Anatomy chp.10

Terminal boutons

(axon terminals) Located at ends of axons Store neurotransmitters

Excitation

1. Nerve signal arrives at knob 2. Knob releases Ach, which binds to muscle's receptors, opening ion gates and exciting muscle 3. Excitation spreads down and through muscle cell

Excitation-contraction coupling

4. Electrical impulse triggers calcium release from SR 5. Calcium binds troponin, which moves tropomyosin to expose actin 6. Myosin breaks down ATP and extends head 7. Myosin forms cross-bridge with actin 8. Myosin pulls actin in power stroke, then detaches, reattaches, pulls again, etc.

Relaxation

9. Nerve signal stops 10. SR reabsorbs calcium, tropomyosin blockade resumes, and tension subsides

A bands and I bands refract polarized light differently

A bands—anisotropic I bands—isotropic

Muscular dystrophy

A group of inherited muscle destroying disease Affected muscles enlarge with fat and connective tissue Muscles degenerate Types of muscular dystrophy: Duchenne muscular dystrophy and Myotonic dystrophy

Fibromyalgia

A mysterious chronic-pain syndrome Affects mostly women Symptoms—fatigue, sleep abnormalities, severe musculoskeletal pain, and headache

Myofilaments

A protein bundle that makes up the microfibrils of the skeleton. Short contractile proteins of two types: thick (composed of myosin) and thin (composed of actin, tropomyosin, and troponin)

Sarcoplasmic reticulum

A specialized smooth ER Interconnecting tubules surround each myofibril Some tubules form cross-channels called terminal cisterns Cisterns occur in pairs on either side of a t tubule Contains calcium ions T tubules

With increased age

Amount of connective tissue increases in muscles Number of muscle fibers decreases Loss of muscle mass with aging: Decrease in muscular strength is 50% by age 80 and Sarcopenia

Fleshy attachments

CT fibers are short

Indirect attachments

CT forms a tendon (connects bone to muscle) or aponeurosis (fibous sheet or flat, tendon)

Two major types of contraction

Concentric contraction—muscle shortens to do work Eccentric contraction—muscle generates force as it lengthens Muscle acts as a "brake" to resist gravity "Down" portion of a pushup is an example

Each muscle is an organ

Consists mostly of muscle tissue Skeletal muscle also contains: Connective tissue, Blood vessels, Nerves

Fast glycolytic fibers

Contain little myoglobin and few mitochondria About twice the diameter of slow oxidative fibers Contain more myofilaments and generate more power Depend on anaerobic pathways Contract rapidly and tire quickly

Extensibility

Contraction of a skeletal muscle stretches the opposing muscle Smooth muscle is stretched by substances within that hollow organ (Food in stomach; urine in urinary bladder). A muscle cell must be capable of extending in length in response to the contraction of opposing muscle cell

Nerves and blood vessels

Each skeletal muscle supplied by branches of: One nerve, One artery, and One or more veins Nerves and vessels branch repeatedly: Smallest branches serve individual muscle fibers The blood vessels deliver to the muscle fibers nutrients and oxygen needed for the production of ATP (adenosine triphosphate). They also remove waste products produced by the muscle fibers.

Muscle Fiber (muscle cell)

Elongated, multinucleated, cylindrical fiber (cell); contains myofibrils, separated from other fibers by delicate layer of areolar connective tissue; exhibits striations

Maintain posture and stabilize joints

Enables the body to remain sitting or standing Muscle tone helps stabilize many synovial joints Postural muscles contract continuously when a person is awake to prevent collapse

Sliding filament mechanism

Explains concentric contraction Myosin head attach to thin filaments at both ends of a sarcomere Then pull thin filaments toward the center of the sarcomere Thin and thick filaments do not shorten Initiated by release of calcium ions from the when a muscle contracts, thick and thin filaments slide past each other, and the sarcomere shortens

Differences in skeletal muscle between males and females

Females—approximately 36% of body mass Males—approximately 42% of body mass Difference is due to androgens in males

The skeletal muscle fiber

Fibers are long and cylindrical: Are huge cells—diameter is 10-100 µm and Length—several centimeters to dozens of centimeters Each cell formed by fusion of embryonic cells Cells are multinucleate Nuclei are peripherally located

