* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Slides - gserianne.com
Premovement neuronal activity wikipedia , lookup
Neural coding wikipedia , lookup
Signal transduction wikipedia , lookup
Neural engineering wikipedia , lookup
Optogenetics wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Axon guidance wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Patch clamp wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neurotransmitter wikipedia , lookup
Neuroregeneration wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Synaptogenesis wikipedia , lookup
Neuroanatomy wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Synaptic gating wikipedia , lookup
Membrane potential wikipedia , lookup
Action potential wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Node of Ranvier wikipedia , lookup
Biological neuron model wikipedia , lookup
Electrophysiology wikipedia , lookup
Single-unit recording wikipedia , lookup
Resting potential wikipedia , lookup
Nervous system network models wikipedia , lookup
Chemical synapse wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Visual Anatomy & Physiology First Edition Martini & Ober Chapter 11 Nervous System I Lecture 18 1 Lecture Overview • • • • • • • • Overview of the NS Review of nervous tissue Functions of the Nervous System (NS) Histology and Structure of the NS Classification of Neurons Neurophysiology Nerve impulse transmission Synaptic transmission 2 Function of the Nervous System • The nervous system is a coordination and control system that helps the body maintain homeostasis. It – Gathers information about the internal and external environment (sense organs, nerves) – Relays this information to the spinal cord and the brain – Processes and integrates the information – Responds, if necessary, with impulses sent via nerves to muscles, glands, and organs 3 Overview of the Nervous System 4 Divisions of the Nervous System Figure from: Hole’s Human A&P, 12th edition, 2010 Know all of these subdivisions of the nervous system 5 Major subdivisions CNS PNS Nervous Tissue • found in brain, spinal cord, and peripheral nerves • conduction of nerve impulses • basic cells are neurons • sensory reception and motor impulses • neuroglial cells are supporting cells 6 Figure from: Hole’s Human A&P, 12th edition, 2010 Neuron Structure (soma) rER *Initial segment (origin of nerve impulses) Identify/label the structure/parts of a neuron shown here. State the function of dendrites, the cell body, axons, initial segment, and synaptic knobs 8 Figure from: Hole’s Human A&P, 12th edition, 2010 Neuron function and Nerve Connections Figure from: www.erachampion.com (fast) (slow) The major functions of a neuron are to 1) collect input from other neurons 2) integrate the signals 3) send (or not) an appropriate type of signal to neurons it synapses with 9 Structural Classification of Neurons Figure from: Hole’s Human A&P, 12th edition, 2010 Bipolar • two processes • sense organs Unipolar • one process • ganglia Multipolar • many processes • most neurons of CNS **Classification is based on the number of processes coming directly out of the cell body 10 Functional Classification of Neurons Sensory Neurons • afferent, ascending • carry impulse to CNS • most are unipolar • some are bipolar Interneurons • link neurons • integrative • multipolar • in CNS Motor Neurons • efferent, descending • multipolar • carry impulses away from CNS • carry impulses to effectors Figure from: Hole’s Human A&P, 12th edition, 2010 Notice the directionality – one-way 11 Neuroglia (glia = glue) Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Know the information contained in the Table on following slide. 12 Summary Table of Neuroglia Name of Cell Location Function(s) Satellite Cells Ganglia of PNS Regulate microenvironment of neurons Astrocytes CNS Regulate microenvironment of neurons; scar tissue in CNS Schwann Cells PNS Myelination of axons; structural support for nonmyelinated axons Oligodendrocytes CNS Myelination of axons; structural framework Microglia CNS Phagocytes of the CNS Ependymal Cells CNS Assist in producing and controlling composition of CSF 13 Intro to Cell Response/Signaling • How does a neuron “know” its being stimulated? • When stimulated by multiple inputs, how does a neuron “know” whether it should send a nerve impulse (action potential) or not? Answer: Changes in cellular ionic composition But recall that ions are ‘hydrated’ and cannot pass through a cell membrane. How do they pass from outside to inside or from inside to outside? CHANNELS 14 Intro to Transmembrane Potential For activation of neurons, ions need to pass from one side of the cell membrane to the other. Would that happen if there was an equal concentration of those ions on both sides of the membrane? NO! Therefore, it is necessary to have the cell in a ready state to let ions flow from one side of the membrane