Chapter 4Chapter 4

Neuromotor Basis for Motor ControlNeuromotor Basis for Motor Control

Concept: The neuromotor system forms the foundation for the control of movement

IntroductionIntroduction

The Neuromotor SystemThe Neuromotor System–Components of the central nervous system (CNS) Components of the central nervous system (CNS)

and peripheral nervous system (PNS) involved in the and peripheral nervous system (PNS) involved in the control of coordinated movementcontrol of coordinated movement

Focus of current chapter is CNS structure and Focus of current chapter is CNS structure and functionfunction

–Chapter 6 will include PNS related structure and Chapter 6 will include PNS related structure and function for tactile, visual, and proprioceptive sensory function for tactile, visual, and proprioceptive sensory systemssystems

The NeuronThe Neuron

Neuron = Nerve cellNeuron = Nerve cell–Basic component of Basic component of

the nervous systemthe nervous system–Range in size from 4 Range in size from 4

to 100 micronsto 100 microns

General StructureGeneral Structure [[see Fig. see Fig. 4.14.1]]

– Cell bodyCell bodyContains nucleusContains nucleus

– DendritesDendritesExtensions from cell body – Extensions from cell body – range from 1 to thousands range from 1 to thousands per neuronper neuron

Receive information from Receive information from other cellsother cells

– Axon (also known as a Axon (also known as a “nerve fiber”)“nerve fiber”)

Extension from cell body – Extension from cell body – one per neuron with one per neuron with branches (known as branches (known as collaterals)collaterals)

Sends information from Sends information from neuronneuron

Types and Functions of Types and Functions of NeuronsNeurons

Three Types of NeuronsThree Types of Neurons

1. Sensory Neurons 1. Sensory Neurons [[see Fig. 4.2see Fig. 4.2]]

–Also known as “Also known as “aafferent” fferent” neuronsneurons

–Send information to CNS Send information to CNS from sensory receptorsfrom sensory receptors

–Unipolar – 1 axon; no Unipolar – 1 axon; no dendritesdendrites

–Cell body and most of the Cell body and most of the axon located in PNS; only axon axon located in PNS; only axon central process enters CNScentral process enters CNS

Types and Functions of Neurons, Types and Functions of Neurons, contcont’d’d

2. Motor Neurons 2. Motor Neurons [[see Fig. 4.2see Fig. 4.2]]

–Also known as “Also known as “eefferent” neuronsfferent” neurons–Two types influence voluntary movement:Two types influence voluntary movement:

1. Alpha motor neurons1. Alpha motor neurons Predominantly in spinal cord – axons synapse on Predominantly in spinal cord – axons synapse on

skeletal musclesskeletal muscles

2. Gamma motor neurons2. Gamma motor neurons In intrafusal fibers of skeletal musclesIn intrafusal fibers of skeletal muscles

Types and Functions of Neurons, Types and Functions of Neurons, cont’dcont’d

3. Interneurons 3. Interneurons [[see Fig. 4.2see Fig. 4.2]]

–Specialized neurons that originate and Specialized neurons that originate and terminate in the brain or spinal cordterminate in the brain or spinal cord

–Function as connections between: Function as connections between: Axons from the brain and synapse on motor Axons from the brain and synapse on motor

neuronsneurons

Axons from sensory nerves and the spinal Axons from sensory nerves and the spinal nerves ascending to the brainnerves ascending to the brain

Central Nervous System Central Nervous System (CNS)(CNS)Two components: Brain and spinal cordTwo components: Brain and spinal cordThe BrainThe Brain

4 structural components most directly involved in the 4 structural components most directly involved in the control of voluntary movement:control of voluntary movement:

1. Cerebrum1. Cerebrum2. Diencephalon2. Diencephalon3. Cerebellum3. Cerebellum4. Brainstem4. Brainstem

Brain Components: Brain Components: 1. 1. CerebrumCerebrum

One of two components of forebrain One of two components of forebrain Two halvesTwo halves

–Right cerebral hemisphereRight cerebral hemisphere–Left cerebral hemisphereLeft cerebral hemisphere

Covered by cerebral cortexCovered by cerebral cortex–Gray tissue; 2- to 5-mm thickGray tissue; 2- to 5-mm thick–Undulating covering ofUndulating covering of

Ridges – each is called a Ridges – each is called a gyrusgyrusGrooves – each is called a Grooves – each is called a sulcussulcus

–Cortex motor neuronsCortex motor neuronsPyramidal cellsPyramidal cellsNonpyramidal cellsNonpyramidal cells

