Motor Cortex

Question 1

Motor Cortex

Answer 1

– involved in planning, initiating and directing voluntary movements
o Movement supervised by the motor cortex is improved with practice
o Records what we’re doing and allows us to learn more about the movement

Question 2

Brainstem

Answer 2

(medulla, pons, and mesencephalon) – generates basic movements and postural control
o Responsible for reflexive responses that developed through our evolution and are born with them
 Ex: baby grasping a finger/pencil place in its hand

Question 3

Spinal Cord

Answer 3

– circuits for muscle contraction and movement through interneurons and motor neurons
o Interneurons – used for reflex coordination
o Motor neurons of descending system can be

Question 4

Basal Ganglia

Answer 4

– gating proper initiation of movement

Question 5

Cerebellum

Answer 5

– sensory motor coordination

Question 6

Motor Circuits

Answer 6

o Motor cortex is highly interconnected with different parts of the brain in feed forward mechanism (anticipation)
 Anticipate your next step and the motor cortex sends a signal about what to do next
 Sensory receptors on muscle (or bone) send back information (feedback) that eventually returns to the motor cortex
o Every signal from motor cortex eventually makes its way back to the motor cortex as feedback
 Move right arm and sensory receptor in arm will send a signal back to spinal cord and eventually same area of motor cortex that initiated the movement

Question 7

Corticospinal (Direct) Pathway

Answer 7

– signal sent directly from motor cortex to spinal cord
o Spinal cord has motor neurons going to muscles for contraction and movement
o Muscles have sensory receptors that send information back to spinal cord
o Spinal cord shuttles this sensory information to the thalamus
o Thalamus sends the information back to the cortex

Question 8

Indirect Loop

Answer 8

– signal sent from motor cortex to brainstem then to spinal cord
o Spinal cord has motor neurons going to muscles for contraction and movement
o Muscles have sensory receptors that send information back to spinal cord
o Spinal cord shuttles this sensory information to the cerebellum
o Cerebellum sends information to thalamus and then back to the cortex

Question 9

Cortico-cerebellar Pathway

Answer 9

– information sent from cortex to cerebellum then either cortex or brainstem
o VERY fast pathway; functions to check whether or not particular movement has been performed

Question 10

Primary Motor Cortex

Answer 10

(BA 4) – located in the Precentral Gyrus
o Anterior to Central Sulcus
o Execution of voluntary movements
o Will influence force, speed, direction, and duration of muscle contraction/movement

Question 11

Primary Somatosensory Cortex

Answer 11

(BA 1,2,3) – located in Postcentral Gyrus
o Posterior to Central Sulcus
o Plays a role in movement since it receives sensory feedback from muscle

Question 12

Premotor Cortex

Answer 12

(BA 6) – anterior to Precentral Gyrus
o Premotor Area (PMA) – lateral
 Complex movement involving multiple joints and resembling natural coordinated hand shaping or reaching movements
o Supplementary Motor Area (SMA) – superior
 Plays a role in programming/planning of complex sequence of movements
 Gives rise to bilateral movements coordinated on two sides of the body

Question 13

Posterior Parietal Cortex

Answer 13

(BA 5,7) – located in posterior parietal cortex
o Involved in movement, particularly in integrating sensory information
o Transforming visual information about the properties and location of objects
o Proprioceptive input from muscles and integration of auditory/visual sensory modalities will send information to the PMA which will eventually send information to the primary motor cortex

Question 14

BA 8

Answer 14

anterior to premotor cortex (BA6)

– involved in the conjugation of eyes

Question 15

Somatotopic Organization of Primary Motor Cortex

Answer 15

o Neurosurgeons observed movement when portions of cortex were stimulated with probes
 Movements were seen contralateral to the area of the brain stimulated
• Ex: stimulating left cortex will move the right body part
o Most laterally – tongue
o Medial, ventral portion – face
o Superior to face portion (but still lateral) – hand and trunk
o Inside longitudinal fissure – leg (knee  toes)

