Chapter 8 Muscular System

Introduction Three types of muscles: Skeletal Smooth Cardiac

Structures of Skeletal Muscle Tissues present in skeletal muscle Muscle, nervous, connective (including blood) Skeletal muscle is held in place by layers of fibrous connective tissue called fascia *fascia covers the muscle

Structures of Skeletal Muscle Fascia extends beyond the end of a skeletal muscle to form a cord like tendon (muscle to bone) When connective tissues extend beyond the muscle to form a sheet-like structure, it is called an aponeuroses Attach to bone or to adjacent muscles

Structures of Skeletal Muscle Fascicles are bundles of skeletal muscle fibers The connective tissue that covers each muscle fiber within a fascicle is the endomysium *the muscles are enclosed and separated into compartments by epimysium and perimysium (figure 8.1) *blood vessels and nerves pass through layers

Analogy Time! Pretend you are going to play a joke on someone and give them 100 pencils. The pencils will represent muscle fibers. First you wrap each individual pencil in tissue paper (dense tissue paper of course!). This would be endomysium. Then you take about 10 pencils in a bundle (a fascicle) and wrap them in paper (Perimysium). Then you take all the bundles and wrap them in gift wrap (epimysium). But you are going to mail this joke, so you also have to wrap it in brown paper representing the fascia.

Skeletal Muscle Fiber Single muscle fiber Single cell, thin, elongated, contracts Sarcoplasm (cytoplasm) contains Many nuclei and mitochondria Myofibrils (parallel)

Skeletal Muscle Fiber Make note of this! Myofibrils Fundamental role in contraction 2 kinds of protein filament Thin – actin Thick – myosin

Skeletal Muscle Fiber What are sarcomeres? (figure 8.3) Functional units of muscle contractions 1st are light bands of actin filaments which are attached to Z lines. 2nd are A bands which contain myosin filaments - overlap actin filaments. The segment of a myofibril from one Z line to the next Z line is known as a sarcomere Myofibrils are sarcomeres joined end to end

Skeletal Muscle Fibers The network of membranous channels in the cytoplasm of muscle fibers is the sarcoplasmic reticulum. A second set of channels is the tranverse tubules which extend inward from the fibers membrane. These channels activate muscle contraction when the fiber is stimulated.

Questions to Answer What is tendinitis? What causes two of the most common forms of muscular dystrophy? What causes muscle strain? What is the difference in a mild form and a severe form? *Write your answers on a piece of scrap paper

Labeling Part D of “Structure of a Skeletal Muscle”

Neuromuscular Junction Write these notes below “D” on page 58 Motor neurons – neurons that control effectors Synapse – functional connection between a motor neuron and a skeletal muscle fiber Muscle fibers and motor neurons not directly connected – a gap between them called synaptic cleft

Neuromuscular Junction Neurotransmitters – chemicals released by the neurons to allow communication with the cells (tell fibers when to move) Neuromuscular Junction – connection between motor neuron and muscle fiber

Neuromuscular Junction End of Motor Neuron – rich in mitochondria and synaptic vesicles (store neurotransmitters) Motor end plate – muscle fiber membrane is folded and contains many nuclei and mitochondria Nerve impulse  end of motor neuron  release neurotransmitters  motor end plate  muscle contraction!

Skeletal Muscle Contraction “Sliding Filament Theory” Roles of Actin and Myosin Actin - have a binding site for the myosin cross bridges Myosin - have cross bridges that “pull” actin for contraction *Part B is answered by notes on page 58

Skeletal Muscle Contraction “Sliding Filament Theory” Use highlighter and Figure 8.8 printout to highlight key steps The sliding filament model gets its name from the way the sarcomeres shorten The filaments do not change, they slide past one another Actin slides toward the center of the sarcomere from both ends

Skeletal Muscle Contraction “Sliding Filament Theory” Acetylcholine (neurotransmitter) and Calcium ions (Ca+) Nerve impulse  motor neuron  releases acetylcholine  diffuses to muscle fiber  causes muscle impulse  allows diffusion of Ca+ into muscle fiber  binding sites open  muscle contraction begins

Skeletal Muscle Contraction “Sliding Filament Theory” What are cross bridges? formed when the projecting parts of the myosin filament that will occupy a binding site on the actin filament and pull

Skeletal Muscle Contraction “Sliding Filament Theory” The action of acetylcholine is halted by the enzyme acetylcholinesterase The enzyme decomposes the neurotransmitter

Skeletal Muscle Contraction Review Handout Write on own sheet of paper Will finish in class tomorrow Worth 20 points

Skeletal Muscle Contraction How does ATP supply energy for muscle contraction? ATP = stored energy ADP + P = released energy What do these equations mean?

Skeletal Muscle Contraction How does creatine phosphate supply energy for muscle contraction? Stores energy generated by the mitochondria much like ATP 4 to 6 times more abundant than ATP Energy is transferred to ADP molecules, converting them back to ATP

Skeletal Muscle Contraction What happens when creatine phosphate is exhausted due to heavy work? (think back to Biology) How is commercially produced creatine used?

Skeletal Muscle Contraction What substance in muscle seems able to store oxygen temporarily? Myoglobin, a pigment, is synthesized in muscle cells and imparts the reddish-brown color of skeletal muscle tissue It is able to combine loosely with oxygen, allowing temporary storage *hemoglobin in red blood cells acts in the same way

Skeletal Muscle Contraction Why is oxygen necessary for muscle contraction? Cellular respiration of glucose, which supplies the energy needed for a sufficient amount of ATP Is this process aerobic or anaerobic?

Skeletal Muscle Contraction How does the muscle continue to contract in the absence of oxygen? Anaerobic respiration Glucose  pyruvic acid  lactic acid Yields a much smaller amount of energy than aerobic respiration Glucose can be synthesized from lactic acid in the liver

Skeletal Muscle Contraction When do you experience oxygen debt? Lactic acid accumulation in the liver Oxygen debt = amt. of oxygen liver cells require to convert lactic acid into glucose + amt. of oxygen muscle cells require to restore ATP and creatine phosphate *repayment could take several hours *training can help increase your bodies ability to repay its oxygen debt by increasing glycolytic enzmes, mitochondria, and capillaries

Skeletal Muscle Contractions What is meant by muscle fatigue? A muscle has lost its ability to contract What causes it? Interruption in the blood supply Accumulation of lactic acid (most likely) Lowers pH, fibers no longer respond to stimulation Cramps are likely due to a lack of ATP

Skeletal Muscle Contractions Less than half the energy released by cellular respiration is available for metabolic processes. The rest is lost as heat.

Steroids and Athletes Read “Topic of Interest” page 186 Class discussion on use of steroids and creatine