Chapter 1 - Nerve Cells & Nerve Impulses

Question 1

How do neurons transmit signals?

Answer 1

Neurons use electricity and chemistry to convey information. Electricity is transmitted along the wire like axon and chemicals across the synapse to another neuron.

Question 2

What do astrocytes do?

Answer 2

Astrocytes are glia cells that can control synaptic communication. There are the same neurotransmitter receptors on glia as neurons.

Question 3

How were the purposes of glia discovered?

Answer 3

Using video and laser-illuminated video by adding tracer dyes to cells. When a neuron was stimulated the neuroglia flashed back. The glia had sensed electrical impulse in neurons and calcium ions floodied into them.

Question 4

What purpose does the astrocyte have?

Answer 4

Neurotransmitters released from the astrocyte boosted the strength of an electrical impulse in the axon.

Question 5

How do glia communicate?

Answer 5

Glia can communicate widely. This occurs slowly by chemicals and often as a wave taking seconds to tens of seconds (i.e. learning leads to structural changes to white matter)

Question 6

What types of glia cells cling to axons? What do they do?

Answer 6

Oligodendrocytes (in the brain) and Schwann cells (in the body). These glia cells wrap around the axon creating a mylien insulation which increases the transmission speed by up to 50 times.

Question 7

What do microglia do? What are they attributed to being responsible for?

Answer 7

Microglia serve as the brains defence against disease. They seek out and kill germs and promote recovery from injury. Microglia are thought to be responsible for many neurological disorders.

Question 8

What role do microglia have in Alzheimer’s?

Answer 8

Microglia become weaker with age and begin to degenerate. In Alzheimers, the microglia surround amyloid palaques.

Question 9

What role do glial cells have in pain?

Answer 9

Malfunctions of glial cells may account for persistent pain and diminishing impact on power of pain-relieving drugs. Microglia and astrocytes respond to hyperactivity in pain circuits after injury by releasing compounds to help with the healing process. These substances stimulate neurons.

Question 10

What role do glia have in preventing healing of spinal injuries?

Answer 10

Proteins in myelin cells from oligodendrocytes stop injured axons from sprouting and repairing damaged circuits.

Question 11

How are microglia related to OCD?

Answer 11

The chemical cytokine which is released by immune cells and microglia is related to OCD.

Question 12

What role do glia have in mental health disorders?

Answer 12

The biological basis for most mental health disorders is an imbalance in neurotransmitter chemicals in circuits controlling perception, emotion and thought. Astrocytes regulate neurotransmitter levels at the synapses.

Question 13

What are glia cells and what percentage of the brain do they make up?

Answer 13

Glia cells interact with neurons, control them, work alongside them. Their functions are myriad. Glia make up 85% of our brain cells.

Question 14

What is the blood-brain barrier?

Answer 14

The blood-brain barrier is a layer of special, tightly-knit cells that line the inner walls of the small blood vessels that reach into the brain and spinal cord. These endothelial cells only allow certain molecules to pass through.

Question 15

How do endothelial cells stop molecules from getting through?

Answer 15

Tough proteins tie endothelial cells together, filling the spaces so nothing can squeeze through. Molecules must pass through the endothelial cells to reach the brain.

Question 16

What is and how does diffusion work?

Answer 16

Some gases (oxygen and carbon dioxide) and a few substances (i.e. ecstasy, alcohol, caffiene, nicotine, heroin) can diffuse across the barrier.

Question 17

What can cause damage to the blood-brain barrier?

Answer 17

A few substances (i.e. ecstasy) damage the barrier as they pass through it. They allow the blood-brain barrier to be more permeable for an extended time period (years).

Question 18

How do rabies, meningitis and cholera enter the brain?

Answer 18

Certain viruses and bacteria attack proteins on the endothelial cells forcing open the gates.

Question 19

How is the brain affected by multiple sclerosis?

Answer 19

Immune cells enter the brain forcing an inflammatory reaction. The immune cells attache myelin sheaths around nerves. As the sheaths are destroyed, nerve impulses become erratic and destructive.

Question 20

How do export pumps work?

Answer 20

Therapeutic drugs are usually too large to diffuse unnoticed. The export pump snare foreign molecules and expel them back into the blood stream. Researchers are trying to get drugs past export pumps or temporarily disable them. One approach has been to get drugs in through spheres of lipids and with natural chemicals attached that allow the brain to let it through.

Question 21

What are receptor-mediated transcytosis?

Answer 21

Transferrin binds to a receptor in the endothelial cell membrane that transforms itself into a vesicle container and transports to the other side.

