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Chapter 4

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University of Toronto Scarborough
Steve Joordens

Chapter 4 Biology of Behaviour Brain has 3 major functions: 1. Controlling behaviour 2. Processing and retaining information 3. Regulating the bodys physiological processes Structure of the Nervous System Central nervous system: 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. Nerve: A bundle of fibres 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 fibres 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 fibres attached to the spinal cord; conveys sensory information from the body and carries messages to muscles and glands. 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; provides 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 3 mm thick. Grey matter: The portions of the central nervous system that are abundant in cell bodies of neurons rather than axons. The colour 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 colour derives from the presence of the axons myelin sheaths. Gyri: bulges on the brain extend SA of brain Fissures: Large grooves on the brain Cells of the Nervous System Neuron: A nerve cell; consists of a cell body with dendrites and an axon whose branches end in terminal buttons that synapse with muscle fibres, gland cells, or other neurons. Specialize in receiving, processing and transmitting info. glial (glue) 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 form synapses. dendritic spine: A small bud-like protuberance on the surface of a neurons 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. Large Axons are insulated by myelin 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. Myelin sheath: The insulating material that encases most large axons. The excitable Axon: The Active 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. 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 form synapses with muscle fibres. When an action potential travels down its axon, the associated muscle fibres will twitch. Synapses Synapse: The junction between the terminal button of one neuron and the membrane of a muscle fibre, a gland, or another neuron. 2 steps Excitatory (when the axon fires, the terminal button release a transmitter substance that excites the post synaptic neurons with which they form synapses.) and inhibitory (more active, they lower the likelihood that axons of the postsynaptic neurons will fire). presynaptic neuron: A neuron whose terminal buttons form synapses with and excite or inhibit 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. 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 Behaviour Effects of Drugs on Synaptic Transmission: 1. Stimulating or Inhibiting the Release of Neurotransmitters - Some drugs stimulate certain terminal buttons to release their neurotransmitter continuously, even when the axon is not firing. Other drugs prevent certain terminal buttons from releasing their neurotransmitter when the axon fires. 2. Stimulating or Blocking Postsynaptic Receptors - Neurotransmitters produce their effects by stimulating postsynaptic receptors; this excites or inhibits postsynaptic neurons by opening ion channels and permitting ions to enter or leave the neurons. Some drugs mimic the effects of particular neurotransmitters by directly stimulating particular kinds of receptors. 3. Inhibiting Reuptake Molecules of the neurotransmitter are released by a terminal button, stimulate the receptors in the ostsynaptic membrane for a fraction of a second, and are then taken back into the terminal button. Some drugs inhibit the process of reuptake so that molecules of the neurotransmitter continue to stimulate the postsynaptic receptors for a long timeNeurotransmitters, Their Actions, and Drugs That Affect Them: 1. Glutamate The most important excitatory neurotransmitter in the brain and spinal cord. 2. GABA The most important inhibitory neurotransmitter in the brain, causes relaxations, sedation and even loss of consciousness. Barbiturate: 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). 3. Acetylcholine (Ach) - A neurotransmitter found in the brain, spinal cord, and parts of the peripheral nervous system; responsible for muscular contraction. botulinum toxin: A drug that prevents the release of acetylcholine by terminal buttons. Black widow spider venom: A drug that stimulates the release of acetylcholine by terminal buttons. 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. 4. Monoamine: A category of neurotransmitters that includes dopamine, norepinephrine, and serotonin. Dopamine (DA): A monoamine neurotransmitter involved in control of brain mechanisms of movement and reinforcement. Parkinson s disease: A neurological disorder characterized by trem
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