Chapter 15: Sense Organs
PowerPoint by John McGill
Supplemental Notes by Beth Wyatt
I.
SENSORY RECEPTORS
(Receptors)


Distal Ends of
Dendrites of Afferent
Neurons
Located in Sense
Organs
SENSORY RECEPTORS
GENERAL FUNCTION
Receive Stimulus(Detect Change)
 Convert Stimulus to NI (NI Begins at
Receptors)
 The Nervous Impulse (NI) Is Carried Along
Afferent Neuron into CNS; Once in CNS the
Result May be



1) Sensation and/or
2) Reflex
SENSORY RECEPTORS
CHARACTERISTICS

1. SPECIALIZED


Each Receptor Responds Best to a Particular
Stimulus
2. EXHIBIT ADAPTATION


In Response to a Continuous Stimulus, Receptors
Becomes Less Sensitive ---> Conduct Fewer
NI ---> Perception of Sensation Decreases
Adaptation Time Varies with Receptor
SENSORY RECEPTORS
CLASSIFICATION


BASED STIMULUS TYPE
THAT ACTIVATES
RECEPTOR
1. MECHANORECEPTORS
(Pressoreceptors)


2. CHEMORECEPTORS


temperature
4. NOCICEPTORS


chemicals
3. THERMORECEPTORS


pressure
Pain (tissue damage)
5. PHOTORECEPTORS

light
SENSORY RECEPTORS
Mechanoreceptors



Pressoreceptors
Activated by a Stimulus That Deforms or Changes the
Position of the Receptor
Example: Pressure Receptors
SENSORY RECEPTORS
CHEMORECEPTORS


Activated by Chemicals
Example: Smell, Taste Receptors
SENSORY RECEPTORS
THERMORECEPTORS


Activated by Hot/Cold
Example: Hot, Cold Receptors in Skin
SENSORY RECEPTORS
NOCICEPTORS


Activated by Intense Stimulus That Causes Tissue Damage
Example: Pain Receptors
PAIN
SENSORY RECEPTORS
PHOTORECEPTORS


Activated by Light
Example: Vision Receptors
LOCATION & TYPES
Receptors Are Located in Sense Organs
 2 Kinds of Receptors



RECEPTORS RESPONSIBLE FOR GENERAL
(SOMATIC) SENSES
RECEPTORS RESPONSIBLE FOR SPECIAL
SENSES
FOUND IN SPECIAL SENSE ORGANS
 Nose, Tongue, Ears, Eyes

RECEPTORS RESPONSIBLE FOR
GENERAL (SOMATIC) SENSES

FOUND IN GENERAL SENSE ORGANS
 Skin,
Mucous Membranes, Connective
Tissues, Muscles, Tendons, Joints, Viscera
 TYPES (Based on Location)
EXTEROCEPTORS
 VISCEROCEPTORS
 PROPRIOCEPTORS (Special Type of
Visceroceptors)

GENERAL SENSE ORGANS:
EXTEROCEPTORS



Lie Close to the Body's
Surface (Skin, Mucous
Membranes,
Connective Tissues)
Respond to External
Stimuli
Responsible for Hot,
Cold, Pressure, Pain,
Touch
Thermoreceptor
GENERAL SENSE ORGANS:
VISCEROCEPTORS



Located Within the
Viscera
Respond to Internal
Stimuli
Responsible for
Sensations in
Organs: Hunger,
Nausea, Thirst, Pain
in Organs, etc.
RECEPTORS RESPONSIBLE
FOR GENERAL (SOMATIC)
SENSES



PROPRIOCEPTORS
(Special Type of
Visceroceptors)
Located in Muscles,
Tendons, and Joints
Responsible for
Kinesthesia
(Proprioception)
RECEPTORS RESPONSIBLE
FOR SPECIAL SENSES

FOUND IN SPECIAL
SENSE ORGANS


Nose, Tongue, Ears,
Eyes
TYPES




OLFACTORY
RECEPTORS
TASTE BUDS
HEARING/EQUILIBRIUM
RECEPTORS
VISION RECEPTORS
OLFACTORY RECEPTORS


Located Within
Nose
(Receptors for
Cr. Nerve I)
Responsible
for Smell
TASTE BUDS


Located on the
Surface of the
Tongue (Receptors
for Cr. Nerves VII
and IX)
Responsible for
Taste
HEARING/EQUILIBRIUM
RECEPTORS


Located Within Inner Ear (Receptors for Cr. Nerve VIII)
Responsible for Hearing and Equilibrium
VISION RECEPTORS


Located Within Eye
(Receptors for Cr.
Nerve II)
Responsible for
Vision
SENSE OF HEARING AND
BALANCE: THE EAR

