Overview of Motor Systems Flashcards
What does it mean to say that the motor system are backwards from the sensory systems
The sensory systems begin in the outside world and end in the brain, whereas the motor systems begin in the brain and lead to movement of muscles in the outside world!
- Motor processing begins with internal representation of desired movement
- Programming starts in Cortex which transmits signals to the lowers levels of the CNS which via neural signals causes muscle movement/contractions (muscles are the effectors)
Described the organization of the motor system in two words
hierarchical (in series) and parallel
WHat does is mean to say that the motor system is hierarchical
-small, simple elements (at spinal cord) are
integrated into complex patterns at higher levels of CNS
AND
-Higher levels of brain (brainstem and cortex) specify
more complex aspects of task
so small things are integrated into patterns via the CNS. and the CNS higher levels are responsible for complex tasks (things you really have to think about)
Describe the parallel pathways of the motor system
-Are parallel pathways for motor control that are somewhat redundant
- some pathways go directly from the cerebral cortex to the spinal cord motor neurons,
- some go from the cortex to the brainstem
- some go from the cortex to the basal ganglia and then to the brainstem
- and really there are just a lot of pathways
What two things influence the “final common pathway” to cause movement
- Higher motor commands in the brain
2. sensory input
What is the final common pathway
LOWER motor neurons
What are the 3 major components and levels of control of motor systems
- Spinal cord (bottom)
- Brainstem
- Cortex (top)
All three major components and levels of control (spinal cord, brainstem, and cortex) are modulated by what 2 independent subcortical structures
- Basal Ganglia
- caudate nucleus
- putamen
- globus pallidus
- substantia nigra
- subthalamic nucleus - Cerebellum
What two pairs does the thalamus mediate communication between
Basal ganglia ⇒ cortex
AND
Cerebellum ⇒ cortex
What mediates the communication between the basal ganglia and the cortex
thalamus
What mediates communication between the cerebellum and the cortex
thalamus
There are two types of neurons in spinal cord that are
involved in motor systems. What are they
Motor neurons and Interneurons
Where are motor neurons located and what is a clinical point about them
motor neurons are located in the ventral horn of the spinal cord
- lower motor neurons project directly to muscles
- this causes contraction and therefore movement of limbs
- lower motor neurons are the “final common pathway” of the entire motor system
What projects directly to muscle
LOWER motor neurons
-the project directly to muscle and therefore directly stimulate muscle contraction which leads to limb movement
Where are interneurons located and what do they do
- in intermediate zone and they project to lower motor neurons
- Form circuits that connect and coordinate motor neurons
- ⇒ So…groups of muscles contract for specific tasks.
what does it mean to say an interneuron is segmental
project within a given spinal level (short) (local)
What does it mean to say an interneuron is Propriospinal:
project between multiple spinal cord levels (longer)
Motor neurons are somatototpically organized in the spinal cord. What do medial motor neurons innervate and what are they responsible for?
medial motor neurons innervate proximal trunk, axial muscles
– control balance, posture, movement of trunk
Motor neurons are somatototpically organized in the spinal cord. What do lateral motor neurons innervate and what are they responsible for?
Lateral motor neurons innervate limb muscles
- control movement of specific limbs and digits
- motor neurons that control proximal limbs are more medial
- motor neurons that control distal limbs and digits more lateral
What generally modulates the action of spinal motor circuits
the brainstem
What are the two types of motor neurons in the brainstem
- Motor nuclei contain lower motor neurons that directly innervate muscles in head, face (Occulomotor nucleus contains MNs that control
Extraocular muscles; Hypoglossal nucleus contains MNs that control tongue; Facial nucleus contains MNs that control facial expression) - Neurons that send descending axons down to spinal cord and modulate the spinal cord (lower MNs, interneurons). Upper motor neurons – send their axons into the medial and lateral descending brainstem pathways (tracts).
how are the brainstem pathway tracts named?
based on origin and end points
What are the 3 Medial brainstem pathways:
Reticulospinal reticular formation ⇒ spinal cord
- Vestibulospinal vestibular nuclei ⇒ spinal cord
- Tectospinal Tectum (superior colliculus) ⇒ spinal cord
Where do the medial brainstem pathway descend and where do they terminate
descend in medial ventral white matter and Terminate in ventral horn on medial motor neurons.
What are the medial brainstem pathways responsible for
- Influence axial, trunk, proximal muscles
- Provide basic postural control system upon which cortical motor areas can organize more highly differentiated movement control
Lateral brainstem pathways:
- Rubrospinal tract (main one)
Red nucleus ⇒ spinal cord
Where does the lateral brainstem pathway descend and where does it terminate
Descend in contralateral dorsolateral white matter Terminate in dorsolateral ventral horn
What is the lateral brainstem pathway responsible for
- Influences motor neurons that control distal muscles in limbs, digits
- Modulate goal-directed movements of limbs reaching for, manipulating objects
Function of the cerebral cortex in motor movement
- Modulates action of motor neurons in brainstem and spinal cord (top of hierarchy)
Descending commands to motor neurons in spinal cord and brainstem.
* Gives us ability to organize complex motor acts and execute fine movements with precision.
