Brain Anatomy

Biological Basis of Behavior

What the College Board is asking for:

Students need to understand the relationship between biology and behavior. An effective introduction to this section of the course is an exploration of the range of techniques scientists have used to learn about brain function, from procedures such as ablation, direct stimulation, EEG, and PET scans, and MRI. Students study the brain as a key part of the body's nervous system, paying particular attention to the anatomical and functional relationships among the central, somatic, and autonomic nervous systems.

The course also helps students gain an understanding of how the nervous sysytem functions on a cellular level by examining the structure and function of the neuron in the electrochemical transmission of impulses. Students then explore the interrelationship of the nervous system and the endocrine system. They examine hereditary influences on behavior through a brief study of behavioral genetics that focuses on the inheritance of human traits.

Magnetic Resonance Imaging

MRI's are safer than CAT scans because they don't use X rays. They rely upon the physical principle called nuclear magnetic resonance. This refers to the fact that the nuclei at the center of atoms hjave their own resonant frequencies: If you perturb them, they sing like tuning forks as they bounce back to normal. Because the structures of the brain have different chemical compositions, the nuclei of their atoms sing differently. An MRI scan will send an impulse of magnetic fields through the brain, by means of electromagnets surrounding the patient's head. As this magnetic energy passes through the brain the singing of the atoms is detected by magnetic sensors within the scanner. The scanner can show tumors, sites of tissue degeneration, and the blood clots that may lead to a stroke.

The Positron Emission Tomography was the breakthrough that allowed in-depth, three-dimensional localizaiton of the brain. The PET participant is injected with a dose of radioactive sugar that resembles glucose (the only metabolic food the brain can use). When the brain uses this "glucose" it emits subatomic particles called positrons. The part of the brain most active will release more of these positrons, which are then detected and from which an image is assembled for scientists to view. It can tell a doctor which part of the brain is abnormally active or inactive, and this may suggest a tumor, a lesion, or a psychological disorder. Many studies on the difference between men's and women's brains uses the PET.

The CAT scan is a brain imaging device that employs a narrow beam of X rays that is aimed through the patient's head and hits a deterctor on the opposite side. This beam moves in a slow circular arc, and the detector moves along with it. The computer constructs an image of the brain by determing the amount of X rays blocked at different angles. Density of brain tissue varies. Aides in seeing brain abnormalities.

You are responsible for knowing all of these parts of the brain and their function. You can find much of this information in my notes. Also make sure you are familiar with the following terminology:

Split Brain Surgery, contralateral control, left and right brain functions, Broca's area, Wernicke's area, amygdala, hippocampus, basal ganglia, and the fissures of the brain (valleys)

The neuron is a single cell with three subdivisions; the dendrites, the cell body, and the axon. The dendrites receive impulses from other neurons and the axon carries the impulse to another neuron. The axon may split into several forks called axonal branches or telodendria. There are two major types of neurons: afferent and efferent. Afferent neurons are sensory neurons and efferent neurons are motor neurons. One neuron can be as long as two or more feet (from end of toe to base of spinal cord). A neuron is surrounded by a layer of fatty cells called myelin sheath. This myelin insultes and speeds the axons action potential.. The degenearation of myelin around a motor neuron leads to multiple schlerosis. Neurons fire on an all-or-none principle. They can be fired by pressure, heat, light, or chemical from another neuron. The neuron communicates electro-chemically. This nerve impulse travels between 2-225 mph. Chemical changes in a neuron cause an electric charge to be transmitted along their lengths. A neuron in a resting state (when neuron is not stimulated) has more Na+ ions outside the neuron in the bodily fluid. There are more Cl- ions inside the neuron. This gives the neuron an inside negative charge in relation to the outside. The resting potential is -110 millivots. When a resting neuron is adequately stimulated the cell membrane changes permiability to allow NA+ ions to enter, causing a change in the charge of the neuron. This inside change is called action potential, of +40 millivolts. This action causes the neuron to fire, releasing the neurotransmitters across the synaptic gap, and trigger the next neuron. Once the neuron has fired, NA+ ions are pumped out of neuron, so to return it to its resting potential.

Also make sure you are familiar with the following terminology: neurotransmitters (acetylcholine, dopamine, and serotonin), antagonist, agonist, synaptic gap