Movement L5 Flashcards
whats motor association cortex used for?
location?
planning and prepoaration of movement
rostral to primary motor cortex
The motor cortex mediates which kind of movements, e.g. where movements are made to interact with objects in space.
The motor cortex mediates goal directed or voluntary movements, e.g. where movements are made to interact with objects in space.
Unilateral mild stroke produces
…
Unilateral mild stroke produces contralateral hemiparesis (one-sided weakness and partial paralysis)
severe unilateral stroke will cause….
severe unilateral stroke will cause contralateral hemiplegia (one-sided paralysis).
can larger strokes lead to the unmasking of spinal reflexes?
yes
stroke site:
anterior cerebral artery infarction affects?
, middle cerebral artery infarction affects ?
anterior cerebral artery infarction affects lower limbs,
middle cerebral artery infarction affects upper limbs and face.
Middle cerebral artery infarctions that affect the outflow of the motor cortex thought the _____ ______ are devastating.
Middle cerebral artery infarctions that affect the outflow of the motor cortex thought the internal capsule are devastating.
describe how the motor cortex exerts control over descending motor pathways
all mamals:
particularly the reticulospinal and rubrospinal pathways
most mammals:
a distinct corticospinal tract that has a direct effect spinal interneurons which in turn control motoneurons.
T or F
In quadrupeds that use the forelimbs for manipulation (cats and rodents) there is a corticospinal tract as well
T
The __________ pathway is the most important route through which willed or voluntary movements are mediated in mammals
The corticospinal pathway is the most important route through which willed or voluntary movements are mediated in mammals
were doe the corticospinal tract cross the mid line?
Most Corticospinal tract fibres cross the midline in the low medulla (the motor decussation)
describe the path of the corticospinal tract fibres
- The fibres descend through the ventral part of the brainstem.
- In the forebrain these fibres lie in the internal capsule
- In the midbrain the fibres form the cerebral peduncle
- In the medulla the old name for the fibres is the pyramid (hence pyramidal tract). In the medulla many cortical output fibres branch to terminate in regions that control brainstem motornuclei.
- cros midline
- continuing into the spinal cord as the lateral corticospinal tract in the dorsolateral funiculus of the spinal cord.
Pictre:
motor cortex gives rise to which skils?
motor cortex in primates allows the control of precise, independent movement of the extremities (e.g. fingers).
manual dexterity
T or F
There is huge species diversity in the corticospinal tract.
T
A small stroke may cause a ……
A larger stroke may cause a ……
A small stroke may cause a contralateral hemiparesis (weakness)
A larger stroke may cause a contralateral hemiplegia (paralysis).
“Upper motoneuron lesion” to refer to motor cortex lesions that are complicated by ,….
“Upper motoneuron lesion” to refer to motor cortex lesions that are complicated by spasticity
compared to “lower motoneuron lesions”, which cause ….
compared to “lower motoneuron lesions”, which cause flaccid paralysis
issue with this picture
- lead people to think the motor cortex controls individual muscles.
- but single neurones control groups of muscles
- Different groups of motor cortex neurons thus provide alternative ‘libraries’ of muscle synergies which might be used in different movements
give some sources of input to the motor cortex
- Motor association areas (direct cortico-cortical connections)
- Cerebellum (via VL thalamus)
- Basal Ganglia (via VL thalamus)
- Sensory afferents (via VL thalamus and sensory cortex)
describe how the motor cortex uses sensory feedback
both tactile and proprioceptive afferents.
allow correction
eg: reguation of force grip
- initial estimate
- cutaneous afferents detect slippage
- grip strengthened (60ms response time)
- until slip stops
Negative feedback - slow and reactive.
describe motor association areas - where do they get input from?
where do they project to?
inputs from higher cortical association areas (prefrontal and parietal) and from the cerebellum and basal ganglia.
direct projections to primary motor cortex
motor associatio areas are involved in?
planning
Two regions of motor association cortex were initially recognised in primates:
what are the?
Two regions of motor association cortex were initially recognised in primates:
lateral Premotor Cortex
and Supplementary Motor Area (SMA)
describe the Supplementary Motor Area function?
most important in internally generated or self-paced movement (you decide when and how to move) and bimanual movements.
d: Lateral premotor cortex
more important for movements that are dependent on a sensory trigger signal, or when sensory information constrains the options (e.g. interacting with an external object – to catch something. You can only catch something if your hands are in the right place at the right time!).
major inputs to lateral Premotor Cortex and Supplementary Motor Area (SMA).
Cerebellum provides major input to lateral premotor cortex;
the basal ganglia to the supplementary motor area.
Lateral premotor cortex lesions leads to?
Lateral premotor cortex lesions lead to
an inability to appropriately incorporate
sensory information (visual, tactile) into
motor actions, particularly into
grasping.
descrbie the visuomotor grasp circuit
the location of objects in egocentric space is represented is an area of the posterior parietal cortex (area AIP - the apex of the ‘where’ visual stream). This projects to lateral premotor cortex, which in turn projects to primary motor cortex.
There is a heavy interconnection between these
areas and the cerebellum.
Lesions in these areas do not prevent attempts at movement, but this movement is often poorly organised in relation to objects in the outside world.
humans with lesions in the lateral premotor cortex show what condition?
apraxias
where were mirror neurones first described?
Part of the lateral premotor cortex is the site at which ‘mirror neurons’ were first described
what are mirror neurones (specifically in the lateral premotor cotex)
useful for imitation
these are neurons that fire in relation to making a grasping movement, but also when seeing another person making the same grasping movement – e.g. they contribute to action, but also 2 action observation. This may be useful in imitation, but much has been made of this beyond motor control (see link to video on Moodle site).
role of the SMA?
SMA helps predict the sequence of movements needed to achieve a particular end point and in understanding their consequences. This type of activity is an essential element of feedforward motor control,
SMA important in feeforward control too
T or F
The very large amounts of cortex in the motor association areas in man are poorly understood
T
there are areas and the medial part of the hemisphere (part of the cingulate cortex) which have motor functions. These areas are thought to be involved in emotionally driven and related movements.
give an esxmaple
An example might be the limbic laugh: voluntary facial paralysis in patients who suffer a primary motor cortex a stroke these them unable to voluntarily smile or laugh (or pretend to laugh), yet they can laugh when told a genuinely funny joke.
may types of apraxia?
Several forms of apraxia have been described for example an inability to make gestures or movements when instructed (ideomotor apraxia), inability to link the elements of a sequence of movements correctly (ideational apraxia) or an inability to link physical structures or pictures/shapes in an appropriate way (constructional apraxia).
fat
mamba
