7.2 Neurons and Nerve Impulses

Question 1

What are neurons? And what other name can you give them?

Answer 1

They are one of the major types of cells found in the nervous system. They’re also called nerve cells.

Question 2

What are neurons specialized in?

Answer 2

They are specialized to carry information quickly for one body part to another in the form of electrical signals known as nerve impulses.

Question 3

List some characteristics of neurons.

Answer 3

They share some characteristics with other cells such as: having a cytoplasm, a nucleus, and a cell membrane.

Question 4

What is the cell body of a neuron?

Answer 4

The cell body is the spherical part of the neuron that contains the cytoplasm and most of the organelles, including the nucleus.

Question 5

What type of unique structural features help nerve cells to perform their function?

Answer 5

Thin, cytoplasmic-filled lengths of cell membrane that extend out from the cell body of a neuron, namely, the axon and the dendrites.

Question 6

What are dendrites?

Answer 6

They are short, branched fibers that receive nerve impulses from other neurons and may transmit them to the cell body.

Question 7

What does the cytoplasm of the dendrites contain?

Answer 7

Most of the organelles found in the cell body.

Question 8

What does the axon do?

Answer 8

The axon generally carries impulses away form cell body towards the effectors or other neurons.

Question 9

Describe the features of the axons.

Answer 9

Axons are very long, some reaching more than one meter in length.

Question 10

List some examples of the longest cells in the body.

Answer 10

The neurons that control the movement of the toes are some of the longest cells in the body.

Question 11

Why are the toe neurons one of the longest neurons in the body?

Answer 11

Because their axons extend form the lower back region of the spinal coed to the toes, which in some people is more than one meter.

Question 12

Which is more branched?

Answer 12

The axons are typically less branched than dendrites, except at the axon terminal, where extensive branching could be observed.

Question 13

What could be found in the cytoplasm of the axon?

Answer 13

They contain most of the organelles found in the cytoplasm of the dendrites and cell body with 2 major exceptions: the rough endoplasmic reticulum (RER) and the Golgi apparatus.

Question 14

What happens since axons lack 2 major organelles?

Answer 14

Since the RER and Golgi apparatus are required for protein synthesis and packaging, the needed proteins are transported to an axon from the cell body.

Question 15

What are axons wrapped around in some neurons?

Answer 15

In some neurons, axons can be wrapped by a fatty insulating layer called myelin sheath.

Question 16

How is myelin sheath secreted?

Answer 16

It is secreted by specialized cells that are present on the axons of neurons.

Question 17

Describe how the myelin sheath covers the axon.

Answer 17

The myelin sheath covers segments of an axon, leaving certain exposed regions called nodes of Ranvier.

Question 18

What do these segmented insulation do?

Answer 18

Allows the nerve impulse to be conducted very rapidly along the axon.

Question 19

Why happens to the electrical impulse? Explain the process of saltatory conduction.

Answer 19

The electrical impulse, traveling down a myelinated axon, cannot move through the axon in the insulated regions and, thus skips over these insulated regions, jumping from one node to the next in a process called saltatory conduction.

Question 20

How can different types of neurons be distinguished?

Answer 20

based on function.

Question 21

List some different types of neurons.

Answer 21

motor neurons, sensory neurons, and relay neurons, or interneurons.

Question 22

What is the function of motor neurons?

Answer 22

It carries the nerve impulses from the CNS to the effectors.

Question 23

How are motor neurons characterized?

Answer 23

These neurons are generally characterized by the presence of many dendrites and a single axon.

Question 24

What is the function of sensory neurons?

Answer 24

It carries nerve impulses form the sensory receptors to the CNS.

Question 25

How are sensory neurons characterized?

Answer 25

Typically, a sensory neuron has a process that extends form the cell body and branches into 2 relatively long processes.

Question 26

Explain the 2 long process of sensory neurons.

Answer 26

One of the two processes is peripheral and extends towards a sensory region. While the other process is central and extends towards the CNS. The two processes make up an axon; the peripheral process is described as an axon even though it carries nerve impulses toward the cell body.

Question 27

What is the function of relay neurons?

Answer 27

They are neurons that conduct nerve impulses between different parts of the CNS, for example, between the spinal cord and the brain.

