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