5.2.1 Plasticity After Brain Damage 2

Question 1

A neuron of the peripheral nervous system has its cell body in the spinal-cord (for motor neurons) or in a ganglion near the spinal-cord (for sensory neurons). In either case, the axon extends into one of the limbs. A crushed axon grows back toward the periphery at a rate of about 1 mm per day. Following its myelin sheath to the ____ ____.

Answer 1

original target

Question 2

With an immature mammalian brain or spinal-cord, ____ ____ do not regenerate, or do so only slightly.

Answer 2

damaged axons

Question 3

Several problems limit axon regeneration in mammals. First, a cut in the nervous system causes a scar to form creating a ____ ____. That scar tissue is beneficial immediately after the damage, but it blocks regrowth of axons later.

Answer 3

mechanical barrier

Question 4

A second problem that limits axon regeneration is it neurons on the two sides of the cut ____ ____.

Answer 4

pull apart

Question 5

A third problem limiting axon regeneration is the glia cells that react to CNS damage release ____ ____ ____ axon growth.

Answer 5

chemicals that inhibit

Question 6

Researchers developed a way to build a ____ ____, providing a path for axons to regenerate across a scar-filled gap.

Answer 6

protein bridge

Question 7

Also, injecting ____ at appropriate locations helps axons grow and establish normal synapses.

Answer 7

neurotrophins

Question 8

A third possibility, infant axons grow under the influence of protein called in mTOR (which stands for ____ ____ of ____). Deleting a gene responsible for inhabiting mTOR enables regrowth of axons in the adult spinal-cord.

Answer 8

mammalian Target Of Rapamycin

Question 9

Ordinarily, the surface of dendrites and cell bodies is covered with synapses, and a vacant spot doesn’t stay vacant for long. After a cell loses input from an axon it secretes neurotrophins that induce other axons to form new branches, or ____ ____, that take over the vacant synapses.

Answer 9

collateral sprouts

Question 10

If most of the axons that transmit dopamine to some brain area die or become inactive, the remaining dopamine synapses become more responsive, more easily stimulated. This process of enhanced response is known as ____ ____ or receptor supersensitivity.

Answer 10

denervation supersensitivity

Question 11

Denervation supersensitivity helps compensate for decreased ____.

Answer 11

input

Question 12

However denervation supersensitivity can also have unpleasant consequences, such as ____ ____.

Answer 12

chronic pain

Question 13

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

Answer 13

combination

Question 14

In the case of an amputated limb, areas that were previously sensitive to the fingers may now become sensitive to areas on the face. This is due to the face being close to the hand in the ____ cortex.

Answer 14

somatosensory

Question 15

Now consider what happens when something activates the neurons in a ____ ____. Previously, those cells responded to arm stimulation, but now they receive information from the face.

Answer 15

reorganised cortex

Question 16

Physicians have long noted that many people with amputations experience a ____ ____, continuing sensation of an amputated body part.

Answer 16

phantom limb

Question 17

Modern methods have demonstrated that phantom limbs develop only if the relevant portion of the somatosensory cortex ____ and becomes ____ to alternative inputs.

Answer 17

recognises : responsive

Question 18

Amputees to learn to use an artificial arm report that their phantom sensations gradually ____.

Answer 18

disappear

Question 19

Much recovery from brain damage is based on ____.

Answer 19

learning

Question 20

Someone with brain damage may have lost some ability totally or maybe able to find it with enough ____.

Answer 20

effort

Question 21

We say limb is ____ because it has lost its afferent (sensory) input. In the case of someone who no longer feels a limb, although the motor nerves are still connected to the muscles.

Answer 21

deafferented

Question 22

Therapy for people with brain damage focuses on encouraging them to practice skills that are ____ but not lost. Treatment begins with careful evaluation of the patient abilities and disabilities.

Answer 22

impaired

Question 23

The brain has increased plasticity during the first ____ after damage.

Answer 23

days

Question 24

One important note is that behaviour recovered after brain-damaged is ____, and its recovery is precarious. A person with brain damage who appears to be functioning normally is working harder than usual.

Answer 24

effortful

Question 25

The recovered behaviour after brain injury ____ markedly after drinking alcohol, physical exhaustion, or other kinds of stress that would minimally affect most other people. It also deteriorates in old age.

Answer 25

deteriorates