Movement L4 Flashcards
charactersitics of damage at each level?
Descending motor pathways occupy 2 major locations in the spinal cord white matter - what are they?
Descending motor pathways occupy 2 major locations in the spinal cord white matter:
one dorsolateral,
the other ventromedial.
VENTROMEDIAL PATHWAYS are evolutionarily …..
VENTROMEDIAL PATHWAYS are evolutionarily ancient, and exist in all vertebrates.
what do ventromedial pathways control?
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.
examples of ventromedial pathwaysd
Reticulospinal pathway
Vestibulospinal systems
Tectospinal (from superior/rostral colliculus)
decribe the dorsolateral systems
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.
examples of dorsolateral systems
- Rubrospinal pathway - arises from the red nucleus - probably vestigial in man.
- Corticospinal Tract arising from motor areas of cerebral cortex
the vestibular system. This system is important for many movements, but particularly for …..
the vestibular system. This system is important for many movements, but particularly for postural control.
Many systems can contribute to postural stability:
such as?
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.
descrbie the structure of the vesibular system
The vestibular system receptors are
sensory hair cells located in the labyrinth in semicircular canals and the otolith organs (the saccule and utricle)
the hair cells in the vestibular system are the same as ?
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.
In the utricle and saccule, hair cells do what?
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).
The hair cells associated with the semicircular canals do what?
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.
The canals therefore signal ….
The canals therefore signal angular rotation of the head.
There is a labyrinth on each side; the canals on the 2 sides act as complementary pairs, with appropriate projections into the ______ nuclei
There is a labyrinth on each side; the canals on the 2 sides act as complementary pairs, with appropriate projections into the vestibular nuclei
The Vestibular system is a _________ system, detecting head position and movement.
The Vestibular system is a proprioceptive system, detecting head position and movement.
activation of
vestibular receptors may indicate what?
activation of
vestibular receptors may indicate
postural instability
the learning of the vestibular signals relies on the ?
cerebllum
T or. f
Vestibular effects are powerful, but we are usually unaware of them.
T
Damage to the vestibular system is not uncommon - how might it be damaged?
problems associated?
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.
Describe neck reflexes
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.
eye movement uses only _ muscles
eye movement uses only 6 muscles
the eye rotates in the orbit, essentially under _________ load (interestingly these muscles
have no stretch reflex!),
the eye rotates in the orbit, essentially under predictable load (interestingly these muscles
have no stretch reflex!),
in binocular species the eyes must move together (________).
in binocular species the eyes must move together (consensually).
T or F
The visual system is poor at resolving changing (moving images): a static image is important for visual acuity
T
where is the control system of eye movements based?
Eye movements must be consensual, so the control system that coordinates the 2 sides is based in the brainstem, not the motor cortex.
describe Gaze-fixing mechanisms
- 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
describe the path the vestibulo ocular refledx takes?
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).
The VOR is a ________ control mechanism (vestibular signals are used to generate a prediction of the eye movements needed to stabilize gaze).
The VOR is a feedforward control mechanism (vestibular signals are used to generate a prediction of the eye movements needed to stabilize gaze).
When the eye deviates far from its axis within the orbit, fast re- setting movements (_______) move the eye back close to the central axis
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
Physiologically nystagmus can occur in response to ……
Physiologically nystagmus can occur in response to sustained optokinetic or vestibular stimuli.
Pathologically, nystagmus follows damage to the systems that control gaze fixing ……..
Pathologically, nystagmus follows damage to the systems that control gaze fixing – cerebellar or vestibular damage.
Saccades your most frequent movements that you make, how many per second?
Saccades your most frequent movements that you make, 2/3 per second.
describe the process of saccades focussing on a new point of interest in the visual field
- 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.
*
describe where deep layer sof the superior colliculus project to further integrate other systems in to tjhe eye movement
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.
which strucutres are involved in coordinating whether the superior colliculus is allowed to drive saccade movements of the euye?
basal ganglia
cerebral cortex
Describe smooth pursuit
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.
fat
mamba
