STRUCTURE AND MECHANISM OF MUSCLE CONTRACTION PRESENTED BY
STRUCTURE AND MECHANISM OF MUSCLE CONTRACTION PRESENTED BY MISS SUBHAPRADA LENKA (Lect. in Zoology) KHEMUNDI COLLEGE , DIGAPAHANDI 8 -1
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Introduction: A. The three types of muscle in the body are 1. Skeletal 2. Smooth 3. Cardiac 8 -2
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Structure of a Skeletal Muscle A. Muscle is made of -skeletal muscle tissue -connective tissues -nervous tissue -blood 8 -3
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. B. Connective Tissue Coverings 1. Fascia-fibrous connective tissue that separates the individual muscles 2. This connective tissue extends beyond the ends of the muscle and gives rise to tendons that are fused to the periosteum of bones. 8 -4
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 3. 4. 5. 6. 7. 8 -5 Aponeuroses-connective tissue that attaches muscle to muscle The layer of connective tissue around each whole muscle is the epimysium; Fascicles-individual muscle compartments Perimysium-separates the fascicles Each muscle cell (fiber) is covered by a connective tissue layer called endomysium.
STRUCTURE OF A SKELETAL MUSCLE 8 -6
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 8 -7
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. C. Skeletal Muscle Fibers 1. Each muscle fiber is a single, long, cylindrical muscle cell. 2. 8 -8 Sarcolemma-cell membrane Sarcoplasm-cytoplasm with many mitochondria and nuclei; -has myofibrils. -myofibrils are separated into compartments called sarcomeres that contain thick filaments and thin filaments.
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. a. b. c. 8 -9 Thick filaments of myofibrils are made up of the protein myosin. Thin filaments of myofibrils are made up of the protein actin. The organization of these filaments produces striations.
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 3. 8 - 10 A sarcomere extends from Z line to Z line. a. I bands -light bands -made up of actin -anchored to Z lines b. A bands -dark bands -made up of overlapping thick and thin filaments. c. In the center of A bands is an H zone, consisting of myosin filaments only.
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 8 - 11
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 4. Beneath the sarcolemma of a muscle fiber lies the sarcoplasmic reticulum (endoplasmic reticulum), which is associated with transverse (T) tubules (membrane channels) - activate the muscle contraction mechanism 8 - 12
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 8 - 13
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Neuromuscular Junction 1. The site where the motor neuron and muscle fiber meet a. The muscle fiber membrane forms a motor end plate -nuclei and mitochondria are abundant. b. Neurotransmitters (chemicals) are stored at the end of the motor neuron -these are released from the motor neuron and stimulate the muscle 8 - 14
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 8 - 15
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Skeletal Muscle Contraction A. 2 events take place in a muscle contraction -shortening of sarcomeres -pulling of the muscle against its attachments. 8 - 16
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. B. Role of Myosin and Actin 1. Myosin consists of two twisted strands with globular cross-bridges projected outward along the strands. 2. Actin is a globular protein with myosin binding sites; -tropomyosin and troponin are two proteins associated with the surface of the actin filaments. 8 - 17
8 - 18
8 - 19
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 3. 8 - 20 sliding filament theory of muscle contraction -the myosin crossbridge attaches to the binding site on the actin filament and bends, pulling on the actin filament -it then releases and attaches to the next binding site on the actin, pulling again.
How does ATP help? n Myosin has an enzyme ATPase u Breaks down ATP into ADP t This releases energy for the muscle cell. • This energy causes myosin crossbridge to attach and pull on the actin. u ADP will be made back into ATP through cell respiration u After one pull, another ATP attaches on for the myosin to attach to the next actin. 8 - 21
8 - 22
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. How does a muscle know to contract? 1. The motor neuron must release the neurotransmitter acetylcholine -this triggers the stimulus 2. Protein receptors in the motor end plate detect the neurotransmitters, and a muscle impulse spreads over the surface of the sarcolemma and into the T tubules, where it reaches the sarcoplasmic reticulum. 8 - 23
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 3. 4. 8 - 24 sarcoplasmic reticulum releases calcium to the sarcoplasm The high concentration of calcium in the sarcoplasm interacts with the troponin and tropomyosin molecules, which move aside, exposing the myosin binding sites on the actin filaments.
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 5. 8 - 25 Myosin cross-bridges now bind and pull on the actin filaments, causing the sarcomeres to shorten.
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 8 - 26
Relaxation -After the nervous impulse has been received, acetylcholinesterase (enzyme) rapidly decomposes the acetylcholine. -Then, calcium is returned to the sarcoplasmic reticulum, and the linkages between myosin and actin are broken. 8 - 27
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Energy Sources for Contraction 1. Energy for contraction comes from molecules of ATP. This chemical is in limited supply and so must often be regenerated 2. Creatine phosphate, which stores excess energy released by the mitochondria, is present to regenerate ATP from ADP and phosphate. 8 - 28
Copyright The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 3. 4. 8 - 29 Whenever the supply of ATP is sufficient, creatine phosphokinase promotes the synthesis of creatine phosphate. As ATP decomposes, the energy from creatine phosphate can be transferred to ADP molecules, converting them back to ATP.
THANK YOU 8 - 30
- Slides: 30