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The Nervous System Chapter 11 Functions of the Nervous system I Sensory (input): Light Sound Touch Temperature Taste External Chemical Smell Internal Chemical Pressure Stretch Functions of the Nervous system II Integration: Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope). Motor (output): The response to the sensory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli. The Basic Scheme Organization of the Nervous system The CNS compared with the PNS Support Cells of the Nervous system the Central Nervous System Astrocytes Microglia Oligodendrocytes Ependymal Cells the Peripheral Nervous System Schwann Cells (a.k.a. Neurolemmocytes) Satellite Cells Astrocytes & microglia Astrocytes & microglial cells protect the neurons of the CNS. Astrocytes & microglia Functions of astrocytes: 1. Connect neurons to capillaries. This makes up the “blood-brain barrier”. 2. Maintain the the electrochemical environment • Capture and recycle neurotransmitters • Absorb and return K+ and other ions. • Connected to one another and capable of communicating via gap junctions. Function of microglial cells: 1. Dendritic macrophages that phagocytize microbes and necrotic (dead) tissue. Ependymal Cells & oligodendrocytes Ependymal Cells & oligodendrocytes Functions: Ependymal Cells - Line the ventricles of the brain an central canal of the spinal cord. They aid in the circulation of cerebrospinal fluid (CSF). Oligodendrocytes - These cells have processes that wrap around the axons of neurons. This creates an insulation coating called a myelin sheath. Schwann Cells & satellite cells •These are the support cells in the peripheral nervous system. •Schwann cells provide the myelin sheath for peripheral axons. •Satellite cells serve a slightly similar function to astrocytes, supporting the cell bodies of peripheral neurons. Neurons - the “action cells” Characteristics of neurons Long-lived Generally last a life time with 90% are formed by the time you are 6 years old. The rest are produced when as you go through puberty. Amitotic Until recently it was thought that neurons didn’t regenerate at all! Some may but generally what you have at adulthood is all you get. High metabolic rate This means high oxygen demand and lots of mitochondria. Neurons also require glucose. Myelin Myelin is a lipid-rich component of the cell membranes of Schwann cells and oligodendrocytes. It acts kind of like the insulation on an electrical wire. Chemically gated ion channels Voltage gated ion channels A Resting Membrane Potential Because there is a higher concentration of Na+ outside than there is K+ inside. This leads to an electric charge or electric potential. Relative ion concentrations Ions have differential permeability. The RMP is maintained by the pumping action of a Na+/K+ pump, powered by ATP Polarization (subthreshold) and hyperpolarization A stimulus leads to a depolarization A change in ion concentrations leads to a reversal of the charge separation. Ion flow in a neuron The depolarization spreads along the cell membrane by serial opening and closing of ion gates. A graded potential Graded potentials are not “all-ornone”, like action potentials The cycle of an Action Potential Propagation of an Action Potential Propagation of an Action Potential Propagation of an Action Potential Temporal summation Anatomy of an Action Potential Salutatory conduction Different types of synapses A Chemical Synapse EPSPs & IPSPs Integration: summation of potentials Synthesis of Neurotransmitters Mechanisms of Neurotransmitter activity A Basic Neural Circuit Type of neurons Three structural classes of neurons Multipolar Most numerous Many dendrites Motor and association neurons Unipolar Second most numerous Rounded body with one process Somatic & general sensory neurons Bipolar Least common, found in special sensory organs Comparison of neuron types Functional categories of neurons This is it for 231 Lecture Final at 10 am next Tuesday. Lab Practicals: Tuesday, 6/8 @ 2 pm Thursday, 6/10 @ 10 am .