Motor Systems Flashcards
What is the basal ganglia and frontal cortexs actions in the hierarchy ?
Deciding and initiating a task
All senses project into these structures
What is the pathway for functional hierarchy of motor systems?
General strategy - plan - build a motor programme - execution of a programme - movement - end point
What is the function of the cerebellum and primary motor area in the hierarchy of motor output ?
Reaching
Proprioceptors, vision and hearing project into cerebellum and colliculus to localise reaching
What is the function of the primary motor cortex in the hierarchy of action ?
It’s involved in grasping and actually carrying out the activity
Skin, joints and muscle project into M1 and reticular formation for manipulation of grasp
What is the direct pathway from the motor cortex to spinal cortex ?
Primary motor cortex and medial and lateral Premotor cortex to lateral part of the ventral horn
- this is to initiate movements of distal limbs
What is the indirect pathway from the primary motor cortex to spinal cortex ?
Primary motor cortex and medial and lateral Premotor cortex to reticular formation to medial parts of ventral horn
- to make postural adjustments which support movement
What is the purpose of the descending upper motor neurons from basal ganglia to motor cortex ?
Planning, initiating and directing voluntary movements
What is the purpose of the descending upper motor neurons projection to the BRAINSTEM centres ?
For basic movement and postural control
What are the main functions of brain in motor control?
Initiation, integration and coordination
What are the main functions of the spinal cord in motor movements ?
Simple reflexes, coordination, pattern generation and integration
How are the motor systems organised ?
In hierarchical and parallel arrangements
This ensures that the motor output doesn’t fail
What areas do the Premotor areas directly control ?
Primary motor cortex
BRAINSTEM
Spinal cord
What are the 3 cortical pathways ?
Lateral corticospinal tracts - skilled limb movements
Ventral corticospinal tracts- axial muscle control
Corticobulbar tracts - controls facial muscles, jaw muscles, muscles for speaking and swallowing
What are the 4 BRAINSTEM motor pathways ?
Rubrospinal tract - originates in red nucleus and is involved in limb control
Tectospinal tract - originates in superior colliculus and is involved in head-eye coordination during gaze
Reticulospinal tracts involved in many autonomic movements and posture
Vestibuli spinal tracts - posture and balance
What pathway only terminates on motor neurons in humans and primates ?
Corticospinal
What is a motor unit ?
Motor neurones associated with their muscle fibres creating a functional entity
How do motor units vary ?
Size
Amount of tension produced
Speed of contraction.
Degree of fatigability
Where motor neurons which innervate axial and distal musculature located ?
Axial- located medially
Distal - located laterally
In motor control why do we have a feedback system and what structure is involved in this ?
Takes into account any errors and the cerebellum is involved
Ensures that a task is carried out meaningfully
What do alpha motor neurons innervate ?
Skeletal muscle
What is a motor neuron pool ?
Collection of alpha motor neurons that innervates a single muscle
What are the 3 inputs to lower motor neurons ?
1- dorsal root ganglion cells with axons to innervate muscle spindle to provide feedback on muscle length
2- upper motor neuron inputs from motor cortex and BRAINSTEM for initiation and control of voluntary movements
3- interneurons in the spinal cord which can be excitatory and inhibitory and these generate spinal motor programmes
Describe fast motor units
Rapidly fatiguing white fibres
Alpha motor neurons are bigger with large diameters for fast conduction
Describe slow motor units
Slowly fatiguing red fibres
Alpha motor neurons are smaller with smaller diameters for slower conduction
What are muscle spindles ?
They are proprioceptors
They have group 1a sensory axons wrapped around their centre to detect stretch of the muscle - this is important feedback because it stops the muscle tearing
Group 1a axons fire more when muscle is stretched
Where do group 1a axons project into and what do they synapse with ?
Project into spinal cord via dorsal roots
Synapse with interneurons and alpha motor neurons
When 1a synapses onto alpha motor neurons it causes them to increase their firing rate
How is an action potential generated in group 1a axons ?
The axons have mechanosensitive ion channels which open when muscle is stretched
What are extrafusal muscle fibres ?
On outside of spindle and form bulk of muscle
Only these fibres are innervates by alpha motor neurons.
What are intrafusal muscle fibres ?
Fibres that lie within fibrous capsule
Innervates by gamma motor neurons - innervate the fibres at 2 ends of the spindle
What is the stretch reflex ?
It is a feedback loop
Set point is determined and then deviations from this point are detected by 1a axons and compensated for by alpha motor neurons and extrafusal muscle fibres
What is the pathway for the stretch reflex ?
Gamma motor neurons Intrafusal muscle fibres 1a afferent axons Alpha motor neurons Extrafusal muscle fibres
What is the Golgi tendon organ ?
It monitors muscle tension or force of contraction.
