1. Communication in the Nervous System Now that you know the structures of Neurons, let’s see how they actually do the talking.

2. Neuron’s chatting  Neurons don’t actually touch each other end to end  They are separated by a tiny space called the “synaptic cleft” where the axon terminal of one neuron nearly touches a dendrite or cell body of another.  Synapse= The site where transmission of a nerve impulse from one nerve cell to another occurs (includes the axon terminal, synaptic cleft, and receiver membrane =the dendrite or cell body)  An axon can have hundreds/thousands of terminals- could result in a ton of communication links

3. Development of Synapse *When we are Born- we don’t have many synapses formed… but they do form at a great rate afterwards. *Why? New learning and stimulating environments produce new neurons thus increasing synaptic complexity *When you don’t use it, you lose it! – Synaptic connections are “pruned away” (cells or their branches die and are not replaced) if they aren’t used. *Both pruning and increases in synaptic density are continued all throughout life! *Your brain is constantly modifying in response to info., challenges, and changes in the environment *this could explain why people with brain injuries have amazing recoveries!

4. The Neuron Language= Chemicals & the Electric Slide  When a nerve cell is stimulated, a change in electrical potential occurs between the inside and outside of the cell  There is a sudden inflow of +charged sodium ions on the cell membrane, followed by an outflow of +charged potassium ions.  As a result- there is a change in electrical voltage- called action potential – which produces an electric current or impulse.  If the axons are not myelinated, the axon will give rise to a new action potential like fire on a fuse to a firecracker.  Conduction under the myelin sheath is impossible (because the ions can’t pass through the membrane except at the nodes (breaks between the myelin’s “sausages”)  so the action potential hops between the nodes  This arrangement allows the impulse to travel faster than if the action potential had to be regenerated at each point along the axon. (babies don’t have fully developed myelin sheaths so the nerve impulses travel slower) Therefore, hopping is faster.

5. When the neural impulse reaches the Axon Terminal’s button-like lip:  It must get across the synaptic cleft to the other cell!  Synaptic vesicles, sacs on the tip of the terminal which open and release a few thousand molecules of a chemical substance called a neurotransmitter  Like sailors traveling from one island to another, the molecules can diffuse across the cleft

6. When the molecules make it to the other side  They bind briefly to the receptor sites (special molecules in the receiving neuron’s dendrites/cell body), fitting like a key to a lock  Reaction of the receiving neuron’s membrane is excitatory or inhibitory  Excitatory- voltage shift in the + direction =probability that the receiving neuron will “fire” (transmit a message to other neurons) increases  could become overwhelming, producing convulsions  Inhibitory- voltage shift in the – direction = probability the receiver will “fire” decreases  need this to sleep or coordinate our movements **The Neuron will then do whatever had the highest probability –not based on which is stronger, but on how many neurons are firing, what types are firing, where the neurons are- so basically how it all gets averaged out.

7. The Chemical Messengers  3 Main ones- Neurotransmitters, Endorphins, Hormones

8. Looking Deeper at the Chemicals  Neurotransmitters- the nature depends on the level of the neurotransmitter, its location, and type of receptor it binds with  Better known neurotransmitters-  Serotonin- affects neurons involved in sleep, appetite, sensory perception, temperature regulation, pain suppression, and mood  Dopamine- affects neurons involved in voluntary movement, learning, memory, emotion, pleasure/reward  Both at low levels are associated with severe depression and other mental disorders  Norepinephrine- affects neurons involved in increased heart rate and slowing of intestinal activity during stress, neurons involved in learning, memory dreaming, waking up, and emotion  GABA- functions as the major inhibitory neurotransmitter in the brain  abnormal levels of GABA are associated with sleep/eating disorders, and epilepsy  Glutamate- functions as the major excitatory neurotransmitter in the brain, released by about 90% of the brain’s neurons

9. Neurotransmitters cont.  UGH! It is tough pinning the relationship between neurotransmitter levels and behavioral/physical abnormalities  As you saw, neurotransmitters play multiple roles / some overlap!  Sometimes it is hard to tell if the abnormal neurotransmitter levels are causing disorders or are the result of them!  Drugs and food can effect the blocking or enhancing of neurotransmitters

10. Endorphins- the Brain’s natural opiates  Endorphins- reduce pain, promote pleasure, play a role in appetite, mood, learning, and memory.  Some function as neurotransmitters, but usually by altering the affects of neurotransmitters (limiting or prolonging effects of them)  Endorphin levels shoot up when an animal or person are under stress or afraid  Makes the pain bearable- gives us the evolutionary advantage!  Physical pain- may keep a soldier injured on the battle field, endorphins can be partially helpful to get them out of there!  Social contact- mother’s stimulates an infants’ endorphins which strengthens their bond/ also can explain the “falling in love” with somebody feeling

11. Hormones: long-distance messengers  Hormones are released directly into the bloodstream, which carries them to organs and cells that may be far away  Neurotransmitters and hormones are not always chemically distinct: they can be like two clubs that admit the same members  Melatonin- in the brain, promotes sleep and biological rhythms  Adrenal hormones- involved in emotion and stress, and also rise in response to heat, pain, injury, cold, burns, exercise, and some drugs (nicotine/caffeine)  The outer part boosts energy, the inner increases adrenaline  Prepares you for action!  Sex hormones- set puberty in motion for both sexes (testosterone vs. estrogen)