1. Motor control

2. Proprioception and movement
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Proprioception and movement
in general we are not aware of information coming from proprioceptors though they belong to somatosensory receptors
these receptors detect stretching of the muscles and tension in tendons and induce reflexes as well as provide information for the control of movement
receptors in joints detecting the angle of the joints also belong to this category
they also provide input for the control of movement
these facts justify treatment of these receptors in the framework motor control

3. Final common pathway
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somatic and visceral motor systems represent the output of the CNS
in the somatic system the final common pathway is the motor neuron in the ventral horn of the spinal cord or in the motor nucleus of cranial nerves in the brainstem
in the visceral system the final common pathway means the motor neuron in the lateral horn of the spinal cord or in the vegetative nucleus of cranial nerves in the brainstem
final common pathway means (Sherington) that executive organs can be only accessed through these motor neurons, integration occurs at this or at a higher level
in the somatic system, fibers innervate targets (skeletal muscle) directly, in the visceral (smooth muscle and gland cells) through an intercalated neuron

4. Hierarchical organization
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areas where stimulation causes movements are classified as motor areas
these areas receive somatosensory input as well, thus they are sometimes referred to as somatomotor areas and systems
regulation is done on several levels – the higher the level the more complicated movements are controlled, though lower levels are influenced by descending effects as well
cortical areas are able to control motor neurons in the spinal cord and brainstem directly, but they also exert their effects on the spinal cord indirectly through the brain stem
in addition to these pathways, cerebellum and basal ganglia also participate in motor control by influencing brain stem and cortical areas
somatotopy is present at every level

5. Organization of motor system
cortex
basal ganglia
thalamus
brain stem
cerebellum
motor neuron sensory pathway
brain stem and spinal cord
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6. Muscle spindle
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Berne and Levy, Mosby Year Book Inc, 1993, Fig. 12-1
muscle spindle is 4-10 mm long, it is made up by 6-8 modified muscle fibers, and is located in parallel with regular muscle fibers
muscle spindle is encased in a connective tissue capsule
within the muscle spindle, the middle part of intrafusal fibers is modified for receptor function, terminal parts are able to contract
usually there are 2 nuclear bag (one dynamic, one static) and 5-6 nuclear chain fibers (all static) in a spindle 
primary terminals form spirals around the middle part of all three types of receptors - annulospiral terminal - Ia (Aα) afferent
secondary terminals (flower spray endings) target static nuclear bag and nuclear chain fibers - II (Aβ) afferent 
Berne and Levy, Mosby Year Book Inc, 1993, Fig. 12-2

7. Operation of the muscle spindle
when extrafusal (regular) fibers contract, intrafusal fibers are shortened and relax
when extrafusal fibers are stretched, then intrafusal fibers are also stretched – elongation of receptor terminals increase the discharge rate
in case of continuous stretch polar regions of dynamic nuclear bag receptors lengthen due to their viscoelastic properties, thus excitation of the nerve terminal decreases
regular muscle fibers are innervated by A axons, intrafusal fibers by A axons – excitation is parallel, thus sensitivity of the receptor remains constant
previously a servo-mechanism was suggested
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8. The tendon organ tendon organs are in series with muscles
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tendon organs are in series with muscles
they are 1 mm long structures surrounded by a capsule
collagen fibers of the tendon penetrate the muscle
perpendicularly Ib afferents, branches run between fibers or wrap around them
they are deformed with increasing tension – excitation
tendon organs inform about the contraction and passive extension of muscles, but they are more sensitive to the former
thus, they provide information about forces developing in the muscles

9. Spinal reflexes I.
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Berne and Levy, Mosby Year Book Inc, 1993, Fig
the lowest level in the hierarchy of the motor control is represented by the spinal reflexes
the myotatic (stretch) reflex is monosynaptic: afferents terminate on the motoneuron of the same muscle – proprius (Latin): one’s own
stretching of muscle spindle induces contraction of the same muscle
patella reflex, Achilles tendon reflex – mostly in extensors, though in flexors as well (biceps)
collateral of Ia afferent inhibits antagonist motoneuron through an inhibitory interneuron – reciprocal innervation is characteristic for the spinal cord – simultaneous contraction is organized always at a higher level 
myotatic reflex can be dynamic or tonic, in the second type secondary terminals also participate