Connected by the corpus callosum

Cerebral CortexCerebral CortexFour lobesFour lobes

–FrontalFrontal–ParietalParietal–OccipitalOccipital–TemporalTemporal

Sensory cortex Sensory cortex –Posterior to central sulcusPosterior to central sulcus–Receives neuron axons Receives neuron axons

specific to type of sensory specific to type of sensory informationinformation

Named according to nearest skull bone

Cerebral CortexCerebral Cortex, , cont’dcont’dAssociation areasAssociation areas [ [see Fig. 4.4see Fig. 4.4]]

LocationLocation–Adjacent to specific sensory areas of sensory cortexAdjacent to specific sensory areas of sensory cortex

Function Function –To “associate” information from the several different sensory cortex areasTo “associate” information from the several different sensory cortex areas–Allow the interaction between perceptual and higher-order cognitive Allow the interaction between perceptual and higher-order cognitive

functionsfunctionse.ge.g., selection of the correct response in a choice-RT situation., selection of the correct response in a choice-RT situation

–Possible locations for transition between perception and actionPossible locations for transition between perception and action

Cerebral CortexCerebral Cortex, , cont’dcont’d

Location & StructureLocation & Structure–Frontal lobe just anterior to central Frontal lobe just anterior to central

sulcussulcus–Contains motor neurons that send Contains motor neurons that send

axons to skeletal musclesaxons to skeletal muscles

Function Function

Involved in control of:Involved in control of:–Initiation and coordination of Initiation and coordination of

movements for fine motor skillsmovements for fine motor skills–Postural coordinationPostural coordination

Primary motor cortex

Cerebral Cortex, Cerebral Cortex, cont’dcont’d

Premotor areaPremotor area

–Location:Location: Anterior to the primary motor cortex Anterior to the primary motor cortex–Functions includeFunctions include

Organization of movements before they are initiated Organization of movements before they are initiated

Rhythmic coordination during movement Rhythmic coordination during movement

-- enables transitions between sequential -- enables transitions between sequential movements of a serial motor skill (e.g. keyboard movements of a serial motor skill (e.g. keyboard typing, piano playingtyping, piano playing))

Control of movement based on observation of Control of movement based on observation of another person’s performing a skillanother person’s performing a skill

Cerebral CortexCerebral Cortex, , cont’dcont’d

Supplementary motor area (SMA)Supplementary motor area (SMA)–Location:Location: Medial surface of frontal lobe Medial surface of frontal lobe

adjacent to portions of the primary motor adjacent to portions of the primary motor cortexcortex

–Functions include involvement in the Functions include involvement in the control ofcontrol of

Sequential movements Sequential movements

Preparation and organization of Preparation and organization of movementmovement

Cerebral CortexCerebral Cortex, , cont’dcont’d

Parietal lobe Parietal lobe

LocationLocation–One of the 4 lobes of the cerebral cortexOne of the 4 lobes of the cerebral cortex

FunctionFunction–Involved inInvolved in the integration of the integration of

movement preparation and execution movement preparation and execution Interacts with the premotor cortex, primary Interacts with the premotor cortex, primary

motor cortex, and SMA before and during motor cortex, and SMA before and during movementmovement

Subcortical Brain Area Subcortical Brain Area Important in Motor ControlImportant in Motor Control

Basal GangliaBasal Ganglia–Buried within cerebral hemispheresBuried within cerebral hemispheres–Consist of 4 large nucleiConsist of 4 large nuclei

Caudate nucleusCaudate nucleus

PutamenPutamen

Substantia nigraSubstantia nigra

Globus pallidusGlobus pallidus

–Function involves control ofFunction involves control ofMovement initiationMovement initiation

Antagonist muscles Antagonist muscles

during movementduring movement

ForceForce

- Receive info from cerebral cortex and brainstem- Send info to brainstem

Basal Ganglia, Basal Ganglia, cont’dcont’d

Parkinson’s DiseaseParkinson’s Disease–Common disease associated with basal Common disease associated with basal

ganglia dysfunctionganglia dysfunctionLack of dopamine production by substantia nigraLack of dopamine production by substantia nigra

–Motor control problems Motor control problems [BART][BART]BBradykinesia (radykinesia (slow movementslow movement))

AAkinesia (kinesia (reduced amount of movementreduced amount of movement))

RRigidity of musclesigidity of muscles

TTremorremor

Brain Components: Brain Components: 2. Diencephalon2. Diencephalon

22ndnd component of forebrain component of forebrain

Contains two groups of nucleiContains two groups of nuclei–ThalamusThalamus

Functions:Functions:–A type of relay station - receives and integrates sensory info A type of relay station - receives and integrates sensory info

from spinal cord and brainstem; sends info to cerebral cortexfrom spinal cord and brainstem; sends info to cerebral cortex

