5.2 Motor cortex and voluntary movement
3 min read•august 15, 2024
The motor cortex plays a crucial role in voluntary movement. It's organized into specific areas that control different body parts, with more space devoted to parts needing fine control. This organization helps us understand how the brain plans and executes complex movements.
are pre-planned movement sequences stored in the brain. They're executed through the and can be adjusted based on feedback. The helps coordinate these programs, ensuring smooth and accurate movements.
Motor Cortex Organization
Primary Motor Cortex and Somatotopic Organization
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- Located in the frontal lobe, just anterior to the central sulcus in the precentral gyrus
- Somatotopically organized, different body parts are represented in specific areas of the cortex
- "" depicts this organization
- Feet and legs represented medially
- Trunk and arms in the middle
- Hands and face represented laterally
- "" depicts this organization
- Size of cortical representation for each body part is proportional to the degree of fine motor control required, not physical size
- Neurons send axons through the to directly control skeletal muscle contraction
Premotor and Supplementary Motor Areas in Movement Planning
- located just anterior to the primary motor cortex
- Involved in planning and preparing for movement
- Receives input from prefrontal cortex and basal ganglia to integrate sensory and cognitive information for movement planning
- (SMA) located on the medial surface of the frontal lobe
- Involved in planning and coordinating complex movements
- Important for planning and executing movement sequences and bimanual coordination
- Both premotor cortex and SMA send projections to the primary motor cortex and spinal cord to influence execution of planned movements
Motor Programs and Execution
Concept of Motor Programs
- Pre-planned sequences of muscle contractions stored in the brain
- Can be executed with minimal conscious effort
- Thought to be stored in the premotor cortex, supplementary motor area, and cerebellum
- Execution involves activation of the primary motor cortex, sending signals through the corticospinal tract to appropriate muscles
- Can be modified and adapted based on sensory feedback and changes in the environment for flexible and adaptive movement
Role of the Cerebellum
- Plays a crucial role in the timing and coordination of motor programs
- Ensures smooth and accurate execution of movements
- Receives input from various brain regions and sensory systems to fine-tune motor control
- Damage to the cerebellum can lead to impairments in motor coordination () and difficulty with smooth, accurate movements
Descending Motor Pathways
Corticospinal Tract
- Primary descending motor pathway
- Originates in the primary motor cortex and terminates in the spinal cord
- Responsible for the control of fine, precise movements, particularly in the distal muscles of the hands and fingers
- Damage to the corticospinal tract can lead to weakness, paralysis, or difficulty with fine motor control (corticospinal tract syndrome)
Other Descending Motor Pathways
-
- Originates in the red nucleus of the midbrain
- Involved in the control of proximal muscles and maintenance of muscle tone
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- Originates in the reticular formation of the brainstem
- Involved in the control of posture, locomotion, and automatic movements
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- Originates in the vestibular nuclei of the brainstem
- Involved in the maintenance of balance and posture
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- Originates in the superior colliculus of the midbrain
- Involved in the control of head and neck movements in response to visual stimuli
Key Terms to Review (27)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a critical role in transmitting signals between nerve cells and muscles, as well as in various brain functions. It is involved in several important processes, including muscle contraction, memory formation, and modulation of attention, making it essential for both motor control and cognitive functions.
Ataxia: Ataxia refers to a lack of muscle coordination during voluntary movements, which can affect balance, speech, and overall motor control. It often results from dysfunction in the cerebellum or other parts of the nervous system that are responsible for coordinating movement. Understanding ataxia requires looking at how various brain structures, such as the cerebellum and motor cortex, interact to produce smooth and precise movements.
Cerebellum: The cerebellum is a major structure of the brain located at the back of the skull, responsible for coordinating voluntary movements, balance, and motor learning. It plays a crucial role in ensuring smooth and precise execution of motor tasks by integrating sensory information with motor commands, linking it closely to various aspects of brain function and behavior.
