cortical mechanisms of motor control Flashcards
What are the two major types of descending motor pathways?
Learning Objective 1: Descending Motor Systems
Pyramidal (Corticospinal) Tracts - Responsible for voluntary movement, originating from the motor cortex.
Extrapyramidal Tracts - Indirect motor pathways originating from the brainstem, controlling posture and involuntary movements.
What are the major components of the corticospinal tract?
Learning Objective 1: Descending Motor Systems
Originates in the Primary Motor Cortex (Layer V Pyramidal Neurons).
Upper Motor Neurons (UMNs) descend via the corticospinal tract.
UMNs synapse on Lower Motor Neurons (LMNs) in the spinal cord.
Decussation (crossing) occurs at the medullary pyramids for lateral corticospinal tract.
Lateral corticospinal tract controls distal musculature, anterior corticospinal tract controls proximal musculature.
What is the function of the extrapyramidal motor system?
Learning Objective 1: Descending Motor Systems
The extrapyramidal system controls involuntary motor functions, including posture and balance, via:
Rubrospinal Tract - Excites flexor muscles, inhibits extensors.
Vestibulospinal Tract - Maintains posture and balance.
Tectospinal Tract - Coordinates head and eye movement in response to stimuli.
Reticulospinal Tract - Provides an alternative pathway for cortical motor control.
What are the roles of the brainstem motor centers?
Learning Objective 1: Descending Motor Systems
The Superior Colliculus (tectum) coordinates eye and head movements.
The Reticular Formation helps regulate posture and locomotion.
The Vestibular Nuclei contribute to balance and spatial orientation.
What are the three main subdivisions of the motor cortex?
Learning Objective 2: Motor Cortex Structure and Function
Primary Motor Cortex (M1) - Directly controls voluntary movement, located in the precentral gyrus.
Premotor Cortex (PM) - Involved in motor planning and preparation.
Supplementary Motor Area (SMA) - Coordinates complex movement sequences and bilateral movements.
How is the primary motor cortex organized?
Learning Objective 2: Motor Cortex Structure and Function
Somatotopic Organization: The body is mapped onto M1 in a motor homunculus.
Different regions control different body parts with more cortical area dedicated to fine motor control (e.g., hands, face).
What is the cytoarchitecture of the primary motor cortex?
Learning Objective 2: Motor Cortex Structure and Function
Composed of Layer V Pyramidal Neurons (Betz cells) that project down to spinal motor neurons.
It has a dense output to the spinal cord for movement execution.
Neural coding in M1 is based on population vector coding, meaning movements are directed by the combined activity of multiple neurons.
How are movements represented in the motor cortex?
Learning Objective 3: Motor Representation and Plasticity
Individual neurons encode force, direction, extent, and speed of movement.
Movement representation is population-based, meaning groups of neurons contribute to movement control.
Directional tuning: Neurons fire more for movements in preferred directions.
What is motor cortex plasticity?
Learning Objective 3: Motor Representation and Plasticity
Motor maps can change with learning, injury, or practice.
Examples:
After nerve damage, adjacent neurons take over the function of lost connections.
Training and rehabilitation can reshape the motor cortex.
Long-term potentiation (LTP) and long-term depression (LTD) contribute to motor learning
What is the role of the posterior parietal cortex in movement control?
Learning Objective 4: Role of Posterior Parietal Cortex in Movement Planning
Integrates sensory information to guide movement planning.
Converts visual stimuli into motor commands (e.g., reaching and grasping).
Helps coordinate eye-hand interactions.
What happens when the posterior parietal cortex is damaged?
Learning Objective 4: Role of Posterior Parietal Cortex in Movement Planning
Can cause Constructional Apraxia, where patients struggle with tasks involving spatial manipulation (e.g., drawing, assembling objects).
Impairs goal-directed reaching and grasping due to disrupted sensorimotor integration.
Can lead to Optic Ataxia, a condition where visually guided movements become inaccurate.
What is the function of the basal ganglia in movement?
Learning Objective 5: Basal Ganglia and Motor Control
Involved in movement initiation, action selection, and inhibition of unwanted movements.
Consists of caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra.
Works via two pathways:
1) Direct Pathway - Facilitates movement by reducing inhibition on the thalamus.
2) Indirect Pathway - Inhibits movement via increased inhibition of the thalamus.
What motor disorders result from basal ganglia dysfunction?
Learning Objective 5: Basal Ganglia and Motor Control
Parkinson’s Disease - Caused by loss of dopamine in the substantia nigra, leading to bradykinesia, tremors, and rigidity.
Huntington’s Disease - A genetic disorder causing excessive movement (chorea) due to loss of striatal neurons in the indirect pathway.
What are mirror neurons, and where are they found?
Found in the Premotor Cortex.
Fire both when performing an action and when observing the same action in others.
Important for learning by imitation and understanding intentions of others.
How can the motor cortex be used in Brain-Machine Interfaces (BMIs)?
Neurons in motor and parietal cortex encode movement intention.
Their signals can be decoded to control prosthetic limbs or robotic arms.
