Motor system includes

Transcription

1 Motor system includes Muscles & Peripheral nerves Motor Tracts Corticospinal [Pyramidal](skillful Voluntary movement) Corticobulbar and Bulbospinal [Extrapyramidal] Basal Ganglia (regulator) Cerebellum (regulator) 2 Cerebral CEREBRAL Cortex Cerebral CORTEX Cortex Corticospinal tracts BASAL GANGLIA Corticobulbar tracts THALAMIUS BRAIN STEM CEREBELLUM Bulbospinal tracts SENSORY INPUT SPINAL CORD FINAL COMMON PATH

2 MOTOR CORTEX Is divided into three subareas, each of which has its own topographical representation of muscle groups and specific motor functions: (1) the primary motor cortex (2) the premotor area (3) the supplementary motor area THE PRIMARY MOTOR CORTEX This area is the same as area 4 in Brodmann s classification of the brain cortical areas with higher degrees of representation of the different muscle areas as mapped by Penfield and Rasmussen Note that more than one half of the entire primary motor cortex is concerned with controlling the muscles of the hands and the muscles of speech.

3 SUPPLEMENTARY MOTOR AREA In general, this area functions in concert with the premotor area provide body-wide attitudinal movements, fixation movements of the different segments of the body positional movements of the head and eyes as background for the finer motor control of the arms and hands by the premotor area and primary motor cortex. PREMOTOR AREA premotor cortex, basal ganglia, thalamus, and primary motor cortex constitute a complex overall system for the control of complex patterns of coordinated muscle activity.

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5 Degree of representation of the different muscles of the body in the motor cortex. More than one half of the entire primary motor cortex is concerned with controlling the muscles of the hands and the muscles of speech DESCENDING TRACTS TWO MAJOR GROUPS 1. CORTICOSPINALOR PYRAMIDAL TRACTS 2. EXTRAPYRAMIDAL TRACTS

6 PYRAMIDAL TRACTS The corticospinal tract originates: 30% from the primary motor cortex, 30% from the premotor & supplementary motor areas, 40% from the somatosensory areas posterior to the central sulcus Large myelinated fibers originate from giant pyramidal cells The majority of the pyramidal fibers then cross in the lower medulla to the opposite side and descend into the lateral corticospinal tracts 80% to 90% Anterior or ventral corticospinal tract is formed by uncrossed fibers are primarily concerned with the control of fine movements that require dexterity.

7 EXTRAPYRAMIDAL MOTOR TRACTS Originate in the midbrain and brain stem regions If the pyramidal tracts of an experimental animal are cut, electrical stimulation of the cerebral cortex, cerebellum, and basal nuclei can still produce movements. The term extrapyramidal motor system is widely used in clinical circles to denote all those portions of the brain and brain stem that contribute to motor control but are not part of the direct corticospinal-pyramidal system. Types of motor activities Voluntary movements. Reflex movements. Rhythmic motor activity. 15

8 Levels of motor control Cerebral cortex Brain stem Spinal cord and cranial motor nuclei. 16 MOTOR UNIT

9 Types of muscle fibers Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron) Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by γ - motor neuron) Types of motor neuron α motor neuron γ - motor neuron

10 MUSCLE SPINDLE (INTRAFUSAL FIBERS) MUSCLE EXTRAFUSAL FIBERS MUSCLE INTRAFUSAL FIBERS

11 Nuclear bag fiber Muscle spindle Nuclear chain fiber Sensory innervations of muscle spindle Ia nuclear bag & nuclear chain fibers II nuclear chain fibers Motor supply γ motor neuron Dynamic & Static TRANSVERS SECTION OF SPINAL CORD

12 Reflex Definition Components of reflex arc Receptor Afferent pathway Center Efferent pathway Effector organ Components of reflex arc

13 Classification of reflexes Monosynaptic or stretch reflex or tendon jerk eg. Bicep jerk tricep jerk, supinator jerk knee jerk, ankle jerk Polysynaptic reflex eg. Withdrawal reflex Abdominal reflex Plantar reflex Visceral reflex eg. Micturation, defecation reflex KNEE JERK MONOSYNAPTIC REFLEX

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15 POLYSYNAPTIC REFLEX WITDRAWEL REFLEX - POLYSYNAPTIC REFLEX

16 DIFFERENT REFLEXES SHOWN

17 Motor cortex corticospinal (pyramidal tract) Upper motor neuron (pyramidal & extrapyramidal tracts) Lower motor neuron Difference between upper & lower motor neuron lesion (UMNL & LMNL)

18 MOTOR TRACTS

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20 CORTICOSPINAL (PYAMIDAL ) TRACT 40

21 FUNCTIONS 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. 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. 42 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. 43

22 DIFFERENCE BETWEEN UPPER & LOWER MOTOR NEURON LESION UMN LESION Paralysis affect movement rather than muscles Muscle wasting is only from disuse, therefore slight. Occasionally marked in chronic severe lesions. Spasticity of claspknife type. Muscles hypertonic. LMN LESION Individual muscle or group of muscles are affected. Wasting pronounced. Flaccidity. Muscles hypotonic. Tendon reflexes increased. Clonus often present. Superficial reflexes diminished or modified. Abdominal reflex absent. Babinski s sign +ve, Increased jaw jerk. Tendon reflexes diminished or absent. Superficial reflexes often unaltered.

23 Includes Cortical Motor Areas 1. Primary Motor Cortex (M-I) 2. Supplementary Motor Area (M-II) 3. Premotor Cortex (PMC) 4. Frontal Eye Field Area 5. Broca s Area for speech 46 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. Premotor and supplementary motor cortex also project to primary motor cortex and is involved in coordinating & planning complex sequences of movement (motor learning). 47

24 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 as 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:- Is used in execution of skilled movements also in codes the direction, force and velocity of movements. 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. 49

25 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. Lesions: Produces awkwardness in performing complex activity like bimanual coordinated activity. 50 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. 51

26 Location: Premotor Cortex (PMC) 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. 52 Lesion: It results in re-emergence of suckling and grasp reflex in adults. Its lesion do not cause 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.

27 EXTRAPYRAMIDAL SYSTEM 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. 55