The Motor System Overview

The Motor System

• The motor system allows for voluntary, complex movements.
• Extrapyramidal disorders are common in people taking psychiatric medications.
• Information flows across multiple control centers, using negative and feed-forward mechanisms.
• Negative feedback adjusts movements by comparing intended and actual movements.
• Feed-forward utilizes memory to anticipate and adjust for rapid movements.

How the Motor System Works

• Motivation for movement originates in subcortical areas (limbic areas, hypothalamus, cerebellum, basal ganglia).
• Motor programs (intended movement sequences) are developed in premotor and supplementary motor areas and relayed to the primary motor cortex.
• Motor commands travel along two main pathways:
  • Upper Motor Neuron (UMN): Initiates movement from the brain cortex.
  • Lower Motor Neuron (LMN): Connects to muscles, enabling movement.
• UMN lesions cause spasticity, exaggerated reflexes, and a positive Babinski sign.
• LMN lesions result in flaccid paralysis, muscle atrophy, and loss of reflexes.

Major Pathways of Axons from the Brain

• A loop, or pathway, involving the cerebral cortex, basal ganglia, thalamus, and back to the cortex has components: one for direct facilitation and another indirect inhibition.
• Output from the Globus Pallidus Internal (GPi) and Substantia Nigra pars reticulata (SNr) is inhibitory to the thalamus.
• Lateral Pathways (Direct): Control fine, voluntary movements; direct pathway inherent / spontaneous GPi activity is ↓ by striatal activity, leading to disinhibition, and facilitating movements.

The Cerebellum

• Located in the back of the brain.
• Crucial for movement coordination by receiving sensory information and adjusting muscle actions.
• Its 4 deep nuclei (dentate, globose, emboliform, and fastigial, or interpositus) are largely responsible for output.
• Cerebellar organization has zones for control of midline, limbs, and digits.
• Input to the cerebellum occurs via mossy and climbing fibers.
• Mossy fibers originate from diverse sources (cortex, spinal cord, and brainstem) to stimulate granule cells, and have weak excitatory input to Purkinje cells.
• Climbing fibers originate in the inferior olivary nucleus, and provide strong excitatory input to Purkinje cells, leading to complex neural spikes.
• Purkinje cells output to deep cerebellar nuclei.

Deep Cerebellar Nuclei

• Signal: Inhibitory GABAergic output.
• Target: Various brain regions, including the thalamus, red nucleus, and vestibular nuclei.
• Signal: Excitatory output for modulating motor control and coordination.
• The cerebellum's role encompasses timing and coordination of movement, motor learning, and balance and posture maintenance. It acts as a fine-tuning mechanism for movement.

Basal Ganglia

• Five interconnected subcortical nuclei (caudate, putamen, globus pallidus, subthalamic nucleus, and substantia nigra).
• Crucial for initiating and regulating movement.
• Extensive connections between basal ganglia and motor areas of the brain.
• Primary input from the cerebral cortex, output via thalamus, back to the cortex.
• Direct pathway in facilitates movement by reducing inhibition.
• Indirect pathway suppresses unnecessary movement by increasing inhibition.
• Disorders can result in hyperkinetic (excessive movement) or hypokinetic (reduced movement) symptoms.

Differences Between Basal Ganglia and Cerebellum

• Basal Ganglia: Controls movement initiation and pattern selection
• Cerebellum: Refines and coordinates ongoing movement
• Basal ganglia involved in cognitive movement planning, while the cerebellum adjusts movements in real-time.
• Key Point : Basal gangliia are involved in cognitive planning of movement and the cerebellum adjusts real-time movements.

Explore the intricate workings of the motor system, focusing on how voluntary movements are initiated and controlled. This quiz covers key concepts such as motor pathways, feedback mechanisms, and the impact of motor neuron lesions. Perfect for those studying neuroscience or related fields.