Closed-loop control: Closed-loop control refers to a self-regulating system that uses feedback to adjust and optimize performance during a task or movement. This mechanism allows the brain and motor cortex to constantly monitor the outcomes of movements, enabling real-time corrections and adjustments based on sensory input. It is essential for voluntary movement, ensuring accuracy and coordination by comparing the intended action with the actual outcome.
Corticospinal tract: The corticospinal tract is a major neural pathway that conveys motor commands from the brain's cortex to the spinal cord, enabling voluntary movement control. This tract is crucial for fine motor skills, allowing for precise movements of limbs and digits. The corticospinal tract originates in the primary motor cortex and descends through the brainstem and spinal cord, making it integral to both voluntary motor activity and coordination.
Dopamine: Dopamine is a neurotransmitter that plays a crucial role in sending messages between nerve cells in the brain, influencing mood, motivation, and movement. It is involved in many essential functions such as reward processing, motor control, and regulating emotional responses, making it a key player in various aspects of brain function.
Dynamic Systems Theory: Dynamic systems theory is a framework for understanding how complex systems evolve over time through the interactions of their components. In the context of motor control, it emphasizes that movement emerges from the dynamic interplay between various factors, including neural, mechanical, and environmental influences, rather than being solely dictated by pre-programmed motor commands. This perspective highlights the adaptability and variability of voluntary movements as individuals respond to changing conditions.
Electromyography: Electromyography is a diagnostic technique used to measure the electrical activity of muscles through electrodes placed on the skin or inserted into the muscle tissue. It provides insight into muscle function and can help assess the integrity of the motor cortex and connections to voluntary movements, as well as the coordination of those movements through structures like the cerebellum.
Fine motor skills: Fine motor skills refer to the coordination of small muscles in movements that require precision, such as those in the hands and fingers. These skills are crucial for tasks that involve intricate movements like writing, sewing, or playing a musical instrument. Fine motor skills rely on the complex interplay of various brain regions, particularly those involved in voluntary movement and motor coordination.
Functional MRI: Functional MRI (fMRI) is an imaging technique that measures and maps brain activity by detecting changes in blood flow and oxygen levels in the brain. This method allows researchers and clinicians to observe the brain's functioning in real-time, making it invaluable for studying various cognitive processes, sensory experiences, and neurological conditions.
Gross motor skills: Gross motor skills refer to the large movements of the body that involve the use of major muscle groups, enabling actions such as walking, running, jumping, and climbing. These skills are essential for physical activities and play a crucial role in overall development, influencing coordination and balance. The development of gross motor skills is closely linked to brain function and neural pathways, which are managed by various brain regions, particularly those involved in voluntary movement and coordination.
Motor homunculus: The motor homunculus is a visual representation of the areas of the brain that control different muscles in the body, particularly within the motor cortex. This 'little man' model illustrates how various regions of the motor cortex correspond to specific body parts, with larger areas allocated to muscles that require finer motor control, such as the hands and face. It highlights the organization and functioning of the motor cortex in relation to voluntary movements.
Motor memory: Motor memory refers to the process by which the brain encodes, stores, and retrieves information related to motor skills and movements. This type of memory plays a crucial role in learning and executing physical tasks, allowing individuals to improve their coordination and proficiency through practice and repetition. Motor memory is closely linked to the motor cortex, which is responsible for planning, controlling, and executing voluntary movements.
Motor programs: Motor programs are pre-structured sets of commands that are stored in the brain and executed to produce coordinated movements. These programs help the brain control the timing and force of muscle contractions during various tasks, allowing for fluid and efficient voluntary movement. Understanding motor programs sheds light on how the motor cortex organizes complex sequences of movements to achieve specific goals.
Open-loop control: Open-loop control is a type of motor control system where actions are performed without the use of feedback to adjust or correct movements during execution. This means that once a command is initiated, it proceeds without relying on sensory input to modify the action, making it faster but potentially less accurate. In the context of motor functions, this form of control allows for quick responses in tasks that do not require constant adjustments based on environmental changes.
