Unit 1.2

Question 1

If axons used electrical conduction, what velocity could they approach?

Answer 1

The speed of light

However, due to the body’s composition, this is not how axons function.

Question 2

How does the axon function to transmit impulses?

Answer 2

Regenerates an impulse at each point

This method prevents the weakening of the impulse during transmission.

Question 3

What is the range of speeds at which axons transmit information?

Answer 3

Less than 1 meter/second to about 100 m/s

This speed variation affects how quickly different parts of the body perceive touch.

Question 4

True or false: A touch on your shoulder reaches your brain at the same time as a touch on your toes.

Answer 4

FALSE

A touch on your shoulder reaches the brain sooner due to the varying speeds of impulse transmission.

Question 5

In vision, why does the brain need to know the timing of stimuli?

Answer 5

To detect movement accurately

Small timing differences help determine the direction of light movement across the retina.

Question 6

What compensates for the timing differences in the visual system?

Answer 6

Axons from more distant parts of the retina transmit impulses slightly faster

This compensation prevents inaccurate perception of movement.

Question 7

What is the thickness of the neuron’s membrane?

Answer 7

About 8 nanometers (nm)

This thickness is about one ten-thousandth the width of an average human hair.

Question 8

What are embedded among the phospholipids in the neuron’s membrane?

Answer 8

Cylindrical protein molecules

These proteins allow certain chemicals to pass through the membrane.

Question 9

What do the protein channels in the neuron’s membrane permit?

Answer 9

Certain ions to cross through the membrane

This occurs at a controlled rate.

Question 10

What is the electrical gradient in a resting neuron also known as?

Answer 10

Polarization

It refers to the difference in electrical charge between the inside and outside of the cell.

Question 11

When at rest, the inside of the neuron’s membrane is slightly negative with respect to what?

Answer 11

The outside of the cell

This is mainly due to negatively charged proteins inside the cell.

Question 12

What is the difference in voltage across the neuron’s membrane called?

Answer 12

Resting potential

It is the electrical potential maintained by the neuron when it is not actively sending signals.

Question 13

What is the function of the sodium-potassium pump?

Answer 13

Transports three sodium ions out and two potassium ions into the cell

This process is an active transport that requires energy.

Question 14

What happens to the membrane potential if charged ions could flow freely across it?

Answer 14

It would depolarize, eliminating the negative potential inside

This indicates the importance of selective permeability in maintaining membrane potential.

Question 15

Which ions cross through membrane channels that are sometimes open and sometimes closed?

Answer 15

• Sodium
• Potassium
• Calcium
• Chloride

These ions have specific channels that regulate their flow across the membrane.

Question 16

What is meant by selective permeability of the membrane?

Answer 16

Some chemicals pass through it more freely than others

Oxygen, carbon dioxide, urea, and water cross freely through always-open channels.

Question 17

When the membrane is at rest, what is the state of the sodium and potassium channels?

Answer 17

Closed, permitting almost no flow of sodium and only a small flow of potassium

This state is crucial for maintaining the resting membrane potential.

Question 18

What is the concentration of sodium ions outside the membrane compared to inside?

Answer 18

More than 10 times more concentrated outside than inside

This gradient is maintained by the sodium-potassium pump.

Question 19

What is the concentration of potassium ions inside the membrane compared to outside?

Answer 19

More concentrated inside than outside

This is essential for the proper functioning of cells.

Question 20

What is the charge of potassium?

Answer 20

Positively charged

This charge influences its movement across the cell membrane.

Question 21

What is the electrical gradient effect on potassium?

Answer 21

Tends to pull potassium into the cell

The inside of the cell is negatively charged, attracting positively charged potassium.

Question 22

What is the concentration gradient effect on potassium?

Answer 22

Drives potassium out of the cell

Potassium is more concentrated inside the cell than outside.

Question 23

What is the role of the sodium-potassium pump?

Answer 23

Pulls potassium into the cell

It counteracts the ions that leak out.

