motor control Flashcards
neuromuscular junction
specialized synapses between the nervous system and muscle fibers
lateral corticospinal motor tract
involved in fine movement of distal limb muscles (arms, hands, fingers, lower leg and foot)
tract crosses entirely from one side of the brain to the opposite side of the body (contralateral)
medial motor tract
involved in control of movements of the trunk and proximal limb muscles
involved in posture and bilateral movements
projects both contralaterally and ipsilaterally
cerebellum motor control
plays an important role in coordinating timing of muscle movement, planning movement and learning motor skills
organized into 3 main divisions that each receives a distinctive type of info a sends out input to distinct portions of the nervous system
info flowing through these cerebellar loops allows it to modulate motor processing
movements that are not modified once they have been started
vestibulocerebellum
damage causes difficulty with balance and postural instability
spinocerebellum
damage causes difficulty with smooth muscle control of movement and movement of proximal muscles
cerebrocerebellum
damage causes difficulty with the regulation of highly skilled movement that requites sensorimotor learning
cerebellar ataxia
difficulties in coordinating movement after cerebellar damage
tradition test: patient touches their nose and then neurologist’s finger
occurs when activity of agonist and antagonist muscles are not coordinated
disrupts coordination of multi-joint movements. to compensate patients will move of join at a time in serial manner
difficulties in sensory motor learning after damage to lateral portions of the cerebellum.
agonist
contracts during movement
antagonist
relax/lengthen during movement
forward model theory of cerebellar function
theory argues that the cerebellum helps predict the sensory consequences of motor plans
forward models not influenced by feedback from periphery
subcortical nuclei in the basal ganglia
caudate nucleus
putamen
nucleus accumbens
globus pallidus
substantia nigra
subthalamic nucleus
roles of the basal ganglia
setting the motor system with regard to posture
preparing the nervous system to accomplish a voluntary motor act
acting as an autopilot for well-learned sequential movements
controlling the timing and switching between motor acts
because they receive both motor and nonmotor info, the basal ganglia are also thought to assist in motor planning and learning
movements that take time to initiate or stop
theories of the basal ganglia function
- the basal ganglia facilitate the synchronization of cortical activity underlying the selection of appropriate movements while inhibiting inappropriate ones
- the basal ganglis chunch individual actions into coordinated, stereotyped and habitual units of action
- the basal ganglia aid the ability to execute movements with varying levels of vigor
direct route of the basal ganglia
contributes to sustaining/ facilitating ongoing action
indirect route of the basal ganglia
important for supressing unwanted movement
works in opposition of the other
parkinsons
results from damage to the cells of the substantia nigra
loss of dopamine neurons
tremors - rythmic, oscillating movements
akineria - inability to initiate spontaneous movement
bradykinesia - slowness of movement
what does neuron death in the substantia nigra cause
inadequate input to the basal ganglia
causes overactivation of th indirect pathway
increases activity in the internal portion of the globus pallidus
inhibits the thalamus and decreases motor activity
treatment for parkinsons
levodopa
deep brain stimulation
levodopa
cannot give dopamine directly
monoamine oxidase (MOA-B) inhibitors
deep brain stimulations (DBS)
aerobic exercises and behaviour intervention
thalamonoty or pallidotomy
grafting of fetal tissue to the striatum
huntington’s disease
involuntary, uncontrollable and undesired movements
chorea
dystonia
chorea
rapid, jerky movements that appear coordinated but are performed involuntary in an irregular manner
dystonia
slower movements causes by increased muscle tone and contractions that lead to abnormal posture
huntingtons disease indirect pathway
loss of striatal neurons to globus pallidus
external globus pallidus is no longer inhibited
increases inhibition of the subthalamic nucleaus
the internal globus pallidus is not excited so output is reduct. this lessens inhibitions of the thalamus which increases cortical motor activity
huntington’s etiology
an inherited neurological disease resulting in striatum degeneration
produces abnormal movements, cognitive deficits and psychiatric symptoms
caused by a rare, autosomal dominant disease
gene produces mutant huntingtin protein causing striatum atrophy
symptoms typically manifest between 30-45 years of age
it involves a slow decline for 10-15 years and eventually leads to death
tremors
tremors - rythmic, oscillating movements
akineria
akineria - inability to initiate spontaneous movement
bradykinesia
bradykinesia - slowness of movement
huntington’s treatment
no cure, treatments can provide some symptom relief
