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