The document summarizes the special senses and their receptors. It discusses how different sensory receptors transduce various forms of energy into nerve impulses. It classifies receptors according to the type of signal they transduce, such as chemoreceptors, photoreceptors, thermoreceptors, and mechanoreceptors. It specifically describes nociceptors, which sense pain when tissues are damaged. The document also discusses the ears and hearing, covering the vestibular apparatus, which provides a sense of equilibrium, and the anatomy of the middle and inner ear.

1. SPECIAL SENSES
Last revised: 12/7/2011

2. The Senses
 Sensory receptors transduce different forms of energy
in the ―real world‖ into nerve impulses.
 Different sensory perceptions (sound, light, pressure)
arise from differences in neural pathways.
 If the optic nerve delivers an impulse, the brain interprets it as
light.

3. Functional Categories of Sensory Receptors
 Receptors can be classified according to the type of
signal they transduce:
 Chemoreceptors – sense chemicals in the environment
 Taste, smell, or blood
 Photoreceptors – sense light
 Thermoreceptors – respond to cold or heat
 Mechanoreceptors – stimulated by mechanical deformation of the
receptor.
 Touch
 Hearing
 Nociceptors – sense pain; damaged tissue release chemicals that
excite sensory endings

4. Nociceptors
 Pain receptors that depolarize when tissues are damaged.
 Stimuli can include heat, cold, pressure, or chemicals
 Glutamate and substance P are the main neurotransmitters.
 May be activated by chemicals released by damaged tissues,
such as ATP.
 Perception of pain can be enchanced by emotions and
expectations
 Pain reduction depends on endogenous opioids.
 Nociceptors can be myelinated or unmyelinated
 Sudden, sharp pain is transmitted by myelinated
neurons.
 Dull, persistent pain in transmitted by unmyelinated
neurons.

5. Tonic and Phasic Receptors
 Receptors can be categorized based on
how they respond to a stimulus.
 Phasic: respond with a burst of activity when
a stimulus is first applied but quickly decrease
their firing rate—adapt to the stimulus—if the
stimulus is maintained. (fast-adapting)
 Alerts us to changes in the environment
 Allow sensory adaptation
 Smell, touch, temperature
 Tonic: maintain a high firing rate as long as
the stimulus is applied. (slow-adapting)

6. Cutaneous Receptors
 Pain, cold, and heat receptors are naked
dendrites
 Cold receptors – located close to epidermis
 Warm receptors – located deeper in the dermis.
 Hot receptors – pain experienced by a hot stimulus is
sensed by a special nociceptor called a capsaicin
receptor.
 Touch and pressure receptors have special
structures around their dendrites.
 Meissner’s corpuscles
 Encapsulated dendrites in connective tissue
 Changes in texture and slow vibration
 Pacinian corpuscles
 Encapsulated dendrites by concentric lamellae of
connective tissue structures
 Deep pressure and fast vibrations
 Ruffini endings
 Sustained pressure
 Enlarged dendritic endings with open, elongated
capsule
 Merkel’s discs
 Expanded dendritic endings
 Sustained touch and pressure
 Slow adapting

7. Two-Point Threshold Test
 Measures the density of touch receptors
 The minimum distance at which two points of contact
can be felt.
High density of receptive fields =
shorter minimum distance
Low density of receptive fields =
longer minimum distance

8. The Ears
HEARING AND EQUILIBRIUM

9. Vestibular Apparatus
 Provides a sense of equilibrium
 Located in the inner ear
 Consists of:
 Otolith organs
 Linear acceleration
 Utricle (horizontal)
 Saccule (vertical)
 Semicircular canals
 Rotational acceleration
 Both structures in the vestibular
apparatus are:
 Filled with endolymph
 Contain sensory hair cells which
are activated by bending.

