Movement L4

Question 1

charactersitics of damage at each level?

Answer 1

Question 2

Descending motor pathways occupy 2 major locations in the spinal cord white matter - what are they?

Answer 2

Descending motor pathways occupy 2 major locations in the spinal cord white matter:

one dorsolateral,

the other ventromedial.

Question 3

VENTROMEDIAL PATHWAYS are evolutionarily …..

Answer 3

VENTROMEDIAL PATHWAYS are evolutionarily ancient, and exist in all vertebrates.

Question 4

what do ventromedial pathways control?

Answer 4

They control axial (trunk) and proximal limb muscles and play a role in whole body movement (locomotion/posture).

These tend to produce stereotypic whole-body movements and postures.

Question 5

examples of ventromedial pathwaysd

Answer 5

Reticulospinal pathway

Vestibulospinal systems

Tectospinal (from superior/rostral colliculus)

Question 6

decribe the dorsolateral systems

Answer 6

most important route through which goal directed movements of the limbs are driven, especially movements of the hands, feet and face (and other prehensile structures, like the lips).

These systems control the more individuated movements of the limbs, rather than whole body postures and movements.

Question 7

examples of dorsolateral systems

Answer 7

1. Rubrospinal pathway - arises from the red nucleus - probably vestigial in man.
2. Corticospinal Tract arising from motor areas of cerebral cortex

Question 8

the vestibular system. This system is important for many movements, but particularly for …..

Answer 8

the vestibular system. This system is important for many movements, but particularly for postural control.

Question 9

Many systems can contribute to postural stability:

such as?

Answer 9

Somatosensory Systems can inform us of the balance of forces on each foot, stretch and other proprioceptive reflexes can tell us about the state of the muscles of supporting limbs.

The Visual System can tell us whether we are vertical with respect to the outside world

The Vestibular System can inform us of head position and movement.

Question 10

descrbie the structure of the vesibular system

Answer 10

The vestibular system receptors are

sensory hair cells located in the labyrinth in semicircular canals and the otolith organs (the saccule and utricle)

Question 11

the hair cells in the vestibular system are the same as ?

Answer 11

The hair cells are identical to the receptors in the cochlea: the transduction mechanism was covered in the auditory system lectures: hair cells have directional sensitivity and respond best to movement in a specific direction.

Question 12

In the utricle and saccule, hair cells do what?

Answer 12

hair cells project into a jelly-like mass on which gravity acts.

Different hair cells are arranged to have different preferred directional sensitivity, so specific sets of hair cells will be activated when the head is in different positions.

These afferents provide information on the effective direction that gravity is acting (linear acceleration due to gravity): when immobile this can be considered to be a head position signal.

When moving it signals head translation (up/ down, left/ right, backward/ forward).

Question 13

The hair cells associated with the semicircular canals do what?

Answer 13

The hair cells associated with the semicircular canals are embedded in a jelly-like mass that almost closes the canal called the cupula. The cupula is neutrally buoyant in the fluid (endolymph) in the canals so with the head stationary it is also stationary.

The hair cells are activated when the cupula is deflected. This usually happens when the head rotates: the fluid in the canals has inertia, so tends to remain stationary and since the cupula is fixed to the head, it is deflected.

Question 14

The canals therefore signal ….

Answer 14

The canals therefore signal angular rotation of the head.

Question 15

There is a labyrinth on each side; the canals on the 2 sides act as complementary pairs, with appropriate projections into the ______ nuclei

Answer 15

There is a labyrinth on each side; the canals on the 2 sides act as complementary pairs, with appropriate projections into the vestibular nuclei

Question 16

The Vestibular system is a _________ system, detecting head position and movement.

Answer 16

The Vestibular system is a proprioceptive system, detecting head position and movement.

Question 17

activation of
vestibular receptors may indicate what?

Answer 17

activation of
vestibular receptors may indicate
postural instability

Question 18

the learning of the vestibular signals relies on the ?

Answer 18

cerebllum

Question 19

T or. f

Vestibular effects are powerful, but we are usually unaware of them.

Answer 19

T

Question 20

Damage to the vestibular system is not uncommon - how might it be damaged?

problems associated?

