Visual, Hearing, Vestibular system

Question 1

What protects the eye?

Answer 1

1. Bony socket in skull
2. Eyelids: shutters to protect from environmental hazards
3. Eyelashes: trap fine, airborne debris before falling into the eye
4. Tears: lacrimal glands and conjunctiva lubricate, cleanse and act as bacteriocide.

Question 2

What are the three tissue layers that enclose the eye?

Answer 2

1. Sclera/cornea,
2. choroid/ciliarybody/iris
3. Retina

Question 3

What is the sclera?

Answer 3

Tough outer layer of connective tissue, forms visible white part of the eye

Question 4

What is the cornea?

Answer 4

Anterior, transparent layer continuous with sclera that allows passage of light rays

Question 5

What is the choroid?

Answer 5

Middle layer underneath sclera which contains blood vessels that nourish retina and contain melanin under retina for absorption of light

Question 6

What is the ciliary body?

Answer 6

Continuous tissue of muscle from choroid layer that controls the curving and flattening of the lens.

Question 7

what is the retina?

Answer 7

Innermost layer under choroid consisting of outer pigment cells, rods and cones, and axons of visual nerve fibres.

Question 8

What are the two fluid filled cavities separated by the lens?

Answer 8

1. Vitreous humor: gelatinous, between lens and retina
2. Aqueous humor: fluid, between cornea and lens

Question 9

What is the iris?

Answer 9

Contains circular and radial smooth muscle that control the amount of light entering the eye.

Question 10

What is the pupil?

Answer 10

Opening through which light enters the eye

Question 11

What is the lens?

Answer 11

Part of eye that bends light to focus it on the retina.

Question 12

What is the tapetum lucidum?

Answer 12

Additional reflective layer within the choroid that reflects light back towards retina. It improves sensitivity of vision under low light but causes blurriness in high light.

Question 13

Why do we change pupil size?

Answer 13

Control of light for optimization of light and dark conditions and providing a wide dynamic range.

Question 14

What is the relationship between depth of field and pupil size?

Answer 14

Small aperture (pupil size) = large depth of field

Large aperture (pupil size) = small depth of field

Question 15

What causes pupil size to change?

Answer 15

Parasympathetic stimulation contracts circular muscle, constricting pupil

Sympathetic stimulation contracts radial muscle, dilating pupil

Question 16

How does the lens work?

Answer 16

Light from distant source must enter parallel for the lens to focus the image on the retina. If the image is close, the light is not parallel and the lens must become strong and round to keep it in focus.

Question 17

What is accomodation?

Answer 17

Change in strength of lens to focus on an image, regulated by effect of parasympathetic branch of autonomic nervous system on ciliary muscle.

Question 18

What is the shape of the lens as it acommodates near and far images?

Answer 18

When ciliary muscle is relaxed, ligaments pull on and flatten the lens. When ciliary muscle contracts, ligaments release tension and brings lens back to its relaxed rounded shape.

Question 19

What is myopia, hyperopia, and amblyopia?

Answer 19

Myopia: Near sightedness when the focal point falls in front of the retina.

Hyperopia: Far sightedness when the focal point falls behind the retina

Amblyopia: weakness of ocular muscles despite normal development of visual cortex (adult) or lack of development (children)

Question 20

What is the order of organization of the retina from closest to the lens to furthest?

Answer 20

1. Fibers of optic nerve + ganglion cell: travel to thalamus
2. Amacrine cell: interneuron
3. Bipolar cell: connect retinal cell (rod/cone) to to ganglia
4. horizontal cell: interneuron
5. Cones and Rods

Question 21

What is the difference between rods and cones in terms of amount, type of vision, sensitivity, convergence and location?

Answer 21

Rods:
1. more
2. grayscale
3. high sensitivity (collect more light), low acuity
4. more convergence
5. peripheral retina

Cones:
1. Fewer
2. colour vision
3. low sensitivity (collect less light), high acuity
4. Less convergence
5. fovea

Question 22

What is the macula?

Answer 22

Area of high concentration of cones where images are focused to ensure highest resolution

Question 23

What is the fovea?

Answer 23

Area where light strikes photoreceptors directly, containing the highest density of cones. Single photoreceptors synapse with bipolar neurons that synapse onto single ganglion cells.

Question 24

What are the steps of phototransduction?

Answer 24

1. Light bleaches rhodopsin, turning cis-retinal inside opsin to trans-retinal, activating opsin.
2. Activated rhodopsin activates G protein transducin
3. Transducin activates phosphodiesterase (PD) that degrades cGMP
4. Decrease in cGMP causes Cyclic nucleotide gated Na+/Ca++ channels to close as it would have acted as the ligand.
5. Closing Na+/Ca++ and continually leaking K+ hyperpolarizes the cell
6. Hyperpolarization causes less release of neurotransmitter onto bipolar cells

Question 25

What is the information flow in the visual pathway?

