7.1 Motor cortex and motor planning
4 min read•august 16, 2024
Motor control is a complex process involving multiple brain regions. The motor cortex, located in the frontal lobe, plays a crucial role in planning and executing voluntary movements. It's organized into primary, premotor, and supplementary areas, each with distinct functions.
The directly controls muscle activity, while premotor and supplementary areas handle planning and sequencing. This system allows for precise movement control and adapts through experience. Understanding these areas helps explain motor deficits and guides rehabilitation strategies.
Motor Cortex Role in Movement
Primary Motor Cortex Function and Importance
Top images from around the web for Primary Motor Cortex Function and Importance
Primary Motor Cortex – KINES 200: Introductory Neuroscience View original
Is this image relevant?
Motor cortex - Wikipedia View original
Is this image relevant?
Brain | Biology for Majors II View original
Is this image relevant?
Primary Motor Cortex – KINES 200: Introductory Neuroscience View original
Is this image relevant?
Motor cortex - Wikipedia View original
Is this image relevant?
1 of 3
Top images from around the web for Primary Motor Cortex Function and Importance
Primary Motor Cortex – KINES 200: Introductory Neuroscience View original
Is this image relevant?
Motor cortex - Wikipedia View original
Is this image relevant?
Brain | Biology for Majors II View original
Is this image relevant?
Primary Motor Cortex – KINES 200: Introductory Neuroscience View original
Is this image relevant?
Motor cortex - Wikipedia View original
Is this image relevant?
1 of 3
- Motor cortex located in frontal lobe controls voluntary movements
- Primary motor cortex (M1) sends direct commands to spinal cord and brainstem
- M1 controls muscle activity through descending motor pathways
- Neurons in motor cortex encode specific movement parameters (direction, force, velocity)
- Motor cortex integrates sensory information and internal signals
- Generates appropriate based on integrated information
- Electrical stimulation of motor cortex elicits specific muscle contractions
- Stimulation of hand area causes finger movements
- Stimulation of leg area causes toe movements
- Damage to motor cortex results in various motor deficits
- Contralateral paralysis (opposite side of body affected)
- Impaired fine motor control (difficulty with precise movements)
Motor Cortex Plasticity and Adaptation
- Motor cortex exhibits in response to experience and learning
- Cortical maps can reorganize following injury or amputation
- Adjacent areas may take over function of damaged regions
- Motor skill learning leads to expansion of cortical representations
- Musicians show enlarged hand representations in motor cortex
- Rehabilitation techniques exploit motor cortex plasticity
- Constraint-induced movement therapy for stroke recovery
- Brain-machine interfaces utilize motor cortex adaptability
- Allow control of prosthetic limbs through motor cortex signals
Motor Planning and Neural Basis
Neural Circuits and Structures Involved in Motor Planning
- and crucial for motor planning
- Select and sequence appropriate motor programs
- Motor planning activates neural circuits representing intended movement
- Occurs before actual movement execution
- modulate and refine motor programs
- Involved in action selection and initiation
- Cerebellum contributes to motor planning
- Helps with timing and coordination of movements
- Mirror neurons in premotor cortex fire during action performance and observation
- Play role in action understanding and imitation
- Motor planning influenced by various factors
- Sensory feedback (visual, proprioceptive)
- Previous experiences (learned motor skills)
- Internal models of body and environment
Neuroimaging and Experimental Evidence
- Neuroimaging studies show increased activity in motor planning areas
- Activation occurs during movement preparation
- Precedes onset of muscle activity
- Readiness potential (Bereitschaftspotential) observed in EEG
- Negative brain potential preceding voluntary movement
- Transcranial magnetic stimulation (TMS) studies
- Disruption of premotor cortex impairs movement preparation
- Delayed-response tasks reveal neural correlates of motor planning
- Sustained activity in premotor areas during delay period
- Neuropsychological studies of patients with planning deficits
- patients show impaired ability to plan complex actions
Somatotopic Organization of Motor Cortex
Motor Homunculus Structure and Properties
- Motor cortex exhibits somatotopic organization (motor homunculus)
- Different body parts represented in specific cortical areas
- Cortical representation size proportional to movement precision and complexity
- Not related to physical size of body part
- Inverted organization of motor homunculus
- Lower body parts represented near top of cortex (leg area)
- Upper body parts represented near bottom (face area)
- Adjacent body parts generally represented in adjacent cortical areas
- Hand area next to arm area
- Foot area next to leg area
- Disproportionate representation of certain body parts
- Large areas devoted to hands, face, and tongue
