the eye Flashcards
superior rectus
Oculomotor (III) elevation, adduction, medial rotation of eyeball
inferior rectus
Oculomotor (III) depression, adduction, lateral rotation of eyeball
medial rectus
oculomotor (III) adduction of eyeball
Lateral rectus
abducent(VI) abduction of eyeball
Superior Oblique
Trochlear (IV) depression, abduction, medial rotation of eyeball
inferior oblique
Oculomotor (III)elevation, abduction, lateral rotation of eyeball
levator palpebra superioris
Oculomotor (III)elevation of upper eyelid
blind spot
located about 15 degrees lateral to the central point of vision no rods or cones in this area, called the optic disc, exit point for axons of the ganglion cells
Emmetropia- normal.
Light focuses on retina
Hypertropia-farsighted
Light focuses behind the retina and is corrected with a convex lens
Myopia- nearsighted
Light focuses in front of retina and is corrected with a biconcave lens.
Astigmatism
Curvature of the lens is not uniform and is corrected with a cylindrical lens Bumpy Cornea
Presbyopia
This is loss of accommodation power of the lens that occur with aging. The near point (closest point on which one can focus by accommodation of the lens) moves farther from the eye and is corrected with a convex lens. Caused by progressive denaturation of the proteins of the lens. Makes the lens less elastic. Begins about 40-50 years of age.
Cataracts
Cloudy or opaque area of the lens Caused by coagulation of lens proteins
Miosis
constriction of pupillary aperture due to stimulation of parasympathetic nerves that excite the pupillary sphincter muscle
Mydriasis
dilation of pupillary aperture due to stimulation of sympathetic nerves that excite the radial fibers of the iris
Intraocular fluid
keeps the eyeball round and distended. 2 fluid chambers
Aqueous Humor
Freely flowing fluid In front of lens
Vitreous Humor
Gelatinous mass between lens and retina Little flow
Production of Aqueous Humor
It is produced by the ciliary processes of the ciliary body at a rate of 2-3 microliters/min. Flows between the ligaments of the lens, through the pupil into the anterior chamber, goes between the cornea and the iris, through a meshwork of trabeculae to enter the canal of Schlemm which empties into aqueous veins and then into extraocular veins.
Glaucoma
due to resistance to fluid flow through trabecular spaces , causes increase IOP MCC of blindness due to compression necrosis of the axons of the optic nerve
Eye Cones
light cones
rods
night rods
Kerotin
from carrots
Light receptors
Consist of rods and cones (not present on the optic disk –blind spot ) Pigment layer of the retina contains the black pigment melanin that prevents light reflection in the globe of the eye Lack of pigmentation in albinos results poor visual acuity because of the scattering of light
vitamin a deficiency
Vitamin A deficiency causes Night Blindness
Pigement layer of retina
Pigment layer of the retina contains the black pigment melanin that prevents light reflection in the globe of the eye Lack of pigmentation in albinos results poor visual acuity because of the scattering of light
RODS
Sensitive to low-intensity light; night vision. low visual acuity dark adaptation- rods adapt later no color vision
CONES
Sensitive to high intensity light; day vision. higher visual acuity. cones adapt first to dark adaptation yes for color vision
nasal field of vision
nasal field located on the temporal side of the retina
temporal field of vision
temporal field located on the nasal side of the retina
fields of vision interruption
interruption of the visual pathway at different points leads to very specific visual field defects
Blinds spots
located about 15 degrees lateral to the central point of vision no rods or cones in this area, called the optic disc, exit point for axons of the ganglion cells
cutting the optic nerve
causes blindness in the ipsilateral eye
cutting the optic chiasm
causes heteronymous bitemporal hemianopia (tunnel vision in pituitary gland adenoma)
Cutting of the optic tract
Cutting of the optic tract causes homonymous contralateral hemianopia
Cutting the geniculocalcarine tract
Cutting the geniculocalcarine tract causes homonymous hemianopia with mecular sparing
Optic Pathways and Lesions
…
optic chiasm
Growing adenoma of the pituitary grand will slice the optic chiasm.
Eye injury during anesthesia
The eyes are vulnerable to injury secondary to prolonged lateral decubitus or prone position Retinal ischemia / blindness Dryness of cornea
Eye injury during anesthesia-prevention
Padding around the orbit Eye lubricants
Outer ear
Directs the sound wave into the auditory canal
Middle ear
Is air-filled Contains the tympanic membrane (ear drum) and the auditory ossicles (malleus, incus and stapes). The stapes inserted into the oval window, a membrane between the middle ear and the inner ear. Ossicles amplify sound. Sound waves cause the tympanic membrane to vibrate. In turn , the ossicles vibrate , pushing the stapes into the oval window (in and out like piston) and displacing fluid in the inner ear (ripple effect)
Inner ear
Is fluid-filled Consist of a bony labyrinth (semicircular canals, cochlea and vestibule ) and series of ducts within bony labyrinth are membranous labyrinth. The fluid outside the ducts is perilymph; the fluid inside the ducts is endolymph.
