1.
2.
3.
4.
Review List three body systems that work
together to create a response to a stimulus
Sequence What is the correct sequence of the
following in response to a stimuli: interneuron,
motor neuron, sensory neuron, muscle
Review What are two general ways in which
nervous systems differ among animal groups
Review Give an example of an animal with a very
simple sensory system and an example of one
with a complex sensory system
CH 28 ANIMAL SYSTEMS II
28.1 Response

Neurons
 Specialized
nerve cells in the nervous system
 Acquire information from their surroundings, interpret
that information, and then “decide” what to do about
it.
Detecting Stimuli

Stimulus
 Information
in the
environment that causes an
organism to react

Sensory neurons
 Specialized
stimuli.
cells that detect



Each type of sensory neuron responds to a
particular stimulus such as light, heat, or chemicals
Animals notice light, taste, odor, temperature,
sound, water, gravity, and pressure
Humans don’t notice very weak electric currents or
Earth’s magnetic field.
Interneurons

Process information and
determine how an
animal responds to
stimuli.

Number of interneurons and the ways those
interneurons process information, determine how
flexible and complex an animal’s behavior can be.

Some invertebrates have
very few interneurons and
are capable of only simple
responses to stimuli.

Vertebrates have more
highly developed nervous
systems with large numbers
of interneurons and are
capable of more-complex
behaviors.
Response



Specific reaction to a stimulus
Responses are directed by the nervous system
Responses are usually not carried out by nerve
cells.
Motor Neurons

Carry “directions” from
interneurons to muscles.
Invertebrate Nervous Systems

Range from simple collections of nerve cells to
complex organizations that include many
interneurons.
Nerve Nets


Simple nervous systems
Consist of neurons
connected into a netlike
arrangement with few
specializations.

Ganglia
 Interneurons are
grouped together and connect with
one another
 Largest ganglia typically located in the head region and
called cerebral ganglia.

Brain
 Further
organized cerebral ganglia.
Vertebrate Chordates


Show high degree of cephalization and have highly
developed nervous systems
Interneurons in brain are connected with each
other and with sensory neurons and motor
neurons in the head and elsewhere in the body.
Parts of the Vertebrate Brain
Cerebrum



“Thinking” region of the brain
Receives and interprets sensory information and
determines a response
Also involved in learning, memory, and conscious
thought.

Cerebellum
 Coordinates

movement and controls balance
Medulla oblongata
 Controls
functioning of many internal organs.

Optic lobes
 Involved

in vision
Olfactory bulbs
 Involved
in the sense of smell.

Vertebrate brains connected to rest of the body by
a spinal cord
 Thick
collection of nerves
 Runs through a tube in the vertebral column.

Brain evolution follows a trend of increasing size
and complexity from fishes, through amphibians
and reptiles, to birds and mammals.
Invertebrate Sense Organs

Detect light, sound, vibrations, movement, body
orientation, and chemicals in air or water.

Flatworms, for example, have simple eyespots that
detect only the presence and direction of light.

More-cephalized invertebrates have specialized
sensory tissues and well-developed sense organs
 Octopus
have complex eyes that detect motion and
color and form images
 Compound eyes of mosquitoes detect minute changes
in movement and color.
Chordate Sense Organs

Nonvertebrate chordates have few specialized
sense organs.

Most vertebrates have
highly evolved sense
organs
 Mammalian
ears have the
same basic parts, they
differ in ability to detect
sound.