Neurons

Psy391h - Class 3

(This page last updated 24 Jan 2006.)

Neural Components

• Soma
• Nucleus
• Dendrites
• Synapses
• Axon
• Terminal Button
• Neurotransmitter

Neural Signaling

• electrotonic (decremental) conduction
  • strength decreases with distance
• action potentials
  • in axon
  • all or none
  • threshold of excitation
  • variations in strength represented by variations in firing rate.

Membrane Potentials in Neurons

• resting potential
  • approximately -70 mV
• depolarization and hyperpolarization
• diffusion
• electrostatic pressure
• ion channels
  • voltage-dependent ion channel
• sodium/potassium (Na+/K+) pump
• high concentration of K+ inside neuron
  • electrostatic pressure helps keep it in
  • diffusion pushes it out
• high concentration of Na+ outside neuron
  • Both diffusion and electrostatic pressure push it in
• action potential
  • depolarization reaches thereshold of excitation
  • voltage-gated Na+ channels open, allowing Na+ in
  • depolarization increases, potential becomes more positive
  • K+ channels open, allowing K+ out
  • potential returns to negative range

Action Potentials in Myelinated Axons

• gap in myelin at node of Ranvier
• passive cable properties carry potential from one node of Ranvier to next
• action potential regains strength at node of Ranvier

Synapse

• synaptic vesicles
• vesicles fuse with presynaptic membrane
• postsynaptic receptors
• transmitter-dependent ion channels
  • Can be indirectly coupled via second messengers
• can produce EPSPs or IPSPs
• cleanup
  • reuptake
  • enzymatic deactivation

next: Brain Organization

Psych 391h: Cognitive Neuroscience Kyle Cave Psychology Dept. U. Mass.