brief discussion on special senses, Basic level class for technicians. topics discussed include eyes and vision, nose and sense of smell, tongue and sense of taste and ears and hearing
4. ďTaste buds are found in papillae of the tongue mucosa
ďPapillae - three types: filiform, fungiform, and
circumvallate
ďFungiform and circumvallate papillae contain taste buds
ďAppx 10,000 taste buds - each taste bud has 40-100
epithelial cells made of 3 major types:
ďź Supporting Cells: separate and insulate
ďź Receptor Cells: deal with taste
ďź Basal cells: like stem cells, they give rise to new cells
Taste Buds
5. Taste Sensation
⢠There are five basic taste sensations
â Sweet â sugars, saccharin, alcohol, and
some amino acids
â Salt â metal ions
â Sour â hydrogen ions
â Bitter â alkaloids such as quinine and
nicotine
â Umami â elicited by the amino acid
glutamate
6. ďActivation
ď To be tasted, first must be dissolved in saliva, diffuse into the
pore and make contact with gustatory hairs which trigger
neurotransmitters to elicit action potentials in these fibers.
ď Adapt rapidly 3-5 seconds & completely in 1-5 minutes
ďTaste Transduction
ď Process in which stimulus energy is converted into a nerve
impulse due to influx of different ions
Physiology of Taste
7. Taste is carried by two cranial nerves
ď Facial: anterior 2/3rds of tongue
ď Glossopharyngeal: posterior 1/3rd
ď Taste triggers reflexes in digestion such as increasing saliva &
gastric juice
Gustatory Pathway
Influence of other sensations on taste
â˘Taste is 80% smell, when olfactory
receptors are blocked food becomes
bland
â˘Thermoreceptors, mechanoreceptors,
nociceptors, temperature and texture can
enhance or detract
8. Sense of Smell (Olfaction)
⢠The organ of smell is the olfactory epithelium,
which covers the superior nasal concha
⢠Olfactory receptor cells are bipolar neurons with
radiating olfactory cilia
⢠Olfactory receptors are surrounded and cushioned
by supporting cells
⢠Basal cells lie at the base of the epithelium
9.
10. ďOlfactory epithelium
ďDetects chemicals in solution
ďCovered by mucous to trap airborne molecules
ďPhysiology
ďSubstance must be in a gaseous state
ďMust be water soluble to dissolve in olfactory epithelium
ďBind to protein receptors which open ion channels that send action
potentials to olfactory bulb
ďPathway
ďSend impulses from bulb down tract
ďThalmus ď Frontal Lobe or Hypothalmus to interpret and elicit
emotional responses to odor
ďImablances include anosmia (without smells) from head injuries; unicinate
fits (olfactory hallucinations)
Olfaction
11. Vision
Accessory Structures
ďEyebrows
ďśShade the eyes
ďśPrevent perspiration into eye
ďEyelids
ďśPalpabrae protects eye
ďśLevator palpebrae superioris raises eyelid
ďśEyelashes trigger blinking
ďConjunctiva
ďśMucous membrane over eyelids and anterior
surface of eyeball (white part)
ďśVascular, when irritated eyes are blood shot
12.
13. ďExtraocular muscles
ď Movement is controlled by 6 muscles
ď Four Rectus muscles: Superior,
Inferior, Lateral, Medial
ď Two Oblique muscles: Superior,
Inferior
ď Nerve Innervation: abducens,
trochlear, oculomotor
ďLens : Divides eye into anterior
and posterior segments
ď Transparent, flexible structure that
can change shape to allow focus of
light on retina
ď Avascular
ď Becomes less elastic through life
causing focus impairment
ď Cataract â cloudy lens due to
thickening of lens or diabetes
15. Lacrimal Apparatus
⢠Consists of the lacrimal gland and
associated ducts
⢠Lacrimal glands secrete tears
⢠Tears
â Contain mucus, antibodies, and lysozyme
â Enter the eye via superolateral excretory
ducts
â Exit the eye medially via the lacrimal
punctum
â Drain into the nasolacrimal duct
18. Fibrous Tunic
⢠Forms the outermost coat of the eye and is
composed of:
â Opaque sclera (posteriorly)
â Clear cornea (anteriorly)
⢠The sclera protects the eye and anchors
extrinsic muscles
⢠The cornea lets light enter the eye
19. Vascular Tunic (Uvea)
⢠Has three regions: choroid, ciliary
body, and iris
⢠Choroid region
âA dark brown membrane that
forms the posterior portion of the
uvea
âSupplies blood to all eye tunics
20. Vascular Tunic
⢠A thickened ring of tissue surrounding the
lens
⢠Composed of smooth muscle bundles
(ciliary muscles)
⢠Anchors the suspensory ligament that holds
the lens in place
Ciliary Body
21. ⢠The colored part of the eye
⢠Pupil â central opening of the iris
â Regulates the amount of light entering the eye
during:
⢠Close vision and bright light â pupils constrict
⢠Distant vision and dim light â pupils dilate
⢠Changes in emotional state â pupils dilate when
the subject matter is appealing or requires
problem-solving skills
Iris
23. Sensory Tunic: Retina
⢠A delicate two-layered membrane
⢠Pigmented layer â the outer layer that
absorbs light and prevents its scattering