STRUCTURE (3
Divisions)



EXTERNAL EAR
MIDDLE EAR
INNER EAR
EXTERNAL EAR

AURICLE
(PINNA)


Appendage
Attached to the
Side of the Head
EXTERNAL
AUDITORY
MEATUS (Ear
Canal)
MIDDLE EAR:
TYMPANIC MEMBRANE

Eardrum; Separates
External from Middle Ear
MIDDLE EAR:
TYMPANIC MEMBRANE

Eardrum;
Separates
External from
Middle Ear
http://www.entusa.com/eardrum_and_
middle_ear.htm
MIDDLE EAR:
AUDITORY BONES

MALLEUS, INCUS, STAPES (All Connected)
OPENINGS INTO
MIDDLE EAR


FROM EXTERNAL EAR: EXTERNAL AUDITORY MEATUS
COVERED BY TYMPANIC MEMBRANE
FROM INNER EAR



FROM EUSTACHIAN TUBE



a. OVAL WINDOW: STAPES FITS HERE (& COVERED BY
MEMBRANE)
b. ROUND WINDOW: COVERED BY MEMBRANE
Eustachian Tube: Direct Opening into Middle Ear from Throat
(Behind Nose)
Function: Equalizes Pressure in Middle Ear
FROM MASTOID SINUSES


Located in Mastoid Processes (Temporal Bones)
Also Direct Openings into Middle Ear
INNER EAR (LABYRINTH)



Inner Ear is Composed of
Bone (Bony Labyrinth) and
Membrane (Membranous
Labyrinth)
Membranous Labyrinth is
Located Within the Bony
Labyrinth
BONY LABYRINTH (3
Regions)
 VESTIBULE: Central
 COCHLEA: Snail’s Shell
 SEMICIRCULAR
CANALS: 3 Canals That
Lie At Right Angles to
One Another
MEMBRANOUS LABYRINTH:


Fits Inside Bony Labyrinth;
4 Regions

UTRICLE,SACCULE
(WITHIN VESTIBULE)


COCHLEAR DUCT
(WITHIN COCHLEA)


Contains Equilibrium
Receptors
Contains Hearing
Receptors
MEMBRANOUS
SEMICIRCULAR CANALS
(WITHIN SEMICIRCULAR
CANALS)

Also Contains Equilibrium
Receptors
FLUID


ENDOLYMPH: LOCATED WITHIN MEMBRANOUS LABYRINTH
PERILYMPH: LOCATED BETWEEN MEMBRANOUS AND BONY
LABYRINTH
FUNCTION

HEARING

Sound Waves Must
be Projected From the
External Environment
into the Cochlear Duct
of the Inner Ear
(Contains Hearing
Receptors)
PROJECTION OF
SOUND WAVES



1. AIR - EXTERNAL EAR
2. BONE - MIDDLE EAR
3. FLUID - INNER EAR






Vibration Creates Sound
Waves
As Sound Waves Pass
Through the External Ear,
They Travel Through Air,
as They Pass Through the
Middle Ear,
They Travel Through Bone,
and
as They Pass Through the
Inner Ear They Travel
Through Fluid
STIMULATION OF HEARING
RECEPTORS for CRANIAL NERVE VIII


Movement of the Fluid of the Inner Ear Stimulates the Hearing
Receptors in Cochlear Duct
Mechanoreceptors
CONDUCTION OF NERVE IMPULSES
http://hyperphysics.phyastr.gsu.edu/hbase/sound/anerv.html

(ALONG CRANIAL
NERVE VIII) TO
AUDITORY AREA OF
CEREBRAL CORTEX

Once the Hearing
Receptors are
Stimulated, Nerve
Impulses are
Conducted Along
Cranial Nerve VIII to the
Auditory Area of the
Cerebral Cortex for
Interpretation
EQUILIBRIUM

POSITION CHANGES
OF THE HEAD


The Stimulus for
Maintaining the Sense of
Equilibrium is Head
Position
Position Changes of the
Head Sets in Motion the
Fluid of the Inner Ear
EQUILIBRIUM: Utricle & Saccule

Equilibrium Receptors in Utricle, Saccule Most Important in
Static (Stationary) Equilibrium
EQUILIBRIUM: Semicircular Canals

Equilibrium Receptors in Membranous SC Canals
Most Important in Dynamic (Moving) Equilibrium
STIMULATION OF EQUILIBRIUM RECEPTORS
(RECEPTORS FOR CRANIAL NERVE VIII)

