Unit 4: Nervous System
Lab 4: Human Eye and Vision
Lab 5: Human Ear
Jessica Radke-Snead, RD, MS
Bio 241 Anatomy & Physiology
Human Eye and Vision:
Practice Questions
1. Which intrinsic eye muscle dilates the pupil?
2. What type of neurons stimulate pupil
dilation?
3. Which intrinsic eye muscle constricts the
pupil?
4. What type of neurons stimulate pupil
dilation?
5. Which muscle changes the tightness of
zonular fibers to change shape of the lens?
Human Eye and Vision:
Practice Questions
1. What is the dense CT that forms the shape of
each palpebrae called?
2. What is the crease of the upper eyelid called?
3. What is the difference between palpebral
and bulbar conjunctiva, if any?
4. The ___ regulates the amount of light that
enters the eyeball?
5. The ciliary processes secrete ___ ___?
Human Eye and Vision
• 3 Layers of the eyeball
– Fibrous tunic: cornea, sclera
– Vascular tunic: choroid, ciliary body and iris
– Retina
• Pigmented layer: between choroid and neural layer; helps
absorb light rays
• Neural layer: processes visual data before sending impulses into
the optic nerve
• Rods: allows vision in dim light; no color
• Cones: produce color vision
• Optic disc contains no rods or cones  “blind spot”
– Blind spot test
Internal anatomy of the eye:
Anterior Cavity
• Anterior to
the lens
• 2 Chambers
– Anterior:
between
cornea and
iris
– Posterior:
between the
iris and the
zonular
fibers
Internal anatomy of the eye:
Anterior Cavity
• Aqueous
humor
– Nourishes
the lens and
cornea
– Replaced
every ~90
min
4
5
2
1
3
Internal anatomy of the eye:
Posterior Chamber
• Vitreous body: jelly-like substances that holds
the retina against the choroid
– No replacment; contains phagocytic cells to
ensure unobstructed vision
• What pressure maintains the shape of the
eyeball and prevents it from collapsing?
Lacrimal Apparatus
What action pumps tears from the lacrimal sac to the
nasolacrimal duct?
Histology of the Retina
Histology of the Retina
Outer limiting
membrane
Sclera
Lab 5: The Human Ear
External Anatomy of the Ear
• Auricle/Pinna:
external ear
• Cartilage
designed to
funnel sound
into the
external
auditory
meatus
– Internal surface of tympanic membrane  Handle
of malleus  incus  stapes  Oval window 
Cochlea (inner ear)
– What type of joints connect the ossicles?
Middle Ear (Tympanic Cavity)
• Auditory ossicles
Middle Ear
• Muscles of the tympanic cavity
– Tensor tympani (malleus): controls vibrations on the
tympanic membrane to prevent damage to the
internal ear from loud noise
– Stapedius (stapes): Reduces large vibrations from
loud noise to protect the oval window
• Eustachian (auditory) tube: connects the middle
ear with the nasopharyx
– Normally closed at medial/pharyngeal end
• Opens during swallowing/yawning  air movement to
equalize middle ear pressure with atmospheric pressure 
promotes normal tympanic membrane vibrations
Bony and Membranous labyrinth
Cochlear Duct of the Inner Ear
• Cochlea: receptors for auditory sensations;
series of cavities in the petrous portion,
temporal bone:
– Bone on outside of the cochlea (bony labyrinth):
Contains perilymph that surrounds the
membranous labyrinth
– Cochlear duct surrounded by membranes
internally  membranous labyrinth that contains
endolymph
Cross Section of Cochlear Duct
• Scala vestibuli: channel above the cochlear duct
that ends at the oval window
• Scala tempani: channel below the cochlear duct
that ends at the round window  tympanic space
• Cochlear duct hosts Organ of Corti
– Vestibular membrane: separates cochlear duct from
scala vestibuli
– Basal membrane supports the organ of corti
– Ciliated cells run the length of the cochlear duct
•
•
Inner row: single cell
Outer row: rows of 3
– Tectoral membrane: sits over hair cells
