Cortical and brainstem control of movement

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Every day we complete an incredible number of movements. Whenever we walk, pick up something, speak or smile, our central nervous system coordinates the activity of a vast number of neurons to ensure that we contract the right muscles at the right time, and that everything goes according to plan once we start moving.

When we decide to move, our brain sends motor commands to our muscles to make them contract. These signals are carried by two major descending pathways:

• The pyramidal tracts (corticospinal and corticobulbar) originate from upper motor neurons in the motor cortex, especially the primary motor cortex, and synapse with cranial nerves in the brainstem and with other lower motor neurons in the spinal cord. This pathway is mainly responsible for voluntary, precise movements
• The extrapyramidal tracts (reticulospinal, vestibulospinal, tectospinal and rubrospinal) originate from the brainstem and regulate involuntary muscle contractions. These tracts are especially important for functions like maintaining balance, posture and muscle tone

Besides stimulating muscle contraction, other brain areas contribute to the control of movement. Once the decision to move is made, the secondary motor areas (premotor and supplementary motor cortex) refine the motor plan. These areas communicate with three major brain regions to improve the motor plan:

• The sensory cortex, especially the posterior parietal lobe, to obtain information about the state of the body and of the environment
• The cerebellar lobes, which help plan movement sequence and timing to ensure smooth execution
• The basal ganglia, or basal nuclei, which regulate movement initiation and suppression through direct and indirect pathways

Once the motor plan is formulated and movement has started, the cerebellum is the main structure responsible for monitoring ongoing movement. The cerebellum compares the descending motor commands from the motor cortex with the actual movement (for example, through sensory feedback from muscles and joints). If differences between the planned and actual movement are identified, the cerebellum corrects the motor output by communicating with the motor cortex and with the extrapyramidal system.

Together with spinal reflexes, these circuits ensure that movements are planned, executed and monitored effectively.

Find out more about how our brains control movement in the videos below.

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Movement planning and initiation

Movement planning and initiation concerns the identification and selection of the appropriate motor actions that need to be performed to achieve the intended goal. The main structures and pathways involved are illustrated below.

Movement execution

Movement execution refers to the activation of descending pathways that carry the motor commands from the brain to the muscles. The main structures and pathways involved are illustrated below.

The pyramidal tracts originate from the motor cortex and primarily regulate voluntary movements. 

The extrapyramidal tracts originate from the brainstem and mainly regulate involuntary movement.

The rubrospinal tract originates in the red nucleus, decussates immediately and descends through the pons and medulla oblongata to enter the lateral funiculus of the spinal cord. These neurons synapse with lower motor neurons at all levels of the spinal cord. The rubrospinal tract is thought to contribute to the regulation of involuntary movement like the tone of agonist and antagonist limb muscles, as well as fine motor control.

The tectospinal tract (or colliculospinal tract) originates in the superior colliculus of the midbrain and reaches lower motor neurons in the cervical spinal cord. It mediates reflex postural movements of the head in response to visual and auditory stimuli.

The reticulospinal tracts originate from the reticular formation. It is subdivided into the lateral reticulospinal tract, which originates from nuclei in the medulla and descends in the lateral white column of the spinal cord; and the medial reticulospinal tract, which originates from nuclei in the pons and descends in the anterior spinal cord. Both tracts extend along the entirety of the spinal cord. The reticulospinal tracts receive inputs from various brain areas including the secondary motor areas, and are important for the control of posture and muscle tone.

The vestibulospinal tract is subdivided into the medial and the lateral vestibulospinal tracts. The lateral vestibulospinal tract originates from the lateral vestibular nucleus and descends along the anterior white column of the spinal cord, reaching all vertebral levels. The medial vestibulospinal tract originates from the medial vestibular nucleus and descends within the medial longitudinal fasciculus, reaching the mid-thoracic spinal level. The vestibulospinal tracts are regulated by the vestibular system and the cerebellum, and their output mainly activates antigravity muscles in the context of posture and balance. The medial vestibulospinal tract primarily innervates neck muscles.

Movement monitoring

Movement monitoring refers to the continuous assessment and correction of ongoing movement. The main structures and pathways involved are illustrated below.

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Summary