Special Senses Lecture Anatomy and Physiology - Dr Joel G. Soria

1. Special Senses
Joel G. Soria, MD

2. Special Senses
Sense organs carry
messages about the
environment to the
central nervous system

3. General Senses
Widely distributed throughout the body and includes the
senses of touch, pressure, pain, temperature, vibration,
itch, and proprioception.
Receptors – sensory nerve endings or specialized cells
capable of responding to stimuli

4. RECEPTORS
Mechanoreceptor – Respond to mechanical stimuli
Chemoreceptor – Responds to chemicals
Photoreceptors – Responds to light
Thermoreceptors – Responds to temperature changes
Nociceptors - Responds to sensationb of pain
Free Nerve Endings – Structurally the simplest and most
common type of receptor nerve ending

5. Touch (pressure)
Mechanoreceptors
Free nerve endings
Pacinian corpuscles
Ruffini corpuscles
Merkel receptors
Meisaner's corpuscles
Barroreceptors

7. Cutaneous sense
Also known as tactile sense

9. The gate control theory of pain modulation

10. REFERRED
PAIN

11. OLFACTION

12. OLFACTION
Sense of smell
Occurs in response to
airborne odorants that
enter the nasal cavity
Olfactory neurons – bipolar
neurons within the olfactory
epithelium lining the superior
part of the nasal cavity.

14. CHEMOSENSES: Olfaction
Routes of information
transfer through the CNS
(1) Cranial nerve I → olfactory bulb (mitral cells & glomeruli)
(2) From olfactory bulb to parts of paleocortex in the telencephalon,
including the:
• Amygdala (emotions)
• Entorhinnal, pyriform, & orbitofrontal cortex.
(3) From there the information goes to
• Hypothalamus (emotions, motivations),
• Hippocampus (in temporal lobe: memory)

15. TASTE
How many different “tastes” are there?
Four or Five
1. Salty
2. Sweet
3. Bitter
4. Sour
5. Kiamoy?

18. CN- VII
CN- IX
Primary ‘gustatory’ cortex (near region where the mouth is represented)
Also to: amygdala, hypothalamus, orbital prefrontal cortex
Medulla
Pons
Thalamus

20. Vision

22. Physical information from the world (light)
Hue (“color”): wavelength
Saturation: purity of the light wave
Brightness: intensity of the electromagnetic
radiation
Specialized sense organ (eye)
Specialized neural tissue (retina)
Specialized sensory receptors (rods,cones)
sensory transduction: light - neural activity

24. Anatomy of the Visual
System
Pupil:
Adjustable opening
in the iris that
regulates the
amount of light that
enters the eye
Iris:
Pigmented ring of
muscles situated
behind the cornea
Cornea:
Transparent outer covering of the eye that admits light

27. Extra-occular
muscle

28. • Ciliary body and lens divide the anterior cavity of the eye into
posterior (vitreous) cavity and anterior cavity
• Anterior cavity further divided
• anterior chamber in front of eye
• posterior chamber between the iris and the lens

29. Fluids in the Eye
re-enters circulation
Vitreous humor fills
the posterior cavity.
Not recycled –
permanent fluid
Aqueous humor circulates within the eye
diffuses through the walls of anterior chamber, passes
through canal of Schlemm

30. Lens:
Consists of a series of transparent, onion-like layers. Its
shape can be changed by contraction of ciliary muscles.
Accommodation:
Changes in the thickness of the lens, accomplished by the
ciliary muscles, that focus images of near or distant objects
on the retina

31. Accommodation
• Posterior to the cornea and forms
anterior boundary of posterior
cavity
• Posterior cavity contains vitreous
humor
• Lens helps focus
• Light is refracted as it passes
through lens
• Accommodation is the process by
which the lens adjusts to focus
images
• Normal visual acuity is 20/20

35. Photoreceptors:
Retina:
The neural tissue and photoreceptive cells located on
the inner surface of the posterior portion of the eye.
Rod:
Photoreceptor cells of the retina, sensitive the light of
low intensity.
Cone:
Photoreceptor cells of the retina; maximally sensitive
to one of three different wavelengths of light and hence
encodes color vision.

36. Fovea:
Area of retina that mediates the most acute vision.
Contains only color-sensitive cones.
Optic Disk:
Location on retina where fibers of ganglion cells exit
the eye. Responsible for the blind spot.

