Download Motor System: Motor Neurons

Corticospinal Tract and Other Motor
Pathways
• Lundy-Ekman
• Dr. Donald Allen
• Sherrington – Motor systems are the only
way we can understand what is happening
in the nervous system
• How does movement start?
– Decision made in anterior frontal lobe of
cerebral cortex
– Activation of motor planning areas
– Control areas (basal ganglia and cerebellum
– Descending tracts (upper motor neurons)
– Spinal interneurons
– Lower motor neurons
– Skeletal muscles (contraction)
Motor Control Hierarchy
Cerebral Cortex
BG
Thal
Brainstem UMN
Cerebellum
Segmental
LMNs
Muscle

Muscles
• Tone
Lower motor neurons
• Multipolar neurons
• Location
–
–
Classification of motor neurons
• Alpha motor neurons
• Gamma motor neurons
Motor neurons
• Synapse
• Neurotransmitter
• Receptors
• Motor Unit
Types of motor units
• Slow twitch or fast twitch
– Speed of muscle contraction
– Metabolic sources of energy
– Resistance to fatigue
• Determined by the alpha motor neurons
Motor Neurons
-motor neuron
diameter
Innervated
muscles
Recruitment
order
Speed generation
Sources of
energy
Fatigue
Slow-Twitch
smaller
Fast-Twitch
larger
postural
Movement
first
slow
Aerobic
Later (we need
more force)
fast
Anaerobic
Resistant
Sensitive
Spinal Reflexes
• Components
Sensory Receptors
• Muscle spindles
• Golgi tendon organs
• Cutaneous receptors
Muscle Spindle Reflexes
• Phasic stretch reflex
• Tonic stretch reflex
Tonic Stretch Reflex
GTO reflex
Cutaneous Reflexes
• Withdrawal reflexes
• Respond to nociceptive input
Upper Motor Neurons
• Locations in CNS
–
–
• Project to
–
–
Pathways to spinal cord
• Classified based on where they synapse in
the ventral horn
• Medial activating systems
• Lateral activating systems
• Non-specific activating systems
Medial Activating Systems
• Anterior Columns of Spinal Cord
• Muscles innervated
• 5 tracts
5 tracts
Tectospinal tract
Medial
Reticulospinal
Tract
Medial vestibulospinal tract
Lateral vestibulospinal tract
Medial
Corticospinal Tract
Lateral
Activating
Systems
Lateral Corticospinal Tract
• AKA: pyramidal tract
• Origin (p215)
Cortical Areas of Brodmann
• Primary Motor
Cortex
– Area 4
• Secondary Motor
Cortex
– Area 6, 8?
– Premotor Cortex,
Supplementary
Motor Cortex
• Primary
somatosensory
cortex
– Area 3, 1, 2
Motor Homunculus
Premotor Cortex
Supplementary Motor Cortex
Right
Corona
Motor Radiata
Cortiospinal Tract
9,10,11
Ctx
Internal
Capsule
7u 7l
4
12
5
6
3
SC
Pyramidal Decussation
Pyramids
Motor
Ctx
Left
Cerebral
Peduncle
3
12
6
4
5
7u 7l
9,10,11
SC
Right
Corona
Motor Radiata
Corticobulbar Tract
9,10,11
Ctx
Internal
Capsule
7u 7l
4
Motor
Ctx
Left
Cerebral
Peduncle
5
3
6
3
6
4
5
12
SC
12
SC
7u 7l
9,10,11
Rubrospinal Tract
• Red nucleus
– midbrain
Lateral Reticulospinal Tract
Non-specific Motor Pathways
• Raphespinal tract
• Ceruleospinal tract
Basal Ganglia, Cerebellum and
Movement
• BG and Cb adjust activity in descending
motor tracts
• DO NOT have direct connections with
lower motor neurons
• Connections
–
–
Basal Ganglia
• Caudate –
• Putamen
• Globus pallidus
– Globus pallidus internus (medial) – Globus pallidus externus (lateral) –
• Subthalamic nucleus – diencephalon
• Substantia nigra – midbrain
– Pars compacta –
– Pars reticulata –
Pathways in BG for motor
systems
• Input regions
• Processing regions
– Two pathways through BG
• Direct pathway –
• Indirect pathway –
• Output regions
Direct pathway
Motor and Somatosensory Cerebral cortex
Putamen Excited
Inhibited Output nuclei
Excited
Pedunculopontine nucleus
Inhibited
Reticulospinal and
vestibulospinal tracts
Motor Thalamus Excited
Motor areas of
cerebral cortex Excited
Indirect pathway
Motor and Somatosensory Cerebral cortex
Putamen Excited
Excited
Inhibited
Globus pallidus externus
Reticulospinal and
vestibulospinal
tracts
Excited Subthalamic nucleus
Excited
Output nuclei
Lateral Activating
Systems
Inhibited
Substantia Nigra compacta
Output Regions of the BG
• Globus pallidus internus
• Substantia nigra reticularis
Functions of the Basal Ganglia
• Sequencing movements
• Regulating muscle tone and force
• Selecting synergies (direct pathway) and
inhibiting synergies (indirect pathway)
• Motor learning
Basal Ganglia Disorders
• Hypokinetic
– Parkinson’s Disease
• Hyperkinetic
–
–
–
–
Huntington’s disease
Dystonias
Choreoathetotic cerebral palsy
Hemiballismus
Parkinson’s Disease
• Most common BG disorder
• Neurodegenerative disease
–
•
Coffee drinking and PD
Honolulu Health Program
Parkinsonism and Parkinsonian
Syndrome
Huntington’s Disease
Dystonia
• Genetic movement disorder
– Dysfunction in basal ganglia
– Usually non-progressive
• Involuntary sustained muscle contractions
– Twisting or repetitive motions or abnormal
posture
• Focal dystonias are most common type
Focal Dystonia
• Affects one part of body
• Often limited to a particular activity
• Focal dystonia of hand
– Writer’s cramp
• Deteriation in handwriting due to involuntary
muscle contractions in upper limb
– Musician’s cramp
• Usually 4th and 5th fingers flexing involuntarily
Choreoathetotic Cerebral Palsy
• Damage to basal ganglia structures
• Chorea
• Athetotic movements
Hemiballismus
• Damage to:
• Ballistic movements
• Side affected
Cerebellum (Little Brain)
• Location:
• Functions:
Cb Anatomy
• Gray matter
• White matter
• Deep cerebellar nuclei
Gross anatomy of Cb
• Arbor vitae
• Folia
Cellular anatomy of the Cb
• Three layers of cells
– Outer and inner layers
• Interneurons
–
–
–
–
Granule cells
Golgi cells
Stellate cells
Basket cells
– Middle layer
• Purkinje cell bodies
• Project to deep cerebellar nuclei and
vestibular nuclei
Gross Anatomy of the Cb
• We can divide the Cb two
different ways
• Medial to lateral
– Vermis
– Cerebellar hemispheres
• Intermediate or paravermal region
• Lateral region
• Anterior to Posterior
– Anterior Lobe
– Primary Fissure
– Posterior Lobe
– Flocculonodular lobe
Cerebellar Peduncles
• Inferior
Cerebellar Peduncles
• Middle