Contraction changes the striation pattern

Fully relaxed—thin filaments partially overlap thick filaments Contraction—Z discs move closer together Sarcomere shortens I bands shorten; H zone disappears A band remains the same length

Muscle fiber length and 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

Fast oxidative fibers

Have an intermediate diameter Contract quickly like fast glycolytic fibers Are oxygen dependent Have high myoglobin content and rich supply of capillaries Somewhat fatigue resistant More powerful than slow oxidative fibers

Muscle tissues experience few disorders

Heart muscle is the exception Skeletal muscle (Remarkably resistant to infection) Smooth muscle (Problems stem from external irritants)

Skeletal muscle fibers are categorized according to two characteristics

How they manufacture energy (ATP) How quickly they contract Oxidative fibers—produce ATP aerobically Glycolytic fibers—produce ATP anaerobically by glycolysis

Titin

Is a springlike molecule that resists overstretching Molecules extend from the Z disc to thick filaments to the M line Two functions: Holds thick filaments in place and Unfolds when muscle is stretched

Muscle

Latin word for "little mouse the primary tissue in the: Heart (cardiac muscle tissue) and Walls of hollow organs (smooth muscle tissue) Skeletal muscle: Makes up nearly half the body's mass Multiple fascicles housing many muscle fibers, connective tissue coverings, blood vessels, nerve fibers

Muscle attachments

Most skeletal muscles run from one bone to another One bone will move; other bone remains fixed Origin—less movable attachment Insertion—more movable attachment Muscles attach to origins and insertions by connective tissue (CT): Fleshy attachments and Indirect attachments Bone markings present where tendons meet bones: Tubercles, trochanters, and crests

Heat generation

Muscle contractions produce heat Helps maintain normal body temperature Likewise, you shiver when you are cold because your muscles are contracting and relaxing to produce heat

Muscle extension

Muscle is stretched by a movement opposite that which contracts it

Muscle tissue develops from myoblasts

Myoblasts fuse to form skeletal muscle fibers Skeletal muscles contract by week 7 of development

Contractility

Myofilaments are responsible for shortening of muscles cells Actin and myosin are two type of myofilaments. Shortening results in either a pull on bones of the skeleton or the movement of specific body parts.

Excitability

Nerve signals excite muscle cells, causing electrical impulses to travel along the sarcolemma.In other words, muscle cells are very responsive to input from stimuli.

Motor neurons innervate skeletal muscle tissue

Neuromuscular junction, Terminal boutons, Synaptic cleft

Smooth muscle tissue

Occupies the walls of hollow organs Cells lack striations Innervated by involuntary division of the nervous system

Cardiac muscle tissue

Occurs only in the walls of the heart Cells are striated Contraction is involuntary

Skeletal muscle tissue

Packaged into skeletal muscles Makes up 40% of body weight Cells are striated Skeletal muscle is innervated by voluntary division of the nervous system Composed of the four tissue types: epithelial, connective, muscle, and nervous.

Myofascial pain syndrome

Pain is caused by tightened bands of muscle fibers

Functions of Muscle Tissue

Produce movement (Skeletal muscle, Smooth muscle), Open and close body passageways, Maintain posture and stabilize joints, Heat generation

Muscle Tissue Throughout Life (Cardiac muscle)

Pumps blood 3 weeks after fertilization

Elasticity

Recoils after being stretched. Is not the muscle's ability to stretch, but its ability to return to its original length when tension is released.

Slow oxidative fibers

Red color due to abundant myoglobin Obtain energy from aerobic metabolic reactions Contain a large number of mitochondria Richly supplied with capillaries Contract slowly and resistant to fatigue Fibers are small in diameter

Connective tissue and fascicles

Sheaths of connective tissue bind a skeletal muscle and its fibers together: Epimysium, Perimysium, Endomysium. These layers provide protection, sites for distribution of blood vessels and nerves, and a means of attachment to the skeleton.

