Download Essentials of Human Anatomy Special Senses Special Senses

Essentials of Human Anatomy
Special Senses
Special Senses
• sensory receptors are within large, complex sensory
organs in the head
• smell in olfactory organs
• taste in taste buds
• hearing and equilibrium in ears
• sight in eyes
Sense of Smell
Olfactory Receptors
• chemoreceptors
• respond to chemicals dissolved in liquids
Olfactory Organs
• contain olfactory receptors and supporting epithelial
cells
• cover parts of nasal cavity, superior nasal conchae,
and a portion of the nasal septum
Olfactory Receptors
Olfactory Nerve Pathways
Once olfactory receptors are stimulated, nerve impulses
travel through
• olfactory nerves
olfactory bulbs
olfactory
tracts
limbic system (for emotions) and
olfactory cortex (for interpretation)
Olfactory Stimulation
• olfactory organs located high in the nasal cavity
above the usual pathway of inhaled air
• olfactory receptors undergo sensory adaptation
rapidly
• sense of smell drops by 50% within a second after
stimulation
Sense of Taste
Taste Buds
• organs of taste
• located on papillae of tongue, roof of mouth, linings of
cheeks and walls of pharynx
Taste Receptors
• chemoreceptors
• taste cells – modified epithelial cells that function
as receptors
• taste hairs –microvilli that protrude from taste
cells; sensitive parts of taste cells
Taste Receptors
Taste Sensations
Four Primary Taste Sensations
• sweet – stimulated by carbohydrates
• salty – stimulated by salts
• sour – stimulated by acids
• bitter – stimulated by many organic
compounds
Spicy foods activate pain receptors
Taste Nerve Pathways
Sensory impulses from
taste receptors travel
along
• cranial nerves to
• medulla
oblongata to
• thalamus to
• gustatory cortex
(for interpretation)
Hearing
Ear – organ of hearing
Three Sections
• External
• Middle
• Inner
External Ear
• auricle
• collects sounds waves
• external auditory meatus
• lined with ceruminous glands
• carries sound to tympanic
membrane
• terminates with tympanic
membrane
• tympanic membrane
• vibrates in response to sound
waves
Middle Ear
• tympanic cavity
• air-filled space in temporal
bone
• auditory ossicles
• vibrate in response to tympanic
membrane
• malleus, incus, and stapes
• oval window
• opening in wall of tympanic
cavity
• stapes vibrates against it to
move fluids in inner ear
Auditory Tube
• eustachian tube
• connects middle ear to
throat
• helps maintain equal
pressure on both sides
of tympanic membrane
• usually closed by
valve-like flaps in throat
Inner Ear
• complex system of labyrinths
• osseous labyrinth
• bony canal in temporal
bone
• filled with perilymph
• membranous labyrinth
• tube within osseous
labyrinth
• filled with endolymph
Inner Ear
Three Parts of Labyrinths
• cochlea
• functions in hearing
• semicircular canals
• functions in
equilibrium
• vestibule
• functions in
equilibrium
Cochlea
Scala vestibuli
• upper compartment
• leads from oval window to
apex of spiral part of bony
labyrinth
Scala tympani
• lower compartment
• extends from apex of the
cochlea to round window
• part of bony labyrinth
Cochlea
Cochlear duct
• portion of membranous
labyrinth in cochlea
Vestibular membrane
• separates cochlear duct
from scala vestibuli
Basilar membrane
• separates cochlear duct
from scala tympani
Organ of Corti
• group of hearing receptor cells (hair cells)
• on upper surface of basilar membrane
• different frequencies of vibration move different parts of basilar membrane
• particular sound frequencies cause hairs of receptor cells to bend
• nerve impulse generated
Auditory Pathway
Cochlear branch of CN VIII
To cochlear
nucleus of
medulla
To inferior colliculus of
opposite side of midbrain
To thalamus
To auditory cortex
The Sense of Vision
• Visual receptors (photoreceptors) in the eyes to detect
light, color, and movement.
• Accessory structures of the eye.
– provide a superficial covering over its anterior exposed surface
(conjunctiva)
– prevent foreign objects from coming into contact with the eye
(eyebrows, eyelashes, and eyelids)
– keep the exposed surface moist, clean, and lubricated (lacrimal
glands)
Lacrimal Apparatus
• lacrimal gland
• lateral to eye
• secretes tears
• canaliculi
• collect tears
• lacrimal sac
• collects from canaliculi
• nasolacrimal duct
• collects from lacrimal
sac
• empties tears into nasal
cavity
Structure of the Eye
• hollow
• spherical
• wall has 3 layers
• outer fibrous tunic
• middle vascular tunic
• inner nervous tunic
Cavities and Chambers of the Eye
• The internal space of the eye is subdivided by the lens
into two separate cavities.
– anterior cavity
– posterior cavity
Cavities and Chambers of the Eye
• The anterior cavity is
– the space anterior to the
lens and posterior to the
cornea
• The iris of the eye
subdivides the anterior
cavity further into two
chambers.
– anterior chamber is between
the iris and cornea
– posterior chamber is
between the lens and the iris
Vitreous Humor
• Posterior cavity is posterior to the lens and anterior to
the retina.
• Transparent, gelatinous vitreous body which completely
fills the space between the lens and the retina.
Optic Disc
• Optic disc lacks photoreceptors.
• Called the blind spot because no image forms there.
• Just lateral to the optic disc is a rounded, yellowish
region of the retina called the macula lutea containing a
pit called the fovea centralis (the area of sharpest
vision).
– contains the highest proportion of cones and almost no rods
Visual Pathways
• Each optic nerve conducts
visual stimulus
information.
• At the optic chiasm, some
axons from the optic nerve
decussate.
• The optic tract on each
side then contains axons
from both eyes.
• Visual stimulus information
is processed by the
thalamus and then
interpreted by visual
association areas in the
cerebrum.
Extrinsic Eye Muscles
Superior rectus
• rotates eye up and medially
Lateral rectus
• rotates eye laterally
Medial rectus
• rotates eye medially
Inferior rectus
• rotates eye down and medially
Superior oblique
• rotates eye down and laterally
Inferior oblique
• rotates eye up and laterally
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