6. Control of Movements

Hierarchy of Control

1. Planning via cortex

2. Equilibrium via mid-brain

3. Posture via brainstem

4. Execution via spinal cord

Voluntary and Involuntary movements require?

Utilization of motor end unit to cause contraction

Voluntary movements are

Learned behaviors/movements

Involuntary movements are

Controlling body posture

Descending Spinal Pathways

Lateral - hands voluntary movement of distal limb

Ventromedial - controls posture

Corticospinal Tract

Lateral Pathway

Motor nerve > UMN> Mid-brain> Pons>Medulla>Spinal cord

Lesions of the corticospinal tract

Cause inability to manipulate the lips and tongue; deficit in forelegs; conscious proprioception deficit, spastic paralysis

Rubiospinal Tract

Lateral pathway

Red nucleus> Lateral reticular nucleus>Lateral white column of spinal cord> interneurons throughout spinal cord - mainly cervical

Lesion of the Rubiospinal Tract

Results in ataxia & impaired movement of distal limb; precision and grasp impaired

Reticulospinal Tract

Ventromedial pathway

2 tracts

Medually reticulospinal > reticular formation (medulla)

Pontine reticulospinal > reticular formation ( pons)

Medullary Reticulospinal Tract

Descends bilaterally in lateral funiculus

Controls flexor motor neurons

Inhibits Pontinue Reticulospinal tract

Pontine Reticulospinal Tract

Descents ispsilaterally in the anterior funiculus

Controls axial & extensor motor neurons

Inhibits Medullary Reticulospinal Tract

Lesion of the Reticulospinal Tracts

Lack of anticipatory adaptation; increased reflex activity; impaired motor movement; abnormal posture

Vestibulospinal Tract

Ventromedial pathway

Vestibular nuclei > interneurons w/i caudal gray horn of spinal cord

Part of Extrapyramidal system

Input on reflex & antigravity muscle tone

Lesion of the Vestibulospinal Tract

Lost of antigravity muscle tone; posture destabilization, vestibular axatia

Tectospinal Tract

Ventromedial pathway

Superior colliculus > Tectum > Reticular foramen > Caudal gray of spinal cord

Brainstem houses

Motor & sensory nuclei

Function of Brainstem

Motor & sensory functions of the face and head - respiration, cardio, GIT, equilibrium, eye movements

Central Pattern Generators (CPG)

Specific repeatable motor output without rhythmic input - running, walking, swimming

What CPG is modulated by the brainstem?

Breathing, swallowing, chewing, & some eye movement

What CPG is modulated by the spinal cord

Walking, trotting, cantering, protecting motions

Components of Cerebral Cortex

Primary & Secondary Motor Cortex

Primary Motor Cortex

Modulate discrete powerful movement

Premotor area controls patterns of movement

Secondary Motor Cortex

Modulate bilateral movement & fixation movements

Utilize corticospinal & corticobulbar pathways

Motor Cortexes receive

Somatosensory

Frontal

Audio & visual inputs

Within the Cerebellum & basal ganglia

Basal Ganglia

Interconnected nuclei

Stratium > largest portion

Straium

Largest part of the basal ganglia

Caudate nucleus & Putamen

Gross movement initiation & visual limb placement

Stratium Afferent Fibers

Premotor & supplemental motor areas of the cortex, somatosensory cortex & substantia nigra

Stratium Efferent Fibers

Globus pallidus > Cortex

Globus pallidus

2 segments - internal & external

Motor relay & tonic background contractions

Internal Segment (GPi)

Inhibitory output > Thalamus > Cortical activity influence (efferent)

External Segment (GPe)

Receive input from Straium & projects to Subthalamus nucleus (afferent)

Subthalamic nucleus

Small

Deep w/i nucleus

Role in motor control - receive input from GP

Substantia Nigra

2 Portions - Pars Compacta, Pars Reticulata

Pars Compacta (SNc)

Produces dopamine - crucial in motor control

Pars Reticulata (SNr)

Output pathway of Basal ganglia

Send inhibitory signal to Thalamus

Thalamus

Conntected to B.G,

Relay site between B.G. and Cortex

Influence motor & cognition > modulated via dopamine

The Thalamus is associated with what conditions?

Parkingson’s, Huntington’s, & Dystonia

Due to neurotransmitter inbalance

Dopamine

Substantia nigra > Caudate nucleus

Acetycholine

Cortex > Putamen > Caudate nucleus

GABA

Caudate > Putament > Globus pallidus & Substantia nigra

How do the Thalamus & Cortex communicate

Thalamus > Basal Ganglia > Cortex (inhibitory signal)

Cortex > Pons> Cerebellum > Thalamus (excitatory signal)

Lesions of the Basal Ganglia

Contralateral signs

Lesions of the Cerebellum

Ipsilateral signs

Disorders of the Basal Ganglia

Bradykenesis, rapid alternating movements, tremor, postural abnormality, gait disorder

Function of Cerebellum

Comparison of cortical will to the body via ipsilateral spinocerebellar tracts

Why is the Cerebellum called “The great comparator”

Advises how much, how many, how fast based on comparison to muscle tenstion, joint position & tone; sends revised signals

Yellow Star Thistle

Consumption for >30d leads to Nigropallidal Encephalomalacia in equine

Nigropallidal Encephalomalacia

Fatal neurodegenerative disease in equine, due to Yellow Star Thistle consumption