Chapter 42: Cells of the Nervous System (Part 1, Week 10)

Question 1

What is the coordinated circuits of cells that sense internal and environmental changes and transmit signals that enable an animal to respond in an appropriate way?

Answer 1

Nervous System

Question 2

What helps us exert control over our bodies, sense the outside world, initiate actions and respond to demands not to mention regulate internal processes?

Answer 2

The nervous system!

Question 3

What is the scientific study of nervous systems?

Answer 3

Neuroscience

Question 4

What are nervous systems composed of which are highly specialized cells that communicate with each other and with other types of cells by electrical or chemical signals?

Answer 4

Neurons

Question 5

What is the organ of the central nervous system of animals that functions to process and integrate information?

Answer 5

The brain - neurons become organized into a central processing area of the nervous system

Question 6

How does the brain send commands to and receives signals from various parts of the body?

Answer 6

Through nerves!

Bundles of neuronal cell extensions encased in connective tissue and projecting to and from various
tissues and organs.

Book Definition
A structure found in the peripheral nervous system that is composed of multiple myelinated axons bound by connective tissue; carries information to or from the central nervous system.

Question 7

[Start 42.1 Cellular Components of Nervous Systems]

What, in vertebrates, consists of the brain and spinal cord?

Answer 7

Central Nervous System (CNS)

Question 8

What is the structure that connects the brain to all areas of the body and together with the brain constitutes the central nervous system?

Answer 8

Spinal cord

Question 9

What, in vertebrates, consists all nerves and ganglia outside the brain and spinal cord?

Answer 9

Peripheral Nervous System (PNS)

Question 10

Fact:

The evolution of nervous systems has given animals the ability toreceive information about the environment via their PNS, transmit that information along nerves to a CNS where the information is interpreted, and, if necessary, initiate a behavioral response via their PNS

Answer 10

N/A

Question 11

What does the nervous systems transfer?

Answer 11

Signals from one part of the body to another and direct the activities of cells, tissues, organs, and glands.

Question 12

What are the two unique classes of cells in nervous systems? And what are their function?

Answer 12

Neurons, which function in signaling, and Glia, which have numerous support roles.

Question 13

What does the number of neurons in nervous systems depend on – kind of?

Answer 13

The size of the head and brain and the complexity of behavior.

Question 14

What is a part of a neuron that contains the cell nucleus and other organelles?

Also called a soma!

Answer 14

Cell body

Question 15

What are the two types of extensions or projections that arise from the cell body of a neuron?

Answer 15

dendrites and the axon

Question 16

WHat is a treelike extension of the plasma membrane of a neuron that receives electrical signals from other neurons?

Answer 16

Dendrite (dendron meaning tree)

May be single projections of the cell body but more commonly are elaborate treelike structures with numerous branching extensions that provide a large surface area for contacts with other neurons.

Question 17

What receives electrical and chemical signals from other neurons and does the signal reach the cell body of a neuron?

Answer 17

dendrites receive the signals, and then generate an electrical signal that moves towards the cell body.

Question 18

With the signals that the cell body of a neuron recieves from dendrites and the ones recieved directly, where does it send an outgoing signal?

Answer 18

An axon

Question 19

What is an extension of the plasma membrane of a neuron that is involved in sending signals to neighboring cells?

Answer 19

An axon

An axon may be only a few micrometers long or as long as 2 m, such as those in very large or long-limbed animals. A typical neuron has a single axon.

Within an animal’s body, many axons tend to run in parallel bundles to form nerves, within and around which are protective layers of connective tissue

Question 20

What is the part of the axon closest to the cell body; typically where an action potential begins?

Answer 20

Axon hillock

Question 21

What is the end of an axon, which conveys electrical or chemical messages to other cells?

Answer 21

Axon terminal

Question 22

What are cells that surround the neurons; a major class of cells in nervous systems that perform various functions?

Answer 22

Glia

Question 23

What is one type of glia that provide metabolic support for neurons and are also involved in forming the blood-brain barrier, which is a physical barrier between blood vessels and most parts of the CNS?

