Term
| What are neurons, and how do they transmit information? |
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Definition
| Neurons are the elementary components of the nervous system, the body’s speedy electrochemical information system. Sensory neurons carry incoming information from sense receptors to the brain and spinal cord, and motor neurons carry information from the brain and spinal cord out to the muscles and glands. Interneurons communicate within the brain and spinal cord and between sensory and motor neurons. A neuron sends signals through its axons, and receives signals through its branching dendrites. If the combined signals are strong enough, the neuron fires, transmitting an electrical impulse (the action potential) down its axon by means of a chemistry-to-electricity process. The neuron’s reaction is an all-or-none process. |
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Term
| How do nerve cells communicate with other nerve cells? |
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Definition
| When action potentials reach the end of an axon (the axon terminals), they stimulate the release of neurotransmitters. These chemical messengers carry a message from the sending neuron across a synapse to receptor sites on a receiving neuron. The sending neuron, in a process called reuptake, then normally absorbs the excess neurotransmitter molecules in the synaptic gap. The receiving neuron, if the signals from that neuron and others are strong enough, generates its own action potential and relays the message to other cells. |
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Term
| How do neurotransmitters influence behavior, and how do drugs and other chemicals affect neurotransmission? |
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Definition
| Each neurotransmitter travels a designated path in the brain and has a particular effect on behavior and emotions. Acetylcholine affects muscle action, learning, and memory. Endorphins are natural opiates released in response to pain and exercise. Drugs and other chemicals affect communication at the synapse. Agonists excite by mimicking particular neurotransmitters or by blocking their reuptake. Antagonists inhibit a particular neurotransmitter’s release or block its effect. |
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Term
| What are the functions of the nervous system’s main divisions? |
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Definition
| One major division of the nervous system is the central nervous system (CNS), the brain and spinal cord. The other is the peripheral nervous system (PNS), which connects the CNS to the rest of the body by means of nerves. The peripheral nervous system has two main divisions. The somatic nervous system enables voluntary control of the skeletal muscles. The autonomic nervous system, through its sympathetic and parasympathetic divisions, controls involuntary muscles and glands. Neurons cluster into working networks. |
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Term
| How does the endocrine system—the body’s slower information system—transmit its messages? |
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Definition
| The endocrine system is a set of glands that secrete hormones into the bloodstream, where they travel through the body and affect other tissues, including the brain. The endocrine system’s master gland, the pituitary, influences hormone release by other glands. In an intricate feedback system, the brain’s hypothalamus influences the pituitary gland, which influences other glands, which release hormones, which in turn influence the brain. |
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Term
| How do neuroscientists study the brain’s connections to behavior and mind? |
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Definition
| Clinical observations and lesioning reveal the general effects of brain damage. MRI scans now reveal brain structures, and EEG, PET, and fMRI (functional MRI) recordings reveal brain activity. |
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Term
| What are the functions of important lower-level brain structures? |
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Definition
The brainstem is the oldest part of the brain and is responsible for automatic survival functions. Its components are the medulla (which controls heartbeat and breathing), the pons (which helps coordinate movements), and the reticular formation (which affects arousal). The thalamus, the brain’s sensory switchboard, sits above the brainstem. The cerebellum, attached to the rear of the brainstem, coordinates muscle movement and helps process sensory information.
