Transcript Anatomical localization motor pathways

CHAPTER V
Movement disorders
Part I: Anatomy and physiology of
motor system
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.
Midline
Lateral system
Cortex
(MI)
Internal capsule
Nucleus ruber
Brainstem
Pyramids
Propriospinal
interneuron
Spinal cord
a motoneuron
Distal limb muscles
Medial system
Motor pathways
The motoneurons
(alpha motoneurons)
are the final common
pathways
The alpha-motoneurons (common final pathway) receive many inputs
Some are facilitating and some are inhibitory
Motor pathways
Somatotopic
organization
of the motor
cortex
Two motoneurons receiving input from cortical cells
Colony
Colony
Terminations of the
corticospinal tract
projections of
sensory pathways
Motor areas
Sensory areas
Renshaw inhibition
Midline
Corticospinal
tracts
Propriospinal
interneuron
Fibers of the
corticospinal
tract terminate on
motoneurons or
interneurons
a motoneuron
a motoneuron
Renshaw cell
Muscle
Supraspinal
input
Segmental
input
Ia interneuron
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
Monosynaptic stretch reflex
Presynaptic
(Axo-axonic)
synapse
Muscle spindel
afferent
From supraspinal
sources
Interneuron
DRG
la fibers
Muscle
a motoneuron
A
Hoffman reflex
Stimulus
EMG
Motor
Antidromic
motor
Orthodromic
motor (reflex)
M-wave
B
H-reflex
10ms
Stimulus
C
M
8
6
H
4
2
0
40
80
Stimulus strength (V)
120
Reflexes are modulated from
supraspinal sources
Reciprocal spinal reflex
Supraspinal
input
la interneuron
Stretch reflex arc
Inhibition on
a motoneuron
DRG
Muscle
spindel
Agonist
muscle
a motoneuron
Antagonist
muscle
From semicircular canals
Descending vestibular
pathways
Medial
vestibular
nucleus
From uticulus
Lateral
vestibular
nucleus
Medial
vestibular
spinal tract
Lateral
vestibular
spinal tract
a motoneurons
motoneurons
Spinal cord
Medial system
Posture and
automatic functions
Tendon reflex
Reticulospinal tract
Golgi tendon
afferent
Tendon
Muscle
la interneuron
DRG
a Motoneuron
(inhibitory input)
Flexor reflex
Reticulospinal pathway
Flexor reflex
afferents
la interneuron
Inhibitory
interneuron
Excitatory
interneuron
a Motoneuron
a Motoneuron
Extensor
muscle
Flexsor
muscle
Convergence of
excitatory inputs
Convergence of inhibitory
and excitatory inputs
A
A
B
B
a motoneuron
a motoneuron
Input A
Input B
Intracellular
potential in
a motoneuron
Interneuron
Input A
Input B
Intracellular
potential in
a motoneuron
Input to propriospinal neurons of the forelimb of the cat
Decending motor tracts
Forelimb
afferents
lb inhibitory
la excitatory
a motoneuron
Muscle
Magnetic stimulation of motor cortex in an
awake individual
From Rosler Fig 2B
Input to an Ia inhibitory interneuron
Ipsi. vestibular tract
Propriospinal input
FRA
Corticospinal tract
and interneurons
Contralat. Vest.
Spinal, FRA etc.
Renshaw
From agonist
muscle spindle
la afferents
Agonist
a motoneuron
Muscle
From
antagonist
muscle
spindle
Antagonist
a motoneuron
Muscle
Input to an Ib (inhibitory) interneuron
Decending motor tracts
Joint receptors
Dorsal reticular
spinal tract
Skin receptors
Norepinephrine
serotonin tract
la
lb
a motoneuron
Muscle
BASAL GANGLIA
Extrapyramidal system
Pyramidal system
Cortex
Thalamus
Basal
ganglia
To spinal cord
Motor cortex
Two descending
motor tracts
The alphamotoneuron is
the final
common
pathway
Basal
ganglia
Thalamus
Cerebellum
Corticospinal
tract
Brain stem
motor pathways
Interneurons
a motor neuron
muscle
Anatomical localization
motor pathways
Fig 5.27B
Motor cortex
Caudate
nucleus
Claustrum
Thalamus
Putamen
Globus
pallidus
Substantia
nigra
Subthalamic
nucleus
Basal ganglia
Parkinson’s
disease
Huntington’s
disease
Direct and indirect pathways
SMA/PMC/CM
Indirect
Direct
Putamen
GPe
STN
Brainstem
Spinal Cord
GPi/SNr
VLo
VApc/mc
CM
Basal ganglia
connect to
supplementary
motor areas and
primary motor
cortex
SMA
MI
Putamen
SMA:
Supplementary
motor area
STN:
Subthalamic
nucleus
Globus pallidus
Thalamus
Vlo-CM
STN
Involvement of
the cerebellum
Cortex
Thalamus
Dentate
nucleus
Pontine
nuclei
Cerebellar
cortex
Involvement of the
cerebellum and
pontine nuclei
Cerebral cortex
(MI and SI)
Thalamus
Red
nucleus
Cerebellar
nucleus
Pontine
nuclei
Cerebellar
cortex
Rubrospinal
tract
From
spinal cord
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
Motor cortex
Two descending
motor tracts
The alphamotoneuron is
the final
common
pathway
Basal
ganglia
Thalamus
Cerebellum
Corticospinal
tract
Brain stem
motor pathways
Interneurons
a motor neuron
muscle
Motor cortex
Thalamus
Basal
ganglia
Cerebellum
Brainstem
Spinal cord
Effect from
spasticity
120
Soleus H-reflex:
Effect on Ib
inhibition on
reflex response
110
Hemiplegic side
100
90
Normal side
80
2
3
4
5
6
7
8
9
Conditioning-test interval (ms)
10
Inhibitory supraspinal input to motoneuron pool
Supraspinal input
Segmental input
la
(from muscle spindles)
lb
(from Golgi tendon organs)
a motoneuron
Muscle
Visceral afferent
innervation in the
lower body and
motor (efferent)
innervation.
Spinal cord
DRG
T11-L4
Viceral
afferents
DRG
Viceral
afferents
S 3-S 4
Viceral
afferents
Uterus
Efferent
Viceral
receptors
Pain
fibers
Bladder
Nociceptors