25/11/19 eye/ear

Question 1

Explain crossing of the optic nerve:

Answer 1

• info from R interpretted by left, info from L interpreted by R.
• Info from R visual field hits medial R retina (needs to cross to L where its interpreted) and lateral L eye (doesn’t have to cross).
• Info from L visual field hits medial L retina (needs to cross to R where its interpreted) and lateral R eye (doesn’t have to cross).
• Thalamus is rely station to primary visual cortex and superior colliculi (visual reflex center) through optic radiations.

Question 2

3 major areas of ear?

Answer 2

external
middle
inner

Question 3

Function of external ear?

Answer 3

• visible
• Auricle (ear lobe)
• External acoustic meatus:
  funnels sound into ear, then sends it to middle ear.
• external ear ends at tympanic membrane.

Question 4

What is the tympanic membrane?

Answer 4

Tympanic membrane: boundary between external and middle ear; vibrates with sound waves.

Question 5

Function of middle ear?

Answer 5

• Air-filled cavity behind tympanic membrane
• has 3 bones (auditory ossicles - Malleus, Incus, Stapes).
• Pharyngotympanic tube (Eustachian tube) is continuous with nasopharynx.

Question 6

Auditory Ossicles?

Answer 6

3 bones that transmit vibration from tympanic membrane to oval window
Malleus
Incus
Stapes

Question 7

Sound vibration in middle ear?

Answer 7

Tympanic membrane vibrates = it vibrates auditory ossicles (3 bones) = transmit vibrations to oval window.

Question 8

Interesting fact about Pharyngotympanic tube (AKA eustachian tube)?

Answer 8

Kids get more ear infections because eustachian tube is more horizontal and shorter = easier for bacteria to get to ear.

• as well as being continuous with nasopharynx

Question 9

What connects middle ear to inner ear?

Answer 9

Oval window

Question 10

Function of inner ear?

Answer 10

Bony labyrinth (membranes with fluid)

• sound enters and shakes tympanic membrane - oval window - fluid shakes = sound
• has perilymph (fluid)
• has 3 regions: vestibule, semicircular canals, cochlea.

Membranous labyrinth (series of sacs and ducts) within the bony labyrinth.
- has endolymph (fluid)

Question 11

Function of vestibule? (one of three regions of bony labyrinth along with semicircular canals, and cochlea).

Answer 11

• contains oval window
• Two parts of the membranous labyrinth; the saccule and utricle, are located within the vestibule
• Vestibule has receptors (maculae) that respond to linear acceleration and change in head position (elevator, bending down, walking).

Question 12

Function of semicircular canals? (one of three regions of bony labyrinth along with vestibule, and cochlea).

Answer 12

• Bony labyrinth has semicircular canals here.
• Membranous labyrinth has semicircular ducts here (each duct has an ampulla, has an equilibrium receptor region called a crista ampullaris)
• respond to change in angular rotation.

Question 13

Functions of the cochlea? (one of three regions of bony labyrinth along with vestibule and semicircular canal).

Answer 13

• has three chambers (scala vestibuli, scala media (cochlear duct), scala tympani.
• cochlear duct (part of membranous labyrinth) runs through center of cochlea - contains endolymph

Question 14

Function of cochlear duct?

Answer 14

• Has receptor called “spiral organ of corti” - gets excited so you can hear.

Question 15

Three chambers of the cochlea?

Answer 15

Scala vestibuli:
- part of bony labyrinth (has perilmph). Continuous with vestibule and begins at oval window.

Scala media (cochlear duct):
- part of membranous labyrinth (has endolymph)

Scala tympani:
- part of bony labyrinth (has perilymph).

Question 16

Where is the hearing receptor of the ear located?

Answer 16

The cochlear duct (scala media) of the cochlea.

Question 17

Structures around the spiral organ of corti?

Answer 17

Tectorial membrane on top (t for top)
Basilar membrane on bottom (b for bottom)
+ Hair cells in between these two (innervated by afferent fibers of cochlear nerve).
- spiral organ of corti runs the length of the basilar membrane.

