Control of Body Movement

Chapter 10 To learn how NS system and interact with each other in the initiation and control of body movements

成大生理所 張雅雯老師 hierarchy

10.1 Motor control hierarchy運動控制之層次結構 Higher-center “command” Generate an intention The middle-level structures Receive input and create/adjust motor program Local-level neurons Carry out the desired action Middle level of the motor control hierarchy Five components of the middle level of the motor control hierarchy Proprioception本體感覺 Afferent information about the position of the body and its parts in space Include balance, coordination and agility Enable the body to move and control limbs without directly looking at them With/without ever reaching the level of conscious

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Voluntary and involuntary actions Voluntary actions (1) the movement is accompanied by a conscious awareness of what we are doing and why we are doing it (2) our attention is directed toward the action or its purpose Involuntary actions Unconscious, automatic,

Almost all motor behavior involves both actions Not easy to make a distinction between these actions http://images.slideplayer.com/14/4207261/slides/slide_11.jpg; http://4.bp.blogspot.com/-KKp2zY_IeTc/UvoCbGoqs7I/AAAAAAAAA2Y/FM4DVIFL8ng/s1600/Slide09.jpg Local control of motor neurons

10.2

Motor neurons always form the final common pathway to the muscles Interneurons中間神經元 directly with the motor neurons Most of the synaptic input to motor neurons from the descending pathways and afferent neurons does not go directly to motor neurons but, rather, goes to interneurons that synapse with the motor neurons Comprise 90% of neurons

90%

http://faculty.pasadena.edu/dkwon/PNS%20and%20propioception/peripheral%20nervous%20system%20and%20propioception_files/images/image27.png Lengthen-monitoring system Stretch receptors牽張受器 Monitor muscle length and the rate of change in muscle length Located in 肌梭 embedded within muscles Two kinds of stretch receptors (muscle-spindle stretch receptors) (1)Nuclear chain fibers核鏈纖維 Respond best to how much a muscle is stretched (2)Nuclear bag fibers核袋纖維 Respond to both the magnitude of a stretch and the speed with which it occurs

https://image.slidesharecdn.com/centralnervoussystem-131213101109-phpapp02/95/central-nervous-system-71-638.jpg?cb=1386929620; http://www.edoctoronline.com/media/19/photos_98f67791-7ea8-406a- 810b-afa8b957de38.jpg More/faster stretched, greater firing The more/faster the muscle is stretched, the greater the rate of stretch receptor firing (a) Passive stretch of the muscle by an external load activates the spindle stretch receptors and causes an increased rate of action potentials in afferent nerve (b) Contraction of the extrafusal fibers肌梭外肌細 胞 removes tension on the stretch receptors and decreases the rate of firing Alpha–gamma coactivation同步活化 Simultaneous activation of alpha and gamma motor neurons results in maintained stretch of the central region of intrafusal fibers肌梭內肌細胞 Prevent the central region of the muscle spindle from going slack during a shortening contraction Afferent information about muscle length continues to reach the CNS Stretch reflex牽張反射

Knee-jerk reflex膝跳反射 Tapping the patellar tendon stretches extensor muscle伸肌 The only known monosynaptic reflex arcs單突觸反射弧 Indicate a functioning normally of the afferent fibers, balance of synaptic input to motor neurons, motor neurons, neuromuscular junctions, and muscles Paths A/C: compensatory contract this and other extensor muscles Path B (reciprocal innervation神經 交互投射): relax flexor muscles屈肌 Path D: send information about muscle length to the Tension-monitoring system張力偵測系統 Motor neurons Less stretch monitor the tension Fewer action via feedback by potential More stretch activating Golgi More action tendon organs potential Feedback is necessary to inform the motor control systems of the tension actually achieved Muscle tension depends on muscle length, the load on the muscles, and the degree of muscle fatigue Golgi tendon高爾基肌鍵器 Neural pathways underlie of the local control system Contraction of extensor muscles causes tension in the Golgi tendon organ and increases the firing rate of action potential in Path A: inhibit the motor neurons of extensor muscle and its synergists Path B: excite the motor neurons of flexor muscle Monitor muscle length and tension