Question 28

What’s another function of relay neurons?

Answer 28

They can also transmit impulses between sensory and motor neurons.

Question 29

Where are relay neurons found?

Answer 29

Only within the CNS. Typically have extensively branched dendrites and multiple terminals at the end of their axons.

Question 30

What happens when a nerve impulse is carried along an axon? In what form is it carried?

Answer 30

It’s carried in the form of electrical signals that causes a redistribution of charges between the inner and the outer sides of the axonal cell membrane.

Question 31

What happens to the nerve impulse when it reaches the axon terminal?

Answer 31

It is transmitted to the membrane of the adjacent neurons.

Question 32

What is the synaptic cleft? Explain the process.

Answer 32

The membranes of the adjacent neurons (e.g. the membrane if the axon of one neuron and the membrane of the dendrite of the adjacent neurons) are separated by a microscopic gap called the synaptic cleft.

Question 33

What is the presynaptic neuron?

Answer 33

The neuron transmitting the impulse from its axon.

Question 34

What is the postsynaptic neuron?

Answer 34

The neuron on the other side of the synaptic cleft.

Question 35

What is triggered when the nerve impulse arrives at the axon terminal of the presynaptic neuron?

Answer 35

It triggers the release of the chemical, called neurotransmitter (or a transmitter substance), form the presynaptic axon terminal into the synaptic cleft.

Question 36

Where is the neurotransmitter stored?

Answer 36

Stored in vesicles located in the presynaptic axon terminal and are released from these vesicles by exocytosis.

Question 37

What happens when neurotransmitter are released?

Answer 37

The molecules diffuse across the synaptic cleft and attach to their specific receptors on the postsynaptic neuron.

Question 38

What happens when stimulation of postsynaptic receptors by neurotransmitter occurs?

Answer 38

It may produce a nerve impulse that can then continue along the postsynaptic neuron.

Question 39

To what does the neurotransmitter bind?

Answer 39

It binds only to its specific receptors; neurotransmitter and its unique receptor are complementary in shape.

Question 40

Give one example of a neurotransmitter.

Answer 40

Acetylcholine, which is broken down by a specific enzyme, almost as soon as the presynaptic neuron releases it.

Question 41

How is the duration of neurotransmitter regulated?

Answer 41

The breakdown or removal of a neurotransmitter after its released helps prevent the nerve impulse from being sent continuously, regulating its duration.

Question 42

What is synapse?

Answer 42

The junction between 2 adjacent neurons, which includes the synaptic cleft together with the ends of the presynaptic and the postsynaptic neurons on either side of the cleft, called a synapse.

Question 43

In which direction does the nerve impulse travel?

Answer 43

It can travel in one direction across the synaptic cleft.

Question 44

What happens when a nerve contains more than one neuron?

Answer 44

Even though a nerve impulse can only travel in one direction along an axon, a nerve, which contains more than one neuron, may conduct impulses in opposite directions, because it may contain both sensory and motor axons, each carrying its own nerve impulses.

Question 45

How do drugs affect the transmission of nerve impulses across synapses?

Answer 45

Some drugs so closely resemble a natural neurotransmitter in the body that they can bind to the receptors of this neurotransmitter. A drug may either imitate the action of the neurotransmitter or block its normal function.

Question 46

Describe the drug heroin.

Answer 46

It’s a drug that resembles a particular neurotransmitter that is normally present in the brain; however, heroin can stimulate the receptors of this natural neurotransmitter more strongly, causing a more intense response than what normally occurs in the body.

Question 47

How do other drugs exert their effects?

Answer 47

Some drugs exert their effects by acting on the enzymes that break down the neurotransmitter in the synapse, thus increasing the time the neurotransmitter spends in the synapse and enhancing its action.

Question 48

Explain an illusion of what happens during the transmission of nerve impulse across a synapse.

Answer 48

1- impulses arrives down the axon of the presynaptic neuron.
2- neurotransmitters are released from vesicles by exocytosis.
3-neurotransmitters diffuse across the synaptic cleft.
4-neurotransmitters attach to their receptors on the membrane of the postsynaptic neuron.
5-the impulse can continue along the postsynaptic neuron.