Question 1

____ occurs as a surviving axon grows a new branch to replace the synapses left vacant by a damaged axon.

Accepted Answer

Collateral sprouting is the process by which a surviving axon grows new branches to replace the synapses left vacant by a damaged axon. This occurs in response to injury or damage to the nervous system, and allows for the recovery of lost function. Degeneration supersensitivity and denervation supersensitivity are related processes, but refer to changes in the postsynaptic neuron that occur in response to the loss of input from damaged axons. Axon sprouting is a more general term that can refer to the growth of new axons in a variety of contexts, including during development or in response to injury. However, in the context of replacing lost synapses, collateral sprouting is the most specific and accurate term.

Question 2

After central nervous system damage, myelin:

Accepted Answer

After central nervous system damage, myelin secretes proteins that inhibit axon regrowth. This is one of the main factors that make it difficult for axons to regenerate after injury in the central nervous system.

Question 3

Central nervous system axons regenerate much better in fish than in mammals because fish:

Accepted Answer

Myelin in fish does not secrete proteins that inhibit axon growth, which allows for better regeneration compared to mammals.

Question 4

After learning strengthens one set of synapses, other synapses:

Accepted Answer

This phenomenon is called synaptic pruning, where the brain eliminates weaker or unnecessary synapses to make room for new connections. This helps to improve the efficiency and effectiveness of neural pathways involved in learning and memory.

Question 5

Central nervous system axons regenerate much better in fish than in mammals because:

Accepted Answer

Fish do not produce as much scar tissue as mammals, which allows for better regeneration of axons in the central nervous system. Scar tissue can inhibit and prevent axon regrowth, so the lower amount of scar tissue in fish is a significant factor in their superior regenerative ability.

Question 6

If some of the axons innervating a given cell are destroyed or if they become inactive, what compensatory process takes place in the remaining presynaptic cells?

Accepted Answer

When some axons innervating a given cell are destroyed or inactive, the remaining presynaptic cells undergo collateral sprouting, which means they extend their axons and form new synapses onto the same postsynaptic cell. This allows for compensation and reestablishment of neural connections.

Question 7

Certain axons innervating a given neuron are damaged. What compensatory change is likely to take place in that postsynaptic cell?

Accepted Answer

Denervation supersensitivity occurs when a postsynaptic neuron becomes more sensitive to neurotransmitters following the loss of input from damaged axons.

Question 8

If a brain area loses a set of incoming axons, we can expect some combination of ____ by the remaining axons and collateral sprouting by other axons that ordinarily attach to some other target.

Accepted Answer

When a brain area loses a set of incoming axons, denervation supersensitivity occurs. This means that the remaining axons that attach to the target become more sensitive to the neurotransmitters or signaling molecules they receive. Additionally, collateral sprouting by other axons that ordinarily attach to some other target may occur, allowing them to make new connections with the target area. These changes can compensate for the loss of the original set of axons, but can also lead to maladaptive changes and pathological conditions in some cases.

Question 9

One reason why axons regenerate better in the peripheral nervous system of mammals than in the central nervous system is that the peripheral nervous system:

Accepted Answer

The peripheral nervous system produces a chemical that promotes axon growth called nerve growth factor (NGF). This is not present in the central nervous system, which may explain why axons regenerate better in the peripheral nervous system.

Question 10

After damage to the connections to the left hippocampus from the left entorhinal cortex, sprouts develop from the:

Accepted Answer

Sprouts develop from the right entorhinal cortex when the connections to the left hippocampus from the left entorhinal cortex are damaged. This is known as sprouting, a phenomenon where surviving neurons develop new branches to make new connections in response to injury or damage.

Question 11

What is one impediment to regeneration of axons in the mammalian central nervous system?

Accepted Answer

Glia cells release chemicals that inhibit axon growth and regeneration in the mammalian central nervous system. These chemicals include chondroitin sulfate proteoglycans and myelin-associated inhibitors.

Question 12

Heightened sensitivity to a neurotransmitter after the destruction of an incoming axon is known as:

Accepted Answer

When an incoming axon is destroyed, the postsynaptic neuron may become more sensitive to the neurotransmitter released by other axons, leading to an increased response. This phenomenon is called denervation supersensitivity. Choice A (axon supersensitivity) and B (disuse supersensitivity) are not accurate terms used to describe this phenomenon. Choice C (enervation supersensitivity) is a misspelling of denervation supersensitivity.

Question 13

What is the term for the new branches that may form in uninjured axons after damage to surrounding axons?

Accepted Answer

The term for new branches that may form in uninjured axons after damage to surrounding axons is collateral sprouts.

Question 14

After damaging input to the hippocampus, collateral sprouting is associated with improvements in:

Accepted Answer

The hippocampus is a brain region that plays a critical role in the formation and retrieval of new memories. Damage to the hippocampus can lead to deficits in memory function. Collateral sprouting refers to the process by which remaining neurons in the hippocampus send out new branches or connections to compensate for the loss of damaged neurons. This process has been associated with improvements in memory function, suggesting that collateral sprouting may be a mechanism by which the brain can repair itself after injury. Therefore, the correct choice is A) memory.

Question 15

____ helps compensate for decreased axon input.

Accepted Answer

Denervation supersensitivity refers to an increase in sensitivity of postsynaptic receptors after a loss of input from presynaptic neurons. This compensatory response helps maintain normal function despite decreased axon input.

Question 16

If a tree branch is cut, the surrounding branches may grow enough to fill in the empty space left by the missing branch. When this same type of event occurs in the nervous system following brain damage, it is called:

Accepted Answer

Collateral sprouting is the phenomenon where neighboring neurons, after a neuron has been damaged, grow new branches in order to compensate for the loss of function. This is similar to how surrounding tree branches might grow to fill in the empty space left by a missing branch. Hemiplegia refers to paralysis on one side of the body, while denervation supersensitivity is a different aspect of nerve regeneration. "Tree branching" is not a recognized term in neuroscience.

Question 17

In some cases, ____ enables people to maintain nearly normal behavior even after losing most of the axons in some pathway.

Accepted Answer

Receptor supersensitivity occurs when remaining receptors become more sensitive to compensate for the loss of input, allowing for nearly normal behavior despite the loss of axons.

Question 18

If most of the axons that transmit dopamine to some brain area die or become inactive, the remaining dopamine synapses become:

Accepted Answer

If most of the axons that transmit dopamine to some brain area die or become inactive, the remaining dopamine synapses will need to work harder to compensate for the loss. This can lead to increased responsiveness or sensitivity to dopamine. Therefore, the best choice is D - more responsive.

Question 19

After damage to a set of axons, neurotrophins induce nearby:

Accepted Answer

Neurotrophins are signaling molecules that promote survival and growth of neurons. In the situation of damage to axons, neurotrophins promote nearby uninjured axons to form new branches and help compensate for the lost function caused by the damaged axons.

Question 20

Damage to some of the axons that innervate a given structure may give rise to:

Accepted Answer

Damage to axons may result in a phenomenon called collateral sprouting, whereby healthy axons can branch out and eventually take over the function of the damaged axons. Additionally, denervation supersensitivity may occur, which means the remaining functional axons become more responsive than normal to neurotransmitters, leading to exaggerated responses to stimuli. Therefore, both collateral sprouting and denervation supersensitivity may occur as a result of damage to axons.

Quiz 5: Development and Plasticity of the Brain