Question 22

What did Santiago Ramon y Cajal do?

Answer 22

Developed a staining technique to show the gap between neurons. Cajal made detailed drawings of the nervous system.

Question 23

What is the neuron’s cell surface and what does it do?

Answer 23

The cell surface of a neuron is its membrane. It separates the inside of the cell from the outside environment. Most chemicals cannot cross the membrane but protein channels permit a controlled flow of water, oxygen, potassium, calcium and chloride and other chemicals.

Question 24

What does the nucleus contain?

Answer 24

The nucleus contains the chromosomes.

Question 25

What do mitochondrion do?

Answer 25

Mitochondrion perform metabolic activities, providing energy for the cell.

Question 26

What are ribosomes?

Answer 26

Ribosomes are where the cell synthesises new protein molecules. Proteins provide building materials and facilitate chemical reactions. Some ribosomes float freely but others are attached to the endoplasmic reticulum.

Question 27

What are endoplasmic reticulum?

Answer 27

A network of thin tubes that transport newly synthesised proteins elsewhere.

Question 28

What else do neurons have?

Answer 28

Dendrite, soma, axon and presynaptic terminals.

Question 29

How do motor neurons work?

Answer 29

The soma (cell body) is in the spinal cord and it receives excitation through its dendrites and conducts impulses along its axon to a muscle.

Question 30

What do sensory neurons do?

Answer 30

Sensory neurons are specialised at one end to be highly sensitive to a particular type of stimulation.

Question 31

What are dendrites and dendritic spines?

Answer 31

Dendrites are branching fibres that get narrower near their ends. They are lined with synaptic receptors which receive infromation from other neurons. Dendritic spines are short outgrowths that increase surface area available for synapses.

Question 32

What is a soma and what does it contain?

Answer 32

A soma is a cell body. It contains the nucleus, ribosomes, mitochondiron. The soma is covered in synapses.

Question 33

What is the axon and what does it do?

Answer 33

An axon is a thin fibre of constant thickness. The axon conveys an impulse towards other neurons, an organ or a muscle. An axon has many branches which swell at the end forming a presynaptic terminal. Here the axon releases chemicals that cross the junction between the neurons. A neuron can have many dendrite but one axon. Many axons are covered in myelin sheaths with interruptions known as nodes of Ranvier.

Question 34

What do afferent and efferent axons do?

Answer 34

An afferent (admit) brings information into a structure. An efferent (exit) axon carries information away from a structure.

Question 35

What is an interneuron or intrinsic neuron?

Answer 35

When the cell dendrites and axons are entirely one structure.

Question 36

What are astrocytes and what do they do?

Answer 36

Star shaped glia that wrap around the presynaptic terminals of a group of functionally related axons. Astrocytes:

• shield neurons from chemicals in its surrounding
• takes up ions released by neurons and releases them back, synchronising the activity of axons
• guide the formation and elimination of synapses
• remove waste material when neurons die
• control blood flow - during heightened activity they dilate blood vessels increasing blood flow

Question 37

What do microglia do?

Answer 37

Microglia act as part of the immune system removing waste materials, viruses, fungi from the brain. Microglia are necessary for survival in early life. They contribute to learning by removing the weakest synapses.

Question 38

What are oligodendrocytes and Schwann cells? Where are they located and what do they do?

Answer 38

Oligodendrocytes are located in the brain and Schwann cells are located in the rest of the body. They build the myelin sheath that surround and insulate axons. They provide axons with nutrients for functioning.

Question 39

What are radial glia and what do they do?

Answer 39

Radial glia guide the migration of neurons and their axons and dendrites during embryonic development. When development finishes most radial glia turn into neurons with some being astrocytes and oligodendrocytes.

Question 40

What is Korsakoff’s syndrome?

Answer 40

The body consumes glucose which the liver makes. To use glucose the body needs vitamin B1 (thiamine). Prolonged thiamine deficiency (common in alcoholism) can lead to the death of neurons and severe memory impairments. This is called Korsakoff’s syndrome

Question 41

What covers a neuron?

Answer 41

A membrane consisting of 2 layers of phospholipid group (chains of fatty acids and phosphate). Embedded in the phospholipids are cylindrical protein molecules through which chemicals can pass.

Question 42

What is the resting potential?

Answer 42

When at rest, the membrane maintains an electrical gradient (polarisation) - there is a difference in the electrical charge between inside and outside of the cell - the neuron has a slightly positive charge mainly because of negatively charged proteins inside the cell. The difference in voltage is the resting potential.

Question 43

How does the membrane allow chemicals into the neuron?

