Brunel University London - Cell Signalling and Movement - PDF

Introduction to Medical Sciences 1 Cell Signalling and Movement Sarcomeres and Sliding Filament Theory Part 2 Copyright © Brunel University London v.3 2024. All rights reserved. Cell Signalling and Movement Dr Julianna Gal Version 3 2024 Copyrig...

Introduction to Medical Sciences 1 Cell Signalling and Movement Sarcomeres and Sliding Filament Theory Part 2 Copyright © Brunel University London v.3 2024. All rights reserved. Cell Signalling and Movement Dr Julianna Gal Version 3 2024 Copyright © Brunel University London v.3 2024. All rights reserved. Cell Signalling and Movement Sarcomeres and Sliding Filament Theory Part 2 Copyright © Brunel University London v.3 2024. All rights reserved. Sarcomeres and Sliding Filament Theory Part 1: Skeletal muscle organisation and structure of sarcomeres Part 2: Skeletal muscle contraction and the sliding filament theory Part 3: Control of skeletal muscle force and role of calcium Copyright © Brunel University London v.3 2024. All rights reserved. Sarcomeres and Sliding Filament Theory Part 2: Skeletal muscle contraction and the sliding filament theory Overview Sarcomere changes and evidence for the sliding filament theory Force-length properties of sarcomeres and implications for whole muscle Copyright © Brunel University London v.3 2024. All rights reserved.  How does muscle contraction happen? Length change occurs within the sarcomeres Conduct experiments where muscle fibres are stimulated and allowed to contract or are forcibly stretched then quickly prepared for microscopy and then inspect sarcomeres Resulting observations support sliding filament hypothesis Copyright © Brunel University London v.3 2024. All rights reserved. Fully relaxed sarcomere of a skeletal muscle fibre Copyright © Brunel University London v.3 2024. All rights reserved. Fully contracted sarcomere of a skeletal muscle fibre Copyright © Brunel University London v.3 2024. All rights reserved. Experimental observations that support sliding filament hypothesis Distance between Z-discs changes I-band thickness changes A-band thickness remains unchanged Copyright © Brunel University London v.3 2024. All rights reserved.  Sliding Filament Theory of Muscle Contraction Thick filament myosin head binds to thin filament: cross-bridge formed Biochemical reaction causes ‘shape change’ of myosin head, which pulls on the thin filament Repeated attachment, shape change, pulling, and detachment of myosin heads pull Z-discs closer together, shortening the sarcomere Myosin thick filaments and actin thin filaments SLIDE relative to one another, changing the length of the sarcomere without changing the lengths of either thick or thin filaments themselves Copyright © Brunel University London v.3 2024. All rights reserved. Cross-Bridge Cycle couples ATP hydrolysis to sarcomere contraction Copyright © Brunel University London v.3 2024. All rights reserved. Further evidence for sliding filaments, sarcomere length and muscle fibre force? Conduct experiments where muscle fibres are positioned and held at shortened or stretched lengths (by an external force) Then stimulate muscle fibres to induce ‘isometric contraction’ measure length of target sarcomere measure force generated by muscle fibre Copyright © Brunel University London v.3 2024. All rights reserved. Muscle fibres stimulated to produce force at various initial lengths show maximum force production at a distinct range of sarcomere lengths Copyright © Brunel University London v.3 2024. All rights reserved.  The sliding filament theory offers a mechanism for explaining sarcomere length change and how it is linked to force production Sarcomeres lie in series along a muscle fibre Muscle fibres are bundled together as fascicles and whole muscle Muscle fibre force is collectively and ultimately transferred to tendon Tendon is attached to bone Muscle force pulls on bone If whole muscles behave similarly to sarcomeres, then there exist muscle lengths and therefore joint angles (or collectively, postures), wherein muscles can generate maximum force (or torque) Copyright © Brunel University London v.3 2024. All rights reserved. Summary Repeated attachment, shape change, pulling, and detachment of myosin heads pull Z-discs closer together, shortening the sarcomere, creating pulling force Myosin thick filaments and actin thin filaments SLIDE relative to one another, changing the length of the sarcomere without changing the lengths of either thick or thin filaments themselves Sarcomeres exhibit optimal length for maximising force production Copyright © Brunel University London v.3 2024. All rights reserved. Slide images adapted from the following sources Slide 7 and 8 Marieb, E.N. and Hoehn, K. Human Anatomy & Physiology Ninth Edition. p. 285. Copyright 2013, Pearson Education, Inc. Slide 11 Blaustein, Mordecai P. Cellular Physiology and Neurophysiology, 14, 185-199. Copyright 2020, Elsevier, Inc. Slide 13 Blaustein, Mordecai P. Cellular Physiology and Neurophysiology, 16, 217-235. Copyright 2020, Elsevier, Inc. Copyright © Brunel University London v.3 2024. All rights reserved. Dr Julianna Gal Copyright © Brunel University London v.3 2024. All rights reserved.