Lesson 6: Neural Basis of Behavior, pt. 2 Flashcards
Bat Detection by Noctuid Moths
Why sometimes the
moth dives and
other times simply
gets out of the way
Noctuid moth ears
The ear of the moth consists of a thin tympanum that
vibrates in response to sound. There are two nerve cells:
A1 and A2
Sensory neurons in ear signal to the flight muscles and brain
There are two paths that
information can follow:
- A reflex path goes from the
ear to the flight muscles,
bypassing the brain - A path to the brain via
interneurons in the thoracic
ganglia along the nerve
cord
A1 and A2 receptor cells respond to the same
sounds differently
Habituation in the A1 cell allows
stimulus filtering of background sound
Measuring a moth’s detection distance
Set up for measuring
how close a bat can
get before the moth
detects it – the
detection distance
A1 starts responding
in the orange range,
and A2 starts
responding in the red
range
An evolutionary arms race: ’quiet’ bats
Top: Detection
distance for ‘quiet’
bat by a noctuid
moth
Bottom: Detection
distance for typical
bat
Habituation
an animal becomes accustomed to
a stimulus and its reaction to the stimulus
becomes reduced or even eliminated
Sensitization
an animal’s response to a
stimulus becomes extreme after some sort of
negative event
Fun with
Synapses!
1.When an action potential
arrives at the axon terminal,
Na+ enters the area and the
area becomes positive.
2.The positive effect of the
action potential causes
voltage-sensitive Ca2+
channels to open and Ca2+
rushes into the area
- The entry of Ca2+ causes
the synaptic vesicles
containing
neurotransmitter to fuse
with the cell membrane
and dump neurotransmitter
into the synaptic cleft - The neurotransmitter binds
to receptors on the surface
of the postsynaptic cell and
causes ion channels to - In an EXCITATORY
synapse, the
neurotransmitter causes
POSITIVE ions (e.g., Na+)
to enter the “postsynaptic
cell” and creates an EPSP
(excitatory postsynaptic
potential) - If the “presynaptic cell”
fires enough action
potentials fast enough,
then new EPSPs will arrive
before the previous one
has subsided and the post
synaptic cell will reach
threshold and produce its
own action potentials
In an INHIBITORY synapse,
the neurotransmitter causes
POSITIVE ions (e.g., K+) to
leave the “postsynaptic cell”
(or sometimes NEGATIVE
ions enter) and creates an
IPSP (inhibitory postsynaptic
potential) that takes the
postsynaptic cell away from
threshold.
How Habituation Works
If touch the siphon one time, the
animal will show a gill
withdrawal reflex.
If you touch it again, it will show
the reflex again.
But, if you touch it repeatedly,
then, after several touches, the
animal seems to start ignoring
you and the reflex will not
happen. This works as long as
your touch is harmless
– short term response
Testing How Habituation Works
The basic approach
was to 1) stimulate and
2) record electrical
activity from the
different cells in the
circuit under different
conditions
Could the muscles just be
fatigued so that they don’t
respond to stimulation?
No, if stimulate with an
electrode to create a
artificial signal, the muscles
contract just fine
Do the nerve cells all
function during the
stimulation:
Sensory cell: Yes, fires
action potentials when
siphon touched
Do the nerve cells all function
during the stimulation:
The Interneuron and
Motorneuron do not fire
action potentials:
Are they fatigued? NO – if
stimulate with an electrode
they still show the ability to
fire action potentials
So, the muscles,
Interneuron and
Motorneuron all work – but
they don’t do anything in
the habituated animal:
The Sensory cell does fire
action potentials in
response to the signal but
the signal does not reach
the Motorneuron or
Interneuron
That results say the
synapses are not
working
So there is a Loss of Ca++
going in which causes…
No neurotransmitter release
No signal received by
motorneuron
No signal sent to muscles so
no gill withdrawal
If touch the siphon and
simultaneously pinch the
animal,
the animal will become
sensitized to a touch on the
siphon.
So the next time the siphon is
touched, the animal will seem
to overreact by producing a
super-strong and super-long
contraction
