Lecture 7: Motor Cortex and Voluntary Movement Flashcards
What are two areas of the brain that affect the descending systems (UMN)
- basal ganglia
- cerebellum
What are the descending systems (UMN)? what are their fxns?
- motor cortex: planning, initiating and directing voluntary movements
- Brainstem centers: basic movements and postural control
What are the two pathways that UMN can take? Indirect or direct?
- Interneruons (indirect)-> reflex coordination
- Motor neuron pools(direct)-> LMN
What does LMN lead to?
skeletal muscles
What are two important areas of the brain for motor?
- Primary motor cortex
- premotor cortex
(next to each other)
what is in gray matter and white matter?
- gray: cell bodies
- white: axons
What are the 2 cells in the primary motor cortex
- Betz cells
- Non-Betz pyramidal neurons (smaller)
Where is lower extremity and trunk located on brain? upper extremeity and face?
- Lower (and trunk): medial
- Upper (and face): lateral
What is the topographic map for?
- Patterns of facial weakness and their importance for localizing neurological injury
For somatotopic organization, what is medial? lateral?
- Medial: Ankle control
- Lateral: Face, mouth, mastication control areas.
What areas are larger in the somatopic organization? why?
Face and fingers representations are larger. There is a greater degree of cortical control of these regions of the body.
The motor cortex controls the spinal cord through both _ and _ pathways
direct and indirect
What does the majority of the corticospinal axons do in the lateral corticospinal tract? What about the minority?
- About 90% of the corticospinal axons cross at the pyramidal decussation and travel in the lateral Corticospinal tract
- About 10% remain in an ipsilateral ventral corticospinal tract and project bilaterally to medial motor neurons serving axial muscles
IN CAUDAL MEDULLA
explain the difference of lateral and ventral corticospinal tract when they hit the spinal cord
- Lateral (90%): only inn. neurons on the same side of the spinal cord
- Ventral (10%): sends bilaterally to both sides of the spinal cord
Explain the Corticobulbar tract
Motor cortex down to middle medulla
- Corticobulbar will synapse to reticular formation
- Then the reticulospinal tract will go down to spinal cord
Subcortical motor projections to the spinal cord come from?
- Reticular formation
- Vestibular nuclei (medial and lateral) (NOT MOTOR CORTEX)
- “Red” nucleus (Rubrospinal pathway is well known in non-human primates – preliminary evidence in human beings).
What are the feedforward and feedback mechanism of postural control
- Feedforward for “anticipated” postural instability
- Feedback for unanticipated postural instability
Explain the babinski sign and what is it used for? When cannot we not use this?
- Normally when we use a pointed tool up the bottom of the foot, then the toes would curl in (flexion)
- With babinski sign, the toes will fan out and have a externsor plantar response
- The Babinski sign can indicate an upper motor neuron lesion constituting damage to the corticospinal tract.
- Normal in infants until 12-24 months so we cannot use this test
The somatotopic organization of the motor cortex is “ _ ”
plastic
Representations and neuron properties can be altered with:
- Pathological or traumatic changes -> diease, lose hand, etc
- Normal experience (e.g., motor-skill learning)
- Therapy
explain the somatoptoic reorganization with experience
A rat was trained to a wheel spin task with distal forarm and lever press task with proximal forelimb to get an reward. Measure map of the brain and it showed that the brain remapped itself to be better at the tasks
- Wheel spin task requires use of distal forelimb ->Increased space in cortex devoted to distal forelimb after training
- Lever task requires use of proximal forelimb ->increased space devoted in cortex to proximal forelimb after training
explain the training induced plasticity of apical spine dnesity in individual C8-projecting cortical motor neurons
There is a untrained, active control and skilled grasp (complex)
- Skilled has more dendrites and higher density so they can do the task better. More dendrites= better neuron fxn
- Training and continued experiences can also lead to increased dendritic density of cortical motor neurons. In theory, this could lead to increased efficacy when conducting specific movements.
Explain the robot based hand motor therapy after stroke
Therapy may also lead to somatotopic re-organization in the brain leading to increased efficacy when conducting specific movements.
