Lesson 5: Neural Basis of Behavior pt. 1 Flashcards
Ion channels
Ion channels allow charged particles
(ions) to cross the lipid bilayer of the cell
membrane
An important point is that the channels
are not always open – they only allow
ions to pass under specific
circumstances
Paramecium avoidance behavior
- Contact with object triggers stretch-sensitive Ca2+
channels to open at that location - Ca2+ enters the cell and triggers biochemical events
that lead to reversal of the nearby cilia. - The reaction seems to flow along the length of the
cell so that eventually all the cilia are reversed - After time, the Ca2+ channels close. The first cilia to
reverse now resume forward motion, then the next
ones and so on - Because of the timing of reversal and recovery and
the shape of the cell itself, the cell is twisted to a new
path when it resumes forward swimming
Neurons and their operation: Terminology
- Dendrites
- Cell body
- Axon
- Axon terminal
- Synaptic cleft
- Membrane
potential - Resting potential
- Action potential
information flow through neurons
1 - dendrites (collect electrical signals)
2- cell body (integrates incoming signals and generates outgoing signal to axon)
3 - axon (passes electrical signals to dendrites of another cell or to an effector cell)
membrane potential
- The membrane potential is the
voltage difference between the
inside and the outside of the cell.
resting potential
The resting potential of a
neuron is the membrane
potential when the cell is at rest
(NOT sending a signal)
action potential
The action potential describes
the changes in membrane
potential when a signal is being
produced
action potential pt. 2
Is a means of signaling
electrically within the
nervous system
- Depends on opening &
closing of ion channels - Does not vary in size
within the same cell - Strength of stimulus
conveyed by frequency
of action potentials
CNS
the central nervous system
consisting of the brain and nerve
cord – instead of one brain, there
may be multiple ganglia (sing.
ganglion)
PNS
The peripheral nervous system
consisting mostly of the outlying
sensory neurons (and sometimes
interneurons and other types of
neurons).
3 basic kinds of neurons
sensory, interneuron, motorneuron
sensory neuron
senses environmental features
and/or conveying info back to central nervous
system
interneuron
receives information from one nerve cell and can excite or inhibit the next nerve
cell
motorneuron
triggers muscle contraction
locust flight
- Locust flight is powered by “indirect” flight muscles
- Locusts have two sets of wings arising from the thorax
1.Use of a Command Center: Locust flight
the brain issues commands to
the wings to go up or down
2.Response to Sensory Feedback: Locust flight
For example: sensors
in wings indicate “wings are up” causing the central nervous
to respond by signaling the flight muscles to lower the
wings
Central Pattern Generator - Locust
: A system in the central nervous system is turned on and produces the wing pattern without decision-making in the brain or input from the sensory system
Locust flight: locust on a stick
- Testing flight control in locust using a rigid
tether - First, make the locust fly by removing platform
beneath feet
Test Command Center
idea by removing
brain (!?)
Next, test requirement for sensory feedback by
removing sensory structures in the wings
What’s Left
Only the nervous structures in the thoracic ganglia – which must somehow turn the system on and keep it going. Which is the definition of a
central pattern generator
Neural control of escape behavior in Tritonia
- Brain consists of fused ganglia containing the cell bodies of neurons large enough to see with the naked eye.
- In addition, the neurons are identifiable between individuals.
- The brain is immobilized on a small
wax platform, but the body is
otherwise unrestrained, allowing
researchers to record from nerve
cells while the animal demonstrates
swimming behavior - Recordings from neurons that are active when Tritonia swims: the DFN are the dorsal flexion neurons and the VFN are ventral flexion neurons.
- These neurons are MOTORNEURONS that cause muscles of the body wall to contract. Note the alternate firing
more on neural control
Sensory info comes to the DRI
which processes all the info – if
enough excitatory info is received,
DRI fires an action potential
Events in the Tritonia Central Pattern Generator
1 . Sensory info is processed by the DRI (dorsal ramp interneuron). DRI then excites the DSI.
- DSI excites the DFN to trigger dorsal flexion AND inhibits the VSI to prevent ventral flexion
- Simultaneously the DSI excites the C2 cell which fires synchronously with the DSI and then, after a short delay, excites the VSI
- The VSI excites the VFN to trigger ventral flexion AND inhibits the DSI to prevent dorsal flexion
- VSI also inhibits the C2 cell; this inhibition, coupled with the inhibition of the DSI, shuts
down excitation of the VSI. Ventral flexion ends. - The DSI, released from inhibition, will jump above threshold and fire again, starting the next cycle.
- Cycles repeat until the ion channels of the DSI “run down” and the DSI no longer jump above threshold.
- The number of cycles depends on the initial stimuli processed by the DRI. If a lot of excitation reaches the DRI then the DRI will fire more action potentials which causes the DSI to stay near threshold longer
Interpreting Sensory Input
A “Stimulus Filter”
allows the nervous
system to pay attention to
those features of the
environment that matter
most to the animal
Interpreting Sensory Input:
Worm Detection in Toads
Toads are “sit-and-wait” predators
1. They wait until prey moves close
2. They turn to face the prey
3. and then they zap with their long
sticky tongues
More on Toad Experiment
In this experiment, toads
were presented with images
of different shapes and
sizes
Researchers measured the
rate of turning toward the
image as the image was
moved
In the graph at right,
“stimulus edge length”
indicates the length of the
longest edge
Information Flow from Visual field to Brain
inhibitory photoreceptor and exicitatory photoreceptor – ganglion cell – optic tectum of toad brain
