Did You Know?
Nerve impulses between different neural structures of the brain can travel as fast as 260 mph.
The globus pallidus is an important component of the basal ganglia, which is located deep within the forebrain. The basal ganglia refers to a group of interconnected nuclei that are situated on either side of the thalamus. It consists of 3 main structures that include caudate nucleus, putamen, and the globus pallidus.
The globus pallidus, a pale-colored spherical structure can be separated into two portions, the internal globus pallidus (GPi) and the external globus pallidus (GPe). The caudate and putamen (together called the striatum) are the source of input for both GPe and GPi. However, the GPi is the major output pathway of the basal ganglia. The thalamus receives output from the GPi.
Regulation of Voluntary Movements
- Regulating voluntary movements is the main function of the globus pallidus. So any issues with this neural structure are likely to cause difficulty in movement. In short, impaired motor activity is the result of damage to the globus pallidus.
- Disorders of the basal ganglia involving the globus pallidus can cause slowness in movement. As a damaged globus pallidus cannot perform its muscle regulatory function, it can cause involuntary movement such as tremors while taking rest.
- In movement disorders like Parkinson's disease, the globus pallidus is found to be hyperactive. Hence, patients suffer from lack of muscle control, which is typically marked by stiff and inflexible muscles and trembling. In such circumstances, surgical procedures such as pallidotomy may be recommended, in which a small portion of the globus pallidus is eliminated.
- Huntington's disease that is marked by substantial neuronal loss in the globus pallidus can also cause abnormal, uncontrolled movements in different regions of the body.
Contrary to the popular belief, initiation of movement does not take place in the basal ganglia. Movements are always initiated in the cortex but motor signals from the cortex pass through the circuitry of basal ganglia. Hence, proper working of the globus pallidus is critical to normal voluntary movements.
Inhibits Excitatory Effect of the Cerebellum
- The cerebellum sends its output to the motor cortex, which in turn transmits it to the basal ganglia. It is observed that the output of the cerebellum is excitatory, which needs to be curbed in order to ensure a coordinated movement. This is done by the Gpi of the basal ganglia, which provides inhibitory action.
- This balance between the excitatory and inhibitory signals is necessary for smooth controlled movement. Imbalance in excitatory and inhibitory neurotransmitters results in purposeless movements that manifest in the form of tremors. Some of the inhibitory output of GPI is also sent to the neural structures lying in the midbrain, which supposedly provides better stability to our back.
- The globus pallidus in the basal ganglia essentially applies brakes on one movement so as to properly execute other motor activities. For instance, in order to stand straight in one position, the global pallidus withholds all unnecessary movements, barring one that is required for a stable erect posture.
In short, the globus pallidus nullifies unwanted reflexes to promote the desired movements. So when the regulatory function of the globus pallidus is not proper, one faces trouble executing the required movements.
The cerebral cortex relays motor commands to the striatum. The striatum acts as a source of input for the globus pallidus, which transmits signals to the thalamus. The thalamus then sends the output to the cortex. Thus, a loop of connections is formed that begins and terminates in the motor cortex. This loop provides the momentum to select and initiate voluntary movements.