Sensory organs. Organ of smell
and taste
Sensory Function and Vision…
The General Senses…
• Sensory receptors
– specialized cells that monitor the environment
and relay information to the CNS.
– Free nerve endings are the simplest type:
they are the dendrites of sensory neurons
– Complex receptors (eyes) are housed in
organs
– Some receptors respond to only one kind of
stimulus
All sensory receptors send info to
the CNS via an action potential…
• At the CNS, info is routed according to the
stimulus and its location
• The stronger the stimulus, the higher the
frequency of action potentials
• Some receptors adapt, that is their
sensitivity to a stimulus is reduced if the
stimulus is continually applied (smell)
– The RAS can heighten or reduce awareness
of sensory information
General versus special senses…
• General sense receptors
included those for
temperature, pain,
pressure, touch, vibration
& proprioception (body
position)
• These receptors are very
simple in nature
“Special” senses
• Special senses
monitor vision,
hearing, olfaction,
gustation, and
equilibrium through
specialized sense
organs
• These sense organs
are highly specialized
“General sense” receptors…
• Are simple, found everywhere and are classified
by their stimulus:
• Nociceptors – sensitive to pain
• Thermoreceptors – respond to heat
• Mechanoreceptors–respond to touch/pressure
• Chemoreceptors – response to chemicals
• Only 1% of the info they provide ever reaches
the cerebral cortex (our consciousness)
Nociceptors/Pain receptors:
• found in joints, periosteum of bone and skin
• do not adapt!
• 2 types of axons carry the painful sensations:
– Fast pain sensations (localized, shooting pain) are
carried by myelinated axons
– Slow pain sensations (generalized, aching pain) are
carried by unmyelinated axons: it is difficult to pinpoint
the stimulus location
• Referred pain is the perception of pain coming
from a body area that is NOT stimulated:
– Pain originating in viscera is felt on body surfaces
Referred pain:
• For example, pain
produced by a heart
attack may feel as if it
is coming from the
arm because sensory
information from the
heart and the arm
converge on the
same nerve cells in
the spinal cord.
Thermoreceptors…
• Free nerve endings in skin, muscle, liver,
and hypothalamus
• they adapt quickly
• Cold receptors respond to temps <50
– 4X’s as numerous as warm receptors
• Warm receptors respond to temps >113
• Both are structurally identical
Mechanoreceptors…
• Membrane distortion opens mechanically
regulated ion channels to create impulses.
There are 3 classes:
– Tactile – respond to touch
– Baroreceptors – respond to pressure
– Proprioceptors – respond to changes in body
position
Tactile receptors…
• May be simple or complex,
superficial or deep, fine
(provide detailed information)
or crude (provide little
information)
• Merkel’s – fine touch and
pressure
• Pacinian – deep pressure
• Meissner’s – fine touch
and pressure in select
areas
• Ruffini – pressure or
distortion in deep dermal
layers
Baroreceptors are….
• stretch receptors that
monitor changes in
organ pressure in
distensible organs
• rapidly adapting
• Generate an AP from
their dendrites when
organs are stretched
or change position
• They monitor BP,
respiration, digestion,
and urinary control
Chemoreceptors…
Only respond to dissolved chemicals
• Rapidly adapting: found in olfaction, taste
& the CNS at:
– Medulla – receptors are sensitive to pH/CO2
changes in CSF– trigger respiratory
adjustments
– Aortic/Carotid bodies – sensitive to changes
in pH/CO2/O2 blood levels – trigger
adjustments in respiration and cardiovascular
activity
Proprioceptors….
• Monitor joint position & muscle contraction
• DO NOT ADAPT
• Structurally complex – are 2 types
– Tendon organs – monitor tendon strain
– Muscle spindles – monitor muscle length
• Most information from these receptors is
monitored subconsciously
• Are vital for normal skeletal motor function
Olfaction -The Sense of Smell
• Consists of paired olfactory organs made of
epithelium containing olfactory receptors,
supporting cells & stem cells
• the receptor cells are highly modified
neurons (chemoreceptors)
• Contains olfactory glands that produce a
multifunctional mucus
• Sensory Pathway:
olf.epithelium>olf.bulbs>olf.tracts>cortex
• http://www.bbc.co.uk/science/humanbody/bo
dy/factfiles/smell/smell_ani_f5.swf
The organs of taste & smell
C. Chain reaction involved in smelling:
–
Receiver =
–
–
–
Transformer =
–
–
–
nerve cells of olfactory membrane
They transform the odours into nerve impulses
Conductor =
–
–
–
Nose
It receives the stimuli which are odours
Olfactory nerve
It conducts nerve impulses from the olfactory membrane to
the olfactory bulb in the brain
Analyzer =
–
–
Brain
It analyses incoming nerve impulses from the olfactory nerve
I Olfactory
• Functions in the special sense of smell or olfaction.
The olfactory organs…
OLFACTORY SYSTEM
• Sensory receptors in the nasal mucosa are
stimulated by odors.
• These stimuli are detected by the olfactory bulb.
• Nervous impulses then travel through the
olfactory tract to terminate in the anterior
perforated substance.
• There are intimate connections with the
entorhinal cortex, amygdala, hippocampus and
other parts of the limbic system.
Gustation….taste
• http://www.bbc.co.uk/science/humanbody/body/f
actfiles/taste/taste_ani_f5.swf
• Taste buds are organs containing gustatory &
supporting cells that lie within papillae
• Chemicals contact taste hairs which change the
MP of taste cells & leads to an AP in the sensory
neuron
• 4 primary taste sensations – sweet, salt, sour,
bitter
• Sensory Pathway: sensory receptors>medulla>
thalamus>primary sensory cortex
The organs of taste & smell
Taste (the tongue):
• It is mainly composed of muscles
• It is covered with a mucous membrane
• Small nodules of tissue (papillae) cover the
upper surface of the tongue
• Between the papillae are the taste buds, which
provide the sense of taste.
–
–
In addition to taste, the tongue functions in moving
food to aid chewing and swallowing,
It is also important in speech.
The organs of taste & smell
•
Taste (tongue):
– Taste buds or papillae (location &
function):
•
Tongue is a muscular organ that contains most of
the body’s taste buds
– Conditions needed for tastes to be
perceived:
•
•
•
Be in solution in the saliva
Contain a sufficient number of flavourful
molecules
Come into contact with the papillae (taste buds)
C. Chain reaction involved in taste:
– Receiver =
– Tongue
– Receives the stimuli which is tastes
– Transformer =
– Taste buds
– Transforms tastes into nerve impulses
– Conductor =
– Gustatory nerve
– Conducts nerve impulses to the taste center of the brain
– Analyzer =
– Brain
– Analyzed incoming nerve impulses from the gustatory
nerve
D. 4 basic taste sensations:
Salty, Sweet, Sour, Bitter
Tongue to label
Tongue to label