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Chapter 4

Chapter 4 Biology of Behavior

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Steve Joordens

Chapter 4 Biology of Behavior --------The brain and its components Nerve cells of the brain are indeed organized in modules- clusters of nerve cells that communicate with each other ***structure of the nervous system The brain has three major functions: controlling behavior; processing and retaining the information we receive from the environment; regulating the body’s physiological processes Central nervous system is consists of the brain and the spinal cord. Spinal cord: a long, thin collection of nerve cells attached to the base of the brain and running the length of the spinal column (it contains circuits of nerve cells that control some simple reflexes) The central nervous system communicated with the rest of the body through nerves Nerve: a bundle of fibers that transmits information between the central nervous system and the body’s sense organs, muscles, and glands Peripheral nervous system: the cranial and spinal nerves; that part of the nervous system peripheral to the brain and spinal cord Cranial nerve: a bundle of nerve fibers attached to the base of the brain; conveys sensory information from the face and head and carries messages to muscles and glands Spinal nerve: a bundle of nerve fibers attached to the spinal cord; conveys sensory information from the body and carries messages to muscles and glands (Information from the head and neck region reaches the brain through the cranial nerves; sensory information from the rest of the body reaches the spinal cord through the spinal nerves) The human brain has three major parts: the brain stem, the cerebellum, and the cerebral hemispheres Brain stem: the “stem” of the brain, including the medulla, pons, and midbrain Cerebral hemisphere: the largest part of the brain; covered by the cerebral cortex and containing parts of the brain that evolved most recently Cerebellum: a pair of hemispheres resembling the cerebral hemispheres but much smaller and lying beneath and in back of them; controls posture and movements, especially rapid ones Vertebra: one of the bones that encase the spinal cord and constitute the vertebral column Meninges: the three-layered set of membranes that enclose the brain and spinal cord Cerebrospinal fluid (CSF): the liquid in which the brain and spinal cord float; provide a shock-absorbing cushion Blood-brain barrier: a barrier between the blood and the brain produced by the cells in the walls of the brain’s capillaries; prevents some substances from passing from the blood into the brain Cerebral cortex: the outer layer of the cerebral hemispheres of the brain, approximately 3mm thick Grey matter: the portions of the central nervous system that are abundant in cell bodies of neurons rather than axons. The color appears grey relative to white matter White matter: the portions of the central nervous system that are abundant in axons rather than cell bodies of neurons. The color derives from the presence of the axons’ myelin sheaths Gyrus and fissure ***cells of the nervous system Neuron: a verve cell; consists of a cell body with dendrites and an axon whose branches end in terminal buttons that synapse with muscle fibers, gland cells, or other neurons (it contain structures specialized for receiving, processing, and transmitting info) Glial cell: a cell of the central nervous system that provides support for neurons and supplies them with some essential chemicals Dendrite: a tree-like part of a neuron on which other neurons from synapses Dendritic spine: a small bud-like protuberance on the surface of a neuron’s dendrite Soma: a cell body; the largest part of a neuron Axon: a long, thin part of a neuron attached to the soma; divides into a few or many branches, ending in terminal buttons Terminal button: the rounded swelling at the end of the axon of a neuron; releases transmitter substance Neurotransmitter: a chemical released by the terminal buttons that causes the postsynaptic neuron to be excited or inhibited Many axons, especially long ones, are insulated with a substance called myelin. (The principal function of myelin is to insulate axons from one another and thus to prevent the scrambling of messages) Myelin sheath: the insulating material that encases most large axons ***the excitable axon: the action potential Action potential: a brief electrochemical event that is carried by an axon from the soma of the neuron to its terminal buttons; causes the release of a transmitter substance Ion: a positively or negatively charged particle; produced when many substances dissolve in water Ion channel: a special protein molecule located in the membrane of a cell; controls the entry or exit of particular ions Ion transporter: a special protein molecule located in the membrane of a cell; actively transports ions into or out of the cell An action potential is an all-or-none event All-or-none law: the principle that once an action potential is triggered in an axon, it is propagated, without getting smaller, to the end of the axon Sensory neuron: a neuron that detects changes in the external or internal environment and sends information about these changes to the central nervous system Motor neuron: a neuron whose terminal buttons from synapses with muscle fibers. When an action potential travels down its axon, the associated muscle fibers will twitch ***synapses (the junction between the terminal button of one neuron and the membrane of a muscle fiber, a gland, or another neuron) Presynaptic neuron: a neuron whose terminal buttons from synapses with and excites or inhibits another neuron Postsynaptic neuron: a neuron with which the terminal buttons of another neuron form synapses and that is excited or inhibited by that neuron Two types of synapses: excitatory synapses and