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