In series with muscle fibres not like muscle spindle which is parallel
Innervates by 1b axons
1b enter spinal cord and synapse on interneurons in ventral horn
What is the reverse stretch reflex ?
Protects muscle from being overloaded
As muscle tension increases the inhibition of alpha motor neurons increases
As muscle tension decreases the inhibition of alpha motor neurons decreases and muscle contraction increases
Thought to be involved in proper execution of fine motor acts and manipulation of objects
What are spinal interneurons ?
Input onto alpha motor neurons making poly synaptic inputs
Receive inputs from primary sensory axons descending from brain and collateral of lower motor neurons
What is reciprocal inhibition ?
Helps in the execution of movements
Contraction of one set of muscles accompanied by relaxation of antagonist muscles
Occurs by collaterals of 1a axons synapsing on inhibitory interneurons which contact alpha motor neurons supplying the antagonistic muscle
What is the flexor reflex ?
Used to withdraw a limb from an aversive stimuli
Many interneurons intervening making it slower than stretch reflex
What is the crossed extensor reflex ?
Activation of extensor muscles and inhibition of flexor muscles
Used to compensate for extra load imposed by the limb withdrawing
What are central pattern generators ?
Give rise to rhythmic motor activity
What is the highest level of the central motor system ?
Association areas of neocortex and basal ganglia
For strategy
What is the middle level of the central motor system ?
Motor cortex and cerebellum
For tactics
What is the lowest level of the central motor system?
BRAINSTEM and spinal cord
For execution
What is the highest level of sensory feedback to he motor control hierarchy ?
Sensory info which produces a mental image of the body and the relationship to the environment
What is the middle level of sensory feedback to the motor hierarchy ?
Tactical decisions based on memory of sensory info from past experience
What is the lowest level of sensory feedback to the motor hierarchy ?
Sensory feedback used to maintain posture, muscle length and tension before and after voluntary movements
What are the descending spinal tracts ?
Lateral pathways and ventromedial pathways
- lateral= involved in voluntary movements of distal musculature and under direct cortical control
- ventromedial= involved in control of posture and locomotion under BRAINSTEM control
What is the corticospinal tract ?
Most important lateral descending pathway
Originates in neocortex -2/3 in areas 4&6 while others are from somatosensory areas of parietal lobe
Tracts terminate in dorsal arterial region of ventral horn to have an affect on distal musculature
What is the course for axons in the corticospinal pathway which originate in the cortex ?
Axons pass through internal capsule
Bridging telencephalon and thalamus to course to base of cerebral peduncles
Then through pons and then forming a bulge on the ventral surface of the medulla
At medullary pyramids axons decussates forming lateral corticospinal tract to dorsal lateral region of ventral horn
What is another lateral descending pathway ?
Rubrospinal pathway
Originates in the red nucleus and decussates in the pons to join lateral corticospinal pathway
What are the 4 ventromedial pathways ?
Vestibulospinal, tectospinal, pontine reticulospinal,and medullary reticulospinal
Originate in BRAINSTEM and terminate amount interneurons in the spinal cord
Control distal and proximal musculature
What motor area innervates distal motor units and which innervates proximal motor units ?
Supplementary motor area innervate distal motor units
Premotor are innervates proximal motor units
What is apraxia ?
Selective inability to perform complex motor acts
What is the ready set go theory ?
Readiness- dependent on activity in frontal and parietal lobes receiving info to control awareness and. Alter ness
Set - dependent upon activity in sma and PMA where movement strategies are devised
Go- activity of the primary motor cortex which receives major input from are 6
Where does the basal ganglia send info to ?
The VLo of the ventral lateral nucleus of the thalamus
What is a major subcortical input to area 6 ?
VLo of the ventral lateral nucleus of the thalamus
Where does the basal ganglia receive inputs from ?
Cerebral cortex - frontal, parietal and prefrontal
So there is a loop of info that cycles from cortex through basal ganglia back to cortex
What is the basal ganglia made up of ?
Caudate nucleus Putamen Globus pallidus - internal and external Subthalamic nucleus Substantia nigra
What makes up the striatum ?
Caudate nucleus and putamen
Target of cortical input to basal ganglia
What is the globus pallidus of the basal ganglia important for ?
Source of output to the thalamus
Which layer of m1 does the activation of lower motor neurons originate ?
5
What do the neurons of m1 encode ?
Both force and direction of voluntary movements
What is ataxia ?
Uncoordinated and inaccurate movements
Why is dysnergia ?
Decomposition of synergistic multipoint movements
What is dysmetria ?
People who have this will have finger movements which either come up short or shoot past the nose
What is the cerebellum critical for?
Proper execution of planned, voluntary and multipoint movements
Instructs m1 with respect to movement directions, timing and force
Predictions the cerebellum makes are based on past experience therefore it’s involved in motor learning
