4 Muscles - Muscles I. Skeletal Muscle a. Multinucleated b....

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Muscles I. Skeletal Muscle a. Multinucleated b. Two types b.i. Type I- Slow Twitch Muscle Fibers b.ii. Type II- Fast Twitch Muscle Fibers c. Innervations c.i. Constantly need nerve innervations in order to not undergo atrophy c.ii. Alpha motor neuron - nerves that innervate skeletal muscle c.iii. acetylcholine (Ach) – excitatory; Only neurotransmitter that is released by alpha motor neuron c.iii.1. Action potential comes down cause synaptic vesicles to release Ach Ach binds to nicotinic receptor Ca+2 released Muscle Contraction c.iii.2. Lab tests have shown that if you remove neuron to stop contraction muscle cell has already started to undergo atrophy c.iv. ↑ Age- motor neurons get de-innervated (not being used as much) c.v. Theory: c.v.1. Take single muscle fiber from old and young cell and look at dynamic properties (force generation) c.v.2. There is very little difference between old and new c.v.3. Supports that innervations ratio in old individuals plays important factor in generating force d. As we age, see changes: d.i. less nucleated cells in muscle cells decrease in the amount of DNA in muscle cells d.ii. Motor neurons become de-innervated d.iii. Structural changes d.iv. Chronic diseases d.v. Diseases related to medications d.v.1. Statins -drug that lowers cholesterol and lower LDL levels cause muscles to become weak over time d.vi. Disuse atrophy due to muscles not being used and not exercising d.vii. Malnutrition d.vii.1. Muscles are made out of protein and need a lot of energy to make protein d.vii.2. We are going to break down proteins for energy and nutrition source II. Muscle changes over time a. Decrease in weight related to body weight: Age weight protein 20 60kg 94kg 60 60kg 64kg *body weight didn’t change but protein content changes b. Sarcopenia - decrease in muscle mass and muscle volume b.i. 30-40% decrease in muscle mass and volume between ages 30 and 80. b.i.1. Majority of it is found after age 60. b.ii. The amount of mass you have in a muscle is related to force b.ii.1. Mass = force (thought for awhile but not sure if it is true) b.ii.2. Contradiction- innervations of that muscle determines an important role in force generation
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c. Atrophy c.i. Due to differential loss in muscle types c.ii. By age 70 we have a complete loss in number and size of Type II muscle fibers c.iii. Animals that undergo caloric restriction –don’t see this change d. Extensive proliferation of the tubular system d.i. In order for muscle to contract, AP must go deep deep down into muscle using Tubular Systems (t-tubules). Sarcoplasmic Reticulums (contain Ca+2) surround t-tubules and are same thing as endoplasmic reticulum d.ii. When AP goes down tubules stimulates sarcoplasmic reticulum Ca+2 gets released into muscle cell Ca+2 leads to muscle contraction d.iii. When we age, ↑ # of t-tubules , but become irregular T-tubules not in perfect alignment with the sarcoplasmic reticulum it takes longer for AP to stimulate
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4 Muscles - Muscles I. Skeletal Muscle a. Multinucleated b....

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