The Special Senses : or

1
The Special Senses or

• Do I Really Have Rocks in My Head?

2
There are five special senses

• 1. Hearing (auditory

• 2. Taste (gustatory)

• 3. Smell (olfactory)

• 4. Sight (vision)

5. Equilibrium
3
Receptors for Special Senses

• Can be large, complex sensory organs,
• such as the eye and ear

Can be localized clusters of receptors, such as
the taste buds or the olfactory epithelium
4
External Anatomy of the Eye

• Eyelids protect the eye

• Eyelashes trap foreign material
• Meibomian glands oily secretion that lubricates
  the eye
• Ciliary glands modified sweat glands produce
  part of the tears
• Medial canthus medial corner of the eye
• Lateral canthus lateral corner of the eye

5

• Lacrimal Apparatus produce tears

• Lacrimal glands lateral aspect of the upper
  eyelid tears are produced by these glands
• Lacrimal canals medial canthus drain tears
  from the eye
• Lacrimal sac and nasolacrimal duct drain tears
  from the eye and into the nasal passage

6
Extrinisic Eye Muscles

• There are 6 extrinsic (outside the eye) muscles
  that move the eyeball

• Lateral rectus moves the eye laterally

Medial rectus moves the eye medially

• Superior rectus rolls the eye upward

Inferior rectus roll the eye downward

• Inferior oblique elevates the eye and turns it
  laterally

Superior oblique depresses the eye and turns it
laterally
7
Conjunctiva

• Thin membrane that lines the eyelids and covers
  part of the eyeball

• Secretes mucus that helps keep the eyeball moist

• Conjunctivitis (pinkeye) inflammation of the
  conjunctiva
• usually a bacteria or a virus and is contagious

8
Eyeball Coverings (Tunics)

• The eye itself is called the eyeball or the
  globe

• Sclera the outermost tunic
• Thick, white, tough
• Called the fibrous tunic
• The white of the eye
• Cornea the anterior, clear portion of the sclera

9
Eyeball Coverings (Tunics)

• Choroid the middle coat of the eyeball

• Rich blood supply
• Contains a dark pigment

Anteriorly is modified
Ciliary body smooth muscles to which the lens
is attached

• Iris the colored part of the eye
• Contains many small muscles that change the
  diameter of the pupil
• This regulates the amount of light entering the
  eye

10
(No Transcript)
11
The Retina

• Also called the sensory tunic

The innermost tunic
Extends anteriorly to the ciliary body
Contains photoreceptors
Most concentrated posteriorly

• Optic disk the site where the optic nerve exits
  the eyeball
• no receptors (the blind spot)

Fovea centralis lateral to the optic disk the
site of greatest concentration of photoreceptors
12
Photoreceptors

• Rods allow us to see gray shades in dim light
• Night blindness interference with rod function

• Cones respond to colors
• 3 types of cones respond to blue, green and red
  light
• Color blindness interference with function of
  cones

13
(No Transcript)
14
Mechanism of Vision

• Light energy causes changes in certain chemicals
  (called pigments)

• Rhodopsin well studied visual pigment
• a purple pigment found in rods

• Formed by the union of a protein called opsin
  with retinal (modified Vitamin A)
• that has a kinked shape

• when light strikes rhodopsin the retinal loses
  the kinked shape
• this unbinds the opsin.

15
Mechanism of Vision 2

• The unbonded rhodopsin loses the purple color
  called bleaching

• Retinal changes into Vitamin A

Rhodopsin is reformed as Vitamin A is converted
into retinal and bonds with opsin
Other visual pigments operate in a similar manner
16
Lens

• The lens focuses light rays onto the retina

• Held in place by suspensory ligaments that attach
  to the ciliary body

Is a flexible, bi-convex crystal like structure
Contractions of the ciliary body change the shape
of the lens and allow us to focus on near and far
objects
Produces a real (upside down) image on the retina
Divides the eye into two chambers anterior
segement and posterior segment
17
Fluids in the Eye

• Anterior chamber filled with a clear watery fluid
  called
• the aqueous humor

Posterior chamber filled with a thick, jelly like
material called the vitreous humor or the
vitreous body
Aqueous humor constantly produced by the
choroid. It provides nutrients for the lens and
cornea and helps maintain normal intraocular
pressure
Reabsorbed into the blood stream in the canal of
schlemm located where the sclera and cornea meet
Glaucoma aqueous cannot drain
18
Pathway for Light

• Light rays are refracted as they pass from air
  into the cornea,
• through the aqueous humor, lens, and vitreous
  humor.

Lens changes shape to very the amount of
refraction to allow us to focus our eyes
Accommodation the ability of the eye to focus
on close objects (less than 20 feet away).
Emmetropia images focused correctly on the
retina
19
(No Transcript)
20
Pathway for Light 2
Myopia nearsightedness - light from far away
objects in focused in front of the retina
image is then blurred
Hyperopia farsightedness light from close
objects is focused behind the retina image is
blurred
21
Visual Fields and Pathways
Axons from rods and cones are bundled together
ans leave the eyeball as the optic nerve

• Optic chiasma fibers from the medial side of
  each
• optic nerve cross over to the opposite side

The resulting fiber tracts are called the optic
tracts and contain lateral fibers fromthe same
side of the body and medial fibers from the
opposite side of the body
These tracts continue into the thalamus
22
Visual Fields and Pathways 2