–Important role in control of attention, mood, and perception of Important role in control of attention, mood, and perception of painpain

–HypothalamusHypothalamus Critical center for the control of the endocrine system and Critical center for the control of the endocrine system and

body homeostasisbody homeostasis

Brain Components: Brain Components: 3. 3. CerebellumCerebellum

Location:Location: Behind cerebrum and attached to Behind cerebrum and attached to brainstem brainstem [[See Fig. 4.3See Fig. 4.3]]

Structure includesStructure includes–Cortex coveringCortex covering–Two hemispheresTwo hemispheres–White matter under the cortex containsWhite matter under the cortex contains

Red nucleus – Where cerebellum’s motor neural pathways Red nucleus – Where cerebellum’s motor neural pathways connect to spinal cordconnect to spinal cord

Oculomotor nucleusOculomotor nucleus

Brain Components: Brain Components: 3. Cerebellum 3. Cerebellum cont’dcont’d

FunctionsFunctions–Involved in control of smooth and accurate Involved in control of smooth and accurate

movementsmovements Clumsy movement results from dysfunctionClumsy movement results from dysfunction

–Involved in control of eye-hand coordination, Involved in control of eye-hand coordination, movement timing, posturemovement timing, posture

–Serves as a type of movement error detection and Serves as a type of movement error detection and correction systemcorrection system

Receives copy of motor neural signals sent from motor Receives copy of motor neural signals sent from motor cortex to muscles (cortex to muscles (efference copyefference copy))

–Involved in learning motor skillsInvolved in learning motor skills

Brain Components: Brain Components: 4. Brainstem4. BrainstemLocationLocation

Beneath cerebrum; Beneath cerebrum; connected to spinal cordconnected to spinal cord

3 components involved 3 components involved in motor controlin motor control

–PonsPons–MedullaMedulla–Reticular formationReticular formation

FunctionsFunctionsPonsPons

–Involved in control of various Involved in control of various body functions (e.g. chewing) and body functions (e.g. chewing) and balancebalance

MedullaMedulla–Regulatory center for internal Regulatory center for internal

physiologic processes (e.g. physiologic processes (e.g. breathing)breathing)

Reticular formationReticular formation–Integrator of sensory and motor Integrator of sensory and motor

infoinfo–Inhibits / Activates neural signals Inhibits / Activates neural signals

to skeletal musclesto skeletal muscles

Spinal CordSpinal CordA complex neural system vitally involved in motor A complex neural system vitally involved in motor controlcontrol

Structure [Structure [See Fig. 4.5See Fig. 4.5]]–Gray matterGray matter – H-shaped central portion – H-shaped central portion

Consists of cell bodies and axons of neuronsConsists of cell bodies and axons of neurons

Two pairs of “horns”Two pairs of “horns”–Dorsal (posterior) hornsDorsal (posterior) horns – Cells transmit sensory info – Cells transmit sensory info–Ventral (anterior) hornsVentral (anterior) horns – Contains alpha motor neurons with – Contains alpha motor neurons with

axons terminating on skeletal muscleaxons terminating on skeletal muscle

Interneurons (Interneurons (Renshaw cellsRenshaw cells) – In ventral horn) – In ventral horn

Sensory Neural PathwaysSensory Neural Pathways

Several neural tracts (called Several neural tracts (called ascending tractsascending tracts)) –Pass through spinal cord and brainstemPass through spinal cord and brainstem–Connect to sensory areas of cerebral cortex and cerebellumConnect to sensory areas of cerebral cortex and cerebellum

2 tracts to sensory cortex especially important for motor 2 tracts to sensory cortex especially important for motor controlcontrol

–Dorsal columnDorsal column–Anterolateral systemAnterolateral system

Tract to cerebellum important for motor controlTract to cerebellum important for motor control– Spinocerebellar tract –Spinocerebellar tract – Primary pathway for proprioceptive Primary pathway for proprioceptive

infoinfo

Motor Neural PathwaysMotor Neural Pathways

Descending tractsDescending tracts –Travel from brain through spinal cordTravel from brain through spinal cord

Pyramidal tracts (Pyramidal tracts (corticospinal tractscorticospinal tracts))–60% from motor cortex60% from motor cortex–Most fibers cross to other side body (Most fibers cross to other side body (decussationdecussation) in medulla ) in medulla

of brainstemof brainstem–Involved in control of fine motor skill performanceInvolved in control of fine motor skill performance