Question 24

What type of ions sustain the membrane’s polarization inside the cell?

Answer 24

Negatively charged proteins

These proteins contribute to the overall negative charge inside the cell.

Question 25

Where are **chloride ions** mainly located?

Answer 25

Mainly outside the cell ## Footnote Chloride ions are negatively charged and influence membrane potential.

Question 26

What are messages sent by axons called?

Answer 26

action potentials ## Footnote Action potentials are essential for transmitting signals in the nervous system.

Question 27

What is **hyperpolarization**?

Answer 27

Increased polarization ## Footnote Hyperpolarization occurs when a negative charge is applied to the neuron, increasing its negative potential.

Question 28

When the stimulation ends after hyperpolarization, what happens to the charge?

Answer 28

It returns to its original resting level ## Footnote This return to resting level is crucial for the neuron's ability to fire action potentials again.

Question 29

What is the **All-or-None Law** in relation to action potentials?

Answer 29

The amplitude and velocity of an action potential are independent of the intensity of the stimulus, provided the stimulus reaches the threshold. ## Footnote This means that once the threshold is met, action potentials are produced at a consistent amplitude and velocity.

Question 30

True or false: The intensity of the stimulus can cause a neuron to produce a bigger or smaller action potential.

Answer 30

FALSE ## Footnote Action potentials are approximately equal in amplitude and velocity regardless of stimulus intensity.

Question 31

What happens when a stimulus reaches the **threshold**?

Answer 31

An action potential is produced. ## Footnote This is analogous to flushing a toilet: a certain strength of press is needed to initiate the flush.

Question 32

How do **thicker axons** affect action potentials?

Answer 32

* Convey action potentials at greater velocities * Convey more action potentials per second ## Footnote The characteristics of action potentials can vary from one neuron to another based on axon thickness.

Question 33

What can an axon change to signal the difference between a weak stimulus and a strong stimulus?

Answer 33

The timing of action potentials. ## Footnote This is similar to varying the speed or rhythm of flashing lights to convey different messages.

Question 34

In the nervous system, how does a taste axon respond to different tastes?

Answer 34

It shows different rhythms of responses for sweet and bitter tastes. ## Footnote This demonstrates the use of timing in coding information.

Question 35

What ion is primarily involved in the **depolarization** of the axon during an action potential?

Answer 35

Na+ ## Footnote Sodium ions (Na+) enter the axon, leading to depolarization.

Question 36

What happens to the **next point** on the axon when enough sodium enters to depolarize it?

Answer 36

Produces an action potential ## Footnote This occurs when the depolarization reaches the threshold at that point.

Question 37

The action potential flows along the axon while remaining at **equal strength** throughout. True or False?

Answer 37

TRUE ## Footnote The action potential maintains its strength as it propagates along the axon.

Question 38

What ion exits the axon to restore the **resting potential** after an action potential?

Answer 38

K+ ## Footnote Potassium ions (K+) exit the axon behind each area of sodium entry.

Question 39

Fill in the blank: An action potential occurs at one point on the axon, leading to enough sodium entering to depolarize the next point to its **_______**.

Answer 39

threshold ## Footnote This depolarization must reach a certain level to trigger an action potential.

Question 40

What is the **velocity** of action potentials in the thinnest axons?

Answer 40

Less than 1 meter/second ## Footnote Increasing the diameter of the axon can increase the conduction velocity up to about 10 m/s.

Question 41

What is the **myelin sheath** composed of?

Answer 41

* Fats * Proteins ## Footnote The myelin sheath acts as an insulating material for vertebrate axons.

Question 42

What are the **nodes of Ranvier**?

Answer 42

Short sections of axon about 1 micrometer wide ## Footnote These nodes interrupt the myelin sheath and are crucial for the process of saltatory conduction.

Question 43

What happens at the **first node of Ranvier** when an action potential occurs?

