Chapter 9: The Muscular System PDF

The Muscular System Skeletal Muscle Tissue and Muscle Organization Chapter 9 Intro Many physiological processes and almost all dynamic interactions with the environment involve muscle tissues. Muscle tissue is one of the 4 Primary types defined in Ch. 3 Muscle tissue can be divided into three types:...

The Muscular System Skeletal Muscle Tissue and Muscle Organization Chapter 9 Intro Many physiological processes and almost all dynamic interactions with the environment involve muscle tissues. Muscle tissue is one of the 4 Primary types defined in Ch. 3 Muscle tissue can be divided into three types: 1. Skeletal: moves the by pulling on the bones 2. Cardiac: pushes through the vessels of the cardiovascular system 3. Smooth: pushes fluids and solids along the tract and other systems All 3 muscle types share 4 properties: 1. Excitability: The ability to respond to (nerves & hormones) 2. Contractibility: The ability to shorten or exert a that is harnessed by connective tissue (tendons) 3. Extensibility: The ability to contract over a range of resting 4. Elasticity: The ability to return ot its original after contraction For this exam we focus on the skeletal muscle: Cardiac will be included in the cardiovascular Smooth will be discussed at various times is different body systems Functions Skeletal muscles are contractile organs directly or indirectly attached to bones. They Function to: 1. 2. 3. 4. 5. Produce skeletal movement Maintain body posture Support soft tissues Regulate the entry/exit of materials Maintain body temperature Organization of Skeletal Muscle epimysium : dense irregular connective tissue that surrounds muscle perimysium : divides muscle into internal compartments containing the fascicles endomysium: surrounds each muscle fiber Tendons : Attach muscle to bone, cartilage, skin or other muscle Microanatomy of the Skeletal Muscle Skeletal muscles vary from the typical muscle plan described in Ch 2 in many ways: The membrane of skeletal muscle is called Sarcolemma & the cytoplasm is referred to as sarcoplasm Skeletal muscles are much larger than typical muscles Muscles cells are multinucleate Deep indentions in the sarcolemma form a network of transverse Tubules (T-Tubules) extending into the sarcoplasm The sarcoplasm contains 100s to 1000s of cylindrical fibers called myofibrils The active shortening of myofibrils is responsible for contraction They are composed of protein filaments called myofilaments 2 Types: Thick and thin Contain actin and myosin proteins that interact during muscular contraction Organized into repeating units called Sarcomeres Surrounding the myofibrils is the sarcoplasmic reticulum Similar to the Smooth ER of other cells Responsible for the storage of Ca ions Sarcomere Organization Sarcomeres are the Smallest functional unit of muscle fibers Differences in the size, density, and distribution of the thick/thin filaments give the sarcomere a Banded appearance Thin Filaments: a twisted strand containing 4 proteins: 1. F-actin 2. Nebulin 3. Tropomyosin 4. Troponin Troponin & Tropomyosin are Regulatory proteins: Tropomyosin covers the active site preventing Actin-Myosin interaction Troponin holds tropomyosin in place, must move in order to initiate contraction Thick Filaments: composed of bundles of myosin Form cross-bridges when interacting with thin filaments during contraction Muscle Contraction A contraction occurs when a muscle exerts a pull, or tension, as it Shortens in length. Contractions result from the Interactions between thin and thick filaments within each sarcomere The mechanism of contraction is explained in the Sliding-filament Theory At the microscopic level a contraction is seen as a change in size of the sarcomere as the positions of the A-band, I-band, H-zone & Z lines change Neural Control of Contractions The CNS controls skeletal muscle contraction through the interaction of the motor-neuron and the motor end plate of the sarcomere: This intersection is referred to as the Neuro-muscular junction The process of contraction involves the following steps: Motor units and Muscular Control A motor unit (MU) is a single motor neuron and all of the muscle fibers that it controls. The Smaller the MU the finer the control of movement The Larger the MU the more force that can be generated Skeletal muscle contraction occurs when MUs are stimulated Force is determined by 2 things: 1. 2. The The of MUs involved & of stimulation of the MUs MUs contract on the All or none Principle Leads to motor unit Recruitment Gradual increase in the number of Mus as force increases Recruitment from smallest to largest Hypertrophy vs Atrophy Hypertrophy: results from repeated, exhaustive stimulation Muscles develop more myofibrils & Mitochondria Enlarges the size of the muscle belly V VS Atrophy : results from a lack of regular stimulation to the muscle Loss of muscle tone and mass Muscle is smaller and weaker due to loss of intracellular contractile proteins Types of Muscle Fibers Different muscles are designed for different actions, the types partly determine this action. There are 3 Fiber Types in the Human body: 1. Fast ( White ) Fibers have: Large diameter, densely packed myofibrils, large glycogen reserves, and few mitochondria The Majority of skeletal muscles are fast type due their rapid response when stimulated 2. Slow ( Red ) Fibers have: Smaller diameter and many more mitochondria than Fast Fibers Take 3x’s longer to contract as they are specialized for long & sustained contractions 3. Intermediate ( Pink ) Fibers have: Characteristics in between fast and slow fibers Organization of Skeletal Muscle Muscle Terminology Each skeletal muscle is attached at two locations within the skeleton: Muscles begin at the origin The fixed or most proximal location of attachment Muscles terminate at the insertion The moving part, also the most Distal point of attachment Skeletal Muscles are grouped int 4 categories based on their primary actions: 1. 2. 3. 4. Agonist: prime mover of a limb Antagonist: actions opposed the agonist Synergist: Assists the Agonist in a particular move Fixators: Stabilize joints Break