BIO10004 Week 4.2 Muscles 1 PDF

Muscles 1 Dr Greg Davis Martini Chapter 10 Copyright notice  Learning objectives and reading At the end of this lecture you should be able to: 1. Specify the function of skeletal muscle 2. Describe the organisation of muscle at the tissue level 3. Describe...

Muscles 1 Dr Greg Davis Martini Chapter 10 Copyright notice  Learning objectives and reading At the end of this lecture you should be able to: 1. Specify the function of skeletal muscle 2. Describe the organisation of muscle at the tissue level 3. Describe the characteristics of skeletal muscle fibres and identify the structural components of a sarcomere 4. Identify the components of the neuromuscular junction and summarise the events involved in the neural control of skeletal muscle contraction and relaxation 5. Identify the structural and functional difference between skeletal, cardiac and smooth muscle fibres Reading guide (textbook): Sections:10-1, 10-2, 10-3 , 10-4, 10-5, 10-8 Figures: 10-1, 10-3, 10-6, 10-7, 10-8, 10-10, 10-22, 10-23 Tables: 10-3 Questions: 1, 2, 9, 11, (20, 23)  Muscle tissue One of the 4 tissue types Has various roles in the body Important to understand for muscular system 3 types of muscle tissue – Skeletal – Cardiac – Smooth Required to move, circulate blood, push solids and fluids in digestive tract and other organs Focus on skeletal muscle initially  Functions of skeletal muscle Produce skeletal movement Maintain posture and position Support soft tissues Guard body entrances and exits Maintain body temperature Store nutrients  Skeletal muscle structure Muscle tissue Epimysium Connective tissue Perimysium Endomysium Blood vessels Nerves Skeletal muscle Skeletal muscle fibres  Detailed structure Each muscle fibre has ~100-1000s of myofibrils – 1-2 µm in diameter – Same length as muscle cell Each myofibril has protein bundles or myofilaments (2 types) – Thin (actin) – Thick (myosin) Each myofilament has ~10,000 sarcomeres (with bands) – Interactions between sarcomeres create contractions – I band, A band, H band (M line) Sarcomere structure  Saromere bands A band – Overlapping myosin (thick) actin (thin) filaments – M line is centre of the band (M = middle) – H band only thick filaments – Zone of overlap has both thin and thick filaments I band – Thin filaments only – Z line mark boundaries between adjacent sarcomeres Thick filaments  Sliding filaments The filaments slide over each other Provide a ratcheting motion for shortening Muscle action  Muscle contraction Important to note Muscle shortening – contraction is the active process Muscles lengthening – passive by being pulled externally Muscles pull but do not push  Nervous/muscular Site of action is the neuromuscular junction 1. Axon contains neurotransmitter (ACh) 2. Action potential travels along axon 3. Triggers release when reaches terminal 4. ACh diffuses across synaptic cleft 5. Na+ inrush triggers muscle action potential The cytoplasm of the axon terminal contains vesicles filled P The stimulus for ACh release is the arrival of an electrical When the action potential reaches the neuron's axon ACh molecules diffuse acrass the synaptic cleft and bind to ACh The sudden inrush of sodium ions results in the generation of an with molecules of acetylcholine, impulse, or action potential, terminal, permeability receptors on the surface of the action potential in the sarco­ or ACh. Acetylcholine is a at the axon terminal. An action changes in its membrane motor end plate. ACh binding lemma. ACh is removed from the neurotransmitter, a chemical potential is a sudden change in trigger the exocytosis of ACh alters the membrane's permeabil­ synaptic cleft in two ways. ACh released by a neuron to change the membrane potential that into the synaptic cleft. ity to sodium ions. Because the either diffuses away from the the permeability or other travels along the length of the Exocytosis occurs as vesicles extracellular fluid contains a synapse, or it is broken down by properties of another cell's plasma axon. fuse with the neuron's plasma high concentration of sodium AChE into acetic acid and choline. membrane. The synaptic cleft and membrane. ions, and sodium ion This removal inactivates the ACh the motor end plate contain concentration inside the cell is receptor sites. The muscle fiber molecules of the enzyme very low, sodium ions rush into pictured above indicates the acetylcholinesterase (AChE), the cytosol. propagation of the action which breaks down ACh. potential along the sarcolemma. Motor end plate ACh receptor site  Cardiac muscle tissue Found only in the heart Excitable tissue Short, small cells – 10-20 µm diameter – 50-100 µm length Striated appearance Conductive ends – Intercalated disks – Electrical connection Aerobic metabolism  Action of cells Intercalated disks make electric continuity – Heart effectively is one large cell in some respects Cells are spontaneously active – Even when single cells are isolated – Has faster (pacemakers) and slower cells (triggered) – Fastest rate in atria, slowest in ventricles Rate modulated by action of nervous system – Sympathetic increase rate and force – Parasympathetic slow rate and reduce force  Smooth muscle Different to skeletal & cardiac muscle Regulatory role – Sheaths around most organs, blood vessels – Integumentary, cardiovascular, respiratory, digestive, urinary, reproductive No striations (sarcomeres) – 5-10 µm diameter – 30-200 µm length Contractions spontaneous ‘Bunch up’ effect Very little nervous innervation Mainly hormonal control Comparison table  Summary Muscle tissue – Functional role of skeletal muscle Skeletal muscle structure – Fibres, connective tissue, blood vessels, nerves – Sarcomeres – Bands and sliding filaments Neuromuscular junction Cardiac muscle Smooth muscle