The Special Senses

1
The Special Senses

• Taste, Smell, Touch (later),
• Vision, and Hearing

2
Sense of Taste

• Gustatory cell (taste) receptors detect chemicals
  dissolved in saliva
• Taste buds sensory receptor cells for taste.
• located on and between papillae (pimplelike
  protuberances on the tongue)
• Also located on palate (roof of mouth), throat,
  and epiglottis
• A child has approx 10,000 taste buds
• With age the number of taste buds will drop to
  fewer than 5,000

3
(No Transcript)
4
Taste Buds

• Each taste bud is structured like an orange whose
  segments consist of approx 25 gustatory
  receptor cells.
• The receptor cells have hairlike tips that
  project into a hole (the taste pore) in the
  tongues surface.

5
Primary Sensations

• Tip of tongue sweet and salty
• Sides of tongue sour
• Back of tongue bitter
• 80 of taste is actually smell
• Other influences thermoreceptors (temperature),
  mechanoreceptors (texture), nocioreceptors (pain)

6
Sense of Smell

• Specialized neurons with olfactory cilia in upper
  nasal cavity
• Sniffing draws air forcefully into the nose
• Neurons detect molecules or tiny particles known
  as odorants floating on the air
• Smell is more sensitive than taste and is able to
  distinguish between more than 10,000 odors.
• Sensory cells are affected by a variety of
  factors age, nutrition, hormones, drugs,
  therapeutic radiation

7

• Smell is long-lasting and stimulation by similar
  smells can trigger memory of events that occurred
  long ago
• Olfactory receptors easily fatigue- adaptation
  occurs
• Process of conforming to the environment after
  continuous stimulation of constant intensity
• These changes in awareness of odors allows us to
  continue to function at an optimum level

8
Homeostatic Imbalances Anosmias

• Some genetic causes
• Head injuries that tear olfactory nerves
• After effects of nasal cavity inflammation
• Cold, allergy, smoking
• Physical destruction of nasal cavity due to
  polyps
• Aging

9
Sense of Touch

• Sensory receptors make it possible for the body
  to respond to environmental stimuli
• Specialized endings of nerve cells in the skin or
  in deeper tissues
• Receptors respond to a stimulus and convert the
  stimulus to a nerve impulse
• Nerve impulses travel by afferent sensory neurons
  to the brain for interpretation

10
Touch

• Mechanoreceptors/extroreceptors located on the
  body surfaces respond to touch, stretch, and
  pressure
• Meissners corpuscles in fingertips, lips, and
  hairless parts for fine touch
• Pacinian corpuscles in skin, joints and genitals
  for deep pressure and stretch
• Krauses end bulbs in eyelids, lips, and
  genitals for light touch
• Ruffinis corpuscles found in skin for
  continuous touch

11

• Heat/Cold thermoreceptors
• Pain nocioreceptors free nerve endings for
  pain, tickle, itch
• noci/o (pain, injury)

12
Sense of Vision- Anatomy

• Eyebrows physical protection of eyes short,
  coarse hairs
• Eyelids (palpebrae) physically protect the eye
  and prevent the cornea from drying via blink
  reflex
• Eyelashes hairs with glands at the base for
  lubrication inflammationsty
• Meibomian glands secrete a lipid tear film
  spread by blinking reduces evaporation of tear
  film, prevents tear film from running down face,
  gives even spread over eyeball

13

• Lacrimal glands secrete aqueous tear film
  containing globulins and lysozyme supplies
  nourishment to the cornea and provides
  antimicrobial activity nasolacrimal duct empties
  into nasal cavity secretions decrease with age
• Conjunctiva membranes that lines the eyelid
  secretes a mucous tear component that helps
  reduce surface tension accumulates in the medial
  canthus as sleep inflammation pinkeye

14

• Extrinsic eye muscles
• Sclera outermost white covering of the eyeball
  anchor site for muscles
• Cornea transparent front of the sclera no blood
  vessels but richly supplied with sensory nerves
  depends on tear film for nutrition, O2, and
  removal of waste window for light to enter
  extraordinary capacity for regeneration
• Choroid highly vascular middle layer of the eye
  pigment absorbs light to prevent scatter and
  reflection internally

15

• Ciliary body encircles the lens
• Iris visible colored part of the eye regulates
  amount of light entering the lens
• Pupil round central opening of the iris allows
  light to enter
• Lens transparent disk of tissue that changes
  shape for near or far vision
• Retina thin layer of light sensitive rod and
  cone cells absorbs light
• Fovea composed of cone cells visual acuity
• Optic disc the blind spot where neurons exit
  the eyeball as the optic nerve

16
(No Transcript)
17
Sequence of Vision

• Rays of light enter the eye through the clear,
  domed front of the eyeball, the cornea, where
  they are partly bent (refracted).
• Rays then pass through the transparent lens,
  which changes shape to fine-focus the image,
  mechanism known as accommodation.
• Light continues through the fluid within the
  eyeball and shines and upside-down image onto the
  retina lining.

