MC 4 (vestibular system and reflexes)

Question 1

Where is the vestibular system located?

Answer 1

inner ear

Question 2

What does the vestibular system give information about?

Answer 2

head position
spatial orientation (w/ respect to gravity)
acceleration of the head

Question 3

What functions are the vestibular system key for controlling?

Answer 3

control of balance and posture
eye movement
perception of orientation in the environment while moving

Question 4

What fluid lies within the vestibular canals?

Answer 4

endolymth

Question 5

What’s the overarching name given to the structure of the vestibular system?

Answer 5

labyrinth

Question 6

What 5 sensory ‘organs’ (elements) make up the labyrinth?

Answer 6

3 semicircular canals

2 otolith organs (utricile and saccule)

Question 7

What is the name of the receptors within the vestibular system

Answer 7

hair cells

Question 8

What do hair cells respond to?

Answer 8

flexion of the hairs as a response of endolymth movement

Question 9

What is the name of the short hairs on a hair cell?

Answer 9

stereocillia

Question 10

What is the name of the long hairs on a hair cell?

Answer 10

kinocillium

Question 11

What occurs in the hair cell as a response of the small hairs (stereocillia) moving towards the long hairs (kinocillium)?

Answer 11

depolarisation of membrane

increase in action potentials

Question 12

What occurs in the hair cell as a response of the long hairs (kinocillium) moving towards the small hairs (stereocillia)?

Answer 12

hyperpolarisation of membrane

decrease in action potentials

Question 13

If hairs are organised from small to large (left to right), what is the response of the hair cells being deflected to the right?

Answer 13

depolarisation of membrane

increase in action potentials

Question 14

What are the canals of the vestibular system sensitive to?

Answer 14

angular ACCELERATION

Question 15

What direction does endolymth move in response to the angular motion of the head to the left

Answer 15

to the right

Question 16

Does the fluid (endolymth) move immediately with the acceleration of the canal walls?

Answer 16

no

takes a moment coz inertia

Question 17

What is the response of the hair cells to a constant motion of the head?

Answer 17

resting / regular firing rate

hair cells respond to angular ACCELERATION

Question 18

What are the 3 semicircular canals and what type of angular acceleration do they each respond to?

Answer 18

1. Horizontal canal : acceleration about the verical axis (i.e. left and right)
   2&3. Anterior & Posterior canals:
   acceleration from flexion, extension of neck and lateral tilt (ear to ear axis)

Question 19

There is an inner ear on each side of the head. As a result, hair cells of one inner ear will respond to acceleration oppositely to the other side.
if….
left side = high firing rate
right side = low firing rate

How does the CNS make sense of all this information to know you’re turning left?

Answer 19

Interconnection of interneurons cause affect on firing rate of other side neuron as well.

Increased activity (left) = increased excitation of interneuron (to right) = greater inhibition of neuron (right) = decreased firing of neuron (right)

Lower activity (right) = reduced excitation of interneuron (to left) = lesser inhibition of neuron (left) = increased firing of neuron (left)

Increased activity on one side leads to even greater dampening of activity on the other side, and vice-versa.

Question 20

What movements are the otilith organs sensitive to?

Answer 20

> head tilt

> linear accelerations

Question 21

How are the hair cells orientated…

1. in the semicircular canals
2. in the otilith organs?

Answer 21

1. in the same direction

2. not all in the same direction

Question 22

What is the effect of a forward head tilt on the hair cells in the otilith organs?

Answer 22

gravity has an effect on the crystals that lay above the hair cells.
Displaces hair cells
Deflects kinocillium towards the stereocillia, hyperpolarising membrane and decreases the firing rate

Question 23

What is the effect of a backward head tilt on the hair cells in the otilith organs?

Answer 23

gravity has an effect on the crystals that lay above the hair cells.
Displaces hair cells
Deflects stereocillia towards the kinocillium, depolarising membrane and increases the firing rate

Question 24

Forward linear acceleration of the head has a similar effect to head tilt in which direction?

Answer 24

backwards tilt

… increased firing rate of hair cells

Question 25

Backward linear acceleration of the head has a similar effect to head tilt in which direction?

Answer 25

forwards tilt

…. decreased firing rate of hair cells

Question 26

How can the CNS tell whether your head is tilting or accelerating linearly?

Answer 26

integration of information from the otilith organs and semicircular canals.

Semicircular canals are not active during linear acceleration but are to an extent during some phases of head tilt (coz angular acc)

Therefore, if semicircular canals are active, then tilt.
If canals are not active, then linear acceleration

Question 27

What effect does a strong stimulus have to the magnitude and latency of the response?

Answer 27

Bigger response

Shorter latency

Question 28

Describe the monosynaptic stretch reflex pathway in the context of a bicep stretch

Answer 28

muscle spindle in bicep fires action potentials to the spinal cord, activating alpha motor neuron(s) to fire motor unit(s) in the affected muscle (bicep) causing the bicep to contract.
Other elbow flexors (brachialis) may be activated to counteract stretch in the fibres in the bicep.

Additionally, inhibitory interneuron may decrease the activity of the alpha motor neuron on the antagonist (tricep), therefore, less active, generating less force, facilitating the action of the agonist (arm flexion).

Question 29

Is the monosynaptic stretch reflex pathway a phasic or tonic response?

Answer 29

Phasic,

V.quick

Question 30

Describe the withdrawal reflex

Answer 30

Step on a pin.
Inhibits quad activity
Stimulates hamstring activity, removing leg from painful stimulus

Alternatively, may have increased stimulation of the quad on the other leg, causing shift onto other leg.

Question 31

What 2 methods can the brain modulate reflex mechanisms through?

Answer 31

1. Reflex suppression
2. Reflex potentiation

e. g. response when pricking the foot with a pin when…
a) in standing posture
b) when laying down

reflex suppression during (b) as need to maintain balance and posture is not as high.

Question 32

How can the natural reflex as a child to extend the body during backward head tilt and turn the body to the left when looking left aid adults during a sporting situation?

Answer 32

> Catching a ball above head and to the left during baseball, the reflex facilitates the extension of the left side limbs when focusing on watching the ball and looking upwards.

> looking up during a squat leads to better body extension than when looking downward.

Question 33

What is muscle synergy?

Answer 33

a group of muscles connected by neural circuitry and act following a coordinated pattern
reduces attention that must be payed to each part of the system, making controlling movement easier.

Question 34

What is the name given to the reflex that brings head position to neutral should it move unintentionally

Answer 34

vestibulocollic reflex

Question 35

How is it possible to ‘override’ the vestibulocollic reflex in order to maintain a tilted head posture?

Answer 35

Through modulation activities (inhibition or excitation) in the brain higher centres, they inform receptors that the tilted position is okay and intended

Reflex is suppressed.

Feedback loop for the vestibulocollic reflex is altered as the CNS has set the reference point for desired head tilt angle as other than neutral