Exam 3 Review Topics Lesson 12 What are the functions of neuroglia Neuroglia glial cells Cells that support and protect neurons What are the different types of neuroglia and what are their functions Which neuroglia are found in the CNS Which are found in the PNS Cells with highly branched processes contact neuroglia directly Four Types of Neuroglia in the CNS 1 Ependymal cells Large cell bodies with many processes Smaller cell bodies with fewer processes 2 Astrocytes 3 Oligodendrocytes 4 Microglia Neuroglia of the Peripheral Nervous System 1 Satellite cells Smallest and least numerous neuroglia with many fine branched processes 2 Schwann cells Also called amphicytes Regulate environment around neuron Surround ganglia Masses of neuron cell bodies in the PNS Also called neurilemma cells One Schwann cell sheaths one segment of axon Form myelin sheath neurilemma around peripheral axons What is the difference between white matter and grey matter Myelination causes nervous tissue to appear white White matter Gray matter Regions of CNS with many myelinated nerves Unmyelinated areas of CNS Nissl bodies make neural tissue appear gray Dense areas of RER and ribosomes What are the steps to Wallerian degeneration It is a Neural Responses to Injuries in the PNS Axon distal to injury site degenerates Macrophages migrate into area and remove debris What is the difference between axonal regeneration in the CNS and PNS CNS PNS Schwann cells form path for new growth o Wrap new axon in myelin Nerve Regeneration in CNS limited by Many more axons likely to be involved Astrocytes that Release chemicals that block growth Produce scar tissue 1 Fragmentation of axono and myelin occurs in distal stump 2 Schwann cells for cord grow into and cut and unite stumps Macrophages engulf degenerating axon and myelin 3 Axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells 4 Axon continues to grow into distal stump and is enclosed by Schwann cells Lesson 13 14 What is the difference between a resting potential a graded potential and an action potential Which involves passive channels chemically gated channels and voltage gated channels Five Main Membrane Processes in Neural Activities 1 Resting potential 2 Graded potential 3 Action potential 4 Synaptic activity The transmembrane potential of resting cell Temporary localized change in resting potential Caused by stimulus to the cell An electrical impulse produced by graded potential Propagates along surface of axon to synapse Releases neurotransmitters at presynaptic membrane Produces graded potentials in postsynaptic membrane 5 Information processing Response integration of stimuli of postsynaptic cell 1 Chemically Gated Channels Open in presence of specific chemicals e g ACh at a binding site Found on neuron cell body and dendrites 2 Voltage gated Channels Respond to changes in transmembrane potential Have activation gates open and inactivation gates close Characteristic of excitable membrane Found in neural axons skeletal muscle sarcolemma cardiac muscle 3 Mechanically Gated Channels Respond to membrane distortion Found in sensory receptors touch pressure vibration How is the resting membrane potential generated and maintained Why is the sodium potassium exchange pump important Because the plasma membrane is highly permeable to potassium ions The electrochemical gradient for sodium ions is very large but the membrane s permeability to these ions is very low The sodium potassium exchange pump ejects 3 Na ions for every 2 K ions that it brings into the cell It serves to stabilize the resting potential when the ratio of Na entry to K loss through passive channels is 3 2 At the normal resting potential these passive and active mechanisms are in balance The resting potential varies widely with the type of cell A typical neuron has a resting potential of approximately 70 mV What is the difference between chemical and electrical gradients and why are they important in the transmembrane potential 1 Chemical gradients 2 Electrical gradients Concentration gradients chemical gradient of ions Na K Separate charges of positive and negative ions Result in potential difference They re important because transmembrane potential rises or falls in response to temporary changes in membrane permeability from opening or closing specific membrane channels What are the three states of gated channels Three States of Gated Channels 1 Closed but capable of opening 2 Open activated 3 Closed not capable of opening inactivated DIFFERENT THAN Three Classes of Gated Channels 1 Chemically gated channels 2 Voltage gated channels 3 Mechanically gated channels Why is that important in action potential generation Action Potentials Propagated changes in transmembrane potential Affect an entire excitable membrane Link graded potentials at cell body with motor end plate actions Initiated by Initial stimulus A graded depolarization of axon hillock large enough 10 to 15 mV to change resting potential 70 mV to threshold level of voltage gated sodium channels 60 to 55 mV All or none principle An action potential is either triggered or not o If a stimulus exceeds threshold amount an action potential is generated The action potential is the same no matter how large the stimulus What does depolarization repolarization and hyperpolarization mean in terms of the transmembrane potential Depolarization A shift in transmembrane potential toward 0 mV Events include Produces local current Movement of Na through channel Depolarizes nearby plasma membrane graded potential Note change in potential is proportional to stimulus Repolarization occurs when the stimulus is removed the transmembrane potential returns to normal Hyperpolarization caused by increasing the negativity of the resting potential Result of opening a potassium channel Opposite effect of opening a sodium channel Positive ions move out not into cell What are the four basic characteristics of graded potentials 1 The transmembrane potential is most changed at the site of stimulation and the effect decreases with distance 2 The effect spreads passively due to local currents 3 The graded change in transmembrane potential may involve either depolarization or hyperpolarization The properties and distribution of the membrane channels involved determine the nature of the change For example in a resting membrane the opening of sodium channels causes depolarization whereas the opening of potassium channels causes
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