 Taste,
smell, sight, hearing, and balance
 Special sensory receptors
Large complex organs (eyes, ears)
 Localized clusters of receptors (taste buds)
 confined to the head region

 Visual
organs
 70% of all sensory receptors are in the eyes
 40% of the cerebral cortex is involved in
processing visual information
Lacrimal apparatus –
keeps the surface of the
eye moist
 Lacrimal gland –
produces lacrimal
fluid
 Lacrimal sac – fluid
empties into nasal
cavity
Eyelids- anterior protection
 Eyelashes
 Meibomian glands

Modified sebaceous glands at eyelid edges
 Secrete oily lubricant for the eye


Ciliary glands
Between eyelashes
 Modified sweat glands


Conjuctiva
Delicate membrane that lines eyelids and covers part
of eye.
 Fuses with corneal epithelium
 Secretes mucus to keep eyes moist

 Controlled
by 6
external muscles
 Hollow
sphere.
 Fluid filled interior- helps maintain shape
 Walls composed of 3 tunics

Fibrous tunic- outermost (white of the eye)
Thick connective tissue
 Composed of two regions of connective tissue
 Sclera – posterior five-sixths of the tunic



White, opaque region
Provides shape and an anchor for eye muscles
Cornea – anterior transparent window
 Limbus – junction between sclera and cornea
 Scleral venous sinus – allows aqueous humor to drain


Vascular tunic- middle coat
Composed of choroid, ciliary body, and iris
 Choroid – vascular, darkly pigmented membrane





Brown color – from melanocytes
Prevents scattering of light rays within the eye
Choroid corresponds to the arachnoid and pia maters
Ciliary body- attachment to lens and iris


Iris- smooth muscle fibers that act like the diaphragm of
a camera.
Pupil- opens to let light in

Sensory tunic- innermost layer (retina)

Composed of two layers
 Pigmented layer – single layer of melanocytes
 Neural layer – sheet of nervous tissue

Contains three main types of neurons
 Photoreceptor
cells
Rod cells – more sensitive to light
• Allow vision in dim light
 Cone cells – operate best in bright light
• Enable high-acuity, color vision

 Bipolar
cells
 Ganglion cells
 Macula
lutea –
contains mostly
cones
 Fovea centralis –
contains only
cones

Region of highest
visual acuity
 Optic
spot
disc – blind
 The
lens and ciliary zonules divide the eye
 Posterior cavity

Filled with vitreous humor




Clear, jelly-like substance
Transmits light
Supports the posterior surface of the lens
Helps maintain intraocular pressure
 Anterior

cavity
Divided into anterior and posterior chambers



Anterior chamber – between the cornea and iris
Posterior chamber – between the iris and lens
Filled with aqueous humor



Renewed continuously
Formed as a blood filtrate
Supplies nutrients to the lens and cornea
A thick, transparent, biconvex disc held in
place by its ciliary zonule.
 Color

Blindness
Lacking one type of cone
 Cataracts

Lens becomes hard and opaque due to age
 Glaucoma

Increased pressure in eyes due to lack of
drainage for aqueos humor
 Structures
in the eye bend light rays
 Light rays converge on the retina at a single
focal point
 Light bending structures (refractory media)

The lens, cornea, and humors
 Accommodation
– curvature of the lens is
adjustable

Allows for focusing on nearby objects
Each side of the brain
receives images from both
eyes.
Each eye sees a slightly
different view, but visual
fields overlap.
This gives us binocular
vision.
 Age-related

macular degeneration (AMD)
Involves the buildup of visual pigments in the retina
Wet
 Retinopathy

in diabetes
Vessels have weak walls – causes hemorrhaging
and blindness
 receptor
organ for hearing and equilibrium
 Composed of three main regions



Outer ear – functions in hearing
Middle ear – functions in hearing
Inner ear – functions in both hearing and
equilibrium
 The

The auricle (pinna)


part we think of as the ear.
Helps direct sounds
External acoustic meatus
Canal lined with skin
 Contains hairs, sebaceous glands, and ceruminous
glands (secrete yellow wax)


Tympanic membrane

Forms the boundary between the external and
middle ear

The tympanic cavity



A small, air-filled space
Located within the petrous portion of the temporal bone
Contains ossicles that transmit vibration from eardrum
to fluids of inner ear.




Medial wall is penetrated by:



Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Oval window
Round window
Pharyngotympanic tube (auditory or eustachian tube)

Links the middle ear and pharynx
 Inner
ear – also called the bony labyrinth
 Lies within the petrous portion of the
temporal bone behind the eye socket
 cavity consisting of three parts



Semicircular canals
Vestibule
Cochlea
 Membranous


Series of membrane-walled sacs and ducts within
the bony laryrinth.
Consists of three main parts




Semicircular ducts
Utricle and saccule
Cochlear duct
Filled with a clear fluid – endolymph


labyrinth
Confined to the membranous labyrinth
Bony labyrinth is filled with perilymph

Continuous with cerebrospinal fluid
Figure 16.20
The central part of the bony labyrinth (actually a
cavity)
 Lies medial to the middle ear
 Utricle and saccule – suspended in perilymph



Two egg-shaped parts of the membranous labyrinth
House the macula – a spot of sensory epithelium
that contains receptor cells
 Monitor the position of the head when the head is
still
 Contains columnar supporting cells
 Receptor cells – called hair cells

Synapse with the vestibular nerve
 Lie
posterior and lateral to the vestibule
 Anterior and posterior semicircular canals

Lie in the vertical plane at right angles
 Lateral

semicircular canal
Lies in the horizontal plane
 Semicircular
duct – snakes through each
semicircular canal
 Membranous ampulla – located within bony
ampulla

Houses a structure called a crista ampullaris

Responsible for maintaining static equilibrium.
Figure 16.22
A
spiraling chamber in the bony labyrinth
 contains receptors for hearing
 The


Transmits information on the position and
movement of the head
Most information goes to lower brain centers
(reflex centers)
 The

equilibrium pathway
ascending auditory pathway
Transmits information from cochlear receptors to
the cerebral cortex
 Motion

sickness – carsickness, seasickness
Popular theory for a cause – a mismatch of
sensory inputs
 Meniere’s
syndrome – equilibrium is greatly
disturbed

Excessive amounts of endolymph in the
membranous labyrinth
Normal
Meniere’s
 Deafness

Conduction deafness

Sound vibrations cannot be conducted to the inner ear

Ruptured tympanic membrane, otitis media,
otosclerosis
Normal tympanic
membrane
Ruptured tympanic
membrane
Otitis media
 Deafness

Sensorineural deafness

Results from damage to any part of the
auditory pathway
mild
severe
 Taste

receptors
Occur in taste buds




Most are found on the surface of the tongue
Located within tongue papillae (circumvallate and
fungiform)
Collection of 50-100 epithelial cells
Contain three major cell types
 Supporting cells
 Gustatory cells-respond to chemicals in saliva


Contain long microvilli – extend through a taste pore
Basal cells
 Four




basic qualities of taste
Sweet (responds to sugars and amino acids)
Sour (respond to hydrogen ions or acidity)
Salty (respond to metals)
Bitter (responds to alkaloids)
 No
structural difference among taste buds
 Taste
information reaches the cerebral
cortex



Primarily through the facial (VII) and
glossopharyngeal (IX) nerves
Some taste information through the vagus nerve
(X)
Sensory neurons synapse in the medulla

Located in the solitary nucleus
 Receptors
occupy a postage-stamp sixe area
in the roof of each nasal cavity.
 Olfactory receptor cells

Neurons with olfactory hairs that transmit to the
olfactory nerve.