Lecture 34 Continued

Question 1

What are the two types of photoreceptor in the eye?

Answer 1

Rods and cones

Question 2

Approximately how many words and codes are there in the human eye?

Answer 2

125million per Eye

Question 3

What may a mechano-receptor hair cell be used for?

Answer 3

Hearing and vestibular senses

Question 4

What is a hair cell mechanic-receptor connected to ?

Answer 4

A ganglion cell axon.

Question 5

What structures exist at the top of hair cells?

Answer 5

Cillia - collectively known as stereocilia

Question 6

How many stereocillia tend to be on top of one mechanism receptor hair cell ?

Answer 6

40-60

Question 7

How do you identify which of the stereocillia on a mechanic receptor hair cell is the kinocillium ?

Answer 7

The kinocillium is always the longest cillia on the mechanics receptor cell.

Question 8

How is a hair cell mechanic receptor stimulated and what happens following this stimulation?

Answer 8

Distortion of the stereocillia especially the kinocillium causes a change in membrane potential Leading to the release of neuro transmitter onto ganglion cell axon which shall report information to the brain.

Question 9

Why is the vestibular system important?

Answer 9

It is key to maintaining our balance and posture ( however the vestibular system isn’t the only system in charge of balance and posture)

Question 10

Other than vestibular receptors what other receptors does one require to balance?

Answer 10

Tactile and kinesthetic receptors in the body and limbs especially in contact with supporting surfaces

Vision - rods and cones - especially of the ground plane

Question 11

Where is the vestibular apparatus found?

Answer 11

In the inner ear inside the cranial cavity.

Question 12

What are the five parts of the inner ear?

Answer 12

Convoluted bony outer shell called the bong labyrinth.

Inside the convoluted tube is a fluid called a perilymph.

Suspended in the perilymph is a membrane made of connective tissue called the membranous labyrinth

Sensory hair cells for both the auditory and vestibular systems sit in different places on the membranous labyrinth.

These same hair cells are also bathed in another fluid called endolymph.

Question 13

Where is the vestibular apparatus housed ?

Answer 13

In the hard (petrous) part of the temporal bones.

Question 14

What are the three sensory part of the inner ear?

Answer 14

Cochlea ( specifically involved in hearing)

Vestibule ( containing utricle &saccule)

3 semi circular canals

Question 15

Which parts of the inner ear made up the vestibular apparatus?

Answer 15

The utricle and saccule (both encloses in the vestibule) and the 3 semi circular canals.

Question 16

What do the utricle and saccule respond to ?

Answer 16

Linear head acceleration and deceleration of which the effect of gravity is a special example.

(I.e they would be able to tell u were running forward)

Question 17

What so the three semi circular canals respond to ?

Answer 17

They respond to angular head acceleration and deceleration

Question 18

Are vestibular hair cells multidirectional signallers, bidirectional signallers or unidirectional signallers ?

Answer 18

Bi-directional signallers

Question 19

What does it mean to be tonically active?

Answer 19

At rest they are regularly releasing an exciting neurotransmitter, producing a steady action potential firing

Question 20

What is an example of a tonically active cell?

Answer 20

A vestibular hair cell

Question 21

How does a vestibular hair cell work- I.e what is it’s stimulus and how does it respond?

Answer 21

Motion in one direction bends their stereocillia towards the kinocillium exciting/depolarising the hair cell , increasing its neurotransmitter release and the nerve firing rate.

Motion in the opposite direction bends the stereocilia away from the kinocillium inhibiting/hyoerpolarising the hair cell,reducing its neurotransmitter release and the nerve firing rate

Question 22

What does the bending of the stereocillia towards or away from the kinocillium do?

Answer 22

Bending of the stereocillia towards the kinocillium opens potassium channels in the hair cell membrane, so K+ ions enter it from the endolymph &it’s inside becomes more positively charged (depolarised) ,causing an increase in excitatory neurotransmitter release.

Where are bending the stereocilia away from the kinocillium closes the potassium channels so k+ ions stop entering the hair cell and it becomes more negatively charged (hyperpolarised) , causing a decrease in excitatory neurotransmitter release.

(Cillia are attached by myosin threads so that bending them physically opens or closes K+ channels)

Question 23

Where in the vestibule are concentrated hair cells present ?

