Chapter 8a Neurons Cellular and Network Properties 2013 Pearson Education Inc About This Chapter Cells of the nervous system Electrical signals in neurons Cell to cell communication in the nervous system Integration of neural information transfer 2013 Pearson Education Inc Table 8 1 Synonyms in Neuroscience Figure 8 1 ESSENTIALS The Organization of the Nervous System Figure 8 2 2 ESSENTIALS Neuron Anatomy Parts of a Neuron Nucleus Axon hillock Axon initial segment Myelin sheath Postsynaptic neuron Cell body Dendrites Input signal Integration Output signal Presynaptic axon terminal Synaptic cleft Postsynaptic dendrite Synapse The region where an axon terminal communicates with its postsynaptic target cell Figure 8 2a b ESSENTIALS Neuron Anatomy Functional Categories Sensory Neurons Somatic senses Dendrites Neurons for smell and vision Schwann cell Axon Structural Categories Pseudounipolar Bipolar Pseudounipolar neurons have a single process called the axon During development the dendrite fused with the axon Bipolar neurons have two relatively equal fibers extending off the central cell body Figure 8 2c d ESSENTIALS Neuron Anatomy Functional Categories Interneurons of CNS Axon Dendrites Axon Anaxonic Multipolar Anaxonic CNS interneurons have no apparent axon Multipolar CNS interneurons are highly branched but lack long extensions Figure 8 2e ESSENTIALS Neuron Anatomy Figure 11 8 THE ADRENAL MEDULLA SECRETES EPINEPHRINE INTO THE BLOOD Adrenal cortex is a true endocrine gland Adrenal medulla is a modified sympathetic ganglion Adrenal gland Kidney ACh The chromaffin cell is a modified postganglionic sympathetic neuron Blood vessel Adrenal medulla Epinephrine is a neurohormone that enters the blood To target tissues Spinal cord Preganglionic sympathetic neuron Cells of Nervous System NS Axons Transport Moves material by axoplasmic cytoplasmic flow at 0 2 Moves organelles at rates of up to 400 mm day Forward or anterograde transport from cell body to Backward or retrograde transport from axon terminal to Slow axonal transport 2 5 mm day Fast axonal transport axon terminal cell body 2013 Pearson Education Inc Figure 8 3 FAST AXONAL TRANSPORT Rough endoplasmic reticulum Soma Lysosome Peptides are synthesized on rough ER and packaged by the Golgi apparatus Fast axonal transport walks vesicles and mitochondria along microtubule network Golgi apparatus Vesicle contents are released by exocytosis Synaptic vesicle Retrograde fast axonal transport Old membrane components digested in lysosomes Synaptic vesicle recycling Figure 8 4 The growth cone of a developing axon Figure 8 5 2 ESSENTIALS Glial Cells GLIAL CELLS are found in Peripheral Nervous System contains Schwann cells Satellite cells form Myelin sheaths secrete Neurotrophic factors Support cell bodies Figure 8 5 1 ESSENTIALS Glial Cells GLIAL CELLS are found in Central Nervous System contains Ependymal cells Astrocytes Microglia modified immune cells Oligodendrocytes act as Scavengers form Myelin sheaths create take up secrete help form provide Barriers between compartments Source of neural stem cells K water neurotransmitters Neurotrophic factors Blood brain barrier Substrates for ATP production Figure 8 5b ESSENTIALS Glial Cells Glial Cells of the Central Nervous System Interneurons Ependymal cell Microglia Astrocyte Section of spinal cord Axon Node Myelin cut Oligodendrocyte Capillary Figure 8 5d ESSENTIALS Glial Cells Myelin Formation in the Peripheral Nervous System Nucleus Schwann cell wraps around the axon many times Axon Schwann cell nucleus is pushed to outside of myelin sheath Myelin Figure 8 5c ESSENTIALS Glial Cells Each Schwann Cell Forms Myelin Around a Small Segment of One Axon Cell body 1 1 5 mm Schwann cell Node of Ranvier is a section of unmyelinated axon membrane between two Schwann cells Axon Myelin consists of multiple layers of cell membrane Nervous I Anatomy Review Interactive Physiology Animation Nervous I Anatomy Review 2013 Pearson Education Inc Figure 8 6 PERIPHERAL NEURON INJURY When an axon is cut the section attached to the cell body continues to live The section of the axon distal to the cut begins to disintegrate Site of injury Connective tissue Myelin Proximal axon Disintegrating distal axon Under some circumstances the proximal axon may regrow through the existing sheath of Schwann cells and reform a synapse with the proper target Electrical Signals Nernst Equation Describes the membrane potential that a single ion would produce if the membrane were permeable to only that ion Membrane potential is influenced by Concentration gradient of ions Membrane permeability to those ions 2013 Pearson Education Inc Table 8 2 Ion Concentrations and Equilibrium Potentials Resting Membrane Potential A P FlixTM Resting Membrane Potential 2013 Pearson Education Inc Electrical Signals GHK Equation Predicts membrane potential that results from the contribution of all ions that can cross the membrane 2013 Pearson Education Inc Electrical Signals Ion Movement Resting membrane potential determined primarily by K concentration gradient Cell s resting permeability to K Na and Cl Gated channels control ion permeability Threshold voltage varies from one channel type to Mechanically gated Chemically gated Voltage gated another 2013 Pearson Education Inc Unfigure 8 3 page 250 20 0 20 60 100 V m l a i t n e t o p e n a r b m e M Resting membrane potential difference Vm Vmdepolarizes Vmhyperpolarizes Time msec Table 8 3 Comparison of Graded Potential and Action Potential in Neurons Figure 8 7a ESSENTIALS Graded Potentials Graded Potentials Reflect Stimulus Strength Local current flow is a wave of depolarization that moves Graded potentials lose strength as they move through the through the cell cell due to Current leak Cytoplasmic resistance If strong enough graded potentials reach the trigger zone in the axon hillock and initial segment Excitatory versus inhibitory 2013 Pearson Education Inc Figure 8 7b ESSENTIALS Graded Potentials Subthreshold Graded Potential A graded potential starts above threshold T at its initiation point but decreases in strength as it travels through the cell body At the trigger zone it is below threshold and therefore does not initiate an action potential Stimulus Synaptic terminal Cell body Trigger zone Axon No action potential 40 55 70 mV 40 55 70 mV 40 55 70 mV Stimulus Time Graded potential below threshold Time Time Figure 8 7c ESSENTIALS Graded Potentials Suprathreshold Graded Potential A stronger