Lectures 17 & 18 (Nick Glossop) Flashcards

Question

How are linear accelerations transduced? | (4 points) ## Footnote Week 9 - Vestibular Systems

Answer 1

* movement deflects the hair bundles, eliciting an electrical response in the hair cells. * The macula of each utricle is oriented to lie in the horizontal plane. * Any substantial acceleration within the horizontal plane will deflect at least some of the utricle hair cells. * The hair cells are oriented within the macula so that their axes of greatest mechanosensitivity lie in all possible directions.

Answer 2

* There will be maximal acceleration of one group of cells while another group of oppositely oriented hair cells will be suppressed. * cells w/ intermeidate orientations are not affected

Answer 3

one of the bundles of stereocilia alone can detect where the head is moving → you can ablate a large poriton of the utricle and you’ll still be able to detect linear motion + + have a utricle in each ear, and they do the same thing

Answer 4

similarly to utricle - hair cells have their axes of greatest mechanosensitivity lying in all possible directions within macula there are also some saccular hair cells attuned to accelrations in the horizontal plane, particulrly in the anterior posterior axis

Answer 5

Verical accelerations (bungee jumping roller coasters etc)

Answer 6

Brainstem sends inputs to hair cells of vestibular systems - these can have dramatic effects on the sensitivity of hair cells

Answer 7

The utricle is activated by either linear acceleration or head tilt, so the signal on its own is ambigious as to which is going on. Semi-circular canals detect angular acceleration so provide signal during head tilt or have absent signal during linear acceleration

Answer 8

* Whenever an object alters its rate of rotation about an axis * head undergoes this frequently (turning, tilting, dancing etc)

Answer 9

The three semi-circular canals in each vistibular labyrinth

Answer 10

closed tubues filled w/ endolymph that extend from the saccule & utricle

Answer 11

Using the motion of the endolymphatic fluid - specifically the mass of the endolymph

Answer 12

* A gelantinious diagphram spread across the canals widest region * it firmly attatches to the epithelium except at the ampullary crista (where it is penetrated by the stereocilia of around 7k hair cells)

Answer 13

It presses against the cupula, causing it to bow.

Answer 14

Angular acceleration in one direction excites the hair cells, while an angular acceleration in the opposite direction suppresses them

Answer 15

They act in pairs Horizontal left SC canal paired with horizontal right SC canal if not simple horizontal rotation, the pairs of semicircular canal activation can be compliated

Answer 16

Left horizontal canal hairs are activated, right horizontal canal hairs are inhibited

Answer 17

Actual human movements elicit complex redundant patterns of activity from all receptor organs on both sides of the body.

Answer 18

because even simple movements like getting out of a car evoke extremely complex spatiotemporal patterns of activation within the vestibular system.

Answer 19

to get used to the new patterns of vestibular stimulation associated with flying.

Answer 20

Disorientation & vertigo because of conflicting infomation from the two inner ears | (one set of correct info > two sets of conflicting info)

Answer 21

learns to associate a specific pattern of vestibular activity for each motor behavior, and any unusual vestibular responses usually evoke a protective reflex.

Answer 22

surgical removal of the labyrinth

Answer 23

* described by sporadic relapsing vertigo lasting from 10 mins to 10 hours * effects receptor cells of vestibular labyrinth * associated w/ tetanus (white noise in ears) and distorted hearing, suggesting cochleae involved * cause unknown, but suggested to be poor drainage of endolymph * Surgically implanted shunts that bypass this drainage port sometimes work

Answer 24

Endolymph normally exits the vestibular labyrinth via the endolymphatic duct before being reabsorbed into the spinal fluid in the endolymphatic sac.

Answer 25

A system by which the vestibular system tells the oculomotor system how fast and in which direction the head is rotating. This allows the oculomotor system to move the eyes to compensate for head movements and stabilise vision.

Answer 26

Visual processing is much slower and less efficient than vestibular processing for image stabilisation. If you lose the reflexes, you'll have a hard time reading text - especially when locomoting. You'll also have problems recognising friends while walking - you'll need to stop to do so.

