L14 Motor Control - PSC 101

Motor Control

Lecture Information

  • Course: PSC 101- Bio Psych

  • Lecture Number: 14

  • Date: February 26th, 2026

Learning Objectives

  • 14.1: Explain how the motor system enables the nervous system to interact with the world.

  • 14.2: Describe how the direct and indirect pathways of the basal ganglia can regulate motor function. Discuss how Parkinson’s and Huntington’s disease can interfere with these functions.

  • 14.3: Describe how the primary motor cortex is organized and how the brain uses population vectors to control motor movements.

Importance of Muscle Control in Bio-Psychology

  • Students were asked to reflect individually on why understanding muscle control is essential for bio-psychology.

  • Possible key points discussed:

    • Dysfunction in muscle control affects mental status.

    • Connection between body and brain.

Motor System Overview

  • The motor system translates thoughts into actions, enabling interaction with the environment.

  • It consists of a complex network of brain areas and neural circuits that interact with skeletal muscles, inducing actions.

Reflexes

  • Definition: Simplest circuits for controlling motor movements, comprising a few spinal cord neurons.

  • Function:

    • Receive basic stimuli (e.g., muscle stretching).

    • Induce immediate motor actions (e.g., muscle contraction).

  • Reflexes do not involve brain communication and can be suppressed by the brain.

Motor Control

  • Reflexes are relatively rare compared to other motor movements.

  • Most motor actions are planned, controlled, and executed by a more complex network integrated within the central nervous system (CNS).

Brain Areas Involved in Motor Control

  • Key regions for motor function:

    • Basal Ganglia

    • Primary Motor Cortex

Basal Ganglia Introduction

  • Location: Centrally located collection of brain areas.

  • Type: Subcortical structures.

  • Function: Essential for regulating motor movements.

  • Acts as a gating mechanism, determining which motor actions should be executed or inhibited by communicating with the frontal cortex.

Frontal Cortex

  • Responsible for:

    • Executive Functions (EF)

    • Motor Planning

    • Motor Control

  • Creates goals and assesses motor actions to achieve those goals.

  • Communicates with both the basal ganglia and premotor cortex to decide on execution of specific motor plans.

Connectivity and Pathways within the Basal Ganglia

  • The basal ganglia interact with various brain regions to manage motor actions through two competing pathways:

    • Direct Pathway: Excites motor plans.

    • Indirect Pathway: Inhibits motor plans.

  • Determines if motor action is executed or blocked.

Direct and Indirect Pathways

  • Direct Pathway:

    • Excitation of the cortex leading to motor action execution.

  • Indirect Pathway:

    • Inhibition of the cortex preventing motor action execution.

Balance of Basal Ganglia Pathways

  • The competition between the direct and indirect pathways is essential for controlled motor function.

  • Metaphor:

    • Direct pathway = Gas pedal.

    • Indirect pathway = Brake pedal.

Dopamine (DA) in the Basal Ganglia

  • Dopamine is a key signaling molecule.

  • Direct Pathway: Utilizes D1 receptors, which are excitatory.

  • Indirect Pathway: Utilizes D2 receptors, which are inhibitory.

  • The substantia nigra produces dopamine and sends it to the basal ganglia, affecting both pathways accordingly.

Dopamine Release and Motor Action

  • When dopamine is released, it:

    • Excites the direct pathway.

    • Inhibits the indirect pathway.

    • Results in the execution of motor actions.

Disorders of the Basal Ganglia

  • Disorders arising from basal ganglia dysfunction include:

    • Parkinson’s Disease

    • Nature: Progressive, genetic disease causing the death of DA-producing cells in the substantia nigra, leading to diminished DA release.

    • Effects: Decreased excitation in the direct pathway and reduced inhibition in the indirect pathway, leading to blocked motor actions (hypokinesia).

    • Huntington’s Disease

    • Nature: Genetic disorder causing the breakdown of subregions in the indirect pathway while sparing the direct pathway.

    • Effects: Excessive stimulation of direct pathway leads to the execution of inappropriate motor plans (hyperkinesia).

    • Results include involuntary movements and cognitive deficits (e.g., executive function, memory, emotional regulation).

Implications of Basal Ganglia Disorders

  • Parkinson’s and Huntington’s diseases illustrate the critical nature of balanced motor control systems.

Motor Control Communication

  • The basal ganglia do not set goals or execute plans; these functions are the responsibility of the cortex.

Primary Motor Cortex (M1)

  • Location: Most rostral part of the frontal cortex, anterior to the central sulcus.

  • Purpose: Receives input from the premotor cortex and sends output to the spinal cord to control muscle movements.

Structure of Primary Motor Cortex

  • Similar to somatosensory cortex (S1) with a topographic organization.

  • Contains columns that correspond to specific body regions and movements.

  • Activation of these columns results in specific motor actions (e.g., reaching and retracting).

Population Vectors

  • Concept of population vectors involves clusters of M1 columns that work collaboratively to direct motor actions.

  • Columns are tuned for specific movement directions, contributing to movement decisions based on their activity levels.

  • Mechanism: Population vector neurons relay information to spinal cord neurons, which synapse with muscles to execute movements through neuromuscular junctions, involving neurotransmitter release (acetylcholine).

Summary of Motor Control Process

  • The process is hierarchical: the Prefrontal Cortex (PFC) establishes goals, which the premotor cortex translates into motor plans communicated to the primary motor cortex (M1). M1 codes for movements using population vectors, ultimately resulting in muscle contractions via the PNS.

Conclusion

  • The interplay between the basal ganglia and primary motor cortex is vital for executing coordinated motor actions, with disruptions leading to disorders that exemplify the necessity of a balanced motor control system.