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ANATOMY AND PHYSIOLOGY OF MOTOR
SYSTEMS
CHAPTER V
Motor pathways
Somatotopic organization of the motor cortex
Cortical motor areas
The central sulcus divides motor and sensory areas
SUPPLEMENTARY CORTICAL AREAS PROVIDE INPUT TO MOTOR CORTEX
LATERAL DESCENDING SYSTEM
• CORTICOSPINAL TRACT– CONNECT DIRECTLY TO ALPHA
MOTONEURONS, OR THROUGH PROPRIOSPINAL INTERNEURONS
• RUBROSPINAL TRACT– FROM NUCLEUS RUBER TO
PROPRIOSPINAL INTERNEURONS
Descending motor pathways
Lateral system
Cortex(MI)
Internal capsule
BrainstemNucleus ruber
Midline
Propriospinalinterneuron
Pyramids
Spinal cord
a motoneuron
AROUSAL
Distal limb muscles
Fig 5.1
Vestibular nuclei
Midline
Crossed
tectospinal tract
Crossed
vestibular tract
Uncrossed
tectospinal tract
Uncrossed
vestibular tract
Reticular
formation
Tectrum
Reticulospinal
tract
Fig 5.2
The medial descending motor pathways
Motor pathwaysfrom the brainstem
Initiation of the corticospinal tract
Fig 6.3 Brodal Fig 12.6
Termination of the corticospinal tractin the dorsal horn
Projections from motor cortex (MI)to the spinal cord
Projection of dorsalhorn to the somatosensory cortex
Corticospinaltracts
Propprio spinalinterneuron
Supraspinal input
Segmental input
Renshaw cell
Muscle
INPUT TO a MOTONEURONSFROM CORTICOSPINAL TRACT
Fig 5.4
a motoneuron
Cortex
To spinal cord
Thalamus
Basalganglia
Fig 5.23A
Connections between the basal ganglia and the primary motor cortex (MI)
INFORMATION FROM THE MOTOR CORTEX IS
PROCESSED IN THE BASAL GANGLIA AND RETURNED TO
THE MOTOR CORTEXTHE THALAMUS CONDUCT THE
INFORMATION BACK TO THE MOTOR CORTEX
THE DISTINCTION BETWEEN PYRAMIDAL AND EXTRAPYRAMIDAL
SYSTEMS THEREBY BECOMES IRRELEVANT
CEREBRAL CORTEX
Substantia Nigra
Pallidum
Striatum Thalamus
Fig 5.23B
Motor systems are complex
Two descending motor tracts
The alpha-motoneuron is the final common pathway
Fig 5.22
Anatomical localization of basal ganglia and motor thalamus
Cortex
Thalamus
Dentatenucleus
Pontinenuclei
Fig 5.28
Cerebellarcortex
Connections between the cerebral cortexand the cerebellum
The alpha-motoneuron innervates muscles
The alpha-motoneurons (common final pathway) receive many inputsSome are facilitating and some are inhibitory
The anatomical basis for the stretch reflex
Motoneurons receive excitatory input from muscle spindles (length), and inhibitory input from tendon organs (tension)
Recording from the exposed spinal cord
D and I waves
Blood supply to the spinal cord
• Mainly two sources:– The anterior spinal artery– Posterior spinal artery– Segmental arteries
• Dorsal and ventral portions of the spinal cord have mostly different blood supplies
• Large degree of individual variability
Blood supply to the spinal cord
Anterior spinal artery
Number of feeder arteries varies
Two posterior spinal arteries
Number of feeder arteries varies
Activation of motor tracts
• Transcranial magnetic stimulation of the motor cortex
• Transcranial electrical stimulation of the motor cortex
• Electrical stimulation of the spinal cord
Magnetic stimulation of the motor cortex
• Non-invasive
• Technically difficult to apply
• Need trains of stimulation, which is difficult to achieve
Transcranial electrical stimulation of the motor cortex
• Non-invasive
• Can easily produce trains of impulses
• High voltage may seem a risk
Electrical stimulation of the spinal cord
• Produces effective stimulation of spinal cord
• Invasive
• Not clear if only motor pathways are stimulated
