Unit 1.2: Neuroanatomy and Physiology

The motor neuron system plays a crucial role in controlling muscle movement through the interaction between upper and lower motor neurons. Upper motor neurons originate in the brain and carry signals down to the spinal cord, where they synapse with lower motor neurons. Lower motor neurons then transmit the signals from the spinal cord to the muscles, causing them to contract. At the neuromuscular junction, the point of communication between motor neurons and muscle fibers, a neurotransmitter called acetylcholine is released from the motor neuron and binds to receptors on the muscle fiber. This binding triggers a series of events that ultimately lead to muscle contraction. Motor units consist of a single motor neuron and the muscle fibers it innervates. The size and recruitment pattern of motor units vary depending on the type of muscle and the level of force required for a specific movement. Smaller motor units are recruited for fine movements that require precision, while larger motor units are recruited for more powerful movements. Understanding the architecture of the motor neuron system, the differences between upper and lower motor neurons, the structure and function of the neuromuscular junction, and the physiology of motor units is essential for understanding how movement is controlled and coordinated in the body.