1 / 29

Module 632 Lecture 7 JCS

Module 632 Lecture 7 JCS. Muscle types, structure, activation and energy use. MODULE - 632 Lecture 7 Lecture outcomes:   At the end of this lecture a student will be aware of:   1) the different types of muscle 2) that basic function of muscle is to produce force and movement

lesley-good
Download Presentation

Module 632 Lecture 7 JCS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Module 632 Lecture 7 JCS Muscle types, structure, activation and energy use

  2. MODULE - 632 Lecture 7 • Lecture outcomes: •   At the end of this lecture a student will be aware of: •   1)the different types of muscle • 2)that basic function of muscle is to produce force and movement • 3) that a variety of muscles exist where the outputs – force and movement occur to different degrees • 4) that most muscles work by being attached to a skeleton but that, • 5)some work between or within non-skeletal tissues– e.g. heart, vascular • 6)most muscles work in pairs, • 7)that muscles are attached to skeletons through tendons or tendon- like structures • 8)that muscles move skeletons • 9)that pairs of muscles move joints, • 10) the ultrastructure of striated muscle • 11) the energy sources for muscle contraction and • 12) How muscle contraction of is activated

  3. Striated muscle

  4. Three main types of vertebrate muscle • Smooth (smooth muscle myosin II – 1 isoform) • Smooth appearance (no cross-striations) • Involuntary • Blood vessels, gut, sphincters • Skeletal (striated muscle myosin II – 8 isoforms, including a cardiac isoform in ‘slow’ muscle) • Striated appearance • Voluntary control • Biceps, triceps, quadriceps etc. • Cardiac (cardiac myosin II – 2 isoforms a & b) • Sarcomeric structure (striated) - not as ordered as skeletal. • Rhythmic contractions • Highly specialised function

  5. Striated skeletal muscle is very diverse: • Within an organism (e.g. human muscles): • Structural architectures (pennate, styloid, long/short sarc.) • Fibre types – many muscles contain a mix of the two Type 1 – slow – postural/slow to fatigue Type II –fast • Myosin isoforms (fast, intermediate and slow ATPase activities)

  6. Striated Skeletal Muscle Architecture:

  7. Muscles usually work in antagonistic pairs Vert. upper limb muscles - human Frog leg muscles

  8. 2006 Note: Not same as handout Flexion, extension, adduction, abduction Muscles are often named by the effects of their action and the bones they attach to. In general: Flexors: bends a joint; move limbs away from ‘corpse’ position Extensors: straightens a joint; returns them to corpse position Adductors: ‘add’ the limb towards the rest of the body (pulls the body to wards the midline) Abductors: moves them away from the midline

  9. Muscle has a hierarchical structure: Each muscle is a contractile organ: it contains: muscle fibres blood vessels peripheral ends of nerves/muscle endplates fibrous connective tissue/tendons and is covered with a connective layer. Each muscle fibre is a multinucleated single cell (a syncitium) It contains approx. 1000 myofibrils; specialised contractile organelles, which run the length of the fibre. Each myofibril consists of serial contractile units known as sarcomeres.

  10. Muscle has a hierarchical structure UK ‘fibre’

  11. Muscle – Fibre – myofibril – myofilaments

  12. 0.5mm Acto-myosin in muscle : Myosin containing, thick filament 1 mm 0.5 mm Actin containing, thin filaments 0.1 mm Sarcomere acto-myosin “cross-bridges”

  13. Filament sliding causes muscle to shorten Light micrograph myofibril Electron micrograph sarcomere Myosin molecules (purple bars) move over the F-actin (turquoise).This movement is powered by ATP.

  14. Highly specialised striated muscles (1): • Many specialised muscles exist in different animalse.g. • Asynchronous insect flight muscle - drives insect wingbeats at >200Hz (Drosophila 220Hz). • Tympal muscles that allow crickets to sing • Molluscan “Catch” muscle - keeps shell closed for long periods • Molluscan adductor muscle - fast closing of shell for swimming.

  15. Highly specialised striated muscles (2): Asynchronous insect flight muscle - isometric; requires Ca++ +applied strain to activate- contracts in an oscillatory fashion at frequencies >200Hz myosin.

  16. Pecten maximus Catch muscle Adductor muscle Highly specialised striated muscles (3):Molluscan catch + adductor muscles: Catch muscle – keeps shell closed with minumum energy requirement (slow) Adductor muscle – for swimming.

