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functions of muscle tissue

1) movement (skeletal and smooth muscles), 2) maintenance of posture, 3) joint stability, 4) heat generation

special functional features of muscle tissue

1) contractility, 2) excitability, 3) extensibility, 4) elasticity

Types of muscle tissue

1) skeletal, 2) cardiac, 3) smooth and can be characterized by two main features: 1) the presence or absence of light and dark stripes, called striations, in the muscle cells and 2) whether control is voluntary or involuntary

skeletal muscle tissue

packaged into skeletal muscles; makes up 40% of body weight; specific banding pattern with light and dark; striated and volunatry

cardiac muscle tissue

occurs only in the walls of the heart; intercalated discs; straiated and involunatry

smooth muscle tissue

found in the walls of hollow internal organs other than the heart, such as the stomach, urinary bladder, blood vessels, and respiratory passages; unstriated and involuntary

similarities among muscle tissues

1) the cells of skeletal and smooth muscle tissue are called fibers because they are elongated; 2) in all three types, muscle contraction depends on myofilaments; 3) the plasma membrane is called a sarcolemma and the cytoplasm is called sarcoplasm

fibers

the cells of the skeletal and smooth muscle tissues

myofilaments

specific tpes of microfilaments that are responsible for the shortening of muscle cells. There are two kinds: one containing actin (thin) and the other containing myosin (thick)

sarcolemma

the plasma membrane of muscle cells

sarcoplasm

the cytoplasm of muscle cells

basic features of a skeletal muscle

1) connective tissue and fascicles that bind a skeletal muscle and its fibers together; 2) nerves and blood vessels that branch repeatedly in the intramuscular connective tissue, with the smallest branches serving individual muscle fibers; 3) muscle attachments where a muscle connects to the bone and extends from one bone to another, crossing at least one moveable joint; when the muscle contracts, the other bone remains fixed; muscle attaches to origins and insertions by connective tissue; bone markings present where tendons meet bones

epimysium

dense irregular connective tissue surrounding entire muscle

perimysium

surrounds each fascicle (group of muscle fibers)

endonysium

a fine sheath of connective tissue wrapping each muscle cell

neuromuscular junction

signals the muscle to conttact

origin

the attachment of the muscle on less moveable bone

insertion

the attachment on the more moveable bone

direct or fleshy attachments

the attaching strands of connective tissue are so short that the muscle fascicles themselves appear to attach directly to the bone

indirect attachments

the connective tissue extends well beyond the end of the muscle fibers to form either a cordlike tendon or a flat sheet called an aponeurosis; more common than direct or fleshy attachments

the skeletal muscle fibers

fibers are long (several cms to dozens of cms) and cylindrical; cells are huge (diameter is 10-100um); each cell formed by fusion of embryonic cells; cells are multinucleate; nuclei are peripherally located

myofibrils

long rods within cytoplasm; makes up 80% of the cytoplasm; are specialized contractile organelle found in muscle tissue

sacromeres

a long row of repeating segments in a myofibril; it is a basic unit of contraction in skeletal muscle

Z discs or Z lines

the boundarie sat the two ends of each sacromere

thin (actin) filaments

attached to the Z disc and extending toward the center of the sacromere which consists primarily of the protein actin

thick (myosin) filaments

a cylindrical bundle in the center of the sacromere and overlapping the inner ends of the thin filaments' largely consists of myosin molecules and ATPase enzymes that split ATP (energy-storing molecules) to release the energy required for muscle contraction

The sacromere structure

1) A bands - darker middle part of the sarcomere where the thick and thin filaments overlap; 2) H zone - the center of each A band which contains thick but no thin filaments; 3) M line - in the center of the H zone that contains tiny rods that hold togethers together thick filaments; 4) I band - region with only thin filaments

sarcoplasmic reticulum

The smooth ER of a muscle cell, enlarged and specialized to act as a Ca2+ reservoir that trigger the sliding filaments mechanism. The SR winds around each myofibril in the muscle cell; some tubules form cross channels called terminal cisternae

T tubules

Small, cylindrical invaginations of the sarcolemma of striated muscle fibers (cells) that conduct muscle action potentials toward the center of the muscle fiber

triad

the complex of a T tubule flanked by two terminal cisternae at each A-I junction

sliding filament mechanism

myosin heads attach to actin in the thin filaments, then pivot to pull in thin filaments inward the center of the sacromeres

mechanism of contraction

2 types of muscle contraction involved in producing movement: concentric and eccentric contraction

concentric contraction

the more familiar type in which the muscle shortens and does work

eccentric contraction

occurs when w muscle generates force as it lengthens; essential for controlled movement and resistence to gravity (going down stairs, landing from a jump, going down on a push up)

muscle extension

muscle fibers are stretced (extended) back to their original length after they contract

muscle fiber length and the force of contraction

greatest force produced when a fiber starts out slightly stretched; myosin heads can pull along the entire length of the thin filaments

titin

a spring-like molecule in sacromeres that resists overstretching; has two functions: 1) holds thick filaments in place, 2)unfolds when muscle is stretched

muscle contraction

ultimately controlled by nerve-generated impulse, which travels along the sarcolemma of the muscles cells

motor neurons

the nerve cells that innervate skeletal muscle tissue

neuromuscular junction

the point where nerve ending and muscle fibers meet

axon terminal

the endpoint of a neuron where neurotransmitters are stored

synaptic cleft

space between two connecting neurons where neurotransmitters are released

motor unit

a motor neuron and all the muscle fibers it innervates (stimulates)

types of skeletal muscle fibers

categorized according to two characterisitics: 1) how they manufacture energy (ATP) and 2) how quickly they contract; slow oxidative fibers (type I), fast glycolytic fibers (type IIx), and fast oxidative fibers ( type IIa)

oxidative fibers

muscle fibers that predominantly produce ATP aerobically (using oxygen)

glycolytic fibers

muscle fibers that produce ATP anaerobically (without oxygen)

slow oxidative fibers (Type I)

red slow twitch; resist fatigue; located in the postural muscles of the lower back; goes very slow; aerobic

fast glycolytic fibers (Type IIx)

white fast twitch; myoglobin holds oxygen for longer period of time; fast bursts and tired right away; anaerobic; located in upper limbs

fast oxidative fibers (Type IIa)

intermediate fibers; aerobic; located in lower limbs

disorders of skeletal muscle tissue

muscular dystrophy, myofascial pain syndrom, fibromyalgia

muscular dystrophy

a group of inherited muscle-destroying diseases that generally appear in childhood; fat replaces muscle fibers and continue to lose the muscles and become weak; most common is Duchenne muscular dystrophy (inherited as a sex-linked recessive disease) and myotonic dystophy (skeletal muscle spasms followed by muscle weakness and abnormal heart rhythm)

myofascial pain syndrome

pain is caused by tightened bands of muscle fibers that twitch when the skin over them is touched; associated with overused or strained postural muscles

fibromyalgia

a mysterious chronic-pain syndrome of unknown cause; symptoms include severe musculoskeletal pain, fatigue, sleep abnormalities, and headache; pain must be present in 11 of 18 standardized points to be considered this disease

sarcopenia

the loss of muscle mass, strength, and function that comes with aging

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