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Unformatted text preview: heir nutrient supplies (capillaries) Control the chemical environment Astrocytes Figure 11.3a Microglia Phagocytes protection from disease (remove debris and foreign invaders) Microglia and Ependymal Cells Figure 11.3b, c Ependymal cells Line the central cavities of the brain and spinal cord Involved in the production of CSF (cerebrospinal fluid) Cilia to help circulate CSF Microglia and Ependymal Cells Figure 11.3b, c Oligodendrocytes Branched cells that wrap around axons of several neurons Myelin phospholipid covering, insulating function Figure 8-6a Figure 8-5 (2 of 3) Neuroglia (PNS) Schwann Cells Surround axon of one neuron Many Schwann cells per axon (up to 500) Produce myelin sheaths (20-30 layers) Node of Ranvier gap in between Schwann cells Figure 8-6, bc Satellite Cells Surround neuron cell bodies Function? Neurophysiology Neurons are excitable, irritable ability to respond to stimuli and convert into action potentials (nerve impulses) Stimulus = capable of altering RMP (resting membrane potential) If stimulus is strong enough (threshold) action potential intiated Resting Membrane Potential (Vr) Figure 11.8 Membrane potential changes (depolarization, hyperpolarization, repolarization) produced by: Changes in membrane permeability to ions changes ion concentrations Role of membrane channels Graded potentials and action potentials result Membrane Ion Channels Passive, or leakage, channels Chemically-gated channels Voltage-gated channels Mechanically-gated channels Graded Potentials Short-lived, local changes in membrane potential Dendrites, cell body location Dies out over distance Magnitude depends on strength of the stimulus (how many ion channels are open/closed) Sufficiently strong graded potentials can initiate action potentials Figure 8-7 If graded potential is of threshold value when it reaches the axon hillock (trigger zone), an action potential will be initiated and will propagate down the length of the axon to the axon terminals. Weak (subthreshold) stimuli are not relayed into action potentials Strong (threshold) stimuli are relayed into action potentials Figure 8-8a Figure 8-8b Action Potentials (APs) Do not die out over...
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This note was uploaded on 04/29/2009 for the course BIOL 425 taught by Professor Tondi during the Fall '08 term at George Mason.
- Fall '08