Department of Physiology, 2nd Medical School, Charles University Copyright © 2013 Luděk Nerad...

Department of Physiology, 2nd Medical School, Charles University Copyright © 2013 Luděk Nerad

Motor controlMotor controlNeurophysiologyNeurophysiology

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A tour through the motor side of the A tour through the motor side of the human central nervous sytemhuman central nervous sytem

A tour through the motor side of the A tour through the motor side of the human central nervous sytemhuman central nervous sytem

- simple to more complex

We will proceed from:

- fundamental to supplementary

- phylogenetically old to phylogenetically new



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'Stimulus-response' design of the NS'Stimulus-response' design of the NS'Stimulus-response' design of the NS'Stimulus-response' design of the NS

StimulusStimulus Simple reflexSimple reflex

Simple behaviourSimple behaviour

CognitionCognition



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1. Spinal reflexes1. Spinal reflexes1. Spinal reflexes1. Spinal reflexes

- involuntary

Are:

- stereotyped

- triggered by always the same stimulus

- single (non-repetitive) events



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1. Spinal reflexes1. Spinal reflexes1. Spinal reflexes1. Spinal reflexes

Conclusion

Simple reflexes are not enough to producebehaviours that are typical for animals, such aslocomotor, consumatory, and copulative acts.

More elaborate networks of neurones are needed inwhich movement-relatedactivity is generated andmaintained in the absenceof a stimulus.



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3. Central pattern generators (CPGs)3. Central pattern generators (CPGs)3. Central pattern generators (CPGs)3. Central pattern generators (CPGs)

Examples: walking, running, chewing,scratching, swimming, respiration

CPGs are:

- stereotyped

- repetitive

- involuntary but can be controlled from other CNS structures

- produced by neurones or network of neurones

CPG



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CPG and decerebrated animals

Reflexive movements andmovements produced by CPGsare driven by local neuralcircuits and do not requirecontrol from higher CNScentres. They are presenteven after the transectionof neuraxis above their CPG.

When an important part of the brainstem is spared, an animal can live without the head.Mike the rooster lived for 18 months.



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Mollusks: Ganglia contain CPGs

Pedal gangliaPedal ganglia



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2. Central pattern generators2. Central pattern generators2. Central pattern generators2. Central pattern generators

Conclusion

The CPGs are local networks that control a limitedrange of skeletal muscles. Some of them aretriggered by a stimulus and then maintain theiractivity for a while, some are active all the time(e.g., breathing).

Together with simple reflexes, the CPGs aresufficient to support life functions of primitiveorganisms or simple decerebrate vertebrates.



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3. Extrapyramidal system3. Extrapyramidal system3. Extrapyramidal system3. Extrapyramidal system

Rubrospinal tractcontralateral α and γ motoneurones

Pontine reticulospinal tractipsilateral γ motoneurones

Tectospinal tractcontralateral α and γ motoneurones

Vestibulospinal tractipsilateral α and γ motoneurones

Olivospinal tractcontralateral α and γ motoneurones

Medullary reticulospinal tractbilateral α and γ motoneurones



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Rubrospinal

Reticulosp.

Olivospinal

Vestibulosp.

Tectospinal



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Red nucleus – rubrospinal tractStimulates upper limb flexors

Pontine reticular nucleus - medial reticulospinal tractStimulates antigravity muscles

Medullary reticular nucleus - lateral reticulospinal tractInhibits axial extensor muscles

Vestibular nuclei – vestibulosp. tr.Head and eye coordination, upright posture, balance, by stimulating antigravity muscles



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Superior colliculus- tectospinal tractReflexive head and eye movements as part of the orienting reaction

Inferior olivary nucleus- olivospinal tractAccuracty of movement, reflexes to proprioceptor stimulation



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3b. Cranial nerves – motor part3b. Cranial nerves – motor part3b. Cranial nerves – motor part3b. Cranial nerves – motor part

V Trigeminal (mandib.) - trigeminal motor nucl.Muscles of mastication

IV Trochlear – contralateral trochlear nucl.Superior oblique muscle

III Oculomotor – oculomotor nucleusLevator palpebrae superioris muscle,superior, medial & inferior recti muscles

