The Sensory System (Hearing, Nose & Tongue)

Hearing

interpreted in the auditory cortex of the temporal lobe

Equilibrium (balance)

interpreted in the cerebellum

The External Ear

Involved in hearing only

Pinna (auricle)

collects sound

External auditory canal

channels sound inward

• Narrow chamber in the temporal bone-

through the external auditory meatus

• Lined with skin

• Ceruminous (wax) glands are present

• Ends at the tympanic membrane

(eardrum

The Middle Ear or Tympanic Cavity

-Air-filled cavity within the temporal bone

• Only involved in the sense of hearing

Eardrum- The opening from the auditory canal is

covered by the tympanic membrane

Eustacian tube

•The auditory tube connecting the middle ear

with the throat

Inner Ear or Bony Labyrinth

• Also known as

osseous labyrinth-

twisted bony

tubes

• Includes sense

organs

for hearing and

balance

• Filled with perilymph

•Vibrations of the stapes push and pull

on the membranous oval window, moving

the perilymph through the cochlea. The

round window is a membrane at the

opposite end to relieve pressure

Bones of the Tympanic Cavity

• Vibrations from

eardrum move

the malleus

• These bones

transfer sound

to the inner ear

Upper Chamber-

The scala Vestibuli

Lower chamber

the scala tympani

Organ of Corti

• Located within the cochlea

• Receptors = hair cells on the basilar membrane

Gel-like tectorial membrane is capable of bending hair cells

endolymph in the membranous labyrinth of the cochlear duct flows over it and pushes on the membrane

Cochlear nerve attached

to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Mechanisms of Hearing

Vibrations from sound waves move tectorial membrane (pass through the endolymph fluid filling the membranous labyrinth in the cochlear duct)

Hair Cells

bent by the membrane

Continued stimulation can lead to adaptation

over stimulation to the brain makes it stop interpreting the sounds

Static equilibrium

in the vestibule

Dynamic equilibrium

in the semicircular canals

Chemical Senses – Taste and Smell

• Both senses use chemoreceptors

•Stimulated by chemicals in solution

•Taste has four types of receptors

•Smell can differentiate a large range of

chemicals

• Both senses complement each other

and respond to many of the same

stimuli

Olfactory receptors

in the roof of the nasal

cavity

• Neurons with long cilia

• Chemicals must be dissolved in mucus for

detection

Interpretation of smells is made in the cortex

olfactory area of temporal lobe

Taste buds

house the receptor organs; found on the sides of papillae

Tongue

is covered with projections called papillae

Filiform papillae

sharp with no taste buds

Fungifiorm papillae

rounded with taste buds

Circumvallate papillae

large papillae with taste buds

Gustatory cells

are the receptors

• Have gustatory hairs (long microvilli)

• Hairs are stimulated by chemicals dissolved

in saliva

Impulses are carried to

the gustatory complex

________ by

several cranial nerves

because taste buds are

found in different areas

pareital lobe