Foundations for Physiotherapy Practice 2024-25 Muscle Anatomy and Physiology PDF

Foundations for Physiotherapy Practice 2024-25 Muscle Anatomy and Physiology 2024 University of Hertfordshire Physiotherapy Learning Outcomes By the end of this session and associated independent study you should be able to: Discuss how skeletal muscle contracts....

Foundations for Physiotherapy Practice 2024-25 Muscle Anatomy and Physiology 2024 University of Hertfordshire Physiotherapy Learning Outcomes By the end of this session and associated independent study you should be able to: Discuss how skeletal muscle contracts. Understand how skeletal muscle generates force at both the macro and microscopic levels. Discuss the factors that affect the force and velocity generation of muscle. 2024 University of Hertfordshire Physiotherapy  Muscle types: Skeletal Cardiac Smooth Attached to bones or skin Walls of the heart Other hollow visceral organs Voluntary contraction Involuntary contraction Involuntary contraction Speed of contraction -slow Speed of contraction -slow Speed of contraction -v to fast slow 2024 University of Hertfordshire Physiotherapy Skeletal Muscle Remember: A muscle has to contract to produce a force. Muscle power is the rate at which a muscle works = force x velocity of contraction. 2024 University of Hertfordshire Physiotherapy  Skeletal Muscle What anatomical or physiological factors can affect the force of muscle contraction? 2024 University of Hertfordshire Physiotherapy Factors Affecting Skeletal Muscle Force Production - there are many more factors including age & pathology but we are going to focus on the following anatomical & physiological factors of the normal muscle: Anatomically: Gross muscle structure (also refer to biomechanics and analysis of mvt 1 sessions) Fibre types No. of fibres Size of fibres Neurologically Frequency of stimulation Recruitment of Motor units Functionally Muscle length Velocity of contraction 2024 University of Hertfordshire Physiotherapy Gross muscle structure 2022 University of Hertfordshire Physiotherapy Gross Muscle structure Organisation of fascicles 2024 University of Hertfordshire Physiotherapy Gross Muscle Structure – Connective Tissue Epimysium – surrounds the whole muscle. Perimysium surrounds the fascicles. Endomysium surrounds the individual fibres. Nerve and Blood Supply. Nerve, artery and veins branch profusely within the connective tissue of the muscle. 2024 University of Hertfordshire Physiotherapy Structure of a skeletal muscle 2024 University of Hertfordshire Physiotherapy Structure of a myofibril / sarcomere 2024 University of Hertfordshire Physiotherapy  Arrangement of filaments in a sarcomere – Sliding filament theory 2024 University of Hertfordshire Physiotherapy Synapse Post synaptic membrane Identify the labelled parts 2024 University of Hertfordshire Physiotherapy Excitation contraction coupling Understand the basics steps involved. Appreciate the complexity - see next slide. 2024 University of Hertfordshire Physiotherapy Excitation contraction coupling 1 Acetylcholine (ACh) is released from the axon terminal of a motor neuron and binds to receptors in the motor end plate. This binding elicits an end-plate potential, which triggers an action potential in the muscle cell. Axon terminal Neuromuscular junction Synaptic cleft Sarcolemma ACh 2 Action potential T tubule propagates along Sarcoplasmic Motor end the sarcolemma reticulum (SR) plate and down T tubules ACh 6 Ca2+ is actively receptors transported back into lumen of SR Ca2+ following the action potential Ca2+ 7 Tropomyosin blocks myosin-binding sites 3 The action potential (muscle fiber relaxes) triggers Ca2+ release from SR Ca2+ 4 Ca2+ binds to troponin, exposing myosin-binding sites 5 Crossbridge cycle begins (muscle fiber contracts) 2024 University of Hertfordshire Physiotherapy Fig. 12.8 Stanfield & Germann Summary 1. AP arrives at the axon terminal 2. Voltaged-gated Ca channels open, Ca rushes in 3. Triggers the release of ACh 4. ACh diffuse across the cleft and binds to the receptors on motor end plate 5. ACh triggers opening of Na & K channels and so an AP 6. AP spread along the muscle membrane 7. ACh degraded by enzyme – acetylecholinesterase 8. Choline is re-uptaken by the terminal From Action potential to muscle contraction 1. AP trigger Ca2+ release 2. Ca triggers crossbridge cycling 3. Filaments slide, mm contracts 2024 University of Hertfordshire Physiotherapy Factors Affecting Skeletal Muscle Force Production – there are many more factors including age, & pathology but we are going to focus on the following anatomical & physiological factors of the normal muscle: Anatomically: Gross muscle structure (also refer to biomechanics and analysis of movement sessions) Fibre types No. of fibres Size of fibres Neurologically Frequency of stimulation Recruitment of Motor units Functionally Muscle length Velocity of contraction 2024 University of Hertfordshire Physiotherapy  Type