Movement of the Fluid of the Inner Ear Stimulates the
Equilibrium Receptors in Utricle, Saccule, and Membranous
Semicircular Canals (Mechanoreceptors)
CONDUCTION OF NERVE IMPULSES
(ALONG CRANIAL NERVE VIII) TO
CEREBELLUM AND SKELETAL MUSCLES

Once the Equilibrium
Receptors are Stimulated,
Nerve Impulses are
Conducted Along Cranial
Nerve VIII to the Cerebellum
(Equilibrium) and Skeletal
Muscles
VISION: THE EYE

STUCTURE

3 LAYERS OF
EYEBALL



SCLERA
CHOROID
RETINA
THE EYE: SCLERA
Outermost Layer
 Divided into 2
Portions


SCLERA PROPER:
POSTERIOR
PORTION
 White, Tough


CORNEA: ANTERIOR
PORTION

Transparent
THE EYE: CHOROID


Middle Layer
Divided into 2
Portions


CHOROID
PROPER:
POSTERIOR
PORTION
CILIARY BODY,
SUSPENSORY
LIGAMNETS, IRIS:
ANTERIOR
PORTION
THE EYE: CHOROID

CHOROID PROPER:



POSTERIOR PORTION
- Vascular
- Contains Black Pigment
THE EYE: CILIARY BODY, SUSPENSORY
LIGAMNETS, IRIS

Anterior Choroid Consists of 3
Structures

Ciliary Body



Suspensory Ligaments:


Thickened Portion of Choroid (Bt
Iris & Choroid Proper)
Contains Ciliary Muscles: Smooth
Muscle that Controls the Shape of
the Lens (Bulges Lens for Near
Vision)
Hold Lens in Place
Iris




Anteriormost Part of Choroid
(Behind Cornea)
Colored Portion of Eye
Shaped Like Doughnut (Hole in
Center is Pupil)
Consists of Smooth Muscle:
Controls Pupil Size
THE EYE: RETINA

Innermost Layer of Eye

INCOMPLETE (NO
ANTEROR PORTION);
THIN; NERVOUS TISSUE


Majority of Retina is
Neurons (3 Layers)
NEURONS (Listed in the
Order in Which They
Conduct NI)



PHOTORECEPTOR
NEURONS: RODS &
CONES
BIPOLAR NEURONS
GANGLIONIC NEURONS
THE EYE: RETINA

PHOTORECEPTOR
NEURONS: 1st Layer
Neurons

VISION RECEPTORS:
RODS & CONES


Distal Ends of These
Neurons Contain Vision
Receptors
(Photoreceptors)
2 Kinds Vision Receptors
Based on Shape


Rods: Responsible for
Night Vision
Cones: Responsible for
Day and Color Vision
THE EYE: RETINA
THE EYE: RETINA-MACULA

FOVEA CENTRALIS:
MACULA LUTEA

Macula Lutea:


Yellowish Area Approx. in
Center of Retina
Fovea Centralis


Depression in Center of
Macula
Contains Heaviest
Concentration of Cones so
Its the Area of Sharpest
Vision
THE EYE: BIPOLAR NEURONS

2nd Layer Neurons
THE EYE: GANGLIONIC
NEURONS






FORM OPTIC DISC/BLIND
SPOT
3rd Layer Neurons
Form Optic Disc (AKA Blind
Spot)
Optic Disc
Where All the Axons of the 3rd
Layer of Neurons Converge
(Then Emerge From Eyeball as
Optic Nerve)
AKA Blind Spot Because
Contains No Receptors, only
Axons
THE EYE: CAVITIES

ANTERIOR
CAVITY


Located in Front
of the Lens,
Subdivided into 2
Chambers
POSTERIOR
CAVITY

Located Behind
the Lens, Larger
THE EYE: HUMORS

AQUEOUS HUMOR:


Thin and Watery,
Located (and
Circulates) in Anterior
Cavity
VITREOUS HUMOR:

Thick and Jellylike,
Located in Posterior
Cavity, Helps Hold
Retina in Place

* Humors Maintain
Pressure Within
Eyeball to Prevent
Collapse
THE EYE: VITREOUS HUMOR
MUSCLES - Eye Has 2 Kinds


EXTRINSIC (External)
 SKELETAL
INTRINSIC (Internal)


Intrinsic Muscles are Part
of the Choroid Layer
SMOOTH
(INVOLUNTARY)
EYE MUSCLES: EXTRINSIC

External
Attached to Outer Surface of
Eyeball and Bones of Orbit

SKELETAL (VOLUNTARY)



