Chapter 10 - Muslce Tissue Flashcards
What are the four key functions of muscular tissue?
- Produce body movement
- Stabilize body position
- Storing and moving substances within the body
- Generate heat
How does muscle tissue contribute to homeostasis?
By producing body movements, moving substances through the body and producing heat to maintain normal body temperature
What is myology?
The study of muscles
What are the three different kinds of muscle tissue?
Skeletal
Cardiac
Smooth
What is skeletal muscle tissue?
Moves the bones of the skeleton
Striated muscle
Work in a voluntary manner
However, some are unconscious … Muscles to maintain posture or stabilize body position, diaphragm for breathing
What is cardiac muscle tissue?
Contained only in the heart
Striated muscle
Involuntary actions
What is autorhythmicity?
Built-in rhythm of the heart
Several hormones and neurotransmitters can adjust heart rate by speeding or slowing the automatic pacemaker of the heart
What is smooth muscle tissue?
Located in the walls of hollow internal structures (blood vessels, airways), in the skin
Non striated muscle - hence … Smooth muscle
Usually involuntary
Some smooth muscles have autorhythmicity (gastrointestinal tract)
Part of autonomic nervous system
What is a sphincter?
Ring-like band of smooth muscle that prevents the outflow of the contents of a hollow organ
What is thermogenesis?
The heat produced from muscle tissue
What is shivering?
Involuntary contractions of the skeletal muscles can increase the rate of heat production
What are the four special properties of muscle tissue?
- Electrical excitability
- Contractility
- Extensibility
- Elasticity
What is electrical excitability?
Ability to respond to certain stimuli by producing electrical signals called action potentials
For muscle cells, what two main types of stimuli trigger action potentials?
- Electrical signals - autorhythmic, arising from the muscle tissue itself (heart’s pacemaker)
- Chemical stimuli - neurotransmitters released by neurons, hormones distributed by the blood or even local changes in pH
What is contractility?
The ability of muscular tissue to contract forcefully when stimulated by action potentials
What is extensibility?
The ability of muscular tissue to stretch, within limits, without being damaged
What kind of tissue allows muscle tissue to stretch?
Connective tissue - limits the range of extensibility and keeps it within the contractile range of the muscle cells
What kind of muscle tissue is subject to the greatest amount of stretching?
Smooth muscle tissue (example - stomach)
What is elasticity?
The ability of muscular tissue to return to its original length and shape after contraction of extension
What separates muscle from the skin?
Subcutaneous layer or hypodermis
Composed of areolar connective tissue and adipose tissue
Provides a pathway for nerves, blood vessels, lymphatic vessels
What is fascia?
A dense sheet of broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body
What are the functions of fascia?
Holds muscles with similar functions together
Allows free movement of muscles
Carries nerves, blood vessels, lymphatic vessels
Fills space between the muscle
What is the epimysium?
The outermost layer of dense, irregular connective tissue, encircles the entire muscle
What is the perimysium?
A layer of dense irregular connective tissue, surrounds groups of 10-100 muscle fibres, separating them into bundles called fascicles
What is a fascicle?
A bundle of structures, such as nerve or muscle fibres
What is the endomysium?
Penetrates the interior of each fascicle and separates each individual muscle fibres from each other
Mostly reticular fibres
What is a tendon?
Connective tissue that attaches muscle to bone
What happens if the three connective tissue layers of muscle extend beyond the muscle fibres?
Forms a ropelike tendon
Attaches a muscle to the periosteum of a bone
What is the calcaneal (achilles) tendon?
Attaches the gastrocnemius (calf) muscle to the calcaneus (heel bone)
What is aponeurosis?
When the connective tissue of muscle extend as a broad, flat sheet
What is fibromyalgia?
Chronic, painful, nonarticular rheumatic disorder that affects the fibrous connective tissue components of muscles, tendons and ligaments
What does skeletal muscle consist of?
Individual muscle fibers (cells) bundled into fascicles and surrounded by three connective tissue layers that are extensions of the fascia
Which connective tissue coat surrounds groups of muscle fibres, separating them into fascicles?
Perimysium bundles groups of muscle fibres into fascicles
Which neurons stimulate skeletal muscles to contract?
Somatic motor neurons - each somatic neuron has a threadlike axon that extends from the brain or spinal cord to a group of skeletal muscle fibres
What kind of blood vessels are plentiful in muscular tissue?
Capillaries - each muscle fibre is in close contact with one or more capillaries
How many arteries and veins accompany each nerve that penetrates the skeletal muscle?
1 artery
1 or 2 veins
What is the diameter of a mature skeletal muscle fibre?
Ranges from 10 to 100 micrometers
1 micrometer equals 1/25,000th of an inch
What is the length of a typical skeletal muscle fibre?
10 cm
How does a skeletal muscle fibre arise during embryonic development?
From the fusion of a hundred or more small mesodermal cells called myoblasts
Therefore, each skeletal muscle fibre has a hundred or more nuclei
Is a skeletal muscle fibre able to divide?
No! Once the myoblasts have fused to become a skeletal muscle fibre, it loses its ability for cellular division
The number of skeletal muscle fibres are set before you are born, most of these cells last a lifetime
Where are the nuclei of skeletal muscles located?
