Introduction to Motor Control: Nervous System Organization and Function

Skilled Performance and Motor Learning

Introduction to Motor Control

Motor control refers to the processes by which the nervous system coordinates movement, integrating sensory input, cortical processing, and motor output. Understanding motor control is foundational for psychology students studying biological psychology, sensation and perception, and learning.

• Movement is produced by complex neural networks.

• Involves activation and coordination of muscles and limbs.

• Includes reflexive, reactive, and voluntary mechanisms.

• Key processes: sensory afference, cortical processing, motor/action efference, and coordination.

• Example: Returning a ball in tennis involves planning (premotor cortex), seeing (visual cortex), and motivation (amygdala, hypothalamus).

Nervous System Overview

Central and Peripheral Components

The nervous system is divided into central and peripheral components, each with distinct anatomical and functional roles.

• CNS (Central Nervous System): Brain and spinal cord.

• PNS (Peripheral Nervous System): Peripheral nerves and ganglia.

• CNS and PNS are anatomically separated but functionally interconnected.

Cellular Components of the Nervous System

The nervous system is composed of two major cell types: neurons and glia.

• Neurons: Specialized for communication; approx. 100 billion in the human brain, forming about 100 trillion connections.

• Glia: Support and protect neurons; involved in homeostasis and myelination.

Neuron Structure

Neurons have four main regions, each with a specific function in signal transmission.

• Dendrites: Receive incoming signals.

• Cell body (soma): Integrates signals and contains the nucleus.

• Axon: Transmits electrical impulses away from the cell body.

• Presynaptic boutons: Release neurotransmitters to communicate with other neurons.

Functional Classification of Neurons

Neurons are classified by their function in the nervous system.

• Sensory neurons (afferent): Transmit information from sensory receptors to the CNS.

• Motor neurons (efferent): Control muscle contraction; cell bodies in the spinal cord's ventral horn.

• Interneurons: Integrate and relay signals between sensory and motor neurons; vastly outnumber other types.

Central Nervous System (CNS)

Main Regions of the CNS

The CNS consists of several key regions, each with specialized functions.

1. Spinal Cord: Transmits signals between brain and body; involved in reflexes.

2. Brainstem: Includes medulla (life support regulation), pons (relay between regions), and midbrain (eye movements, reflexes).

3. Cerebellum: Coordinates movement and balance.

4. Thalamus: Relay station for sensory and motor signals.

5. Cerebral Hemispheres (Forebrain): Higher cognitive functions.

Structure of the Spinal Cord

The spinal cord is organized into gray and white matter, each with distinct roles.

• Gray Matter: Contains cell bodies; dorsal horn (sensory neurons), ventral horn (motor neurons).

• White Matter: Contains myelinated axons; dorsal, lateral, and anterior columns for ascending and descending tracts.

Somatotopic Organization of Ventral Horn

The ventral horn of the spinal cord is organized so that different regions correspond to different muscle groups.

• Medial to lateral: proximal to distal muscles.

• Dorsal to ventral: flexor to extensor muscles.

Brainstem

Components and Functions

The brainstem is essential for basic life functions and serves as a relay between brain regions.

• Medulla: Regulates vital functions (e.g., breathing, heart rate).

• Pons: Connects cerebellum and higher brain regions to spinal cord.

• Midbrain: Controls reflexive eye movements and auditory/visual reflexes.

Cerebral Cortex

Structure and Organization

The cerebral cortex is highly folded, allowing a large number of neurons to fit within a limited volume.

• Gyri: Raised convolutions or bumps.

• Sulci: Valleys between gyri.

• Fissures: Deep sulci dividing major brain regions.

Subdivisions of the Cerebral Cortex

The cortex is divided into four main lobes, each with specialized functions.

Lobe	Main Functions
Frontal	Movement, planning, reasoning
Parietal	Bodily sensation, spatial processing
Temporal	Hearing, smell, taste, visual perception, speech (left hemisphere)
Occipital	Vision

Primary and Secondary Areas

Specific regions of the cortex are dedicated to processing sensory information or motor commands.

• Primary somatosensory cortex: Localizes and identifies sensory stimuli.

• Primary motor cortex: Triggers and executes movement commands.

Association Areas

Association areas integrate information from multiple sources for complex functions such as perception, movement, and motivation.

• Responsible for higher-order processing and purposeful action.

Gray and White Matter in the Cortex

Gray matter consists of neuron cell bodies, while white matter contains myelinated axons that connect different cortical regions.

Peripheral Nervous System (PNS)

Subdivisions of the PNS

The PNS is divided into somatic and autonomic systems, each serving distinct roles.

Subdivision	Main Functions
Somatic	Transmits information to/from CNS about muscle and limb position, and the external environment
Autonomic	Regulates viscera, smooth muscle, exocrine glands; includes sympathetic and parasympathetic divisions

Navigating the Nervous System

Directional Terms and Planes

Understanding anatomical terminology is essential for describing locations and directions in the nervous system.

• Dorsal vs Ventral: Back vs front

• Superior vs Inferior: Above vs below

• Anterior vs Posterior: Front vs back

• Rostral vs Caudal: Toward nose vs toward tail

• Medial vs Lateral: Toward midline vs away from midline

• Distal vs Proximal: Farther vs closer to origin

• Ipsilateral vs Contralateral: Same side vs opposite side

• Planes: Horizontal, coronal, sagittal

Summary

• Motor behaviors involve sensory, motor, and motivational systems.

• Neurons: structure and types (sensory, motor, interneuron).

• CNS: organization and main components.

• Gray and white matter: roles in CNS and cortex.

• PNS: somatic and autonomic subdivisions.

• Directional terms for navigating the nervous system.

Additional info: This material is foundational for understanding biological psychology (Ch. 3), sensation and perception (Ch. 4), and learning (Ch. 6) in college-level psychology courses.