Lecture 6: Motor and Premotor Cortex Flashcards
what are the 3 sections of the motor cortex
Primary motor cortex (M1)
Premotor cortex
Supplementary motor
area
which area of the motor cortex has somatotopic organization
the primary motor cortex (M1)
which areas are enlarged in the primary motor cortex’s somatotopic organization?
motor maps for movements are requiring fine motor control are enlarged (fingerers, face, etc)
what kind of movement is the primary motor cortex involved with
voluntary movements of contralateral body parts
what about movement does the primary cortex encode
force, direction, distance, and speed of movement
what is alien hand syndrome
only contralateral primary motor cortex is activated
involuntary uncontrollable movement of the upper extremity
where is the premotor cortex
anterior to the M1 (primary motor cortex) in frontal lobe
what is the function of the premotor cortex?
Motor planning - select the appropriate movement to perform
- Mirror neurons for action observation (watching something we want to learn)
how does the premotor cortex influence motor behaviour
primarily via connections with M1
less commonly via axons projecting though the pyramidal tracts
what do premotor cortex lesions cause
Impaired:
Speed and automaticity of
reaching/grasping
Sequential movements
Gait and posture
what is the function of the Supplementary Motor Area (SMA)
Programming complex sequences and coordinating bilateral movements
- Selects movements based on previous experience
- Active during motor imagery practice (imagining doing an action)
what does an unilateral lesion of the supplementary motor area cause
complete lack of contralateral movement and impaired ipsilateral movement
Antiphase movements can be affected (arms or legs doing different motions like typing or walking)
what are the 3 inputs to the motor cortex to create movement?
intention - prefrontal cortex
planning - premotor cortex +SMA
programming and execution - primary motor cortex
LMNs receive instructions from which 3 sources?
- Upper Motor Neurons
– Descending pathways - Local Circuit Neurons/Interneurons
- Sensory inputs
how are LMNs organized in the anterior horn
▪ Medial = proximal muscles
▪ Lateral = distal muscles
what are interneurons / local circuit neurons?
the “middle man” that branches locally to innervate other neurons
primarily inhibitory towards unwanted movement
do interneurons / local circuit neurons project contra laterally or ipsilaterally?
both
what are the two types of interneurons / local circuit neurons?
long distance
short distance
both link to anterior horn in spinal cord
what are long distance interneurons?
activate medial aspect of anterior horn
span multiple levels of spinal cord and can cross sides
bilateral control of Proximal muscles for balance and postural control
what are short distance interneurons?
Activate lateral aspect of anterior horn
Span few spinal levels and ipsilateral
Distal muscles for fine motor control
what are the 2 kind of tracts of the descending motor pathways
Pyramidal tracts
Extrapyramidal tracts
what are the pyramidal tracts responsible for
skilled, voluntary movements of the limbs
where do extrapyramidal tracts originate
in the brainstem
what are the extrapyramidal tracts responsible for
posture balance, gait
what are the 3 pyramidal pathways
lateral corticospinal pathway
anterior corticospinal pathway
corticobubar pathway
what are the 4 extrapyramidal pathways
- Vestibulospinal Tract
- Reticulospinal Tract
- Tectospinal Tract
- RubrospinalTract
where are the extrapyramidal pathways located?
most are in the medial part of spinal cord
where does the lateral cortocospinal tract originate?
motor cortex, mostly M1
where does 85% of the corticospinal tract cross
the pyramidal decussation
what is the destination of the lateral corticospinal tract
lateral LMN of spinal cord or short distance interneurons
what would a lesion on the lateral corticospinal tract cause
Impairments on contralateral side
does the anterior corticospinal tract cross to the other side?
not at the medulla, but most of it crosses in the spinal cord
what is the destination of the anterior corticospinal tract
Terminates bilaterally in spinal cord
- via long distance interneuron networks
what is the function of the anterior corticospinal tract
Gross control of proximal postural muscles
what happens if there is a lesion on the anterior corticospinal tract
there is minimal clinical effect
do most corticospinal fibers synapse directly with LMNs
some do that are involved with finer muscle control
most synapse with spinal interneurons that in turn synapse with LMNs
where does the corticobulbar tract originate?
motor cortex
what is the function of the corticobulbar tract?
Controls efferent activation of cranial nerves
what is the destination of the corticobulbar tract
Most terminate bilaterally on local circuit neurons in brainstem
LMN nuclei of cranial nerves
What region of the face is the primary motor cortex responsible for?
lower face (contralateral)
what would an UMN injury (in the corticobublar tract) cause
Weakness in contralateral inferior facial
muscles
very concerning
what would a LMN injury in the facial nerve cause
Weakness in ipsilateral superior and
inferior facial muscles
injury is outside of brain so less concerning
If there is a lesion to the right facial nerve, where would you expect there to be weakness?
inferior and superior right side of face
what happens with a transverse cord lesion
both sides of the level of spinal cord
Bilateral loss of pain/temperature, vibration/position sense, and voluntary motor function at and below lesion
What part of the brain would you expect to have a lesion if you have difficulty tapping your head and rubbing your belly at the same time?
Supplementary motor
area
what happens with a hemicord lesion (Brown-Sequard Syndrome)
damage to one half of spinal cord
Ipsilateral loss of vibration/position sense and voluntary motor function
Ipsilateral loss of pain and temperature over 1-2 segments near lesion
Contralateral loss of pain and temperature
what is the destination of the extrapyramidal pathways
Innervates bilateral local long interneuron circuits
what is the function of the rubrospinal tract
Modulation of flexor muscle tone
what is the function of the Vestibulospinal tract
posture and balance
what is the function of the Reticulospinal tract
gait, posture, excites/inhibits muscle tone
what is the function of the Tectospinal tract
Eye/head motion
what are the 4 clinical presentations of extrapyramidal disorders?
Slowing or loss of voluntary and automatic movements
Postural instability
Abnormal movements
Usually bilateral deficits
which system controls volitional control
pyramidal tracts
which system controls automatic control
extrapyramidal tracts
do the pyramidal systems have more long or short local circuit neurons
Mostly short distance local circuit neurons (except anterior corticospinal tract)
do the extrapyramidal systems have more long or short local circuit neurones
Long distance local circuit neurons
What is the function of the Lateral Corticospinal Tract
Main voluntary motor pathway
- Skilled, voluntary movements of the limbs
Consider the lateral corticospinal tract originating from the left motor cortex. If this tract was injured below the pyramidal decussation, where would you expect to see motor deficits?
In the extremities on the right side of the body
Which part of the brain is active while you watch Serena Williams hit a tennis serve?
Premotor cortex
If there is damage to the primary motor cortex, which deficits might you observe?
Difficulty swallowing
Weakness in the contralateral hand
Weakness in the lower face
All of the listed answers are correct
All of the listed answers are correct
Link the following descending pathway to the appropriate interneuron network
Anterior Corticospinal Tract and short distance interneuron network
Vestibulospinal Tract and long distance interneuron network
Lateral Corticospinal Tract and long distance interneuron network
Reticulospinal Tract and short distance interneuron network
Vestibulospinal Tract and long distance interneuron network
Which part of the brain is active when you are imagining yourself performing a motor task?
Supplementary Motor Area
what is the Cingulate Motor Area responsible for
the upper face, bilaterally
_______ motor neuron injuries typically cause more wasting than ________ motor neuron injuries
Lower, Upper
If there was damage to short distance local circuit neurons in the spinal cord, what would you expect to see?
Problems with fine motor control
