neurons: anatomy & physiology
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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 - PowerPoint PPT PresentationTRANSCRIPT
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