I Type IIA (2a) Type IIB (2b) Muscle Fibre Types Slow oxidative Fast oxidative Fast glycolytic Speed of slow Moderately fast fast contraction Pathway for ATP aerobic Aerobic (some anaerobic) Anaerobic synthesis glycolysis Resistance to high Fairly high low fatigue Size of motor small medium large neuron Recruitment order 1st 2nd 3rd Force production low medium high Activities best Running Sprinting, walking Hitting a baseball suited for marathon, posture 2024 University of Hertfordshire Physiotherapy  Motor unit - a motor neuron plus all the muscle fibres it innervates 1. One motor neuron innervates many fibres 2. One fibre innervated by only one neuron 3. Same type of fibres within the motor unit 2024 University of Hertfordshire Physiotherapy Motor unit physiology MU’s can develop different amounts of tension Ex. Fast MU (compared to slow MU’s) innervate fast mm fibres innervate more mm fibres Innervate fast mm fibres that are larger 2024 University of Hertfordshire Physiotherapy Factors Affecting Skeletal Muscle Force Production – there are many more factors including age, & pathology but we are going to focus on the following anatomical & physiological factors of the normal muscle: Anatomically: Gross muscle structure (also refer to biomechanics and analysis of mvt 1 sessions) Fibre types No. of fibres Size of fibres Neurologically Frequency of stimulation Recruitment of Motor units Functionally Muscle length Velocity of contraction 2024 University of Hertfordshire Physiotherapy Neurologically Principles of tension generation in a motor unit All or none Principle Gradation of Force Recruitment patterns Frequency of stimulation 2024 University of Hertfordshire Physiotherapy The size principle Small motor units with small fibres are highly excitable and activated first, gradually larger motor units with larger fibres are activated and so the force of contraction is increased Recruitme nt of Motor Units (Marieb and Hoehn 2010) 2024 University of Hertfordshire Physiotherapy Frequency of stimulation and summation of twitches The nervous system controls the skeletal muscle by altering the firing rate of the motor neurons. As the rate of firing increases the resultant muscle twitches are summated resulting in a fused tetanus. This produces a smooth contraction. 2024 University of Hertfordshire Physiotherapy Frequency of stimulation and summation of twitches Fig. 12.17 Stanfield & Germann 2006 2024 University of Hertfordshire Physiotherapy Factors Affecting Skeletal Muscle Force Production – there are many more factors including age, & pathology but we are going to focus on the following anatomical & physiological factors of the normal muscle: Anatomically: Gross muscle structure (also refer to biomechanics and analysis of mvt 1 sessions) Fibre types No. of fibres Size of fibres Neurologically Frequency of stimulation Recruitment of Motor units Functionally Muscle length Velocity of contraction 2024 University of Hertfordshire Physiotherapy Sarcomere length (Guyton and Hall 2010) 2024 University of Hertfordshire Physiotherapy Muscle length The effect of muscle length on tension produced in a whole intact muscle (isometric contraction) 2024 University of Hertfordshire Physiotherapy Force-velocity Relationship of muscle (Everett and Kell 2010) 2024 University of Hertfordshire Physiotherapy Force-Velocity relationship of muscle Force varies with the velocity of movement If the force generated is equal to the load then there will be no movement i.e. an isometric contraction The greater the velocity of a concentric contraction the smaller the tension generated 2024 University of Hertfordshire Physiotherapy Velocity of contraction Muscle fibre types: 1. Slow oxidative fibres – contract slowly, primary energy source is oxidative 2. Fast oxidative fibres – contract fast primary energy source is oxidative 3. Fast glycolytic fibres – contract fast, primary energy source is glycolytic 2024 University of Hertfordshire Physiotherapy Speed of contraction (Marieb and Hoehn 2010) 2024 University of Hertfordshire Physiotherapy Learning Outcomes - revisit By the end of this session and associated independent study you should be able to: Discuss how skeletal muscle contracts. Understand how skeletal muscle generates force at both the macro and microscopic levels. Discuss the factors that affect the force and velocity generation of muscle. 2024 University of Hertfordshire Physiotherapy 2024 University of Hertfordshire Physiotherapy References Everett T and Kell C (2010) Human Movement An Introductory Text 6th ed. Churchill Livingstone. A useful text for many areas of Movement Studies. Guyton A.C and Hall J.E (2016) Textbook of Medical Physiology, 13th ed. Elsevier Health. Marieb, E. N., & Hoehn, K. (2018) Human anatomy & physiology 11th ed. Harlow: Pearson Education Limited. Stanfield, C. L. (2017). Principles of human physiology (Sixth, global ed.). Harlow, England: Pearson. 2024 University of Hertfordshire Physiotherapy