Download Essentials of Human Anatomy 12

Essentials of Human Anatomy
Special Senses
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG
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
Vestibular Complex:
• Semicircular canals with ampullae
(mutually perpendicular)
• Saccule and utricle (= fill up vestibule)
Two Receptor Organs: Maculae of
Vestibule (or: macula of saccule plus
macula of utricle)
Macula
• responds to
changes in head
position
• bending of hairs
results in generation
of nerve impulse
Crista Ampullaris
•sensory organ of ampulla
• hair cells and supporting
cells
• rapid turns of head or
body stimulate hair cells
Equilibrium
• Rotation of the head
causes endolymph within
the semicircular canal to
push against the cupula
covering the hair cells,
resulting in bending of
their stereocilia and the
initiation of a nerve
impulse.
Equilibrium
Static Equilibrium
• vestibule
• sense position of
head when body is
not moving
Dynamic Equilibrium
• semicircular canals
• sense rotation and
movement of head and
body
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
THE END