What are the Major areas of cerebral cortex involved in motor control:
a) Primary motor cortex:
b) Premotor cortex:
c) Supplementary motor area:
Function of the Primary motor cortex:
– Executes commands to motor neurons
– Coordinates force and direction of movement
– Contains somatotopic map of body
Electrical stimulation of spots causes movement of body parts on opposite side
Function of Premotor cortex:
– Integrates motor movements with
sensory input (esp. visual system)
– Coordinates complex sequences
of movement (motor learning)
Function of Supplementary motor area:
– Important for internally-driven, will-driven
movements. Formulate intention to make
a movement
– “Idea” for movement; Plan movement
in advance
Function of Primary somatosensory cortex (SI):
– Regulates incoming sensory info from dorsal horn of spinal cord (coming up via medial lemniscus, anterolateral tracts)
Function of Posterior parietal cortex:
– Helps localize WHERE object is
with respect to body
– Helps motor system coordinate reaching
in right direction for an object
Describe the Changes in blood flow in cortex in response to simple movements:
ex: flexing your left index finger
You will have an increase in blood flow to the right primary motor cortex
Describe the Changes in blood flow in cortex in response to complex movements:
You will experience an increase in blood flow to the contralateral primary motor cortex
You will ALSO experience an increase in blood flow to the supplementary motor area bilaterally. (both sides)
Describe the changes in blood of doing a complex task after you have rehearsed it several times
You will have an increase in blood flow only in the supplementary motor area, bilaterally
What motor area is particularly is important in planning complex Internally-generated movements
Supplementary motor area
Describe the cerebral cortex somatotopy for motor systems
feet medial face lateral. and more segmented than sensory
Cerebral cortex acts on spinal motor neurons via two descending pathways what are they
- Lateral corticospinal tract: (pyramidal system)
- Ventral corticospinal tract:
Where does the Lateral corticospinal tract: (pyramidal system) descend and terminate
Also what is it responsible for
The lateral corticospinal tract descends in dorsolateral white matter, and terminates in the lateral ventral horn
- Controls contralateral limb and digit muscles, movement of extremities.
- goal-directed reaching, manipulating
Where does the ventral corticospinal tract descend and terminate
what is it responsible for
it descends in the ventromedial white matter and terminates in the medial ventral horn
it controls neck and trunk muscles; postural control
-Similar to brainstem pathways; parallel pathways give redundancy
The higher structures are responsible for _____
The lower structures are responsible for______
The higher structures are responsible for complex tasks, like deciding to and then stepping on the break at a yellow light
the lower structures are good for simple motor movements like reflexes where no cognition is required
describe the energy demand difference between cognitive motor activities and reflexes and why one would be more associated with complicated tasks
- Reflexes are fast and automatic
- Cognitive motor activities take more time, energy, neural processing
- so cognitive motor activities are Preserved for more complicated tasks
What is the value of motor systems being organized in parallel
cortex ⇒ spinal cord
brainstem ⇒ spinal cord
-Provides flexibility in control
-When cortical, brainstem or spinal
cord lesions occurs, alternative
pathways can partly compensate.
-Person may retain basic
motor functions (after a lesion)
** Redundancy gives flexibility and
plasticity in movements, esp. after injury.
What are the three general types of movements
- Reflex movements
- Autonomic postural adjustments
- Voluntary movemetns
Describe reflexes
- what are they
- what do they involve
- general examples
- Simple, involuntary, unconscious, coordinated patterns of muscle contraction and relaxation evoked by peripheral stimuli
- The involve spinal cord, motor neurons, sensory neurons
- general examples are withdrawing from a painful stimulus, and repetitive rhytmic motor patterns (walking, running, chewing, swallowing, breathing
How do higher level cortical regions use reflexes
** Higher level cortical systems use this reflex
circuitry to coordinate muscles during
complex, voluntary movements. Also, saves
energy expended by cortex.
What are reflexes tested to diagnose
level of lesion/damage and cause
Describe Autonomic postural adjustments
- defintion
- what do they involve
More complex, more flexible than simple reflexes
-Involve brainstem, spinal cord, motor neurons
Describe the autonomic postural adjustment example of standing on a boat that is tipping up and down
- Vestibular systems conveys information to midbrain about posture
- Descending motor pathways from brainstem to motor neurons make a compensatory shift in mass to maintain balance
- It really depends on the context. If a person is holding onto a rail while on the boat motor pathway will induce less of a compensatory shift
Describe voluntary movements
- definition
- what do they involve
- organized around a purposeful act and movements are goal directed and very flexible
- involve cerebral cortex, brainstem , spinal cord, and motor neurons
ex:
- - Put on brakes when light turns red
- - Rush to catch a fly ball; swing a golf club
- - Play complicated piece on piano
- - Handwriting
- - Learn to snowboard
- - Speech and language
Improve with practice: nervous system learns to anticipate and correct for environmental obstacles
Voluntary movements allow you to improve and control movement. But there is a cost to this what is it?
the response time for voluntary movements is much longer than for reflexes because additional processing time and energy is required by multiple inputs from higher order CNS structures. SO learning takes time, effort and energy