Types of Muscle Tissue

Skeletal muscle tissue, Cardiac muscle tissue, Smooth muscle tissue

Skeletal muscle fibers are divided into three classes

Slow oxidative fibers: Red slow oxidative fibers Fast glycolytic fibers: White fast glycolytic fibers Fast oxidative fibers: Intermediate fibers

Synaptic cleft

Space between axon terminal and sarcolemma

Open and close body passageways

Sphincters function as valves: contract at the openings, or orifices (or′i-fis; orificium = opening), of the gastrointestinal and urinary tracts. These sphincters may be voluntarily closed (to store the material within an organ) or opened (to facilitate movement of materials). Open to allow passage of a substance and Contract to close the passageway

Myofibrils and Sarcomeres

Striations result from internal structure of myofibrils Basic unit of contraction of skeletal muscle: Z disc (Z line), Thin (actin) filaments, and Thick (myosin) filaments A bands, H zone, M line, I line

Muscle Tissue Throughout Life (Satellite cells)

Surround skeletal muscle fibers Resemble undifferentiated myoblasts Fuse into existing muscle fibers to help them grow

Myofibrils

The sarcoplasm of a skeletal muscle fiber contains hundreds to thousands of long, cylindrical structures termed this. Make up 80% of the cytoplasm Are a specialized contractile organelle found in muscle tissue Are a long row of repeating segments called sarcomeres Long, cylindrical contractile element within muscle fiber; as long as the muscle fiber itself; composed of myofilaments; exhibits striatio

Connective tissue sheaths are continuous with tendons

When muscle fibers contract, pull is exerted on all layers of connective tissue that are tendon Sheaths provide elasticity and carry blood vessels and nerves

Endomysium

a fine sheath of connective tissue wrapping each muscle cell (endon = within) Is the innermost connective tissue layer.

Skeletal muscle

attached to skeleton: Moves body by moving the bones

terminal cisterns

blind sacs of the sarcoplasmic reticulum. they are the reservoirs and specific sites for calcium ion release to initiate muscle contraction, and they interact with the T-tubules during muscle contraction. Together, the two terminal cisternae and the centrally placed T-tubule form a structure called a triad.

Z disc (Z line)

boundaries of each sarcomer. A thin transverse protein structure in the center of the I band that serves as an attachment site for thin filament ends

H zone

center part of A band where no thin filaments occur

superficial fascia

deep fascia is deep or internal to a certain facia (also called the subcutaneous layer). This fascia is composed of areolar and adipose connective tissue that separates muscle from skin.

T tubules

deep invaginations of sarcolemma that extend into the sarcoplasm of skeletal muscle fibers as a network of narrow membranous tubules Triad—T tubule flanked by two terminal cisterns helps stimulate and coordinate muscle contractions

Epimysium

dense regular connective tissue surrounding entire muscle. layer of dense irregular connective tissue that surrounds the whole skeletal muscle. epi=upon

Thin (actin) filaments

extend from Z disc toward the center of the sarcomere. bundles of thin filaments.

fascicles

fascis = bundle), which are bundles of muscle fibers. Muscle fibers, in turn, contain cylindrical structures called myofibrils, which are composed of myofilaments

A bands

full length of the thick filament and dark Includes inner end of thin filaments

sarcomeres

functional unit of skeletal muscle tissue. defined as the distance from one Z disc to the next adjacent Z disc

M line

in center of H zone Contains tiny rods that hold thick filaments together

Sarcopenia

is the degenerative loss of skeletal muscle mass

Thick (myosin) filaments

located in the center of the sarcomere Overlap inner ends of the thin filaments Contain ATPase enzymes. Bundles of regular filaments.

Sarcolemma

plasma membrane of muscle cells

Sarco

prefix meaning "flesh"

Myo and mys

prefixes meaning "muscle"

I band

region with only thin filaments Lies within two adjacent sarcomeres

calcium ions

released when muscle is stimulated to contract Calcium ions diffuse through cytoplasm Trigger the sliding filament mechanism

Smooth muscle

squeezes fluids and other substances through hollow organs

Perimysium

surrounds each fascicle (group of muscle fibers) peri = around

Sarcoplasm

the cytoplasm of the muscle fiber is called

Neuromuscular junction

the point where nerve ending and muscle fiber meet. synaptic knob, synaptic vessels, motor end plate, synaptic cleft, ach receptors, AChE.

deep fascia

three connective tissue layers are ensheathed by it (fash′ē-ă; band or filler), an expansive sheet of dense irregular connective tissue that separates individual muscles, binds together muscles with similar functions, and forms sheaths to help distribute nerves, blood vessels, and lymphatic vessels, and to fill spaces between muscles