Answer 27

The rotational vestibulo-ocular reflex The translational vestibulo-ocular reflex The ocular counter-rolling response

Answer 28

Compensates for head rotation. (Shaking head side to side)

Answer 29

Compensates for linear head movements. (How you focus when looking out a car window).

Answer 30

Compensates for head tilt in the vertical plane. (How you track a target whilst nodding your head).

Answer 31

It causes the eyes to slowly rotate in the opposite direction to any rotational head movement detected by the vestibular system. Eventually, the eyes reach the edge of their orbit and will make a rapid resetting movement back across the centre of gaze.

Answer 32

Nystagmus is involuntary eye movement can be part of the vestibulo-ocular reflex. The eyes moving first in the direction of the lesioned side followed by a quick correction to the opposite side or away from the lesioned side. (Or when you are doing a rotational VOR and you reach edge of orbit, you snap back via nystagmus). The direction of nystagmus is defined by the direction of its quick phase.

Answer 33

The vestibular signal drive the slow phase of nystagmus. Brain stem circuits generate the quick phase (when the eyes are near the edge of orbit)

Answer 34

If the vestibular is damaged, it sends erroneous signals to the oculomotor system. Patients will report feeling dizzy, double vision, constantly flickering eyes side to side.

Answer 35

They compensate for linear head movements by taking into account the distance of the object being viewed. It's a complex process because of this factor of depth. (Looking out a train window and things move by at different speed depending on their distance to you)

Answer 36

Gravity exerts a constant acceleration on the head so the vestibular system can sense the orientation of the head relative to gravity. Therefore, the vestibular system is used to estimate the tilting of the head in the vertical plane and initiates the counter-rolling response of the eyes to compensate. (Think intorsion/extorsion).

Answer 37

It habituates. The vestibular system does not respond well to very slow head movements.

Answer 38

It uses the fact that as we move our eyes in space, the world moves in the opposite direction. When large parts of a scene move, the optokinetic reflex drives our eyes in the direction of the observed image motion. If this response is perfect, it should stabilise the image on the retina.

Answer 39

It takes time to develop: - It provides a motion signal that takes over as the vestibular signal decays. It is activated by very slow visual image motion: - Vestibular system isn't good at slow motion.

Answer 40

Sitting in an enclosed cylinder with black and white stripes on the walls. As it slowly rotates around you, you perceive it to slow down until it 'stops' moving ~30 secs in. Then you will feel like you're moving. This is due to the optokinetic reflex slowly kicking in.

Answer 41

As the vestibular system should tell you that you are not moving (cause you're not) it means that the visual system MUST be able to stimulate the vestibular nuclei. This is what allows this illusion to give the false impression that the vestibular system is working when it is not.

Answer 42

When large parts of a scene move. This happens because vision-related neurons project to the vestibular nuclei and stimulate it. (So visual neurons can stimulate the same neurons as vestibular system - inducing the feeling of motion)

Answer 43

Recordings from the vestibular nuclei of head fixed primates presented with circular vection showed activity even though there was no vestibular activation. Which accounts for the sensations experienced by human observers and provides evidence that the vestibular system can be activated by visual inputs.

Answer 44

The vestibular nuclei respond identically to movement of an image on the retina and head movements. However, there is a difference in latency and duration of these. The vestibular input fires quickly (low latency) but decays exponentially to zero with continued rotation (due to endolymph rotating at the same speed as you) At the same time, the optokinetic pathway generates an exponentially rising signal into the vestibular brain stem nuclei. In normal circumstances, the summed output of these two signals results in a constant response.

Answer 45

Once you are spinning at a constant rate, the endolymph in the semi-circular canals will spin at the same rate you are. Once you stop spinning, the fluid continues to spin and trigger the hair cells which tells you that you are still moving when you are not. This = dizzy.

