Mind, Brain

1
Mind, Brain Behavior

• Wednesday
• January 29, 2003

2
Ion Channels

• Chapter 7

3
Ion Channels

• Found in all cells throughout the body.
• Open and close in response to signals.
• Selectively permeable to specific ions
• High rate of flow (conductance)
• Resting channels usually open
• Gated channels open and close
• Refractory period temporarily cannot be opened

4
Control of Gating

• Binding of neurotransmitters, hormones, or second
  messengers from within the cell.
• Phosphorylation energy comes from a phosphate
  that binds with the channel.
• Dephosphorylation removal of the phosphate.
• Voltage-gated responds to a change in the
  membrane potential.
• Stretch or pressure gated mechanical forces.

5
Effects of Drugs

• Exogenous ligands drugs that come from outside
  the body.
• Endogenous ligands naturally occurring
• Agonist binds with and opens a channel.
• Endogenous or exogenous (e.g., drug)
• Antagonist binds with and closes a channel.
• Reversible (curare) or irreversible (snake venom)

6
Importance of Calcium

• Voltage-gated calcium (CA2) channels permit CA to
  enter the cell.
• As CA2 rises, it binds with the neuron,
  preventing additional calcium from entering.
• Increased calcium concentrations can cause
  dephosphorylation or permanent inactivation of a
  channel.
• Calcium signals neurotransmitter release.

7
Goldman Nernst Equations

• Described in detail in Chapter 8 (optional)
• Membrane potential Vm Vin Vout
• Nernst Equation -- resting potential depends on
  the proportions of ions on the inside and outside
  of the cell and the temperature.
• Goldman Equation combines effects of different
  ions within the same neuron.

8
Propagation of an Action Potential

• Axon diameter affects the speed with which an
  action potential travels down the axon.
• The larger the diameter of the axon, the faster
  the transmission.
• Less permeability of the cell membrane increases
  transmission speed.
• Depolarization spreads down the axon instead of
  outward.
• Myelination increases the speed of transmission.

9
Diseases Causing Demyelination

• Multiple Sclerosis (MS)
• Varied, unpredictable symptoms over entire brain
  functioning, not disabling, may be remitting
• Early intervention slows progression, chronic
• Guillain-Barre syndrome
• Muscle weakness paralysis on both sides of
  body, may affect breathing.
• May be related to auto-immune functioning.
• Goes away gradually within a few months.