13 Motor system II Introduction http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Introduction http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg http://images.persianblog.ir/559630_iXFiuRo0.jpg Hierarchic organization of motor system http://www.slideshare.net/drpsdeb/presentations Hierarchic organization of motor system http://www.slideshare.net/drpsdeb/presentations Reflex • Reflex movement – Stereotype (predictable) – Involuntary • Proprioceptive • Exteroceptive • Monosynaptic • Polysynaptic • Monosegmental • Polysegmental http://www.slideshare.net/CsillaEgri/presentations Proprioceptive reflex • Myotatic reflex – Monosynaptic – Monosegmental – Muscle spindle • Homonymous muscle - activation • Antagonist muscle - inhibition • Phasic response (Ia) – Protection against overstretch of extrafusal fibrers • Tonic response (Ia a II) – Maintains muscle tone http://www.slideshare.net/CsillaEgri/presentations http://www.slideshare.net/drpsdeb/presentations http://www.slideshare.net/drpsdeb/presentations Proprioceptive reflex • Inverse myotatic reflex – Monosegmental – Disynaptic/polysynaptic – Golgi tendon organ • Homonymous muscle – inhibition • Antagonist muscle– activation • Protection against muscle damage caused by extensive force http://www.slideshare.net/CsillaEgri/presentations http://www.slideshare.net/drpsdeb/presentations Exteroceptive reflex • Polysynaptic • Polysegmental http://images.slideplayer.com/15/4638059/slides/slide_37.jpg http://www.easynotecards.com/uploads/920/77/1c7a7974_150bb922c9b__8000_00004383.png Subcortical (stem) pathways controlling lower motoneurons Medial system • Axial muscle control • Tr. Vestibulospinalis – Reflex control of balance and postural control • Tr. Reticulospinalis – Muscle tone regulation (postural control) • Tr. Tectospinalis – Coordination of head and eyes movements Lateral system • Distal muscle control • „Reflex“ control of the limbs • Replaced by tr. corticospinalis • Tr. Rubrospinalis • Tr. Rubrobulbaris Fixed action pattern and rhythmic movement • Fixed action pattern (e.g. Swallowing) – Neuronal networks for complex motor activity • Central pattern generator (e.g. Walking breathing) – Neuronal networks generating rhythmic activity – „Spontaneously repeated fixed action patterns“ – No need of feedback • Localization – Walking - lower thoracic and upper lumbar spinal cord – Breathing – brain stem – Swallowing - medulla oblongata/brain stem • Variously expressed voluntary control – Walking (full control) – Breathing (partial control) – Swallowing (limited control) Fixed action pattern and rhythmic movement • Fixed action pattern (e.g. Swallowing) – Neuronal networks for complex motor activity • Central pattern generator (e.g. Walking, breathing) – Neuronal networks generating rhythmic activity – „Spontaneously repeated fixed action patterns“ – No need of feedback • Localization – Walking – brain stem, lower thoracic and upper lumbar spinal cord – Breathing – brain stem – Swallowing - medulla oblongata/brain stem • Variously expressed voluntary control – Walking (full control) – Breathing (partial control) – Swallowing (limited control) Fig. 1. Neural control of locomotion. A) Increments in the intensity of stimulation of the MLR in the high decerebrate cat increased the cadence (step cycles/sec) of locomotion. Adapted from Shik et al. 1966.[22] B) Schematic of the velocity command hypothesis: a command signal specifying increasing body velocity descends from deep brain nuclei via the MLR to the spinal cord and drives the timing element of the spinal locomotor CPG to generate cycles of increasing cadence. Extensor phase durations change more than flexor phase durations. The command signal also drives the pattern formation layer to generate cyclical activation of flexor and extensor motoneurons. Loading of the activated muscles (e.g. supporting the moving body mass) is resisted by the muscles' intrinsic spring-like properties. This is equivalent to displacement feedback. Force and displacement sensed bymuscle spindle and Golgi tendon organ afferents reflexly activate motoneurons. A key role of these afferents is to adjust the timing of phase transitions, presumably by influencing or overriding the CPG timer. Adapted from Prochazka & Ellaway 2012.[23] https://en.wikipedia.org/wiki/Central_pattern_generator Whelan PJ. Shining light into the black box of spinal locomotor networks. Philosophical Transactions of the Royal Society of London B: Biological Sciences. 2010;365:2383– 2395. Cortical control of lower motor neuron Tractus corticospinalis Tractus corticobulbaris Voluntary motor activity Voluntary motor activity Idea Association cortex Premotor + Motor cortex Basal Ganglia Lateral cerebellum Movement Intermediate Cerebellum ExecutionPlanning http://www.slideshare.net/drpsdeb/presentations Voluntary motor activity • Result of cooperation of upper and lower motor neuron • Basal ganglia – Motor gating – initiation of wanted and inhibition of unwanted movements • Cerebellum – Movement coordination http://www.slideshare.net/drpsdeb/presentations • Upper motor neuron – Primary motor cortex • Lower motor neuron – Anterior horn of spinal cord • Tractus corticospinalis lateralis – 90% of fibers • Tractus corticospinalis anterior – 10% of fibers – Cervical and upper thoracic segments • Tractus corticobulbaris Pyramidal tract http://images.slideplayer.com/14/4330915/slides/slide_34.jpg Primary motor cortex http://www.emunix.emich.edu Motor cortex • Primary motor cortex (area 4) – Somatotopic organization – Control of lower motor neuron • Premotor cortex (area 6 laterally) – Preparation of strategy of movement • Sensor motor transformation • Movement patterns selection • Supplementary motor cortex (area 6 medially) – Involved in planning of complex movements • Movement of both limbs • Complex motion sequences – Activated also by complex movement rehearsal http://www.slideshare.net/CsillaEgri/presentations