Brain Areas and Their Roles in Movement Control

Overview of Brain Areas Involved in Movement
- The motor cortex is the primary area of the brain that controls movement through neurons that connect directly to muscle-control neurons.
- Other areas like the basal ganglia and cerebellum play supportive roles in movement but do not connect directly to muscles.
- Vision is integrated with movement through specialized brain regions.

The cerebral cortex is responsible for complex voluntary movements, such as:
- Writing, typing, sewing, knitting, sculpture, and walking.
The primary motor cortex (M1), located just anterior to the central sulcus, is crucial in controlling skeletal muscles.
Neurons in M1 directly synapse with alpha motor neurons; for example, between M1 neurons and alpha motor neurons, there is often just one synapse for controlled movements (like fingers), allowing precise control.
However, many muscles have indirect pathways, involving multiple synapses before reaching the muscles, resulting in a typical delay of about 300 milliseconds between motor cortex activity and the initiation of movement.

A motor map of the primary motor cortex shows that different body parts have varied representation based on their complexity and need for fine motor control:
- Greater neurons dedicated to hands and face compared to the trunk.
- Swallowing involves significant neural resources due to its importance.
Discovery of Motor Map
- Stimulations during brain surgeries revealed that specific areas stimulate movements of certain body parts.
- Brief stimulations caused simple muscular jerks, while longer stimulations produced complete movements.

Neurons in the primary motor cortex can generate complete and meaningful movements, not just simple muscle twitches, allowing complex actions like reaching for an object.
The premotor cortex is involved in planning movements before the primary motor cortex executes them, integrating visual information for spatial awareness.
The posterior parietal cortex contributes to understanding spatial relationships and is crucial for planning movements based on visual and bodily awareness.
- Damage here can lead to neglect of certain space areas, affecting movement efficiency.

The supplementary motor area (SMA) is involved in planning and executing skilled movements and likely stores motor programs.
Internally cued movements (decided movements) are associated with SMA activity, while externally cued movements (prompted by an external cue) involve the lateral premotor cortex.

The cerebellum, crucial for motor control, timing, and error correction, predicts necessary corrections during movements by comparing intended movements with actual feedback.
Predictive Error Correction: Adjusts muscle actions before errors occur based on pre-analyses of intended movements.
- Consists of specialized cells (Purkinje cells) for timing representation, which transmit information without feedback loops.

The basal ganglia are involved in selecting desired movements and suppressing unwanted ones, particularly for learned movements.
- They enhance the vigor of movement and can impact various psychological disorders if damaged.
- Facilitate integration of sensory information for guiding motor activity and improving execution.

The lateral corticospinal tract is mostly responsible for fine motor control (like hand movements) via a crossover at the medulla, while the medial corticospinal tract coordinates more gross movements across both sides of the body.
The red nucleus relays information for coordination from the cerebellum to the motor areas during these pathways.