Download CHAPTER 11: SPECIAL SENSES: The Eyes and Ears

THE SENSES
CHAPTER 9
Receptors and Sensations
Five general types of receptors are recognized:
1. Chemoreceptors: Are sensitive to changes in
chemical concentrations. Sense of smell and taste fall into
this category.
2. Nociceptors: These are pain receptors that detect
tissue damage.
3. Thermoreceptors: Sensitive to temperature changes.
4. Mechanoreceptors: Respond to changes in pressure
or movement.
5. Photoreceptors: Respond to light energy.
SENSATIONS
Sensations are feelings that occur when the brain
receives sensory impulses from the peripheral
nervous system.
The impulses are relatively the same; it is the
brain’s interpretation that makes them seem
different and unique.
SOMATIC SENSES
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Somatic senses involve receptors
associated with the skin, muscles, joints,
and visceral organs. If they occur at the
body surface, they are called
exteroceptive senses and include touch,
pressure, and temperature.
Sensations associated with changes
occurring in visceral organs are called
visceroceptive senses.
TOUCH AND PRESSURE SENSES
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Touch results from sensation of tactile
receptors just beneath the skin.
Pressure sensations result from
stimulation of receptors in deeper tissue.
Each sensation is triggered by a degree of
displacement of tissues involved.
Types of Touch/Pressure
Sensors
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Three types:
1. Free ends of Sensory Nerves
2. Meissner’s Corpuscles are receptors for
light touch. They are also used when a
person wants to judge the texture of
something. Are found in the dermal
papillae of the skin. Are abundant in
hairless areas like lips, clitoris, palm.
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3. Pacinian Corpuscles: Detect deep
pressure or vibrations. Located in
subcutaneous tissues, deep submucosal
tissues, and serous membranes. Found
around joints, tendons, muscles,
mammary glands, external genitalia,
pancreas, and urinary bladder.
Temperature Senses
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Thermal sensations are perceptions of
degrees of warmth and coolness (extreme
heat or cold are experienced as pain).
Receptors include two groups of free
nerve endings located in the skin:
1. Heat Receptors are sensitive to
temperatures above 77F and become
unresponsive above temperatures of 113F
– pain receptors kick in and report the
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sensation of burning.
2. Cold receptors respond to
temperatures between 50F and 68F. If
temperatures are below 50F, a freezing
sensation is reported by pain receptors.
Both heat and cold receptors adapt
quickly.
SENSE OF PAIN
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Pain receptors consist of free nerve
endings that are stimulated when tissues
are damaged.
Protect the body by signaling damage and
identifying changes that may cause longterm damage.
Aid medical professionals in diagnosing
specific diseases or malfunctions of the
body.
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Pain receptors, called nociceptors, are
widely distributed throughout the skin and
internal tissues.
Tissue injury releases chemicals called
prostaglandins and kinins that stimulate
nociceptors.
Pain persists after initial tissue injury
because these chemicals linger and there
is little to no adaption for these receptors.
PAIN – ACUTE OR CHRONIC
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ACUTE: Occurs very rapidly and is typically
not felt in deeper tissues of the body. Is
usually described as sharp or stabbing pain.
Acute pain fibers are thin, myelinated fibers
that carry impulses rapidly and cease when
the stimulus stops.
CHRONIC: Has a slower onset and builds
slowly in intensity over a period of seconds or
minutes. Often described as burning, aching,
or throbbing. Chronic pain fibers are thin,
unmyelinated fibers that conduct impulses
slowly and continue sending impulses long
after the stimulus stops.
VISCERAL PAIN
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Visceral pain receptors are the only
receptors in the viscera that produce
sensations. Response of pain receptors is
quite different from those associated with
surface tissues.
Localized stimulation of the viscera does
not evoke much of a response, but
widespread stimulation may elicit a strong
response.
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Stretching of visceral tissues or a decrease
in blood flow elicits the most painful
responses.
Visceral pain often seems to come from
somewhere other than its actual origin.
This is called referred pain. It occurs
because of common nerve pathways: the
two areas are served by the same
segment of the spinal. Example, an MI is
felt as pain in the arm.
Stretch Receptors
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Stretch receptors are proprioceptors that
deal with sensations from the lengthening
and stretching muscles. The two main
types are Golgi tendon organs and muscle
spindles.
Golgi Tendon Organ: Found in tendons
at the point of attachment to their
respective muscles. Are stimulated by
increased tension in the skeletal muscle.
Golgi Tendon Organ (Cont’d)
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Sensory impulses from these receptors
produce an inhibiting reflex for muscle
contraction. This helps to prevent the
muscle from pulling away from its
insertion point and to maintain posture.
