1 - Overview of Motor Systems Flashcards
What is the motor system?
It’s how the nervous system controls movement of the body.
How is motor information transmitted? Describe the pathway.
Motor processing begins with internal representation of desired movement. Programming starts in cortex and goes to lower levels of the CNS. Neural signals cause muscle contraction to move muscles (effectors).
What are two general characteristics/organizations of motor control?
Its hierarchical(in series): small, simple elements (at sp cd) are integrated into complex patterns at higher levels of the CNS. -Higher levels of the brain (brainstem and cortex) specify more complex aspects of task. It’s parallel: Parallel pathways for motor control are somewhat redundant.
Describe the “final common pathway” that causes movement.
Higher motor commands in the brain together with sensory input influence the final common pathway (ie motor neurons) and cause movement.
MOTOR NEURONS ARE THE FINAL COMMON PATHWAY THAT CONTROL MUSCLE CONTRACTION.
What are the three major components/levels of control of the motor system?
- The Spinal Cord 2. Brainstem 3. Cortex
The three major components of the motor system are modulated by what two independent subcortical structures? What mediates most communication between these two structures and the cortex?
Basal ganglia Cerebellum Thalamus mediates communication between each structure and the cortex.
What are the components of the basal ganglia?
Caudate nucleus, putamen, globus pallidus, substantia nigra, and the subthalamic nucleus.
What are the two types of motor neurons in the spinal cord that are involved in motor systems?
- Motor neurons in ventral horn: cause movement of body and limbs 2. Interneurons in intermediate zone: project to motor neurons to form circuits that connect and coordinate motor neurons.
Where do lower motor neurons project to?
Directly to muscles to ultimately cause contraction.
What are the types of interneurons in the intermediate zone and where do they each project to?
Segmental: project within a given spinal level (short) Propriospinal: project between multiple spinal cord levels (longer)
Describe the somatotopy of motor neurons.
Medial motor neurons innervate proximal trunk and axial muscles to control balance, posture, and movement of trunk. Lateral motor neurons innervate limb muscles: control movement of limbs. -Motor neurons controlling proximal limbs are more medial -Motor neurons controlling distal limbs and digits are more lateral.
What is the function of the brainstem in motor systems? What are the two types of motor neurons in the brainstem?
Modulates the action of spinal motor circuits.
Motor neurons in the brainstem:
- Motor nuclei contain lower motor neurons that directly innervate muscles in the head and face (ie hypoglossal nu. contains motor neurons that control extraoccular eye muscles, etc.)
- Upper Motor neurons: send descending axons into medial and lateral descending pathways (tracts) down to spinal cord and modulate the spinal cord
What are the medial brainstem pathways and where do they project to?
Reticulospinal: from reticular formation to the spinal cord
Vestibulospinal: vestibular nuclei to the spinal cord
Tectospinal: tectum (superior colliculus) to the spinal cord
Describe the location of medial brainstem pathways? What is their function?
They descend in medial ventral white matter and terminate in the ventral horm on medial motor neurons.
Influence axial, trunk, and proximal muscles to provide a basic postural control system upon which cortical motor areas can organize more highly differentiated movement control.
What is the lateral brainstem pathway? Where does it go?
The rubrospinal tract travels from the red nucleus to the spinal cord.
What is the location of the lateral brainstem pathway (the rubrospinal tract)? What is its function?
It descends in contralateral corsolateral white matter and terminates in the dorsolateral ventral horn.
Influences motor neurons that control distal muscles in limbs and digits and modulates goal-directed movements of limbs reaching for, manipulating objects
What is the function of the cerebral cortex in motor systems?
Modulates action of motor neurons in brainstem and spinal cord (top of hierarchy).
Gives descending commands to motor neurons in sp cd and brainstem which gives us ability to organize complex motor acts and excetute fine movements.
What are the major areas of the cerebral cortex involved in motor control?
- Primary motor cortex
- Premotor cortex
- Supplementary motor area
What is the function of the primary motor cortex?
- Executes commands to motor neurons
- Coordinates force and direction of movement
- Contrains somatotopic map of body (electrical stim of spots causes movement of body parts
What is the function of the premotor cortex?
Integrates motor movements with sensory input (esp. visual system.
Coordinates complex sequences of movement (motor learning)
What is the function of the Supplementary motor area?
Important for internally-driven, will-driven movements.
Formulates intention to make a movement (ie the “idea” for movement and planning movement in advance).
What is the location and function of the primary somatosensory cortex (SI)?
Regulates incoming sensory info from dorsal horn of sp cd (coming up via medial lemniscus, anterolateral tracts)
What is the location and function of the posterior patietal cortex?
Helps localize WHERE object is with respect to body.
Helps motor system coordinate reaching in the right direction for an object.
Describe the somatotopy of the primary motor cortex?
Motor is more fragmented than somatosensory.
The cerebral cortex acts on spinal motor neurons via what two descending pathways?
The Lateral Corticospinal tract (pyramidal system) and the Ventral Corticospinal tract.
What is the path and function of the lateral corticospinal tract (pyramidal system)?
Descends in the dorsolateral white matter; terminates in the lateral ventral horn.
Controls CONTRALATERAL limb and digit muscles, movement of extremeties, and is involved in goal-directed reaching and manipulation
What is the path and function of the ventral corticospinal tract?
Descends in the ventromedial white matter; terminates in medial ventral horn.
Controls neck and trunk muscles; postural control.
Similar to brainstem pathways; parallel pathways give redundancy.
Describe the hierarchically organization of motor systems?
Cortex is the higher brain structures involved in complex tasks. Lower structures are in the brainstem and spinal cord and are invovled in more simple tasks that don’t require cognition. Muscle movement is involved in reflexes that are fast and automatic.
What is the benefit of having parallel pathways in motor systems?
Redundancy gives flexibility and plasticity in movements after injury.
(When cortical, brainstem, or spinal sord lesions occur, alternative pathways can partly compensate and therefore the person may retain basic motor functions.)
What are reflex movements? What components are involved?
Simple, involuntary, unconscious coordinated patterns of muscle contraction and reflaxation evoked by peripheral stimuli. Allows you to withdrawl from painful stimuli and do repetitive rhythmic motor patterns such as chewing and swallowing.
Involves the spinal cord, motor neurons, and sensory neurons.
What do higher level cortical systems use reflex circuitry to do?
Coordinate muscles during complex, voluntary movements. Saves energy expended by cortex.
What is automatic postural adjustment? What structures are involved and how do they work?
More complex and flexible than simple reflexes. Involves the brainstem, spinal cord, and motor neurons.
Vestibular system conveys info about pisture to midbrain, descending motor pathways from brainstem to motor neurons make a compensatory shift in mass to maintain balance.
It depends on context.
What structures are involved in voluntary movements? What are characteristics of voluntary movements? What is the cost?
Organized around a purposeful act; movements are goal-directed and flexible. Improves with practice.
Involves cerebral cortex, brainstem, spinal cord, and motor neurons.
Cost: response time is much longer than for reflexes because of processing time. Learning takes time, effort, and energy.
What is the function of upper motor neurons?
They work with lower motor neurons and interneurons to impact muscle movements. They do NOT directly control muscle contraction.
What part of the brain is invovled in will-driven and planning of movement?
The supplemental area - blood flow will increase bilaterally when planning movement and when carrying out tasks that involve thinking about what you’re doing.
