Muscular System - Lecture notes 4 PDF

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Covers essentials for Human Anatomy and Physiology final exam...

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The Muscular System Objective Checklist 1. Compare the different types of muscle tissue -Smooth -Cardiac -Skeletal Look at: Shape, striations, location, and function Smooth Muscle Characteristics • No striations (**as actin and myosin filaments are randomly placed) • Involuntary – no conscious control • Located mainly in the walls of blood vessels and hollow organs • eg. Stomach, Bladder, blood vessels

** To accommodate substantial stretch and still retain contractility, actin and myosin myofilaments are arranged randomly in smooth muscle. For this reason, there are no repeating areas of myofilament overlap.

Cardiac Muscle Characteristics • Striations – has visible banding • Involuntary - controls itself with help from nervous and endocrine systems • Located only in the heart

Skeletal Muscle Characteristics • Striated – has visible banding • Voluntary – subject to conscious control • Most are attached by tendons to bones • Cells are surrounded and bundled by connective tissue • Responsible for all locomotion also maintains posture, stabilizes joints, and generates heat

2. Describe the gross (can see with naked eye) structure of skeletal muscle BoneTendon Whole muscle (wrapped in epimysium) Fascicles (fascicle bundles are held together by perimysium Muscle fibres (muscle cell) wrapped in endomysium Myofibrils (wrapped in sarcoplasmic reticulum)

3. Briefly describe the microscopic structure of a skeletal muscle cell Myofibrils Myofilaments: -Actin (thin/blue lines) -Myosin (thick/red lines) both overlap •Myofibrils are aligned to give distinct bands •Surrounded by sarcoplasmic reticulum (SR) which stores calcium Sarcomere: Z line to Z line, contractile unit of a muscle fibre

4. Describe how muscle cells are stimulated to contract and outline the sequence of events at the neuromuscular junction

1. An action potential arrives at Axon terminal of a motor neuron 2. Calcium ions diffuse into axon terminal via calcium channels and helps to release neurotransmitter (Acetylcholine) from vesicles 3. Neurotransmitter diffuses across synaptic clef 4. Attaches to protein receptors on the sarcolemma (plasma membrane) 5. Channels open for Na+ to rush in and K+ leaks out to cause depolarization of sarcolemma (ie. A new action potential to travel down sarcolemma) 6. Action potential ceases when acetylcholine diffuses away or is broken down by enzyme. Re-enters axon to be remade. 7. Action potential (AP) travels along sarcolemma and down T tubules to reach proteins

5. Outline the sliding filament mechanism of skeletal muscle action 1. Action potential (AP) travels along sarcolemma and down T tubules to reach proteins 2. AP causes proteins attached to SR to open releasing calcium from SPR into sarcoplasm. 3. Calcium travels through the sarcoplasm and binds to protein on the actin filament. 4. This rotates the protein to expose Myosin binding sites on the actin filament 5. This allows myosin heads to attach to binding sites on actin (like a magnet) forming cross bridges

6. Myosin heads pivot which moves actin filaments toward the M line so H zone gets smaller (muscle contraction) 7. ATP attaches to Myosin head causing it to detach from the binding site 8. ATP hydrolysis causes Myosin head to be re-cocked 9. When action potential stops, calcium is reabsorbed into SR and protein shifs back to old position covering binding sites. No more contraction.

6. Describe factors that influence force production in skeletal muscle 1. Number of motor units activated (how many neuromuscular junctions) Motor unit is the group (Nerve plus attached muscle fibres) 2. Frequency of motor unit activation Number of action potentials created 3. Size of the muscle Number of fibres 4. Length of the Muscle -Short muscle length before contraction means that there is actin – actin overlap, reducing the number of cross bridges that can be formed. -Long muscle length before contraction means that the actin and myosin overlap is reduced, so there is a reduced number of cross bridges that can be formed. -At optimal muscle length there is optimal actin – myosin overlap and the maximum number of cross bridges can be formed increasing force strength potential. Factors that decrease force production (causing muscle fatigue) -Reduced ATP. -Increased lactic acid (H+). -Reduced K+ and Na+ gradients across the sarcolemma. -Decreased Ca++ levels -Decreased muscle glycogen or blood glucose. -Decreased central nervous system drive.

7. Briefly describe the terminology related to muscle movement • Isotonic contractions = (Dynamic): Iso = same….Tonic = tension Tension remains unchanged and the muscle's length changes.

Tension = same Muscle = shortens

Tension = same Muscle = lengthens

• Isometric contraction = (Static): Iso = same…Metric = length Muscle generates force without changing length •Force in the muscle increases •The muscle is unable to shorten (eg. Pushing a wall)

8. Name the main muscles of the human body •Deltoid  Top of shoulder •Pectoralis major  chest •Trapezius  From neck to midline between shoulder blades •Latissimus dorsi  Surfer rib muscles •Triceps  Back of upper arm •Biceps  Front of upper arm •Wrist flexors  Inner forearm •Wrist extensors  Outer forearm •Rectus abdominis  abs •Quadriceps Front of thigh •Hamstrings Back of thigh •Gluteas maximus Butt •Gluteals  Side of leg by butt used for abduction •Adductors  Inner thigh used for adduction •Gastrocnemius  Upper calf muscle •Soleus  Lower calf muscle •Tibialis anterior  Shin muscles

Study tips! Try and practice anatomical terms (eg. Anterior, posterior, inferior, etc) using the proper names of the bones and muscles. This is a fun way to memorise them  Buddy up with someone and explain to them the whole process of cross bridge formation from when the action potential reaches the axon terminal – to when ATP braks myosin heads off of binding sites and calcium detaches from the protein. This process of saying out loud each step will show your strengths and weaknesses and identify areas where you need to focus your attention! Check out YouTube vids if you are more of a visual learner! Especially with certain processes such as formation of crossbridges. I didn’t grasp the concept until I saw it in a video –then having that to remember in the exam helped me to remember the written steps!...