Flashcards in Block 3 Deck (37):
What is epiphora?
Overflow of tears onto the face - clinical sign that indicates insufficient tear drainage - Under control of the ANS (parasympathetic)
Where is the refractive power greater, cornea or lens?
How does distance vision work?
-Rays are coming in parallel to eye/flat
-Muscle is relaxed and zonules are constricted
-Lens is flat and has less refracting power
How does near vision work?
-First, the object is focused behind the retina
-Then eyeball is stimulated to accommodate
-Then the ciliary muscle contracts
-This makes lens fatter and corrects near vision
-Zonules are relaxed at this time
What is myopia?
-AL > FL
-Eyeball is too long and/or too strong of lens
-Corrected with concave lens
What is hyperopia?
-AL (axial length) < FL (focal length)
-Eyeball is too short and/or too weak lens
-Corrected with convex lens
What is presbyopia?
Decrease in accommodative power of lens with age
What does the ciliary muscle do?
Changes shape of lens, not diameter of the pupil when it contracts. The diameter of the muscle becomes less.
What happens if the ciliary muscle is relaxed?
Zonules are tight --> pulls lens flatter (looking at long distance objects)
What happens if the ciliary muscle is contracted?
Zonules are loose --> lens gets fatter/wider (looking at short distance objects)
What is the innervation to the ciliary muscle?
-Preganglionic from Edinger-Westphal nucleus
-Post-ganglionic from ciliary ganglion via oculomotor nerve
-Activation of M3 receptors causes contraction -> dec. diameter of ring -> releases tension in zonular fibers -> rounding of lens
What causes Mydiasis?
Sympathetic - Innervation from superior cervical ganglion -> releases NE & alpha1 -> contracts dilator muscle
What causes miosis?
Parasympathetic - Innervation from Ciliary ganglion -> Releases ACh -> Contracts sphincter muscles
Describe the pathway of the pupillary light reflex:
1. Light enters through the pupil and hits the retina
2. Transferred through optic tract to the 2nd order neuron
3. Message is sent to preganglionic parasympathetic neurons of the Edinger-Westphal Nucleus in Aqueduct
4. Information is transferred via the preganglionic parasympathetic part of the oculomotor nerve to the ciliary ganglion.
5. Ciliary ganglion causes pupil constriction (innervates constrictor muscle of the iris)
What is the blind spot?
Where all the ganglion cell axons leave the retina to go to the brain. There are no photoreceptors here.
What is the macula-lutea?
The yellow spot where blood vessels have been pushed away.
What do photoreceptors encode?
Frequency which equates to color
Intensity which equates to brightness
What kind of light is your eye detecting?
What are the three types of cones?
1. Blue (short wavelength)
2. Green (medium wavelength)
3. Red (long wavelength)
What cells does energy pass through in the eye to get to the optic nerve?
Photoreceptors --> Bipolar cells --> Ganglion cells
What are the steps in phototransduction?
1. Light activates rhodopsin (visual pigment)
2. Activation of G protein (conversion of GTP -> GDP)
3. Activation of PDE (phosphodiesterase)
4. PDE converts cGMP to GMP
5. Closing of cGMP dependent Na+ channels - Na+ no longer flows into the cell
6. Channel closing causes the cell to hyperpolarize (become more negative in Eqpot and generate a signal that is sent on to the optic nerve)
Describe the visual cycle:
1. Rhodopsin is hit by light in the rod
2. Rhodopsin splits into opsin & all-trans-retinal
3. All trans-retinal becomes all-trans-retinol
4. All-trans-retinol is transported to the RPE (retinal pigment epithelium)
5. In RPE, all-trans-retinol is converted to 11-cis retinal
6. Then 11-cis-retinal is brought back into the rod converted to rhodopsin
(all-trans-retinal originally comes from capillary to the RPE)
What happens in conductive hearing loss?
Increase in hearing threshold due to decrease in sound transmission through the external and/or middle ear. Air conduction is reduced in these cases but bone conduction remains the same.
What are common causes of conductive hearing loss?
-Intra-tympanic fluid (caused by otitis media)
What are the two main structural components of the inner ear and what do they contain?
1. Bony (osseous) labyrinth - contains Na+ - rich perilymph
2. Membranous labyrinth - contains K+ - rich endolymph
What are the two types of inner ear receptors?
1. Type I (inner hair cells) - true sensory receptors
2. Type II (outer hair cells) - biological amplifiers (act as motor units)
What is the mechanical transduction that happens in the cochlea?
-Displacement toward the tallest stereo ciliacauses depolarization
-In cochlea, this occurs when the basilar membrane moves toward the scala vestibuli
[Negative deflection - toward scala tympani - results in hyperpolarization]
What detects head rotation (angular acceleration)?
What detects gravity (linear acceleration)?
Otolith organs (utricle & saccule)
How do the saccule and utricle detect head position?
Otoconia (rocks) embedded in the otolith membrane produce drag on the stereo cilia when the head position changes relative to the ground.
How are the semicircular canals paired?
Depolarization occurs on the same side as head rotation. Ex: head goes left and depolarization happens in left canals, hyperpolarization in the right canals
If you tilt your head forward, what canals depolarize and what hyper polarize?
The canals tilting forward depolarize and the canals in the opposite plane that end up tilting up hyperpolarize.
What does scala media contain?
What does scale vestibule and scala tympani contain?
What does the stria vascular produce?
Endolymph and it generates the endocochlear potential (+80 mV).
On the cochlea, where are high and low frequencies transduced?
High frequencies - base
Low frequencies - apex