Just beneath the sarcolemma
What is the sarcolemma?
The plasma membrane of the muscle cell
What are transverse (T) tubules?
Thousands of tiny invaginations of the sarcolemma
Tunnel in from the surface toward the center of each muscle fibre
Filled with interstitial fluid
Where do muscle action potentials travel through? What does this arrangement ensure?
Along sacrolemma, through the T tubules, quickly spreading throughout the muscle fibre
Ensures that the action potential excites all parts of the muscle five at essentially the same instant
What is sacroplasm? Where is it located?
Within the sarcolemma
The cytoplasm of a muscle fibre
What is myoglobin?
Protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibres from interstitial fluid
Releases the oxygen molecules when it is needed by the mitochondria for ATP production
Where are mitochondria found in muscle fibre?
Lie in rows throughout the muscle fibre, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly
What are myofibrils?
Contractile organelles of skeletal muscle
2 micrometers in diameter, extend the entire length of the muscle fibre
Prominent striations make the entire skeletal muscle fibre appear striped (striated)
What is the sacroplasmic reticulum?
Fluid-filled system of membranous sacs that encircle each myofibril
What are terminal cisterns?
Dilated end sacs of the sacroplasmic reticulum that butt against the T tubule from both sides
What forms a triad?
A transverse tubule and two terminal cisterns on either side of it
What cation triggers muscle contraction?
Ca+2
Release of calcium from the terminal cisterns of the sacroplasmic reticulum triggers muscle contraction
What is muscular hypertrophy?
Muscle growth that occurs after birth by enlargement of existing muscle fibres
What is muscular hyperplasia?
An increase in the number of fibres
What causes muscular hypertrophy?
Due to increased production of myofibrils, mitochondria, sacroplasmic reticulum and other organelles
How can damaged muscle cells regenerate?
A few myoblasts persist in mature skeletal muscle as satellite cells
They retain the ability to fuse with one another or with damaged cells
What is fibrosis?
The replacement of muscle fibres by fibrous scar tissue
This occurs if the number of satellite myoblasts in not significant
What is muscular atrophy?
A wasting away of muscles
Individual muscle fibres decrease in size as a result of progressive loss of myofibrils
What are filaments?
Also called myofilaments
Contained within myofibrils, smaller protein structures
What is the difference between thin and thick filaments?
Thin filaments are 8 nanometers in diameter, 1-2 micrometers long
Thick filaments are 16 nanometers in diameter, 1-2 micrometers long
Thin filaments are mainly composed of the protein actin
Thick filaments are mainly composed of the protein myosin
What are filaments involved in?
Muscle contraction
What are sarcomeres?
Basic functional unit of a myofibril
How thin and thick filaments are arranged in a myofibril
What is a Z disc?
Separates one sarcomere from another
Narrow, plate-shaped region of dense protein
To what extent do thin and thick ligaments overlap?
Depends on whether the muscle is contracted, relaxed or stretched
What is the A Band?
The darker middle part of the sarcomere
Extends the entire length of the thick filaments
What happens at the ends of each A band?
A zone of overlap
Where thin and thick filaments lie side by side
What causes the striations that can be seen in skeletal muscle?
The pattern of overlap between the thin and thick filaments
Can be seen in both single myofibrils and in whole muscle fibres
What is the I band?
A lighter, less dense area that contains the rest of the thin filaments but NO thick filaments
What passes through the centre of each I band?
Z disc
What is the H zone?
A narrow zone in the center of each A band that contains thick filaments but NO thin filaments
What is the M line?
The middle of the sarcomere
Supporting proteins that hold the thick filaments together at the center of the H zone
Myofibrils are built from what three kinds of proteins? Describe them.
- Contractile proteins - generate force during contraction
- Regulatory proteins - help switch the contraction process on and off
- Structural proteins - keep thick and thin filaments in the proper alignment, gives myofibril elasticity/extensibility, and link the myofibrils to the sarcolemma and extracellular matrix
What are the two contractile proteins in muscle?
- Myosin
2. Actin
What is myosin?
The main component of thick filaments and functions as a motor protein in all three types of muscle tissue
Has a head and tail
What do motor proteins do?
Pull various cellular structures to achieve movement by converting the chemical energy ATP to the mechanical energy of motion
The production of force
In skeletal muscles, how many molecules of myosin form a single thick filament?
About 300
What are anchored to the Z discs?
Thin filaments
What is actin?
The main component of thin filaments
Individual actin molecules join to form an actin filament that is twisted into a helix
One each actin molecule, there is a myosin-binding site, where a myosin head can attach
What are the two regulatory proteins in skeletal muscle fibres?
- Tropomyosin
- Troponin
Both components of thin filaments
What are the key structural proteins in skeletal muscle fibres?
Titin A-actinin myomesin Nebulin Dystrophin
What does tropomyosin do?
In a relaxed muscle, myosin is blocked from binding to actin b/c strands of tropomyosin block the binding sites on actin
What holds the tropomyosin strands in place?
Troponin molecules
What is tinin?
Structural protein that connects the Z disc to the M line of a sarcomere
Helping to stabilize the thick filament position
Can stretch and spring back unharmed
Accounts for much of the elasticity and extensibility of myofibrils