The limbic system is linked to emotions, memory, and drives. Its neural centers include the amygdala (involved in responses of aggression and fear) and the hypothalamus (involved in various bodily maintenance functions, pleasurable rewards, and the control of the hormonal system). The pituitary (the “master gland”) controls the hypothalamus by stimulating it to trigger the release of hormones. The hippocampus processes memory. |
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Term
| What functions are served by the various cerebral cortex regions? |
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Definition
| In each hemisphere the cerebral cortex has four lobes, the frontal, parietal, occipital, and temporal. Each lobe performs many functions and interacts with other areas of the cortex. The motor cortex controls voluntary movements. The sensory cortex registers and processes body sensations. Body parts requiring precise control (in the motor cortex) or those that are especially sensitive (in the sensory cortex) occupy the greatest amount of space. Most of the brain’s cortex—the major portion of each of the four lobes—is devoted to uncommitted association areas, which integrate information involved in learning, remembering, thinking, and other higher-level functions. |
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Term
| To what extent can a damaged brain reorganize itself? |
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Definition
| If one hemisphere is damaged early in life, the other will pick up many of its functions. This plasticity diminishes later in life. Some brain areas are capable of neurogenesis (forming new neurons). |
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Term
| What do split brains reveal about the functions of our two brain hemispheres? |
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Definition
| Split-brain research (experiments on people with a severed corpus callosum) has confirmed that in most people, the left hemisphere is the more verbal, and that the right hemisphere excels in visual perception and the recognition of emotion. Studies of healthy people with intact brains confirm that each hemisphere makes unique contributions to the integrated functioning of the brain. |
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Term
| How does handedness relate to brain organization? |
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Definition
| About 10 percent of us are left-handed. Almost all right-handers process speech in the left hemisphere, as do more than half of all left-handers. |
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Term
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Definition
| a branch of psychology concerned with the links between biology and behavior. (Some biological psychologists call themselves behavioral neuroscientists, neuropsychologists, behavior geneticists, physiological psychologists, or biopsychologists.) |
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Term
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Definition
| a nerve cell; the basic building block of the nervous system. |
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Term
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Definition
| neurons that carry incoming information from the sensory receptors to the brain and spinal cord. |
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Term
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Definition
| neurons that carry outgoing information from the brain and spinal cord to the muscles and glands. |
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Term
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Definition
| neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs |
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Term
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Definition
| the bushy, branching extensions of a neuron that receive messages and conduct impulses toward the cell body |
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Term
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Definition
| the extension of a neuron, ending in branching terminal fibers, through which messages pass to other neurons or to muscles or glands |
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Term
| myelin [MY-uh-lin] sheath |
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Definition
| a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next. |
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Term
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Definition
| a neural impulse; a brief electrical charge that travels down an axon |
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Term
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Definition
| the level of stimulation required to trigger a neural impulse. |
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Term
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Definition
| the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or synaptic cleft. |
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Term
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Definition
| chemical messengers that cross the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse. |
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Term
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Definition
| a neurotransmitter’s reabsorption by the sending neuron |
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Term
| endorphins: [en-DOR-fins] |
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Definition
| “morphine within”—natural, opiatelike neurotransmitters linked to pain control and to pleasure. |
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Term
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Definition
| the body’s speedy, electrochemical communication network, consisting of all the nerve cells of the peripheral and central nervous systems. |
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Term
| central nervous system (CNS) |
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Definition
| the brain and spinal cord. |
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Term
| peripheral nervous system (PNS) |
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Definition
| the sensory and motor neurons that connect the central nervous system (CNS) to the rest of the body. |
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Term
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Definition
| bundled axons that form neural “cables” connecting the central nervous system with muscles, glands, and sense organs. |
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Term
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Definition
| the division of the peripheral nervous system that controls the body’s skeletal muscles. Also called the skeletal nervous system. |
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Term
| autonomic [aw-tuh-NAHM-ik] nervous system |
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Definition
| the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasympathetic division calms. |
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Term
| sympathetic nervous system |
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Definition
| the division of the autonomic nervous system that arouses the body, mobilizing its energy in stressful situations. |
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Term
| parasympathetic nervous system |
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Definition
| the division of the autonomic nervous system that calms the body, conserving its energy. |
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Term
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Definition
