Neurons: Anatomy & Physiology Review: Chapter 2 of textbook. Information from prerequisite classes, that I assume you know.

Neurons n Basic functional unit of N.S. n Specialized cell u All cells have same basic properties n information processing u Transmits u Integrates u Stores n Regulation of behavior ~

Stimuli n Dendrites & soma l Receive & Integrate information ~ n Axon carries information away from soma l Electrical signal n Axon terminal releases chemical message l neurotransmitter (NT) ~

Neuronal Membrane n Common Cellular Properties l Compartmentalization n Semipermeable n Fluid Mosaic Model l Phospholipids l Proteins ~

Hydrophilic heads Hydrophobic tails Phospholipid Bilayer

Membrane Proteins: Ionophores n Ions Channels n Nongated n Gated l mechanically -gated l electrically-gated (voltage-gated) l chemically -gated ~

Membrane Proteins OUTSID E INSIDE NT

n More negative particles inside than out u unequal distribution of ions n Bioelectric Potential u like a battery l Potential for ion movement u current ~ Membrane is polarized

Resting Membrane Potential Membrane outside inside A-A- K+K+ Na + Cl -

Forces That Move Ions n Concentration (C) l particles in fluid move from area of high to area of low concentration l diffusion, random movement n Electrostatic (E) l ions = charged particles l like charges repel l opposite charges attract ~

C Organic anions - Membrane impermeable Opposing electrical force not required A-A- V m = -65 mV

Chloride ion C E Cl - V m = -65 mV n E Cl- = - 65 mV n Concentration gradient equal to electrostatic gradient. n *No net movement at resting potential ~

K + C E V m = -65 mV Potassium ion n E K = - 75 mV n Concentration gradient greater than electrostatic gradient. n Leaks out neuron ~

Sodium ion V m = -65 mV n E Na+ = +55 mV n Concentration gradient and electrostatic gradient into neuron. ~ Na + CE

Neural Signaling n Inside neuron l Electrical signal l 2 types of current n Postsynaptic potentials l dendrites & soma n Action potential (AP) l carries information down axon l triggers NT release into synapse ~ Neural Communication

Postsynaptic Potentials - PSPs n Chemically-gated ion channels n Graded l Summation n Passive current (electrotonic) l Fast l Decremental n Relatively long-lasting l msec ~

n Excitatory Postsynaptic Potential n Depolarization (+) l E m becomes more positive l more likely to trigger AP n Na+ influx ~ EPSPs

n Inhibitory Postsynaptic Potential n similar to EPSPs l EXCEPT opposite n hyperpolarization (-) l E m becomes more negative l less likely to trigger AP n K+ efflux ~ IPSPs

Integration n EPSPs & IPSPs summate l become stronger l or cancel each other n Net stimulation l determines message u excitation u or inhibition ~

Postsynaptic Potentials n EPSP l Excitatory l Depolarization l Na+ influx l AP more likely n IPSP l Inhibitory l Hyperpolarization l K+ efflux l AP less likely n Soma & Dendrites n Chemically-gated channels n Passive current n Graded n Summation

Action Potentials n Large and rapid change in membrane potential l Occurs in axon only n voltage-gated channels n triggered by EPSPs l at axon hillock l threshold potential ~

Time VmVm

Time Depolarization Na+ influx VmVm

Time Repolarization K+ efflux VmVm

Time After- hyperpolarization K+ efflux VmVm

AP Characteristics n Voltage-gated channels n All or none n Self-propagated u regenerated l Non-decremental l Slow n Short-lived change in E m l 1-2 msec ~

Frequency Code n Pattern = Intensity of stimulus l # APs per second n Place = type of stimulus l Visual, auditory, pain, etc. l Brain area that receives signal ~

Subthreshold stimulus Moderate stimulus Strong stimulus Injected Current -65 mV 0 mV Time 

PSPs vs APs GradedAll-or-none Summation chemical-gatedvoltage-gated longer duration short msec 1-2 msec passive spreadpropagated instantaneousslow decrementalnondecremental