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General and Special Senses
Ch. 49
AP Biology
Ms. Haut
Classification of Sensory System
by structural Complexity

General Senses
– Nocioreceptors
– Thermoreceptors
– Mechanoreceptors
– Chemoreceptors

Special Senses
– Olfaction
– Vision
– Hearing
– Taste
– Equilibrium
Sensory Receptors



Gather information and
pass it on to the CNS.
Specialized cells or cell
processes monitoring
conditions in/outside
body
Specific for a certain
type of stimulus →
“receptor specificity”
Sensory Transduction



Sensory transduction
– Conversion by sensory
receptors of stimuli into
electrical signals.
Receptor potentials
– Changes in membrane
potentials caused by
sensory stimuli.
– Vary in intensity,
depending on the
strength of the
stimulus.
Receptor potential
transmitted to CNS
Sensory Integration


Receptor potentials are integrated through
summation
In sensory adaptation,
– Some sensory receptors become less
sensitive when they are stimulated
repeatedly.
– Make wearing clothing uncomfortable
without it
Complexity Range of Receptors
Free nerve
ending
Encapsulated
nerve ending
Specialized
receptor cells
Types of Sensory Receptors





Mechanoreceptors
Chemoreceptors
Electromagnetic receptors
Thermoreceptors
Nocioreceptors (pain receptors)
Sensory Receptors
– A section of human
skin

Reveals why the
surface of our body is
sensitive to such a
variety of stimuli.
Mechanoreceptors

Respond to physical distortion of cell membrane
(pressure, touch, stretch, motion, and sound)
–
Baroreceptors Sensitive to internal pressures:
blood pressure, lung stretch, digestive tract
tension
–
Proprioceptors monitors of muscle stretch
–
Tactile receptors - touch, pressure, vibration

Unencapsulated: free nerve endings, Merkels dics fine touch

Encapsulated: Meissners corpuscles - fine touch;
Pacinian corpuscles - deep pressure
Chemoreceptors

Respond to small
concentration changes
of specific molecules
(chemicals)

Internal chemoreceptors
monitor blood
composition (e.g. Na+,
pH, pCO2 )

Found within aortic and
carotid bodies

Very important for
homeostasis
http://ecc-book.com/assets/images/carotid_and_aortic_bodies.jpg
Electromagnetic Receptors





Detect various forms of electromagnetic
energy (visible light, electricity, magnetism)
Photoreceptors—detect visible light
Snakes have infrared receptors—detect body
heat
Some fishes use electroreceptors—locate
objects and prey
Birds, salmon, sea turtles use Earth’s
magnetic field for migration
Thermoreceptors

Respond to changes in temperature

In dermis, skeletal muscles, liver and
hypothalamus

Free nerve endings
– Cold receptors
– Warm receptors
http://lpc1.clpccd.cc.ca.us/lpc/zingg/anat/alecture/alect_stud/ach18_s.ppt
.

Respond to heat, mechanical
stress and chemicals associated
with tissue damage
– Most concentrated in skin
– Function is protection
against further tissue
damage
– Generally do not adapt to
continual stimuli.

Visceral Pain:
– Only visceral receptors that
produce sensations;
– Stretch receptors are
stimulated by pressure
and/or a decrease in oxygen
levels
– May feel as if its coming from
another area of the body =
referred pain.
http://lpc1.clpccd.cc.ca.us/lpc/zingg/ana
t/alecture/alect_stud/ach18_s.ppt.
Nocioreceptors (Pain Receptors)
http://lpc1.clpccd.cc.ca.us/lpc/zingg/anat/alecture/alect_stud
/ach18_s.ppt.
Pain Management


Prostaglandins increase pain by sensitizing
receptors
Aspirin and Ibuprofin reduce pain by inhibiting
prostaglandin synthesis
Special Senses
 Hearing
 Equilibrium
 Vision
 Olfaction
 Taste
Hearing