to the other when the time is right. This requires that an UNEQUAL concentration of ions exist BEFORE the cell decides its time to move ions from one place to the other. HOW IS THIS DONE? 15 Intro to Transmembrane Potential • Positive and negative charges attract • Whenever + and – charges are held apart, a potential difference exists • Size of a potential difference is measured in Volts (V) or millivolts (mV = Volt/1,000) • If + and – charges are allowed to flow toward one another, a current develops • The opposition to a current is called resistance Let’s look at the origin of the membrane potential… 16 A Cell With Zero Electrical Membrane Potential Extracellular 1 K+ 20 Na+ 21 Cl- (major extracellular anion) Leak channel Total charge = 0 Intracellular 19 K+ 1 K+ 21 protein- (major intracellular anion) 1 Na+ Where would K+ tend to go? Why? What stops it? Where would Na+ tend to go? Why? What stops it? 17 Establishing Resting Membrane Potential Extracellular 1 K+ 1 K+ + + Intracellular - - 19 K+ 21 Cl- + + + + 1 K+ 1 20 Na+ Na+ - 21 protein- This process continues until the inside of the cell membrane is about -70 mV (negative) relative to the outside of the cell membrane – the membrane is said to be polarized. The INSIDE of the cell membrane is now negative relative to the outside mainly due to the outward flow of K+ ions. 18 Transmembrane Potential A potential difference of -70 mV exists in the resting neuron due to the electrochemical gradient – membrane is polarized -3 mV • inside is negative relative to the outside • *polarized membrane due to distribution of ions • Na+/K+ATPase pump 19 Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Membrane Channel Proteins • Passive channels are ALWAYS open – Also called ‘leak’ channels – Passive K+ channels always allow K+ through • Active (gated) channels open or close in response to signals – Mechanical – respond to distortion of membrane – Ligand-gated (Chemical) • Binding of a chemical molecule, e.g., ACh on MEP • Present on dendrites, soma, sometimes on axons – Voltage-gated • Respond to changed in electrical potential • Found on excitable membranes, e.g., axons, sarcolemma 20 Mechanically-gated Channels From: http://www.ionchannels.org/content/images/3-01.jpg 21 Ligand-gated Channels From: http://en.wikipedia.org/wiki/Ligand-gated_ion_channel 22 Voltage-gated Channels ---- From: http://courses.cm.utexas.edu/jrobertus /ch339k/overheads-2.htm ++++ 23 Changes in Membrane Potential 0 • If membrane potential becomes more positive than its resting potential, it has depolarized (Movement of ? charges causes this?) • A membrane returning to its resting potential from a depolarized state is being repolarized (Movement of ? charges causes this?) • If membrane potential becomes more negative than its resting potential, it has hyperpolarized 24 Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Action Potentials • Action potential = nerve impulse (neuron must reach THRESHOLD before an action potential occurs) • Begins at initial segment of axons (high density of voltageregulated Na+ channels) • all-or-none (think: finger on a gun’s trigger) • Does not weaken with distance • refractory period • absolute - time when threshold stimulus does not start another action potential (Na+ channels inactivated) • relative – time when stronger threshold stimulus can start another action potential (Na+ channels restored, K+ channels begin closing) 25 Action Potentials Begin at the Initial Segment Figure from: Hole’s Human A&P, 12th edition, 2010 Ligand-gated Na+ channels Voltage-gated Na+ channels Action potential begins here, in the initial segment. Note the high number of voltage-gated channels. 26 Threshold and Action Potential Figure from: Hole’s Human A&P, 12th edition, 2010 = Nerve impulse What causes depolarization? Repolarization Influx of Na+ Efflux of K+ Depolarization What causes repolarization? Threshold Steps in Action Potential: 1) depolarization 2) repolarization 3) hyperploarization 4) return to resting potential 27 How does a neuron ‘know’ when to fire? Any one neuron receives many THOUSANDS of inputs from other neurons. Not all of these will make the neuron generate a nerve impulse. How does this work? 29 Figure from: Hole’s Human A&P, 12th edition, 2010 Local (Graded) Potential Changes • Caused by various stimuli • chemicals • temperature changes • mechanical forces • Cannot spread very far (~ 1 mm max) – weaken rapidly • Uses ligand-gated Na+ channels • On membranes of many types of cells including epithelial cells, glands, dendrites and neuronal cell bodies • General response method for cells • Can be summed (so that an action potential threshold is reached; change in membrane potential stimulus strength • Starting point for an action potential 30 * Channels on Neurons Figure from: Hole’s Human A&P, 12th edition, 2010 Note the high number of ligand-gated channels