Skeletal Muscles_ Anatomy and Physiology.pdf

Skeletal Muscles Anatomy and PHR2001M Physiology Dr Taghread Hudaib  Objectives By the end of this session, you should be able to: Describe skeletal muscle structure and function. Define a muscle fibre, myofibril, sarcomere, sarcoplasm and the proteins inv...

Skeletal Muscles Anatomy and PHR2001M Physiology Dr Taghread Hudaib  Objectives By the end of this session, you should be able to: Describe skeletal muscle structure and function. Define a muscle fibre, myofibril, sarcomere, sarcoplasm and the proteins involved in muscle contraction Identify the sarcomere regions and their changes during muscle contraction Explain the muscle contraction and the sliding filament process  Muscle Anatomy Each muscle is an organ with high demand of energy and oxygen Each muscle is supplied by nerve fibbers, blood vessels and 3 connective tissue layers (sheaths) that enclose it, wrap the muscle fibres and provide support to the muscle. The epimysium is an irregular dense connective tissue that allows muscle to contract, move independently and maintain its structure. It also separates muscle from nearby organs and tissues. Muscles can be directly attached to other organs or tissues (like the bones) or indirectly by tendons. The perimysium: organise muscle fibres into bundles The endomysium: a thin layer of collagen and reticular fibres, surrounds the extracellular matrix of the cells and plays a role in transferring force produced by the muscle fibres to the tendons. https://open.oregonstate.education/aandp /chapter/10-2-skeletal-muscle/ https://www.youtube.com/watch?v=XoP1diaX VCI&ab_channel=greatpacificmedia short video Sarcomere Sarcoplasm Myofibril Epimysium Perimysium Endomysium https://open.oregonstate.education/aandp/chapter/10-2-skeletal-muscle/  Types of Muscle Tissue There are 3 types of Muscles – Skeletal muscles: voluntary, striated, multinucleated – Cardiac muscles: striated, involuntary – Smooth muscles: nonstriated, involuntary https://www.123rf.com/clipart-vector/cardiac_muscle.html?sti=lpn108nw8w4qqemhma|&mediapopup=103545652  Anatomy of Muscle Fibre – Multinucleate cell (~30 cm long) – Sarcolemma (plasma membrane) – Myofibril = rod like, contains contractile sarcomeres – Light (I) and dark (A) bands – Sarcomere is the smallest contractile unit of muscle Fibre, region between 2 successive Z discs https://courses.lumenlearning.com/ap1/chapter/skeletal-muscle/ https://biology-forums.com/index.php?action=gallery;sa=view;id=74  Functions of Muscles Movement Body position Joints support Generate heat Other organs https://br.pinterest.com/pin/599682506614700194/ control: valves, pupils… Special Characteristics of muscles – Excitability: they can respond to stimuli – Contractility: they can contract – Extensibility: they can be stretched – Elasticity: they can shrink and return to original https://www.slideshare.net/drpriya07/properties-of-skeletal-muscle length after contracting or stretching  Terminology Protein myofilaments: Myosin: thick filaments (protein) Actin: thin filaments (protein) Myosin head: forms cross bridges with thin filaments to contract muscle cell https://www.crossfitinvictus.com/blog/muscle-contraction- Tropomyosin: protein strand really-cool-protein-called-myosin/ stabilizes actin Troponin: binds actin, affected by Ca2+  More Terminology Each myofibril is surround by Sarcoplasmic Reticulum (SR) which is a specialized smooth ER that stores and releases calcium T Tubule is a part of the sarcolemma that triggers the release of calcium and conducts https://en.wikipedia.org/wiki/T-tubule nerve impulses to sarcomeres.  More terminology Nerve Impulse: 1 nerve cell (neuron motor) stimulates many muscle cells Motor unit:1 neuron + muscle stimulated cells Axon: extension of neuron Axon terminal: end of axon Neuromuscular junction (NMJ): where axon terminal meets muscle fibre Synaptic cleft: space between neuron & muscle fibre http://howmed.net/physiology/neuromuscular-junction-nmj/ Acetylcholine (ACh): neurotransmitter  Sliding Filament Model Thin filaments slide past thick filaments and they overlap during contraction Myosin heads tie to active sites on actin and form a cross- bridge https://www.onlinebiologynotes.com/sliding-filament-model-of-muscle- contraction/ (visit the link)  Basic muscle contraction steps Stimulation by nerve impulse Generate and send electrical current (action potential) along sarcolemma Rise in calcium ion levels to trigger contraction http://nh-chs-anatomy.pbworks.com/w/404/Muscle%20Contractions-%20Yauger  