Physiology
In the human brain, there is a map of every skeletal muscle, called the motor cortex. It is a collection of upper motor neurons, each of which initiates a signal down the spine to the muscle it corresponds to. The brain is constantly trying to anticipate and prepare for actions, so signals are constantly being sent to these muscles. If there is no inhibition of these signals, purposeless movements would constantly occur. The basal ganglia have evolved to provide a locking mechanism here.The basal ganglia are a system of neural circuitry which provides logical processing of these signals before they can continue to reach the body. They consist of the striatum, globus pallidus, ventral pallidum, substantia nigra, and subthalamic nucleus. These each behave differently and they interact like components of an electronic microchip. Most of the components have an overall inhibitory effect on outgoing signals. They block unnecessary motor neuron signals.
When a healthy person decides to contract their bicep muscle to flex their arm, the brain sends signals to the basal ganglia, which tell neurons there to release a neurotransmitter called dopamine. The dopamine bind to other neurons and switches the activity "mode" of the cells. This has an effect of removing inhibition on the outgoing signals. The basal ganglia do not only modulate motor signalling. They have connections to the oculo-motor, associative, limbic and orbitofrontal circuits. The motor function is the easiest to assess and the most vital for survival, so it is the most well-researched.
No comments:
Post a Comment