Week 1 PDF Neuromechanics PDF

What is neuromechanics? MEDI258: HUMAN NEUROMECHANICS Textbook ref: pgs 195-229 Neuromechanics u Neuromechanics: an area that attempts to understand the effects of body dynamics, muscles, sensory organs and central nervous system control systems to exp...

What is neuromechanics? MEDI258: HUMAN NEUROMECHANICS Textbook ref: pgs 195-229 Neuromechanics u Neuromechanics: an area that attempts to understand the effects of body dynamics, muscles, sensory organs and central nervous system control systems to explain human motion Motion analysis Nervous system stimulation Electromyography Applications of Neuromechanics u Exercise prescription for performance enhancement u Exercise prescription to limit or reverse the neuromuscular effects of ageing u Exercise prescription to restore lost movement function after disuse or injury u Prosthetic design u Exoskeleton design u Humanoid robot development Neuromechanics @ UOW MEDI330: Sensorimotor Control MEDI222: Foundations of Biomechanics MEDI151: Healthy EXSC370: Clinical Ageing Biomechanics MEDI258: Human Neuromechanics MEDI350: Research Projects How does MEDI258 relate to MEDI222? Muscle mechanics u Force production Gait mechanics u Moment arms and torque Arm movement mechanics Throwing/striking mechanics u Momentum Mechanical changes with: Stretching u Work, energy & power Fatigue u Analysing movement Ageing Strength training u Projectile motion Simple reflex control u Fluid mechanics Spinal cord control of locomotion Cortical control of voluntary movement Neural adaptations driving acute and chronic movement changes Generating force with muscle Activity: Muscle force fluctuations during fatigue u Squat to fatigue u Think about what you feel as you become fatigued u Why do you think this happens? Learning outcomes u Understand how neuronal action potentials are converted into muscle contraction u Understand the basic function of electromyography u Describe how motor units operate to produce smooth muscle contraction Muscle structure/function Excitation/contraction coupling 1-3: Muscle fibre action potential travels into the fibre and activates the sarcoplasmic reticulum. 4. Calcium is released 5. Calcium reuptake into sarcoplasm 6. Calcium attaches to Troponin molecules – changes structure of actin filament 7. ATP binds to myosin heads, which are then able to detach from actin Cross-bridge cycle 1. Myosin head attached to actin filament 2. ATP binds to myosin head, which detaches from actin filament 3. Calcium binds to troponin, allowing myosin heads to bind to actin. ATP is hydrolysed, initiating the power stroke (2 pN of force) 4. ADP is released, returning myosin to base state Measuring muscle activity: electromyography (EMG) Measuring muscle activity: electromyography (EMG) Measuring muscle activity: electromyography (EMG) u EMG is recorded using two ‘differential’ electrodes over a muscle. u Records activation of many muscle fibres at each point in time. u Is related to, although not exactly the same as, muscle force. u Can be used to determine the amount of activity in a muscle relative to itself over time. Motor units - structure u 1 motor unit = 1 motor neuron + all of the muscle fibres it innervates u The motor neuron is the final common pathway for motor commands u Commands from all levels of the nervous system are integrated and sent to muscle  Innerv 600 300 0 0 20 40 60 80 100 120 Motor unit number Motor units – how many in a Figure 6.10 Distribution of innervation number across the 120 motor units that innervate ~48,000 fibers in a hand muscle (Enoka & Fuglevand, 2001). The exponential relation is based on the distribution of motor unit forces within a muscle. A similar E5984/Enoka/fig06.10/487220/alw/r1-pulled relation likely exists for most muscles. muscle? Table 6.4 Anatomical Estimates of the Number of Alpha Motor Axons, Muscle Fibers, and Average Innervation Number in Selected Human Skeletal Muscles Alpha motor Number of muscle Innervation Muscle Specimen axons fibers number u Why does the innervation number vary Abductor digiti minig 10 adults 380 72,300 190 across muscles? Abductor pollicis brevis h 10 adults 171 15,400 90 Adductor pollicish 10 adults 128 13,600 106 a) Larger muscle = higher innervation Biceps brachiib,d Stillborn infants 774 580,000 750 number Brachioradialis f Man, 40 yr 337 >129,000 >410 First dorsal interosseusf Man, 22 yr 119 40,500 340 b) Smaller muscle = lower innervation First lumbrical f Man, 54 yr 93 10,038 108 number Woman, 29 yr 98 10,500 107 c) High dexterity = low innervation Flexor pollicis brevish 10 adults 172 15,300 89 number Masseter Man, 54 yr 1,452 929,000 640 c Opponens pollicis b,d,h 10 adults 172 15,300 89 d) Low dexterity = high innervation Medial gastrocnemiusf Man, 28 yr 579 1,120,000 1,934 number Plantarise 10 cadavers 204 64,300 372 Rectus lateralis i 2 cadavers 4,150 22,000 5 Stapediusa 20 cadavers 256 1,081 7 Temporalis c Man, 54 yr 1,331 1,247,000 936 Tensor tympani i 2 cadavers 146 1,100 8 Tibialis anteriorf Man, 40 yr 445 250,000 562 Blevins 1967; bBuchthal 1961; cCarlsöö 1958; dChristensen 1959; ede Carvalho 1976; fFeinstein et al. 1955; gSanto Neto et al. 1985; hSanto a Neto et al. 2004; iTorre 1953. the muscle unit per 100 fibers in the muscle. Consequently, a given volume of muscle contains 20 to 50 different muscle units. Similarly, the territory of a muscle unit in the cat tibialis anterior muscle can range from 8% to 22% of cross-sectional area, whereas in the soleus muscle the terri- tory ranges from 41% to 76%. Moreover, the fibers in a muscle unit often do not extend from the proximal to the distal attachment of a muscle, such as in the medial gastrocnemius and sartorius muscles of humans. Motor units – types u Identification of muscle fibre type based on myosin heavy chain isoform u Type I: slow oxidative u Type IIA: fast oxidative u Type IIX: fast glycolytic u Each motor unit involves one muscle fibre type u Type S: slow twitch, fatigue resistant u Type FR: fast twitch, fatigue resistant u Type FF: fast twitch fatigable Vastus lateralis Motor units – types u Muscle performance defined by its motor units Motor units – recruitment u How do we control force output? u Henneman size principle u Small (slow, low force) motor units recruited first u Larger (faster, higher force) motor units recruited as force demand becomes higher u Rate coding u Force output of a single motor unit can be increased with higher discharge rates Activity: Muscle force fluctuations during fatigue u So, how do you explain what you felt during the squat to fatigue? Learning outcomes u Understand how neuronal action potentials are converted into muscle contraction u Understand the basic function of electromyography u Describe how motor units operate to produce smooth muscle contraction