Much of our early knowledge about the functions of the hemispheres came from surgical operations to control seizures which involved the severing of the corpus callosum, the communicating link between the hemispheres. Without this link, one side of the brain doesn't know what the other is doing; it's like having two brains in one skull. However, the two halves do not duplicate each other's function; rather, they function together like a committee, with various areas serving as 'subcommittees' to carry out specific kinds of tasks. The
Brain chemistry: Neurons produce 30+ neurotransmitters that we
currently know of. Not only do neurons produce neurotransmitters to release into
the synapses, they also produce other psychoactive chemicals that are secreted
into the fluids around the neuronal cells. These neuropeptides, which diffuse
through the brains' fluids, can block or alter (limit or enhance) the effects of
the neurotransmitters at the synapses. One type of neuropeptide, enkephalins,
produced in the brain, have a structure similar to opium and can both reduce pain and
stress and bring about an elevated mood. One example is the 'runner's high':
long distance runners often experience a 'high' that results from enkephalins
produced by the act of running for long periods. Thus, for some people, running
can be considered an addiction, in that the runner suffers withdrawal symptoms a
when prevented from running as usual. When artificial or plant-derived opiates
are taken into the body, they mimic the function of the enkephalins on the
pleasure centers of the brain, causing an artificial 'high' and withdrawal
symptoms if the person becomes addicted or habituated to their use.
How have scientists found out about the structure and function of the brain?
| Case records: Below is a computer reconstruction of the path the steel rod took through Phineas Gage's brain.....He had been a mild-mannered and responsible husband, father and worker prior to his accident. After the accident, his whole personality changed and he became very impulsive, with an explosive temper and an unreliable character. What does it tell you about the function of these areas of the brain? | ||
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- Case studies: accidents and illness can cause brain damage which is associated with specific behavioral changes. (See Phineas Gage, above) Surgery or post-mortem dissection and examination can then examine the physical damage that may be related to the behavioral changes. Also, surgery (such as the split-brain surgery sometimes used to control life-threatening seizures, or surgery to remove a tumor, etc) gives us valuable information about how the brain functions.
- EEG: electroencephalogram measures waves of electrical activity in the brain. Different patterns are correlate with specific function (or malfunctions). (A flat EEG - no brain waves recording on the EEG - indicates 'brain death', the person's brain stem may maintain his/her 'vegetative' functions, but the person will never regain consciousness or the use of the cortex.
- CT scan: a series of x-rays of the brain's structure is fed into a computer which then constructs a 3-D picture of the brain.
- PET scan: radioactive markers on glucose are introduced into the blood supply to the brain; radioactive particles are then emitted by active neurons using the glucose to conduct neural functions. This method can show the activity of the brain more specifically than the EEG.
- MRI: neurons respond to a strong electromagnetic field to produce 3-D or flat images of the brain. (This procedure avoid the introduction of radioactive materials into the brain.)
- fMRI: functional MRI, a motion study of the activity of the brain in action, either in response to stimuli or to doing a task.
- Recording with microelectrodes from single brain cells to learn about how they react to stimulation.
Handouts: articles on developmental brain plasticity
("Miracles of Mind" about a hemispherectomy at 17 months of
age), the brain's neurochemical
processes that cause addiction and affect personality ("How It
All Starts Inside Your Brian"), and one about fetal tissue
transplants.Then we viewed several videos that illustrated various aspects
of what we are studying.
VIDEOs: "The Addicted Brain", "A New Life for
Andrew", "Building Better Brains", and a segment of the
Oprah show on Traumatic Brain Injury. I discussed again the concept of
'plasticity': that experience 'wires' or connects the neurons into
circuits or nerve pathways and that the brain's way of functioning changes
in response to each individual's experiences. No two brains are alike,
and, after an injury, the brain can regain many functions by putting new
areas to work on tasks previously performed by the part that is now no
longer functional.
The endocrine system: another communication system for the body and brain: The endocrine system is made up of a series of special glands that produce certain chemicals, hormones, in response to stimulation by the nervous system. Hormones, traveling through the body in the bloodstream, affect tissues throughout the body causing longer-lasting changes than those brought about by stimulation by neurons.
Glands secrete hormones, substances, similar in structure and function to neurotransmitters, that affect other tissues and organs in the body. Tears and digestive juices are secreted into the area immediately surrounding the glands, but endocrine glands secrete their substances, hormones, into the blood stream, where they are circulated to the rest of the whole body.
Hormones relay information to the rest of the body more slowly than the nervous system and the substances linger in the system much longer before being broken down.
Hormones act upon the nervous system in that they are similar to neuropeptides that block or modify (enhance or interfere with) neurotransmitters at the synapses.
The glands are ultimately controlled by the nervous system through the hypothalamus in the brain. The hypothalamus stimulates the pituitary, the 'master gland', which sends instruction to the other glands in the endocrine system.
| Example of nervous system and endocrine system interacting... | For instance, if something frightens a person, the hypothalamus, in response to fear, produced by the limbic system, stimulates the pituitary, which then stimulates the adrenal glands to produce adrenaline which speeds the heart rate, providing better circulation for the quick burst of energy needed to deal with the situation ('fight or flight'). After the crisis is over, the parasympathetic system works to calm the body down but it takes the body a while to get rid of the adrenaline and other stress hormones that are circulating throughout the bloodstream. |
Know the major endocrine glands and their main functions.