Muscle spindle and Golgi tendon organ mediate local homeostatic control and supply the higher-level motor control systems with information about muscle length and tension to modify the ongoing motor program Monitor length by stretch receptor

Length

Tension Withdrawal reflex 回縮反射 In response to pain Detect by Stimulate ipsilateral flexor muscle’s motor Crossed-extensor reflex交互伸肌反射 Opposite limb is extended to support the body’s weight Activate extensor’s motor neurons Inhibit flexor’s motor neurons Inputs to the local motor control system (1) Muscle stretch receptor: monitor muscle length (2) Golgi tendon organ: monitor muscle tension (3) : monitor painful stimulation of skin

Length

Tension

Pain The brain motor centers and the descending pathways they control

10.3 Motor control hierarchy運動控制之層次結構 Higher-center “command” neurons Generate an intention The middle-level structures Receive input and create/adjust motor program Local-level neurons Carry out the desired action Major motor areas of the

Sensorimotor cortex感覺運動皮質 control muscle movement Contain primary motor cortex主要運動皮質, premotor area前運動皮質, somatosensory cortex體感覺, supplementary motor cortex輔助運動皮質 , parietal-lobe association cortex頂葉聯絡皮質 Subcortical mechanisms of the motor control system Subcortical and nuclei indirectly transmitted to the motor neurons By ascending pathways to the cerebral cortex By descending pathways from the brainstem nuclei

Play a prominent role in planning and monitoring movement Important in learning skilled movements Either facilitate or suppress movements Cerebellum Indirectly influence posture and movement By input to brainstem nuclei By way of thalamus to regions of sensorimotor cortex that give rise to pathways that descend to the motor neurons Receive information from sensorimotor cortex, vestibular system, eyes, skin, muscles, joints, and tendons

Provide timing signals to cerebral cortex and spinal cord for precise execution of the different phases of a motor program Help coordinate movements involving several joints and store the memories Plan movements integrating space information Descending pathways Corticospinal pathway皮 質脊髓通路 Pyramidal tract椎體徑路 or pyramidal system椎體系統 Originate in cerebral cortex Cross in brainstem to descend in the opposite side of spinal cord Control muscles involved in fine, isolated movements, particularly those of the fingers and hands Brainstem pathways皮質 腦幹通路 Descending pathways Corticospinal pathway皮 質脊髓通路 Brainstem pathways皮質 腦幹通路 Extrapyramidal system椎體外 系統 Originate in the brainstem Most uncrossed Coordination of the large muscle groups used in the maintenance of upright posture, in locomotion, and in head and body movements Muscle tone

10.4 Muscle tone肌肉張力 Muscle tone Skeletal muscle is relaxed but with a slight resistance Due to the passive elastic properties of the muscles and joints Due to the degree of ongoing alpha activity An important diagnostic tool for clinicians assessing a patient’s neuromuscular function Abnormal muscle tone Hypertonia肌張力過高 Spasticity痙攣; rigidity僵直; spasms攣縮; cramps抽筋 Disorders of descending pathways Hypotonia肌張力過低 Flaccid肌肉無力 Cerebellar disease, diseases of the alpha motor neurons or muscle http://www.msunites.com/wp-content/uploads/Hypertonia-Header1.jpg; https://englishforphysio.files.wordpress.com/2016/05/img_1158.jpg?w=660 Maintenance of upright posture and balance

10.5 Crossed-extensor reflex交互伸張反射 Use to maintain upright posture Maintain balance Walking

10.6 Walking The activity of networks in spinal cord brings about the cyclical, alternating movements of locomotion These pattern generators are controlled by corticospinal and brainstem descending pathways and affected by feedback and motor programs