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January 6, 2018 | Author: Anonymous | Category: Science, Health Science, Histology
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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

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

• 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

• 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

• 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

• 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

• 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

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

Contraction video

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