5.2.1 Plasticity After Brain Damage 2 Flashcards
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 ____ ____.
original target
With an immature mammalian brain or spinal-cord, ____ ____ do not regenerate, or do so only slightly.
damaged axons
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.
mechanical barrier
A second problem that limits axon regeneration is it neurons on the two sides of the cut ____ ____.
pull apart
A third problem limiting axon regeneration is the glia cells that react to CNS damage release ____ ____ ____ axon growth.
chemicals that inhibit
Researchers developed a way to build a ____ ____, providing a path for axons to regenerate across a scar-filled gap.
protein bridge
Also, injecting ____ at appropriate locations helps axons grow and establish normal synapses.
neurotrophins
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.
mammalian Target Of Rapamycin
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.
collateral sprouts
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.
denervation supersensitivity
Denervation supersensitivity helps compensate for decreased ____.
input
However denervation supersensitivity can also have unpleasant consequences, such as ____ ____.
chronic pain
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.
combination
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.
somatosensory
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.
reorganised cortex
Physicians have long noted that many people with amputations experience a ____ ____, continuing sensation of an amputated body part.
phantom limb
Modern methods have demonstrated that phantom limbs develop only if the relevant portion of the somatosensory cortex ____ and becomes ____ to alternative inputs.
recognises : responsive
Amputees to learn to use an artificial arm report that their phantom sensations gradually ____.
disappear
Much recovery from brain damage is based on ____.
learning
Someone with brain damage may have lost some ability totally or maybe able to find it with enough ____.
effort
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.
deafferented
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.
impaired
The brain has increased plasticity during the first ____ after damage.
days
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.
effortful
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.
deteriorates
