Muscular System Lecture Slides 2024 PDF

Muscle Tissue (Introduction) One of the four primary tissue types Consists of elongated muscle cells specialized for contraction Three types of muscle tissue 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Copyright © 2020, 2017, 2013 Pearson Education, Inc. All...

Muscle Tissue (Introduction) One of the four primary tissue types Consists of elongated muscle cells specialized for contraction Three types of muscle tissue 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Skeletal Muscles Composed of skeletal muscle tissue Also contain connective tissue, nerves, blood vessels Directly or indirectly attached to bones Muscular system includes about 700 skeletal muscles Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Skeletal Muscle Functions Producing Movement Maintain posture and body position Support soft tissues Guard entrances and exits Maintaining body temperature Storing Nutrients Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Organization of Skeletal Muscle Tissue Skeletal muscles contain: – Skeletal muscle tissue – Connective tissues – Blood vessels – Nerves Each skeletal muscle cell called a muscle fiber Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Figure The Organization of Skeletal Muscles Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Connective Tissue Organization 1. Epimysium – Covers the entire muscle 2. Perimysium – Divides the muscle into fascicles or bundles of muscle fibers – Contains blood vessels and nerves supplying fascicles 3. Endomysium – Covers each muscle fiber and ties fibers together – Contains capillaries and nerve fibers Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Features of Skeletal Muscle Fibers Can be very long (up to 60 c m or 24 inches) enti eter Each fiber is multinucleate (contains hundreds of nuclei) Have a repeating pattern that gives them a striped or striated appearance Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Figure Organization of a Skeletal Muscle Fiber Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Sarcolemma and Transverse Tubules ________________ is a muscle cell’s plasma membrane Surrounds the sarcoplasm or cytoplasm Contains openings that lead into network of tubules called ________________________, or ___________________ __________ allow electrical impulses from sarcoplasm to reach cell’s interior – Allows unified contraction of entire muscle fiber Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Myofibrils Cylinder-shaped structures running the length of a muscle fiber Hundreds to thousands in each fiber Encircled by T tubules Composed of bundles of thick and thin ______________ – __________ molecules are found in thin filaments – __________ molecules are found in thick filaments Their shortening creates muscle fiber contraction Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Sarcoplasmic Reticulum Specialized smooth endoplasmic reticulum Forms network around each myofibril Expanded portion on either side of T tubules is the terminal cisterna – Contains high concentrations of calcium ions, whereas that of the cytosol (fluid portion of cytoplasm) is very low Triad – Combination of two terminal cisternae and one T tubule Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Sarcomeres Repeating functional units of myofilaments – Smallest functional unit of skeletal muscle fiber – Each myofibril has about 10,000 sarcomeres end to end Arrangement of thick and thin filaments produce the banded or striated appearance of the fiber – Thick filaments lie in the center of the sarcomere – Thin filaments are at either end of a sarcomere Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Sarcomere Organization Figure The Organization of a Skeletal Muscle Fiber Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Sarcomere Lines Z lines – Mark the boundary at each end of the sarcomere M line – Located in the center of each sarcomere – Made of proteins that connect central portions of the thick filaments Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Thin Filament Thin twisted strand of mainly protein actin At rest, active sites covered by strands of tropomyosin Tropomyosin strands held in position by troponin Contains active sites where thick filament can bind Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Thick Filaments Composed of protein called myosin Each myosin molecule has tail and globular head Tails point inward; heads project outward Heads interact with active sites on actin during contraction – Requires movement of troponin and tropomyosin to uncover active sites – Calcium unlocks active sites, by binding to troponin and removing the tropomyosin Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Sliding Filament Theory(Model) Explanation for sarcomere contraction Based on observed changes in sarcomere – I bands get smaller – Z lines move closer together – H bands decrease – Zones of overlap get larger – Length of A bands remain the same – Conclusion: thin filaments are sliding toward the center of the sarcomere and thick filaments are not moving Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Mechanism for Sliding Filaments Myosin heads of thick filaments bind to active sites on thin filaments – Upon binding, myosin heads are called cross-bridges Heads then pivot toward center of sarcomere, pulling thin filament in that direction Cross-bridges detach (due to the binding of a molecule of ATP) and return to original position (as ATP splits into ADP and P) Cycle repeats Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Neuromuscular Junction (1 of 2) Specialized intercellular connection between a motor neuron and a skeletal muscle fiber Consists of an axon terminal of a motor neuron and a motor end plate of a muscle fiber – Axon terminal of the neuron ▪ Expanded end that contains vesicles filled with acetylcholine (ACh), a neurotransmitter – Motor end plate is portion of muscle fiber sarcolemma Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Neuromuscular Junction (2 of 2) ACh released from axon terminal Diffuses across synaptic cleft Binds to the receptor on the motor end plate Synaptic cleft and the motor end plate contain acetylcholinesterase (AChE) – Enzyme that breaks down ACh Neurons generate an action potential (electrical impulse) in sarcolemma Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Contraction Cycle Series of molecular events that enable muscle contraction. Action potential travels over the sarcolemma, down into the T tubules Triggers release of calcium from the terminal cisternae of the sarcoplasmic reticulum Calcium binds to troponin and the contraction cycle starts Active sites exposed, myosin heads bind to them forming cross-bridges Functions as a hinge that lets the head pivot, moves towards M line, movement is called power stroke Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Steps that Initiate a Muscle Contraction Figure Steps Involved in Skeletal Muscle Contraction and Relaxation Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Steps that End a Muscle Contraction Figure Steps Involved in Skeletal Muscle Contraction and Relaxation Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Amount of Tension Produced Amount of tension produced in an individual muscle fiber depends on number of cross-bridges pivoting in a muscle fiber All sarcomeres in a muscle fiber are involved in contraction – Individual muscle fibers are either fully contracted (“on”) or relaxed (“off”) – Cannot vary tension by changing number of contracting sarcomeres Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  25 Motor Unit (1 of 2) Stimulation of a muscle by a nerve impulse is required before a muscle can shorten and produce movement A motor neuron is the specialized nerve that transmits an impulse to a muscle, causing contraction Neuromuscular junction (NMJ): Point of contact between a nerve ending and the muscle fiber Motor unit: Combination of a motor neuron with the muscle fibers it controls (Figure 8-5) Copyright © 2020 by Elsevier Inc. All rights reserved. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Motor Unit Arrangement Figure The Arrangement of Motor Units in a Skeletal Muscle Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  27 Muscle Stimulus (1 of 2) A muscle will contract only if an applied stimulus reaches a certain level of intensity – Threshold stimulus: Minimal level of stimulation required to cause a muscle fiber to contract Once stimulated by a threshold stimulus, a muscle fiber will contract completely, a response called “all or none” Copyright © 2020 by Elsevier Inc. All rights reserved. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Muscle Tone Muscle tone – Resting tension in skeletal muscle – Some motor units in each muscle are active at all times, even when muscle is relaxed – Stabilizes position of bones and joints – Maintains posture and body position Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  29 Muscle Stimulus (2 of 2) Different muscle fibers in a muscle are controlled by different motor units having different threshold- stimulus levels – Although individual muscle fibers always respond “all or none” to a threshold stimulus, the muscle as a whole does not – Different motor units responding to different threshold stimuli permit a muscle as a whole to execute contractions of graded force Copyright © 2020 by Elsevier Inc. All rights reserved. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Types of Skeletal Muscle Contraction Isotonic contraction – Tension rises and length of the muscle changes – Then tension remains constant until relaxation – Examples: lifting a book, walking Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Isometric Contraction Isometric contraction – Muscle length stays the same – Tension produced does not exceed the load – Example: pushing against a wall Most daily activities involve a combination of isotonic and isometric contractions. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  32 Types of Muscle Contraction. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  33 Movements Produced by Skeletal Muscle Contractions (1 of 2) Angular movements – Flexion: Decreases an angle – Extension: Increases an angle – Abduction: Away from the midline – Adduction: Toward the midline Circular movements – Rotation: Around an axis – Circumduction: Move distal end of a part in a circle – Supination and pronation: Hand positions that result from twisting the forearm Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  34 Movements Produced by Skeletal Muscle Contractions (2 of 2) Special movements –Dorsiflexion and plantar flexion: Ankle movements (upward and downward foot movement) –Inversion and eversion: Ankle movements (sideways) Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  35 Flexion and Extension of the Elbow A and C: Courtesy Rolin Graphics.. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  36 Flexion and Extension of the Knee A and C: Courtesy Rolin Graphics. Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  37 Examples of Body Movements Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved ATP is Energy Source for Muscle Contraction Muscle contraction requires large amounts of energy in the form of ATP Resting muscle fiber contains only enough energy reserves to maintain contraction until more ATP is generated During contraction, muscle generates ATP at same rate as it is used Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Aerobic Metabolism Requires oxygen Normally provides 95 percent of resting muscle cell’s ATP needs Occurs in the mitochondria Involves breaking down organic substrates through a series of chemical reactions End products are ATP, water, and carbon dioxide Resting muscle fibers depend mainly on aerobic fatty acid metabolism to produce ATP Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Glycolysis Breaks glucose down to pyruvate Occurs in the cytoplasm of the cell Is an anaerobic process (does not require oxygen) – Can continue to provide ATP when mitochondria are limited by low oxygen levels – Only yields 2 ATP per glucose If pyruvate produced faster than can be used by mitochondria: – Pyruvate is converted to lactic acid – Potentially causing a pH problem in cells Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Muscle Fatigue Muscle will no longer perform at required level, even if stimulated – Caused by depletion of energy reserves or a decline in pH from lactic acid production Affects muscles of endurance athletes after using stores of glycogen and lipids Affects sprinters more quickly as they rapidly build up lactic acid, lowering the tissue pH Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved The Recovery Period Time of returning muscle to normal pre-exertion conditions by: – Restoring oxygen levels – Removing lactic acid – Replacing intracellular energy reserves – Losing heat produced during contraction Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Muscle Performance Measured in force – Maximum amount of tension produced by a muscle or muscle group Measured in endurance – Amount of time a particular activity can be performed Two factors determine performance 1. Types of fibers in muscle (fast-twitch and slow-twitch) 2. Physical conditioning or training Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  Divisions of Skeletal Muscles 1. Axial muscles – Arise on the axial skeleton – About 60 percent of skeletal muscles in this category – Position head and spinal cord and move rib cage 2. Appendicular muscles – Stabilize or move the appendicular skeleton Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Major Skeletal Muscles, Anterior View An Overview of the Major Skeletal Muscles Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved Major Skeletal Muscles, Posterior View An Overview of the Major Skeletal Muscles Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved  Health Promotion Exercise Engages Multiple Systems Muscular system – Active muscles consume oxygen and generate CO2 and heat Cardiovascular system – Increases heart rate and speeds up delivery of oxygen Respiratory system – Increases rate and depth of respiration Integumentary system – Dilation of blood vessels and sweating combine to increase cooling Nervous and endocrine systems – Control heart rate, respiratory rate, and release of stored energy Copyright © 2020, 2017, 2013 Pearson Education, Inc. All Rights Reserved