Recording of responses
• Electromyographic potentials
• Compound action potentials from motor nerves
Electromyographic potentials
• Large potentials
• Cannot be done with muscle relaxation
Compound action potentials
• Can be recorded with muscle relaxation
• Amplitude is small
Recording from the exposed spinal cord
D and I waves
Fig 5.6
Recordings from the surface of the spinal cord in a monkey in response to stimulation of the cerebral cortexTranscranial magneticstimulation
Transcranial electricalstimulation
Direct electrical stimulation
D
I1
Fig 5.7
Recordings from the surface of the spinal cord in a 14 year old patient Undergoing a scoliosis operation. Transcranial electrical stimulation at different strengths (100%=750V at Cz and 6 cm anterior)
Effect of placement of stimulating electrodes
Deletis and Shils 2002
Deletis and Shils 2002
Comparison between transcranial and directstimulation of the motor cortex
Deletis and Shils 2002
Techniques for recording motor evoked potentials
EFFECT OF REPETITION RATE AND NUMBEROF IMPULSES ON THENAR MUSCLE MEPFROM TRANSCRANIALELECTRICAL STIMULATION
EFFECT OF PULSEWIDTH, POLARITYAND INTENSITY
Repeating trains can increase the EMG responses from the right abductor hallucisbrevis in response to trains of five electrical impulses to scalp (C3-C4).
Deletis and Shils 2002
Deletis and Shils 2002
Using BSM, surgeon can get anatomical guidance to enter the brainstem safely.
From Morota N, Deletis V, Epstein FJ, et al: Brain stem mapping: neurophysiological localization of motor nuclei on the floor of the fourth ventricle. Neurosurgery 37: 922-930, 1995
Corticobulbar MEPs - Recordings in IV Ventricle Mapping - Recordings
From supraspinalsources
InterneuronPresynaptic(Axo-axonic)
synapse
Muscle
Muscle spindelafferent
la fibers
DRG
Fig 5.10
a motoneuron
Modulation of the monosynaptic stretch reflex
Fig 5.11
The Hoffmann reflex
Amplitude of Hoffmann (H) Response, and the direct muscle (M) response.
DESCENDING MOTOR ACTIVITY IS AFFECTED BY
ATTENTION
From Rosler Fig 2BFig 5.5B
Magnetic stimulation of motor cortex in an awake individual
DESCENDING MOTOR ACTIVITY IS AFFECTED BY
ANESTHESIA
EFFECT OF INCREASING CONCENTRATION OF ISOFLURANE ON COMPOUND MUSCLE ACTION POTENTIAL IN RESPONSE TO TRANSCRANIALELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING CONCENTRATION OF ISOFLURANE ON EPIDURAL RESPONSE (D AND I WAVES) TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING CONCENTRATION OF NITROUS OXIDE ON COMPOUND MUSCLE ACTION POTENTIAL IN RESPONSE TO TRANSCRANIALELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING CONCENTRATION OF NITROUS OXIDE ON EPIDURAL RESPONSE TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING DOSES OF ETOMIDATE ON COMPOUND MUSCLE ACTION POTENTIAL IN RESPONSE TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING DOSE OF ETOMIDATE ON THE EPIDURAL RESPONSE TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING DOSES OF PROPOFOL ON COMPOUND MUSCLE ACTION POTENTIAL IN RESPONSE TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
EFFECT OF INCREASING DOSES OF PROPOFOL ON EPIDURAL RESPONSE TO TRANSCRANIAL ELECTRICAL MOTOR CORTEX STIMULATION
FROM SLOAN 2002
RECORDINGS FROM THE EPIDURAL SPACE WITH AND WITHOUT MUSCLE RELATION IN RESPONSE TO TRANSCRANIAL ELECTRICAL STIMULATION
FROM SLOAN 2002
OPERATIONS FOR SPINAL DEFORMITIES
TEST OF LEVEL OF MUSCLE RELAXATION
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