10. Spinal reflexes II.
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diagnostic value: motoneuron excitability – direct stimulation: H or Hoffman reflex
its function is to keep posture, thus it is stronger in extensors than in flexors, but sloth
divergence and convergence in respect of agonist muscles are both present – though the reflex remains segmental
muscle tone (resistance against passive moving) is due to this reflex: a subset of motor units are always slightly contracted
myotatic reflex, thus muscle tone is continuously modified by descending effects through setting the sensitivity of the motoneuron (e.g. REM)
collateral of Ia afferent terminates on neurons belonging to the column of Clarke: spinocerebellar tract

11. Spinal reflexes III. inverse myotatic reflex starts from tendon organs
Berne and Levy, Mosby Year Book Inc, 1993, Fig
Spinal reflexes III.
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inverse myotatic reflex starts from tendon organs
incoming fibers target agonist motoneuron through inhibitory interneurons, antagonist through excitatory ones
main function is to protect muscle and tendon against overstretching
it also supplements myotatic reflex: when tension in tendon decreases – weaker inhibition – contraction 
flexion withdrawal reflex starts from nociceptors (exteroceptive), its function is to remove extremity from the noxious stimulus source
it is polysynaptic, in addition to activate antagonist muscles, it also induces crossed extension reflex
the reflex is intersegmental, many muscle groups can participate 
Berne and Levy, Mosby Year Book Inc, 1993, Fig

12. Motor stereotypes
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spinal cord is able to organize simple motor stereotypes – these are intersegmental
scratching reflex involves rhythmically alternating movements, frequency is independent from the strength of the stimulus, it only increases duration
afterdischarge is characteristic (reverberating circuits)
stereotypes are generated by a central rhythm generator no feedback from proprioceptors is needed – based on mutual inhibition, adaptation and rebound
walking has similar central organization, but feedback from proprioceptors is needed and central descending effects influence frequency (walk, trot, canter, gallop)

13. Spinal cord organization I.
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location of motor neurons follows somatototopy
motor neurons of proximal and distal muscles are located medially and laterally, respectively
axial muscles in the midline of the trunk belong to the most medial motor neurons
these motor neurons receive input from interneurons on both sides – bilateral control – posture
motor neurons of extensors and flexors are located ventrally and dorsally, respectively
motor neurons controlling a given muscle are found in 1-4 neighboring segments – motor neuron pool
within the pool muscle fibers innervated by 1 motor neuron form the motor unit – 10 (eye), 100 (hand), 2000 (foot) fibers
all fibers in a unit are the same type

14. Types of muscle fibers tonic fibers slow-twitch (type I) fibers
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tonic fibers
postural muscles in amphibians, reptiles and birds
muscle spindles and extraocular muscles in mammals
no AP, motor axon forms repeated synapses
slow shortening – effective isometric contraction
slow-twitch (type I) fibers
mammalian postural muscles
slow shortening, slow fatigue – high myoglobin content, large number of mitochondria, rich blood supply – red muscle
fast-twitch oxidative (type IIa) fibers
specialized for rapid, repetitive movements – flight muscles of migratory birds
many mitochondria, relatively resistant to fatigue
fast-twitch glycolytic (type IIb) fibers
very fast contraction, quick fatigue
few mitochondria, relies on glycolysis
breast muscles of domestic fowl – white muscle

15. Spinal cord organization II.
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reflexes activate only part of the motor units – fractionization principle
reflexes and voluntary movements can be graded – more and more units get involved – recruitment
activation follows size principle – first small units are activated – motor neurons are also small, EPSPs are more effective
the largest units contain fast-twitch glycolytic fibers (white muscle) – they are only activated when really necessary
in addition to recruitment, frequency can be also increased - during voluntary movements 8-25 Hz causing incomplete tetanus – motor units contract asynchronously

