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3. Biology: What is Life? life study of Properties of Life
Cellular Structure: the unit of life, one or many
Metabolism: photosynthesis, respiration, fermentation, digestion, gas exchange, secretion, excretion, circulation--processing materials and energy
Growth: cell enlargement, cell number
Movement: intracellular, movement, locomotion
Reproduction: avoid extinction at death
Behavior: short term response to stimuli
Evolution: long term adaptation

4. Structure and Function
Neuron
Structure and Function

5. This stimulus (touch) causes an action potential!
The leaves of Mimosa pudica are touch responsive using pulvini (pressure-based movement)
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This stimulus (touch) causes an action potential!

6. The neural network in a Hydra
This system is not centralized and thus local stimulation gives mostly local response.
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7. A slightly more centralized nerve system in jellyfish:
Neural ring around opening of medusa is the “central” system for coordinating swimming motions
Peripheral nerves connect to cnidoblast, so when a nematocyst is fired, a signal goes back to the nerves in the mouth to direct it to potential prey
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8. In flatworms there is an evolutionary progression from:
…to a cephalized system with two major longitudinal nerves.
…a nerve net as in the hydra.
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9. The nerve system in round worms has less than 300 nerves, but a complex map with a centralized area and a large ventral nerve
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10. In earthworms, the two ganglia are dorsalized, but connect to the major ventral nerve cord.
The rest of the segments have individualized nerve connections
The first few segments have many sensory neurons
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11. This is the sea slug, Aplysia, a marine mollusc
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12. The morphology of a sea slug:
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13. The sea slug’s gills are vulnerable to fish attack at the siphon:
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14. After the touch by the fish, the siphon is “instantly” withdrawn into the mantle:
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15. This cartoon shows the nerve system that operates in this touch response:
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Sensory nerves connect sensors to motor neurons at the ventral nerve cord…with sufficient signal, the motor neurons fire, muscles contract and the siphon and gills are withdrawn.

16. The squid giant neuron has been heavily studied:
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17. Insect larvae have double-ganglia in the anterior segments and a dual ventral nerve cord extending to the posterior segments
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18. Insects have the open circulation system found in chitons, etc.
The segmentation is not too far from the annelids.
Much of the internal system is similar to molluscs.
The major difference: spiracles on abdominal segments lead to tracheal tubes inside for gas exchange.
The ventral nerve cord is a double item with ganglia along its length. A large ganglion in the head segments serves as the brain.

19. The basic form of neurons (nerve cells):
These are invertebrate neurons.
You can tell because the cell body is outside the path of electrical flow from dendrite to axonic synapse.
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20. In a simple system, many sensory neurons receive touch information
In a simple system, many sensory neurons receive touch information. Some send “I am touched” signals, others are sending “I am not touched” signals.
The interneuron receives the conflicting information and, with sufficient positive inputs,responds by sending a signal to the target motor neuron
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21. The interneuron can receive inputs from many sensory or other neurons.
The sensory synaptic terminals can connect with the dendrites or the cell body of the interneuron.
Again, when sufficient information exceeds a threshold, the interneuron sends a signal down its axon
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22. Here is a SEM of a cell body in Aplysia with many synaptic connections:
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23. These synaptic connections are indirect:
The electrical stimulus travels down the axon.
The synaptic vesicles release transmitter substances across the synaptic cleft.
Receptors in the post-synaptic cell membrane receive the transmitters and respond…
…if a nerve cell, by sending an electrical action potential down the cell
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24. Here is the TEM of the synapse, corresponding with the cartoon:
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25. Differential responses to inputs is explained by different transmitter substances being released
sero-tonin
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GABA
acetyl choline

26. In vertebrate neurons, the cell body is IN the information pathway:
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27. A motor neuron synapses on several muscle fibers (cells)
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28. ©1996 Norton Presentation Maker, W. W. Norton & Company

29. The neuro-muscular junction: Acetyl Choline
H3C-COO-CH2-CH2-N+(CH3)3
vesicles containing acetyl choline
presynaptic membrane
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exocytosis
synaptic cleft
postsynaptic membrane
muscle cell responds with contraction

30. A pectoral reflex arc:
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31. A pelvic reflex arc:
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32. Reflex arcs are connected to the CNS too: OUCH! (late!)
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The beauty of the reflex is that you take defensive action BEFORE it registers in your brain that you have a problem!

33. Autonomic Nerve System-“self-naming” system
Operates without conscious thought
Involves opposing nerve systems instead of opposing muscles
Nor-epinephrine
Fright
Fight
Flight
Acetyl-choline
Calming
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HO-
-CHOH-CH2-NH2
H3C-COO-CH2-CH2-N+(CH3)3