Function in Voluntary Eye
Movements
NAMES (Total of 6/Eye)
 RECTUS MUSCLES
(4): SUPERIOR,
INFERIOR, MEDIAL,
LATERAL
 OBLIQUE MUSCLES
(2): SUPERIOR,
INFERIOR
EYE MUSCLES: EXTRINSIC
EYE MUSCLES: INTRINSIC


Internal
CHOROID COAT



Intrinsic Muscles are Part
of the Choroid Layer
SMOOTH
(INVOLUNTARY)
NAMES


IRIS: Controls Pupil
Size
CILIARY MUSCLES :
Bulges Lens for Near
Vision
EYE MUSCLES: IRIS
ACCESSORY (Assisting)
STRUCTURES


EYEBROWS AND
EYELASHES (Protection)
EYELIDS (CONJUNCTIVA)



Conjunctiva is MUCOUS
Membrane that Lines the
Eyelids and the Front Surface
of the Eyeball
Provides Protection
LACRIMAL APPARATUS


Series of Structures that
Secretes Tears and Drains
Them Across the Surface of
the Eye and into the Nose
Provides Moisture
EYE FUNCTION:
THE MECHANISM OF VISION

Vision Occurs in 3 Steps
1. FORMATION OF
RETINAL IMAGE
 2. STIMULATION OF
RECEPTORS
 3. CONDUCTION OF
NERVE IMPULSES TO
VISUAL CORTEX
(CEREBRAL
CORTEX)
http://wunmr.wustl.edu/EduD
ev/LabTutorials/Vision/Vision.
html


1
3
2
EYE FUNCTION:
THE MECHANISM OF VISION

FORMATION OF
RETINAL IMAGE



First an Image must be
Formed on the Retina
This Requires that Light
Rays be Focused on the
Retina
The Mechanism is
Different for Viewing Far
Objects as Opposed to
Viewing Near Objects
WHEN VIEWING FAR
OBJECTS: REFRACTION


Far Objects: Objects
20 Feet or Further
Formation of a
Retinal Image when
Viewing Far Objects
Requires Refraction
(Bending of Light
Rays)
WHEN VIEWING NEAR OBJECTS:
INCREASED REFRACTION REQUIRED

ACCOMMODATION


Near Objects: Objects
Closer than 20 Feet
Formation of a Retinal
Image when Viewing
Near Objects Requires
Increased Refraction
Which Requires
Accommodation
WHEN VIEWING NEAR OBJECTS:
INCREASED REFRACTION REQUIRED

ACCOMMODATION


Focusing near objects
Accommodation:
Changes that Allow for
Near Vision (3)



BULGING OF LENS
CONSTRICTION OF
PUPIL (NEAR REFLEX)
CONVERGENCE OF
EYES
Accommodation:
BULGING OF LENS


Ciliary Muscles
Contract, Lens
Bulges Forward
(Causes More Acute
Refraction)
Note:


Lense bulges
When object is
closer
Accommodation:
CONSTRICTION OF PUPIL



NEAR REFLEX
Iris Contracts, Pupil
Constricts (Limits the
Amount of Light that
Enters the Eye Since
More Acute Refraction
Must Occur)
Pupil Constriction when
Viewing Near Objects is
Known as the Near
Reflex
FAR OBJECT
NEAR OBJECT
Accommodation:
CONVERGENCE OF EYES

Movement of the 2
Eyeballs Inward
(Causes Light Rays
to Focus on Correct
Regions of the
Retina)
*Note: Reason for Accomodation



Light Rays Enter the
Eye More Divergent
when Viewing Near
Objects
as Opposed to
Parallel when Viewing
Far Objects
Means Light Rays
Must be More Acutely
Bent in Order to get
them Focused on the
Retina
STIMULATION OF RECEPTORS



RECEPTORS FOR
CRANIAL NERVE II
Once Light Rays are
Focused on the Retina
and the Image is
Formed
This Causes the Vision
Receptors
(Photoreceptors) to
Become Stimulated
and the NI Begins
STIMULATION OF RECEPTORS:
PHOTOPIGMENTS



Rods and Cones
Contain Photopigments
(Pigments that
Breakdown in Light)
The Photopigments in
Rods are Sensitive to
Dim Light
The Photopigments in
Cones are Sensitive to
Bright Light and Colors
(Red, Green, Blue)
Rhodopsin & Change in
Membrane Potential
CONDUCTION OF NERVE IMPULSES
TO VISUAL CORTEX (CEREBRAL CORTEX)



Nerve Impulses are
Conducted Along
Cranial Nerve II
to the Visual Cortex
of the Cerebral
Cortex for
Interpretation
http://wunmr.wustl.edu/EduD
ev/LabTutorials/Vision/Vision.
html