Cerebellar Peduncles
• Superior
Cerebellar Peduncles
• Inferior
Functional Anatomy
• Types of Movements
Fine Movement
Balance
Gross Movement
Cerebrocerebellum
Fine Movement
• Lateral Hemispheres
Cerebrocerebellum Pathways
Cerebral
Cortex
Thalamus
Corticospinal and
corticobulbar
tracts
DCN
Rubrospinal
tract
Red Nucleus
Pons
Cb
Cerebrocerebellar Function
Distal Control
Planning
Coordination
Rhythm
Spinocerebellum
• Vermal region
• Paravermal region
Vermal
• Spinal cord
• Vestibular N
• Auditory + Vestibular
 BS
Vermal
• Vestibular and Reticular N
• Motor Cortex
Vermal - function
Paravermal
Spinal Cord
Motor Cortex
Red Nucleus
Vestibulocerebellum
Vestibulocerebellum
• Vest. Apparatus
• Vest. N.
• Vestibular N.
Vestibulocerebellum - Function
Cerebellar Disorders
• Side
• Tone
Ataxia
• Truncal
• Limb and Gait
• Hand
Vestibulocerebellum
• Balance
• Eye movement
Spinocerebellar Lesions
Vermal
Spinocerebellum - Paravermal
Limb Ataxia
• Dysdiadochokinesia
• Dysmetria
• Action tremor
• Difficulties with time
intervals
Cerebrocerebellum
• Dysarthria
• Hand ataxia