HAN 200 ,, Special Senses

Eyebrows

Shade from the sun

Eyelids (Palpebrae)

Protection/glands

Conjunctivia

Transparent membrane

Lacrimal Apparatus

Tears

Extrinsic Eye Muscles

CN 3, 4, and 6

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Superior Rectus

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Inferior Rectus

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Medial Rectus

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Inferior Oblique

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Trochlear

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Superior Oblique

Moves Eyes Laterally

CN VI (Abducens)

Moves Eyes Medially

CN III (Oculomotor)

Elevates Eyes and Turns it Medially

CN III (Oculomotor)

Depresses Eyes and Turns it Medially

CN III (Oculomotor)

Elevates Eyes and Turns it Laterally

CN III (Oculomotor)

Depresses Eyes and Turns it Laterally

CN IV (Trochlear)

Fibrous Wall of the Eyeball

Sclera and cornea (avascular, outermost CT)

Vascular Wall of the Eyeball

Iris, ciliary body, choroid (middle pigmented layer)

Sensory Wall of the Eyeball

Retina (delicate two-layered membrane)

Internal Cavity is FIlled With ____.

Humors

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Suspensory Ligament

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Ciliary Body

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Pupil

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Anterior Chamber

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Cornea

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Lens

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Optic Nerve

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Macula

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Iris

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Vitreous Body

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Choroid

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Retina

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Sclera

Sclera (Whites of the Eye)

Protects and shapes the eyeball; continuous with the dura mater of brain

Cornea

Bends light as it enters the eye; numerous pain receptors contribute to blinking and tearing reflexes

Choroid Region

Supplies blood to all the layers of the body

Ciliary Body

Smooth muscle bundles control lens shape

Iris

The colored part of the eye

Pupil

Central opening that regulates the amount of light entering the eye

Pigmented Outer Layer of the Retina

Absorbs light and prevents its scattering

Neural Inner Layer of the Retina

Photoreceptor to transduce light energy

Photoreceptors Pathway

Rods/Cones → Bipolar Cells → Ganglion cells where action potential is generated

Blind Spot

The optic disc has no photo receptor cells and the brain fills in the area (visual filling)

Rods

Operates in dim lights; provides indistinct, fuzzy, non color peripheral vision

Cones

Operate in bright lights; provide high acuity color vision; concentrated in the fovea centralis

Fundus of Eye

The only place where small vessels can be observed directly

Posterior Segment of the Internal Chamber

Contains vitreous humor that transmits light and holds the neural retina firmly against the pigmented layer

Anterior Segment of the Internal Chamber

Contains aqueous humor

Anterior Chamber of the Internal Chamber

Between the cornea and the iris

Posterior Chamber of the Internal Chamber

Between the iris and the lens

Glaucoma

Compression of the retina and optic nerve if drainage of humors is blocked; second leading cause of blindness in the US

Lens

Biconvex, transparent, flexible, elastic, and avascular; allows for precise focusing of light on the retina

Cataracts (Clouding of the Lens)

Occur as a consequence of aging, diabetes, heavy smoking, and frequent exposure to intense sunlight

Pathway of Light Entering the Eye

Cornea → aqueous humor → lens → vitreous humor → neural layer of retina → photoreceptors

Light is Refracted Three times

At the cornea, entering the lens, and leaving the lens

Focusing for Close VIsion

Parasympathetic activation

Light Adaptation

Occurs when moving from darkness into bright light; cones and neurons rapidly adapt

Dark Adaptation

Occurs when moving from bright light into darkness; cones stop functioning in low-intensity light

Visual Pathway

CN 2 leaves the eye → some fibers cross at the optic chiasma → most fibers continue to the thalamus → fibers connect to the primary visual cortex in the occipital lobes

Depth Perception

Both eyes view the same image from slightly different angles, resulting in cortical fusion

External and Middle Ear

Involved with hearing

Internal Ear

Hearing and equilibrium

The Cochlea

Spiral bony chamber

Physiology of Hearing

Sound waves cause eardrums to vibrate → movement of auditory ossicles → fluid of inner ear moves → tiny hair cells are excited and stimulate local neurons of CN VIII

Auditory Processing

Impulses from specific hair cells are interpreted as specific pitches

Loudness

Detected by increasing numbers of action potentials that result when the hair cells experience large deflections

Three modes of input for balance and orientation

Vestibular receptors, visual receptors, and somatic receptors

Sensory Mismatch

Causes car sickness, seasickness, and dizziness on heights

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Middle ear

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Inner ear

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Vestibular nerve

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Temporal bone

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Tympanic membrane

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Vestibule

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Cochlear duct

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Saccule

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Cochlear nerve

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Cochlea nerve

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Ampullae

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Utricle

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Semicircular canals

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Outer ear

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Scala Tympani

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Scala vestibuli

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Helicotrema

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Scala media

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Basilar membrane