Sensory Pathways
and Sensations
• Humans can distinguish
among many different
types of internal and
external stimuli because
we have highly developed
sensory systems.
• Examples: the taste of
spoiled food, the pain of a
headache.
• Our sensory
systems translate
aspects of the
environment into
electrical signals
and transmit the
information to our
central nervous
system.
• The purpose of
sensations is to
enable the body to
respond
appropriately to
changing situations
in order to maintain
homeostasis.
Sensations follow very precise
pathways that have the
following parts:
1. Receptors - detect changes
and generate impulses
2. Sensory neurons – transmit
impulses from receptors to
the CNS, found in spinal
nerves and cranial nerves.
Sensations follow very
precise pathways that have
the following parts:
3. Sensory tracts – white
matter in the brain or spinal
cord that transmits impulses
to the brain.
4. Sensory area – areas in the
cerebral cortex that feel
and interpret the sensations.
Receptors:
*Sense Receptor – a
neuron that is
specialized to detect a
stimulus.
• There are many types,
classified by the type
of stimuli they
respond to.
Types of Sense Receptors:
• Photoreceptors – respond
to light
• Mechanoreceptors –
respond to movement,
pressure, and tension
Types of Sense Receptors:
• Pain receptors –
respond to tissue
damage.
• Chemoreceptors –
respond to chemicals
• Thermoreceptors –
respond to temperature
• Sensory
receptors are
found all over
the body, but
they are most
concentrated
in the sense
organs.
The Sense Organs
*Sense organ – an organ
that contains sensory
neurons which detect
external stimuli.
• The eyes, ears, nose,
tongue, and skin are
our sense organs.
• When a sense organ
receives the appropriate
stimulation, its sensory
receptors convert the
stimulus into an
electrical signal.
• This action potential goes to the
specific region of the brain
where it can be interpreted.
• The nose controls
your sense of smell
or olfaction.
• There may be a
thousand or more
basic scents.
• Chemicals in the
environment are
perceived by
olfactory
receptors in the
mucous
membranes of our
nasal passages.
• The molecules in the
air bind to these
specialized
chemoreceptors and
stimulate them to
send a signal
through the
ethmoid bone to the
olfactory bulbs.
• From there the
signal goes to
the olfactory
areas in the
temporal lobe of
the cerebral
cortex.
• Adaptation to odors
occurs quickly.
• Both pleasant and
unpleasant scents
may be very
distinct at first but
rapidly seem to
fade.