Download ecture 23- special senses

LESSON # 23
Special Senses:
1- Olfaction (smell)
2- Gustation (taste)
3- Vision
4- Equilibrium and Hearing
Special Senses:
1- Olfaction (smell)
2- Gustation (taste)
3- Vision
4- Equilibrium and Hearing
1- Olfaction (smell)
It is provided by paired olfactory organs, which are located in the nasal cavity on
either side of the nasal septum.
Olfactory bulb
Olfactory tract
Olfactory nerve fibers
Cribriform plate of ethmoid
Olfactory organ:
Olfactory epithelium
Lamina propria
Olfactory Their secretions absorb
(Bowman) water and form a thick
gland
pigmented mucus.
Olfactory
nerve fibers
Lamina propria
It consists of areolar connective
tissue with blood vessels and
nerves.
Olfactory epithelium:
1- Regenerative basal cells
They divide to replace worn
out olfactory receptors cells.
Knob
They are enlargements that
project beyond the epithelial
surface and provide the base
for up to 20 cilia.
Cilia
They contain receptors called odorant-binding proteins that match
specific odorant particles. They can only be stimulated by water-soluble
and lipid-soluble particles that can diffuse through the overlaying mucus.
Depolarization is produced the G protein-second messenger mechanism.
2- Olfactory receptors cells
They are highly modified
neurons sensitive to odorants.
3- Supporting cells
They are epithelial cells
Odorants are small organic
molecules. The strongest smells
are associated with molecules of
high solubility both in water and
lipids.
Olfactory Pathways
Axons leaving the olfactory epithelium
collect into 20 or more bundles and
penetrate cribriform plate of ethmoid to
reach the olfactory bulbs.
Olfactory bulb
Olfactory tract
The parallel distribution of smell
information in the limbic system
and hypothalamus explains the Limbic system
profound emotional and behavioral
Hypothalamus
response, as well as memories, that
can be triggered by certain smells.
Primary olfactory cortex
(temporal lobe)
Arriving information reaches information
centers without first synapsing in thalamus (all
other sensations are relayed from processing
centers in the thalamus).
2- Gustation (taste)
Taste receptors (or gustatory receptors) are distributed on tongue and portions of
pharynx, larynx, and epiglottis.
By the time we reach the adulthood, the taste receptors of the pharynx, larynx
and epiglottis have decreased in importance and abundance.
1- Circumvallated papilla
They for a V near the posterior
margin of the tongue.
They can contain as many as 100
taste buds.
2- Fungiform papilla
They are small and contain about
five taste buds.
3- Filliform papilla
They provide friction that helps the
tongue move objects around the
mouth.
They do not contain taste buds.
Taste Receptors
Transitional They mature to become
cells
gustatory cells.
Basal cells
They divide to
produce daughter
cells that mature
in stages.
Dendrites of sensory
neurons
Cranial nerves VII (facial),
and IX (glossopharyngeal).
Taste pore
Gustatory
Taste hairs
cells
(microvilli)
Dissolved chemicals bind to receptor proteins
and produce depolarization of the cell by two
mechanisms:
1- Open chemically gated ion channels.
2- G protein-second messenger mechanism.
Gustatory Pathways
Cranial nerves that synapse
within solitary nucleus of
medulla oblongata, then on to
thalamus and primary sensory
cortex.
The result of taste receptor stimulation is the release of
neurotransmitters by the receptors cells.
Gustatory cortex
(Insula)
The dendrites of the sensory neurons are tightly wrapped
by folds of the receptor plasma membrane, and
neurotransmitter release generates an action potential in
the afferent fibers.
A conscious perception of taste is produced as the information received from
the taste buds is correlated with other sensory data:
1- Information about the texture of food.
2- Information about taste-related sensations such as “peppering” or “burning hot”.
3- Information about smell from olfactory receptors.
3- Vision
Accessory Structures of the Eye
Lacrimal
gland ducts
Lacrimal
caruncle
Superior and inferior
lacrimal canaliculi
Lacrimal
gland
They carry the tears to
the lacrimal sac.
It produces tears.
Lateral cantus
Medial cantus
Palpebral
conjunctiva
Lower eyelid
Lacrimal sac
It collects tears and
carries them to the
nasolacrimal duct.
Nasolacrimal
duct
It drains excess of tears
to the nasal cavity.
