Post on 22-Jan-2018
Movement disorders Anatomy and physiology of
motor system
Shittu LAJ
Motor systems
• Motor systems are complex and include sophisticated control systems the purpose of which is to serve locomotion, posture and work.
Several feedback systems monitor muscle activity
The length of muscles and the strength of contractions are monitored by:
– Input from proprioceptive receptors in muscles, joints and tendons
– Local feedback from motor nerves (Renshaw inhibition)
Posture
Monitored by:
• proprioceptors,
• vestibular system
• vision
Causes of movement disorders
• More or less anatomically specific neural degeneration
• Injuries (trauma, strokes, surgery, etc)
• Chemicals (alcohol, drugs)
• Inflammations and infections (viral)
• Tumors
• Genetic
• Neural plasticity
• Genetic
• Idiopathic
Motor disorders
• Lack of function
• Inadequate function
• Hyperactivity
Disorders of motor systems
• Hypokinesia
• Hyperkinesia
– Spasticity
• Ataxia
• Gait and balance disturbances
Two different descending motor pathways:
• Lateral system– Fine movements
• Medial system– Posture etc.
Cortex(MI)
Internal capsule
BrainstemNucleus ruber
Midline
Propriospinalinterneuron
Pyramids
Spinal cord
a motoneuron
Distal limb muscles
Lateral system
Medial system
Motor pathways
The motoneurons (alpha motoneurons) are the final common pathways
The alpha-motoneurons (common final pathway) receive many inputsSome are facilitating and some are inhibitory
Motor pathways
Somatotopic organization of the motor cortex
Colony
Colony
Two motoneurons receiving input from cortical cells
Motor areasSensory areas
Terminations of the corticospinal tract projections of sensory pathways
Corticospinaltracts
Propriospinalinterneuron
Supraspinalinput
Ia interneuronSegmental
input
Renshaw cellMuscle
a motoneuron
a motoneuron
Midline
Renshaw inhibition
Fibers of the corticospinal tract terminate onmotoneurons or interneurons
Extensive processing of motor command occurs in the spinal
cord (and brainstem)
• Spinal reflexes play an important role in all motor functions
• Some functions such as walking is programmed in the spinal cord
From supraspinalsources
InterneuronPresynaptic(Axo-axonic)
synapse
Muscle
Muscle spindelafferent
la fibers
DRG
a motoneuron
Monosynaptic stretch reflex
Stimulus
Stimulus
Stimulus strength (V)
Antidromicmotor
Motor
Orthodromicmotor (reflex)
EMG
A
B
C
10ms
M-wave H-reflex
400
2
4
6
8
80 120
M
H
Hoffman reflex
Reflexes are modulated from supraspinal sources
Supraspinalinput
la interneuron
Inhibition ona motoneuron
Agonistmuscle
Antagonistmuscle
Musclespindel
Stretch reflex arc
DRG
a motoneuron
Reciprocal spinal reflex
From semicircular canals
From uticulus
Lateralvestibularnucleus
Medialvestibularnucleus
Medialvestibular
spinal tract
Lateralvestibular
spinal tract
Spinal cord
a motoneurons
motoneurons
Descending vestibularpathways
Medial systemPosture and automatic functions
Reticulospinal tract
la interneuron
Muscle
Tendon
Golgi tendonafferent
DRG
a Motoneuron(inhibitory input)
Tendon reflex
Reticulospinal pathway
la interneuron
Extensormuscle
Flexsormuscle
Flexor reflexafferents
a Motoneurona Motoneuron
Inhibitoryinterneuron
Excitatoryinterneuron
Flexor reflex
Interneuron
Input A
B
A
a motoneuron
Input B
Intracellularpotential ina motoneuron
Input A
B
A
a motoneuron
Input B
Intracellularpotential ina motoneuron
Convergence of excitatory inputs
Convergence of inhibitory and excitatory inputs
Muscle
lb inhibitory
Forelimbafferents
la excitatory
Decending motor tracts
a motoneuron
Input to propriospinal neurons of the forelimb of the cat
From Rosler Fig 2B
Magnetic stimulation of motor cortex in an awake individual
MuscleMuscle
la afferents
Fromantagonist
musclespindle
From agonist muscle spindle
Renshaw
FRA
Corticospinal tractand interneurons
Contralat. Vest.Spinal, FRA etc.
Ipsi. vestibular tractPropriospinal input
Antagonist a motoneuron
Agonista motoneuron
Input to an Ia inhibitory interneuron
Muscle
laNorepinephrineserotonin tract
Dorsal reticularspinal tract
lb
Decending motor tracts
Joint receptors
Skin receptors
a motoneuron
Input to an Ib (inhibitory) interneuron
BASAL GANGLIA
Extrapyramidal system
Pyramidal system
Cortex
To spinal cord
Thalamus
Basalganglia
Cerebellum
Corticospinaltract
Brain stemmotor pathways
Interneurons
Motor cortex
Basalganglia
Thalamus
a motor neuron
muscle
Two descending motor tracts
The alpha-motoneuron is the final common pathway
Fig 5.27B
Anatomical localizationmotor pathways
Motor cortex
Caudatenucleus
Putamen
Claustrum
Globuspallidus Subthalamic
nucleus
Substantianigra
Thalamus
Basal ganglia
Parkinson’s disease
Huntington’s disease
SMA/PMC/CM
GPi/SNr
Putamen
Indirect Direct
GPe
STN
BrainstemSpinal Cord
VLoVApc/mc
CM
Direct and indirect pathways
SMA MI
Putamen
Globus pallidus
STNThalamusVlo-CM
Basal ganglia connect to supplementary motor areas and primary motor cortex
SMA: Supplementary motor area
STN: Subthalamic nucleus
Cortex
Thalamus
Dentatenucleus
Pontinenuclei
Cerebellarcortex
Involvement of the cerebellum
Cerebral cortex(MI and SI)
Thalamus
Cerebellarnucleus
Pontinenuclei
Rednucleus
Cerebellarcortex
Fromspinal cord
Rubrospinaltract
Involvement of the cerebellum and pontine nuclei
Overview of motor pathways
ANATOMICAL LOCATIONS OF THE BASAL GANGLIA
Middle cerebral artery
BASAL GANGLIA
ANATOMICAL LOCATION OF THE CAUDATE NUCLEUS
Somatotopic organization of the motor cortex
Cortical motor areas
The central sulcus divides motor and sensory areas
Overview of motor pathways
Cerebellum
Corticospinaltract
Brain stemmotor pathways
Interneurons
Motor cortex
Basalganglia
Thalamus
a motor neuron
muscle
Two descending motor tracts
The alpha-motoneuron is the final common pathway
Motor cortex
Spinal cord
Basalganglia
BrainstemCerebellum
Thalamus
80
90
100
110
120
2 3 4 5 6 7 8 9 10
Conditioning-test interval (ms)
Effect from spasticity
Soleus H-reflex: Effect on Ib inhibition on reflex response
Hemiplegic side
Normal side
Inhibitory supraspinal input to motoneuron pool
Segmental input
Muscle
la(from muscle spindles)
lb(from Golgi tendon organs)
Supraspinal input
a motoneuron
Spinal cord
T11-L4
S3-S 4
Viceralafferents
Uterus
Efferent
Nociceptors
Viceralafferents
DRGDRG
Viceralafferents
Painfibers
Viceralreceptors
Bladder
Visceral afferent innervation in the lower body and motor (efferent) innervation.