Answer 23

Astrocytes

Astrocytes also help to maintain a stable concentration of ions in the extracellular fluid.

Question 24

What does the blood-brain barrier prevent and accomplish?

Answer 24

This barrier prevents the passage of toxins and other damaging chemicals from the blood into the extracellular fluid around neurons in the CNS, but allows passage of nutrients and gases.

Question 25

What other glia is responsible for participating in immune functions and remove cellular debris produced by damaged or dying cells?

Answer 25

Microglia

Question 26

What, in the nervous system, is an insulating layer made up of specialized glial cells wrapped around the axons?

Answer 26

Myelin sheath

Question 27

What do you call the noninsulated gaps in the myelin sheath that wrap around the axons of neurons?

Answer 27

Nodes of Ranvier

Question 28

In the vertebrate brain and spinal cord, what are the myelin-producing glial cells called that produce the myelin sheath around the axons of neurons?

Answer 28

oligodendrocytes (oligo meaning few)

Question 29

What are the glial cells that form myelin on axons that travel OUTSIDE the brain and spinal cord?

Answer 29

Schwann cells

Question 30

What are the three main categories of neurons?

Answer 30

Sensory neurons, motor neurons, and interneurons.

The structures of each type reflect their specialized functions.

Question 31

What is a neuron that detects or senses information from the outside world, such as light, sound, touch, and heat? They can also detect internal body conditions such as blood pressure and body temperature.

Answer 31

Sensory neurons

Sensory neurons are also called afferent (from the Latin, meaning to bring toward) neurons because they transmit information FROM the periphery TO the CNS.

Question 32

What is unique about the structure of afferent (carry to), or sensory, neurons?

Answer 32

The long axon bypasses the cell body (which is centered), and the signal travels from the PNS to the CNS (peripheral process to the central process).

This arrangement allows for the rapid transmission of a sensory signal to the CNS.

Question 33

What is a neuron that sends signals away from the central nervous system and elicits some type of response from a gland, muscle or other structure?

Answer 33

Motor neuron

Motor neurons are so named because one type of response they cause is movement.

In addition, motor neurons may cause other effects such as the secretion of hormones from endocrine glands.

Because they send signals away from the CNS, motor neurons are also called efferent (from the Latin, meaning to carry from) neurons.

Question 34

What is interesting about the structure of a motor (efferent) neurons?

Answer 34

It does not branch into two processes on either side of the cell body like afferent neurons do. Additionally, it has one axon on one side of the cell body versus the two that afferent neurons have.

They have very long axons to act on distant cells.

Question 35

What is a type of neuron that forms interconnections between other neurons in the CNS?

Answer 35

Interneurons

They tend to have MANY dendrites and are typically very short and highly branched.

Question 36

What is so critical about interneurons?

What is so important about their structure?

Answer 36

The signals sent between interneurons are critical in the interpretation of information that the CNS receives, as well as the response that it may elicit.

Their arrangement of being short and highly branched allows them to form complex connections with many other cells.

Question 37

What is a reflex arc?

Answer 37

A simple circuit that allows an organism to respond rapidly to inputs from sensory neurons and consists of only a few neurons.

Question 38

What is an AMAZING example of a reflex arc?

Answer 38

The stimulus, which is a tap below the kneecap (patella), causes sensory neurons to send a signal to the CNS.

-This tapping on the patella causes the patellar tendon to stretch, which acts as the stimulus.

Within the CNS, little or no interpretation of the signal occurs, because very few, if any, interneurons are involved.

The interneurons then transmit a signal to motor neurons, which elicit a response, in this case, a kneejerk. The response is very quick and automatic.

More indepth explanation

The knee-jerk response is an example of a reflex arc. A tap below the kneecap (also known as the patella) stretches the patellar tendon, which acts as astimulus for a sensory neuron. This stimulus initiates a reflex arc that activates (+) a motor neuron that causes the extensor muscle on top of the thigh to contract. At the same time, an interneuron inhibits (–) the motor neuron of the flexor muscle, causing it to relax.

