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

Neuron Structure and Function

The leaves of Mimosa pudica are touch responsive using pulvini (pressure-based movement) ©1996 Norton Presentation Maker, W. W. Norton & Company This stimulus (touch) causes an action potential!

©1996 Norton Presentation Maker, W. W. Norton & Company The neural network in a Hydra This system is not centralized and thus local stimulation gives mostly local response.

©1996 Norton Presentation Maker, W. W. Norton & Company 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

©1996 Norton Presentation Maker, W. W. Norton & Company In flatworms there is an evolutionary progression from: …a nerve net as in the hydra. …to a cephalized system with two major longitudinal nerves.

©1996 Norton Presentation Maker, W. W. Norton & Company The nerve system in round worms has less than 300 nerves, but a complex map with a centralized area and a large ventral nerve

©1996 Norton Presentation Maker, W. W. Norton & Company In earthworms, the two ganglia are dorsalized, but connect to the major ventral nerve cord. The first few segments have many sensory neurons The rest of the segments have individualized nerve connections

©1996 Norton Presentation Maker, W. W. Norton & Company This is the sea slug, Aplysia, a marine mollusc

©1996 Norton Presentation Maker, W. W. Norton & Company The morphology of a sea slug:

©1996 Norton Presentation Maker, W. W. Norton & Company The sea slugs gills are vulnerable to fish attack at the siphon:

©1996 Norton Presentation Maker, W. W. Norton & Company After the touch by the fish, the siphon is instantly withdrawn into the mantle:

©1996 Norton Presentation Maker, W. W. Norton & Company This cartoon shows the nerve system that operates in this touch response: 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.

©1996 Norton Presentation Maker, W. W. Norton & Company The squid giant neuron has been heavily studied:

©1996 Norton Presentation Maker, W. W. Norton & Company Insect larvae have double-ganglia in the anterior segments and a dual ventral nerve cord extending to the posterior segments

Insects have a ventral nerve cord is a double item with ganglia along its length. A large ganglion in the head segments serves as the brain.

©1996 Norton Presentation Maker, W. W. Norton & Company 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.

©1996 Norton Presentation Maker, W. W. Norton & Company 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

©1996 Norton Presentation Maker, W. W. Norton & Company 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

©1996 Norton Presentation Maker, W. W. Norton & Company Here is a SEM of a cell body in Aplysia with many synaptic connections:

©1996 Norton Presentation Maker, W. W. Norton & Company 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

©1996 Norton Presentation Maker, W. W. Norton & Company Here is the TEM of the synapse, corresponding with the cartoon:

©1996 Norton Presentation Maker, W. W. Norton & Company GABA sero- tonin acetyl choline Differential responses to inputs is explained by different transmitter substances being released

©1996 Norton Presentation Maker, W. W. Norton & Company In vertebrate neurons, the cell body is IN the information pathway:

©1996 Norton Presentation Maker, W. W. Norton & Company A motor neuron synapses on several muscle fibers (cells)

©1996 Norton Presentation Maker, W. W. Norton & Company

The neuro-muscular junction: Acetyl Choline presynaptic membrane postsynaptic membrane synaptic cleft vesicles containing acetyl choline exocytosis H 3 C-COO-CH 2 -CH 2 -N + (CH 3 ) 3 muscle cell responds with contraction

©1996 Norton Presentation Maker, W. W. Norton & Company A pectoral reflex arc:

©1996 Norton Presentation Maker, W. W. Norton & Company A pelvic reflex arc:

©1996 Norton Presentation Maker, W. W. Norton & Company Reflex arcs are connected to the CNS too: OUCH! (late!) The beauty of the reflex is that you take defensive action BEFORE it registers in your brain that you have a problem!

©1996 Norton Presentation Maker, W. W. Norton & Company Nor- epinephrine Fright Fight Flight Acetyl- choline Calming Autonomic Nerve System-self-naming system Operates without conscious thought Involves opposing nerve systems instead of opposing muscles HO- -CHOH-CH 2 -NH 2 H 3 C-COO-CH 2 -CH 2 -N + (CH 3 ) 3