The Motor System.pptx

THE MOTOR SYSTEM INTRODUCTION, ORGANISATION AND RELATION TO THE BRAIN STEM.  Motor System Motor system of brain exist to translate Thought, sensation, emotions into Movements Movement is the end product of Number of control systems Extensive interactions 8...

THE MOTOR SYSTEM INTRODUCTION, ORGANISATION AND RELATION TO THE BRAIN STEM.  Motor System Motor system of brain exist to translate Thought, sensation, emotions into Movements Movement is the end product of Number of control systems Extensive interactions 8/18/24 motor system 2  Nature of Movements In most forms of movements Motion occurs at joints Where two or more bones come together To form a near frictionless pivot Muscles are arranged so that Ends are attached on opposite sides of joint which acts as a fulcrum 8/18/24 motor system 3  Nature of Movements Usually movement of one joint Require fixation of next joint By other muscles Example Movement of forearm Muscles of shoulder Contract to fix the humerus 8/18/24 motor system 4  Neural centers for control of movements Motor cortex Basal ganglia Brain Cerebellum Stem Spinal Skeletal Cord muscles 8/18/24 motor system 5 THE MOTOR SYSTEM Spinal Cord A series of interconnections Has developed in spinal cord Link motor neurons of muscles that Commonly work together All the motor pathways ultimately Converge on a series of simple circuits Link each skeletal muscle with spinal cord From H.T. Sherrief Book of Physiology 8/18/24 motor system 7 Spinal Cord Sensory neurons Carry impulses from muscles Connect to motor neurons Transmit impulses back to muscles This forms a closed loop For regulation of each muscle These circuits May function autonomously From H.T. Sherrief Book of Physiology In simple reflexes 8/18/24 motor system 8  Spinal Cord However, their activities Controlled by centers at higher levels From these centers Tracts descend to spinal cord Giving off fibers at all levels From H.T. Sherrief Book of Physiology 8/18/24 motor system 9 Brain Stem Composed of Midbrain, pons & medulla oblongata Pre spinal integrating center Receive signals from all higher centers Processes them for Transmission to spinal cord 8/18/24 motor system 11 THE BRAINSTEM Basal Ganglia Superimposed on The upper end of brain stem Receives signals from Sensory-motor cortex Processes this information Discharges it into brain stem Provide motor pattern necessary To maintain postural support 8/18/24 motor system 14  Sensory-motor Cortex Highest level in the motor command system Origin of Corticospinal tracts Corticobulbar pathways 8/18/24 motor system 17 THE CORTICOSPINAL TRACT  Cerebellum Interconnected with all levels Acts as an overall Coordinator of motor activity Receives signals from Cerebral cortex Muscles, tendons, joints, skin Visual, auditory, vestibular organs 8/18/24 motor system 21  Cerebellum All this enormous influx Analyzed and integrated by cerebella cortex Efferent fibers pass to Thalamus, red nucleus, vestibular nucleus, reticular formation Cerebellum coordinates Activity of motor circuits at all levels 8/18/24 motor system 22 MOTOR UNIT A motor unit is defined as a single motoneuron and the muscle fibers that it innervates. The number of muscle fibers innervated can vary from a few fibers to thousands of fibers, depending on the nature of the motor activity. Motor Unit Alpha motor nerve, Axon, muscle fibres Number of muscle fibre per one nerve varies 8/18/24 motor system 24  Types of Motor Units Type I (slow twitch) Small in diameter High capillary density Low glycolytic enzymes 8/18/24 motor system 25  Type I Motor Units High mitochondria content High oxidative enzyme content Resistant to fatigue Suited for weak sustained contractions 8/18/24 motor system 26  Type II Motor Units Type II a (fast twitch oxidative) Small in diameter High capillary density High mitochondria content High oxidative enzyme content Has high glycolytic enzymes as well Resistant to fatigue 8/18/24 motor system 27  Type II b Motor Units Fast twitch glycolytic Larger diameter High content of glycogen & glycolytic enzymes Few mitochondria Fatigue easily Suited for brief powerful contractions 8/18/24 motor system 28  Motor Cortex Localization of functions Experimental stimulation in monkeys & man Cause contraction of groups of muscles on opposite side All parts of the body - represented on the motor cortex Hand, fingers, thumb Have the largest representation 8/18/24 motor cortex 30  Motor Cortex Motor cortex not uniformly spread in proportion to muscle size Muscles controlling thumb Are used in many skilled movement Have large representation 8/18/24 motor cortex 32  Motor Cortex Muscles controlling tongue, larynx Used for talking and singing Also have large representation That is; It is skill and finesse That is reflected in the cortical representation 8/18/24 motor cortex 33  Layers of Cerebral Cortex I