Unit 4 Nervous System Lab 4 Human Eye

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 xons ea Optic nerv ells Ganglion c ic layer t p a n y s r e Inn lls Bipolar Ce layer c i t p a n y s Outer limiting membrane Cones & s d o R elium h t i p E ted Pigmen Choroid 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

Cochlear Duct Ve st ib ul ar M em br an e Scala vestibuli Tympanic membrane Org ti Cor f o an 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