within the eye, and the resulting chemical change activates ion channels in the membranes of relay neurons. An odorous molecule in the air that lands on an olfactory receptor and fits itself into a specially shaped compartment opens chemical-sensitive ion channels. When tissue is damaged, injured cells release chemicals that activate channels on a pain nerve. The point here is that, in all our sensory systems, ion channels begin the process of information conduction.

Question 79

What is an End plate?

Answer 79

on a muscle, the receptor–ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron.

Question 80

Different sensory stimuli initiate nerve impulses for each (1) in a similar way.

Answer 80

(1) Sensory system

Question 81

The membrane of a(n ) (1) contains a mechanism for transducing sensory energy into changes in ion channels that, in turn, allow ion flow to alter the voltage of the membrane to the point that (2) channels open, initiating a nerve impulse.

Answer 81

(1) Sensory receptor cell | (2) Voltage-Sensitive

Question 82

Sensory stimuli activate ion channels to initiate a nerve impulse that activates channels on (1) neurons that in turn contract (2) .

Answer 82

(1) Motor | (2) Muscles

Question 83

Why have so many different kinds of ion channels evolved on cell membranes?

Answer 83

The varieties of membrane channels generate the transmembrance charge, meditate graded potentials and trigger the action potential.

Question 84

What is Lou Gehrig's disease?

Answer 84

als is due primarily to the death of spinal motor neurons but can affect brain neurons as well. The technical term, amyotrophic lateral sclerosis, describes its consequences, both on muscles (amyotrophic means “muscle weakness”) and on the spinal cord (lateral sclerosis means “hardening of the lateral spinal cord”). several theories have been advanced to explain why motor neurons suddenly start to die in als victims. recent evidence suggests that als can result from head trauma that activates the cell’s dna to produce signals that initiate the neuron’s death (apoptosis, or programmed cell death). genetic factors are also suspected (allen et al., 2011). at the present time, there is no cure for als, although some newly developed drugs appear to slow its progression and offer some hope for future treatments. There are about 5000 new cases in the united states each year. als strikes most commonly between the ages of 50 and 75, although its onset can be as early as the teenage years. about 10 percent of victims have a family history of the disorder. The disease begins with general weakness, at first in the throat or upper chest and in the arms and legs. gradually, walking becomes difficult and falling common. The patient may lose use of the hands and legs, have trouble swallowing, and have difficulty speaking. The disease does not usually affect any sensory systems, cognitive functions, bowel or bladder control, or even sexual function. death often occurs within 5 years of diagnosis.