Chapter 6 - Nerve Cells and Behavior

Question 1

neurons

Answer 1

transmit electrical signals called action potentials.
Information is encoded in those electrical signals as they
move around the nervous system

Question 1

What has the nervous stem evolved to do

Answer 1

a) detect
relevant events in the environment,
b) determine
appropriate responses to those events
c) coordinate those responses.

Question 2

neurotransmitters

Answer 2

Electrical signals are passed from neuron to neuron
through the release of chemicals called
neurotransmitters. Neurotransmitters may be either
excitatory or inhibitory. The junction of two neurons is
called synapse.

Question 3

3 functional nervous system parts

Answer 3

Sensory, Central, Motor

Question 4

Sensory nervous system

Answer 4

detects sensory
information and sends that information to the central
nervous system for processing. Neurons are called
sensory (or afferent) neurons.

Question 5

Central nervous system

Answer 5

processes sensory
information and makes decisions about appropriate
responses. Neurons are called interneurons.

Question 6

Motor nervous system

Answer 6

carries information from the
central nervous system to target tissues, such as
muscles or glands, to cause a response. Neurons are
called motor (efferent) neurons.

Question 7

Example Escape Behavior of
Cockroaches

Answer 7

Cockroaches have numerous hairlike
receptors that are sensitive to wind. These
receptors are located on two posterior
appendages called cerci.
At the base of each of the hairs on the cerci is a
single sensory neuron that relays wind-related
information to the central nervous system.
* The sensory neuron synapses with an
interneuron (called a giant interneuron in this
case).
* Before reaching the head, this giant interneuron
synapses with another interneuron in the
thoracic area, which then connects with motor
neurons that relay signals to the hind leg
muscles.
There are many sensory hairs on each
cercus. Each hair responds differently
from wind from different directions.
Therefore, the pattern of information from
the sensory neurons encodes information
about the direction of the wind.
However, it does not always just run
directly in the opposite direction. If this
were the case, predators might be able to
predict where their movements. Instead,
the cockroach escapes unpredictably
along a handful of preferred directions.
The job of the sensory nervous system is
not to transmit all available information but
to pass along only that information that is
relevant and useful.
* Therefore, it must filter out non-useful
information while being tuned in to
biologically relevant stimuli.

Question 8

Escape
Responses of
Noctuid Moths

Answer 8

When the bat’s echolocation pulses are
soft, indicating that the bat is still far away,
moths will turn and fly directly away. Loud
pulses cause the moths to fly in
unpredictable loops and fold their wings so
they drop in the air.
A1 cell - Bat is far
A2 cell - Bat is close

Question 9

Processing in the Central
Nervous System

Answer 9

In the case of reflexes (cockroach example), the
“processing” is little more than routing of
electrical signals from the incoming sensory
neurons to the outgoing motor neurons.
* More complicated sensory input (vision, creation
of auditory maps by owls, etc.) requires analysis
of incoming sensory input and a determination of
how to respond, if at all.
Processing is also involved when we
learn. We have to determine what
information is important, and then we have
to store that information. (We also have to
retrieve it later when needed.)
* Learning requires the formation of
memories. Memories can be described as
short-term, intermediate-term, or long-term
memories.

Question 10

Prey Localization by Barn Owls

Answer 10

For the horizontal plane, they use time
differences in the arrival of sound to each
ear.
For the vertical plane, they use differences
of intensities between the two ears. The
differences in intensities in the two ears
vary with the elevation of the sound
primarily because of the arrangement of
the ear canals and facial feathers.
Information on the timing and loudness of sounds in
each ear is sent via the auditory nerve to areas in
the brain known as the cochlear nuclei.
Two cochlear nuclei: magnocellular nucleus and
angular nucleus. Timing information is sent to the
magnocellular n., while intensity information is sent
to the angular n.
These nuclei process the information independently
and then transmit to higher processing centers in
the inferior colliculus, where a map of auditory space
is formed.

Question 11

Intermediate-term Learning in Aplysia
(Sea Hare)

Answer 11

• Sea hares move along the ocean floor
  eating seaweed, with their siphons
  extended and their gills spread open. The
  gills are partially covered by the mantle.
• When the siphon is touched, the gills,
  siphon, and mantle all withdraw into the
  mantle cavity. This is called the gill-
  withdrawal reflex. The gill-withdrawal reflex can be modified with
  learning.

Question 12

Habituation

Answer 12

Learns not to respond to harmless
stimuli

Question 13

Why does habituation occur?

Answer 13

Not due to a decreased electrical response in sensory
neurons.
– Is due to a decrease in amount of neurotransmitter
released from sensory neurons onto motor neurons
(or onto excitatory interneurons that then connect with
the motor neurons).

Question 14

Sensitization

Answer 14

Reflex becomes stronger when a
stimulus that causes withdrawal is preceded by a
strong noxious stimulus (e.g. an electrical shock).
* In this case, sensory neurons from the head or body
(not the siphon) stimulate facilitating interneurons.
These facilitating interneurons release the
neurotransmitter serotonin onto the sensory neurons
from the siphon, which causes them to release more
of their own neurotransmitter. This leads to stronger
signals in the motor neurons, and therefore a
stronger gill-withdrawal response.

Question 15

Song Learning in Birds

Answer 15

Brain changes during learning may include
the birth of new neurons (neurogenesis)
and/or the death of old ones.

Question 16

Locust Flight

Answer 16

Locusts have two pairs of wings. The
wings move up and down about 20 times
per second. The two pairs of wings do not
move synchronously. The hind wings lead
the forewings.
* Two sets of muscles control each wing.
The elevator muscles raise the wings,
while the depressor muscles lower the
wings.
Locusts can be studied while tethered in place,
and tiny electrodes can be placed into the
muscles.
* These studies show that the depressors are
activated when the wings are up, and the
elevators are activated when the wings are
down.
* The timing of the activation of these muscles,
which is controlled by the central nervous
system, is critical.
There are two general hypotheses for the neural
basis of rhythmic behavior (like locust flight).
* The Peripheral-Control Hypotheses states that
each movement stimulates sensory receptors,
which in turn trigger the next movement in the
sequence. The second movement then triggers
sensory receptors that trigger the first
movement. Sensory feedback is necessary for
this hypothesis.
There are mechanoreceptors on the wings of
locusts that send information about wing position
to the central nervous system.
* Studies have shown that when this sensory
information is blocked, the wings still function
rhythmically.
* This indicates that the basic flight pattern of
locusts is not dependent on sensory information
but is generated in the central nervous system
via a central pattern generator.

Question 17

The Central Pattern Generator hypothesis

Answer 17

states that a neuron or network of neurons
within the central nervous system is
capable of generating patterned activity in
motor neurons, even in the absence of
sensory input