16. Inhibitory interneurons
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α-motor neurons are innervated by three types of inhibitory interneurons: Ia, Ib and Renshaw
Ia receives input from the muscle spindle in the antagonist muscle, but it is also activated by descending fibers targeting the antagonist motor neuron
it also receives inhibitory inputs – suspension of reciprocal innervation – „column” function
Ib receives input from the tendon organ, but it is also influenced by descending pathways, receptors in the skin and joints – these control the strength of contraction: touching, stroking
Renshaw receives input from collaterals of α-motor neurons – feedback inhibition
sensitivity is controlled by descending excitatory and inhibitory pathways

17. Brain stem reflexes and posture
lesions of the neuraxis change the tone of postural muscles – Sherington: tone in these muscles is caused by reflexes
tone is modified by descending effects: lifting one leg increases the tone of the others
transection between the n.ruber and the Deiters’ nucleus – decerebrate rigidity in tetrapods
it can be abolished by cutting the reflex arch
Deiters’ nucleus (tr. vestibulospinalis lat.) and pontine RF (tr. reticulospinalis med.) strongly enhances extensor tone
inhibitory effects:
cerebellum
in tetrapods tr. rubrospinalis from n. ruber
in primates it has only effect to the level of cervical segments, cortex is more important
medullary RF – tr. reticulospinalis lateralis
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18. Voluntary movements I.
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the background for voluntary movements is provided by muscle tone control
appropriate rearrangement of muscle tone is needed to preserve posture during voluntary, reflex and stereotype movements
common characteristic of voluntary movements that they become automated through learning and exercise – learning to walk in babies sports, etc.
Fritsch and Hitzig 1870: cortical stimulation in dogs might lead to movements
information about the organization of cortical motor control was collected from five sources:
stimulation studies (Penfield human surgeries)
analysis of brain injuries
unit recording in monkeys
imaging, e.g. PET
anatomical studies

19. Voluntary movements II.
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Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 2-13
based on these data we know what type of damages impair control of voluntary movements, and which areas are activated first – organization of motor control is less clear
primary motor area: Br.4 – gyrus precentralis
somatotopy is similar to the somatosensory area: leg medially, representation is proportional with the sophistication of movements 
secondary motor cortex: Br.6 – in front of primary
it consists of two parts: supplementary motor area and premotor cortex
their role is in the preparation (premotor), and in the planning (supplementary) of movements: electrophysiological and blood flow changes before the movements and during contemplating of movements

20. Voluntary movements III.
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the corticospinal or pyramidal tract is the most important motor pathway
most of the fibers originate from layer V pyramidal neurons in Br.4 and 6, but from other areas as well – upper motor neurons
90% of the axons cross over and run in the „pyramids” on the surface of medulla (name), then in the lateral corticospinal tract, 10% cross in the spinal cord (ant. tr.) before ending
direct effect on α-motor neurons (lower motor neurons), indirect effect through interneurons
motor cortices receive input from the VL (thalamus) and from the somatosensory cortex
VL transmits information from cerebellum and putamen, no direct projection
interaction goes both ways (see before)
movements can be elicited from other cortical areas as well, but with strong stimuli only

21. Cerebellum I.
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cerebellum coordinates motor activities, its injuries impair coordination and execution of voluntary movements
motor learning is also lost
cerebellum has more neurons than the other parts of the CNS 
modular structure, János Szentágothai contributed heavily to its description
principal neurons are inhibitory Purkinje cells, projecting to deep cerebellar nuclei that in turn project to VL
various excitatory (e.g. granule) and inhibitory (e.g. Golgi) interneurons
input: climbing fiber (contralateral oliva inferior) and mossy fiber (cortex, spinal cord, brainstem)
multiple somatotopical representation in the cortex and deep cerebellar nuclei 
Berne and Levy, Mosby Year Book Inc, 1993, Fig
Berne and Levy, Mosby Year Book Inc, 1993, Fig. 14-9

