THE SPECIAL SENSES
PETER REONISTO, MD
MOORPARK COLLEGE
TRADITIONAL SENSES
1) Smell
2) Taste
3) Sight
4) Hearing
5) Equilibrium
SPECIAL SENSES RECEPTORS
• Localized and confined to the head region
• Not free nerve endings of sensory neurons
• Distinct receptor cells
• Receptor cells – neuron-like epithelial cells that transfer sensory information to other neurons in afferent pathways to the brain
• Sensory receptor cells are housed in complex sensory organs (eye or ear) or in distinctive epithelial structures (taste buds or olfactory epithelium)
• Sensory information travels via cranial nerves
CHEMICAL SENSES
TASTE (Gustation)Taste receptors- located
on1) tongue surface 2) posterior palate3) Inner surface of
cheek4) Posterior pharyngeal
wall5) epiglottis
SMELL (Olfaction)
Smell receptors- called olfactory epithelium; located on
1) Superior nasal concha
2) Superior nasal septum
Taste• 10,000 taste buds
in your mouth
• Sweet and salty are least sensitive
• Bitter ones are most sensitive
Your tongue picks up four types of
taste: sweet, sour, bitter, and
salty.
TASTETongue mucosa (papillae):
1) Fungiform papillae- scattered over the entire surface of the tongue.
2) (Circum)vallate papillae- inverted V near the back of the tongue
Taste Buds10,000 taste
buds in the tongue
Tastebuds closeup Molecules of food
stimulate the taste cells to send
messages to your brain. The sweet and salty buds are the least sensitive and the
bitter ones are the most
sensitive.
Posterior 1/3,pharynx
Anterior 2/3VAGUS NERVE
Lower pharynx, epiglottis
THALAMIC NUCLEI
CN VII,IX, XTaste
Buds
Solitary Nucleus
(Medulla Oblongata)
SMELLOdor particles
drift into your nose and cause your smell
receptors to send
messages to your brain.
OLFACTORY BULB (SMELL)
• Olfactory epithelium- pseudostratified columnar epithelium
• Olfactory receptor cell- bipolar neurons
The smell part of the brain is in the limbic
region, and is
connected to feeling
and memory.
Olfactory epitheliumOlfactory receptor cell
Olfactory bulb (CN I)
Limbic Lobe
Vision Your eyes gather visual
information, which is
sent to your brain to be processed
and understood.
ANATOMY OF THE EYE1) SCLERA
Cornea
2) CHOROID Ciliary Body
Iris
3) RETINA CONJUNCTIVA
Vision (retina)Vision: Retina
• Rods sense brightness
• Cones sense color The retina, in the back
of your eye, has cells that are sensitive to light. They connect directly to your brain.
VISUAL PATHWAY
Light/Image
AqeousHumor Vitreous
HumorOptic Nerve
Rods or Cones(Photoreceptors)
RETINAL/GANGLION CELLS
OPTIC NERVE
OPTIC CHIASM
OPTIC TRACT
LATERAL GENICULATE NUCLEUS
OPTIC RADIATION
VISUAL CORTEX
VISUAL FIELD DEFECTS
Hearing Sound waves make your eardrum vibrate.
Then, the small bones in your ear vibrate, and
the vibrations go through the snail-
like cochlea, which turns them into
nerve impulses to your brain.
THE EAR: HEARING AND EQUILIBRIUM
• Regions:
1) Outer (External) Ear
2) Middle Ear
3) Inner (Internal) Ear
EXTERNAL EAR Components:
a) Auricle (Pinna)
b) External Acoustic (Auditory) canal
c) Hair, sebaceous gland, modified apocrine sweat gland (ceruminous gland)
d) Tympanic membrane
1/3 Elastic cartilage
2/3 Temporal bone
MIDDLE EARBoundaries: Petrous part of temporal bonea) Medial boundary (1) superior oval window (vestibular) (2) inferior round window (cochlear)b) Lateral boundary (1) Tympanic membranec) Superior boundary (1) Petrous boned) Posterior wall (1) Mastoid antrum- leadsto the mastoid air cells e) Anterior wall (1) Pharyngotympanic tube- leads to the pharynxf) Inferior boundary (1) thin bony floor where the internal jugular vein lies
MIDDLE EAR
Components:
a) Ossicles
(1) Malleus (hammer)
(2) Incus (anvil)
(3) Stapes (stirrup)
b) Skeletal muscle
(1) Tensor tympani
(2) Stapedius
Origin: cartilage part of Pharyngotympanic tube.Insertion: malleus
Origin: Posterior wallMiddle ear
Insertion: Stapes
INNER EAR (LABYRINTH)Bony labyrinth: (petrous
bone cavity); filled with perilymph
1) Semicircular canals
2) Vestibule
3) cochlea
Membranous labyrinth- membrane-walled sacs and ducts); filled with endolymph
1) Semicircular ducts2) Utricle and saccule3) Cochlear duct
COCHLEA
• Spiraling chamber• Coils for about 2 ½ turns around a pillar
called modiolus• Consist of coiled part of the membranous
labyrinth called cochlear duct (scala media) which contains the receptors for hearing
• Cochlear nerve runs through the core of the modiolus
AUDITORY PATHWAY
Ends with the vestibule
Ends at the roundwindow
Cochlear duct
Reissner’smembrane
Scalamedia
Scalavestibuli
Scalatympani
Outerhair cell
Inner hair cell
Basilarmembrane
Auditorynerve
Tectorial membrane
SpiralOrgan of
Corti
1 row of inner hair cells
3 rows of outer hair cells
AUDITORY PATHWAY
Cochlear division CN VIII
Hair cells (Organ of corti)
Spiral ganglion
Cochlear nuclei (medulla)
Nuclei of lateral lemniscus
Lateral Lemniscus
Inferior colliculi (midbrain)
Brachium of inferior colliculi
Medial geniculate body
Acoustic area (temporal lobe cortex)
SEMICIRCULAR CANAL AND VESTIBULE
Handles EQUILIBRIUM PATHWAY:
1) Cupula (semicircular canals)
2) Macula (Vestibule)
Cupula and Macula
Vestibular nerve
VestibularNuclei in medulla
VestibularNuclei in
cerebellum
Reflex centers
END