Motor System 2024 PDF

Neurophysiology MOTOR SYSTEM University Of Fallujah College Of Medicine Lecture : 7& 8 Stage : second Lecturer :Dr. Mohammed Abdulwahed Al Rawi Department: Physiology Date: 21-1-2025 Motor Areas Pyramidal & Extrapyramidal System  OBJECTIV...

Neurophysiology MOTOR SYSTEM University Of Fallujah College Of Medicine Lecture : 7& 8 Stage : second Lecturer :Dr. Mohammed Abdulwahed Al Rawi Department: Physiology Date: 21-1-2025 Motor Areas Pyramidal & Extrapyramidal System  OBJECTIVES List the function of various parts of motor cortex. Enumerate the function of pyramidal and extrapyrmidal tracts. Define bulbar and pseudobulbar palsy. Differentiate between upper and lower motor neuron lesion. Explain Babiniski reflex  Components of motor neurons Upper motor neuron (corticospinal & corticobulbar). Starts from motor cortex and ends in 1. Cranial nerve nucleus (corticobulbar). 2. Anterior horn of spinal cord in opposite side(corticospinal tracts). Lower Motor Neuron Starts from anterior horn of spinal cord and ends in appropriate muscle of the same side. eg. All peripheral motor nerves.  Cortical Motor Areas Includes 1. Primary Motor Cortex (M-I) 2. Supplementary Motor Area (M-II) 3. Premotor Cortex (PMC) 4. “Voluntary” Eye Movement Field 5. Broca’s Area for speech  Motor cortex Primary motor cortex ( M1) Premotor area (PMA) Supplementary motor area (SMA) Note: All the three projects directly to the spinal cord via corticospinal tract.  Primary Motor Cortex (M-I) Location :- Immediately anterior to the central sulcus and extends to the medial surface of hemisphere also known as Broadmann’s area 4 is a motor homunculus. Description: Body is represented in a crossed way (contralateral)& up side down and stretched on the medial surface where pelvic and leg muscles are represented. Hand and mouth has a greater area of representation and is large because of frequently used (skill). - It controls the musculature of the opposite side of the body. - Face area is bilaterally represented. Functions:- 1. Is used in execution of skilled movements also in codes the direction, force and velocity of movements. 2. Facilitation of stretch reflex Lesions:- Pure M-I lesions are rare. May have contra lateral weakness in distal muscle (fingers). Ability to control fine movements is gone. Ablation of M-I alone cause hypotonia not Spasticity.  Supplementary Motor Area (M-II) Location: Found on both in lateral and medial aspect of the frontal lobe. It extends from cingulate sulcus on the medial side to reach premotor cortex on the lateral surface of the brain. Function: It works together with premotor cortex. Involved in programming of motor sequences. It function in mental rehearsal of movements before performing a complex motor functions.  With premotor cortex it translates the desire to perform a motor task into a series of motor command that will do the task. Lesions: Produces awkwardness in performing complex activity like bimanual coordinated activity.  Premotor Cortex (PMC) Location: Broadmann’s area 6. It lies immediately anterior to primary motor cortex. It is more extensive than primary motor cortex (about 6 times) Functions: It works with the help of basal ganglia, thalamus, primary motor cortex, posterior parietal cortex. It plays role in planning and anticipation of a specific motor act. Lesion: It results in re-emergence of suckling and grasp reflex in adults. Its lesion does not case paralysis but only slowing of the complex limb movement. Lesion may result in loss of short-term or working memory. When damaged with supplementary cortex it may result in APRAXIA.  Broca’s Area and Speech Located in the premotor area lying immediately anterior to the primary motor cortex. Damage to it does not prevent a person from vocalizing, but it does make it impossible for the person to speak whole words only simple word such as “no” or “yes.”  THE MOTER TRACTS The motor tracts (also called the descending tracts) are divided into two groups of tracts; the pyramidal and the extrapyramidal. The pyramidal tracts refer to: (cortico-spinal, cortico-nuclear& cortico- bulbar tracts)  Corticospinal Tract Origin – Sensory cortex, primary Motor Cortex, premotor & supplementary cortex (40%) (30%) (30%) Internal Capsule Cerebral Peduncle (midbarain) Pons Medullary Pyramid Pyramidal Decussation Lat.Cross & Vent. Uncross White matter in spinal cord Ant. Horn of spinal cord through a interconnection α motor neuron of opposite side pyramidal fibers take one of three courses: 1. 