• Each side of the brain receives visual input from
  both eyes

The visual fields from each eye overlap
These two facts produce our binocular vision
23
(No Transcript)
24
Eye Reflexes

• Photopupillary reflex pupil responds to bright
  or dim light
• by contracting or widening

• Accommodation pupillary reflex pupils constrict
  when
• we view close objects

25
The Ear Hearing and Balance
The structures of our ear allow us to detect
sound vibrations form a frequency range of 20
20,000 Hertz
Structures in our ear also provide information
concerning position of our head with respect to
gravity as well as information concerning motion
of our head
26
Anatomy of the Ear
External Ear

• 3 regions external, middle, inner ear

Pinna the cartiledge structure that surrounds
the auditory opening

• External auditory canal leads to the eardrum

• Ceruminous glands produce earwax (cerumen)

• Tympanic membrane the eardrum

27
(No Transcript)
28
Anatomy of the Ear
Middle Ear

• Air filled cavity within the temporal bone

Flanked by the tympanic membrane (lateraly) and
by a bony wall with 2 openings (medially)
The bony wall has two openings the oval window
and the round window

• The auditory tube (eustation tube) enters
• the ventral aspect of the cavity

• Contains 3 small bones called ossicles
• Malleus (hammer), incus (anvil), and stapes
  (sitrrup)

29
(No Transcript)
30
Inner Ear

• Consists of a group of bony chambers called the
  bony labyrinth

• Located deep within the temporal bone

• 3 divisions of the labyrinth
• Cochlea, vestibule,
• semicircular canals

The bony labyrinth is filled with a plasma-like
fluid called perilymph
Membraneous labyrinth a series of membrane sacs
suspended in the perilymph. Filled with a
thicker fluid called endolymph.
31
(No Transcript)
32
Mechanism of Hearing

• Sound waves reach thecochlea through vibrations
  of
• the tympanic membrane, ossicles, and oval window

The cochlea contains the organ of Corti which
contains hearing receptors.

• Hearing receptors (called hair cells) are
  embedded
• in the basilar membrane

• A thick, gel like membrane called the tectorial
  membrane
• lies over the hair cells

High pitch sounds stimulate receptors near the
oval window and low pitched sounds are detected
further along the cochlea.
33
(No Transcript)
34
(No Transcript)
35
Mechanism of Hearing 2

• Sound vibrations that reach the oval window sets
  the fluids
• of the inner ear into motion

• Fluid motion causes the tectorial membrane to move

• Movement of the tectorial membrane stimulates the
  hearing receptors.

• The sound impulses are transmitted via the
  cochlear nerve to the brain

36
(No Transcript)
37
Mechanism of Equilibrium

• Equilibrium receptors are called the vestibular
  apparatus

Two types of equilibrium static and dynamic
Static the position of our head with respect to
gravity

• Dynamic movements of our head

38
Static Equilibrium

• Receptors in the vestibule provide static
  equilibrium

• Within the membraneous sacs arereceptors called
  maculae

• Maculae report on the position of our head with
  respect to gravity

• Each macula contains a patch of receptors
  embedded in a
• jelly-like membrane called the otolithic membrane

• The otolithic membrane also contains tiny stones
  called
• otoliths that respond to the pull of gravity

39
(No Transcript)
40
Static Equilibrium 2

• As the head moves, the otoliths roll in response
  to changes
• in the pull of gravity.

• This movement pulls on the gel (otolithic
  membrane)

• Movements of the otolithic membrane pull on
  receptors that are
• embedded in the membrane

Movement of the receptors provide information on
the position of the head with respect to gravity
The receptors send their nerve impulses along the
vestibular nerve
41
(No Transcript)
42
Dynamic Equilibrium
Receptors for dynamic equilibrium are found in
the semicircular canals

• 3 semicircularcanals postioned at right angles to
  each other (x, y z axes)
• Each semicircular canal contains a receptor
  region called
• the crista ampullaris

• Each crista ampullaris contains a tuft of
  receptor hair cells covered
• by a cap of gelatinous material called the cupula

43
Dynamic Equilibrium 2

• When your head moves, the thick fluid in the
  semicircular canals
• (endolymph) lags behind because of greater
  inertia.
• The fluid moves in the opposite direction and
  drags
• the cupula in the opposite direction along with
  it.

• These impulses provide information on changes in
  motion of your head

These receptors respond to changes in velocity
(acceleration) and not constant motion
44
(No Transcript)
45
Chemical Senses Taste and Smell

• Receptors for taste and smell are called
  chemoreceptors because they
• respond to chemicals in solution

There are four types of taste receptors and one
type of olfactory receptor

• These senses complement each other and respond to
  
• many of the same stimuli

46
Sense of Smell

• There are thousands of olfactory receptors
  located in a
• postage stamp sized area in the roof of each
  nasal passage

• Sniffing causes more air to flow in the upper
  regions of
• the nasal passages and thereby intensifies the
  sense of smell

Olfactory receptor cells have long clia called
olfactory hairs that protrude from the nasal
epithelium and are constantly bathed in mucus.
47
(No Transcript)
48
Sense of Smell 2
They are stimulated by chemicals dissolved in the
mucus
These receptors are very sensitive just a few
molecules can activate them.

• They adapt quickly to unchanging odors we can
  no longer smell them

• Olfaction is tied closely to the emotional
  visceral parts of the brain

• Olfaction is tied closely to memory

49
(No Transcript)