Answer 43

Sodium ions enter the axon and diffuse ## Footnote This diffusion pushes a chain of positive charge along the axon to the next node.

Question 44

What is **saltatory conduction**?

Answer 44

The jumping of action potentials from node to node ## Footnote The term comes from the Latin word *saltare*, meaning 'to jump'.

Question 45

True or false: In myelinated axons, sodium channels are present between nodes.

Answer 45

FALSE ## Footnote Sodium channels are virtually absent between nodes, which is why action potentials can only regenerate at the nodes.

Question 46

How does **saltatory conduction** conserve energy?

Answer 46

Sodium is admitted only at its nodes ## Footnote This reduces the need for the sodium-potassium pump to work continuously along the entire axon.

Question 47

What is the **refractory period** in relation to action potentials?

Answer 47

A period during which the cell resists the production of further action potentials ## Footnote This occurs after the peak of the action potential when sodium gates are shut.

Question 48

What is the **absolute refractory period**?

Answer 48

The first part of the refractory period where the membrane cannot produce another action potential, regardless of stimulation ## Footnote This occurs immediately after the peak of the action potential.

Question 49

What is the **relative refractory period**?

Answer 49

The second part of the refractory period where a stronger-than-usual stimulus is necessary to initiate an action potential ## Footnote This follows the absolute refractory period.

Question 50

What two factors does the **refractory period** depend on?

Answer 50

* Sodium channels are closed * Potassium is flowing out of the cell at a faster-than-usual rate ## Footnote These factors contribute to the inability to generate another action potential during the refractory period.

Question 51

Approximately how long is the **absolute refractory period** in most neurons?

Answer 51

About 1 millisecond (ms) ## Footnote This is the time during which no action potential can be generated.

Question 52

How long is the **relative refractory period** in most neurons?

Answer 52

Another 2 to 4 milliseconds (ms) ## Footnote This is the time during which a stronger stimulus is required to generate an action potential.

Question 53

Fill in the blank: This **period** prevents the cell from producing another action potential during its _______.

Answer 53

refractory period ## Footnote This ensures that action potentials do not endlessly repeat. During a short time right after you flush a toilet, you cannot make it flush again—an absolute refractory period. Then follows a period when it is possible but difficult to flush it again—a relative refractory period—before it returns to normal.)

Question 54

True or false: During the **absolute refractory period**, a stimulus can still generate an action potential.

Answer 54

FALSE ## Footnote The membrane cannot produce another action potential during this period.

Question 55

What are **local neurons**?

Answer 55

Neurons without an axon that exchange information with only their closest neighbors ## Footnote Local neurons do not follow the all-or-none law and have graded potentials.

Question 56

How do local neurons conduct information?

Answer 56

Through graded potentials that vary in magnitude in proportion to the intensity of the stimulus ## Footnote The change in membrane potential is conducted to adjacent areas of the cell, gradually decaying as it travels.

Question 57

Why are local neurons difficult to study?

Answer 57

It is almost impossible to insert an electrode into a tiny cell without damaging it ## Footnote Most knowledge about neurons comes from larger neurons, leading to potential misconceptions.

Question 58

What misconception existed about local neurons in the past?

Answer 58

They were assumed to be immature and a reserve stock not yet utilized in cerebral activity ## Footnote This misconception contributed to the belief that we only use 10 percent of our brain.

Question 59

True or false: The belief that we only use 10 percent of our brain is justified.

Answer 59

FALSE ## Footnote This belief has no justification and has been persistent since the early 1900s.

Question 60

What does the belief that we only use 10 percent of our brain imply?

Answer 60

It suggests that you could lose 90 percent of your brain and still behave normally ## Footnote This is a nonsensical notion, as meaningful thought requires activating some neurons and inhibiting others.

Question 61

What is the role of inhibition in brain activity?

Answer 61

Inhibition is just as important as excitation ## Footnote Any meaningful thought or activity requires a balance of activating some neurons and inhibiting others.