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.