⢠Neural layer, which contains:
â Photoreceptors that transduce light energy
â Bipolar cells and ganglion cells
â Amacrine and horizontal cells
25. The Retina: Ganglion Cells and the
Optic Disc
⢠Ganglion cell axons:
â Run along the inner surface of the retina
â Leave the eye as the optic nerve
⢠The optic disc:
â Is the site where the optic nerve leaves the eye
â Lacks photoreceptors (the blind spot)
27. Retinal Photoreceptors
⢠Rods:
â Respond to dim light
â Are used for peripheral vision
⢠Cones:
â Respond to bright light
â Have high-acuity color vision
â Are found in the macula lutea
â Are concentrated in the fovea centralis
28. Blood Supply to the Retina
⢠The neural retina receives its blood
supply from two sources
â The outer third receives its blood from the
choroid
â The inner two-thirds is by the central artery and
vein
29. Inner Chambers and Fluids
⢠The lens separates the internal eye into anterior
and posterior segments
⢠The posterior segment is filled with a clear gel
called vitreous humor that:
â Transmits light
â Supports the posterior surface of the lens
â Holds the neural retina firmly against the pigmented
layer
â Contributes to intraocular pressure
30. Anterior Segment
⢠Composed of two chambers
â Anterior â between the cornea and the iris
â Posterior â between the iris and the lens
⢠Aqueous humor
â A plasma like fluid that fills the anterior segment
â Drains via the canal of Schlemm
⢠Supports, nourishes, and removes wastes
32. Refraction and Lenses
⢠When light passes from one transparent
medium to another its speed changes and it
refracts (bends)
⢠Light passing through a convex lens (as in
the eye) is bent so that the rays converge to
a focal point
⢠When a convex lens forms an image, the
image is upside down and reversed right to
left
34. ⢠Photoreception â process by which the eye
detects light energy
⢠Rods and cones contain visual pigments
(photopigments)
â Arranged in a stack of disk-like infoldings of the
plasma membrane that change shape as they
absorb light
Photoreception:
Functional Anatomy of Photoreceptors
36. Rods
⢠Functional characteristics
â Sensitive to dim light and best suited for night vision
â Absorb all wavelengths of visible light
â Perceived input is in gray tones only
â Sum of visual input from many rods feeds into a single
ganglion cell
â Results in fuzzy and indistinct images
37. Cones
⢠Functional
characteristics
â Need bright light for
activation (have low
sensitivity)
â Have pigments that
furnish a vividly colored
view
â Each cone synapses with
a single ganglion cell
â Vision is detailed and has
high resolution
38. The Ear: Hearing and Balance
⢠The three parts of the ear are the inner, outer,
and middle ear
⢠The outer and middle ear are involved with
hearing
⢠The inner ear functions in both hearing and
equilibrium
40. Outer Ear
ďAuricle or Pinna
ďear composed of elastic cartilage & skin to direct sound
waves to external auditory canal
ďExternal auditory meatus
ďShort curved tube from auricle to eardrum
ďLined with skin, sebaceous glands, & ceruminous
glands (secrete earwax)
ďTympanic membrane ( ear drum ) boundary
between outer & middle ear
41. Middle Ear (Tympanic Cavity)
⢠A small, air-filled, mucosa-lined cavity
â Flanked laterally by the eardrum
â Flanked medially by the oval and round windows
⢠Epitympanic recess â superior portion of the
middle ear
⢠Pharyngotympanic tube â connects the middle ear
to the nasopharynx
â Equalizes pressure in the middle ear cavity with the
external air pressure
42. Ear Ossicles
⢠The tympanic cavity contains three small
bones: the malleus, incus, and stapes
â Transmit vibratory motion of the eardrum to the
oval window
â Dampened by the tensor tympani and stapedius
muscles
43. Inner Ear
⢠Bony labyrinth
â Tortuous channels worming their way through the
temporal bone
â Contains the vestibule, the cochlea, and the semicircular
canals
â Filled with perilymph
⢠Membranous labyrinth
â Series of membranous sacs within the bony labyrinth
â Filled with a potassium-rich fluid
45. The Cochlea
⢠The scala tympani terminates at the round
window
⢠The scalas tympani and vestibuli:
â Are filled with perilymph
â Are continuous with each other via the
helicotrema
⢠The scala media is filled with endolymph
46. The Cochlea
⢠The âfloorâ of the cochlear duct is composed
of:
â The bony spiral lamina
â The basilar membrane, which supports the
organ of Corti
⢠The cochlear branch of nerve VIII runs from
the organ of Corti to the brain
48. Transmission of Sound to the Inner Ear
⢠The route of sound to the inner ear follows this
pathway:
â Outer ear â pinna, auditory canal, eardrum
â Middle ear â malleus, incus, and stapes to the oval
window
â Inner ear â scalas vestibuli and tympani to the cochlear
duct
⢠Stimulation of the organ of Corti
⢠Generation of impulses in the cochlear nerve