Unit IV: Coordination Vision and Hearing Ch. 15 – pgs

Vision Accessory 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 Lens Choroid 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 point on fovea

Photoreceptors – rod cells – cone cells Pigment epithelium

Photoreceptors Lateral border Fovea Nasal border Visual acuity Fovea Optic disc Low Density of Cones High Density of Cones Low Density of Rods High 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, 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 cerebral hemisphere Right cerebral hemisphere Superior colliculus Projection fibers (optic radiation) Lateral geniculate nucleus Optic tract Diencephalon and brain stem Optic disc Retina Right eye only Left eye only Binocular vision Right side Left 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 Corrected Concave lens Convex 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 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 Sound energy arriving at tympanic membrane

Outer Ear External Ear Middle Ear Inner Ear To nasopharynx External acoustic meatus Elastic cartilages Auricle (pinna) Lobule (earlobe)

Auditory Ossicles Muscles MalleusIncus Stapes Temporal bone Stabilizing ligament Branch of facial nerve VII (cut) External acoustic meatus Tympanic cavity Tympanic membrane Round window Auditory tube Stapedius muscle Tensor tympani muscle Oval window 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 Otolith moves “downhill,” distorting hair cell processes Receptor output increases Vestibule: Saccule and Utricle

Anterior semicircular duct for “yes” Lateral semicircular duct for “no” Posterior semicircular duct for tilting head to the side Inner Ear Cupula Endolymph Hair cells (b)(c) Direction of head rotation Endolymph lags behind due to inertia Cupula is pushed over and stimulates hair cells Crista ampullaris Supporting cells Sensory nerve fibers

Projection Pathway for Equilibrium Figure Stimulation of hair cells. Vestibulocochlear nerve (VIII) The vestibular nuclei Integrate sensory information Superior colliculi The reflexive motor commands distributed to the cranial nerves (N III, N IV, N VI, and N XI) for eye, head, and neck movements. Cerebellum Spinal cord adjust peripheral muscle tone and complement the reflexive movements of the head or neck. Vestibulocochlear nerve (VIII) Cochlear branch Vestibule Vestibular ganglion Semicircular canals

Organ of Corti (Spiral Organ/Acoustic Organ)

Projection Pathway for Hearing Tympanic membrane Round window Movement of sound waves Cochlear duct Tympanic duct Basilar membrane Vestibular duct Vestibular membrane Sound waves arrive at the tympanic membrane. Displacement of the auditory ossicles. Pressure waves in the perilymph of the vestibular duct. The pressure waves distort the basilar membrane Vibration of hair cells against the tectorial membrane. Relayed to the CNS over the cochlear branch of cranial nerve VIII.

Projection Pathway for Hearing Figure Temporal lobe. Perception of pitch is based on what portion of the auditory cortex is stimulated, and your perception of volume by the degree of stimulation at that location. Vestibulocochlear Nerve (VIII) High-frequency sounds stimulate receptors closest to the oval window. Thalamus Inferior colliculus Medulla oblongata To spinal cord through the tectospinal tracts To reticular formation Vestibulocochlear nerve (VIII) To cerebellum Vestibular branch KEY Primary pathway Secondary pathway Motor output High-frequency sounds Low-frequency sounds 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