Question 39

Information about Reflexes

Reflexes are among the evolutionarily oldest and most important features of nervous systems, because they allow animals to respond quickly to potentially dangerous or otherwise important events.

For instance, many vertebrates will immediately cringe, jump, leap, or take flight in response to a loud noise, which could represent sudden danger. Some animals that live in the water will reflexively dive in response to a shadow overhead, which could signify the presence of a passing shark or other predator.

Many infant primates have strong grasping reflexes that help them hold onto their mother as she moves about. Other reflexes, such as the patellar tendon reflex just described, are important for postural changes and locomotion. Countless examples of useful reflexes are found in animals, and their importance is evident from the observation that they arose early in evolution and exist in nearly all animals.

Answer 39

N/A

Question 40

[42.5 Start Electrical Properties of Neurons and the Resting Membrane Potential]

What did Galvani’s animal electricity eventually come from which was discovered later?

Answer 40

Neurons! - which use electrical signals to communicate with other neurons, muscle cells, or gland cells.

Question 41

What are the nerve impulses, or electrical signals, referred as?

Answer 41

Action potentials, which involves changes in the amount of electric charge across a neuron’s plasma membrane

Question 42

What do cell membranes accomplish, much like the plasma membrane of a neuron?

Answer 42

Acts as a barrier that separates charges.

Ion concentrations differ between the interior and exterior of a cell, and this sets the stage for the establishment of differences in the net charge across a membrane.

Question 43

What do the differences in charge across a plasma membrane measured as?

Answer 43

millivolts (mV)

Question 44

T/F Neurons have negative and positive poles, but these are inside and outside surfaces, respectively, of the plasma membrane.

Answer 44

True.

For this reason, a neuron is said to be electrically polarized.

Question 45

What do you call the difference between the electric charges outside and inside a cell?

Answer 45

Membrane potential, or potential difference.

Question 46

What do you call the difference in charges across the plasma membrane in an unstimulated neuron?

Answer 46

Resting membrane potential

Question 47

When investigators first measured the resting potential of neurons, they registered a voltage of WHAT inside the cell with respect to the outside?

Answer 47

-70 mV

This means that the interior of the cell had a more negative charge than the exterior, which turns out to be typical of animal cells in their resting state.

Nonetheless, this tiny difference in charge across the membrane of a neuron is sufficient to provide the means for generating an action potential that can travel from one end of a neuron to the other, as we will see later in this chapter.

Question 48

How is the resting membrane potential determined?

Answer 48

By the ions located along the inner and outer surfaces of the plasma membrane.

Ions of opposite charges align on either side of the membrane because they are attracted to each other due to electrical forces. Negative ions within the cell are drawn to positive ions arrayed on the outer surface of the plasma membrane.

Question 49

T/F Only a fraction of available ions, negative and positive, inside and outside of a neuron contribute to the resting membrane potential.

Answer 49

True.

Question 50

What ions are critical for establishing the resting membrane potential?

Answer 50

Na+ and K+ and, to a lesser extent, Cl-

Question 51

What are the concentrations of ions, in mM, for a typical mammalian neuron?

This is concentrations extracellular and intracellular.

Answer 51

For Na+, extracellular molarity is 145 mM and intracellular is 15 mM

For K+, extracellular molarity is 5 mM and intracellular is 150 mM

For Cl-, extracellular molarity is 110 mM and intracellular is 7 mM

Question 52

What are the two factors that are primarily responsible for determining the resting membrane potential? (think BIO l)

Answer 52

• The Na+/K+-ATPase pump within the plasma membrane CONTINUALLY moves Na+ out of the cell and K+ into the cytosol.

The Na+/K+-ATPase pump uses energy of ATP to transport three Na+ out of the cell for every two K+ it moves into the cell.