VI Abducens – abducens nucleusLateral rectus muscle



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3b. Cranial nerves – motor part3b. Cranial nerves – motor part3b. Cranial nerves – motor part3b. Cranial nerves – motor part

X Vagus – nucleus ambiguusMuscles of the larynx and pharynx

IX Glossopharyngeal – nucleus ambiguusStylopharyngeus muscle

VII Facial – facial nerve nucleusMuscles of the face

XI Abducens – spinal accessory nucleusSternocleidomastoid and trapezius muscle

XII Hypoglossal – hypoglossal nucleusMuscles of the tongue



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Conclusion

Spinal motor tracts belonging to the so-calledextrapyramidal system control most muscles,mainly to maintain optimum muscle tone, posture,balance, and orienting towards stimuli.

Eight cranial nerves have a motor componentthat controls mainly the muscles of the eyes, face,and mouth.



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The rubrospinal tract, which is phylogeneticallyyounger than other extrapyramidal pathways,plays a greater role in animals than in humans.

In humans, the motor control via the rubrospinaltract is present in newborns. As the motor cortexmatures (= reduction of layer IV), the emphasisshifts from the nucleus ruber to the motor cortex.

Conclusion (.. continued)



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Lamprey Frog Trout Shark Crocodile

Pigeon Rabbit Dog

4. Cerebellum4. Cerebellum4. Cerebellum4. Cerebellum



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4. Cerebellum (4. Cerebellum (size size ~ movement ~ movement complexity)complexity)

4. Cerebellum (4. Cerebellum (size size ~ movement ~ movement complexity)complexity)

ElephantElephant



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Click on the picture to start the video



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Neocerebellum

Paleocerebellum

Archicerebellum

Vestibulocerebellum(flocculonodular lobe)

Cerebrocerebellum(lateral part)Spinocerebellum(medial part)

Anatomical division

‘Functional’ division



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Electrical stimulation does not cause muscle contraction

People born without the cerebellum do not need support

Monkeys with the cerebellum removed can move well

In humans:- floccular destruction affects balance and eye movements- destruction of the vermis leads to gait ataxia (drunken sailor)- destruction of the hemispheres leads to upper limb ataxia

In general, the cerebellar dysfunction affects balance, posture,eye movements, and movements controlled by will

Facts:



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4. Cerebellum - Ataxia4. Cerebellum - Ataxia4. Cerebellum - Ataxia4. Cerebellum - Ataxia




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'Stimulus-response' – NS design'Stimulus-response' – NS design'Stimulus-response' – NS design'Stimulus-response' – NS design

VestibularProprioceptiveVestibularProprioceptive Simple reflexesSimple reflexes

CerebellumCerebellumCognitionCognition

MovementsMovements



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Conclusion

The cerebellum serves as a processing unit betweenthe vestibular and proprioceptive inputs and motoroutput paths.

It task is to use available sensory information toproduce fine modifications of efferent motor signals.This helps maintaining proper posture, balance,muscle tone, and timing of muscle contraction.



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5. Corpus striatum5. Corpus striatum5. Corpus striatum5. Corpus striatum

Corpus striatum =

nucleus caudatus+ putamen+ globus pallidus



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5. Basal ganglia5. Basal ganglia5. Basal ganglia5. Basal ganglia

Motor cortex

Putamen

Globus pallidus- external segm.

Globus pallidus- internal segm.

Thalamic ventrolat.nucleus (VL)

Subthalamicnucleus (STN)

Substancia nigra



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5. Basal ganglia - diseases5. Basal ganglia - diseases5. Basal ganglia - diseases5. Basal ganglia - diseases



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Jung and Hassler: “Bilateral destruction of the pallidumdoes not produce any motor symptoms.”


MacLean: “More than 150 years of investigation has failedto reveal specific function of the striatal complex.”

Facts:

Large lesions in the striatal complex result in no obviousmotor disability. Bilateral lesions of the caudate nucleusmay produce behavioural persistence and hyperactivity.

Electrical stimulation has no motor effects. It can causeblocking of voluntary behaviours. Laughing and cryinghas also been described.



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Cooper: “The role of the thalamus in motor activitylikewise appears difficult to define at this time. One mayinterrupt pathways from the globus pallidus, red nucleus,and the cerebellum to the thalamus as well as thethalamo-cortical and cortico-thalamic circuits withoutcausing either motor weakness or faulty coordinationupon the patient.”

