C3.1.7 Output from the cerebral hemispheres to muscles through motor neurons Notes

The Cerebral Hemispheres Control Muscle Movements via Motor Neurons

1. The cerebral hemispheres are the largest part of the brain, responsible for higher-order functions like decision-making, memory, and voluntary movement.
2. Within the cerebral hemispheres lies the primary motor cortex, a specialized region that initiates and controls muscle movements.
3. When you decide to move, the primary motor cortex sends signals to motor neurons that connect to your muscles.

How Motor Neurons Transmit Signals

1. The process begins in the grey matter of the cerebral hemispheres, where motor neurons receive signals from the primary motor cortex.
2. These neurons have long extensions called axons that transmit electrical impulses.
3. The axons travel down the spinal cord, where they connect with a second motor neuron.
4. This second neuron’s axon extends to the target muscle, forming a synapse with muscle fibers.

Stimulating Muscle Contraction

When a motor neuron reaches a muscle, it triggers contraction through a series of steps:

1. The electrical impulse travels along the axon to the neuromuscular junction, where the neuron meets the muscle fiber.
2. At the junction, the impulse causes the release of a chemical messenger called acetylcholine.
3. Acetylcholine binds to receptors on the muscle fiber, generating an electrical signal within the muscle.
4. This signal causes calcium ions to be released inside the muscle fiber, initiating the contraction process.

Integration of the Nervous System

The process of moving a muscle involves seamless coordination between the brain, spinal cord, and peripheral nerves.

1. The brain plans and initiates the movement.
2. The spinal cord transmits the signals to the appropriate motor neurons.
3. Motor neurons activate the muscle fibers, resulting in contraction.