tetrabenazine or neuetrabenazine (deplete or block dopamine transmission
tourettes
main symptom is vocal and/or motor tics that fluctuate in severity
relatively rare disorder that manifests in childhood
definitive neural substrate or cause has not been found
aspects of the disorder point to dysfunction of the basal ganglia and associated cortical-striatal-thalamic-cortical brain circuitry
nature of tics potentially represents an inappropriate from of habit learning (basal ganglia)
forms of tics
simple motor tics that involve just one portion of the body
more complex tics that involve several muscle groups and seem more purposeful
can include echolalia and coprolalia
echolalia
repeating things just said
coprolalia
intypical speech
what is the major role of cortical regions in motor control
planning and guiding skilled movements
movements that require linking sensory inputs with motor outputs
how do cortical regions support a range of motor abilities
picking up an object
producing a gesture in response to a verbal command
moving the eyes to explore the image of a face
where are regions of motor control distributed
across lateral and medial parts of the brain
primary motor cortex
thought to control the force and or direction with which the motor plans are executed
provides the command signal to drive motor neurons to make muscles more
premotor region, supplementary motor complex and frontal eye fields
involved in the specifying, preparing and initiating of a movement
anterior cingulate cortex
important for selecting among particular responses and monitoring whether the execution of those actions occurred apropriately
contains many distinct subregions, each of which contributes to particular cognitive functions (activated across a large range of tasks
- plays a role in allowing the motor system to generate and select a response and then evaluate the consequences
- feedback systems - did this plan work, and if not how will i fix it for next time (learning from your actions)
- most involved when an action is novel of requires cognitive control, such as when a well-engrained response must be overwritten
parietal regions
involved in linking movements to extrapersonal space and sensory info as well as linking movements to meaning
what are my senses telling me
sensations, somatosensory areas
what happens when the primary motor cortex is damaged
a person cannot control the force of which muscles are exerted
severe cases can result in hemiparesis (weakness)
organization of the primary motor cortex
main: the motor cortex is organized so that different subregions of motor cortex control action of specific portions of the body
homunculus organization
alternative: the motor cortex is organized with regard to action relevent for survival. extended stimulation can lead to coordinated movements.
motor plans
are abstract representations of intended movements
brain generates the action plan before the movement starts
the supplementary motor complex comes up with the motor plan at the most abstract level
then premotor areas code for the types of actions that must occur to meet that motor plan (how to execute the motor plan)
primary motor regions execute the commands - send the signal to the body
coarticulation
forming the next sentence before the first one ended
supplementary motor complex
involved with planning, preparing and initiating movements (activity in this region precedes motor action
sequence and order in which actions occur
SMC projects to both the ipsilateral and the contralateral motor cortex, as well as the contralateral SMC
- distinct from primary motor cortex in which activation is predominantly observed contralateral to what is moving
what are the three sub-regions of the SMC
anterior located pre-SMA
Supplementary eye field
posteriorly located SMA
anterior located pre-SMA
involved in selecting what actions should be implemented
initial planning
supplementary eye field
involved in the planning of eye movement
posteriorly located SMA
involved in planning movement of body parts (other than the eyes)
right inferior frontal cortex
suggested to play a role in interupting or inhibiting motor actions
- often assed via the stop-signal paradigm
- the larger tissue loss the more difficulty in response inhibition - stopping an action
the region is also activated when people have to push a button twice rather than aborting a response
- perhaps plays a role in altering actions based on the current environmental context rather than inhibiting actions
parietal lobe
sensation
superior regions interface between movement and sensory info (coordinated movement between these two)
- damage causes inability to guide limbs in a well-controlled manner
inferior regions contribute to the ability to produce complex, well-learned motor acts
- damage to these regions leads to a disorder known as apraxia
apraxia
an inability to perform skiled, sequential, purposeful movement that cannot be accounted for by disruptions in more basic motor processes
commonly observed after a stroke, TBI and in people with neurodegenerative disorders
most typically observed after parietal or frontal lesions of the left hemisphere