  17. Forces produced by the muscle are easily measured How clams etc. can close their shells – a single muscle working against a stiff elastic hinge Highly specialised striated muscles (4):

  18. Crossbridge Cycle All muscle contraction is powered by the cyclical interactions of myosin and actin – the so-called crossbridge cycle. Myosin is an ATPase. By coupling its ATPase to a conformational change, dependent on binding actin we can get: Mg.ATP + H2O  Mg.ADP + Pi + H+ + mechanical work The crossbridge cycle (more in the next lecture) consists of: - a biochemical cycle (changes in nucleotide state - ATP, ADP etc. - and in protein binding actin + myosin) and, - a biomechanicalcycle (conformation of the motor molecule – myosin) that are completely functionally inter-dependent. .

  19. Energy Sources for Muscle Contraction (1) : • For the crossbridge cycle outputs: • Mg.ATP + H2O  Mg.ADP + Pi + H+ + mechanical work • the primary energy source is clearly ATP (produced by the mitochondria) • For very short bursts of activity you will use up your ATP pool. The ATP needs to be replaced. • How? • immediate stores of energy – creatine phosphate • new ATP production: from glycolysis (glucose, glycogen) – but product is lactic acid from oxidative phosphorylation (ATP production by the mitochondria)

  20. Energy Sources for Muscle Contraction (2) : The energy sources used are reflected by the physiological properties of skeletal muscles: Vetebrate skeletal muscle contains two major types of fibres that differ in: - speed of contraction – ‘Fast’ (type 2) or ‘slow’ (type 1), and - their major energy supply - their neural activation – ‘twitch’ and ‘phasic’ (see later). Fast fibres (for sprinting) are ‘glycolytic’ Slow fibres (for slower movements, maintained peformance – e.g. over long distance or time outputs and posture etc) are ‘oxidative’ Most skeletal muscles are a combination of ‘fast’ and ‘slow’ fibres. There is also natural variation in the proportion of these fibre types between individuals in particular muscles – sprinters vs marathon runners. Fibre-typing is now a routine part of assessing ‘olympians’ ‘Red’ and ‘white’ meat reflect these differences. Red – mostly oxidative; white is mostly glycolytic.

  21. Energy Sources for Muscle Contraction (3) : (Fast fibres predominantly) For fairly short bursts of activity you will use up an energy reserve (effectively an ATP storage pool) of creatine phosphate, Cr.P + Mg.ADP  Mg.ATP + Cr Cr = creatine This reaction is readily reversible; the energy from CrP is released very quickly (a few seconds) allowing sprints. In insect muscles: Arginine.P replaces Creatine.P

  22. Energy Sources for Muscle Contraction (4) : ATP ADP Pi PCr Cr Mg2+ Ca2+ Total (mmol/kg) 5 0.8 3 25 13 10 1 Free (mM) 4 0.02 2 25 13 3 0.0001 Note: More Cr.P than ATP Once Cr.P is used up the high requirement for more ATP is met by glycolysis (end-product lactic acid) So these muscle fibres can work anaerobically for brief periods, but accumulate lactic acid. Typically this metabolism predominates in muscles used for sprints - fast glycolytic fibres predominate. After exercise ceases the ATP and PCr must be regenerated and lactic acid metabolised.

  23. Energy Sources for Muscle Contraction (5) : Type 1 fibres: For long periods of sustained work – type 1/oxidative/ tonic or slow twitch fibres i.e. These muscle fibres require a supply of oxygen to enable oxidative phosphorylation to go on in the mitochondria to produce a continuous supply of ATP. Energy sources here are primarily glucose (glycolysis and the TCA cycle) and over longer periods the glycogen stores. Requires the mitochondria. Mitochondria occupy about 30% of volume of the heart and these muscle fibres. It is the high(er) concentration of cytochromes/myoglobin etc. which give these fibres their red colour

  24. Neuromuscular junction – muscle endplate Transmitter is usually acetylcholine Muscle activation by nerves (1)

  25. Muscle activation by nerves (2) Events Leading to Muscle Contraction e.g. acetylcholine

  26. 3-D section of a skeletal muscle cell Muscle activation by nerves (3)

  27. Muscle activation by nerves (4) • Control by nerves – action potentials in motor neurons • Neuromuscular junction • Muscle plasma membrane depolarises • Propagates down ‘T’ tubules into centre of fibre • ‘T’ tubule close to sarcoplasmic reticulum (SR) • Di-hyropyridine receptor  ryanodine receptor • Calcium release from SR - induces further calcium release • Ca++ binds to troponin complex – troponin C (part of the sarcomeric thin filament)

More Related