90% of the fibers cross to the opposite side in the motor decussation and descend in the posterolateral column of the spinal white matter as the "lateral corticospinal tract". They terminate on the ventral horn cells mainly through interneurons, but some fibers terminate directly on ventral horn cells. 2. 8% of the fibers descend directly in the ventral column of the spinal white matter of the same side as the "ventral corticospinal tract". They cross gradually as they descend in the cervical and upper thoracic segments of the spinal cord to terminate on the ventral horn cells of the opposite side. 3. 2% of the fibers descend directly in the posterolateral column of the spinal white matter as the "uncrossed corticospinal tract". They terminate on the ventral horn cells of the same side.  FUNCTIONS 1. Controls primarily distal muscle which are finely controlling the skilled movements of thumb & fingers on the opposite side. eg. Painting writing, picking up of a small object etc. 2. Facilitation of lower motor neurons and stretch reflex. Effect of lesion: loss of distal motor function in opposite side. Pure corticospinal tract lesion cause hypotonia instead of spasticity. The reason is that pure pyramidal tract lesion is very very rare, and spasticity is due to loss of inhibitory control of extrapyramidal tract. The uncrossed corticospinal tract has the following functions: 1. Provide bilateral innervation of some muscles as the respiratory and abdominal muscles. 2. Gross positioning movements controlled by the supplementary motor area. 3. Help partial recovery of movements after injury of the crossed corticospinal tracts.  THE CORTICONUCLEAR TRACT ORIGIN: From the eye field in the motor and the somatosensory areas. DESTINATION: They terminate on the nuclei of cranial nerves III, IV in the midbrain and VI in the pons on both sides. FUNCTIONS 1. Voluntary conjugate movements of the eye to look at different objects. 2. Facilitate the stretch reflex of the external ocular muscles.  THE CORTICOBULBAR TRACT ORIGIN: From the lower part of the motor and sensory" areas of the cerebral cortex. DESTINATION: They cross to the opposite side to terminate on the nuclei of the cranial nerves V, VII, IX, XI and XII. FUNCTIONS 1. Voluntary movement of muscles in the head and neck. 2. Facilitation of stretch reflex of these muscles ❖ The corticobulbar tract innervates cranial motor nuclei bilaterally with the exception of the lower facial nuclei (which innervates facial muscles below the eyes) and the genioglossus muscle, which are innervated only unilaterally by the contralateral cortex. ❖ Among those nuclei that are bilaterally innervated a slightly stronger connection contralaterally than ipsilaterally is observed. ❖ The corticobulbar tract directly innervates the nuclei for cranial nerves V, VII, IX, and XII. The corticobulbar tract also contributes to the motor regions of cranial nerve X in the nucleus ambiguus.  Components of extrapyramidal system 1. Basal Ganglia 2. Midbrain giving rise to following bulbospinal tracts. A. Rubrospinal tract. B. Vestibulospinal Tract. C. Reticulospinal Tract D. Tectspinal Tract. E. Olivospinal Tract.  Rurospinal tract Red Nucleus in Midbrain Decussation at the level of red nucleus Pass down through Pons & Medulla Occupies the lat. White column of spinal cord Ends in ant. Horn of spinal cord  THE RED NUCLEUS It is located in the midbrain and receives projection fibers from the motor cortex (the corticorubral tract) and collaterals from the corticospinal tract as it passes the midbrain. It also receives projection fibers from the globus pallidus of the basal ganglia. All these fibers synapse in the lower part of the red nucleus which contains giant pyramidal neurons similar to Betz cells. Rubrospinal tract originates from these neurons, cross to the opposite side and descend in the spinal cord very closely anterior to the lateral corticospinal tract. Fibers terminate on the ventral horn cells either directly or through interneurons.  FUNCTIONS OF THE RED NUCLEUS 1. It is a relay station in the corticorubrospinal pathway which acts as an accessory pathway for the corticospinal tracts. This pathway can initiate gross movements. 2. It is inhibitory to the motor neurons and stretch reflex through stimulation of the inhibitory reticular formation of the brainstem. 