Answer 43

The membrane is selectively permeable - some chemicals pass through more freely than others. Oxygen, carbon dioxide, urea and water cross freely through channels that are always open. Sodium, potassium, calcium and chloride cross through membrane channels (gates) that are sometimes open and sometimes closed. When the membrane is at rest, Sodium and potassium channels are closed permitting almost no flow of sodium and a small flow of potassium.

Question 44

What is the sodium-potassium pump?

Answer 44

The sodium-potassium pump is a protein complex that transports three sodium out whilst drawing in two potassium ions in. It is an active transport system that requires energy.

Question 45

How does the sodium enter or exit the neuron?

Answer 45

Due to the differences in electrical gradient, the sodium wants to enter the cell. Sodium is also more concentrated outside the cell so it is more likely to enter the cell than leave it. When at rest, the sodium channel is closed and hence there is almost no sodium flow.

Question 46

How does potassium want to move?

Answer 46

Potassium is positvely charged and cell inside is negative so the cell tries to pull potassium in. There is more potassium inside the cell so it tries to go out (concentration gradient)

Question 47

What is responsible for maintaining the resting potential?

Answer 47

The sodium-potassium pump. The resting potential prepares neurons to respond rapidly.

Question 48

What are messages sent by axons called?

Answer 48

Action potentials

Question 49

What is hyperpolarisation?

Answer 49

Increasing a negative charge inside a neuron. It means increasing the polarisation.

Question 50

How are action potentials generated?

Answer 50

Stimulation beyond the threshold of excitation produces a massive depolarisation of the membrane when the potential reaches threshold, the membrane opens its sodium channels and allows sodium to enter the cell.

Question 51

What is the action potential chemical reaction?

Answer 51

1 - At the start, sodium ions are mostly outside the neuron and potassium inside.
2 - When the membrane is depolarised the sodium and potassium channels open.
3 - At the peak of the action potential, sodium channels close.

Question 52

What are voltage-gated channels?

Answer 52

The permeability depends on the voltage difference across the membrane. The channels regulating sodium and potassium are voltage gated.

Question 53

How does an action potential occur?

Answer 53

At resting potential, Na channels are closed and K channels are almost closed. As the membrane becomes depolarised, both channels open allowing their flow. Opening the Na channel allows Na ions to drive into the neuron. When depolarisation reaches the threshold of the membrane, the Na channel opens wide enough to allow Na ions to flow freely. Eventually, the electrical potential across the membrane passes zero to a reversed polarity. At the peak of the action potential the Na gates close. After Na ions have entered, the cell has a slightly positive charge and so K ions exit the cell. Because enough K ions leave, taking their positive charge the membrane goes beyond its usual resting level to a temporary hyperpolarisation. At the end, eventually the membrane returns to resting potential through the Na-K pump restoring Na and K levels to normal.

Question 54

How do local anaesthetic drugs work?

Answer 54

Action potentials require the flow of Na and K. Local anaesthetic drugs attach to the Na channels of the membrane, preventing Na from entering and thereby stopping action potentials from occurring.

Question 55

How do action potentials help learning?

Answer 55

An action potential starts in the axon and propagates without loss along the axon. Once it starts it back propagates into the cell body and the dendrites. They do not conduct action potential but register the event. Back-propagation makes dendrites more susceptible to the structural changes needed for learning.

Question 56

What is the all-or-none law?

Answer 56

The amplitude and velocity of an action potential are independent of the stimulus that initiated it. Thicker axons convey action potentials at greater velocities.

Question 57

What is a refractory period and what does it do?

Answer 57

Immediately after an action potential, the cell is in a refractory period, during which it resists the production of further action potentials. During the first part, the absolute refractory period (lasts about 1ms), the membrane cannot produce another action potential, regardless of the stimulation. During the second part, the relative refractory period (lasts about 3-4ms), a stronger than usual stimulus is required.

Question 58

How do action potentials move down axons?

Answer 58

During an action potential, Na ions enter a point of the axon. That point is positively charged. Positive ions flow down to neighbouring areas, slightly depolarising the next section and opening the Na gates. This is propagation of an action potential. The electrical charge flows in both directions. The areas the action potential has just passed are in its refractory period and therefore the action potential cannot continue towards the centre.

Question 59

What are myelin sheaths?

Answer 59

Myelin sheaths are composed of fats and proteins and they increase the speed of the action potential. In myelinated axons, the action potential starts at the first node of Ranvier. The action potential regenerates at each node of Ranvier. The jumping of action potentials is referred to as salatory conduction. Salatory conduction conserves energy by not having to pump out Na ions as much as the ions only enter at the nodes.

