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COGNITIVE SCIENCE 17 The Electric Brain Part 1 Jaime A. Pineda, Ph.D. INPUT. INTEGRATION. OUTPUT. Law of Dynamic Polarization Dendrites generally receive synaptic input (i.e. are postsynaptic) and axons generally send synaptic output (i.e., are presynaptic). - PowerPoint PPT Presentation
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COGNITIVE SCIENCE 17
The Electric Brain
Part 1 Jaime A. Pineda, Ph.D.
INPUT
INTEGRATION
OUTPUT
Law of Dynamic Polarization Dendrites generally receive synaptic input (i.e. are postsynaptic) and axons generally send synaptic output (i.e., are presynaptic)
Resting Membrane Potential (Vm) is ~ -70 mV in mammals
Vm is the voltage difference between the inside and outside of the cell
50 440
400 20
40 560
many few
Different concentrations of ions inside and outside the cell
Unequal distribution of ions across cellmembrane creates two major forces
osmotic pressure
electrostatic pressure
Other important factors
- Specific protein channels- Na+, K+, Cl-, Ca++
- Selective permeability of channels- leaky channels- K+ > Cl- > Na+
- Sodium-potassium pump
Na+ / K+ Pump
Restores equilibrium
Graded and Action Potentials•Graded
–Are small changes in membrane potential
–Are conducted passively
–Lose energy as they travel down dendrite/axon
•Action
–Are large changes in membrane potential
–Are conducted actively (regenerated)
–Do not lose energy as they travel down the axon
Graded Potentials
• Depolarization (EPSP)– Vm becomes more positive (Na+ flows in) and
the neuron is more likely to produce an action potential
• Hyperpolarization (IPSP)– Vm becomes more negative (K+ flows out) and
the neuron is less like to produce an action potential
Graded Potentials
• AM signals
• Degrade with distance (decremental conduction)
• Short distance
signaling V
Distance from source
Action Potentials
• FM signals
• Do not degrade with distance (non decremental conduction)
• Long distance signaling
Phases of the Action Potential
Firing threshold is the point at which the number ofactivated Na+ channels > inactivated Na+ channels
Absolute refractory period
Relative refractory period