1 Chapter 14: Motor System Chris Rorden University of South Carolina Norman J. Arnold School of Public Health Department of Communication Sciences and Disorders University of South Carolina

2 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)

3 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

4 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.

5 Sensorimotor Cortex Areas (2) Primary Sensory Cortex 40% of motor fibers –Project through motor cortex with modulation of sensory information –Corticopontine tract (pons)

6 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

7 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 Cranial Nerves Spinal Nerves

8 Pyramidal Tract Fibers Internal Capsule, Posterior Limb Lateral Corticospinal Tract Pyramid Internal Capsule, Anterior Limb Corona Radiata (fibers tracts between IC and cortex)

9 Path of upper motor neurons Lateral: Skeletal Muscle Fingers, Toes, Forearm Anterior: Axial and Girdle muscles

10 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

11 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

12 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