1. 6.5 – Neurones and Synapses

2. The human nervous system
A. CNS – central nervous system – brain and spinal cord
B. PNS – peripheral nervous system – composed of nerves
1. Nerves – bundles of neurons
2. Spinal nerves – 31 pairs from spinal cord
3. Cranial nerves – 12 pairs from brain stem

3. Neurons
A. Basic functional unit of nervous system
B. Can be sensory (take info to CNS), motor (take info away from CNS) or interneurons (within the CNS)

5. Neuron Impulses (non-myelinated axon)
A. “Electrical” impulses
B. Resting Potential – ready to receive and send an impulse, but not currently sending
1. Created by the Na+/K+ pump (ATP!)
2. 3 Na+ pumped out, 2 K+ in
3. Leads to a net negative charge inside (Polarized)

6. Depolarization – sending an impulse
Na+ channels open -> Na+ diffuses into cell
Increases the net charge inside the cell
Must reach threshold

7. Repolarization
1. Change of charge cause K+ channels to open so K+ diffuses out of cell
2. Lowers the net charge inside the cell
3. Na+/K+ pump returns ions to original positions
E. Neurons can only send an impulse from resting potential – cannot transmit 2 impulses at once!

9. Saltatory conduction
1. Impulses have to “jump” from one node of Ranvier to the next
2. Ion movement not necessary in myelinated areas
3. Increases speed of impulse and reduces energy expenditure

10. Synaptic Transmission
Communication between neurons (pre-synaptic and post- synaptic)
Neurotransmitters – chemical messengers

11. 1. Chemical messengers 2. Can be excitatory (cause depolarization of postsynaptic cell or inhibitory (cause hyperpolarization)

12. C. Neuron impulse reaches terminal buttons

13. D. Signal Termination 1. Enzymes break neurotransmitter into pieces, causing it to fall away from the receptor (ex. Acetylcholinesterase for Ach) 2. Pieces are reabsorbed by the presynaptic cell, reassembled, and repackaged in vesicles

14. E. Neonicotinoid insecticides
Chemically similar to nicotine
Binds to post-synaptic receptors, blocking acetylcholine and keeping sodium channels open
Stops action potential
Also, not broken down by acetylcholinesterase so receptor is permanently blocked
Paralyzes insects -> death