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Published on October 12, 2007

Author: GenX

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The Nervous System:  The Nervous System Chapter 45 Neuron Organization:  Neuron Organization Sensory neurons carry impulses from sensory receptors to the central nervous system (CNS). Motor neurons carry impulses from the CNS to effectors. Interneurons help provide more complex reflexes and higher associative learning. Sensory and motor neurons constitute the peripheral nervous system (PNS). Neuron Organization:  Neuron Organization Somatic motor neurons stimulate skeletal muscles’ contraction. Autonomic motor neurons regulate activity of smooth muscles, cardiac muscles, and glands. sympathetic parasympathetic Neuron Organization:  Neuron Organization Cell surface integrates the information that arrives at its dendrites. triggers impulses that are conducted away from the cell body along an axon Neurons are supported structurally and functionally by supporting cells (neuroglia). Schwann cells oligodendrocytes produce myelin sheath interrupted by nodes of Ranvier Resting Membrane Potential:  Resting Membrane Potential Potential difference exists across every cell’s plasma membrane. cytoplasm side is negative pole, and extracellular fluid side is positive pole Inside of cell negatively charged because: large, negatively charged molecules are more abundant inside the cell sodium potassium pump voltage-gated ion channels Resting Membrane Potential:  Resting Membrane Potential When a neuron is not being stimulated, it maintains a resting membrane potential. cations outside the cell are attracted to anions inside the cell Resting plasma membrane is more permeable to K+ than other cations, so K+ enters the cell but the sodium-potassium pump is driving K+ out of the cell. equilibrium potential Sodium-Potassium Pump:  Sodium-Potassium Pump Resting Membrane Potential:  Resting Membrane Potential When a nerve or muscle cell is stimulated, sodium channels become more permeable, and Na+ rushes into the cell. sudden influx of positive charges causes the cell to depolarize K+ flows out of cell and the inside of the cell again hyperpolarizes Action Potentials:  Action Potentials Graded potentials are caused by the activation of gated ion channels. closed in normal resting cells chemical- or ligand-gated channels Summation is the ability of graded potentials to combine. Action Potentials:  Action Potentials Generation of action potentials Once a particular level of depolarization is reached, a nerve impulse (action potential) is produced. threshold A depolarization that reaches or exceeds the threshold opens both the Na+ and K+ voltage-gated ion channels. Slide11:  Voltage gated channels Action Potentials:  Action Potentials Propagation of action potentials events are reproduced at different points along the axon membrane positive charges can depolarize the next region of the membrane to threshold Action Potentials:  Action Potentials Saltatory conduction one node of Ranvier depolarizes the next, so that action potentials can skip between nodes saltatory conductions in myelinated axon more rapid than conduction in an unmyelinated axon Structure of Synapses:  Structure of Synapses Synapses are intercellular junctions. The neuron transmitting an action potential to the synapse is the presynaptic cell, while the receiving cell on the other side of the synapse is the postsynaptic cell. synaptic cleft - narrow space separating two cells Structure of Synapses:  Structure of Synapses End of presynaptic axon contains synaptic vesicles, each packed with neurotransmitters. diffuse rapidly to the other side of the cleft, and bind to receptor proteins in the membrane of postsynaptic cell Neurotransmitters and Their Functions:  Neurotransmitters and Their Functions Acetylcholine binds to its receptor proteins in the postsynaptic membrane and thereby causes ion channels within the proteins to open produces an excitatory postsynaptic potential (EPSP) acetycholine eliminated from the synaptic cleft by acetylcholinesterase Neurotransmitters and Their Functions:  Neurotransmitters and Their Functions Glutamate, glycine, and GABA Glutamate is the major excitatory neurotransmitter in the vertebrate CNS. Glycine and GABA are inhibitory neurotransmitters. produces inhibitory postsynaptic potential (IPSP) Fig. 45.18(TE Art):  Fig. 45.18(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Axon Neurotransmitters and Their Functions:  Neurotransmitters and Their Functions Biogenic amines dopamine norepinephrine serotonin Other neurotransmitters neuropeptides substance P - activated by painful stimuli intensity of pain perception depends on enkephalins and endorphins nitric oxide Neurotransmitters and Their Functions:  Neurotransmitters and Their Functions Synaptic integration Small EPSPs add together to bring the membrane potential closer to threshold, while IPSPs subtract from the depolarizing effect, keeping the membrane potential below the threshold. Neurotransmitters and Their Functions:  Neurotransmitters and Their Functions Neurotransmitters and drug addiction If receptor proteins within synapses are exposed to high levels of neurotransmitter molecules for prolonged periods, that nerve cell often responds by inserting fewer receptor proteins into the membrane. may lose ability to respond to stimulus - habituation cocaine nicotine Drug Addiction:  Drug Addiction Fig. 45.21(TE Art):  Fig. 45.21(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cnidarian Earthworm Arthropod Flatworm Echinoderm Human Mollusk Nerve net Nerve cords Central nervous system Peripheral nerves Associative neurons Brain Ventral nerve