MUSCLE SPINDLES
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Muscle spindles are located in muscles near the
origin of the tendons that serve them. Each spindle
is composed of 3-10 specialized muscle fibers called
intrafusal muscle fibers.
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The central region of the spindle has few or no actin
or myosin filaments, but the ends do contain a few.
This central region cannot contract. However, there
are two types of afferent (sensory) fibers inside the
spindle – they have dendrites that wrap around the
central area of the intrafusal fiber. When stretched,
the spindle stimulates the dendrites, which send a
nerve impulse toward the spinal cord.
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Muscle spindle fibers respond to the rate
and degree of length change in a skeletal
muscle. The info is transmitted to the
cerebrum for perception of limb position
and to the cerebellum for coordination of
muscle contraction.
Structures of the Eye
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ADNEXA – accessory
structures
 Orbit
 Eye Muscles
 Eyelids
 Eyelashes
 Conjunctiva
 Lacrimal Apparatus
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The Lacrimal Apparatus – structures that
produce, store, and remove tears
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Lacrimal Glands: secrete lacrimal fluid to
maintain moisture on the anterior surface of
the eyeball
Lacrimal Canaliculi: ducts at the inner
canthus of each eye – collect tears and drain
them into the lacrimal sac
Lacrimal sac: an enlargement of the upper
portion of the lacrimal duct
Lacrimal duct: passageway that drains
lacrimal fluid into the nose
Functions of the Eyes – receive
images and transmit to brain
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Optic: pertaining
to eye or sight
Ocular:
pertaining to the
eye
 Extraocular:
outside the
eyeball
 Intraocular:
within the
eyeball
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ORBIT
Frontal
 Sphenoid
 Ethmoid
 Maxilla
 Zygoma
 Lacrimal
 Palatine
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www.lau-verlag.de/anatom/ skeletal-system.htm
Muscles of the Eye
Superior/Inferior
Rectus
 Superior/Inferior
Oblique
 Lateral/Medial
Rectus
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Eyelids: protect the
eyeball form foreign
matter, excessive
light, and impact
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Canthus: angle where
upper/lower eyelids
meet
 Inner Canthus
 Outer Canthus
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Conjunctiva:
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lines the underside
of each eyelid and
provides protective
covering over
exposed surface of
eyeball
The Eyeball globe
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www.optelec.com/ lv_ref.php
Made up of 3 layers
 Sclera
 Choroid
 Retina
Interior of eye is
divided into
anterior/posterior
segments
The Sclera – the white of the eye
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Outer layer of eye
Maintains shape of
the eye and protects
the delicate inner
layers of tissue
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Cornea: transparent
anterior portion of the
sclera
Provides most of the
optical power of the
eye
The Uveal Tract
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The vascular layer of eye
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Choroid: opaque (light
cannot pass through it) middle
layer of the eyeball – provides
blood supply for entire eye
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Iris: colored layer that
surrounds pupil – it’s muscles
control amount of light
entering eye – decrease muscles contract making
opening smaller (visa versa)
Pupil: black circular opening
in center of iris – permits light
to enter eye
Lens: focuses images on the
retina – located behind iris
and pupil
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Ciliary Body: located
within the choroid, set of
muscles and ligaments
that adjust lens to refine
the focus of light rays on
the retina
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Near-by objects = thicker
Distance objects = thinner
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Nerve layer located
between the posterior
chamber and the
choroid layer at the
back of the eye
Contains light sensitive
rods (black/white
receptors) and cones
(color receptors)
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Receive images and
convert them into nerve
impulses
The Retina
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Optic disk: (blind spot)
– contains no
rods/cones – nerve
endings of retina
gather to form optic
nerve which transmits
nerve impulses from
the retina to the brain
Retina
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Macula lutea – In the central region of the
retina lies a yellowish spot called the
macula lutea.
Within the center of this structure lies a
small depression called the central fovea.
This region of the retina is the area of the
highest visual acuity.
Visual Pathways
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Optic Chiasma – As the axons of the
ganglion cells of the retina leave the eye,
they converge to form the large optic
nerve. These nerves eventually cross at
the base of the brain (just in front of the
pituitary gland) in a formation referred to
as the optic chiasma.
Nerve fibers continue into the posterior
portion of the thalamus of the brain and
enter nerve tracts that “radiate” to the
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occipital lobe of the brain. Some fibers
continue from the lateral geniculate
nucleus to the brainstem where they
contribute to simultaneous eye
movements and control of visual reflexes.
