1. Central Nervous System + Neural Networks
The adult human brain has
~180 BILLION cells
~ 80 billion neurons
neurons have ~15,000 connections (synapses) EACH!

2. Do Now
Propose an analogy for understanding the complexity of the human mind/central nervous system
Draw that analogy

3. Neuron doctrine Billions of cells communicating across synapses
The brain is composed of separate, independent neurons
Information is transmitted from cell to cell across synapses

4. Neurons

5. Neuron Morphology Label the following: Afferent connection
Efferent connection
Axon (send)
Dendrites (receive)
Myelin sheath
Action potential
Terminal buttons (transform impulses to neurotransmitters and releases them)
Soma (cell body)

6. Neuron Variety
The shape and size indicates function

7. Neuron Action Potential
Action potential = change in permeability
Process (less than a millisecond)
Neuron “starts” at resting potential
Greater negative charge inside cell than outside
There are few positive charges in the cell
Guiding rule: concentration gradients
Ions from regions of high concentrations will flood areas of low concentration

8. Neuron Action Potential (II)
2. Electrical charge is generated until inside charge positive
This is the depolarization phase
Na+, K+ flood the cell
3. Positive charge forces potassium and sodium out
This is the repolarization phase
4. Tense unbalanced state restored
Absolute refractory period
Voltages gates closed for period
Potassium pump re-establishes equilibrium
Variables
Size of the neuron
Bigger = faster conductance
Thicker myelin sheaths = faster conductance

9. Action Potential (III): The Party Metaphor
A person is throwing a house party. At the beginning house is relatively empty with a couple of friends inside. A large group of positive friends, sodium and potassium, are waiting outside to come in. (Resting potential)
The doors open and people flood in (depolarization phase)
The house becomes too crowded. People are packed together and at once decide that it is much nicer outside of the house. Everyone rushes out. Its more empty than at the beginning. (refractory period)
Gradually some close friends of the owner enter through the back door and equilibrium is again establish (resting state)

10. Neuron Action Potential (IV)

11. Synaptic Transmission
Process
Action potential reaches terminal
Calcium ions enter, which causes vesicles to fuse with membrane
Transmitter molecules bind with receptors to open channels in the synapse
The IPSPs and EPSPs in postsynaptic cell spread to the axon hillock
EPSP - excite
Excitatory synapse
IPSP - inhibit
Inhibitory synapse
Synaptic transmitter inactivated by enzymes
Synaptic neurotransmitter is removed rapidly from the cleft by transporters

12. The Synapse Label Presynaptic neuron Postsynaptic neuron
axon
Postsynaptic neuron
Dendrites
Receptors
Neurotransmitters
Cleft
Vesicles

13. Neurotransmitters (keys)
Definition: a substance released by a presynaptic neuron that elicits an electrophysiological change in a postsynaptic neuron
Process
Indirect: through effecting the receptors on postsynaptic neuron
Regulates openness
GABA bonds and releases Cl (inhibitor)
Secondary: effects how neuron reacts to other stimuli
Alcohol
Direct: influences presynaptic neuron release
Regulates release or reuptake
Coffee
Adenosine and norepinephrine are released at the same time by the same neuron
Norepinephrine causes an excitatory reaction (increased action)
Adenosine effects release of NE (slows down release)
Caffeine blocks adenosine (NE continually released)

14. Neurotransmitters in specific
Types
Agonist: chemicals that bond to receptors and open channels
Antagonist: binds to ionotrophic channel and blocks other neurotransmitteres from attaching
Doesn’t close door but prevents opening
Examples of neurotransmitters:
acetylchoine (memory, muscle contraction)
Serotonin (arousal, sleep, pain, mood)
Dopamine (movement, attention, reward-seeking behavior)
GABA (inhibitory)

15. Neuromodulators
Neuromodulators effect the post-synaptic cell in long term ways
Effect responses to other neurotransmitter
Slow acting and can help explain changes in mood and learning

16. Neurons and the connections between them are always changing
Neurogenesis
New cells are created within the brain regularly
The debate around stem cells concerns their role in neurogenesis
Hebbian Synapse: neurons that fire together, wire together
Long-term Potentiation (LTP)
potentiation means strengthening
Strengthening of synapses
If prevent LTP, learning is severely limited
If drug is injected in fear learning pathway in amygdala
Prevented conditioning associations
If increase LTP through selective breeding of mice
Memory, spatial learning, conditioning and object recognition.

17. Review