Nonpyramidal tracts (Nonpyramidal tracts (brainstem pathwaysbrainstem pathways))–Fibers do not cross to other side of bodyFibers do not cross to other side of body–Involved in postural control and control of hand and finger Involved in postural control and control of hand and finger

flexion – extensionflexion – extension

The Motor UnitThe Motor UnitAn alpha motor neuron and all the skeletal muscle An alpha motor neuron and all the skeletal muscle fibers it innervatesfibers it innervates [ [See Figure 4.6See Figure 4.6]]

–When a motor neuron activates (fires) all its connected When a motor neuron activates (fires) all its connected muscle fibers contractmuscle fibers contract

The ultimate end of the motor neural informationThe ultimate end of the motor neural information

~ 200,000 alpha motor neurons in spinal cord~ 200,000 alpha motor neurons in spinal cord–Number of muscle fibers served by a motor unit depends on Number of muscle fibers served by a motor unit depends on

type of movement associated with the muscletype of movement associated with the muscle

Fine movementsFine movements

e.ge.g. eye muscles = 1 fiber / motor unit. eye muscles = 1 fiber / motor unit

Gross movementsGross movements

e.ge.g. posture control = many fibers (. posture control = many fibers (up to ~ 700up to ~ 700) / motor unit) / motor unit

Motor Unit RecruitmentMotor Unit Recruitment

Amount of force generated by muscle contraction Amount of force generated by muscle contraction depends on number of muscle fibers activateddepends on number of muscle fibers activated

–To increase force, need more motor unitsTo increase force, need more motor units

Process of increasing number of motor units involved = Process of increasing number of motor units involved = recruitmentrecruitment

Recruitment follows “size principle” Recruitment follows “size principle” –Size =Size = motor neuron cell body diameter motor neuron cell body diameter–Size principle =Size principle = recruit smallest motor units first (i.e., weakest recruit smallest motor units first (i.e., weakest

force produced) then systematically increase size recruited until force produced) then systematically increase size recruited until achieve desired forceachieve desired force

From Intent to Action: The Neural From Intent to Action: The Neural Control of Voluntary MovementControl of Voluntary Movement

Think about the entire process of deciding to Think about the entire process of deciding to perform a skill and actually performing itperform a skill and actually performing it

The neural activity involved in this process The neural activity involved in this process typically follows a hierarchical organization typically follows a hierarchical organization patternpattern

–From higher to lower levels of the neuromuscular From higher to lower levels of the neuromuscular systemsystem

This process is described conceptually in This process is described conceptually in Figure 4.7 and Table 4.1Figure 4.7 and Table 4.1

Neural Control of Voluntary Neural Control of Voluntary MovementMovement

1. Higher centers1. Higher centers– Function - Form complex plans according to intent, Function - Form complex plans according to intent,

communicates with the middle level via command neurons.communicates with the middle level via command neurons.– Structures – areas involved with memory and emotions, SMA, Structures – areas involved with memory and emotions, SMA,

associations cortexassociations cortex

2. Middle level - 2. Middle level - – Function – converts plans to a number of smaller motor Function – converts plans to a number of smaller motor

programs which determine the pattern of neural activation programs which determine the pattern of neural activation required.required.

– Structures – sensorimotor cortex, cerebellum, basal nuclei, Structures – sensorimotor cortex, cerebellum, basal nuclei, brainstem nucleibrainstem nuclei

Lowest levelLowest level– Function – specifies tension of particular muscles and angle of Function – specifies tension of particular muscles and angle of

joints at specific times necessary to carry out programs from joints at specific times necessary to carry out programs from middle control levelmiddle control level

– Structures – brainstem or spinal cord Structures – brainstem or spinal cord

From Intent to Action: Brain Structures From Intent to Action: Brain Structures Associated with MovementAssociated with Movement

Research by Carson and Research by Carson and Kelso (2004)Kelso (2004)

Demonstrated there is more Demonstrated there is more involved in understanding involved in understanding how we control voluntary how we control voluntary coordinated movement than coordinated movement than knowing which brain knowing which brain structures involved in which structures involved in which type oftype of movementsmovements

–Cognitive intention is a Cognitive intention is a critical componentcritical component

ExperimentExperimentParticipants performed finger-Participants performed finger-flexion movement to a flexion movement to a metronomemetronome

–On the beat (synchronize)On the beat (synchronize)

–Between beats (syncopate)Between beats (syncopate)

Task involved exactly the same Task involved exactly the same movement but two different movement but two different cognitive intentionscognitive intentions

fMRI results showedfMRI results showed–Different brain regions active for Different brain regions active for

the two movement intentionsthe two movement intentions