Transcript Neuron - plant phys

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Biology:
life study of
What is Life?
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
Neuron
Structure and Function
©1996 Norton Presentation Maker, W. W. Norton & Company
The leaves of Mimosa pudica are touch responsive using
pulvini (pressure-based movement)
This stimulus (touch) causes an action potential!
This system is
not centralized
and thus local
stimulation
gives mostly
local response.
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The neural network in a Hydra
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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In flatworms there is an evolutionary progression from:
…to a
cephalized
system
with two
major
longitudinal
nerves.
…a
nerve
net as
in the
hydra.
©1996 Norton Presentation Maker, W. W. Norton & Company
©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
In earthworms, the two ganglia are dorsalized, but
connect to the major ventral nerve cord.
The first few
segments
have many
sensory
neurons
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The rest of the segments have
individualized nerve connections
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This is the sea slug, Aplysia, a marine mollusc
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The morphology of a sea slug:
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The sea slug’s gills are vulnerable to fish attack at the siphon:
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After the touch by the fish, the siphon is “instantly” withdrawn
into the mantle:
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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.
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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.
http://www.anselm.edu/homepage/jpitocch/genbios/33-33-InsectAnatomy-L.gif
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
The basic form of neurons (nerve cells):
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
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 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
The interneuron can receive inputs from many sensory or
other neurons.
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Here is a SEM of a cell body in Aplysia with many synaptic
connections:
These synaptic connections are indirect:
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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The electrical
stimulus travels
down the axon.
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Here is the TEM of the synapse, corresponding with the
cartoon:
serotonin
GABA
acetyl
choline
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Differential responses to inputs is explained by different
transmitter substances being released
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In vertebrate neurons, the cell body is IN the information pathway:
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A motor neuron synapses on several muscle fibers (cells)
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The neuro-muscular junction: Acetyl Choline
vesicles
containing
acetyl
choline
presynaptic
membrane
synaptic cleft
postsynaptic
membrane
muscle cell
responds
with
contraction
exocytosis
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H3C-COO-CH2-CH2-N+(CH3)3
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A pectoral reflex arc:
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A pelvic reflex arc:
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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!
Autonomic Nerve System-“self-naming” system
Norepinephrine
Acetylcholine
Fright
Calming
Fight
Flight
HOHO-
-CHOH-CH2-NH2
©1996 Norton Presentation Maker, W. W. Norton & Company
Operates without conscious thought
Involves opposing nerve systems instead of opposing muscles
H3C-COO-CH2-CH2-N+(CH3)3