- Reflects importance of fine motor control in these regions
Plasticity and Clinical Implications of Somatotopic Organization
- Somatotopic organization not fixed, undergoes plasticity
- Changes in response to experience, learning, or injury
- Use-dependent plasticity observed in motor cortex
- Enlarged hand representation in musicians
- Increased representation of reading finger in Braille readers
- Functional magnetic resonance imaging (fMRI) used to map motor cortex
- Allows non-invasive study of somatotopic organization
- Transcranial magnetic stimulation (TMS) used to probe motor representations
- Can create temporary "virtual lesions" to study function
- Understanding somatotopic organization crucial for clinical applications
- Interpreting effects of localized brain injuries
- Developing brain-computer interfaces for motor control
- Rehabilitation strategies target somatotopic reorganization
- Constraint-induced movement therapy promotes cortical remapping
Motor Control: Primary vs Premotor vs Supplementary Areas
Functional Differences Between Motor Areas
- Primary motor cortex (M1) responsible for direct movement execution
- Sends signals to spinal cord and muscles
- M1 neurons encode specific movement parameters (force, direction)
- Premotor cortex involved in motor planning and preparation
- Selects appropriate motor programs based on sensory cues and context
- Plays role in visually-guided movements
- Supplementary motor area (SMA) crucial for complex movement planning
- Coordinates sequential movements
- Involved in internally-generated movements (not cue-dependent)
- Motor areas form distributed network for motor control
- Reciprocal connections between M1, premotor cortex, and SMA
- Integration of planning and execution processes
Clinical Implications and Lesion Effects
- Damage to specific motor areas results in distinct deficits
- M1 lesions often cause contralateral paralysis
- Premotor cortex damage impairs movement initiation
- SMA damage affects execution of complex movement sequences
- Stroke affecting different motor areas leads to varied symptoms
- M1 stroke: contralateral hemiparesis
- Premotor stroke: difficulty initiating movements
- SMA stroke: problems with bimanual coordination
- Neurodegenerative diseases differentially affect motor areas
- : altered activity in premotor areas and SMA
- Huntington's disease: affects basal ganglia-motor cortex circuits
- Neuromodulation techniques target specific motor areas
- Transcranial magnetic stimulation of premotor cortex for stroke rehabilitation
- Deep brain stimulation of motor circuits for movement disorders
Key Terms to Review (19)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a critical role in transmitting signals between nerve cells and muscles. It is involved in various functions, including muscle contraction, memory formation, and attention, connecting it to key brain regions and conditions that affect motor control and cognitive processes.
Apraxia: Apraxia is a neurological disorder characterized by the inability to perform purposeful movements, despite having the physical capability and desire to do so. This condition often arises from damage to specific areas of the brain responsible for motor planning and execution, particularly within the motor cortex. Individuals with apraxia may struggle with tasks like brushing their teeth or waving goodbye, even though they understand the action and can perform it in a different context.
Basal ganglia: The basal ganglia are a group of interconnected brain structures that play a critical role in regulating voluntary motor control, procedural learning, and cognitive functions such as decision-making and reinforcement learning. They help facilitate smooth movement and are crucial for habit formation and reward-based behaviors, connecting motor planning with the execution of actions.
Closed-loop control: Closed-loop control refers to a system that continuously monitors and adjusts its output based on feedback from the current state of the system. This process allows for real-time corrections and optimizations, making it crucial in motor control and planning. In the context of motor functions, closed-loop control enables the brain to refine movements by comparing the intended action with the actual outcome, thereby enhancing precision and adaptability.
Corticospinal tract: The corticospinal tract is a major neural pathway that connects the motor cortex of the brain to the spinal cord, playing a crucial role in voluntary motor control. This tract is essential for executing precise movements by transmitting signals from the upper motor neurons in the brain down to lower motor neurons in the spinal cord, which then innervate muscles. The corticospinal tract is particularly important for fine motor skills and voluntary movements of the limbs.
Dopamine: Dopamine is a neurotransmitter that plays a key role in the brain's reward system, influencing pleasure, motivation, and the regulation of movement. It acts as a chemical messenger that transmits signals between neurons and is crucial for various cognitive functions, including decision-making and motor control, as well as emotional responses.
