can partially alleviate the symptoms of Parkinson’s disease. Accidents involving brain or spinal trauma still produce many cases of paralysis every year. Extensive research efforts using stem cells, neural growth factors, and electrical stimulation continue to be made for these problems.
Neural dysfunctions and mental illness
The history of clinical thought on mental illness is a pendulum ride between organic and environmental causes. In the United States, particularly, the dominance of behaviorism in academic psychology and psychiatry was associated with behavioral and cognitive therapeutic strategies based on “undoing” some sort of bad environmental influence or improper response to a relatively normal environment.
Knowledge of genetics, neurotransmitter systems, and the development of neurotransmitter-analog drugs led to pharmacological treatments that were at least partially effective in many psychiatric patients for whom traditional therapy had provided no relief. Schizophrenia and autism are cases in point. In the mid 20th century, the detection of schizophrenia or autism often was treated by family therapy sessions around behavioral theories such as withdrawn, uncaring so-called “refrigerator mothers” being the cause of these disorders.
Repair and enhancement with artificial brains
Humans increasingly are electronically connected to each other through computers, cellphones, and soon, wearable devices like watches and electronic eyeglasses. It may be a short time before some of this technology is implantable. Brain implants may allow people who are paralyzed to operate computers or control their own or prosthetic limbs.
Deep brain stimulation, originally used widely to relieve Parkinson’s disease symptoms, may also be effective in treating some types of depression. Transcranial magnetic stimulation may also mitigate depression without many of the side effects of electroconvulsive therapy (ECT, commonly referred to as “shock treatment”). Transcranial electrical stimulation has been shown in numerous studies to increase learning rates. A new term electroceuticals has been introduced for the field of electrical brain stimulation for therapeutic effect. Brain scientists live in exciting times!
Chapter 2
Building Neurons from Molecules
In This Chapter
The genes in your body’s cells are the reason you have your mother’s brown eyes and your father’s curly hair. Neurons are cells, and, like all cells in the body, they’re controlled by the expression of the DNA within their nuclei. Although the DNA in all non-reproductive cells in the body is the same, how the genes are expressed is what makes the body’s 300-plus cell types different from each other.
This chapter covers the basic genetics common to all cells, such as genes, chromosomes, and inheritance. It also discusses the universal genetic code, the expression of genes, and protein synthesis. And if you ever wondered what makes neurons so special compared to other cells, read on to find out about their unique features and functions. Bringing these ideas together, the final sections talk about what happens when neurons have genetic defects, such as mutations that lead to neurological illness. I also look at how science may be able to fix these problems.
Getting into Genetics
Genetics is the study of genes and how they control inheritance. We can typically see the results of inheritance in the features of offspring, which has received genes from each of its parents. Genes are sequences of nucleotides (see “Greeting chromosomes and genes,” a bit later on for more) located on chromosomes in the cell’s nucleus. Genes specify the production of amino acid sequences. (Amino acids are the constituent units that make up proteins.)
Long before genes were known to be located on chromosomes composed of DNA, science had worked out some basic principles of inheritance, such as dominant and recessive traits. The upcoming sections explore these concepts in more detail.
Introducing inheritance
Mendelian inheritance is one of the cornerstones of genetics, based on the famous pea experiments of the monk Gregor Mendel. Genes determine the features, or traits, that you inherited from your parents. Some traits you can see, such as height or hair color, and others you can’t, such as blood type. Genes are copied and inherited across generations. Different genes cause different traits to present themselves, and each unique form of a single gene is called an allele. So, for example, the gene specifying blue eyes comes from a different allele than the gene specifying brown eyes.
Doubling genes
Organisms typically have two copies of each gene, one inherited from each parent. Each parent also has two copies of each gene, and passes along to its offspring a single copy by a (nearly) random selection of their two genes. This gene is found on a chromosome present in either the mother’s eggs or the father’s sperm. When the egg and sperm join, they form a double set of genes again.
Phenotype and genotype
The set of expressed traits of an organism are called its phenotype, whereas the genes within the organism are called its genotype. Since Mendel’s experiments, we have known that the traits an offspring expresses (phenotype) are not simply a mixing of the traits it got from the two sets of genes it inherited from its parents (genotype).
Determining dominant and recessive traits
One allele (that is, one particular form of a gene) may completely override the
