unit iv: coordination vision and hearing ch. 15 – pgs 505-533
TRANSCRIPT
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