Facts:

MacLean: “The evidence indicates that the striatalcomplex is not solely a part of the motor apparatusunder the control of the motor cortex.”



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Parent et al.: “The major axonal branches of the GPi arethose that descend within the brainstem, whereas the Gpiinnervation of the thalamus is made up of fine collateralsthat detached from these thick descending fibers. The GPidescending fibers arborise principally in the PPN[pedunculo-pontine nucleus].”

GPi is activated after the activation of the primary motorcortex.

The motor cortex – corpus striatum – thalamus circuitdoes not represent an array of mutually segregated loopsthrough which motor programs reverberate unchanged,as previously thought.



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Strong hypotheses:

BG lesions specifically block the influence of taskincentives on movement vigor.

BG are important for learning new motor skills.The limbic input provides for reinforcement signals thatdetermine what is or what is not to be learnt.

Long-term memories are stored in motor cortices.



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Conclusion

The basal ganglia can be thought of having a similarfunction as the hippocampus in relation to forminglong-term memories in the cerebral cortex.

Both structures serve as processors that storeinformation (sensory-derived in the case of the Hippand motor-derived in the case of BG) in the neocortexbased on its importance or emotional impact. Thislatter aspect is provided to them by the limbic system.



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6. Pyramidal system6. Pyramidal system6. Pyramidal system6. Pyramidal system

Pyramidal tract



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6. Pyramidal tract6. Pyramidal tract6. Pyramidal tract6. Pyramidal tract

Pyramidal tract startsin layer V of MI, PM,SMA areas of the motor cortex (see next slide for abbreviations).

It controls most muscles, mainly the distal ones.



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6. Motor cortex6. Motor cortex6. Motor cortex6. Motor cortex

Primary motor cortex (MI)

Supplemetary motor area (SMA)

Premotor cortex (PM)

PM

SMA

MI

Motor“homunculus”



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6. Motor cortex (fMRI)6. Motor cortex (fMRI)6. Motor cortex (fMRI)6. Motor cortex (fMRI)



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Facts:

MI – Is active during movement. It activates individual muscle groups.PM – Is active before movement. The movement does not have to happen. It is important for the control of learnt automatic movements under the influence of sensory feedback. Speaking, eye control, and writing are some examples.SMA - Is active before movement. The movement does not have to happen. It is active during planning of movement.



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6. Motor cortex (localisation by 6. Motor cortex (localisation by stimulation)stimulation)

6. Motor cortex (localisation by 6. Motor cortex (localisation by stimulation)stimulation)




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Conclusion

The primary motor cortex (MI) has evolved from thesomatosensory cortex. It shares the same functionwith other (sensory) neocortical areas: It serves as asubstrate for conscious awareness and as a store oflong-term memory traces.

The MI stores “motor primitives” (that correspondto individual muscle groups), PM and SMA store morecomplex patterns of movement and behaviour.



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Summary of connections (simplified)Summary of connections (simplified)Summary of connections (simplified)Summary of connections (simplified)

motor cortex

thalamus

cerebellum

corpusstriatum nucleus

ruber

motor nucleiin the pons and medullaoblongata

labyrinth andproprioceptors

spinal cord

pyr

amid

al t

ract

Phylogeneticallyyounger connectionsare light green.

The projections fromfrom the corpusstriatum andcerebellum to thethalamo-corticalsystem allow forawareness of themovement and alsoits storage indeclarative memory.



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Final summaryFinal summaryFinal summaryFinal summary

1. Even the simplest vertebrates can't do with simplereflexes and central pattern generators, despite the factthat they can survive with them.2. Even the simplest vertebrates are able to fine-tunemovement coordination and move in the gravitationalfield (with the help of the cerebellum).3. Even the simplest vertebrates must possess patternsof species-specific behaviours. A major role here is playedby the corpus striatum.4. In man and higher vertebrates, a system has evolved thatconsciously processes information from long-distancesensory modalities – vision and hearing. It has affecteda system that controls behaviour - basal ganglia, and themotor cortex emerged along with its connections with thecerebellum and striatum..

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Department of Physiology, 2nd Medical School, Charles University Copyright © 2013 Luděk Nerad...

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