3. Facilitates flexor muscles (inhibits extensors) antagonist to vestibulospinal tract. Afferent from cerebellum, vestibular apparatus & vestibular nuclei Spinal motor neuron Innervating axial & postural muscles Function : Controls reflexes eg. Postural & righting Control eye movements.  THE VESTIBULAR NUCLEUS OF THE MEDULLA It receives projection fibers from the globus pallidus of the basal ganglia, and gives origin to two descending extrapyramidal tracts; The lateral vestibulospinal tract: Originates from the lateral and inferior vestibular nuclei, descends uncrossed to terminate on the alpha and gamma motor neurons. They mediate some postural reflexes by facilitation of antigravity (extensor) muscles of the leg maintain upright and balanced posture. The medial vestibulospinal tract: Originates from the medial vestibular nucleus, descends on both sides of the spinal cord to terminate on the alpha and gamma motor neurons in the upper cervical cord (C6). It promotes stabilization of head position by innervating the neck muscles, which helps with head coordination and eye movement. Its function is similar to that of the tectospinal tract. The vestibulospinal tracts facilitate the stretch reflex and skeletal muscle tone. The lateral& ventral tecto-spinal tracts Superior & Inferior collicili in midbrain Near Medial longitudinal fasiculus Cervical spinal motor neuron of anterior horn Function: Allow turning of the head in response to visual or Auditory stimuli.  THE TECTUM OF THE MIDBRAIN It receives projection fibers from the globus pallidus of the basal ganglia, and gives origin to two descending extrapyramidal tracts: * The lateral tectospinal tract: Originates from the superior colliculus (the center of visual reflexes), crosses to the opposite side and terminates in the cervical segments of the spinal cord. It is concerned with directing the eye and turning the head towards a light source (visuospinal reflexes). *The ventral tectospinal tract: Originates from the inferior colliculus (the center of auditory reflexes), crosses to the opposite side and terminates in the cervical segments of the spinal cord. It is concerned with turning the head to direct the ears towards a sound source (audiospinal reflexes).  Reticulospinal Tract The reticular formation makes up a central core through much of the brainstem. The reticular nuclei are divided into two major groups: (1) pontine reticular nuclei, and (2) medullary reticular nuclei. These two sets of nuclei function mainly antagonistically to each other, with the pontine exciting the antigravity muscles(the muscles of the neck and trunk and the extensors of the legs) and the medullary relaxing these same muscles. Functions: influence motor functions as for example voluntary & reflex movement and is also responsible for the muscle tone.  The lateral reticulospinal tract: Originates from the inhibitory reticular formation of the medulla. Some fibers cross to the opposite side, but most fibers descend in the same side of the spinal cord. It inhibits the gamma motor neurons, thus inhibiting the stretch reflex and skeletal muscle tone.  The-ventral reticulospinal tract: Originates from the facilitatory reticular formation of the pons. Fibers descend without crossing to terminate on the gamma motor neurons of the ipsilateral side of the spinal cord. It facilitates the gamma motor neurons, thus facilitating the stretch reflex and the skeletal muscle tone.  Olivospinal Tract It arises in the cells of inferior olive of the medulla and is found only in the cervical region of the spinal cord. Function is facilitatory to the stretch reflex and the skeletal muscle tone.  GENERAL FUNCTIONS OF THE EXTRAPYRAMIDAL SYSTEM 1. Mediation of gross movements which involve a group of large muscles. 2. Provides a weaker alternative to the pyramidal system for mediation of some discrete movements. 3. Mediation of fixation and positioning movements which accompany other fine movements. 4. Adjustment of the skeletal muscle tone through facilitation or inhibition. 5. Adjustment of muscle movements to match preset plans to reach a certain target.  