Question 60

What are local neurons?

Answer 60

Neurons with no axon and they only exchange information with their closest neighbours. When a local neuron receives information it has a graded potential (a membrane potential that varies in magnitude in proportion to the intensity of the stimulus. The change in membrane potential is conducted in all directions, decaying as it goes.

Question 61

Which of the following is NOT one of the four major structures that compose a neuron?

Select one:

a. Glia
b. Axon
c. Soma
d. Presynaptic terminal
e. Dendrites

Answer 61

a. Glia

Question 62

Santiago Ramon y Cajal was responsible for which of these discoveries?

Select one:

a. The human cerebral cortex has many specialisations to produce language.
b. Neurons communicate at specialised junctions called synapses
c. The nervous system is composed of separate cells.
d. The brain’s left and right hemisphere control different functions

Answer 62

c. The nervous system is composed of separate cells.

Question 63

Which of these chemicals cross the blood-brain barrier by active transport?

Select one:

a. Oxygen, water, and fat-soluble molecules
b. Viruses
c. Proteins
d. Glucose and amino acids

Answer 63

d. Glucose and amino acids

Question 64

What is the brain’s main source of fuel?

Select one:

a. Glucose
b. Thiamine
c. Proteins
d. Glutamate

Answer 64

a. Glucose

Question 65

Of these species, which probably has the longest axons?

Select one:

a. Giraffes
b. Cheetahs
c. Chimpanzees
d. Humans

Answer 65

a. Giraffes

Question 66

What makes brain cancers so difficult to treat?

Select one:

a. The brain includes more pain receptors than other organs
b. The brain has a very low metabolic rate
c. Brain cancers spread more rapidly than other cancers
d. Nearly all chemotherapy drugs fail to cross the blood-brain barrier

Answer 66

d. Nearly all chemotherapy drugs fail to cross the blood-brain barrier

Question 67

An advantage of the blood-brain barrier is that it keeps out most _______. A disadvantage is that is also keeps out _______.

Select one:

a. viruses….most nutrients
b. waste products……..water
c. harmful gases……..oxygen
d. small molecules……fat-soluble molecules

Answer 67

a. viruses….most nutrients

Question 68

Which of the following is something that glia NOT do?

Select one:

a. Synchronise activity of a group of axons
b. Conduct action potentials
c. Remove waste material
d. Dilate blood vessels to increase blood flow to the most active brain areas

Answer 68

b. Conduct action potentials

Question 69

What does an afferent axon do?

Select one:

a. It carries output from a structure
b. It controls voluntary behaviour
c. It brings information into a structure
d. It controls involuntary behaviour

Answer 69

c. It brings information into a structure

Question 70

What are the widely branching structures of a neuron called? And what is the long, thin structure that carries information to another cell called?

Answer 70

The widely branching structures of a neuron are called dendrites, and the long thin structure that carries information to another cell is called an axon.

Question 71

Which animal species would have the longest axons?

Answer 71

The longest axons would occur in the largest animals. i.e. elephants and giraffes.

Question 72

Identify the four structures that compose a neuron?

Answer 72

Dendrites, soma (cell body), axon and presynaptic terminal.

Question 73

Which kind of cell wraps around the synaptic terminals of axons?

Answer 73

Astrocytes.

Question 74

Identify one major advantage and one major disadvantage of having a blood-brain barrier.

Answer 74

The blood-brain barrier keeps out viruses and also most nutrients.

Question 75

Which chemicals cross the blood-brain barrier passively?

Answer 75

Small, uncharged molecules such as oxygen, carbon dioxide, and water. So do chemicals that dissolve in the fats of the membrane.

Question 76

Which chemicals cross the blood-brain barrier by active transport?

Answer 76

Glucose, amino acids, purines, choline, certain vitamins, iron, and a few hormones.

Question 77

When the membrane is at rest, the concentration gradient tends to draw sodium ions________the cell and the electrical gradient draws them_____the cell.

Answer 77

into…. into

Question 78

odium-potassium pump moves sodium ions ______and moves potassium ions_____.

Answer 78

out of the cell…..into the cell

Question 79

Is it true that we use only 10% of our brain? If so, what does that mean?

Answer 79

No, the statement is false and nonsensical

Question 80

When the neuron’s membrane is at rest, sodium ions are more concentrated_______ the cell, and potassium ions are more concentrated__________.

Answer 80

outside……inside

Question 81

After the action potential reaches its peak, the potential across the membrane falls toward its resting level. What accounts for this recovery?

