psychological psychology
NA19811981
6.SynapticTransmission.pptCommunication between neurons
Recap
- Neuron membrane can be polarized
- Polarization due to number & flow of ions
- Resting Potential—negative inside cell
- Action Potential—sudden shift to positive inside cell
- Action potential flows down axon length
Discussion Question…
- According to the Oxford English Dictionary, there are over 250,000 words in the English language. What would happen to our communication if we only had 100 words? Could we still communicate?
The Synapse
Gap between:
- 2 neurons
- neuron and muscle
- neuron and gland
The Synapse
- Presynaptic neuron (A): releases neurotransmitter
- Postsynaptic neuron (B): receives NT at its receptor sites
Neurotransmitters
- Chemicals: Liquids or gases
- Influence the membrane of Neuron B:
- excite (depolarize)
- inhibit (hyperpolarize)
Neurotransmitters
- > 100 different types (see Table 2.2)
- > 1 NT released by a neuron
| Category: | Example Neurotransmitter: | Is involved with… |
| Amino Acids | Glutamate | Schizophrenia; Alcohol abuse |
| Monoamines | Serotonin | Depression; aggression |
| Dopamine | Pleasure experience; movement | |
| Peptides | Endorphins | Pain control |
| Gases | Nitric Oxide | Increase blood flow to brain areas |
| Acetylcholine | Acetylcholine | Stimulation of muscle fibers |
Neuron A
Synthesis of NTs occurs in:
- Cell body (then transported)
- Axon terminal button
Neuron A
Release– NT into synapse
Action Potential
☟
Ca++ ions enter Neuron A
☟
NT gets released
On Neuron B
NTs fit specific receptor sites (on dendrites/soma)
On Neuron B
NTs fit specific receptor sites
- Open ion channels (ionotropic receptors) or
- Start metabolic reactions (metabotropic receptors)
- >1 receptor type for a single NT
- Example: dopamine (D1, D2, D3, etc.)
On Neuron B
Neurotransmitters fit specific receptor sites
- Open ion channels or starts metabolic reactions in B
- >1 receptor type for a single NT
- Agonists—drugs which fit the receptor sites
- Antagonists—substances which bind and block the receptor sites
Excite or Inhibit?
- “If I could rearrange the alphabet, I would put U and I together.”
- “Baby, somebody better call God, cuz He’s missing an angel!”
- “I play the field, and it looks like I just hit a home run with you.”
- “Your eyes are blue, like the ocean. And baby, I’m lost at sea.”
- “Hey, baby, what’s your sign?”
Excite or Inhibit?
- “What’s a nice neuron like you doing in a brain like this?”
- “I’m new in town…could you give me directions to your dendrites?”
- “So, what does it feel like to be the most beautiful neuron in this brain?”
- “I bet there’s a great-looking axon under all that myelin!”
- “Hey, baby, how’s your action potential?”
Depolarization vs. Hyperpolarization
(of Neuron B)
Depolarization (EPSP):
- Neuron A delivers a good pick-up line
- Moves Neuron B toward excitation
- Less negative inside Neuron B
- Might produce action potential in B
Hyperpolarization (IPSP):
- Neuron A delivers a cheesy pick-up line
- Inhibiting effect on Neuron B
- More negative inside Neuron B
- Action potential less likely in B
Graded Potentials
- Small changes in voltage of Neuron B
*
Ex: horizontal cells of retina
Summation
Graded potentials can be summated to create an action potential in Neuron B:
- Temporal summation – repeated excitatory messages from Neuron A
- Spatial summation – multiple excitatory messages coming from Neuron A1, A2, A3, etc.
- http://www.sagepub.com/garrettbb2study/animations/2.18.htm
Summation
If both Inhibition and Excitation at same time:
- Strongest pattern wins
- Or cancel each other out
What happens to NTs after
they do their job?
- Released by Neuron B receptor sites
- Reuptake by Neuron A
- Metabolized (broken down)
- Inactivated
Hormones-- are neurotransmitters, too