The Anterior Segment –
front 1/3 of eye
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Divided into anterior
and posterior chambers
Anterior chamber
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Posterior chamber
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behind the cornea in
front of the iris
Between the back of the iris and
the front of the lens
These chambers filled with aqueous humor (fluid)
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Nourishes intraocular structures
Constantly filtered and drained which regulates intraocular
pressure (IOP = btwn 12 & 21 mm Hg)
The Posterior Segment –
posterior 2/3 of eye
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Aids in maintaining the
shape of the eye
Contains vitreous
humor
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Lined with retina and
it’s related structures
Normal Action of the Eye
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Accommodation: the eyes make adjustments for
seeing at various distances
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Includes constriction or dilation of the pupil,
movement of the eye, and changes in the shape of
the lens
Convergence: simultaneous inward movement of
both eyes – in an effort to maintain single
binocular vision as an object comes nearer
Visual Acuity: the ability to distinguish object
details and shape at a distance
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Normal vision = 20/20
Snellen Chart: used to measure visual acuity
Summary of Sight
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The eye functions somewhat like a
camera: it receives and focuses light on a
photosensitive receiver, the retina. Light
rays are bent (called refraction) and
brought to focus as they pass through the
cornea and the lens. Once an image is
focused on the retina, stimulated
photoreceptors alter the light signal into
receptor potentials.
Pathology of the Eyes EYELIDS
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Blepharoptosis (A)
Ectropion (B)
Entropion (C)
Hordeolum: (D)
A
C
B
D
Functions of the Ears
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Receive sound
impulses and transmit
them to the brain
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Inner also helps
maintain balance
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Auditory: pertaining
to the sense of
hearing
Acoustic: relating to
sound or hearing
Structures of the Ear
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The Outer Ear
The Middle Ear
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The Auditory
Ossicles
The Eustachian
Tubes
The Inner Ear
The Outer Ear
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Pinna: auricle –
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External portion
 Catches sound
waves and transmits
them into the
external auditory canal
(EAC)
EAC: transmits sound waves from pinna to middle ear
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What is the name for the sticky yellow-brown substance
that functions to prevent bacteria and dust from entering
the middle ear??
CERUMEN (earwax)
The Middle Ear
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Tympanic Membrane (eardrum)
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Transmits sound by vibrating
Surrounded by hollow air spaces – mastoid cells
(which can easily become involved in a middle
ear infection)
The Auditory Ossicles
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3 small bones in the
middle ear
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Transmit sound waves from
the eardrum to the inner
ear by vibration
Named for their shape
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Malleus: hammer
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Incus: anvil
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Stapes: stirrup
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The Inner Ear-
Contains sensory receptors for
hearing and balance
labyrinth
 Cochlea: spiral shaped passage that leads
from the oval window
 Cochlear duct: filled with fluid that vibrates when sound
waves strike it
 Organ of Corti: receptor site
that receives vibrations and
relays them to the auditory
nerve fibers that transmit
them to the auditory center
of the cerebral cortex, where
they are interpreted and heard
 Semicircular canals: helps maintain
equilibrium
Normal Action of the Ears
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Air conduction: sound waves enter the ear
through the pinna, travel down the auditory
canal, and strike the TM between the outer and
middle ear
Bone conduction: as the eardrum vibrates, it
moves the auditory ossicles and these conduct
sound waves through the middle ear
Sensorineural conduction: sound vibrations
reach the inner ear via the oval window where
the structures of the inner ear receive the sound
waves and relay them to the brain
Sense of Equilibrium
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Sense of equilibrium consists of two parts:
Static and Dynamic.
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Static equilibrium helps to maintain the
position of the head and body when they are
still.
Dynamic equilibrium maintains balance when
the head and body suddenly move and rotate.
Static Equilibrium
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Organs are located within the bony
vestibule of the inner ear, inside the
utricle and saccule (expansions of the
membranous labyrinth). Hair cells lie
inside the utricle and saccule.
Gravity causes the gelatin and otoliths to
shift, bending hair cells and generating a
nervous impulse. Impulses travel to the
brain via the vestibular branch of the
vestibulocochlear nerve, indicating the
head position
Dynamic Equilibrium
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Three semicircular canals detect motion of the head and
aid in balancing the head and body during sudden
movement.
Organs involved are called cristae ampullaris and are
located in the ampulla of each semicircular canal of the
inner ear.