Answer 46

Visual Vestibular

Answer 47

As we fall, our head moves from its normal position relative to the force of gravity. The vestibular system then responds MUCH fast than the visual system, signalling to the vestibulospinal reflexes to allow for preventative measures.

Answer 48

An automatic reflex that helps maintain balance, posture, and head stabilisation.

Answer 49

It is a group of four major nuclei which lies on the floor of the fourth ventricle. Forming the front part of the medulla and spanning a bit into the pons.

Answer 50

Medial, Lateral, Superior and Descending.

Answer 51

They combine information from the vestibular labyrinths with those from the visual system, the spinal cord and the cerebellum

Answer 52

They send outputs to the reticular and spinal centres concerned with skeletal movements, the vestibular regions of the cerebellum, the thalamus, and the oculomotor nuclei.

Answer 53

Mainly get inputs from the semi-circular canals. They send outputs to the spinal cord and oculomotor centres.

Answer 54

Medial: - Mostly excitatory. - Glutamatergic. Superior: - Mostly inhibitory. - GABAergic. They help generate gaze reflexes - dealing with rotational velocity.

Answer 55

Gaze is the coordination of head and eye movements to direct the fovea towards a point of interest.

Answer 56

The head is much heavier than the eye. So, during small gaze movements the eye reaches its target well before the head begins to move. Small gaze movement translates into a saccade, followed by a head movement with VOR.

Answer 57

During larger gaze movements the eyes and the head move at the same time. This is because the VOR is suppressed so that they move together (head snaps to target fast so eyes don't need to saccade).

Answer 58

Both the semi-circular canals and the otolith organs send inputs to the lateral nucleus. The lateral nucleus send outputs mainly to the lateral vestibulospinal tract. It is involved with postural reflexes.

Answer 59

Inputs from the otolith organs. It sends outputs to the spinal cord, the cerebellum and reticular formation, as well as to the contralateral vestibular nuclei. It seems to be mainly interested in integrating the central motor signals with vestibular signals.

Answer 60

The relative position of the various parts of the body with respect to one another and the environment.

Answer 61

Static equilibrium: - Refers to a balance of forces acting on the body at rest. Dynamic equilibrium: - Refers to a balance of forces when a body is in motion.

Answer 62

To minimise energy needed to support their weight, elephants lock their knee joints in line with gravity. Smaller quadrupeds tense the muscles around their flexed hindlimb joints, allowing them to flee at the first site of danger.

Answer 63

They are movements that occur prior to postural readjustment to maintain balance. For example: - Lifting one leg sideways while trying to remain balanced on the other leg. - To maintain balance, we shift our weight to the standing leg before lifting the other.

Answer 64

Knowing the position of the head relative to the environment is important in stabilising vision. Knowing its position relative to the rest of the body is important for maintaining erect posture.

Answer 65

Primarily feedforward control. However, feedback control is needed to generate postural adjustments to unexpected events.

Answer 66

Cats can lose the support of one of their legs and remain standing. They can be trained to expect the loss of support from one paw as they learn to shift their centre off balance to be supported by the three remaining limbs.

Answer 67

Patients are unable to make these adaptive changes.

Answer 68

They failed to SCALE their response. (Problems modulating the magnitude of response). They tensed far more than they needed as their baseline rate and did not change it much. Controls show a graded differentiation of contraction dependent on the situation they were in.

Answer 69

Walking on a circular rotating treadmill requires precise neuromuscular control of horizontal sway of the body relative to foot placement on the treadmill. After exposure and learning, healthy controls learnt to walk in a circle blindfolded. People in wheelchairs will always fall off...

Answer 70

Normal cats can learn to walk along a rotating beam without falling. Animal with bilateral labyrinthectomy never recovers this ability. Animal with a unilateral labyrinthectomy can relearn this depending on when they are ALLOWED to. Animals that are restrained for a period of a week during this retraining period (up to 20 days post op) NEVER fully regain the ability.

Lectures 17 & 18 (Nick Glossop) Flashcards

Vestibular system (95 cards)