L14 NPB 101 - Lecture 14 •  SmartSite: – ...

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Unformatted text preview: Lecture 14 •  SmartSite: –  Lecture 14 Notes •  Review –  Motor Control I •  Announcements: –  None •  Motor Control II •  Reading (Recommended): –  Relevant por<ons of Chapters 5 & 8 1 REV: Motor Control I •  Soma<c efferent division of PNS consists of •  Motor output can range from simple reflex to complex movement •  A reflex is a stereotyped response to a fixed s<mulus •  Elements of a reflex: –  Simplest reflex is stretch reflex, we discussed others –  sensor, afferent path, integra<on, efferent path, effector –  Muscle spindle –  Golgi tendon organ (GTO) –  Joint receptor –  axons of motor neurons from spinal cord or brain stem and to skeletal muscle •  Skeletal muscle regula<on uses 3 kinds of receptors: •  Muscle spindle contains both: –  afferent receptors to sense muscle length (stretch) –  efferent fibers (γ ­motor neuron) to maintain sensi<vity 2 Locomo<on •  Rhythmic contrac<on of flexor ­extensor muscle pairs produced at the level of the spinal cord •  Generator ac<vity modified by the brain stem –  Locomotor command center (LMC) LMC –  Locomotor paXern generators (LPG) LPG LeY Leg Right Leg 3 Motor Efferent •  CNS Motor efferents subserve three func<ons: –  Ini<a<on of movement –  Adjustment of posture (level extensor excita<on) –  Coordina<on of muscles •  Upper motor neurons distributed in 2 pathways: •  Lower motor neurons of PNS –  Alpha (α) motor neurons –  Gamma (γ) motor neurons –  Pyramidal fibers from motor cortex to spinal cord –  Extrapyramidal fibers from motor cortex to brainstem to spinal cord 4 Motor System Regula<on •  Feedback regula<on •  Components of CNS –  Spinal Cord –  Brain Stem –  Basal Ganglia –  Thalamus –  Cerebellum –  Cortex (motor, premotor, supplemental) 5 Nega<ve Feedback Regula<on Set Point Controller (CNS) Error Signal Controlled System (Muscle) Nega<ve Feedback Sensor (Muscle spindle) (GTO) (Joint Receptor) Regulated Variables (Length) (Tension) (Posi<on) 6 Primary Motor Cortex •  Control of fine / voluntary movement •  Anatomy –  Located next to and anterior to (in front of) sensory cortex –  Somatotopically organized –  6 cell layer structure –  Two descending pathways (pyramidal & extrapyramidal) –  Linked to somatosensory cortex (feedback) –  Planning (Set Point) 7 Motor Cortex •  Primary Motor Cortex –  Located anterior of the central sulcus of each hemisphere –  Contains a Motor Homunculus –  Coordina<on and planning of complex motor movements •  Addi<onal Motor Cortex Fig. 5 ­9a, pg. 147; Fig. 5 ­10c, pg. 148 8 The Corticospinal Tracts •  Neurons project from the primary motor cortex •  The axons project down through the ipsilateral (same) side of the CNS •  The fibers cross over in different regions –  In the medulla –  In the spinal cord •  The fibers then synapse upon their contralateral (opposite) side targets Fig. 5 ­28b, pg. 175 9 Cerebellum •  Planning & coordina<on of skilled voluntary movement •  Maintenance of balance & posture •  Enhancement of muscle tone •  Many inputs –  Cortex, somatosensory, muscle, visual, auditory, ves<bular –  Receives feedback •  Coordinate, smooth & predict movement •  Pathology (rough, jerky, uncoordinated movements) –  Inten<on tremors –  Overshoot –  Movement decomposi<on 10 Cerebellum SET POINT (Planned Movement) ERROR SIGNAL CONTROLLER SENSORY INFORMATION FEEDBACK Fig. 5 ­19b, pg. 166 11 Basal Ganglia •  Ganglia located in white maXer of brain –  Putamen –  Caudate –  Globus pallidus •  Func<on –  Planning of movement  ­ select/maintain purposeful movement –  Inhibi<on of muscle tone –  Coordina<on of slow sustained movements –  Posture – monitor & coordinate slow/sustained motor ac<vity •  Suppress unwanted movements •  Caudate & Putamen receive input from: –  Cortex –  Thalamus –  Substan<a Nigra (Dopamine; loss of which causes Parkinsons) 12 Basal Ganglia & Thalamus Fig. 5 ­14a, pg. 154 13 Basal Ganglia •  Globus pallidus provides output to: –  Cortex via thalamus –  Modula<on of descending motor signals –  Substan<a nigra –  Res<ng tremor –  Rigidity (increased tone) –  Poverty of movement –  Dyskinesias •  hard to ini<ate •  spontaneous repeated inappropriate movements 14 •  Pathology Thalamus •  •  •  •  Sensory relay ganglia to the cortex Sensory Filter Preliminary synap<c integra<on Posi<ve reinforcement of voluntary motor control 15 Cerebellum vs. Basal Ganglia •  Similari<es –  Monitor and adjust motor ac<vity commands from cortex –  No direct synapses on lower motor neurons –  Subconscious coordina<on of voluntary motor ac<vity •  Differences –  Cerebellum: maintains balance, coordinates smooth fast motor ac<vity, increases muscle tone •  acts as the controller in the motor program feedback pathway –  Basal Ganglia: maintains posture & support (tension), coordinates slow motor ac<vity, inhibits muscle tone •  acts as set point in the motor program feedback pathway 16 Brain Stem •  Oldest region of the brain •  Con<nuous with spinal cord •  All incoming and outgoing fibers traversing between periphery and higher brain centers must pass Brain Stem •  Regula<on of muscle reflexes involved in posture and equilibrium •  Regula<on and integra<on of synap<c input from Spinal Cord Fig. 5 ­19a, pg. 166 17 Summary of Motor Control Fig. 8 ­23, pg. 286 18 ...
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