Role of the Brain Stem in Controlling Motor Function 1. Control of respiration 2. Control of the cardiovascular system 3. Partial control of gastrointestinal function 4. Control of many stereotyped movements of the body 5. Control of equilibrium 6. Control of eye movements Finally, the brain stem serves as a way station for “command signals” from higher neural centers  Buibar&pseudo-bulbar palsy Bulbar palsy refers to impairment of function of the cranial nerves IX, X, XI and XII, which occurs due to a lower motor neuron lesion either at nuclear or fascicular level in the medulla oblongata or from lesions of the lower cranial nerves outside the brainstem. In contrast, pseudobulbar palsy describes impairment of function of cranial nerves IX- XII due to upper motor neuron lesions of the corticobulbar tracts in the mid-pons. For clinically evident dysfunction to occur, such lesions must be bilateral as these cranial nerve nuclei receive bilateral innervation. Bulbar palsy is an assortment of signs and symptoms, not the name of a precise disease. Symptoms: These include: dysphagia (difficulty in swallowing) difficulty in chewing nasal regurgitation slurring of speech difficulty in handling secretions choking on liquids dysphonia (defective use of the voice, inability to produce sound due to laryngeal weakness) dysarthria (difficulty in articulating words due to a CNS problem) Signs: These include: Nasal speech lacking in modulation and difficulty with all consonants Tongue is atrophic and shows fasciculations. Dribbling of saliva. Weakness of the soft palate, examined by asking the patient to say aah. The jaw jerk is normal or absent. The gag reflex is absent. In addition, there may be lower motor neuron lesions of the limbs. The ocular muscles are spared and this differentiates it from myasthenia gravis. Pseudobulbar palsy is a clinical syndrome similar to bulbar palsy but the damage is located in upper motor neurons, that is the nerves cells come down from the cerebral cortex inervating the motor nuclei in the medulla. This is usually caused by stroke. Upper motor neuron lesion: (also known as pyramidal insufficiency) occur in conditions affecting motor neurons in the brain or spinal cord such as stroke, multiple sclerosis, traumatic brain injury and cerebral palsy. Symptoms: 1. Muscle weakness. A pattern of weakness in the extensors (upper limbs) or flexors (lower limbs), is known as 'pyramidal weakness' 2. Decreased control of active movement, particularly slowness 3. Spasticity: results from the loss of inhibition of motor neurons, causing excessive muscle contraction 4. Clasp-knife response where initial higher resistance to movement is followed by a lesser resistance 5. Babinski sign is present, 6. Increase deep tendon reflex (hyper-reflexia). Lower motor neuron lesion: One major characteristic used to identify a lower motor neuron lesion is flaccid paralysis – paralysis accompanied by loss of muscle tone such as neuropathies. This is in contrast to an upper motor neuron lesion, which often presents with spastic paralysis – paralysis accompanied by severe hypertonia. Symptoms: The extensor Babinski reflex is usually absent. Muscle paresis/paralysis, hypotonia/atonia, and hyporeflexia/areflexia are usually seen immediately following an insult. Muscle wasting, fasciculations and fibrillations are typically signs of end-stage muscle denervation and are seen over a longer time period. Another feature is the segmentation of symptoms - only muscles innervated by the damaged nerves will be symptomatic.  Babinski reflex When a firm tactile stimulus is applied to the lateral sole of the foot, two reflex arcs are stimulated at the same time one through the pyramidal system and the other through the extrapyramidal system. In normal condition, the reflex arc of the pyramidal system suppresses that of the extrapyramidal system and therefore downward bending of the toes is elicited in response to sensory stimuli from the bottom of the feet. However, when the damage occurs to the pyramidal system without involving the extrapyramidal system, the same tactile stimulus to the sole will produce extension of the great toe and fanning outward of other toes. This type of response is called the Babinski sign, which used clinically to detect damage specifically in the pyramidal portion of the motor control systems. The cause of this sign is due to the stimulation of the withdrawal protective type of reflex of the extrapyramidal system unopposed by the damaged pyramidal system.  SUMMARY Motor neurons are divided into upper and lower motor neurons. The motor tracts (also called the descending tracts) are divided into two groups of tracts; the pyramidal and the extrapyramidal.