10. Sensory Hair Cells

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Hairs of
hair cells bend
Gelatinous
Otoliths material sags
Macula
of utricle
Hair cells
Sensory nerve fiber Supporting cells Gravitational
force
(a) Head upright (b) Head bent forward

12. Semicircular Canals
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endolymph
Semicircular canal
(a) Head in still position Ampulla
Cupula Crista
ampullaris Crista ampullaris
Hairs
Hair cell
Supporting cells
Sensory (afferent)
nerve fibers
(b) Head rotating (c)
12

13. Clinical Applications
Nystagmus Vertigo
 Involuntary oscillations of the eyes  Loss of equilibrium with the
when spinning is suddenly illusion of spinning
stopped.  May be caused by anything that alters
the firing rate of one of the
 Eyes continue to move in the vestibulocochlear nervers.
direction of the spin, then jerk  May be due to spinning or
rapidly back to the midline. pathologically induced by by viral
 When a person begins spinning, the cupula infections.
bends in the opposite direction.
 If the movement suddenly stops, inertia of
 Tx: Antivert® (meclizine)
endolymph causes it to continue moving in  Anticholinergic action
the direction of the spin.  Blocks conduction in the middle ear
 This is a normal phenomenon that helps
vestibular-cerebellar pathways.
maintain balance during spinning, however,
nystagmus can also be a symptom of certain
diseases, like Meniere’s disease.

14. Anatomy of the Ear

15. Structures of the Middle Ear
 Cavity between the tympanic
membrane and the cochlea
 Contains three bones called
ossicles:
 Malleus  Incus  Stapes
 Vibrations are transmitted
and amplified along the
bones.
 The stapes is attached to
the oval window, which
transfers the vibrations into
the inner ear.

16. Organ of Corti
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Group of hearing receptor cells,
called hair cells.
• On upper surface of basilar Scala vestibuli
(contains perilymph)
membrane Vestibular membrane
• Different frequencies of Cochlear duct
(contains endolymph)
vibration move different parts of Branch of
cochlear
Spiral organ (organ of Corti)
Basilar membrane
basilar membrane nerve
Scala tympani
• Particular sound frequencies (contains perilymph)
cause hairs of receptor cells to (a)
Tectorial
bend membrane
Hair cells
• Nerve impulse generated
Basilar
membrane
Branch of Nerve 16
Supporting
(b) cochlear nerve fibers cells

17. Figure 10-20 Sound transmission through the ear
1 Sound waves strike 2 The sound wave 3 The stapes is attached to
the tympanic energy is transferred the membrane of the oval
membrane and to the three bones window. Vibrations of the
become vibrations. of the middle ear, oval window create fluid
which vibrate. waves within the cochlea.
Cochlear nerve
Incus
Oval
Ear canal Malleus Stapes window
5
Vestibular duct
(perilymph)
3
Cochlear duct
2 (endolymph)
6
4
1 Tympanic duct
(perilymph)
Tympanic Round
membrane window
4 The fluid waves push on the 5 Neurotransmitter release 6 Energy from the waves
flexible membranes of the onto sensory neurons transfers across the
cochlear duct. Hair cells bend creates action potentials cochlear duct into the
and ion channels open, that travel through the tympanic duct and is
creating an electrical signal that cochlear nerve to dissipated back into
alters neurotransmitter release. the brain. the middle ear at the
round window.
Copyright © 2010 Pearson Education, Inc.

18. Clinical Applications
Conduction deafness Sensorineural deafness
 Sound waves are not conducted  Nerve impulses are not conducted
from the outer to inner ear. from the cochlea to the auditory
 May be due to a buildup of earwax, cortex.
too much fluid in the middle ear,  May be due to damaged hair cells.
damage to eardrum, or  May only impair hearing of a
overgrowth of bone in the middle particular sound frequency.
ear.
 May be helped by cochlear
 Impairs hearing of all sound implants.
frequencies.
 Can be helped by hearing aids.

19. The Eyes
VISION

20. Functional Anatomy of the Eye
 Image is inverted on retina
due to refraction of light.
 Degree of refraction
depends on:
 Refractive index (RI) of
media
 RI of air = 1.00
 RI of cornea = 1.38
 Curvature of the interface
between the two media.

21. Functional Anatomy of the Eye

22. Photoreceptors
 Rods: Provide black and
white vision under low light
intensities
 Cones: Provide sharp color
vision when light intensity is
great
 Humans have trichromatic
vision due to the presence
of three different types of
cones: Blue, Green, and
Red.

23. Visual Acuity
 Sharpness of vision
 Depends upon resolving power
 Ability of the visual system to resolve two closely spaced dots
Visual Abnormalities
 Myopia (nearsightedness)
 Hyperopia (farsightedness)
 Astigmatism
 uneven cornea or lens
 Presbyopia
 hardening of the lens
 impedes accommodation