chapter 4 neuromotor basis for motor control concept: the neuromotor system forms the foundation for...
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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
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