Parkinson's Disease: Parkinson's disease is a progressive neurological disorder that primarily affects movement, causing tremors, stiffness, and difficulty with balance and coordination. It arises from the degeneration of dopamine-producing neurons in a specific area of the brain, significantly impacting the communication between various structures involved in motor control and behavior.
Premotor cortex: The premotor cortex is a region of the frontal lobe that plays a critical role in planning and coordinating voluntary movements before they occur. It integrates sensory information to help formulate movement strategies and is involved in the preparation of actions, particularly those that require complex or learned motor skills. The premotor cortex works closely with other areas of the motor cortex to execute smooth and purposeful movements.
Primary motor cortex: The primary motor cortex is a crucial region of the brain located in the frontal lobe that is responsible for the planning, control, and execution of voluntary movements. It plays a key role in controlling movement by sending signals to the spinal cord and muscles, enabling fine motor skills and coordinated actions. This area is essential for activities such as writing, playing an instrument, or any task that requires precise muscle control.
Procedural memory: Procedural memory is a type of long-term memory that enables us to perform tasks and skills automatically without conscious awareness. This form of memory is crucial for learning motor skills and habits, as it allows us to execute actions efficiently after practice. It is primarily associated with the development and refinement of skills, making it essential for daily activities such as riding a bike or typing on a keyboard.
Reticulospinal Tract: The reticulospinal tract is a pathway that originates in the brainstem's reticular formation and descends to the spinal cord, playing a vital role in the regulation of motor control, particularly involuntary movements and posture. This tract connects various brain regions with spinal motor neurons, influencing activities like walking and reflexes, and contributing to the integration of sensory and motor functions.
Rubrospinal tract: The rubrospinal tract is a neural pathway that originates in the red nucleus of the midbrain and descends through the brainstem and spinal cord, primarily influencing motor control. It plays a significant role in the coordination of voluntary movement, particularly those associated with limb flexion. By relaying information from the motor cortex and cerebellum, this tract contributes to fine-tuning muscle movements and posture adjustments.
Somatotopic organization: Somatotopic organization refers to the mapping of different body regions to specific areas within the brain, particularly in the somatosensory and motor cortices. This organization ensures that sensory information from various parts of the body is processed in an orderly fashion, allowing for coordinated movement and sensory perception. It plays a crucial role in how the brain interprets touch, pain, and proprioceptive signals, as well as how it controls voluntary movements.
Spinal cord injury: A spinal cord injury (SCI) is damage to the spinal cord that results in a loss of function, mobility, or sensation. This can occur due to trauma, disease, or degenerative conditions and often leads to paralysis or other neurological impairments. The extent of the injury can vary widely, influencing the motor cortex's ability to control voluntary movements and the overall functioning of the body.
Supplementary motor area: The supplementary motor area (SMA) is a region of the brain located in the frontal lobe, specifically on the medial surface, and plays a critical role in the planning and coordination of voluntary movements. It is involved in the initiation of movement sequences and the integration of sensory information to facilitate complex motor tasks. The SMA works in conjunction with other areas of the motor cortex to execute well-learned and sequential movements, highlighting its importance in the broader framework of motor control.
Tectospinal tract: The tectospinal tract is a neural pathway that originates from the superior colliculus in the midbrain and descends to the cervical spinal cord. It plays a critical role in reflexive head and neck movements in response to visual and auditory stimuli, thus connecting sensory processing with motor control.
Theory of motor control: The theory of motor control refers to the conceptual framework that explains how the brain plans, coordinates, and executes voluntary movements. It integrates various processes, including sensory feedback, motor planning, and execution of movement patterns, to facilitate smooth and precise actions. This theory is crucial for understanding how the motor cortex interacts with other brain areas to produce voluntary movements.
Vestibulospinal tract: The vestibulospinal tract is a neural pathway that originates in the vestibular nuclei of the brainstem and descends to the spinal cord, playing a crucial role in maintaining posture and balance by coordinating head and body movements. This tract integrates sensory information about head position and motion from the inner ear to influence motor responses, thus ensuring stability during voluntary movements.