Answer 81

Potassium ions move out because their channels are open and the concentration gradient pushes them out

Question 82

Which of the following is one way of starting the all-or-none law?

Select one:

a. All stimuli that exceed the threshold produce equivalent responses in the axon
b. The amplitude of the action potential in one axon s the same as that in another axon
c. At a given time, either all axons produce action potentials, or none do.
d. During an action potential, all sodium channels open at the same time

Answer 82

a. All stimuli that exceed the threshold produce equivalent responses in the axon

Question 83

The difference in voltage in a resting neuron is called the resting potential. T or F

Answer 83

True

Question 84

Suppose a neuron has a resting potential of -70mV. If the potential goes to -80mV, the change would be a_____.

Answer 84

Hyperpolarisation

Question 85

To which part or parts of a neuron does the all-or-none law apply?

Answer 85

Axons

Question 86

During the rising portion of the action potential, which ions are moving across the membrane and in which direction?

Answer 86

Sodium ions move in

Question 87

When the membrane is at rest, the concentration gradient tends to draw potassium ions______the cell and the electrical gradient draws them____the cell.

Answer 87

out of….into

Question 88

At the resting potential, the potassium channels are completely closed and the sodium channels are almost closed.​ T or F

Answer 88

False

Question 89

Under what conditions does an axon produce an action potential?

Answer 89

Whenever the membrane’s potential reaches the threshold

Question 90

A prolonged increase in the permeability of the membrane to sodium ions would interfere with a neuron’s ability to have an action potential. T or F

Answer 90

True

Question 91

What does the myeline sheath of an axon accomplish?

Answer 91

It enables action potentials to travel more rapidly

Question 92

Both dendrites and cell bodies are capable of producing action potentials.​ T or F

Answer 92

False

Question 93

When the membrane is at rest, are the sodium ions more concentrated inside the cell or outside? Where are the potassium ions more concentrated?

Answer 93

Sodium ions are more concentrated outside the cell, and potassium is more concentrated inside.

Question 94

When the membrane is at rest, what tends to drive the potassium ions out of the cell? What tends to draw them into the cell?

Answer 94

When the membrane is at rest, the concentration gradient tends to drive potassium ions out of the cell, and the electrical gradient draws them into the cell. The sodium-potassium pump also draws them into the cell.

Question 95

What is the difference between a hyperpolarisation and a depolarisation?

Answer 95

A hyperpolarisation is an exaggeration of the usual negative charge within a cell (to a more negative level than usual). A depolarisation is a decrease in the amount of neg ative charge within the cell.

Question 96

What is the relationship between the threshold and an action potential?

Answer 96

A depolarisation that passes the threshold produces an action potential. One that falls short of the threshold does not produce an action potential.

Question 97

During the rise of an action potential, do sodium ions move into the cell or out of it? Why?

Answer 97

During the action potential, sodium ions move into the cell. The voltage-dependent sodium gates have opened, so sodium can move freely. Sodium is attracted to the inside of the cell by a both an electrical and concentration gradient.

Question 98

As the membrane reaches the peak of the action potential, what brings the membrane down to the original resting potential?

Answer 98

After the peak of the action potential, potassium ions exit the cell, driving the membrane back to the resting potential. Important note: The sodium-potassium pump is NOT responsible for returning the membrane to its resting potential. The sodium-potassium pump is too slow for this purpose.

Question 99

State the all-or-none law.

Answer 99

According to the all-or-none law, the size and shape of the action potential are independent of the intensity of the stimulus that initiated it. That is, every depolarisation beyond the threshold of excitation produces an action potential of about the same amplitude and velocity for a given axon.

Question 100

Does the all-or-none law apply to dendrites? Why or why not?

Answer 100

The all-or-none law does not apply to dendrites because they do not have action potentials.

Question 101

Suppose researchers find that axon A can produce up to 1000 action potentials per second (at least briefly, with maximum stimulation), but axon B can never produce more than 100 per second (regardless of the strength of the stimulus). What could we conclude about the refractory periods of the two axons?

Answer 101

Axon A must have a shorter refractory period, about 1 ms, whereas B has a longer absolute refractory period, about 10 ms.

Question 102

In a myelinated axon, how would the action potential be affected if the nodes were much closer together? How might it be affected if the nodes were much farther apart?

Answer 102

If the nodes were closer, the action potential would travel more slowly. If they were much farther apart, the action potential would be faster as it could successfully jump from one node to the next. When the distance becomes too great, the current cannot diffuse from one node to the next and still remain above threshold, so the action potentials would stop.