• Unequal membrane permeabilities to different ions

The plasma membrane contains ion-specific channels that affect the permeability of the membrane to Na+
and K+. Ungated channels that are specific for Na+ or K+ influence the resting potential by allowing the passive movement of these ions.

An ungated channel, sometimes referred to as a leak channel, is one that is open at rest and that does not require a stimulus such as ligand binding to open.

Question 53

Other than contributing to the charge difference across the plasma membrane of a neuron, what does it more importantly establish?

Answer 53

It establishes concentration gradients for Na+ and K+ by continually transporting them across the membrane in opposite directions.

The charge difference and concentration gradients will determine the directions in which the ions will move by diffusion either into or out of the cell.

Question 54

What is significant about the leak channels that most neurons have that?

Answer 54

Most neurons have about 10 to 100 times more ungated K+ channels than ungated Na+
channels.

Therefore, at rest, the membrane is more permeable to K+ than to Na+.

Question 55

Since there is an unequal number of ion leak channels, which ion contributes more to the resting membrane potential via diffusion?

Answer 55

Since there are more K+ leak channels, and since the concentration gradient is lower outside the cell, then more positive K+ will flow out of the cell through faciliated diffusion than does Na+ through facilitated diffusion into the cell

The concentration gradient for Na+ is much higher outside the cell so Na + will flow into the cell. Remember though, Na+ leaky ion channels are much fewer compared to K+ channels.

Question 56

What is the combined effect of both an electrical and a chemical gradient across a membrane; determines the direction in which ions will move?

Answer 56

Electrochemical gradient

Question 57

What is the membrane potential at which the flow of an ion is at equilibrium, with no net movement in either direction?

Answer 57

Equilibrium potential

Question 58

Explain equilibrium potential in detail.

Answer 58

Consider the concept of an electrochemical gradient for K+, using two compartments separated by a semipermeable membrane that permits the diffusion of only K+.

A. With an electrical gradient (no concentration gradient), the concentration of K+
is equal on both sides of the membrane, but the concentrations of other ions (Na+ and Cl–) are unequal on opposite sides of the membrane and thereby produce an electrical gradient.

Because K+ is positively charged, it is attracted to the side of the membrane with more negative charge.

B. A concentration gradient (no electrical gradient) in which K+ concentration is higher on one side than the other. In this scenario, K+ diffuses from a region of high to low concentration.

C. A balance of forces creating an electrochemical equilibrium. The electrical gradient favors the movement of K+ from left to right, but the concentration gradient favors movement from right to left.

These opposing forces create an electrochemical equilibrium in which there is no net diffusion of K+
in either direction.

Question 59

What is the formula that gives equilibrium potential for an ion at any given concentration gradient?

Answer 59

Nernst equation

For monovalent cations such as Na+ and K+
at 37°C, the Nernst equation can be expressed as

E = 60 mV log10 ([X extracellular] / [X intracellular])

E = equilibrium potential
X = the concentraction of an ion, outsie or inside the cell

60 mV is a value that depends on temperature, valence, and other factors (for anions, the value is -60 mV)

The way log should be read

Say you log (base 10) x (10)

How manys 10s do you need to multiply together to get 10? Just 1 … The log of something tells us the exponent!

Question 60

What does the Nernst equation allow researchers to predict?

Answer 60

When an ion IS or IS NOT in electrochemical equilibrium.

Question 61

When is there a driving force for a specific ion to diffuse across the membrane using te Nernst equation?

Answer 61

When the equilibrium potential for a given ion—calculated by the Nernst equation—and the actual resting membrane potential do not match, there will be a driving force for that ion to diffuse across the membrane.

Question 62

LAST FACT CONCLUSION!

By establishing electrochemical gradients and maintaining them with the Na+/K+-ATPase pump, neurons have the ability to quickly allow ions to move across the plasma membrane by opening additional (gated) channels that were previously closed.

The movement of a charged ion down its electrochemical gradient results in an electric current (a current is any net unidirectional flow of electric charge).

This small current provides the necessary electrical signal that neurons use to communicate with one another, as we will see next.

Answer 62

N/A