Unit IV: CoordinationVision and Hearing

Ch. 15 – pgs 505-533

VisionAccessory Structures

Eyelids

Lacrimal apparatus

Extrinsic eye muscles

Tunics of the Eyeball

Optical Apparatus

• Structures refract light to focus on retina– cornea

– aqueous humor

– lens

– vitreous humor Nose

Iris

LensChoroid

Sclera

Fovea in center of macula lutea:

Retina

Visual axis

Photoreceptors

Ganglion cells

Optic disc (blind spot)Central retinal vein

Central retinal artery

Optic nerve

Sclera

Choroid

Neural Apparatus

• Includes retina and optic nerve

• Retina– Ora Serrata

– Optic Disc – no photoreceptors

– Macula Lutea – high concentration of photoreceptors

– Fovea Centralis – finely detailed images

• Optic nerve

Formation of an Image

• Refraction• Bending of light rays • Cornea refracts light more than lens does• Lens fine tunes image• Accomodation – lens changes shape to keep focal distance constant

For Close Vision: Ciliary Muscle Contracted,Lens Rounded

For Distant Vision: Ciliary Muscle Relaxed,Lens Flattened

Focal pointon fovea

Photoreceptors

• Photoreceptors– rod cells

– cone cells

• Pigment epithelium

Photoreceptors

Lateral border Fovea Nasal border

Vis

ual

acu

ity

Fovea Optic disc

Low Density of Cones

High Density of Cones

Low Density of RodsHigh Density of Rods

Notes on Vision

• Adaptation

− Light Adaptation: 5-10 minutes to adjust retinal sensitivity

− Dark Adaptation: 1-2 minutes for rods to function, 20-30

minutes to reach max sensitivity

• Duplicity theory

− Rods: high sensitivity

− Cones: high resolution

Photoreceptors

Optic nerve (II)

Optic chiasm

Half the fibers cross over to the opposite side

Occipital cortex of the cerebral hemisphere

Visual cortex of the occipital lobes

Left cerebralhemisphere

Right cerebralhemisphere

Superiorcolliculus Projection fibers

(optic radiation)

Lateral geniculatenucleus

Optic tractDiencephalon

andbrain stem

Optic discRetina

Right eyeonly

Left eyeonly

Binocular vision

Right sideLeft side

Combined Visual Field

Projection Pathway

• Binocular vision

• Stereoscopic vision

− Depth perception

Vision Problems

(a) Emmetropia (normal) (b) Hyperopia (farsightedness) (c) Myopia (nearsightedness)

Focal plane

Focal plane

CorrectedConcave lensConvex lens

Uncorrected

Corrected

Uncorrected

Focal plane

• Cataracts – cloudy area in the lens can cause blindness surgically remove affected area

Vision Problems

• Color blindness

• Glaucoma – optic nerve is damaged Increased pressure in eye Laser, surgery temporary treatment

•Macular degeneration – loss of photoreceptors in macula– Retina becomes detached from choroid– Difficult to read or recognize faces

• Astigmatism – refraction error of the eye– Irregular shape of cornea or lens– Difficulties in seeing fine detail– Treatment: glasses, refractive surgery

The Ear

• Sound –− Atmospheric− Internal

• Equilibrium –

Properties of Sound

• Pitch – high/low– higher the frequency (Hz), higher the pitch– 20 – 20,000 Hz range; speech is 1500-4000 Hz

• Loudness – perception of sound energy– Higher the amplitude (dB), louder the sound– 0 dB – 140 range; speech is 60 dB

Time (sec)

Amplitude of a sound

1 wavelength

So

un

d e

ner

gy

arri

vin

g a

tty

mp

anic

mem

bra

ne

Outer Ear

External Ear Middle Ear Inner Ear

Tonasopharynx

Externalacousticmeatus

Elastic cartilages

Auricle(pinna)

Lobule(earlobe)

Auditory Ossicles

Muscles

Malleus Incus Stapes

Temporal bone

Stabilizingligament

Branch offacial nerve

VII (cut)Externalacoustic

meatusTympanic cavity

Tympanic membrane

Round window

Auditory tube

Stapedius muscle

Tensor tympani muscle

Ovalwindow

Middle Ear

Located in the tympanic cavity of the temporal bone.

Inner Ear

Housed in a maze of temporal bone passageways – bony labyrinth

Cochlea

Inner Ear

Otolith

Maculae

Nerve fibers

Gravity Gravity

Otolithmoves

“downhill,”distorting haircell processes

Receptoroutput

increases

Vestibule: Saccule and Utricle

Anterior semicircular duct for “yes”

Lat

eral

sem

icirc

ular

duct fo

r “no”

Posterior semicircular duct for tilting head to the side

Inner Ear

Cupula

EndolymphHair cells

(b) (c)

Direction ofhead rotation

Endolymph lagsbehind dueto inertia

Cupula ispushed overand stimulateshair cells

Cristaampullaris

Supportingcells

Sensorynerve fibers

Projection Pathway for Equilibrium

Figure 15.9 1

Stimulation of hair cells.

Vestibulocochlear nerve (VIII)

The vestibular nuclei Integrate sensory information

Superior colliculi

The reflexive motorcommands distributed to the cranial nerves (N III, N IV, N VI, and N XI) for eye, head, andneck movements.

Cerebellum

Spinal cord adjustperipheral muscle tone andcomplement the reflexivemovements of the head orneck.

Vestibulocochlearnerve (VIII)

Cochlearbranch

Vestibule

Vestibularganglion

Semicircularcanals

Organ of Corti(Spiral Organ/Acoustic Organ)

Projection Pathway for Hearing

Tympanicmembrane

Roundwindow

Movementof sound

waves

Cochlear duct

Tympanic duct

Basilar membrane

Vestibular duct

Vestibular membrane

Soundwaves arriveat thetympanicmembrane.

Displacement of the auditoryossicles.

Pressure wavesin the perilymphof the vestibularduct.

The pressurewaves distortthe basilarmembrane

Vibrationof hair cellsagainst thetectorialmembrane.

Relayed to the CNSover the cochlearbranch of cranialnerve VIII.

Projection Pathway for Hearing

Figure 15.9 3

Temporal lobe. Perception of pitch is based on what portion of the auditory cortexis stimulated, and yourperception of volume by the degree ofstimulation at that location.

Vestibulocochlear Nerve (VIII)

High-frequency sounds stimulate receptors closest to the oval window.

Thalamus

Inferior colliculus

Medulla oblongata

To spinal cordthrough the

tectospinal tracts

To reticularformation

Vestibulocochlearnerve (VIII)

Tocerebellum

Vestibularbranch

KEY

Primary pathway

Secondary pathway

Motor output

High-frequencysounds

Low-frequencysounds

Cochlea

Thalamus

Ear Abnormalities

• Deafness – unable to perceive some frequencies of sound– Dysfunction of any mechanism that conducts sound waves– Loose high frequencies first

• Tinnitus – ringing noise, “phantom sounds”– Hyperactivity of auditory neurons to compensate for input loss– Permanent hearing loss may have already occurred

• Ear tubes – constant ear infections or fluid in middle ear− Tube placed surgically through tympanic membrane