NEUROLOGY
Fully Autonomous system...
MOTOR CONTROL
A significant portion of the brain and nervous system is dedicated to interpreting sensory information to create detailed representations of the surrounding environment.
Through senses such as vision, hearing, touch, and others, we gain an understanding of the world and our position within it. However, this complex sensory processing would have little value without the ability to take action based on what we perceive. These actions might include fleeing from a predator, finding shelter from the rain, seeking food when hungry, speaking to communicate, or engaging in countless other activities that make up daily life.
In some instances, the connection between sensory input and motor response is straightforward and automatic—for example, touching a hot surface triggers an immediate reflex to pull the hand away. More often, however, our intentional actions depend not only on sensory information but also on additional cognitive processes that help determine the most appropriate response for the situation. Ultimately, this process involves sending commands to specific muscles in the body, enabling them to produce force to interact with external objects or forces like gravity. This overall system is referred to as motor control.
8 COMPONENTS OF MOTOR CONTROL
1): VOLITION
The motor system must generate movements that are adaptive and that accomplish the goals of the organism. These goals are evaluated and set by high-order areas of the brain. The motor system must transform the goals into the appropriate activations of muscles to perform the desired movements.
2):Coordination of signals to many muscle groups.
Few movements are restricted to the activation of a single muscle. For example, the act of moving your hand from inside your pocket to a position in front of you requires the coordinated activity of the shoulder, elbow, and wrist. Making the same movement while removing a 2-lb weight from your pocket may result in the same trajectory of your hand, but will require different sets of forces on the muscles that make the movement. The task of the motor system is to determine the necessary forces and coordination at each joint in order to produce the final, smooth motion of the arm.
3): PROPRIOCEPTION
In order to make a desired movement (e.g., raising your hand to ask a question), it is essential for the motor system to know the starting position of the hand. Raising one’s hand from a resting position on a desk, compared to a resting position on top of the head, results in the same final position of the arm, but these two movements require different patterns of muscle activation. The motor system has a set of sensory inputs (called proprioceptors) that inform it of the length of muscles and the forces being applied to them; it uses this information to calculate joint position and other variables necessary to make the appropriate movement.
4): POSTURAL ADJUSTMENTS
The motor system must constantly produce postural adjustments in order to compensate for changes in the body’s center of mass as we move our limbs, head, and torso. Without these automatic adjustments, the simple act of reaching for a cup would cause us to fall, as the body’s center of mass shifts to a location in front of the body axis.
6): COMPENSATION
To exert a defined force on an object, it is not sufficient to know only the characteristics of the object (e.g., its mass, size, etc.). The motor system must account for the physical characteristics of the body and muscles themselves. The bones and muscles have mass that must be considered when moving a joint, and the muscles themselves have a certain degree of resistance to movement.
7): UNCONSCIOUS PROCESSING
The motor system must perform many procedures in an automatic fashion, without the need for high-order control. Imagine if walking across the room required thinking about planting the foot at each step, paying attention to the movement of each muscle in the leg and making sure that the appropriate forces and contraction speeds are taking place. It would be hard to do anything else but that one task. Instead, many motor tasks are performed in an automatic fashion that does not require conscious processing. For example, many of the postural adjustments that the body makes during movement are performed without our awareness. These unconscious processes allow higher-order brain areas to concern themselves with broad desires and goals, rather than low-level implementations of movements.
8): ADAPTABILITY
The motor system must adapt to changing circumstances. For example, as a child grows and its body changes, different constraints are placed on the motor system in terms of the size and mass of bones and muscles. The motor commands that work to raise the hand of an infant would fail completely to raise the hand of an adult. The system must adapt over time to change its output to accomplish the same goals. Furthermore, if the system were unable to adapt, we would never be able to acquire motor skills, such as playing a piano, hitting a baseball, or performing microsurgery.
SPINAL CORD
The spinal cord represents the lowest level of the motor hierarchy and serves as the location of motor neurons. It also houses numerous interneurons and intricate neural circuits responsible for the fundamental processing of motor control. These circuits handle the basic commands needed to generate the appropriate forces in individual muscles and muscle groups, enabling adaptive movements. Additionally, the spinal cord contains specialized networks for rhythmic activities, such as walking. By managing these essential functions, the spinal cord allows higher levels of the motor hierarchy, like the motor cortex, to focus on more complex tasks, such as planning movements, organizing sequences of actions, and coordinating full-body motion, without needing to manage the fine details of individual muscle contractions.
SENSORY INPUT AND MOTOR CONTROL
A key principle of the motor system is that effective motor control relies on sensory input to plan and carry out movements accurately. This relationship holds true across all levels of the motor system hierarchy, from basic spinal reflexes to more complex, higher-level processes. As we will explore throughout this discussion of the motor system, our ability to produce movements that are precise, well-timed, and appropriately forceful is heavily dependent on sensory information, which is integrated at every level of motor control.
ALPHA MOTOR NEURON
Alpha motor neurons, also known as lower motor neurons, connect to skeletal muscles and initiate muscle contractions that produce movement. These motor neurons release the neurotransmitter acetylcholine at the neuromuscular junction, a specialized synapse. When acetylcholine binds to receptors on the muscle fiber, it generates an action potential that travels along the muscle fiber in both directions. This action potential triggers the muscle to contract. While the motor system consists of many types of neurons spread throughout the central nervous system, motor neurons serve as the sole link between the motor system and the muscles. As a result, all movement ultimately relies on the activity of lower motor neurons.
MOTOR NEURONE
Motor neurons are not simply channels for transmitting motor commands from higher levels of the motor hierarchy. Instead, they are integral parts of intricate neural circuits that carry out advanced information processing. Their extensive and highly branched dendritic trees allow motor neurons to receive and integrate input from many other neurons, enabling them to determine the appropriate output needed for movement.
Image from Harvard University. Google´s 3 D brain map.
MOTOR NEURONE
Each individual muscle fiber in a muscle is innervated by one, and only one, motor neuron.
A single motor neuron, can innervate many muscle fibers.
