Module 12.8 Movement Part I: Role of the CNS in Voluntary Movement Flashcards
What are the components involved in the planning and coordination of voluntary movement?
The planning and coordination of voluntary movement are carried out within the Central Nervous System (CNS) and involve the motor areas of the cerebral cortex, basal nuclei, cerebellum, and spinal cord.
What are the three types of neurons directly involved in eliciting muscle contraction?
The three types of neurons directly involved in eliciting muscle contraction are upper motor neurons, local interneurons, and lower motor neurons.
What are the roles of upper motor neurons, local interneurons, and lower motor neurons in voluntary movement?
Upper motor neurons have cell bodies in the motor area of the cerebral cortex or brainstem. Their axons descend through the cerebral white matter to the brainstem and spinal cord, where they synapse with local interneurons. Local interneurons pass messages from upper motor neurons to neighboring lower motor neurons. The cell bodies of lower motor neurons reside in the anterior horn of the spinal gray matter. Their axons, which are components of the Peripheral Nervous System (PNS), exit the CNS to innervate skeletal muscles.
What are the largest white matter tracts formed by the axons from cortical motor areas?
The largest white matter tracts formed by the axons from cortical motor areas are the corticospinal tract, which controls muscles below the head and neck utilizing lower motor neurons of spinal nerves, and the corticonuclear tract, formerly known as corticobulbar tracts, which controls muscles of the head and neck utilizing lower motor neurons of cranial nerves.
What is the pathway of the corticospinal tract?
The axons that form the corticospinal tracts originate from upper motor neuron cell bodies in the primary motor and premotor cortices. These axons unite and descend through the corona radiata and internal capsule on their way to the brainstem (midbrain and pons).
What happens to most fibers in the corticospinal tract pathway at the level of the medullary pyramids?
Most fibers in the corticospinal tract pathway decussate at the level of the medullary pyramids. This means that neurons on the right side of the brain send fibers to the left side of the body and vice versa. The fibers that decussate travel in the lateral funiculi and are known as the right and left lateral corticospinal tracts.
What is the role of the corticonuclear tracts in the motor pathways from the brain through the spinal cord?
The corticonuclear tracts originate from the cell bodies of upper motor neurons and travel with the corticospinal tracts through the corona radiata and internal capsule to the brainstem. They do not enter the spinal cord, but instead synapse on interneurons that communicate with cranial nerve nuclei at various levels of the brainstem.
What is the role of the cerebral cortex in voluntary movement?
The majority of upper motor neurons that control complex movements reside in the primary motor cortex and premotor and motor association areas of the cerebral cortex. These areas plan and initiate voluntary movement by selecting an appropriate motor program and coordinating the sequence of skilled movements.
What is a motor program and what is required for its execution?
A motor program is a selected group of actions that require the simultaneous firing of countless neurons. The execution of any motor program requires the firing of neurons in motor association areas, the firing of upper motor neurons, and input from the basal nuclei, cerebellum, spinal cord, and multimodal association areas such as the prefrontal cortex and various sensory areas. The firing of lower motor neurons in the Peripheral Nervous System (PNS) is necessary to complete the task.
What is the role of the upper motor neurons located in certain nuclei of the brainstem?
The upper motor neurons located in certain nuclei of the brainstem work to maintain posture, balance, and body position, especially during locomotion. They also produce motor responses to sensory stimuli.
How is the primary motor cortex organized and what does this signify?
The primary motor cortex is organized somatotopically, meaning that certain body regions have disproportionately more cortical area devoted to them, especially the lips, tongue, and hands. This signifies the importance of vocalization and manual dexterity to human survival.
What is the role of the basal nuclei in voluntary movement?
The basal nuclei, which are made up of the caudate nucleus, globus pallidus, and putamen, modify the activity of upper motor neurons to produce voluntary movements and inhibit involuntary ones. They play a critical role in inhibiting inappropriate movements and initiating voluntary movement.
What happens when there is damage to any component of the basal nuclei system?
Damage to any component of the basal nuclei system results in a movement disorder. The two main forms of these disorders are the inability to initiate voluntary movement, making simple activities such as walking or talking difficult, and the inability to inhibit inappropriate, involuntary movements, some of which may be severe enough to cause disability
What is the role of the cerebellum in voluntary movement?
The cerebellum monitors ongoing movements and integrates information about the contraction and relaxation of muscles, positions of joints, and the direction, force, and type of movement that is going to occur. Once this information is integrated, the cerebellum determines the motor error, which is the difference between the intended movement and the actual movement that is taking place.
From where does the cerebellum receive input?
The cerebellum receives input from three sources simultaneously: motor areas of the cerebral cortex via upper motor neurons, vestibular nuclei of the pons, and ascending sensory tracts from the spinal cord.