on the dendrites and soma; this is where graded (local) potentials occur Ligand-gated Na+ channels Voltage-gated Na+ channels 31 Refractory Period Figure from: Hole’s Human A&P, 12th edition, 2010 ARP = Absolute Refractory Period RRP = Relative Refractory Period Influx of Na+ (Depolarization) Efflux of K+ (Repolarization) Great summary graphic to know for the exam! Threshold ARP RRP 32 Action Potential Membrane Changes Figure from: Hole’s Human A&P, 12th edition, 2010 Step1: Depolarization to threshold Step 2: Na+ channels open Step 3: Na+ channels close, K+ channels open Step 4: Return to normal polarization Action potentials use voltage-gated Na+ channels 33 Action Potentials Figure from: Hole’s Human A&P, 12th edition, 2010 Shown at left is an example of continuous propagation (~ 1m/s) What keeps the action potential going in ONE DIRECTION, and not spreading in all directions like a graded potential? Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007 Absolute refractory period of the previously depolarized segment. 34 Action Potential Myelination of Axons Figure from: Hole’s Human A&P, 12th edition, 2010 White Matter • contains myelinated axons Gray Matter (CNS) • contains unmyelinated structures • cell bodies, dendrites Smaller axons in PNS In CNS, myelin is produced by ? Oligodendrocytes 35 Saltatory (Leaping) Conduction Figure from: Hole’s Human A&P, 12th edition, 2010 Myelin acts as an insulator and increases the resistance to flow of ions across neuron cell membrane (fast) Ions can cross membrane only at nodes of Ranvier Impulse transmission is up to 20x faster than in non-myelinated nerves. Myelinated axons are primarily what makes up white matter. 36 Regeneration of A Nerve Axon Figure from: Hole’s Human A&P, 12th edition, 2010 Growth = 3-4 mm/day Damage to cell body usually cannot be repaired – neurons lack centrioles and usually cannot divide 37 The Chemical Synapse Figure from: Hole’s Human A&P, 12th edition, 2010 Nerve impulses pass from neuron to neuron at synapses in about 0.5 msec Are there any other kind of synapses besides chemical ones? 38 Chemical Synaptic Transmission Neurotransmitters (ntx) are released when impulse reaches synaptic knob You should understand this process This may or may not release enough ntx to bring the postsynaptic neuron to threshold Chemical neurotransmission may be modified Ultimate effect of a ntx is dependent upon the properties of the receptor, not the ntx How is the neurotransmitter neutralized so the signal doesn’t continue indefinitely? 39 Figure from: Hole’s Human A&P, 12th edition, 2010 Neurotransmitters Table from: Hole’s Human A&P, 12th edition, 2010 * * * Neuromodulators: Influence release of ntx or the postsynaptic response to a ntx, e.g., endorphins, enkephalins 40 Postsynaptic Potentials EPSP • excitatory postsynaptic potential • depolarizes membrane of postsynaptic neuron • action potential of postsynaptic neuron becomes more likely IPSP • inhibitory postsynaptic potential •hyperpolarizes membrane of postsynaptic neuron • action potential of postsynaptic neuron becomes less likely Both of these act by changing the resting membrane potential; either de- or hyperpolarizing it 41 Summation of EPSPs and IPSPs Figure from: Hole’s Human A&P, 12th edition, 2010 • EPSPs and IPSPs are added together in a process called summation • Summation can be temporal or spatial • More EPSPs lead to greater probability of action potential 42 Review • There are two major divisions of the nervous system – CNS – Brain and spinal cord – PNS – Cranial and spinal nerves • The nervous system has three general functions – Sensory – Integrative (associative) – Motor 44 Review • Neurons are the impulse-transmitting cells of the nervous system – – – – Dendrites Soma (cell body) Axon Initial segment • Larger axons of peripheral nerves are myelinated – Schwann cells (PNS) – Myelin and nodes of Ranvier – Increase conduction speed (saltatory) 45 Review • Neurons can be classified according to function or structure – Structural; bi-, uni-, and multipolar – Functional; sensory, associative (interneurons), motor • CNS Neuroglia support and nourish neurons – Astrocytes; support, ion regulation, blood-brain barrier – Oligodendrocytes; myelination in CNS, growth factors – Microglia; support and phagocytosis – Ependyma; line ventricles, choroid plexuses, regulate composition of CSF 46 Review • Important terms in nerve impulse transmission – Resting potential • Na+ / K+ and Na+/K+ Pump – – – – – – – Local potential and summation Action potential Hyperpolarization and depolarization All-or-none response Refractory period Saltatory conduction See Table 10.3 in Hole (good to know!) 47 Review • Communication between nerves and/or effectors takes place at the synapse – EPSP and IPSP – Neurotransmitters mediate synaptic transmission (Acetylcholine, Norepinephrine) • Convergence and divergence 48