Question 16

Motor System Hierarchy

Answer 16

o Posterior parietal, PMA, and SMA cortices that send information to the primary motor cortex
o Primary motor cortex interacts with other parts of the brain to issue commands
o Once command is fulfilled you have input from the sensory system going back to the primary cortex to approve/disapprove of the movement, learn from the movement, and/or refine it
o Basal ganglia and cerebellum can be involved to support the primary motor cortex’s direction and planning of movement
o Removing posterior parietal/PMA/SMA cortex will still result in movement but would lose complex movement with multiple muscles and joints

Question 17

Major Corticofugal Pathways: Corticospinal, Corticobulbar, Corticopontine, Corticorubral, Corticoreticular

Answer 17

o Corticospinal – generated in the cortex and terminates in the spinal cord
 Controls all muscles of body except for the face
o Corticobulbar – generated in the cortex and terminates in the brainstem
 Controls muscles of the face
o Corticopontine – cerebellum
o Corticorubral – red nucleus
o Corticoreticular – reticular formation

Question 18

Corticospinal Tracts

Answer 18

– generated from all areas but mostly BA 1,2,3,4,6
o Most descending pathways generated from layer V with large pyramidal cells (Betz cells)
o At mesencephalon, the mid-portion of crus cerebri will be occupied by corticospinal fibers
 Fibers move through posterior portion of the internal capsule
o At medulla, corticospinal tract forms pyramids
o At intersection of medulla and spinal cord, the corticospinal tract decussates (pyramidal decussation) – where tracts from the brain cross to contralateral side
o Fibers from ventral portion of the brain will move to the lateral portion of the spinal cord
 90% of the corticospinal tract crosses laterally and is the lateral corticospinal tract (LCST) controlling limb movement
• Crosses to the opposite side of the CNS and ends in lateral portion of SC
 10% that does not cross continues anteriorly as the ventral corticospinal tract (VCST) controlling axial/trunk muscles
o Termination:
 Medial anterior horn – cells for proximal muscles
 Lateral anterior horn – cells for distal muscles
 Superior/posterior – cells for flexors
 Inferior/anterior – cells for extensors

Question 19

Positive-Negative Signs after Lesion of Corticospinal Tract

Answer 19

o Positive Sign – acquiring a function that is normally there
 Ex: increased reflexes, increased muscle tone, and Babinski sign
 Babinski Sign – brush sole of foot  indication of corticospinal lesions
• Normal = flexor/plantar response
• Abnormal/Babinski sign = extensor/plantar (Babinski) response of large toe and fanning of remaining toes
o Negative Sign – loss of function (ex: paralysis)

Question 20

Descending Pathways from Brainstem

Answer 20

• Important for the Control of Posture
  o Problems in brainstem can cause odd things in terms of posture
   Decerebrate posture – upper and lower limbs extended
   Decorticate posture – upper limbs flexed and lower limbs extended

Question 21

Rubrospinal Pathway

Answer 21

o Red nucleus (in mesencephalon)  lateral intermediate zone and ventral horn of SC
o Involved in voluntary limb muscle movement
o Crosses over at level of spinal cord and is located very close to the lateral corticospinal tract
 Injury/loss to LCST would result in rubrospinal pathway carrying out same movements EXCEPT for the fingers

Question 22

Reticulospinal Pathway

Answer 22

o Reticular formation  medial zone and ventral horn of SC
o Involuntary movement of axial and limb muscles
o Allows us to move flexors and extensors
 Extensors more important  activated more often
o Lesions cause rigidity in the muscles when flexors and extensors are not properly coordinated in their activation

Question 23

Vestibulospinal Pathway

Answer 23

o Vestibular nucleus medial zone and ventral horn of SC

o Balance with head movement

Question 24

Tectospinal Pathway

Answer 24

o Superior colliculus  medial zone and ventral horn of SC

o Coordinates neck movement with eye movement