The Brain, Biology, and Behavior Chapter 3 The Brain, Biology, and Behavior

Neuron and its parts Neuron: Individual nerve cell Dendrites: Receive messages from other neurons Soma: Cell body; body of the neuron Axon: Carries information away from the cell body Axon Terminals: Branches that link the dendrites and soma of other neurons

Figure 3.1  An example of a neuron, or nerve cell, showing several of its important features. The right foreground shows a nerve cell fiber in cross section, and the upper left inset gives a more realistic picture of the shape of neurons. The nerve impulse usually travels from the dendrites and soma to the branching ends of the axon. The neuron shown here is a motor neuron. Motor neurons originate in the brain or spinal cord and send their axons to the muscles or glands of the body.

Figure 3.2  Activity in an axon can be measured by placing electrical probes inside and outside the axonal membrane. (The scale is exaggerated here. Such measurements require ultra-small electrodes, as described later in this chapter.) At rest, the inside of an axon is about minus 60 to 70 millivolts, compared with the outside. Electrochemical changes in a nerve cell generate an action potential. When positively charged sodium ions (Na1) rush into the cell, its interior briefly becomes positive. This is the action potential. After the action potential, an outward flow of positive potassium ions (K1) restores the negative charge inside the axon. (See Figure 3.3 for further explanation.)

Figure 3.3  The inside of an axon normally has a negative electrical charge. The fluid surrounding an axon is normally positive. As an action potential passes along the axon, these charges reverse, so that the interior of the axon briefly becomes positive.

Figure 3. 4 Cross-sectional views of an axon Figure 3.4  Cross-sectional views of an axon. The right end of the top axon is at rest, with a negatively charged interior. An action potential begins when the ion channels open and sodium ions (Na1) enter the axon. In this drawing, the action potential would travel rapidly along the axon, from left to right. In the lower axon, the action potential has moved to the right. After it passes, potassium ions (K1) flow out of the axon. This quickly renews the negative charge inside the axon, so it can fire again. Sodium ions that enter the axon during an action potential are pumped back out more slowly. Their removal restores the original resting potential.

Figure 3. 5 A highly magnified view of the synapse shown in Fig. 3. 1 Figure 3.5  A highly magnified view of the synapse shown in Fig. 3.1. Neurotransmitters are stored in tiny sacs called synaptic vesicles. When a nerve impulse arrives at an axon terminal, the vesicles move to the surface and release neurotransmitters. These transmitter 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. Transmitter molecules vary in their effects: Some excite the next neuron, and some inhibit its activity.

The Neuron and Neuronal Impulse Please choose the button below that corresponds to the type of operating system you are using:

Neurotransmitters Chemicals that alter activity in neurons; brain chemicals. Some examples: Acetylcholine: Activates muscles Dopamine: Muscle control Serotonin: Mood and appetite control Messages from one neuron to another pass over a microscopic gap called a synapse Receptor Site: Areas on the surface of neurons and other cells that are sensitive to neurotransmitters or hormones

Synaptic Transmission Please choose the button below that corresponds to the type of operating system you are using:

Neural Regulators Neural Peptides: Regulate activity of other neurons Enkephalins: Relieve pain and stress

Neural Networks Central Nervous System (CNS): Brain and spinal cord. Peripheral Nervous System: All parts of the nervous system outside of the brain and spinal cord. Somatic System: Links spinal cord with body and sense organs. Controls voluntary behavior Autonomic System: Serves internal organs and glands. Controls automatic functions such as heart rate and blood pressure Sympathetic: Arouses body Parasympathetic: Quiets body

Figure 3.6 (a) Central and peripheral nervous systems. (b) Spinal nerves, cranial nerves, and the autonomic nervous system.

Figure 3.7 Subparts of the nervous system.

Figure 3.8  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 through a chain of ganglia (clusters of cell bodies) outside the spinal cord.

Figure 3. 9 A simple sensory-motor (reflex) arc Figure 3.9  A simple sensory-motor (reflex) arc. A simple reflex 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. Reflexes provide an “automatic” protective device for the body.

Functional MRI: MRI that also records brain activity Researching the Brain Electroencephalograph (EEG): Detects, amplifies and records electrical activity in the brain Computed Tomographic Scanning (CT): Computer-enhanced X-Ray of the brain or body Magnetic Resonance Imaging (MRI): Uses a strong magnetic field, not an X-Ray, to produce an image Functional MRI: MRI that also records brain activity Positron Emission Tomography (PET): Computer-generated color image of brain activity, based on glucose consumption in the brain. Launch Video

Cerebral Cortex Outer layer of the cerebrum Cerebrum: Two large hemispheres that cover upper part of the brain Cerebral Hemispheres: Right and left halves of the cerebrum Corpus Callosum: Bundle of fibers connecting cerebral hemispheres

Figure 3.15  An illustration showing the increased relative size of the human cerebrum and cerebral cortex, a significant factor in human adaptability and intelligence.