The ear is composed of three regions:
– The outer ear, the middle ear, and the inner
ear
Ear Structure and Function

http://www.lhsc.on.ca/cochlear/images/sound2.jpg
The outer ear
– Consists of the pinna
and the auditory
canal.
– Collects sound
waves and passes
them to the eardrum,
a sheet of tissue that
separates the outer
ear from the middle
ear.
Ear Structure and Function

http://www.hawkeyecollege.edu/faculty/cdostal/A&P%20Powerpoints/Spec
ial%20Senses.ppt#287,34,Slide 34
When sound waves
strike the eardrum,
– It vibrates and
passes the sound
waves to three small
bones.
Ear Structure and Function

http://www.hawkeyecollege.edu/faculty/cdostal/A&P%2
0Powerpoints/Special%20Senses.ppt#287,34,Slide 34
The inner ear
– Consists of fluid-filled
channels in the
bones of the skull.


http://lpc1.clpccd.cc.ca.us/lpc/zingg/anat/alecture/alect_stud/ac
h18_s.ppt.
Semicircular canals—
equilibrium
Cochlea—hearing
Organ of Corti

Actual hearing organ
– Is found within the cochlea.
– Consists of hair cells, the receptor cells of the
ear.
Hearing

When sound waves are collected by the outer ear,
– They are transmitted eventually to the cochlea.
– Hair cells in the organ of Corti bend, which
triggers nerve cells to send signals to the brain.
Auditory Pathway

Cochlear branch of
CN VIII

To inferior colliculus
of opposite side of
midbrain

To cochlear nucleus
of medulla

To thalamus

To auditory cortex

Louder sounds
– Cause greater movement of the hair cells
and more action potentials.
http://www.hawkeyecollege.edu/faculty/cdostal/A&P%20Powerpoints/Special%20Senses.ppt#287,34,Slide
34
Hearing Problems

Deafness, the loss of hearing, can be caused
by infections, injury, or overexposure to loud
noises.
– Conduction hearing loss
– Sensorineurial hearing loss
Conduction Hearing Loss

Caused by anything that interferes with the
transmission of sound from the outer to the inner ear.
– Middle ear infections (otitis media).
– Blockage of the outer ear, most commonly by wax.
– Otosclerosis—ossicles of the middle ear harden
and become less mobile.
– Damage to the ossicles, for example by serious
infection or head injury.
– Perforated eardrum, caused by an untreated ear
infection, head injury or a blow to the ear, or from
poking something in your ear.
Information from: http://www.deafness-and-hearingaids.net/2007/10/25/conductive-and-sensorineural-hearing-loss/
Sensorineural Hearing Loss

Due to damage to the pathway that sound impulses take from
the hair cells of the inner ear to the auditory nerve and the brain.
– Age-related hearing loss (presbyacusis). It’s partly due to the
loss of hair cells in the cochlea.
– Acoustic trauma (injury caused by loud noise) can damage
hair cells.
– Certain viral or bacterial infections such as mumps or
meningitis
– Certain drugs, such as some powerful antibiotics, can cause
permanent hearing loss.
– Acoustic neuroma. This is a benign tumor affecting the
auditory nerve. It needs to be observed and is sometimes
treated with surgery.
– Other neurological (affecting the brain or nervous system)
conditions such as multiple sclerosis, stroke, or a brain
tumor.
Information from: http://www.deafness-and-hearingaids.net/2007/10/25/conductive-and-sensorineural-hearing-loss/
Organs of Equilibrium
 Receptor cells are in two structures
 Vestibule
 Semicircular canals
Figure 8.16a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Organs of Equilibrium
 Equilibrium has two functional parts
 Static equilibrium – sense of gravity at rest
 Dynamic equilibrium – angular and rotary head
movements
Figure 8.16a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Equilibrium

http://www.mnstate.edu/rodenb/Human%20Biology/senses%20lec%20handout.pdf
Inner ear detects the
position of the body with
respect to gravity and
the motion of the body.
Vision
http://209.132.69.82/zbc_uploads/user_image1038344076qxg.jpg
– The human eyes
 Are able to detect a multitude of visual
stimuli.
Structure of the Human Eye
Function of the Structures

Sclera
– Is the outer
covering.