Structure of the cochlea: three tubular canals
The scala vestibuli and scala tympani contain perilymph , which has a increase Na+ The scala media contains endolymph , which has a increase K+ The scala media is bordered by the basilar membrane, which is the site of organ of Corti
Organ of Corti number 28
Is located on the basilar membrane Is located on the basilar membrane Contains the receptor cells (inner and outer hair cells) for auditory stimuli. Cilia protrude from the hair cells and are embedded in the Tectorial membrane. Outer hair cells > Inner hair cells Spiral ganglion contains the cell bodies of auditory nerve (CN VIII ) ,which synapse on the hair cells Sound wave causes vibration of organ of Corti, this causes bending of hair cells against the tectorial membrane Bending in one direction Depolarization Bending in other direction Hyperpolarization This changing potential of the hair cells causes intermittent firing of cochlear nerves. Fibers ascend to auditory cortex
Base of basilar membrane
Base of basilar membrane (close to oval window) responds best to high frequencies
Apex
of basilar membrane responds best to low frequencies
Ear infection
goes into the inner ear- loose high frequency
Conductive deafness
Defects in external or middle ear Defects in transmission of sound to the inner ear due to wax, foreign body, destruction of auditory ossicals, thickening of ear drum due to repeated middle ear infection. Bone conductance > Air conductance
Nerve deafness- sensory
Defects in inner ear or vestibulocochlear nerve ( CN VIII) Both bone & air conductance are reduced Adverse effect of aminoglycoside –gent, neomycin
what is ear wax
its an insect repellant
Pressure changes in middle ear during Nitrous oxide (N2O) anesthesia
There is significant increase in middle ear pressure during administration of Nitrous oxide. Therefore , nitrous oxide should be used with caution in presence of mild middle ear diseases (e.g. otitis media , sinusitis) with obstructed Eustachian tube. This may result hearing loss or tympanic membrane rupture. Nitrous oxide is contraindicated in tympanoplasty, as the pressure difference between middle and external ear can jeopardize the success of operation.
taste
Taste pathways Taste receptor cells line the taste bud Innervation Anterior 2/3 –VII (Facial nerve for salty & sweet taste)- Chorda tympani (a branch of VII) Posterior 1/3 – IX (Glossopharyngeal nerve for sour & bitter taste) Back of throat – X (vagus nerve) Medulla solitary tract solitary nucleus Thalamus taste cortex
Olfaction AP
Second order neuron form olfactory tract and project to prepiriform cortex
Stimulus activates receptor cells lead to activation of G proteins lead to activation of adenylate cyclase which increases cAMP leading to Na+ channels open then AP is generated and propagated
Olfaction
Receptor cells Located in the olfactory epithelium
CN I carries information to olfactory bulb
Fracture of cribriform plate of ethmoid bone , causes hyposmia or anosmia
Nasal cavity considerations…
Nasal cavity is frequent site of bleeding due to high vascularity. Before insertion nasal airways, nosgastric catheters or nasotracheal tubes should be lubricated and advanced at an angle perpendicular to the face to avoid injury to nose Vasoconstrictors are used to cause mucosal shrinkage.
olfactory epithelium supplied by which cranial nerve
Olfactory epithelium is also supplied by CN V (trigeminal), which detect noxious or painful odor like ammonia
Stretch Reflex – Knee jerk
Is monosynaptic. Muscle stretch leadings to excitation of M. Spindles which stimulate group Ia afferents Stimulation of alpha motoneuron in the spinal cord Contraction of the muscle (Extrafusal fibers) and returning to its original length. Knee jerk reflex: tapping on patellar tendon causes the quadriceps to stretch leading to stimulation of afferent fibers leading to activation of alpha motor neurons leading to contraction of quadriceps. Knee jerk increase in upper motor neuron lesion (due to loss of inhibition) , and decrease in lower motor neuron lesions.
Golgi Tendon Reflex
Is opposite or inverse of the stretch reflex Active muscle contraction stimulates the Golgi tendon organs and group Ib Ib afferent stimulates inhibitory interneuron in spinal cord leading to inhibit alpha motoneurons and causes relaxation of the muscle that was originally contracted
Flexor withdrawal reflex(Touching a hot stove)
Is polysynaptic. Flexion on ipsilateral side and extension on contralateral side Somatosensory and pain afferent fibers elicit withdrawal of the stimulated body part from the noxious stimulus (hot stove) Afterdischarge prevents the muscle from relaxing for some time.