| a simple, automatic response to a sensory stimulus, such as the knee-jerk response. |
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Term
| endocrine [EN-duh-krin] system |
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Definition
| “slow” chemical communication system; a set of glands that secrete hormones into the bloodstream. |
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Term
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Definition
| chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues. |
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Term
| adrenal[ah-DREEN-el] glands |
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Definition
| a pair of endocrine glands that sit just above the kidneys and secrete hormones (epinephrine and nor-epinephrine) that help arouse the body in times of stress. |
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Term
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Definition
| the endocrine system’s most influential gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands. |
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Term
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Definition
| tissue destruction. A brain lesion is a naturally or experimentally caused destruction of brain tissue. |
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Term
| electroencephalogram (EEG) |
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Definition
| an amplified recording of the waves of electrical activity that sweep across the brain’s surface. These waves are measured by electrodes placed on the scalp. |
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Term
| PET (positron emission tomography) scan |
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Definition
| a visual display of brain activity that detects where a radioactive form of glucose goes while the brain performs a given task. |
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Term
| MRI (magnetic resonance imaging) |
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Definition
| a technique that uses magnetic fields and radio waves to produce computer-generated images of soft tissue. MRI scans show brain anatomy. |
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Term
| fMRI (functional magnetic resonance imaging): |
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Definition
| a technique for revealing bloodflow and, therefore, brain activity by comparing successive MRI scans. fMRI scans show brain function. |
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Term
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Definition
| the oldest part and central core of the brain, beginning where the spinal cord swells as it enters the skull; the brainstem is responsible for automatic survival functions. |
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Term
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Definition
| the base of the brainstem; controls heart-beat and breathing |
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Term
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Definition
| a nerve network in the brainstem that plays an important role in controlling arousal. |
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Term
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Definition
| the brain’s sensory switchboard, located on top of the brainstem; it directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla. |
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Term
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Definition
| the “little brain” at the rear of the brainstem; functions include processing sensory input and coordinating movement output and balance. |
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Term
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Definition
| neural system (including the hippocampus, amygdala, and hypothalamus) located below the cerebral hemispheres; associated with emotions and drives. |
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Term
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Definition
| two lima bean–sized neural clusters in the limbic system; linked to emotion |
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Term
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Definition
| a neural structure lying below (hypo) the thalamus; it directs several maintenance activities (eating, drinking, body temperature), helps govern the endocrine system via the pituitary gland, and is linked to emotion and reward. |
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Term
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Definition
| the intricate fabric of interconnected neural cells covering the cerebral hemispheres; the body’s ultimate control and information-processing center. |
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Term
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Definition
| cells in the nervous system that support, nourish, and protect neurons |
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Term
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Definition
| portion of the cerebral cortex lying just behind the forehead; involved in speaking and muscle movements and in making plans and judgments. |
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Term
| parietal: [puh-RYE-uh-tuhl] lobes |
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Definition
| portion of the cerebral cortex lying at the top of the head and toward the rear; receives sensory input for touch and body position. |
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Term
| occipital: [ahk-SIP-uh-tuhl] lobes |
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Definition
| portion of the cerebral cortex lying at the back of the head; includes areas that receive information from the visual fields. |
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Term
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Definition
| portion of the cerebral cortex lying roughly above the ears; includes the auditory areas, each receiving information primarily from the opposite ear. |
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Term
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Definition
| an area at the rear of the frontal lobes that controls voluntary movements |
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Term
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Definition
| area at the front of the parietal lobes that registers and processes body touch and movement sensations |
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Term
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Definition
| areas of the cerebral cortex that are not involved in primary motor or sensory functions; rather, they are involved in higher mental functions such as learning, remembering, thinking, and speaking. |
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Term
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Definition
| the brain’s ability to change, especially during childhood, by reorganizing after damage or by building new pathways based on experience |
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Term
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Definition
| the formation of new neurons |
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Term
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Definition
| the large band of neural fibers connecting the two brain hemispheres and carrying messages between them. |
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Term
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Definition
| a condition resulting from surgery that isolates the brain’s two hemispheres by cutting the fibers (mainly those of the corpus callosum) connecting them |
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