Transcript 6.5 – Neurones and Synapses

6.5 – Neurones and Synapses
I.
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
II. 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)
III. 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)
C. Depolarization – sending an impulse
1. Na+ channels open -> Na+ diffuses into cell
2. Increases the net charge inside the cell
3. Must reach threshold
D. 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!
F. 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
IV. Synaptic Transmission
A. Communication between neurons (pre-synaptic
and post-synaptic)
B. Neurotransmitters – chemical messengers
C. Neuron impulse reaches terminal buttons
D. Neonicotinoid insecticides
1. Chemically similar to nicotine
2. Binds to post-synaptic receptors, blocking
acetylcholine
3. Stops action potential
4. Also, not broken down by acetylcholinesterase so
receptor is permanently blocked
5. Paralyzes insects -> death