Chapter 5: Development and Plasticity of the Brain

• The idea that the plasticity of the brain is constantly changing throughout the lifetime.

  Plasticity
• At birth, the human brain weights:

  350 grams
• By the first year, the brain weights:

  1000 grams
• The adult brain weights:

  1200-1400 grams
• The human central nervous system begins to form when the embryo is :

  2 weeks old
• Development of the brain is due to both:

  experience, physical maturation
• The development of neurons in the brain involves 4 processes:

  Proliferation, Differentiation, Myelination, Synaptogenesis
• The production of new cells/neurons in the brain primarily occurs early in life.

  Proliferation
• The movement of the newly formed neurons and glia to their eventual locations.

  Migration
• The forming of the axon and dendrite that gives the neuron its distinctive shape.

  Differentiation
• The process by which glia produce the fatty sheath that covers the axons of some neurons.

  Myelination
• The final stage of neural development and refers to the formation of the synapses between neurons.

  Synaptogenesis
• Undifferentiated cells found in the interior of the brain that generate "daughter cells" which can transform into glia or neurons.

  Stem cells
• Growing axons reach their target area by following a _____in which they are attracted by some chemicals and repelled by others.

  Gradient of chemicals
• Some theorists refer to the idea of the selection process of neural connections as:

  neural Darwinism
• A chemical that promotes the survival and activity of neurons.

  Neurotropin
• Axons that are not exposed to neurotrophins after making connections undergo apoptosis, a preprogrammed mechanism of cell death.
• Nerve growth factor (NGF) is a type of neutrophin released by muscles that promotes the survival and growth of axons.
• Fetal alcohol syndrome is a condition that children are born with if the mother drinks heavily during pregnancy.
• Focal hand dystonia or "musicians cramp" refers to a condition where the reorganization of the brain goes too far.
• A closed head injury refers to trauma that occurs when a sharp blow to the head drives the brain tissue against the inside wall of the skull.
• A stroke or cerebrovascular accident is temporary loss of blood to the brain.
• The mot common type of stroke, resulting from blood clot or obstruction of an artery.

  Ischemia
• A less frequent type of stroke resulting from a ruptured artery.

  Hemorrhage
• The Ischemia and hemorrhage also cause:

  Edema
• It is the accumulation of fluid in the brain resulting in increased pressure on the brain and increasing the probability of further strokes.

  Edema
• A drug called tissue plasminogen activator (tPA) breaks up blood clots and reduces the effects of an ischemic strokes.
• Research has begun to attempt to save cells in the penumbra or region that surrounds the immediate damage by blocking glutamate synapses and opening potassium channels.
• One of the most effective laboratory methods used to minimize damage caused by strokes is to cool the brain.
• Cannabanoids have also been shown to potentially minimize cell loss after brain damage be decreasing the release of glutamate.
• Diaschisis refers to the decreased activity of surviving neurons after damage to other neurons.
• Collateral sprouts are new branches formed by other non-damaged axons that attach to vacant receptors.
• Gangliosides, a class of glycolipids formed by the combination of carbohydrate and fat molecules, also promote the restoration of damaged brains.
• It is the heightened sensitivity to a neurotransmitter after the destruction of an incoming axon and usually a result of increased receptors.

  Denervation supersensitivity
• It is the hypersensitivity to a neurotransmitter after a result of inactivity.

  Disuse supersensitivity
• Phantom limb refers to the continuation of the sensation of an amputated body part and reflects this process.
• Deafferenated limbs are limbs that have lost their afferent sensory input.