Motor System Lecture Notes PDF

Motor system  Objectives: After studying this lecture, the students should be able to: 1. Describe how skilled movements are planned and carried out. 2. Identify the motor cortex. 3. Describe motor tracts (pyramidal and extrapyramidal). 4. Discuss the functions of the cerebellum & basal...

Motor system  Objectives: After studying this lecture, the students should be able to: 1. Describe how skilled movements are planned and carried out. 2. Identify the motor cortex. 3. Describe motor tracts (pyramidal and extrapyramidal). 4. Discuss the functions of the cerebellum & basal ganglia.  MOTOR CORTEX  The motor cortex is divided into three subareas: 1. The primary motor cortex. 2. The premotor area. 3. The supplementary motor area. The primary motor area PMC : 1. Located within the precetral gyrus.  Topographically organized. The degree of representation is proportional to the discreteness (number of motor unit) of movement required of the respective part of the body. (Face and fingers have large representative)(motor homunculus).  The representation is upside down.  Innervate the opposite side (upper part of the face is represented bilaterally). Stimulation of a certain part of PMC can cause very specific muscle contractions but not coordinate movement.  Control of movement The inputs converging on motor neurons sub-serve three functions: 1. Bringing about voluntary activity. 2. Adjustment of body posture to provide a stable background for movement. 3. Coordination of the action of the various muscles to make movements smooth and precise. Posture is continually adjusted (even during movement). Movement is smoothed and coordinated by the cerebellum. There are two types of motor output: 1. Reflexive (involuntary). 2. Voluntary. A subdivision of reflex responses, rhythmic movements such chewing, swallowing, scratching, and walking (involuntary could be adjusted voluntarily). Planning of movement: This is done by the cortex (association area), the basal ganglia and the cerebellum (lateral portions) The basal ganglia and cerebellum funnel information to the premotor and motor cortex. The cerebellum helps to sequence the motor activities and also monitors and makes corrective adjustments in the body’s motor activities while they are being executed.  MOTOR FUNCTION  There are two parallel systems of descending pathways originate in the cerebral cortex (upper motor neuron):  The pyramidal (corticobulbar and corticospinal tracts):  They terminate either in the brainstem (corticobulbar) or spinal cord (corticospinal) and are involved in the control of motor functions of the body.  The extrapyramidal system: Descending tracts concerned with motor function other than the pyramidal (indirect motor pathway). Descending Spinal Pathways pyramidal system  Direct: Mainly controls muscle that make precise movement (skillful).  Cross at the medulla (pyramidal decussation = 80% of corticospinal which innervate the distal musles) the remaining 20% control the proximal muscles (trunk). After that directly synapse with lower motor neurons in brainstem or spinal cord. Descending Spinal Pathways extrapyramidal system Indirect  Rubrospinal, reticulospinal. Tectospinal and vestibulospinal.  The basal ganglia and the thalamus affect these descending tracts.  The extrapyramidal pathways set the postural background needed for performance of skilled movements, control subconscious gross movements and control muscle tone. Summary of control of movement Planning of movement: basal ganglia and cerebellum as well as some cortical areas (association area). Execution of voluntary movement: pyramidal tract for skillful movement whereas the extrapyramidal tract helps in providing the necessary background for performance of skillful movement and subconscious gross movement like swinging of the arms during walking. Coordination of movement: (the cerebellum).  Upper motor Lower motor neuron neuron Cell Cortex of the Grey matter of the body brain spinal cord and brain stem Synapse With the lower With the muscle motor neuron Classifie Classified Divided into alpha d according to the and gamma. pathway they travel in (cortico- spinal and Lower motor neuron lesion Upper motor neuron lesion  Lesion at the anterior  Lesion above the anterior horn cells or below it. horn cells.  Flaccid paralysis  Spastic paralysis or  Hypotonicity. paresis.  Hyporeflexia or  Hypertonicity. areflexia.  Hyperreflexia.  fasiculation.  Clonus.  Muscle atrophy.  Positive Babinski sign.