Chapter 2 Brain and Behavior. Neuron and Its Parts. Neuron: Individual nerve cell Dendrites: Receive messages from other neurons Soma: Cell body; body of the neuron Axon: Fiber that carries information away from the cell body
FIGURE 2.1 A neuron, or nerve cell. In the right foreground you can see a nerve cell fiber in cross section. The upper left photo gives a more realistic picture of the shape of neurons. Nerve impulses usually travel from the dendrites and soma to the branching ends of the axon. The nerve cell shown here is a motor neuron. The axons of motor neuron stretch from the brain and spinal cord to muscles or glands of the body.
FIGURE 2.5 A highly magnified view of a synapse. Neurotransmitters are stored in tiny sacs called synaptic vesicles (VES-ihkels). When a nerve impulse reaches the end of an axon, the vesicles move to the surface and release neurotransmitters. These molecules cross the synaptic gap to affect the next neuron. The size of the gap is exaggerated here; it is actually only about one millionth of an inch. Some transmitter molecules excite the next neuron, and some inhibit its activity.
• Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters
FIGURE 2.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.
FIGURE 2.8 Sympathetic and parasympathetic branches of the autonomic nervous system. Both branches control involuntary actions. The sympathetic system generally activates the body. The parasympathetic system generally quiets it. The sympathetic branch relays its messages through clusters of nerve cells outside the spinal cord.
FIGURE 2.7 Subparts of the nervous system.
FIGURE 2.9 A sensory-motor arc, or re- flex, is set in motion by a stimulus to the skin (or other part of the body). The nerve impulse travels to the spinal cord and then back out to a muscle, which contracts. Such reflexes provide an “automatic” protective device for the body.
FIGURE 2.10 The functions of brain structures are explored by selectively activating or removing them. Brain research is often based on electrical stimulation, but chemical stimulation is also used at times.
FIGURE 2.21 The left and right brain have different information-processing styles. The left brain focuses on the small details; the right gets the big pattern.
FIGURE 2.19 Basic nerve pathways of vision. Notice that the left portion of each eye connects only to the left half of the brain; likewise, the right portion of each eye connects to the right brain. When the corpus callosum is cut, a “split brain” results. Then visual information can be sent to just one hemisphere by flashing it in the right or left visual field as the person stares straight ahead.
FIGURE 2.20 A circle is flashed to the left brain of a split-brain patient, and he is asked what he saw. He easily replies, “A circle.” He can also pick out the circle by merely touching shapes with his right hand, out of sight behind a screen. However, his left hand can’t identify the circle. If a triangle is flashed to the patient’s right brain, he can’t say what he saw (speech is controlled by the left hemisphere). He also can’t identify the triangle by touch with the right hand. Now, however, the left hand has no diffi- culty picking out the triangle. In other tests, the hemispheres reveal distinct skills, as listed above the drawing.
FIGURE 2.23 The lobes of the cerebral cortex and the primary sensory, motor, and association areas on each. The top diagrams show (in cross section) the relative amounts of cortex “assigned” to the sensory and motor control of various parts of the body. (Each cross section, or “slice,” of the cortex has been turned 90 degrees so you see it as it would appear from the back of the brain.)
FIGURE 2.25 This simplified drawing shows the main structures of the human brain and describes some of their most important features. (You can use the color code in the foreground to identify which areas are part of the forebrain, midbrain, and hindbrain.)