An Introduction to Brain and Behavior Third Edition CHAPTER How Do Neurons Transmit Information? 4 PowerPoints prepared by: Paul Smaldino, UC Davis, Department of Psychology Bryan Kolb & Ian Q. Whishaw

Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 4 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 Difference = Electrical Potential (volts) Negative pole (higher charge) Positive pole (lower charge) Current Electron

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

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: meters/second Electricity: 3 x 10 8 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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