PSYC 1100 Section 1.6 Neurophysiology, Neurochemistry and Drug Action

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PSYC 1100 Section 1.6 Neurophysiology, Neurochemistry and Drug Action
2013-10-12 16:55:35

Sec 1.6
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  1. Neurons are
    • - electrically active
    • - chemically active
  2. Neurons transduce (convert one type f a signal into another, one type of energy into another) information
    • sensory information
    • chemical/biochemical signals form other neurons
  3. Neurons also transmit information
    • - neurons are electrically active
    • - electrical impulses are generated in response to stimulation: firing an action potential
    • - chemical signals are sent to other neurons
  4. Resting Membrane Potential
    • at rest, inside of the nerve cell membrane is about
    • - 70 mV
    • relative to the outside
    • - stores charge like a capacitor
  5. Important Ions For Electrophysiology of Neurons
    • Anions
    • Cations
    • Na+
    • K+
    • CL-
    • Ca2+
  6. Forces that move Ions
    • 1. Movement along a chemical gradient (from area of high concentration to area of low concentration)
    • 2. Movement along an electrical gradient (feels like a charge repel, opposite charges attract)
  7. Membrane-Bound Proteins
    • Channels - pores that are open or close, allowing ions to pass through
    • Receptors - detect the presence of the neurotransmitters; transmitter binds to their receptors
    • Enzymes - biological catalysts that promote chemical reactions; they synthesize transmitters and intracellular signals as "second messangers"
    • Transport mechanisms - pump substances across the membrane; e.g. "Na pump" or "Na-K pump"
  8. Resting Membrane Potential
    • Why is it negative?
    • - Something positive(Na+) is actively pumped out
    • - the positive Na+ ions cannot get back in because Na+ channels are closed
    • -  this sets up an electromotive force for sodium; i.e. a 'sodium-powered batter' or capacitor
    • How does the neuron become excited?
    • -  anything that makes membrane more permeable to Na+ will 'discharge' the sodium powered battery
    • - excitation results from increase in Na+ influx into cell
    • - inside of cell moves in positive direction
  9. Electrical Activity of Neurons
    • EPSP - excitatory post synaptic potential; small, transient movement in the positive direction; "depolarization"; can vary in size
    • IPSP - inhibitory postsynaptic potential; small, transient movement in the negative direction; "hyperpolarization"; can vary in size
  10. Action Potential
    • very large, rapid change in positive direction, followed by return to baseline; neurons "fire", also known as a "spike"; action potential fires when voltage crossed the threshold
  11. Propagation of electrical Impulses
    • EPSPs and IPSPs are propagated in a graded and decremental fashion
    • graded - they vary in size, can be larger or smaller depending upon the size of the inputs
    • decremental - they are the largest at the point (i.e. synapse) of initials stimulation, and decrease in size as they move away from that point
    • Ex: EPSPs and IPSPs are like ripples on the surface of a pond
  12. Propagation of Action Potentials
    • Action potentials are not graded or decremental
    • Action Potentials...
    • - are ALL or NONE (either they fire or don't)
    • - remain the same size as they travel down the axon
  13. Examples of Mechanisms that produce EPSPs and IPSPs
    • Excitatory neurotransmitter: Glutamate
    • Inhibitory neurotransmitter: GABA
  14. Chemically Gated Channels
    • - linked to receptors
    • - detection of transmitter by receptor opens channel
    • EPSP: receptors detect glutamate, receptor linked to a positive-ion channel, Na+ goes into cell 
    • IPSP: receptors detect GABA, receptor linked to a negative-ion channel, Cl- goes into cell
  15. Mechanisms underlying Action Potential
    • - voltage shoots up in a positive direction (ascending limb) and then shoots down in a negative direction (descending limb)
    • - these effects are mediated by opening of voltage-gated channels
    • -ascending limb: voltage gated Na+ channels open, Na+ goes in
    • -descending limb: voltage gated K+ open, K+ goes out
  16. Information Processing by Neurons
    • Each neuron receives many excitatory and inhibitory inputs
    • These inputs are integrated (i.e. summed)
    • Over time - temporal summation
    • And space - spatial summation
    • If the integrated excitatory input crosses the threshold at any moment, an action potential is triggered
  17. Information Processing by Neurons
    • EPSPs and IPSPs are graded and decremental.
    • Action Potentials are not graded and not decremental.
    • Action potentials….
    • - are ALL OR NONE (they either fire, or they don’t)
    • - remain the same size as they travel down the axon
    • If they cannot vary in height to convey information, how can action potentials encode for information?
    • - They convey information by their pattern & frequency
  18. Chemical Transmission
    • Neurotransmitter release is triggered by:
    • -The action potential, when it reaches the terminal, opens
    • - voltage-gated Ca++ channel, and Ca flows into the terminal
  19. Examples of Neurotransmitters
    • Glutamate(Glu)
    • GABA
    • Dopamine(DA)
    • Serotonin(5-HT)
    • Norepinephrine(NE)
    • Acetylcholine(ACH)
    • Important neuro modulator: Adenosine

  20. Stages of Chemical Transmission
    • Synthsis - transmitter made by enzyme
    • Storage - stored in vesicles
    • Release - released from terminals
    • Post-synaptic Action - moves across aynapse, acts on receptors
    • Inactivation - by enzymes or uptake
  21. Drugs modify the Process of Chemical Transmission in the Nervous System
    • - Alter neurotransmitter synthesis
    • - block storage of transmitter
    • - stimulate or reduce release
    • - stimulate or block receptors
    • - block inactivation (enzymatic breakdown or uptake) of transmitter
  22. Antidepressant Drugs
    • Prozac
    • Zoloft
    • Block inactivation of serotonin(5-HT)
    • other antidepressants can have actions on other transmitters(NE)
  23. Antipsychotic Drugs
    • Haldol
    • Thorazine
    • Clozapine
    • - Block the receptors for dopamine(DA)
  24. Antianxiety Drugs
    • Valium
    • Librium
    • Xanax
    • - Facilitate the inhibitory actions of GABA on a type of GABA receptor (GABAa)
  25. Major Stimulant Drugs
    • Cocaine
    • Methamphetamine
    • Ritalin
    • - Block the inactivation of dopamine (DA), or stimulate release of DA; also act on NE and 5-HT
  26. Minor Stimulant Drugs
    • Caffeine
    • Theophylline (components of tea, coffee, energy drinks)
    • - Block adenosine receptors