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Chapter 14: Motor System

Chris RordenUniversity of South CarolinaNorman J. Arnold School of Public HealthDepartment of Communication Sciences and DisordersUniversity of South Carolina

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Cortical Level

Prefrontal Cortex Responsible for manipulating

discrete and skilled voluntary movements through planning and innervation of muscles

Refers to highly conscious planning and sequencing

Site of reasoning, thinking, planning

Primary Sensory (parietal)Primary Motor (frontal)

Premotor (frontal)

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Sensorimotor Cortex Areas (1)

Premotor Cortex 30% of Motor Fibers Info from thalamus,

cerebellum, basal ganglia Has some skilled patterns

which are well learned Lesion(s) in the inferior

premotor cortex in the left hemisphere is often associated with verbal apraxia

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Sensorimotor Cortex Areas (2)

Primary Motor Cortex 30% of motor fibers 2% from Betz Cells which are

large to support long axons Corticospinal tract – (superior

2/3) Voluntary Movements of muscles controlled via spinal nerves.

Corticobulbar tract – (inferior 1/3) Facial and Associated Muscles – project to cranial nerve nuclei.

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Sensorimotor Cortex Areas (2)

Primary Sensory Cortex40% of motor fibers

– Project through motor cortex with modulation of sensory information

– Corticopontine tract (pons)

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Physiology of Motor Cortex

Highly Organized in Form of Homunculus

Discovered by Penfield and Roberts who used electrical stimulation of cortex on patients in surgery

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Corticospinal Tract– From upper two thirds of primary motor cortex, premotor cortex and

sensory cortex– Through Corona Radiata to Internal Capsule and Pes Pedunculi in the

Midbrain Corticobulbar Tract

– From lower third of motor cortex and adjacent area to corona radiata through internal capsule, pes pedunculi across midline to lower cranial nuclei

– Crossed: oculomotor, abducens, trigeminal, facial, vagus, glossopharyngeal and hypoglossal

– Uncrossed: trochlear– Some duplication of tracts offers redundancy

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Pyramidal Tract Fibers

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Internal Capsule,Posterior Limb

Lateral Corticospinal Tract

Pyramid

Internal Capsule,Anterior Limb

Corona Radiata (fibers tracts between IC and cortex)

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Path of upper motor neurons

Lateral: Skeletal Muscle Fingers, Toes, ForearmAnterior: Axial and Girdle muscles

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Clinical Considerations

Lesions in corticospinal fibers result in spastic hemiplegia

Lesions in corticobulbar fibers result in paralysis of facial, lingual, palatal and laryngeal muscles. More bilateral innervation causes less paralysis

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Clinical Considerations

Upper Motor Neuron symptoms– Flaccid followed by spastic

hemiplegia– Increased Muscle Tone– + Babinski Sign– Hyperreflexias– Loss of Abdominal Reflexes– Alternating Hemiplegia (Some

Fibers that are crossed and uncrossed)

Normal reflex

Negative Babinski

Abnormal

Positive Babinski

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Clinical Considerations

Lower motor neuron symptoms– Damage to LMN eliminates the function of the

motor unit– Lesion affecting the LMN causes weakness of

muscles and reduces tendon reflexes– Muscle tone is flaccid– Can be seen in muscular dystrophy and

myasthenia gravis– Absent or greatly reduced Babinski