Motor Control

Introduction to the Central Nervous System

CNS

Motor Control Terminology

• Cranial vs. Caudal• Superior vs. Inferior• Dorsal vs. Ventral • Anterior vs. Posterior

Terminology Continued

• Ipsilateral vs. Contralateral

• Medial vs. Lateral• Proximal vs. Distal

Neuron

• Parts of the neuron– Axon-take information away from the cell body– Dendrite-take information toward the cell body– Cell Body

Types of Neurons

• Sensory or Afferent--take information toward the CNS

• Motor or Efferent--take information from the CNS to the muscles

• Interneurons--connect sensory & motor in the CNS

Impulse Transmission from Neuron 1 to Neuron 2

• Dendrite1

• Cell Body1

• Axon1

• Dendrite2

• Cell Body2

• Axon2....

Reflex Components

• Sensory receptor

• Sensory Neuron

• Spinal Cord

• Motor Neuron

• Muscle

Voluntary Action--Components

• Sensory receptor

• Sensory neuron

• Spinal Cord

• Brain

• Spinal Cord

• Motor Neuron

• Muscle

CNS Structures Involved in Motor Control

• Level One: Spinal Cord– Most caudal part of CNS– Contains afferent and efferent pathways

• Receives information from skin, joints, muscles• Receives sensory information from internal organs

– Composed of cervical, thoracic, lumbar, and sacral vertebrae

– Gray matter--contains cell bodies of neurons; middle area of cord; H-shaped; unmyelinated fibers

– White Matter--contains fiber tracts; myelinated fibers

CNS Structures• Level Two:

• Brain Stem--all tracts but corticospinal pass through brain stem– Integrates motor commands– Vestibular Information– Medulla--resembles spinal cord and its organization;

sensory & motor tracts

Central Nervous System (CNS)

Level Two--Brainstem Structures• Midbrain--eye movements; muscle control;

pathways that ascend to thalamus– Reticular formation--sleep, waking, attention

• Control of axial/proximal extremities

– Red Nucleus--Control of distal extremities

• Cerebellum (Little Brain)--Silent area of brain– Electrical stimulation causes no sensation and no

movement– Control of rapid muscle activities, posture and

balance– Error detection and correction– Attached to medulla, pons, and midbrain

Level Three (Forebrain) Structures

• Diencephalon—• oldest area of brain; • connects cerebral hemisphere with midbrain

– Hypothalmus--autonomic nervous system– Thalamus--relay center; input about ongoing movement to

cortex

• Basal Ganglia—• Initiation and directing slower, voluntary movements

– Important for carrying out motor plans– Not motor in function; no direct connections to motor cortex

or descending pathways– Parkinson's Disease--poverty of movement; lack dopamine

Level Four CNS Structures• Cerebral cortex (cerebrum) has 4 lobes

– Frontal Lobe-planning and movement– Parietal Lobe-somatic sensations– Occipital Lobe--vision– Temporal Lobe--audition, learning and memory

• Fissures (Sulci) separate lobes– Longitudinal Fissure--separate into 2 hemispheres – Central Fissure--separate into front and back– Lateral Fissure--runs obliquely behind the ear

• Corpus Callosum--densely packed fiber– Allows two hemispheres to communicate– Bottom of longitudinal fissure

Top View of the Brain

Side View of the Brain

Areas of Cerebral CortexInvolved in Movement

• Primary motor cortex--convergence area – Central role in execution of

voluntary movements

– Neurons project directly to spinal cord

• Secondary motor area (Pre-Motor Cortex)– Analysis and integration of

information

– Process more complex aspects

• Broca's Area (left hemisphere); speech

• Wernicke's Area (left hemisphere)– Integration area for

all sensory-motor functions

– General Interpretative area

Areas of Cerebral CortexInvolved in Movement

Motor Unit

• The functional unit of the muscular system– Axon of a motor neuron and all the skeletal

muscle fibers it innervates

• Neuromuscular Junction– Synapse

• Myelinated vs. Unmyelinated nerve fibers

Neural Control of Muscle Force

• Motor Unit Recruitment– Varying number of activated motor units– Size Principle

• Smallest motor neurons are recruited first and deactivated last; opposite for large ones

• Small motor units (S) are slow contracting, low force, and fatigue resistant

• Large motor units (FF)are fast contracting, high force and fatigue easily

• Rate Coding– Varying the rate at which each active motor unit

generates an action potential

• Vary overall frequency– Tonic motor units-increase discharge rate as

muscle force increases at low levels; small action potential

– Phasic motor units-increase discharge rate as muscle force increases over entire force range

• Vary temporal pattern of action potentials between different motor units

Neural Control of Muscle Force