Figure 3.17  The corpus callosum is the major “cable system” through which the right and left cerebral hemispheres communicate. A recent study found that the corpus callosum is larger in classically trained musicians than it is in nonmusicians. When a person plays a violin or piano, the two hemispheres must communicate rapidly as they coordinate the movements of both hands. Presumably, the size of the corpus callosum can be altered by early experience, such as musical training.

Central Cortex Lobes Occipital: Back of brain; vision center Parietal: Just above occipital; bodily sensations such as touch, pain, and temperature Temporal: Each side of the brain; auditory and language centers Frontal: Movement, sense of smell, higher mental functions Contains motor cortex; controls motor movement

Figure 3. 19 Basic nerve pathways of vision Figure 3.19  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 directed to one hemisphere or the other by flashing it in the right or left visual field as the person stares straight ahead.

Figure 3.20  If a circle is flashed to the left brain and a split-brain patient is asked to say what she or he saw, the circle is easily named. The person can also pick out the circle by touching shapes with the right hand, out of sight under a tabletop (shown semitransparent in the drawing). However, the left hand will be unable to identify the shape. If a triangle is flashed to the right brain, the person cannot say what was seen (speech is controlled by the left hemisphere). The person will also be unable to identify the correct shape by touch with the right hand. Now, however, the left hand will have no difficulty picking out the hidden triangle. Separate testing of each hemisphere reveals distinct specializations, as listed above. (Figure adapted from an illustration by Edward Kasper in McKean, 1985.)

Figure 3.22  Many of the lobes of the cerebral cortex are defined by larger fissures on the surface of the cerebrum. Others are regarded as separate areas because their functions are quite different.

Figure 3.23  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 that you see it as it would appear from the back of the brain.)

When the brain fails to function properly Aphasia: Speech disturbance resulting from brain damage Broca’s Area: Related to language and speech production. If damaged, person knows what s/he wants to say but can’t say the words Wernicke’s Area: Related to language comprehension. If damaged, person has problems with meanings of words, NOT pronunciation Agnosia: Inability to identify seen objects Facial agnosia: Inability to perceive familiar faces

Figure 3.28 Language is controlled by the left side of the brain in the majority of right- and left-handers.

Figure 3.32  A direct brain-computer link may provide a way of communicating for people who are paralyzed and unable to speak. Activity in the patient’s motor cortex is detected by an implanted electrode. The signal is then amplified and transmitted to a nearby computer. By thinking in certain ways, patients can move an on-screen cursor. This allows them to spell out words or select from a list of messages, such as “I am thirsty.”

Subcortex Hindbrain (brainstem) Medulla: Connects brain with the spinal cord and controls vital life functions such as heart rate and breathing Pons (Bridge): Acts as a bridge between brainstem and other structures. Influences sleep and arousal Cerebellum: Located at base of brain. Regulates posture, muscle tone and muscular coordination

Subcortex: Reticular Formation (RF) Reticular Formation (RF): Inside medulla. Associated with alertness, attention and some reflexes Reticular Activating System (RAS): Part of RF that keeps it active and alert. Its alarm clock Activates and arouses cerebral cortex

Forebrain Structures are part of Limbic System: System within forebrain closely linked to emotional response Thalamus: Relays sensory information on the way to the cortex; switchboard Hypothalamus: Regulates emotional behaviors and motives e.g. sex, hunger, rage, hormone release Amygdala: Associated with fear responses Hippocampus: Associated with storing memories

Figure 3.26  Parts of the limbic system are shown in this highly simplified drawing. Although only one side is shown, the hippocampus and the amygdala extend out into the temporal lobes at each side of the brain. The limbic system is a sort of “primitive core” of the brain strongly associated with emotion.

Figure 3.25  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.)

Endocrine System Glands that pour chemicals (hormones) directly into the bloodstream or lymph system Pituitary Gland: Regulates growth via growth hormone Too little means person will be smaller than average Too much leads to giantism: Excessive body growth Acromegaly: Enlargement of arms, hands, feet and facial bones. Too much growth hormone released late in growth period Andre the Giant

Endocrine System Continued Pineal Gland: Regulates body rhythms and sleep cycles. Releases hormone melatonin, which responds to variations in light Thyroid: In neck; regulates metabolism Hyperthyroidism: Overactive thyroid; person tends to be thin, tense, excitable, nervous Hypothyroidism; Underactive thyroid; person tends to be inactive, sleepy, slow, obese Adrenals: Arouse body, regulate salt balance, adjust body to stress, regulate sexual functioning

Figure 3.27 Locations of the endocrine glands in the male and female.

Neurogenesis and Plasticity Plasticity: Brain’s capacity to change its structure and functions Neurogenesis: Production of new brain cells

Figure 3.31  Neuroscientists are searching for ways to repair damage caused by strokes and other brain injuries. One promising technique involves growing neurons in the laboratory and injecting them into the brain. These immature cells are placed near damaged areas, where they can link up with healthy neurons. The technique has proved successful in animals and is now under study in humans.