Molecular layer II outer granular layer III outer pyramidal IV inner granular V inner pyramidal VI polymorphic fusiform 8/18/24 motor cortex 34  Layers of Cortex (I) Molecular layer Dentrites of pyramidal and fusiform cells, axons of stellate cell (II) Small pyramidal cells and stellate cells (III) Pyramidal cells 8/18/24 motor cortex 36  Layers of Cortex (IV) closely packed stellate cells (V) stellate cells, giant cells of Betz (VI) Fusiform cells, pyramidal cells 8/18/24 motor cortex 37  Afferents to Motor Cortex Somatic sensory inputs Skin, joints,muscles Relayed to cortex Via ventrobasal nucleus of thalamus Provide the cortical cells the sensory cues required to guide and direct movements 8/18/24 motor cortex 38  Afferents to Motor Cortex From opposite cerebral cortex Via corpus callossum Coordination of motor activities on two side of the body 8/18/24 motor cortex 39  Afferents to Motor Cortex From cerebellum Through red nucleus, thalamus, Closed loop linking cerebellum and motor cortex Provide signals necessary for coordination between Motor cortex, basal ganglia & cerebellum 8/18/24 motor cortex 41  Afferents to Motor Cortex From Ipsilateral cortical area Cortico-cortical association fibres Indirectly via sub cortical center Though the basal ganglia 8/18/24 motor cortex 43  Afferents to Motor Cortex Other area Visual cortex Important for visually guided movements 8/18/24 motor cortex 44  Afferents to Motor Cortex Distributed to layers I to IV From somatic sensory Relay in thalamus End in layer IV Cerebellar inputs also end in layer IV Non specific fibers from thalamus end in layer I Give collaterals to other layers 8/18/24 motor cortex 45  Afferents to Motor Cortex The 2 deepest layer of cerebral cortex receive little direct sensory inputs Influenced by the discharges from the other 4 layers 8/18/24 motor cortex 48  Output From Motor Cortex Pyramidal (direct cortico spinal tract) Consist of neurons whose cell bodies are in cerebral cortex Axon pass through pyramid - medulla - spinal cord 1 million fibres in each tract 8/18/24 motor cortex 49  Output From Motor Cortex 20% of fibers leaving cortex project as far as spinal cord corticospinal 80% project to sub-cortical nucleus brain stem Corticobulbar 8/18/24 motor cortex 50  Origin of Corticospinal Tracts Corticospinal and corticobulbar tracts Originate in all areas of motor – sensory cortex 30% of fibers come from area 4 30% from area 6 (pre-motor area) 40% from parietal lobe SI, SII (area 3, 1, 2) 8/18/24 motor cortex 51  Origin of Corticospinal Tracts On the way to spinal cord axons give collaterals Thalamus, red nucleus, brain stem, basal ganglia 8/18/24 motor cortex 52  Pyramidal Decussation 75 - 90% of fibers Cross over to opposite side Run in dorsolateral quadrant of spinal cord Lateral corticospinal tract 10 - 25% of fibers Run uncrossed anteromedially This as a rule end in cervical & thoracic area 8/18/24 motor cortex 53  Axonal Ending CST axons make Synaptic contacts with CST inter-neurons Which the synapse with motor neuron Flexors + Extensors - 8/18/24 motor cortex 55  Axonal Ending Monosynaptic connections with alpha motoneurons CST Man & primates Corticospinal tract Excitatory to flexors Inhibitory to extensors Flexors + Extensors - 8/18/24 motor cortex 56  Other Output Fibers The motor cortex gives other output fibers Axons from the giant cells of Betz Send short collaterals to Deep regions of cerebrum Midbrain These provide lateral inhibition Sharpen boundaries of excitatory signals 8/18/24 motor cortex 57  To Basal Ganglia Motor cortex Basal Fibers from motor cortex ganglia Pass to basal ganglia Thalamus Caudate nucleus Putamen Brain stem Spinal cord 8/18/24 motor cortex 59  To Basal Ganglia Motor cortex Basal From the BG ganglia Feedback to motor Thalamus cortex Relayed to brain stem Relay to spinal cord Brain stem Spinal cord 8/18/24 motor cortex 60  To Red Nucleus Fibers from motor cortex Collaterals to red nucleus Then transmitted to Spinal cord Rubrospinal tract 8/18/24 motor cortex 61  To Cerebellum Motor Fibers from motor cortex cortex Give collaterals to cerebellum Cerebellu Pontocerebell m a Olivocerebella Spinal cord 8/18/24 motor cortex 62 Brain Stem  Functional Anatomy Brain stem in the physiological sense is comprised of Medulla, Pons, Mesencephalon (midbrain) Neuronal circuits within this area control many physiological functions BP, respiration, body temp, sleep & wakefulness, GIT 8/18/24 brain stem 64  Functional Anatomy Control of physiological functions Stereotyped movements of the body Equilibrium and balance Eye movement In addition Reticular formation (RF) and Vestibular Nuclei Important components of motor control system 8/18/24 brain stem 65  Functional Anatomy Serves as a way station for Command signals from higher neural centres that command the brain stem to Initiate, modify specific control functions