Answer 25

1. In the retina, photoreceptors synapse with bipolar cells which sends signals to ganglion cells and optic nerves. 2. Optic nerves on the right side of each eye bring light from the left side of each eye to the optic chiasm where they join and synapse at the lateral geniculate nucleus of thalamus 3. Neurons form lateral geniculate nucleus of thalamus synapses at the occipital lobe of cortex as well as the midbrian which controls pupilary constriction

Question 26

What is hearing?

Answer 26

Conversion of mechanical energy of soundwaves to electrical energy. Includes interpretation of frequency (pitch) and amplitude (loudness) of sound waves, as well as distance, direction and movement.

Question 27

What are the 3 parts of the ear?

Answer 27

External ear, middle ear and inner ear.

Question 28

What are the parts of the external ear?

Answer 28

Pinna/Auricle: Elastic cartilage covered with skin Meatus: external auditory canal Tympanic membrane

Question 29

What are the parts in the middle ear?

Answer 29

Eustachian tube Ossicles: malleus (against tympanic membrane), incus, stapes (against oval window)

Question 30

What are the parts of the inner ear?

Answer 30

Bony labyrinth: tunnels in temporal bone Membranous labyrinth: fluid filled organ

Question 31

What are the three parts of the membranous labyrinth?

Answer 31

1. Cochlear duct + organ of corti 2. Three Semicircular ducts, each with one crista ampullaris 3. Utricle/Saccule inside vestibule with one macula each

Question 32

What are the steps of sound transmisison?

Answer 32

1. Sound wave strikes tympanic membrane and becomes vibrations 2. Tympanic membrane vibrates the three bones in the middle ear 3. Stapes vibrates to attached oval window membrane, creating fluid waves within the cochlea 4. Fluid waves push on flexible membranes of cochlear duct, bending hair cells and opening mechanically gated ion channels 5. Opening of channels alter neurotransmitter release onto sensory neurons, which creates action potentials travelling through the cochlear nerve to the brain 6. Energy from waves transfers across cochlear duct into the tympanic duct and is dissipated back into the middle ear via round window

Question 33

What are the parts of the cochlea?

Answer 33

Oval window: where vibrations from stirrup originate Vestibular duct: contain perilymph that creates waves when in contact with vibrations; surrounded by vestibular membrane Cochlear duct: contains endolymph secreted by epithelial cells; contains hair cells on organ of corti Tectorial membrane: flap that covers hair cells of organ of corti Tympanic duct: contains perilymph that passes waves from vestibular duct to round window, lined with basilar membrane

Question 34

What is the structure of a hair cell?

Answer 34

Modified neuron with stereocilia connected by tiplinks. Contain special K+ channel proteins that are mechanically gated.

Question 35

What is the pathway of excitation of a hair cell?

Answer 35

1. At sound vibrations, hair cells bend in towards kinocilium (tallest stereocilium) 2. Bending opens mechanically gated K+ channels 3. Endolymph [K+] > Hair cell [K+], K+ flows inside and depolarizes cell, increasing action potential frequency in the associated sensory neuron

Question 36

What is the pathway of inhibition in a hair cell?

Answer 36

1. Hair cells bend away from kinocilium (tallest stereocilium) 2. Bending closes mechanically gated K+ channels 3. Cell hyperpolarizes and sensory neuron signalling decreases

Question 37

What is basilar membrane displacement relationship with pitch?

Answer 37

Basilar membrane will be more sensitive to low pitch near the round window, and high pitch near the helicotrema.

Question 38

How does each ear synapse in the brain?

Answer 38

1. Primary sensory neurons send axons via vestibulocochlear nerve to cochlear nucleus in the medulla 2. Cochlear nucleus goes to both sides of the superior olivary nucleus in the medulla for sound processing and to cerebellum for sense of balance 3. From the olivary nucleus in the medulla, it synapses to inferior colliculus in the midbrain 4. Inferior colliculus to thalamus 5. Thalamus to auditory cortex

Question 39

What are the three types of hearing loss?

Answer 39

Conductive: easily reversible, damage to eardrum or ear infection Sensorineural: damage to hair cells and primary neurons central: not easily reversible, damage to auditory nerve or auditory cortex

Question 40

What are the parts of the vestibular apparatus?

Answer 40

Otolith organs in vestibula: includes macula (sensor for balance) inside saccula and utricle (linear acceleration + head position) Three semicircular canals: sensitive to rotational acceleration, include crista ampullaris.

Question 41

How does the crista ampullaris work?

Answer 41

Movement of endolymph in cochlear duct pushes on gelatinous cupula, activating hair cells, providing info about rotation of head.

Question 42

How does the macula in saccule and utricle work?

Answer 42

In neutral position, otoliths within macula creates gravitational pressure onto gelatinous otolith membrane, moving along with head/gravity and stimulating hair cells.

Question 43

where do hair cells in vestibular apparatus synapse?

Answer 43

1. Hair cells synapse with neurons of vestibular nerve 2. Vestibular nerve synapses with cerebellum or to vestibular nuclei in medulla to control eye movement 3. From medulla it synapses with midbrain, then thalamus then cortex