Answer 20

Damage to the vestibular system is not uncommon (peripherally, e.g. through labyrinthitis, or centrally e.g., through brainstem stroke or cerebellar damage) and can produce dramatic problems, revealing the potency of everyday vestibular reflexes.

Question 21

Describe neck reflexes

Answer 21

is heda sway due to neck or body?

neck muscle movements compared throguh efference copy.

Imposed movement of the neck produces actions that counteract the vestibular reflexes – ‘neck reflexes’ that are exactly equal and opposite to the vestibular reflexes.

Question 22

eye movement uses only _ muscles

Answer 22

eye movement uses only 6 muscles

Question 23

the eye rotates in the orbit, essentially under _________ load (interestingly these muscles

have no stretch reflex!),

Answer 23

the eye rotates in the orbit, essentially under predictable load (interestingly these muscles

have no stretch reflex!),

Question 24

in binocular species the eyes must move together (________).

Answer 24

in binocular species the eyes must move together (consensually).

Question 25

T or F

The visual system is poor at resolving changing (moving images): a static image is important for visual acuity

Answer 25

T

Question 26

where is the control system of eye movements based?

Answer 26

Eye movements must be consensual, so the control system that coordinates the 2 sides is based in the brainstem, not the motor cortex.

Question 27

describe Gaze-fixing mechanisms

Answer 27

• fast movements - then stabilise new image.
• saccades - vision suppressed during
• vestibulo-ocular reflex (VOR) moves the eyes equal and opposite to the head
• A complementary optokinetic system moves the eyes to follow slow movements of the visual field

Question 28

describe the path the vestibulo ocular refledx takes?

Answer 28

This is a relatively direct connection between semicircular canal afferents, the vestibular nuclei and the motoneurons of the oculomotor nuclei (via the MLF, medial longitudinal fasiculus, a fast conducting fibre tract in the brainstem).

Question 29

The VOR is a ________ control mechanism (vestibular signals are used to generate a prediction of the eye movements needed to stabilize gaze).

Answer 29

The VOR is a feedforward control mechanism (vestibular signals are used to generate a prediction of the eye movements needed to stabilize gaze).

Question 30

Answer 30

Question 31

When the eye deviates far from its axis within the orbit, fast re- setting movements (_______) move the eye back close to the central axis

Answer 31

When the eye deviates far from its axis within the orbit, fast re- setting movements (saccades) move the eye back close to the central axis

Question 32

Physiologically nystagmus can occur in response to ……

Answer 32

Physiologically nystagmus can occur in response to sustained optokinetic or vestibular stimuli.

Question 33

Pathologically, nystagmus follows damage to the systems that control gaze fixing ……..

Answer 33

Pathologically, nystagmus follows damage to the systems that control gaze fixing – cerebellar or vestibular damage.

Question 34

Saccades your most frequent movements that you make, how many per second?

Answer 34

Saccades your most frequent movements that you make, 2/3 per second.

Question 35

describe the process of saccades focussing on a new point of interest in the visual field

Answer 35

• saccades move fovea to new point of interest - organised by suerior (rostral) colliculus (mid brain)
• retina projects onto the superior colliculus in an orderly (retinotopic) way.
• Deep layers of the colliculus project to regions of the brainstem reticular formation which in turn project to the oculomotor nuclei - which control the extraocular muscles.

*

Question 36

describe where deep layer sof the superior colliculus project to further integrate other systems in to tjhe eye movement

Answer 36

Deep layers of the colliculus also project to the cervical spinal cord (via the tectospinal tract), so coordinated neck movements can accompany eye movements.

Deep layers of the colliculus also receive auditory input and allow rapid orienting movement to sounds as well as to visual stimuli.

Question 37

which strucutres are involved in coordinating whether the superior colliculus is allowed to drive saccade movements of the euye?

Answer 37

basal ganglia

cerebral cortex

Question 38

Describe smooth pursuit

Answer 38

lower continuous eye movements can be made but only to ‘follow’ moving objects

feed forward - involving the cerebral cortex

regions of frontal lobe anterior to motor cortex (the - frontal eye fields), as well as brainstem regions, especially the cerebellum.

Question 39

fat

Answer 39

mamba