Answer 23

A region called the macula - there’s a macula of saccule and a macula of utricle

Question 24

When the head is upright what direction are the hair cells or the utricle and saccule ?

Answer 24

Utricle hair cells have a vertical orientation.

Saccule hair cells have a horizontal orientation.

Question 25

What gelatinous membrane are stereocillia embedded in?

Answer 25

Otolithic membrane

Question 26

Other than the stereocillia what else is embedded in the otolithic membrane?

Answer 26

Calcite crystal stones called otoconia - these with down on the hair cells .

Question 27

When you start and stop walking what happens to utricle hair cells?

Answer 27

When you start to walk, INERTIA causes the heavy otolithic membrane to get ‘left behind’, so hair cells bend backwards.

When you suddenly stop, INERTIA causes the heavy otolithic membrane to ‘keep going’ thus hair cells bend forwards.

Question 28

What is stimulated or inhibited when you bop your head up and down when walking ?

Answer 28

The Saccule hair cells as they are sensitive to linear acceleration/deceleration up and down.

Question 29

Where are hair cells located in the semi circular canals?

Answer 29

Hair cells are located in an expanded (ampulla) at one base of each canal.

Question 30

Where do hair cells in the ampulla sit?

Answer 30

They sit on a ridge with their stereocillia embedded in a gelatinous slab called the cupula.

Question 31

What does the cupula do?

Answer 31

It blocks the canal and acts like a swing door - allowing the canals to signal in a Bi-directional way.

Question 32

What are the responses of the semi-circular canals to angular head motion?

Answer 32

When the head is static, the hair cells are not bent and the vestibular system nerve afferents fire at a steady resting rate.

With an abrupt head turn, the SCCs rotate in the same direction. But their endolymph gets ‘left behind’ due to inertia and acts as an accelerator pushing the cupula to swing in the opposite direction. Bending towards the kinocillium results in hair cells excitation and increased firing .

Bending away results in inhibition and Reduced firing.

When the head stops abruptly the endolymph ‘keeps going’ due to inertia pushing the cupula in the opposite direction. So if the SCC was excited by the initial turn it’s now inhibited and vice versa.

Question 33

Which type of angular head action does each semi circular canal respond to?

Answer 33

If the action was shaking your head to say no the the horizontal canals would respond.

If the action was shaking your head to say yes hen the anterior and posterior canals would respond.

If the action was to tilt ur head to either side indicating maybe then all three canals in each ear would be responding.

Question 34

True or false- based on the relative excitation or inhibition of the 3SCCs the CNS can determine head motion.

Answer 34

True

Question 35

What is the eye righting reflex and what is it generated by?

Answer 35

A reflex that Improves fovea fixation of the visual world to compensate for the head tilting. This is generated by the utricle and saccule and it causes both eyes to rotate (a little) in the opposite direction.

Question 36

What is the vestibular- ocular reflex (VOR)?

Answer 36

It is a reflex which:

Stabilises visual world on the retina to compensate for angular head accelerations.
It is generated by the semi-circular canals.
In this reflex both eyes move in the opposite direction.

Question 37

What is the disorder given to someone that doesn’t display the Vestibular-ocular reflex?

Answer 37

Oscillopsia

Question 38

How does the vestibular ocular reflex occur ?

Answer 38

When you turn your head to the right.

The right horizontal Semi circular canal is inhibited and the left semi circular canal is excited.

Therefore there is an inhibition of extraocular muscles on one side and excitation of extraocular muscles on the other side.

Thus the eye compensates by moving to the left.

Question 39

What are symptoms associated with vestibular dysfunctions?

Answer 39

Motion sickness/nausea (mild)

Viral infections of the inner ear/labyrinths (variable)
Inflammation generates convection currents in endolymph fluid mimicking head motion,causing vertigo/dizziness.

Ménière’s disease (severe)
Idiopathic cause- membrane rupture with mixing of endo-& peri-lymph generating toxins damaging to hair cells. Vestibular apparatus and cochlea affected: vertigo, vomiting, inability to stand + howling tinnitus (ring in ear) & major heating loss.

Question 40

The semi circular canals contain hair cells which respond to ?

A) linear acceleration
B) gravity
C)angular acceleration
D) static head tilt

Answer 40

Angular acceleration