Cornea
– Lets light into
the eye and
also helps
focus light.
Function of the Structures


Iris
– Regulates the size of
the pupil, which lets
light into the interior
of the eye.
Lens
– Focuses light onto
the retina by
refracting light rays
and changing shape.
Function of the Structures

Two fluid-filled
chambers make up the
bulk of the eye.
– The large chamber is
filled with vitreous
humor.
– The small chamber
contains aqueous
humor.
Accomodation

Accomplished by
changing the curvature
of the lens
– For distant objects,
the lens needs to be
made flatter
– For near objects the
lens needs to be
made thicker and
more rounded
Seeing in Color

Built into the human retina
– Are two types of photoreceptors named for their
shapes.
http://www.hawkeyecollege.edu/faculty/cdostal/A&P%20Powerpoints/Special%20Senses
.ppt#269,14,Slide 14
Photoreceptors
http://www.medgadget.com/archives/img/retinal_layers.jpg

Cones
– Are stimulated by bright light and can distinguish color.
 3 types which distinguish red wavelengths, blue
wavelengths, and green wavelengths
– Contain visual pigments, photopsins, which absorb
bright light.
Photoreceptors

Rods
– Are extremely sensitive to light and enable us to
see in dim light, though only in shades of gray.
– Contain a visual pigment, rhodopsin, which can
absorb dim light.
Photoreceptors


The fovea contains a high concentration of cones and
is the retina’s center of focus.
Rods are concentrated in the peripheral regions
Visual Pathway

Optic chiasma - optic
nerves partially cross (right
side of the field of each eye
combining and going to the
lateral geniculate on the
right, those from the left to
the left)
Vision Problems and Corrections

Three of the most common visual problems
– Are nearsightedness, farsightedness, and
astigmatism.
– Result from focusing problems.
– Can be helped by corrective lenses or
surgical procedures.
Nearsightedness (myopia)

Occurs when the eyeball is longer than
normal.
Farsightedness (hyperopia)

Occurs when the eyeball is shorter than normal.


Blurred vision
caused by a
misshapen lens or
cornea.
Glasses and
contacts can be
used to correct
problem
http://www.optometrists.asn.au/freestyler/files/Astigmatism.gif
Astigmatism
Chemical Senses – Taste and Smell
 Both senses use chemoreceptors
 Stimulated by chemicals in solution
 Taste has four types of receptors
 Smell can differentiate a large range of
chemicals
 Both senses complement each other
and respond to many of the same
stimuli
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Olfaction – The Sense of Smell
 Olfactory receptors are in the roof of the
nasal cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for
detection
 Impulses are transmitted via the
olfactory nerve
 Interpretation of smells is made in the
cortex
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Olfaction – The Sense of Smell
Olfactory Pathways
Receptor neurons pass into cranium through cribiform
plate and synapse in olfactory bulbs.
Olfactory neurons are the only neurons known
1. to routinely replace themselves
2. to reach the cerebrum without synapsing in the
thalamus
Olfactory discrimination - Although difficult to describe,
the number of different odors recognizable is
immense.
The Sense of Taste
 Taste buds
house the
receptor
organs
 Location of
taste buds
 Most are on
the tongue
 Soft palate
 Cheeks
Figure 8.18a, b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Tongue and Taste
 The tongue is covered with projections
called papillae
 Filiform papillae – sharp with no taste buds
 Fungifiorm papillae – rounded with taste
buds
 Circumvallate papillae – large papillae with
taste buds
 Taste buds are found on the sides of
papillae
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Structure of Taste Buds

Gustatory cells are the
receptors
– Have gustatory hairs
(long microvilli)
– Hairs are stimulated
by chemicals
dissolved in saliva
http://www.lrn.org/Graphics/Senses/figure%208.8.gif
Taste Sensations
 Sweet receptors
 Sugars
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.41
Gustatory Pathway

Impulses are carried to
the gustatory complex
by several cranial
nerves because taste
buds are found in
different areas
– Facial nerve
– Glossopharyngeal
nerve
– Vagus nerve