Excitation of Muscle Cell Action potential travels down axon and arrives at neuromuscular junction Acetylcholine (ACh) is released into synaptic cleft, diffuses across cleft and attaches to ACh receptors on sarcolemma https://www.ecosia.org/images?q=Excitation%20of%20Muscle%20Cell& Sodium (Na+) rushes into addon=chromegpo#id=8821EEB26F019555B1DB72655F64E2C69B4FEDF7 sarcoplasm and produces action potential in sarcolemma ACh then is broken down  Contraction of muscle cell Action potential travels down sarcolemma along T- Tubules Calcium is released from SR and binds to troponin so, myosin binding sites are exposed on actin Myosin cross-bridge forms with actin Myosin head twists and pulls actin towards the M line ATP attaches to myosin and the cross-bridge detaches Myosin is reactivated *Action Potentials and Muscle Contraction Video https://www.youtube.com/watch?v=WrV510gUlco&ab_c hannel=AcademicAlgonquin  Muscle Responses Twitches: single, irregular contractions is not normal, healthy muscle s contract smoothly Graded muscle responses: muscle shortening due to: – Increased frequency of muscle stimulation – Increased number of muscle cells being stimulated – Increasing muscle tension  Muscle tone Normal tone: right amount of tension in the muscle at rest, and the muscle can contract on command (response to passive stretch) Postural tone is a result of steady stretch on tendons and attached muscles (protracted muscle contraction). Phasic tone is a result of rapid stretching of a tendon Normal muscles: firm, healthy, ready for action Paralysis: nerve damage Flaccid muscle: soft and loose Atrophy: wasting away if not stimulated  Energy sources ATP is the only source of energy for muscles ATP is generated by: – Creatine phosphate CP which transfers energy to ATP – Aerobic respiration in which glucose breakdown with O2 presents – Lactic acid fermentation in which glucose breakdown without O2 presents Muscle fatigue: lack of O2, low ATP, lactic acid accumulation, so muscle contracts weakly  https://www.nbsfitness.net/3-muscular-contractions-creating-stability/ Concentric: Muscle fibres shorten Eccentric: Muscle fibres lengthen Isometric: Muscle fibres do not change in length  Skeletal Muscle Activity All muscles cross at least one joint The bulk of a skeletal muscle lies proximal to the joint crossed. All muscles have 2 attachments; origin and insertion Muscles can only pull and never push. During contraction, the muscle insertion moves toward origin.  Muscle Origin and Insertion Every skeletal muscle is attached to bone or connective tissue – Origin: attached to immovable or less movable bone – Insertion: attached to http://bio.rutgers.edu/~gb102/lab_8/8i4m-function.html movable bone  More… Muscles develop from embryonic cells (myoblasts) Regeneration: very limited in skeletal and cardiac muscles and very common in smooth muscle (from the stem cell pericyte) In women, muscles form 36% of body mass In men, 42% With age, muscle mass and strength decrease but exercise helps in retaining mass and strength  Some common muscle disorders Muscle Atrophy: Loss of muscle tissue caused by a lack of physical activity, aging, malnutrition, medications or injuries Muscular Dystrophies: Inherited (mutations) muscle-destroying diseases such as – Duchenne muscular dystrophy (DMD), sex-linked recessive disorder; missing dystrophin protein – myotonic dystrophy can develop at any age – facioscapulohumeral muscular dystrophy, can develop in childhood or adulthood, progresses slowly, not life-threatening – Becker muscular dystrophy related to Duchenne MD but develops later in childhood and is less severe Other muscle disorders – Myasthenia gravis: rare long-term condition that causes muscle weakness, affects mostly the eyes and eyelids controlling muscles – Mitochondrial disorders (metabolic)  Important videos Muscle Physiology: Troponin, Tropomyosin, and Myosin Cross- Bridge Cycle https://www.youtube.com/watch?v=bYAwVEdCEts&ab_channel=Catal ystUniversity 13 min Sliding Filament https://www.youtube.com/watch?v=0kFmbrRJq4w&ab_channel=Sara Egner Muscle Contraction - Cross Bridge Cycle https://www.youtube.com/watch?v=BVcgO4p88AA&ab_channel=Alila MedicalMedia Steps of Excitation-Contraction Coupling in Skeletal Muscle https://www.youtube.com/watch?v=atiMNPURZuI&ab_channel=Catal ystUniversity 20min (optional)  Additional reading Essentials of human physiology for pharmacy chapters 11 and 12 https://www.academia.edu/28272297/essenti als_of_human_physiology_for_pharmacy_pdf