Motor Cortex Flashcards
Motor Cortex
– 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
Brainstem
(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
Spinal Cord
– 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
Basal Ganglia
– gating proper initiation of movement
Cerebellum
– sensory motor coordination
Motor Circuits
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
Corticospinal (Direct) Pathway
– 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
Indirect Loop
– 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
Cortico-cerebellar Pathway
– 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
Primary Motor Cortex
(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
Primary Somatosensory Cortex
(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
Premotor Cortex
(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
Posterior Parietal Cortex
(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
BA 8
anterior to premotor cortex (BA6)
– involved in the conjugation of eyes
Somatotopic Organization of Primary Motor Cortex
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)
Motor System Hierarchy
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
Major Corticofugal Pathways: Corticospinal, Corticobulbar, Corticopontine, Corticorubral, Corticoreticular
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
Corticospinal Tracts
– 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
Positive-Negative Signs after Lesion of Corticospinal Tract
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)
Descending Pathways from Brainstem
- 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
Rubrospinal Pathway
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
Reticulospinal Pathway
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
Vestibulospinal Pathway
o Vestibular nucleus medial zone and ventral horn of SC
o Balance with head movement
Tectospinal Pathway
o Superior colliculus medial zone and ventral horn of SC
o Coordinates neck movement with eye movement