18

• The retina contains over 120 million cone cells
  and about 7 million rod cells
• Rods are scattered through the retina and respond
  to low levels of light, do not differentiate
  colors
• Cones are concentrated in the fovea and take
  bright light to distinguish colors and fine
  detail
• Nerve fibers from the rods and cones connect via
  intermediate retinal cells to the fibers that
  form the optic nerve.
• The image is then transmitted to the visual
  cortex in the brain, where it is turned upright.

19
20/20? Visual Acuity

• Clearness/sharpness of visual perception recorded
  as 2 numbers
• 1st represents the distance in feet between the
  subject and the test chart
• 2nd represents the number of feet a person with
  normal acuity would stand to see clearly
• 20/20 is considered normal acuity
• 20/100 a person can see objects at 20 ft. that a
  person with normal can see at 100.
• Worse than 20/200 after correction is considered
  legally blind

20
Homeostatic Imbalances

• Myopia nearsighted focus falls short of the
  retina far objects are blurred
• Hyperopia farsightedness focus falls behind the
  retina close objects are blurred
• Astigmatism cornea is not spherical, focused
  image is distorted
• Color blindness congenial lack of one or more
  types of cones (red, green, blue) sex-linked

21
Pathological Conditions

• Glaucoma abnormally high pressure inside the eye
  due to buildup of fluid. The pressure may
  permanently damage nerve fibers in the retina or
  the optic nerve.
• Cataracts excess glucose draws water into the
  lens causing opaque changes.
• Diabetic retinopathy small retinal hemorrhages
  occur due to excess glucose in blood- disrupts O2
  to the rods and cones- blindness

22
(No Transcript)
23
Sense of Hearing- External Ear Anatomy

• Auricle (pinna) the flap that funnels sound
  waves helixrim lobuleearlobe
• External auditory meatus opening to the auditory
  canal, lined with cerumen/wax glands
• External auditory canal short, narrow chamber
  extends from auricle to tympanic membrane
• Tympanic membrane the eardrum that stretches
  across the canal and vibrates in response to
  sound waves

24
Middle Ear Anatomytiny cavity in the temporal
bone

• Auditory ossicles 3 bones that vibrate to
  transmit sound waves to the inner ear
• Malleus hammer shaped, handle attached to
  tympanic membrane
• Incus anvil shaped
• Stapes stirrup shaped
• Oval/vestibular window opens to internal ear
• Round/cochlear window covered by membrane, opens
  to internal ear

25

• Pharyngotympanic/auditory/Eustachian tube
  connects middle ear to pharynx helps to equalize
  pressure so eardrum will vibrate
• Myringotomy lancing of eardrum to relieve
  pressure- insertion of tubes for drainage of
  fluid/pus
• Mastoid sinuses air spaces in the temporal bone
  that drain into middle ear

26
Inner Ear Anatomy

• Labyrinth, located in the hollowed out portion of
  the temporal bone
• Vestibule and semicircular canals involved in
  equilibrium
• Cochlea snail like part of the inner ear for
  hearing

27
(No Transcript)
28
Sequence of Hearing

• Sound waves caught by auricle, channeled through
  the auditory canal and strike against the
  tympanic membrane causing it to vibrate
• Vibrations move the malleus, incus, and stapes
  against the oval window
• Pressure is exerted inward to the perilymph of
  the scala vestibuli (within the cochlea)
• Vibrations continue to move to the organ of
  Corti- receptor organ for hearing

29
Homeostatic Imbalances

• Conduction deafness something interferes with
  the conduction of sound vibrations to the fluids
  of the inner ear
• Impacted earwax, perforated/ruptured eardrum,
  otitis media, otosclerosis of ossicles
• Sensorineural deafness damage to neural
  structures at any point from cochlear hair cells
  to auditory cortical cells
• Gradual loss of receptor cells, exposure to
  single loud noise, degeneration of cochlear
  nerve, cerebral infarcts, tumors

30

• Tinnitus ringing or clicking sound in the ears
  in the absence of auditory stimuli can be first
  symptom of cochlear nerve degeneration or
  inflammation of middle/inner ear or side effect
  of medications
• Vertigo may result from disturbance affecting
  the organs of balance in the inner ear, the nerve
  that connects the inner ear to the brain, or
  areas of the brain concerned with balance