Lesson 5: Neural Basis of Behavior pt. 1

Question 1

Ion channels

Answer 1

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

Question 2

Paramecium avoidance behavior

Answer 2

1. Contact with object triggers stretch-sensitive Ca2+
   channels to open at that location
2. Ca2+ enters the cell and triggers biochemical events
   that lead to reversal of the nearby cilia.
3. The reaction seems to flow along the length of the
   cell so that eventually all the cilia are reversed
4. After time, the Ca2+ channels close. The first cilia to
   reverse now resume forward motion, then the next
   ones and so on
5. 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

Question 3

Neurons and their operation: Terminology

Answer 3

1. Dendrites
2. Cell body
3. Axon
4. Axon terminal
5. Synaptic cleft
6. Membrane
   potential
7. Resting potential
8. Action potential

Question 4

information flow through neurons

Answer 4

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)

Question 5

membrane potential

Answer 5

• The membrane potential is the
  voltage difference between the
  inside and the outside of the cell.

Question 6

resting potential

Answer 6

The resting potential of a
neuron is the membrane
potential when the cell is at rest
(NOT sending a signal)

Question 7

action potential

Answer 7

The action potential describes
the changes in membrane
potential when a signal is being
produced

Question 8

action potential pt. 2

Answer 8

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

Question 9

CNS

Answer 9

the central nervous system
consisting of the brain and nerve
cord – instead of one brain, there
may be multiple ganglia (sing.
ganglion)

Question 10

PNS

Answer 10

The peripheral nervous system
consisting mostly of the outlying
sensory neurons (and sometimes
interneurons and other types of
neurons).

Question 11

3 basic kinds of neurons

Answer 11

sensory, interneuron, motorneuron

Question 12

sensory neuron

Answer 12

senses environmental features
and/or conveying info back to central nervous
system

Question 13

interneuron

Answer 13

receives information from one nerve cell and can excite or inhibit the next nerve
cell

Question 14

motorneuron

Answer 14

triggers muscle contraction

Question 15

locust flight

Answer 15

• Locust flight is powered by “indirect” flight muscles
• Locusts have two sets of wings arising from the thorax

Question 16

1.Use of a Command Center: Locust flight

Answer 16

the brain issues commands to
the wings to go up or down

Question 17

2.Response to Sensory Feedback: Locust flight

Answer 17

For example: sensors
in wings indicate “wings are up” causing the central nervous
to respond by signaling the flight muscles to lower the
wings

Question 18

Central Pattern Generator - Locust

Answer 18

: 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

Question 19

Locust flight: locust on a stick

Answer 19

• Testing flight control in locust using a rigid
  tether
• First, make the locust fly by removing platform
  beneath feet

Question 20

Test Command Center

Answer 20

idea by removing
brain (!?)

Question 21

Next, test requirement for sensory feedback by

Answer 21

removing sensory structures in the wings

Question 22

What’s Left

Answer 22

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

Question 23

Neural control of escape behavior in Tritonia

Answer 23

• 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

Question 24

more on neural control

Answer 24

Sensory info comes to the DRI
which processes all the info – if
enough excitatory info is received,
DRI fires an action potential

Question 25

Events in the Tritonia Central Pattern Generator

Answer 25

1 . Sensory info is processed by the DRI (dorsal ramp interneuron). DRI then excites the DSI.

2. DSI excites the DFN to trigger dorsal flexion AND inhibits the VSI to prevent ventral flexion
3. Simultaneously the DSI excites the C2 cell which fires synchronously with the DSI and then, after a short delay, excites the VSI
4. The VSI excites the VFN to trigger ventral flexion AND inhibits the DSI to prevent dorsal flexion
5. VSI also inhibits the C2 cell; this inhibition, coupled with the inhibition of the DSI, shuts
   down excitation of the VSI. Ventral flexion ends.
6. The DSI, released from inhibition, will jump above threshold and fire again, starting the next cycle.
7. Cycles repeat until the ion channels of the DSI “run down” and the DSI no longer jump above threshold.
8. 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

Question 26

Interpreting Sensory Input
A “Stimulus Filter”

Answer 26

allows the nervous
system to pay attention to
those features of the
environment that matter
most to the animal

Question 27

Interpreting Sensory Input:
Worm Detection in Toads

Answer 27

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

Question 28

More on Toad Experiment

Answer 28

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

Question 29

Information Flow from Visual field to Brain

Answer 29

inhibitory photoreceptor and exicitatory photoreceptor – ganglion cell – optic tectum of toad brain