Muscular System Chapter 8

Introduction All movements require muscles They are specialized cells that use chemical energy to contract They provide muscle tone, propel body fluids and food, generate the heartbeat and distribute heat Three types: skeletal, smooth and cardiac We will just talk about skeletal this chapter

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Structure of a Skeletal Muscle It is composed of skeletal muscle tissue, nervous tissue, blood, and connective tissue Muscles > Fascicles > Muscle fiber (cells) > Myofibrils > Thick and thin filaments

Structure of Skeletal muscle: Connective tissue coverings A muscle is covered by layers of fibrous connective tissue called a fascia It may project longer than the muscle and form a tendon by connecting to the bone Sometimes they form aponeuroses which are sheets that connect to adjacent muscles

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All parts of a skeletal muscle are enclosed in layers of connective tissue which form a network Epimyseum > perimyseum > fasicles > endomyseum All of those are connective tissues

Structure of Skeletal Muscle: Skeletal Muscle Fibers SMF is a single cell that contracts in response to stimulation and then relaxes when stimulation ends (may extend full length of muscle) The sacroplasm (cytoplasm) contains many threadlike myofibrils that lie parallel to one another

SMF & Myofibril http://211.174.114.20/catalog/2011%5C2011_08/actinx2.jpg

These alternating bands cause the striations Myofibrils aid in muscle contraction and contain 2 types of protein filaments: Myosin- thick muscle filaments Actin- thin muscle filaments These alternating bands cause the striations http://www.sport-fitness-advisor.com/images/actin_myosin.jpg

2 main parts to striations: I bands are composed of actin (thin/light) directly attached to z lines A bands are composed of myosin (thick/dark) that overlap the thin filaments In the center of the A band is the H zone which is a central region that has the M line inside The segment of a myofibril that extends from one z line to the next is called a sacromere http://site.motifolio.com/images/Arrangement-of-myofilaments-in-the-sarcomere-relaxed-state-9111135.png

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Sacroplasmic reticulum – Membranous network of channels and tubules (similar to ER) Transverse tubules – Membranous channel that extends inward from a muscle fiber membrane and passes through the fiber These two structures activate muscle contraction when fiber is stimulated

Neuromuscular Junction Each SMF connects to an axon from a nerve cell, called a motor neuron Muscle fiber contracts only when stimulated by neuron Neuromuscular junction – connection between the motor neuron and muscle fiber

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The muscle fiber forms a motor end plate The end of the motor neuron has many vesicles that contain chemicals called neurotransmitter (acetocholine) A nerve impulse travels to the neuron which releases some of the neurotransmitters into the gap which stimulates the muscle fiber to contract

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Motor Units One motor neuron may connect to many muscle fibers because they are branched When one impulse is sent it stimulates all of the muscle fibers that the motor neuron is connected to A motor neuron and the muscle fibers that is controls make up a motor unit

Motor Unit Muscle contraction animation http://staff.fcps.net/cverdecc/adv%20a&p/notes/muscle%20unit/contration%20of%20motor/contra36.jpg

Contraction video http://classconnection.s3.amazonaws.com/1517/flashcards/715536/jpg/picture1.jpg

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