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CHAPTER An Introduction to Brain and Behavior Third Edition 4 How Do Neurons Transmit Information? Bryan Kolb & Ian Q. Whishaw PowerPoints prepared by: Paul Smaldino, UC Davis, Department of Psychology How Do Neurons Transmit Information? • Searching for Electrical Activity in the Nervous System • Electrical Activity of a Membrane • How Neurons Integrate Information • Into the Nervous System and Back Out Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 The Basics: Electricity and Electrical Stimulation • Electricity – A flow of electrons from a body that contains a higher charge (more electrons) to a body that contains a lower charge (fewer electrons) • Negative Pole – The source of electrons; higher charge • Positive Pole – Location to which electrons flow; lower charge Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 The Basics: Electricity and Electrical Stimulation • Electrical Potential – An electrical charge measured in volts; the ability to do work through the use of stored potential electrical energy • Volt – A measure of a difference in electrical potential • Voltmeter – A device that measures the difference in electrical potential between two bodies Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electron - - - -- - Current Negative pole (higher charge) - - Positive pole (lower charge) Difference = Electrical Potential (volts) Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Early Clues that Linked Electricity and Neuronal Activity Electrical Stimulation Studies • Galvani (18th Century) – Electrical current applied to a dissected nerve causes the muscle connected to the nerve to twitch; concluded that electricity flows along the nerve – Electrical Stimulation • Passing an electrical current from the tip of an electrode through brain tissue, resulting in changes in the electrical activity of the tissue Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Early Clues that Linked Electricity and Neuronal Activity Electrical Stimulation Studies • Fritsch and Hitzig (Mid-19th Century) – Electrical stimulation of the neocortex causes movement (arms and legs) • Bartholow (1874) – First report of human brain stimulation Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Early Clues that Linked Electricity and Neuronal Activity Electrical Recording Studies • Caton (Early 19th Century) – First to attempt to measure electrical currents of the brain using a voltmeter and electrodes on the skull • Electroencephalogram – Electrical brain graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Early Clues that Linked Electricity and Neuronal Activity Electrical Recording Studies • von Helmholtz (19th Century) – Flow of information in the nervous system is too slow to be a flow of electricity • Nerve conduction: 30-40 meters/second • Electricity: 3 x 108 meters/second • It is not the charge but the wave that travels along an axon (Bernstein, 1886) Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Tools for Measuring a Neuron’s Electrical Activity Giant Axon of the Squid • Much larger in diameter than human axons – Humans: 1 to 20 micrometers – Squid: Up to 1 millimeter (1000 micrometers) • Easier on which to perform experiments – Used by Hodgkin and Huxley in the 1930s and 1940s Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Tools for Measuring a Neuron’s Electrical Activity The Oscilloscope • A device that serves as a sensitive voltmeter • Used to record voltage changes on an axon Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System Tools for Measuring a Neuron’s Electrical Activity Microelectrodes • A set of electrodes small enough to place on or into an axon. • Can be used to: – Measure a neuron’s electrical activity – Deliver an electrical current to a single neuron (stimulation) Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System How the Movement of Ions Creates Electrical Charges • Cations – Positively charged ions • Examples: Sodium (Na+), potassium (K+) • Anions – Negatively charged ions • Examples: Chloride (Cl-), protein molecules (A-) Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System How the Movement of Ions Creates Electrical Charges • Diffusion – Movement of ions from an area of higher concentration to an area of lower concentration through random motion • Concentration Gradient – Differences in concentration of a substance among regions of a container that allows the substance to diffuse from an area of higher concentration to an area of lower concentration Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Searching for Electrical Activity in the Nervous System How the Movement of Ions Creates Electrical Charges • Voltage Gradient – Difference in charge between two regions that allows a flow of current if the two regions are connected • Opposite charges attract • Similar charges repel Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Resting Potential • Resting Potential – Electrical charge across the cell membrane in the absence of stimulation – A store of negative energy on the intracellular side relative to the extracellular side – Approximately -70 mV Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Resting Potential • Four charged particles take part in producing the resting potential – Sodium (Na+) and chloride (Cl-) • Higher concentration outside cell – Potassium (K+) and large proteins (A-) • Higher concentration inside cell Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Resting Potential • Maintaining the Resting Potential – Large A- molecules cannot leave cell: make inside negative – Ungated channels