Electromyography: Electromyography (EMG) is a diagnostic procedure that assesses the electrical activity of muscles by using electrodes placed on the skin or inserted into the muscle. This technique helps in understanding how signals from the nervous system control muscle contractions, making it essential for studying motor functions and planning movements.
Extrapyramidal pathways: Extrapyramidal pathways are a set of neural pathways that originate in the brainstem and are involved in the coordination and regulation of involuntary movements, posture, and muscle tone. These pathways work alongside the pyramidal system, which primarily controls voluntary motor functions, but are crucial for refining motor control and integrating sensory information.
Functional MRI: Functional MRI (fMRI) is a neuroimaging technique that measures brain activity by detecting changes in blood flow and oxygenation levels. It allows researchers to observe brain function in real-time, helping to understand how different brain regions contribute to various processes such as movement, sensory perception, and cognitive tasks.
Motor commands: Motor commands are signals sent from the brain to the muscles to initiate and control voluntary movements. These commands are crucial for coordinating complex actions, such as walking, writing, or playing sports, by ensuring that muscles contract in the right sequence and timing. They originate in the motor cortex, where planning and execution of movements take place, allowing for a wide range of motor activities.
Neuroplasticity: Neuroplasticity refers to the brain's ability to reorganize itself by forming new neural connections throughout life. This remarkable capability allows the brain to adapt in response to learning, experience, and injury, enabling cognitive control, motor functions, and even the treatment of psychiatric disorders.
Open-loop control: Open-loop control is a type of control system that operates without feedback, meaning it does not use output information to adjust its actions. In this system, commands are sent directly to the motor units to execute a movement based solely on predetermined conditions or commands, rather than adjusting based on the actual result of that movement. This type of control is crucial for understanding how movements are initiated and executed in the absence of real-time sensory feedback.
Parkinson's disease: Parkinson's disease is a progressive neurodegenerative disorder that primarily affects movement control. It is characterized by the degeneration of dopaminergic neurons in the substantia nigra, a part of the brain that plays a crucial role in the basal ganglia circuitry involved in action selection and motor planning. The resulting motor symptoms, such as tremors, rigidity, and bradykinesia, reflect a dysfunction in both the basal ganglia and motor cortex, highlighting the interplay between these brain regions in regulating voluntary movements.
Precentral gyrus: The precentral gyrus is a prominent structure located in the frontal lobe of the brain, specifically situated just anterior to the central sulcus. This region is primarily responsible for motor control, serving as the primary motor cortex where voluntary movements are planned and executed. Its organization reflects a topographical arrangement, where different areas correspond to movement control of specific body parts, illustrating its vital role in motor function.
Premotor cortex: The premotor cortex is a region located in the frontal lobe of the brain that plays a crucial role in planning and coordinating voluntary movements. It acts as a bridge between sensory information and motor actions, helping to prepare and organize the necessary sequences of muscle contractions before actual movement occurs. This area also integrates information from various sensory modalities, contributing to the development of complex motor skills.
Primary motor cortex: The primary motor cortex is a critical region of the brain located in the precentral gyrus of the frontal lobe that is responsible for the execution of voluntary motor movements. It plays a key role in planning, controlling, and executing movements by sending signals to various muscles throughout the body. This area is highly organized, with specific regions dedicated to controlling different parts of the body, which is often referred to as the motor homunculus.
Supplementary motor area: The supplementary motor area (SMA) is a region of the brain located on the medial surface of the frontal lobe, involved in the planning and coordination of complex movements. This area plays a crucial role in the preparation and execution of motor tasks, particularly those that require the integration of sensory information and the coordination of multiple muscle groups. The SMA is also implicated in higher-level processes like movement sequencing and the planning of internally generated actions.
Synaptic plasticity: Synaptic plasticity is the ability of synapses, the connections between neurons, to strengthen or weaken over time in response to increases or decreases in their activity. This phenomenon is fundamental for learning and memory, as it allows neural circuits to adapt and reorganize based on experiences. It is a key mechanism underlying various processes in the brain, including motor learning, the coordination of movements, and even pathological conditions like epilepsy.
Trajectory planning: Trajectory planning refers to the process of determining a sequence of movements or positions that an agent (such as a robot or a biological organism) will follow to achieve a specific goal. This involves the coordination of various motor commands over time to ensure smooth and efficient execution of movement, relying on both internal and external cues. In the context of motor planning, trajectory planning is crucial for transforming abstract movement goals into executable motor sequences, integrating sensory feedback, and adapting to dynamic environments.