inhibitory synapses Synaptic cleft: a fluid-filled space between the presynaptic and postsynaptic membranes; the terminal button releases transmitter substance into this space Neurotransmitter receptor: a special protein molecule located in the membrane of the postsynaptic neuron that responds to molecules of the neurotransmitter Reuptake: the process by which a terminal button retrieves the molecules of transmitter substance that it has just released; terminates the effect of the transmitter substance on the receptors of the postsynaptic neuron -----Drugs and Behavior ***Effects of Drugs on Synaptic Transmission Drugs that affect our thoughts, perceptions, emotions and behavior do so by affecting the activity of neurons in the brain. They can stimulate or inhibit the release of neurotransmitters, mimic the effects of neurotransmitters on postsynaptic receptors, block these effects, or interfere with reuptake of a neurotransmitter once it is released *stimulating or inhabiting the release of neurotransmitters *stimulating or blocking postsynaptic receptors *inhibiting reuptake ***neurotransmitters, their actions, and drugs that affect them In the brain, most synaptic communication is accomplished by two neurotransmitters: glutamate, which has excitatory effects, and GABA, which has inhibitory effects *Glutamate: the most important excitatory neurotransmitter in the brain, and in the spinal cord Ex. NMDA receptor, responsible for learning, deactivated by alcohol *GABA Barbiturates: a drug that causes sedation; one of several derivatives of barbituric acid Antianxiety drug: a “tranquilizer”, which reduces anxiety Benzodiazepine: a class of drug having anxiolytic “tranquilizing” effects, such as diazepam (valium) *acetylcholine (Ach): a neurotransmitter found in the brain, spinal cord, and parts of the peripheral nervous system; responsible for muscular contraction Botulinum toxin (prevents) and black widow spider venom (stimulate) could affect the release of acetylcholine Neostigmine: a drug that enhances the effects of acetylcholine by blocking the enzyme that destroys it Nicotine: a drug that binds with and stimulates acetylcholine receptors, mimicking the effects of this neurotransmitter Curare: a drug that binds with and blocks acetylcholine receptors, preventing the neurotransmitter from exerting its effects *monoamines: a category of neurotransmitters that includes dopamine, norepinephrine, and serotonin Monoaminergic neurons thus serve to modulate the function of widespread regions of the brain, increasing or decreasing the activities of particular brain functions Dopamine (DA): A monoamine neurotransmitter involved in control of brain mechanisms of movement and reinforcement Parkinson’s disease: a neurological disorder characterized by tremors, rigidity of the limbs, poor balance, and difficulty in initiating movements; caused by degeneration of a system of dopamine-secreting neurons The best known drugs to prolong and strengthen DA’s effect: amphetamine, cocaine Norepinephrine (NE): a monoamine neurotransmitter involved in alertness and vigilance and control of REM sleep (cause an increase in vigilance) Serotonin: a monoamine neurotransmitter involved in the regulation of mood; in the control of eating, sleep, and arousal; and in the regulation of pain (A deficiency in the release of serotonin is associated with alcoholism and anti-social behavior) The best known drugs to strengthen and prolong its effects are used to treat depression, anxiety disorder… (Prozac, fluoxetine) LSD: stimulates one category of serotonin receptor *peptides: a category of neurotransmitters and neuromodulators that consist of two or more amino acids, linked by peptide bonds Neuromodulator: a substance secreted in the brain that modulates the activity of neurons that contain the appropriate receptors Most neuromodulators are peptides One best known peptide is endogenous opioids: a neuromodulator whose action is mimicked by a natural or synthetic opiate, such as opium, morphine, or heroin (Decreased sensitivity to pain and a tendency to persist in ongoing behavior) Naloxone: (developed to block opioid receptors) a drug that binds with and blocks opioid receptors, preventing opiate drugs or endogenous opioids from exerting their effects *cannabinoids Endogenous cannabinoid: a neuromodulator whose action is mimicked by THC and other drugs present in marijuana Anandamide: the most important endogenous cannabinoid ---------study of the brain ***experimental ablation Brain lesion: damage to a particular region of the brain; a synonym for experimental ablation Stereotaxic apparatus: a device used to insert an electrode into a particular part of the brain for the purpose of recording electrical activity, stimulating the brain electrically, or producing localized damage Electrolytic lesion: passing an electrical current through the electrode, which produces heat that destroys a small portion of the brain around the tip of the electrode Reversible lesion: temporarily suppress action of the region Targeted mutation: a mutated gene (also called a “knockout gene”) produced in the laboratory and inserted into the chromosomes of mice; abolishes the normal effects of the gene ***visualizing the structure of the brain Grows in volume and also modified by experience Neural plasticity: the production of changes in the structure and functions of the nervous system, induced by environmental events Some technique would be helpful in estimating the growth of dendrites and inferring possible changes in the number of synapses; the staining technique used in this study can distinguish the effects on neuronal development of the different mutations CT scanner: a device that uses a special X-ray machine and a computer to produce images of the brain that appear as slices taken parallel to the top of the
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