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The Nervous System
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  1. The Nervous System By Lydia Chang, Lauren Lee, and Diana Zheng

  2. Evolution of the Nervous System • Porifera: no nervous system • Cnidaria: nerve net all throughout body—can react to stimuli from all sides • Platyhelminthes: cephalization; ganglia, eyespots, two main ventral nerve cords • Rhynchocoela: dorsal nerve cord, two lateral nerve cords • Nematoda: ring of nervous tissue around pharynx attached to dorsal and ventral nerve cords • Annelida: pair of brain-like cerebral ganglia and subpharyngeal ganglion • Mollusca: ranges from simple nervous system to relatively complex systems that rival those of mammals • Arthropoda: cerebral ganglion (brain!); sense organs concentrated on head • Echinodermata: decentralized nervous; no brain but have ganglia along radial nerves in some species; sensory neurons within podia

  3. Evolution of the Nervous System • Vertebrates: very centralized and cephalized; well-developed sensory organs; dorsal, hollow nerve cord (spinal cord) • Lampreys and hagfishes: no myelin sheath • Fish: enlarged cerebellum • Amphibians: growing importance of forebrain, but midbrain still important • Reptiles/Birds: many connections between thalamus and hemispheres • Birds: larger cerebellum • Mammals: brain completely dominated by cerebral hemispheres; large surface area; controlled mainly by cortex; large thalamus

  4. The Human Nervous System • Brain: about 2% human body mass • Neocortex: outer layer of brain • Human cerebral cortex (aka pallium): flat sheets of cells in six layers • Frontal lobe: reasoning, speech, motor cortex • Parietal lobe: speech, taste, reading, somatosensory cortex • Temporal lobe: hearing, smell, auditory • Occipital lobe: sight • Cerebellum: ballistic movements, balance, coordination, helps in learning and remembering motor skills

  5. From “Vertebrate Nervous System”

  6. The Brain, cont’d • Diencephalon: major integrating centers information, act as relay stations for info flow • Thalamus: main relay center for sensory information • Hypothalamus: maintains homeostasis • Brain stem: includes the pons, medulla oblongata • transfers info between peripheral and central nervous systems • helps coordinate large-scale body movements (e.g. running) • nerve crossing: right side of brain controls left side of body and vice versa • Midbrain/RAS (reticular activating system): centers for receiving and integrating several types of sensory info • Corpus callosum: connects brain hemispheres

  7. From Wikipedia

  8. Evolutionary Trends • More complex! • This system is necessary for complexity and sophisticated behaviors/responses to environment • Increases chance of survival: more complex NS = more complicated nerve connections, behaviors, movements • The nervous system controls all other body systems!! Except maybe skeletal

  9. Neurons • Neurons • Sensory neurons • Interneurons • Motor neurons

  10. How Neurons work • Resting potential: negative relative to the outside • Sodium-potassium pumps in the plasma membrane • Transport sodium out of the cell and potassium into it • Very few sodium channels • Net negative charge inside cell

  11. Action Potential • Depolarization • Rising phase of the action potential • Falling phase of the action potential • Undershoot: Potassium channels close to bring it back to the concentration needed to be at resting potential • refractory period

  12. Conduction of the Action Potential • Action potential: a “wave” from dendrite to axon • Speed is determined by axon diameter • Evolutionary trend: Because vertebrate axons have narrow diameters, vertebrates have adapted the myelin sheath to enable more efficient conduction • Nodes of Ranvier (nodes between gaps in myelin sheath) allows for saltatory conduction • current jumps from node to node

  13. Synapses • Electrical synapses: contain gap junctions to allow electrical currents to flow from one neuron to another • Chemical synapses (most synapses): neurotransmitter • Examples of neurotransmitters: acetylcholine, biogenic amines (serotonin)

  14. Disorders and Diseases • Cerebrovascular accident (stroke) • Parkinson's disease: • decreased stimulation of the motor cortex by the basal ganglia caused by the insufficient formation and action of dopamine • Multiple sclerosis: immune system damages the myelin • When myelin is lost, the axons can no longer effectively conduct signals

  15. Works Cited and Consulted • AP Bio book • http://faculty.washington.edu/chudler/nsdivide.html • http://parasitology.informatik.uni-wuerzburg.de/login/n/h/0941.html • http://www.daviddarling.info/encyclopedia/V/vertebrate_nervous_system.html • http://infusion.allconet.org/webquest/PhylumMollusca.html • http://www.mindcreators.com/Images/NB_Neuron.gif  • http://en.wikipedia.org/wiki/File:Neurons_big1.jpg