throughout the body 8/18/24 brain stem 67  Brain Stem Motor centres Red nucleus Lateral vestibular nucleus (Deiter’s nucleus) Certain parts of reticular formation in pons and medulla oblongata 8/18/24 brain stem 68  Motor centres Have efferent fibres that influence motor pathways in Spinal cord Cranial motor nerves Form part of efferent pathways from higher motor centres 8/18/24 brain stem 69  The Red Nucleus Lie in the midbrain Receive signals from the Motor cortex, Cerebellum Project signals to the spinal cord: Rubro-Spinal Tract (RUST) Stimulation of the system Excitation of Flexors Inhibition of extensors 8/18/24 brain stem 70  Red Nucleus Red RUST crosses over the nucleus opposite side Runs through the spinal cord close to CST RUST Connect to MN Inhibit extensors Excite flexors - Extensors + Flexors 8/18/24 brain stem 71  Reticular Formation Brain stem reticular formation Two areas with motor control activity Pontine reticular nucleus Medullar reticular nucleus Give rise to reticulospinal tracts 8/18/24 brain stem 72  Reticular formation The two sets of nuclei Function antagonistically to each other Pontine exciting the Antigravity muscles Medullary inhibiting them 8/18/24 brain stem 73  Pontine Reticular Nucleus Pontine reticular Located in the pons, Nucleus extends to midbrain Transmit excitatory signals down the spinal cord Pontine (medial) Reticulospinal tract (M-REST) Terminate on MN Excite extensors (antigravity) + Extensors Inhibit flexors M- REST - Flexors 8/18/24 brain stem 74  Pontine Reticular Nucleus Pontine reticular Pontine (medial) Nucleus Reticulospinal tract (M- REST) Also excite Axial muscles which support body against gravity Muscle of the vertebral Extensor muscles of limbs + Extensors M-REST - Flexors 8/18/24 brain stem 75 Pontine Reticular Nucleus Cells of the Pontine Cerebral cortex, R.N have basal ganglia, cerebellum High degree of Vestibular excitability N., Inhibitor (inherent) Cerebellum Excitatory y signals signals ++ -- Excitability is held Pontine R.N in check by Inhibitory signals Cerebral cortex Basal ganglia Muscle ++ Cerebellum spaciticity α MN, γ MN excitability 8/18/24 brain stem increases 76 Pontine Reticular Nucleus Receive excitatory Cerebral cortex, signals from basal ganglia, cerebellum Vest. Nucleus Vestibular Cerebellum (deep N., Cerebellum Inhibitor nucleus) Excitatory y signals signals ++ -- If unopposed by Pontine R.N medullary syst Causes powerful excitation of antigravity muscles ++ Muscle SPACITICITY spaciticity α MN, γ MN excitability 8/18/24 brain stem increases 77  Medullary Reticular Nucleus Medullar reticular Located in the reticular area Nucleus of medulla Transmit inhibitory signals down the spinal cord Medullar (lateral) Reticulospinal tract (L-REST) L-REST Connect to MN Inhibit extensors - Extensors Excite flexors + Flexors 8/18/24 brain stem 78  Medullar Reticular System Pontine R.N CST, RUST, Receive strong imputes by other motor pathways way of collaterals from CST, RUST, other motor pathways ++ These normally activate the Medullar R.N medullar inhibitory system This counteracts the excitatory effects of Pontine reticular system -- ++ α MN, γ MN 8/18/24 brain stem 79  Medullar Reticular System Medullar R.N Can also receive Pontine R.N inhibitory imputes by CST, RUST, other motor way of collaterals from pathways CST, RUST, cerebellum ++ These normally inhibit -- medullar inhibitory CST, RUST system cerebella When the brain wishes to cause excitation of Pontine reticular system, ++ to facilitate standing α MN,MN 8/18/24 brain stem 80  Vestibular Nucleus Vestibular Nucleus Located in the pons and medullar Project to spinal cord Vestibulospinal tract (VEST) Connect to MN Excite extensors + Extensors Inhibit flexors VEST - Flexors 8/18/24 brain stem 81  Vestibular Nucleus Vestibular Nucleus Provide strong excitatory signals to antigravity muscles Selectively control the excitation of different antigravity muscles To maintain equilibrium and balance in response to + vestibular apparatus VEST Extensors 8/18/24 - Flexors brain stem 82 Brain Stem Motor Effects CST RUST L - REST VEST Flexors excited M- Extensors REST Flexors inhibited inhibited Extensors excited 8/18/24 brain stem 83 LESIONS. Lesions Lesion above midbrain [ A ] Loss of cortical area that inhibit gamma efferent discharge via reticular formation Causes decorticate rigidity Arms flexed and adducted Legs extended  Lesion of mid-level of midbrain [ B ] Leave the pontine, medullary RF as well as the Vestibular nuclei intact Interrupt descending tracts from Cerebral cortex, red nucleus, basal ganglia Medullary inhibitory system non functional Allow full over activity of pontine excitatory system  Development of Decerebrate rigidity (rigidity of antigravity muscles) Muscles of neck, trunk, and extensors of the legs If the brain stem is severed from spinal cord [ C ] Spinal shock develops