cords Cerebrum Cerebellum Spinal cord Cervical nerves Thoracic nerves Lumbar nerves Femoral nerve Sciatic nerve Tibial nerve Radial nerve Nerve ribs Brain Giant axon Evolution of the Vertebrate Brain:  Evolution of the Vertebrate Brain All of the subsequent evolutionary changes in nervous systems can be viewed as a series of elaborations on the characteristics already present in flatworms. hindbrain was the principal component of the brain of early vertebrates devoted to control of motor activity Basic Vertebrate Brain:  Basic Vertebrate Brain Evolution of the Vertebrate Brain:  Evolution of the Vertebrate Brain Dominant forebrain Forebrain in reptiles, amphibians, birds, and mammals is composed of two elements: thalamus - integration and relay center between incoming sensory information and the cerebrum hypothalamus - participates in basic drives and emotions Evolution of the Vertebrate Brain:  Evolution of the Vertebrate Brain Telencephalon (endbrain) is located at the front of the forebrain. called cerebrum in mammals mammals have brains particularly large relative to their body mass largely reflects enlargement of cerebrum center for correlation, association, and learning in mammals Fig. 45.23(TE Art):  Fig. 45.23(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Shark Frog Cat Bird Human Spinal cord Medulla oblongata Optic tectum Cerebellum Midbrain Cerebrum Olfactory tract Crocodile Fig. 45.24(TE Art):  Fig. 45.24(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Corpus callosum Parietal lobe of cerebral cortex Pineal gland Occipital lobe of cerebral cortex Cerebellum Medulla oblongata Pons Hypothalamus Pituitary gland Thalamus Frontal lobe of cerebral cortex Lateral ventricle Optic chiasm Optic recess Temporal lobe of cerebral cortex Human Forebrain:  Human Forebrain Cerebral cortex much of neural activity of the cerebrum occurs within the cerebral cortex contains 10% of all neurons in the brain activities fall into three categories: motor, sensory, and associative portion not occupied by motor and sensory the association cortex, and is the site of higher mental activities Cerebrum:  Cerebrum Fig. 45.26(TE Art):  Fig. 45.26(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tongue Pharynx Jaw Tongue Lips Face Eye Brow Neck Thumb Fingers Hand Wrist Elbow Arm Shoulder Trunk Hip Knee Toes Leg, genitals Hip Trunk Arm Elbow Forearm Hand Fingers Forefinger Eye Nose Face Lips Jaw Teeth Gums Motor Sensory Human Forebrain:  Human Forebrain Basal ganglia aggregates of neuron cell bodies receive sensory information from ascending tracts and motor commands from the cerebral cortex and cerebellum Thalamus primary site of sensory integration Hypothalamus integrates visceral activities Language and Other Functions:  Language and Other Functions Arousal and sleep one section of reticular formation (diffuse collection of neurons) controls consciousness and alertness reticular activating system controls both sleep and waking state sleep not a loss of consciousness Language and Other Functions:  Language and Other Functions Language and spatial recognition left hemisphere dominant hemisphere for language sequential reasoning right hemisphere usually adept at spatial reasoning musical ability Memory and learning fundamental differences between short (stored electrically) and long-term (structural changes in neural connection) memory LTP Alzheimers disease Brain Regions and Language Activities:  Brain Regions and Language Activities The Spinal Cord:  The Spinal Cord Spinal cord is a cable of neurons extending from the brain down through the backbone. protected by vertebral column and layers of membranes (meninges) relays messages, and functions in reflexes knee-jerk reflex is monosynaptic very fast Knee-Jerk Reflex:  Knee-Jerk Reflex Components of the Peripheral Nervous System:  Components of the Peripheral Nervous System Axons of sensory neurons enter the dorsal surface of the spinal cord and form the dorsal root of the spinal nerve. Motor axons leave from the ventral surface and form the ventral root of the spinal nerve. Cell bodies of sensory neurons are grouped together outside each level of the spinal cord in dorsal root ganglia. Fig. 45.30(TE Art):  Fig. 45.30(TE Art) Effector (muscle) Spinal cord Dorsal Ventral Interneuron Cell body in dorsal root ganglion Gray matter White matter Motor neuron Sensory neuron Receptor in skin Stimulus Fig. 45.31:  Fig. 45.31 Bullfrog Nerve in PNS Autonomic Nervous System:  Autonomic Nervous System Autonomic nervous system is composed of the sympathetic and parasympathetic divisions and the medulla oblongata of the hindbrain, which coordinates the system. Autonomic Nervous System:  Autonomic Nervous System Sympathetic division of the autonomic system, together with the adrenal medulla, activates the body for fight or flight responses. produced by norepinephrine Parasympathetic division generally has antagonistic effects. produced by ACh Fig. 45.32(TE Art):  Fig. 45.32(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Viscera Autonomic ganglion Postganglionic neuron Autonomic motor reflex Interneuron Dorsal root ganglion Preganglionic neuron Sensory neuron Spinal cord Fig. 45.34(TE Art):  Fig. 45.34(TE Art) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hypothalamus activates sympathetic division of nervous system Heart rate, blood pressure, and respiration increase Blood flow to skeletal muscles increases Stomach contractions are inhibited Adrenal medulla secretes epinephrine and norepinephrine G Proteins :  G Proteins Indirectly produce many parasympathetic effects of ACh regulated by guanosine diphosphate and triphosphate

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