37. Retina contains rods and cones
Cones densely packed at fovea (center of the
macula lutea)
Retinal pathway
Photoreceptors to bipolar cells to ganglion
cells, to the brain via the optic nerve
Axons of ganglion cells converge at blind
spot (optic disc)
Horizontal cells and amacrine cells modify
the signal passed along the retinal neurons

40. Photoreceptors
Lamella:
A layer of membrane containing photopigments; found
in the rods and cones.
Photopigment:
A protein dye bonded to retinal, a substance derived
from vitamin A; responsible for the transduction of
visual information.
Opsin:
A class of protein that, together with retinal,
constitutes the photopigments

41. Rhodopsin:
A particular opsin found in rods
Transducin:
A G-protein that is activated when a photon of
light strikes a pigment. Activates
phosphodiesterase molecules which destroy
cyclic GMP and close cation channels in the
photoreceptor

44. HEARING
&
BALANCE

45. The Ear

46. The Ear
Organ of hearing and equilibrium
Detects and analyses noises by transduction (or the conversion
of sound waves into electrochemical impulses)
Maintains the sense of balance (equilibrium).

47. Intensity and pitch
• Sound characterised by intensity and pitch
• Pitch is number of cycles per second
• Intensity is the energy of the wave. High energy - high change
in atmospheric pressure - LOUD
• The ear analyses the sound arriving at it - hair cells
• Converts it to electrical energy
• Brain decodes the info

50. Parts of the Ear
Ossicles
The MALLEUS (hammer)
gets the vibrations from
the eardrum, then sends
them to the anvil.
The INCUS (anvil) passes
the vibrations to the
stirrup.
The STAPES (stirrup)
passes the vibrations to
the inner ear.

51. Parts of the Ear
The inner ear is made of the
cochlea and liquid.
The cochlea is in the inner
ear. The cochlea looks like
a shell.
The auditory nerve carries
the hearing information to
the brain and the brain
tells us what we heard.

52. Cochlea

53. VESTIBULAR MEMBRANE – separates the cochlear duct from scala vestibuli.
BASILAR MEMBRANE - separates the cochlear duct from scala tympani.

54. The cochlea is the organ where sound
waves are converted first into fluid
waves, then into chemical signals and
finally into action potentials
The movement of the tectoral membrane by
sound waves moves the cilia on the hair
cells and effects neurotransmitters
released by the hair cells.

56. Transmission of sound to
the hair cells
Hair cells have steriocilia
Vibrations are sent from the oval window
through the cochlea and vibrate Basiliar
membrane - creates shearing force between
the 2 membranes
Stereocilia are moved back and forward
Change in hair cell properties and the creation
of electrical impulses which are sent to the
brain via the auditory nerve
Hair cells responsible for transduction
Inner and outer hair cells
Coil round inside of Organ of Corti & attached to Basilar membrane

57. KKK

58. Summary on Transduction
1.Sound waves cause vibrations in basilar membrane
2.Travelling waves cause sheering between basilar and overlying
tectorial membrane
3.Bends stereocilia back and forward
4.Forward bending creates tension on the protein bridges
5.Tension opens K+ channels
6.Due to K+ gradient K+ floods into hair cells
7.Cells depolarise and transmitter is released
8.Transmitter stimulates auditory nerve

61. The Vestibular System
• Controls the sense of movement and balance
• The first sensory system to fully develop by six months after
conception is the vestibular system
• This system is the sensory system considered to have the most
important influence on the other sensory systems and on the
ability to function in everyday life
• Unifying system in our brain that modifies and coordinates
information received from other systems

62. The vestibular system
• Functions to sense movement (acceleration and deceleration)
and static position
• Resides in the inner ear (labyrinth)
• Consists of 3 semi circular canals, otolith organs (utricle &
sacule) and the superior & inferior nerves
• Semi circular canals and the otolith organs are filled with
endolymph
• Perilymph fills the space between

63. Elements of the
Vestibular Labyrinth
Continues with the cochlea
Three semicircular canals
Detect angular acceleration
Two otolith organs
Utricle & Saccule
Detect linear acceleration
Vestibular nerve fibers
synapse with hair cells

64. The Vestibular Labyrinth

65. Semicircular Canals
• Detect angular acceleration
• There are 3 canals
• Corresponds to the three
dimensions in which you move
• Each canal detects motion in
a single plane
• Paired on opposite sides of
the head
• Each canal is a continues endolymph-filled hoop
• The actual hair cells sit in a small swelling at the base called the
ampulla

66. The Ampulla
Bulge at end = ampulla
Contains a sheet of cells = cristae
The hair cells are arranged as a single tuft that projects up
Cilia of hair cells extend upward into the cupola

67. the Saccule & utricle
Utricle and saccule signal linear
acceleration
Important for posture control
Contains a macule containing
hair cells
Crystals of otolyths move in
response to gravitational
forces
This moves the otolthic
membrane
Steriocilia move

68. Otolith organs & gravity
Each utricle and saccule has a
macula
Macula contains hair cells
Otolith crystals roll around when
the head tilts and this bend
the microvilli
The otolithic organs sense
motion according to their
orientation.
The utricle is horizontal in the
head, and largely registers
accelerations acting in the
horizontal plane.
The saccule is vertical in the head, and registers accelerations in the vertical plane

70. The Vestibular System