Neurons: Anatomy & Physiology

Review: Chapter 2 of textbook.Information from prerequisite

classes, that I assume you know.

Neurons

Basic functional unit of N.S. Specialized cell

All cells have same basic properties information processing

Transmits Integrates Stores

Regulation of behavior ~

Stimuli

Dendrites & somaReceive & Integrate information ~

Axon carries information away from soma Electrical signal

Axon terminal releases chemical message neurotransmitter (NT) ~

Neuronal Membrane

Common Cellular Properties Compartmentalization

Semipermeable Fluid Mosaic Model

Phospholipids Proteins ~

Hydrophilic heads

Hydrophobic tails

Phospholipid Bilayer

Membrane Proteins: Ionophores

Ions Channels Nongated

Gated

mechanically -gated

electrically-gated (voltage-gated)

chemically -gated ~

Membrane Proteins

OUTSIDE

INSIDE

NT

More negative particles inside than out unequal distribution of ions

Bioelectric Potential like a battery

Potential for ion movement current ~

Membrane is polarized

Resting Membrane Potential

Membrane

outside

inside

+ + + + + + + + + + +

-----------

A- K+

Na+ Cl-

Forces That Move Ions

Concentration (C) particles in fluid move from area of

high to area of low concentration diffusion, random movement

Electrostatic (E) ions = charged particles like charges repel opposite charges attract ~

C

Organic anions - Membrane impermeableOpposing electrical force not required

A-

Vm = -65 mV

Chloride ion

C

E

Cl-

Vm = -65 mV

ECl- = - 65 mV Concentration gradient equal to

electrostatic gradient. *No net movement at resting potential ~

K+ C

EVm = -65 mV

Potassium ion

EK = - 75 mV Concentration gradient greater than

electrostatic gradient. Leaks out neuron ~

Sodium ion

Vm = -65 mV

ENa+ = +55 mV Concentration gradient and

electrostatic gradient into neuron. ~

Na+

C E

Neural Signaling Inside neuron

Electrical signal 2 types of current

Postsynaptic potentials dendrites & soma

Action potential (AP) carries information down axon triggers NT release into synapse ~

Neural Communication

Postsynaptic Potentials - PSPs

Chemically-gated ion channels Graded

Summation Passive current (electrotonic)

Fast Decremental

Relatively long-lasting 10 - 100 msec ~

Excitatory Postsynaptic Potential Depolarization (+)

Em becomes more positive more likely to trigger AP

Na+ influx ~

EPSPs

Inhibitory Postsynaptic Potential similar to EPSPs

EXCEPT opposite hyperpolarization (-)

Em becomes more negative less likely to trigger AP

K+ efflux ~

IPSPs

Integration

EPSPs & IPSPs summate become stronger or cancel each other

Net stimulation determines message

excitation or inhibition ~

Postsynaptic Potentials

EPSPExcitatoryDepolarizationNa+ influxAP more likely

IPSPInhibitoryHyperpolarizationK+ efflux AP less likely

Soma & Dendrites Chemically-gated channels Passive current Graded Summation

Action Potentials Large and rapid change in membrane

potential Occurs in axon only

voltage-gated channels triggered by EPSPs

at axon hillock threshold potential ~

-70

-60

0

+40

-80

Time

Vm

-70

-60

0

+40

-80

Time

Depolarization

Na+ influxVm

-70

-60

0

+40

-80

Time

Repolarization

K+ efflux Vm

-70

-60

0

+40

-80

Time

After- hyperpolarization

K+ efflux

Vm

AP Characteristics

Voltage-gated channels All or none Self-propagated

regenerated Non-decremental Slow

Short-lived change in Em

1-2 msec ~

Frequency Code

Pattern = Intensity of stimulus # APs per second

Place = type of stimulus Visual, auditory, pain, etc. Brain area that receives signal ~

Subthresholdstimulus

Moderatestimulus

Strongstimulus

Injected Current

-65 mV

0 mV

Time

PSPs vs APs

Graded All-or-none

Summation

chemical-gated voltage-gated

longer duration short

10-100 msec 1-2 msec

passive spread propagated

instantaneous slow

decremental nondecremental