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The Nervous System Three functions of the nervous system Sensory Input Receipt of information (sensory receptors) & movement of information to integration center Integration Interpretation of input Motor Output Conduction of signals from integration center to effector cells (muscles or glands, i. e.) Two divisions of the nervous system Central Nervous System (CNS) Brain & Spinal Cord Peripheral Nervous System (PNS) Nerves that conduct impulses from the CNS and the rest of the body Nerves—Ropelike bundles of extensions of neurons wrapped in connective tissue Functional Unit of the Nervous System—The NEURON Cell body—contains nucleus & organelles Dendrites—short, highly branched processes (extensions) that receive incoming messages from other cells Axons—usually much longer than dendrites, convey outgoing messages from neurons to other cells Also important in signal conduction. . . Synapse—the site of contact between an axon and a target cell Neurotransmitter—chemical messengers that relay messages across the synapse The simplest nerve circuit—the reflex arc The Nature of Nerve Signals Galvani (18th century)—discovered that frog muscle cells produce electricity Helmholtz (19th century)—found electrical activity of nerve cells carries signals from one end of a cell to the other end and from cell to cell The Nature of Nerve Signals All nerve signals are changes in the voltage across the plasma membrane of cells Voltage changes are caused by movement of ions across the plasma membrane via specialized ion channels The membrane potential of cells Cations ++ --Anions Cations ++ Anions --Anions ----Anions Cations ++ Anions ----Anions Negative charge inside Anions --cell is greater than Anions ----Anions positive charge outside --Anions cell. Membrane is polarized. Cations ++ Cations ++ Cations ++ Cations ++ Resting potential The membrane potential of an unstimulated neuron It is about –70 mV The inside of the cell is more negative than the outside The basis of membrane potential The Ability to Conduct an Impulse Excitable Cells—Neurons & muscle cells that can generate large changes in membrane potential Resting potential—the voltage of an excitable cell in unexcited state Gated ion channels—allow ions to pass only under certain conditions Chemically-gated ion channels Voltage-gated ion channels The Ability to Conduct an Impulse Hyperpolarization—Increase in voltage across a membrane Depolarization—Reduction in the voltage across a membrane Threshold potential—A particular voltage that triggers a particular response Action potential—The response triggered by the threshold potential. The nerve impulse Generating Action Potential Figure 48.9 A Nerve Impulse The Resting Potential The Action Potential Propogation of the Action Potential Communication between cells Types of synapses Excitatory synapses—neurotransmitter causes Na+ to enter and K+ to exit, which depolarizes the cell. If enough “excitation” occurs action potential is the result. Inhibitory synapses—causes membrane to be more permeable to K+ and Cl-, hyperpolarizing the cell. If enough “inhibition” occurs, it is more difficult for an action potential to occur. Neurotransmitters Acetylcholine—usually stimulates muscle cells Dopamine & serotonin—affect sleep, mood, attention, and learning—LSD binds to serotonin receptors in brain Endorphins—decrease perception of pain by CNS. Opium binds to endorphin receptors Vertebrate Nervous Systems Major Components Brain—provides integrative power for complex behavior Spinal Cord—Integrates simple responses (such as knee jerk) and conveys information to & from brain Peripheral Nervous System (PNS)— transmits info to & from CNS & regulates internal environment Divisions of the Peripheral Nervous System The Autonomic Nervous System The human brain The Brainstem Medulla oblongata—controls breathing, heart & vessel activity, swallowing, vomiting, & digestion. Axons carrying instructions about movement cross in medulla. Left side of brain controls movement of the right side of body. Pons—Regulate breathing centers in medulla Midbrain—Contains centers for receipt & integration of sensory information. Sleep & Arousal Reticular Formation—neurons that regulates sleep & arousal It filters or selects which information reaches the cerebrum The more information we receive, the more alert we are Parts of pons & medulla contain nuclei that cause sleep when stimulated Milk contains a lot of trytophan, the amino acid from which serotonin is synthesized Cerebellum Functions in coordination and errorchecking during motor, perceptual and cognitive performances Controls movement & balance such as hand-eye coordination Thalamus & Hypothalamus Major integrating centers Thalamus—main input center for sensory information going to the cerebrum & main output center for motor information leaving cerebrum Hypothalamus—source of posterior pituitary hormoness & releasing hormones for anterior pituitary; contains the body’s thermostat; regulates hunger, thirst & survival mechanisms The real “biological clock” Circadian rhythms—daily patterns Biological clock—the internal component of circadian rhythms Suprachiasmatic nuclei (SCN) in hypothalamus serves as human biological clock Responds to light/dark The Cerebrum Divided into right & left cerebral hemispheres The largest & most complex part of the mammalian brain Left hemisphere receives info from and controls movement of the right side of the body and vice versa Corpus callosum—communicates between left & right cerebral hemispheres Regions of the cerebrum Motor & Somatosensory Areas Lateralization of Brain Function Left hemisphere becomes adept at language, math, logic operations, and processing serial sequences. Right hemisphere is stronger at pattern recognition, face recognition, spatial relations, nonverbal ideation, and emotional processing The Limbic System Form a ring around the brainstem Generates feelings and emotions Mediates behaviors such as laughing & crying