Scala vestibuli
Cochlear Duct
Tympanic membrane
Scala tympani
Developing Sound in the Inner Ear
1. Sound waves from the tympanic membrane pass
through ossicles
1. Stapes presses into/out of the oval window,
creating waves in the perilymph
1. Perilymph creates waves in the Scala vestibuli 
creates waves in the vestibular membrane and
basalar membrane
Developing Sound in the Inner Ear
4. Basalar membrane vibrates, causing hairs to
press against the tectoral membrane  This
elicits an AP that is sent to the brain for
interpretation
Membrane of round window pushes out when
stapes presses into oval window  dissipates the
force of the sound waves
Physiological Aspects of Hearing
• Frequency: number of waves per second (Hz)
– For most people between 20-20,000 Hz
– Most sensitive: 1000-4000 Hz
– Normal speech range: 125-8000 Hz
• Pitch: subjective perception of different
frequencies
• Amplitude: the amount of energy of sound waves
– Typically measured in decibels (Db)
• Loudness: subjective evaluation of amplitude
Physiological Aspects of Hearing
• Conduction deafness
– Blockage of sound waves as they are conducted
through the external and middle ear to the
sensory apparatus in the cochlea
– If any of the structures do not vibrate normally,
sound waves wouldn’t be amplified and the
membrane covering the oval window won’t
vibrate sufficiently
Physiological Aspects of Hearing
• Nerve deafness
– Damage to the nerve pathway between the
internal cochlea to the acoustic areas of the brain
(auditory complex, temporal lobe)
– Inherited or acquired via nerve damage
• Commonly to hair cells (organi of corti)
• Range of hearing is based upon where the hairs are
located within the cochlear duct
Equilibrium
• Static equilibrium
– Maintenance of the position of the body relative
to the force of gravity
• Dynamic equilibrium
– Maintenance of body position in response to
rotational acceleration or deceleration
• Vestibular apparatus
– Saccule, utricle and semicircular ducts
Dynamic Equilibrium
• Bony and membranous labyrinth
• Semicircular canals: receptors for dynamic
equilibrium
– Anterior: acceleration and deceleration (flips)
– Posterior: lateral movement (cartwheels)
– Lateral: rotational (laterally, clockwise/counterclockwise)
• Ampulla at the end of each canal that contains a
crista (sensory apparatus)
– Basalar membrane with hair cells
– Gelatinious mass that covers the hair cells (cupula)
Dynamic Equilibrium
• Vestibule: oval portion of bony labyrinth;
contains receptors for equilibrium
• Utrica and saccule: sacs inside the
membranous labyrinth that respond to
gravitational pull
– Walls contain macula
• Receptors for static equilibrium
• Also detect linear acceleration/deceleration (car
speed)
• Hair cells
Dynamic Equilibrium
• When we move, endolymph moves and bends
the cupula  bends hair cells
• Based on which semicircular canal hosts the
bending of hair cells determines our
orientation to movement
– Anterior: acceleration and deceleration (flips)
– Posterior: lateral movement; cartwheels
– Lateral: rotational; laterally, clockwise/counterclockwise
Static Equilibrium
• Vestibule: oval portion of bony labyrinth; contains
receptors for equilibrium
• Utrica and saccule: sacs inside the membranous labyrinth
that respond to gravitational pull
– Walls contain macula
• Receptors for static equilibrium
• Also detect linear acceleration/deceleration (car speed)
• Hair cells
• Otolithic membrane: gelatinous mass that sits on the
basalar membrane; hair cells project into this
• Otoliths: calcium carbonate “ear rocks” embedded into
otolithic membrane
• When we move our head, gravity pulls on the odoliths, stretches the
odolithic membrane/bends hair cells  interpretation of gravity via
brain