- HOWEVER, studies indicate that therapy induced reorganization occurs during finely detailed training (i.e. robot grasp therapy) and not with brute movement training (i.e. supination therapy).
explain the study with increased sensorimotor cortex activation with therapy, but not with non-practiced supination tasks
can lead to somotoplasticity but needs to be fine detail thearpy
For cortical control of mvt, what is the feedforward and feedback for?
- feedforward: Feedforward for “anticipated” postural instability
- Feedback: Feedback for unanticipated postural instability (sensory)
What is sensory feedback adjusted by?
“optimal feedback control” using an efferent “copy” of the motor command
* basic knowledge
- What is an efference copy or efferent copy?
- This copy can be combined with the sensory input that results from?
- Together with internal models for generating a behavior, efferent copies can serve to enable what?
- An efference copy or efferent copy is an internal copy of an efferent movement-producing signal generated by the motor system.
- This copy can be combined with the sensory input that results from the movement - enabling a comparison of actual movement with the desired movement.
- Together with internal models for generating a behavior, efferent copies can serve to enable the brain to predict the effects of an action.
What does the spike-triggered average of EMG: post spike facilitation of muscle activity
- Evidence that single cortical (upper motor) neurons influence muscle activity.
- Several muscles (and thus several motor neuron pools) may be facilitated by the same cortical (upper motor) neuron
- Conversely, individual muscles are influenced by many neurons in widely distributed regions of the motor cortex
- UMN DOES not touch muscles
_ rather than muscles are represented in cortex
Movement
Primary motor cortex controls what?
simple features of movement
Micro-stimulation sites evokes what?
behaviorally relevant purposeful movements
What is important with the “direction of movement is encoded by populations of cortical neurons”
neurons in motor cortex have a preferred direction which goes hand and hand with somatopy mapping
Upper motor neuron lesion causes weaknesses where? What is that due to?
- weakness of inferior facial muscles alone
- due to compensation
Where is weakness with a lower motor neuron lesion? due to what?
- Weakness of inferior +superior facial muscles
- d/t to lack of compensation at the facial nerve
In the wheel spin task, what part of the brain expands?
In the lever press task what park of the brain expands?
- Wheel spin-distal forelimb
- Lever press-proximal forelimb
What do we have in the dorsal pre-motor cortex?
reaching and grasping
What does reaching require?
info about the target location and the proprioceptive info about the limb to be used
For reaching, peak velocity of movement is _ to the distance of the target
proportionals
For grasping, what is it largely determined by?
the shape of the target object and NOT its location
What happens when the hand moves towards a target object
pre-shapes
What happens to grip size as it approachs the object
increases and then decreases
What is the location of mirror neurons?
ventral pre-motor cortex
When will the mirror neurons fire and not fire?
- mirror neurons fire: executing a specific motor task and observing another individual performing the same motor task
- DO NOT: simply pretend an object (no motor act) and a motor act is presented without a target object
- The primary function of the motor cortex is to generate signals to direct movement of the body. Which of the following is true regarding this region of the brain?
A. It primarily directs involuntary movement
B. The most lateral portion is largely devoted to the face
C. It is not required for learning new motor skills
D. Generates movement plans for tasks such as reaching
B. The most lateral portion is largely devoted to the face
- Collateral projections from the corticobulbar tract synapse at the ________.
A. lateral vestibular nuclei
B. reticular formation
C. medial vestibular nuclei
D. hypoglossal nucleus
B. reticular formation
- A 24-year-old patient is in recovery following a motorcycle accident which caused a small lesion in his spinal cord. All of the following would be potential signs and symptoms of such an injury EXCEPT:
A. Decreased muscle tone
B. Hypoactive deep reflexes
C. Positive Babinski’s sign
D. Severe muscle atrophy
C. Positive Babinski’s sign
- Which of the following is least likely to cause alterations in the somatotopic organization of the motor cortex?
A. Physical therapy to regain hamstring flexibility
B. Traumatic injury to a limb following a car accident
C. Learning a new motor skill such as knitting
D. Robot grasp therapy following a stroke
A. Physical therapy to regain hamstring flexibility
- Which of the following would lead to a significant increase in action potential firing from mirror neurons in the pre-motor cortex?
A. Observing a peer walk across the lecture hall
B. Observing a professor moving their hands
C. Observing Laz as he mimics the patellar reflex
D. Observing a classmate pick-up their backpack
D. Observing a classmate pick-up their backpack