Opening of
nasolacrimal
duct
Extrinsic Muscles of the Eye
(eye looks up)
Trochlea
Superior oblique
(eye rolls, looks down &
to the side)
Superior rectus
Lateral rectus
(eye rotates
laterally)
Medial rectus
(eye rotates
medially)
Inferior oblique
(eye rolls, looks up &
to the side)
Inferior rectus
(eye looks down)
Innervation of the Extrinsic Muscles of the Eye
MUSCLE
ACTION
INNERVATION
SUPERIOR RECTUS
EYE LOOKS UP
OCULOMOTOR (III)
INFERIOR RECTUS
EYE LOOKS DOWN
OCULOMOTOR (III)
MEDIAL RECTUS
EYE ROTATES MEDIALLY
LATERAL RECTUS
EYE ROTATES LATERALLY
SUPERIOR OBLIQUE
INFERIOR OBLIQUE
EYE ROLLS, LOOKS DOWN &
TO THE SIDE
EYE ROLLS, LOOKS UP &
TO THE SIDE
OCULOMOTOR (III)
ABDUCENS (VI)
TROCHLEAR (IV)
OCULOMOTOR (III)
Innervation of the Extrinsic Muscles of the Eye
(eye looks up)
Trochlea
Superior oblique
(eye rolls, looks down &
to the side)
Trochlear
nerve (pair IV)
Superior rectus
Oculomotor
(pair III)
Lateral rectus
(eye rotates
laterally)
Abducens
nerve (pair VI)
Inferior oblique
(eye rolls, looks up &
to the side)
Oculomotor
(pair III)
Medial rectus
(eye rotates
medially)
Oculomotor
(pair III)
Inferior rectus
Oculomotor
(pair III)
(eye looks down)
LAYERS OF THE EYE BALL
1- The fibrous tunic
Sclera or white of the eye (protects and gives
shape to the eyes)
Cornea (clear outer part) (It allows the light to
come in)
Choroid ( vascular layer the nourishes the retina)
2- The vascular tunic
or uvea
Ciliary body
Ciliary muscle (tension the
suspensory ligaments)
Ciliary process (produces the
aqueous humor)
Iris (pigmented areas and intrinsic muscles that
controls the size of the pupil)
3- Neural tunic or
retina
Neural part
Pigmented part
Layers and Chambers of the Eye Ball
Anterior
chamber
Posterior
chamber
Fibrous tunic:
Cornea
Sclera
Anterior
cavity
Lens
Vascular tunic
(uvea):
Iris
Ciliary body
Choroid
Neural tunic
(retina):
Posterior
cavity
Neural part
Pigmented part
Optic disc
It is called also blind spot because
contains no photoreceptors.
Optic nerve
Fovea centralis
It contains only cones,
which are responsible
for the sharpest vision.
Pupil
Lens
It focuses the light
in the retina.
Ciliary Body:
Ciliary processes
It allows the light
to come in.
Cornea
Posterior
cavity
It allows the light to
come in.
It contains vitreous
humor, which
maintains the shape
of the lens &
prevents collapse
Anterior
chamber
Anterior
cavity
Posterior
chamber
It contains aqueous humor that
nourishes the lens & the cornea
because they do not have blood
vessels.
Ciliary muscle
Iris
It controls the size of the pupil.
Sclera venous sinus (canal of Schlemm)
It drains the aqueous humor. The obstruction raises
the intraocular pressure and glaucoma results.
Choroid
It nourishes the retina and absorbs excess of light.
Sclera
It protects & gives the shape to the eyes
Histological Organization of the Retina
Pigmented
part
It absorbs light preventing visual
echoes.
Cones
Photoreceptors
Rods
They provide color vision
They detect light in dim light and
provide black and white vision.
Bipolar They connect the photoreceptors to the ganglion cells.
cells
Ganglion They are neurons whose axons
forms the optic nerve. They carry
cells
visual information.
Neural
part
Light
Amacrine cells They adjust the sensitivity of the
retina by either facilitating or
inhibiting the communication
Horizontal cells between the photoreceptors and
the ganglion cells.
4- Equilibrium and Hearing
Anatomy of the Ear
The special senses of equilibrium and hearing are provided by the ear.
External Ear
Pinna or auricle
Ear canal
Ceruminous glands
Tympanic membrane
Middle Ear
Inner Ear
Ossicles
Pharyngotympanic or
auditory or eustachian tube
External Ear
Membranous labyrinth
Bonny labyrinth
Internal
Ear
Vestibule
Semicircular canals
Cochlea
The External Ear
Tympanic
membrane
Pinna or
auricle
It protects the opening of
the canal and provides
directional sensitivity.
Ear canal
It focus and directs the
sound waves into the
tympanic membrane.
It transmits the sound
waves to the middle
ear ossicles.
The Middle Ear
Incus (anvil)
Malleus (hammer)
Its handle is attached to
the tympanic membrane.
Auditory tube
It equalizes the pressures
on either side of the
tympanic membrane.
Tensor tympani
muscle
It
tenses
the
tympanic
membrane
reducing
the
amount of movement possible.
Stapes (stirrup)
Its base is bound to the oval
window.
Stapedius muscle
It pulls the stapes, reducing
movement of the stapes in the
oval window.
Equilibrium:
Hearing:
1- Linear acceleration (maculae in the vestibule).
2- Gravity (maculae in the vestibule).
3- Rotational movement of head (cristae in the ampulla).
The Internal Ear
Bony labyrinth
Membranous
labyrinth
Organ of Corti in the cochlea.
They contain the cristae
Ampulla (receptors for rotational
movements of the head).
Semicircular canals
Semicircular ducts
Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Vestibule
Utricle Saccule
They contain the maculae
(receptors for sensations of
gravity and linear acceleration).
Cochlea
It contains the organs of
Corti (receptors for hearing).
Equilibrium:
1- Linear acceleration (maculae in the vestibule).
2- Gravity (maculae in the vestibule).
3- Rotational movement of head (cristae in the ampulla).
The basic receptor mechanism is
the same for both senses: hair
cells, which are mechanoreceptors.
Hearing: Organ of Corti in the cochlea.