22. Cerebellum II. three parts (connections, evolution):
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three parts (connections, evolution):
vestibulocerebellum (archeocerebellum) – oldest, caudal part (flocculus, nodulus) 
direct input from semicircular canals, utriculus, sacculus
direct output to Deiters’ nucleus (it can be considered as a deep cerebellar nucleus)
balance and gait, coordination of eye movements, reflex movements of the head
spinocerebellum (paleocerebellum) – middle part of cerebellum (vermis, central, intermediary parts of the hemispheres)
input through the dorsal spinocerebellar tract from sensory afferents – information about the position of extremities and about changes that occurred (external feedback)
input through the ventral spinocerebellar tract about the activity of interneurons: it reflects descending commands (internal feedback)
the cerebellum monitors the execution of motor commands
cerebrocerebellum (neocerebellum) – lateral part of hemispheres
input from the cortex and n. ruber through the pons
output to n. dentatus, thalamus, cortex
planning, starting and stopping as well as learning of movements
Berne and Levy, Mosby Year Book Inc, 1993, Fig

23. Basal ganglia I. basal ganglia consist of:
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basal ganglia consist of:
neostriatum (n. caudatus + putamen)
pallidum or globus pallidus (neostriatum+pallidum= corpus striatum, putamen+pallidum= n.lentiformis)
substantia nigra (pars compacta and pars reticularis)
n. subthalamicus
main functions are in the control of movements and muscle tone – deducted from impairments caused by lost of different cell groups
Parkinson’s disease: muscle rigidity, tremor, slowing or loss of physical movements (see Awakenings) – caused by loss of dopaminergic cell in substantia nigra pars compacta – MPTP (methyl-phenyl-tetrahydropyridine)
Huntington’s chorea: abnormal, jerky, random movements (chorea: Greek word for dance) – cholinergic and GABAergic neurons in the neostriatum die – genetic background is known – prenatal diagnosis – ethical issues

24. Basal ganglia II.
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Berne and Levy, Mosby Year Book Inc, 1993, Fig
outdated conception: pyramidal – extrapyramidal pathways
extrapyramidal was supposed to originate from the neostriatum – incorrect, the term is rarely used now
neurons of the basal ganglia are not activated before cortical neurons – no role in initiating movements
they modify through multiple circuits involving thalamic VA (ventralis anterior), VL (ventralis lateralis) and CM (centre median) the functioning of the motor cortex 
in Parkinson’s disease stimulation of the direct and inhibition of the indirect pathway decrease – less excitation on VA, VL
in Huntigton’s chorea the indirect pathway is affected more - VA, VL inhibition decreases

25. End of text

26. Muscle spindle
Berne and Levy, Mosby Year Book Inc, 1993, Fig. 12-1

27. Afferents in the muscle spindle
Berne and Levy, Mosby Year Book Inc, 1993, Fig. 12-2

28. Myotatic reflex
Berne and Levy, Mosby Year Book Inc, 1993, Fig

29. Inverse myotatic reflex
Berne and Levy, Mosby Year Book Inc, 1993, Fig

30. Flexion withdrawal reflex
Berne and Levy, Mosby Year Book Inc, 1993, Fig

31. Somatomotor cortex
Blumenfeld, Sineauer Assoc. Inc., 2002, Fig. 2-13

32. Cerebellum
Berne and Levy, Mosby Year Book Inc, 1993, Fig. 14-9

33. Divisions of the cerebellum
Berne and Levy, Mosby Year Book Inc, 1993, Fig

34. Somatotopy in the cerebellum
Berne and Levy, Mosby Year Book Inc, 1993, Fig

35. Direct and indirect pathways
Berne and Levy, Mosby Year Book Inc, 1993, Fig