allow K+ and Cl- to move into and out of cell more freely, but gated sodium channels keep out Na+ ions – Na+-K+ pumps extrude Na+ from intracellular fluid and inject K+ Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Graded Potentials • Graded Potential – Small voltage fluctuation in the cell membrane – Restricted to the vicinity on the axon where ion concentrations change – Can be hyperpolarization or depolarization Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Graded Potentials • Hyperpolarization – Increase in electrical charge across a membrane (more negative) – Usually due to the inward flow of chloride ions or outward flow of potassium ions – Tetraethylammonium (TEA) • Depolarization – Decrease in electrical charge across a membrane (more positive) – Usually due to the inward flow of sodium – Tetrodotoxin Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane The Action Potential • Action Potential – Large, brief reversal in polarity of an axon – Lasts approximately 1 millisecond (ms) • Threshold Potential – Voltage on a neural membrane at which an action potential is triggered – Opening of Na+ and K+ voltage-sensitive channels – Approximately −40 mV relative to extracellular surround Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane The Action Potential • Voltage-Sensitive Ion Channels – Gated protein channel that opens or closes only at specific membrane voltages – Sodium (Na+) and potassium (K+) – Closed at membrane’s resting potential – Na+ channels are more sensitive than K+ channels and therefore open sooner Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane The Action Potential • Absolute Refractory Period – The state of an axon in the repolarizing period during which a new action potential cannot be elicited (with some exceptions) because gate 2 of sodium channels, which is not voltage-sensitive, is closed • Relative Refractory Period – The state of an axon in the later phase of an action potential during which increased electrical current is required to produce another action potential – Potassium channels are still open Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane The Nerve Impulse • Nerve Impulse – Propagation of an action potential on the membrane of an axon – Refractory periods create a single, discrete impulse that travels only in one direction – Size and shape of action potential remain constant along the axon • All-or-none law Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Saltatory Conduction and Myelin Sheaths • Myelin – Produced by oligodendroglia in the CNS and Schwann cells in the PNS – Speeds up neural impulse • Node of Ranvier – Part of an axon that is not covered by myelin – Tiny gaps in the myelin sheath – Enables saltatory conduction Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Electrical Activity of a Membrane Saltatory Conduction and Myelin Sheaths • Saltatory Conduction – Saltare: “to dance” (Latin) – Propagation of an action potential at successive nodes of Ranvier Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 How Neurons Integrate Information Excitatory and Inhibitory Postsynaptic Potentials • Excitatory Postsynaptic Potential (EPSP) – Brief depolarization of a neuron membrane in response to stimulation – Neuron is more likely to produce an action potential • Inhibitory Postsynaptic Potential (IPSP) – Brief hyperpolarization of a neuron membrane in response to stimulation – Neuron is less likely to produce an action potential Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 How Neurons Integrate Information Summation of Inputs EPSPs and IPSPs Are Summed • Temporal Summation – Pulses that occur at approximately the same time on a membrane are summed • Spatial Summation – Pulses that occur at approximately the same location on a membrane are summed Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Temporal Summation Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Spatial Summation Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 How Neurons Integrate Information Summation of Inputs • The Role of Ions in Summation – The influx and efflux of ions is what is being summed Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 How Neurons Integrate Information Voltage-Sensitive Channels and The Axon Hillock • The Axon Hillock – Junction of cell body and axon – Rich in voltage-sensitive channels – Where EPSPs and IPSPs are integrated – Where action potentials are initiated Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Into the Nervous System and Back Out How Sensory Stimuli Produce Action Potentials • Several different sensory modalities – Visual, auditory, tactile, chemical (taste and olfaction) • Many different types of sensory receptors – Ion channels on their cell membranes – Example: Stretch-sensitive receptors • Ion channel on a tactile sensory neuron that activates in response to stretching of the membrane, initiating a nerve impulse Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Into the Nervous System and Back Out How Nerve Impulses Produce Movement • Motor neurons generate action potentials in muscle cells to make them contract • End plate – On a muscle, the receptor–ion complex that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Into the Nervous System and Back Out How Nerve Impulses Produce Movement • Acetylcholine – The first neurotransmitter discovered in the peripheral and central nervous systems – Activates skeletal muscles • Transmitter-sensitive channel – Receptor complex that has both a receptor site for a chemical and a pore through which ions can flow Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4