Question 18

Sound wave path?

Answer 18

Sound waves - tympanic membrane - auditory ossicles - oval window - fluid in scala vestibuli = movement in basilar membrane.

Question 19

Function of helicotrema?

Answer 19

• the end of the cochlea.

- point at which scala vestivuli and scala tympani are continuous and communicate.

Question 20

Relationship between frequency and soundwave movement?

Answer 20

• Sounds with freq below hearing range continue to the helicotrema and then around to the round window.
• Sounds with high frequency in the hearing range, cut through the cochlear duct (pushing basilar membrane and deflecting hairs on inner hair cells) and take a shortcut to the round window.

Question 21

Define sound?

Answer 21

Sound is a pressure disturbance. Sound waves are made up of compressed and uncompressed air molecules. Distance between compressed molecules is wavelength.

Question 22

What is the distance between compressed air molecules?

Answer 22

Wavelength.

Question 23

What is frequency? What is the relationship between frequency and pitch?

Answer 23

Frequency is the number of waves over a specific period of time.
High frequency = high pitch
low frequency = low pitch

Question 24

What does sound measure?

Answer 24

Pitch/frequency and loudness/amplitude.

Question 25

What is amplitude?

Answer 25

Height = intensity or loudness

Question 26

Importance of frequency/pitch? Volume?

Answer 26

Frequency/pitch is determined by where shortcut occurs on the cochlear duct.

Volume is determined by how large this push is? The greater the push, the greater the graded potential, the greater the AP.

Question 27

Is the basilar membrane uniform?

Answer 27

No, the basilar membrane is not uniform. Soundwaves push on different points.

High frequency/pitch sounds push near the base of the basilar membrane (closer to oval window) where the fiber is short and stiff.
Low frequency/pitch sounds push near the apex of the basilar membrane (closer to helicotrema) deflecting long, floppy fibers.

Question 28

What happens when movement of basilar membrane occurs?

Answer 28

Movement of Basilar Membrane pushes hair cells of Spiral Organ into tectorial membrane.

Question 29

Sound transduction process?

Answer 29

Waves push basilar membrane - deflects hair cells - they move top links - open channels (caps of stereocilia) - + ions flow into hair cell - hair cell is depolarized - NT released at cochlea nerve - AP at cochlear nerve sent to brain.

Question 30

Stereocilia and tip links?

Answer 30

Hair cells (in between tectorial and basilar membranes) have sterocilia with tip links that close cation channels at top of an open channel.

Question 31

Auditory pathway?

Answer 31

• runs from cochlear nerve to brain.
• multineuronal.
  2 synapses:
  1. inferior colliculi (auditory reflex center)
  2. Thalamus synapse (relay nerves to auditory cortex of brain).

The ascending auditory pathway transrn its auditory information
primarily from the cochlear receptors (the inner hair cells) tothe cerebral cortex. Action potentials generated in the cochlea pass through the spiral ganglion, where the auditory bipolar
cell bodies reside, and along the afferent fibers of the cochlear
nerve to the cochlear nuclei of the medulla (Figure 15.33).
Frorn there, neurons project to the super ior olivary nucleus,
which lies at the junction of the medulla and pons. Beyond this axons ascend in the lateral lemniscus (a fiber tract) to the inferior
colliculus (auditory reflex center in the midbrain), which
projects to the medial geniculate nuclens of the thalamus.
Axons of the thalamic neurons then project to the primary
auditory cortex, which provides conscious awareness of sound.

Question 32

Hearing disorders?

Answer 32

Conduction deafness:
causes:
- one of the structures, tympanic membrane, is perforated, sound not transmitted to auditory ossicles.
or
- caused by otosclerosis (auditory ossicles increase in density. Makes it hard to ossilate and transmit info to oval window).

Sensorineural deafness:

• nerve impulses unable to get to brain
• causes are loss of hair cells and strokes.