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Week 5-Neuromuscular Anatomy and Physiology

by: Tay-La Notetaker

Week 5-Neuromuscular Anatomy and Physiology HES 1823 004

Marketplace > University of Oklahoma > Health and Exercise Science > HES 1823 004 > Week 5 Neuromuscular Anatomy and Physiology
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From week 5 we talked about the types of muscles in the body, their functions, and how they go about functioning in the body.
Scientific Principles of Health and Disease
Xin Ye
Class Notes
neurons, Muscles, functions
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This 4 page Class Notes was uploaded by Tay-La Notetaker on Tuesday September 13, 2016. The Class Notes belongs to HES 1823 004 at University of Oklahoma taught by Xin Ye in Fall 2016. Since its upload, it has received 8 views. For similar materials see Scientific Principles of Health and Disease in Health and Exercise Science at University of Oklahoma.

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Date Created: 09/13/16
Tay­La Jackson Professor Jennifer Russell Health and Disease WK. 5 – 9/19­9/21 Neuromuscular Anatomy and Physiology  There are 3 types of muscles in the body but 1 we’re focusing on: 1. The Skeletal Muscle: o It is connected to the bone o Supports framework o And is under voluntary control (ONLY muscles under voluntary  control)  A skeletal muscle cell is called a muscle fiber:  Oriented along a longitudinal axis of the muscle and have  diameters between 10­100 micrometers.  Muscle can be up to 20 cm. in length.      FUNCTIONS: a) Store energy in muscles b) Maintain posture c) Generates heat d) Contract to pull on bones to produce force  i .         Muscle  contractions (the activation of the muscle to   produce force or tension  provide the basis for all human  movement.  There are about 700 skeletal muscles in the body and make up approx. 45% of  your body weight.  Types of Muscle Contractions: 1. Static/Isometric­ no movement  Load=tension 2. Dynamic­ muscle contraction that makes the skeleton move.  Eccentric(lengthening)­ muscle force is less than external load.  Concentric(shortening)­ muscle force is greater than external load.  Muscle action depends on the origin and the insertion. 1. Origin­ the end of the muscle that is attached to the bone (the tendon) but doesn’t move when the muscle contracts. 2. Insertion­ the end of the muscle that is attached to the bone (the tendon) and  moves when the muscle contracts.  Muscle Actions 1. Flexion= bending movement resulting in a decrease in the angle of the joint.  2. Extension= straightening movement that increases angle of the joint. 3. Adduction= Bringing limb closer to the midline of body. 4. Abduction= taking limb away from midline of body. 5. Supination= rotation of forearms so palms face up and out. 6. Pronation= rotation of forearms so palms face down and back. 7. Rotation= movement around a central axis (Ex. Hips, neck, shoulders) 8. Circumduction= movement of limb in circular motion. (Ex. Arms, legs)  Structure of Skeletal Muscle o Each muscle is bound together by a tissue called the epimysium. (Epi=outside) o The inside of the muscles are divided into bundles of muscle fibers which are  surrounded by the perimysium. (Peri=middle) o Then each fiber is surrounded by the endomysium (endo=inside) Muscle→ fascicles→ muscle fibers→ myofibrils (causes muscles to contract) → sarcomeres→ myofilaments→ myosin (thick filaments) and actin (thin filaments)  Changes in the sizes of muscles are due to the change in the sizes of the cells, NOT in the numbers of muscle fibers (these remain constant). o Hypertrophy= increasing size o Atrophy=decreasing size  A sarcomere is the smallest functional unit of a skeletal muscle fiber. o They are separated by Z discs (lines).     The Sliding Filament Theory of Muscle Contraction 1. Force is generated as actin filaments slide over the myosin filaments 2. The lengths of the filaments DON’T change during contraction 3. The length of the sarcomere decreases as the myosin filaments pull the Z disc together. The tension generated is due to the myosin heads binding to the actin, which forms a ‘cross­ bridge’. The nervous system signals the muscle fibers to begin the cross­bridge cycling.  Cycling of Cross Bridge: (like rowing a boat) Cross­bridge formation → power stroke → return to ‘loaded’ position The force or tension that a muscle can generate is proportional to the number of cross­bridges formed and dependent on the overlap b/w the two filaments (length­tension relationship) and the cross­sectional area (fiber architecture).  Length­Tension Relationship o The amount of tension is related to the initial length of the muscle.  An overstretched muscle has little overlap  A fully shortened muscle cannot shorten anymore  Muscle Fiber Architecture o The arrangements of fascicles in the muscle determine the shape of the  muscle.  (Ex. Longitudinal muscles have an increased ability to shorten but have  fewer sarcomeres. Vice versa for Pennate muscles.) But the degree of Pennation affects the number of sarcomeres per cross­ sectional area. Pennation also results in a loss of force within each fiber because of the short lengths but allows more sarcomeres to be packed into a given area.  Muscle Fiber Type  Type I­Slow Twitch Fibers (think of aerobics, endurance running)  These are the first to be recruited in everyday activities ALWAYS! o Fatigue resistant o Smaller and produce less force o Appear darker under a microscope.  Type II­Fast Twitch Fibers (think of sprinting, weightlifting) o Recruited last o Larger and generate more force quicker o Will fatigue faster o Appear lighter under a microscope  The distribution (percentage) of a fiber type in a given muscle is determined by  the tasks that muscle performs.  What Determines Muscle Fiber Type?  The neuron that controls the fiber determines the muscle fiber type.  Only one neuron innervates a group of skeletal muscle fibers (all are the same  type) and signals them when to contract. The neuron and all the cells it innervates  becomes a motor unit. a. The number of fibers in a motor unit varies: i. Gastrocnemius fibers have about 2,000 muscle fibers per motor  neuron while the eye muscle may have at most 10. ii.   The ratio of muscle fibers to motor neurons can affect the precision of their movement.  b .    The All­or­None Law i.   A motor unit is either activated completely or not at all. Either  they contract or don’t contract. ii. The motor unit recruitment of these fibers are determined by  the intensity of the activity they are needed for.


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