Rapid turning of the head or body generates impulses as
the cupula and hair cells bend, which are interpreted and
modified by the brain to maintain specific positions for
the body. Mechanoreceptors associated with the joints
and the changes detected by the eyes also help maintain
equilibrium
Pathology of the Ears
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Outer Ear
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Middle Ear
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Eustachitis: inflammation of the eustachian tube
Mastoiditis
Otosclerosis: ankylosing of the bones of the middle ear =
hearing loss
Otitis Media
Inner Ear
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Otalgia: earache
Otitis: inflammation of the ear
Otomycosis: swimmer’s ear
Meniere’s syndrome: vertigo, fluctuating hearing loss, tinnitus
(ringing or buzzing in the ears)
Hearing Loss
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Deafness
Noise-Induced hearing loss
Diagnostic Procedures of the Ears
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Audiometry: use of audiometer to
measure hearing
Speech audiometry: measures the
threshold of speech reception and speech
discrimination
Monaural: testing involving one ear
Binuaral: testing involving both ears
Treatment Procedures of the Ears
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Outer Ear
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Middle Ear
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Otoplasty: surgical repair of the pinna of the
ear
Mastoidectomy
Tympanocentesis
Tympanostomy tubes
Inner Ear
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Fenestration
Labyrinthectomy
Labyrinthotomy
DEAFNESS
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Deafness is defined as any reduction of
hearing and is categorized as follows:
conduction-type deafness, sensorineural
deafness, central deafness, mixed-type
deafness, functional deafness, congenital
deafness, and neonatal deafness.
Conduction-Type Deafness
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Occurs when there is an interference with
the transmission of sounds from the
external or middle ear, preventing sound
waves from entering the inner ear.
Sensorineural Deafness
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Also referred to as “nerve deafness” and
involves the cochlear portion of the inner
ear of the cochlear division of the
vestibulocochlear nerve.
Central Deafness
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Involves the acoustic center of the
cerebral cortex.
 Mixed-Type Deafness
Involves both the conduction system and
the nervous system.
 Functional Deafness
Sometimes called “selective” deafness.
Is psychogenic, with no conduction or
nerve problem identified.
Deafness (continued)
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Congenital Deafness
Present at birth. Cause may be hereditary
or may be due to the mother’s exposure
to disease or toxic drugs during the
pregnancy.
Neonatal Deafness
Occurs at the time of birth. Is caused by
prematurity, trauma, or Rh
imcompatability.
SENSE OF TASTE
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Special organs of taste are the taste buds.
They are primarily on the surface of the
tongue and are located within tiny,
numerous elevations called papillae. Each
taste bud consists of cells called gustatory
cells that function as receptors.
Chemicals must be dissolved in saliva that
surrounds the taste cells in order to be
tasted.
Four Types of Taste Buds
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Each taste bud is stimulated by a specific
type of chemical that produces a certain
taste sensation: sweet, sour, salty, and
bitter. (Some recognize two additional
sensations: alkaline and metallic)
Areas of taste receptors on tongue:
Sweet – tip of tongue
Sour – lateral edge of tongue
Salt – tip and upper portion of tongue
Bitter – Back of tongue
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Taste impulses from the anterior two thirds of
the tongue are relayed to the brain via the facial
(VII) nerve.
Taste impulses from the posterior one third of
the tongue and back of the mouth are relayed
via the glossopharyngeal (IX) nerve.
Taste impulses from the base of the tongue and
the pharynx are relayed by the vagus (X) nerve.
Impulses from these nerves are transmitted to
the medulla oblongata, then to the thalamus,
and finally to the gustatory cortex of the parietal
lobe.
SENSE OF SMELL
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Sense of smell is referred to as olfactory senses.
Humans can distinguish approximately 10,000 chemicals.
Nerve pathways for the sense of smell are directly
connected to older, more primitive areas of the brain
(limbic system) that are associated with memory and
basic primal instincts. For example, a whiff of perfume
can bring up memories of an old girlfriend.
Smell is an important component for attraction and
sexuality.
Olfactory senses and taste operate together to aid in
food selection. Smell accounts for 90% of what we think
we taste.
Mechanics of Smell
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The nasal cavity has a patch of tissue the size of a
postage stamp with specialized olfactory receptors.
To be detected, chemicals that enter the nasal cavity
must be in a gaseous state and must be dissolved in the
watery fluid surrounding nasal cilia.
Once olfactory receptors have been stimulated, impulses
are transmitted along axons of the receptor cells of the
olfactory nerves.
The impulse is then transmitted to the olfactory tract
and then to interpreting centers in the base of the
frontal lobes.
The impulse then travels along olfactory tracts to the
limbic system, and lastly to the olfactory cortex within
the temporal lobes
Objectives:
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Describe the functions and structures of the
eyes and adnexa
Recognize, define, spell, and pronounce terms
related to the pathology and diagnostic and
treatment procedures of eye disorders
Describe the functions and structures of the ears
Recognize, define, spell, and pronounce terms
related to the pathology and diagnostic and
treatment procedures of ear disorders