Chapter 10 Flashcards
Cardiac muscle tissue
Skeletal muscle tissue
Autorhythmicity
Built-in rhythm of the heart; the heart beats because it has a natural pacemaker that initiates each contraction.
Smooth muscle tissue
What are the four key functions of muscular tissue?
- Producing body movement.
- Stabilizing body positions.
- Storing and moving substances within the body.
- Generating heat.
Thermogenesis
When muscular tissue contracts, it produces heat.
What is shivering and what is the purpose of it?
Involuntary contractions of skeletal muscle; increases the rate of heat production.
What are the four special properties of muscular tissue?
- Electrical excitability.
- Contractility.
- Extensibility.
- Elasticity.
Electrical excitability
The ability to respond to certain stimuli by producing electrical signals called action potentials (impulses). Action potentials in muscles are referred to as muscle action potentials.
For muscle cells, two main types of stimuli trigger action potentials. One is autorhythmic ______ arising in the muscular tissue itself, as in the heart’s pacemaker. The other is ______, such as neurotransmitters released by neurons, hormones distributed by the blood, or even local changes in pH.
Electrical signals; chemical stimuli.
Contractility
Is the ability of muscular tissue to contract forcefully when stimulated by an action potential.
Extensibility
Is the ability of muscular tissue to stretch, within limits, without being damaged.
Elasticity
Is the ability of muscular tissue to return to its original length and shape after contraction or extension.
Muscle fibers (myocytes)
Long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns. The fiber has a striated appearance.
Subcutaneous layer
AKA hypodermis; separates muscle from skin; is composed of areolar connective tissue and adipose tissue. It provides a pathway for nerves, blood vessels, and lymphatic vessels to enter and exit muscles. The adipose tissue of the subcutaneous layer stores most of the body’s triglycerides, serves as an insulating layer that reduces heat loss, and protects muscles from physical trauma.
Fascia
Is a dense sheet or broad band of irregular connective tissue that lines the body wall and limbs and supports and surrounds muscles and other organs of the body.
Fascicle
Bundle of muscle fibers wrapped in perimysium.
What are the three layers of connective tissue?
- Epimysium
- Perimysium
- Endomysium
Epimysium
Is the outer layer, encircling the entire muscle. It consists of dense irregular connective tissue.
Perimysium
Is a layer of dense irregular connective tissue, but it surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles.
Endomysium
Penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is mostly reticular fibers.
Tendon
Attaches a muscle to the periosteum of a bone; formed by all three connective tissue layers extending beyond the muscle fibers.
Aponeurosis
Sheetlike connective tissue that connects muscle to bone.
Sarcolemma
The plasma membrane of a muscle cell.
Explain the importance of nerves and blood vessels in skeletal muscles?
Skeletal muscles are well supplied with nerves and blood vessels. Microscopic blood vessels called capillaries are plentiful in muscular tissue; each muscle fiber is in close contact with one or more capillaries. The blood capillaries bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism.
Transverse (T) tubules
Tiny invaginations of the sarcolemma; tunnel in from the surface towards the center of each muscle fiber; muscle action potentials travel along the sarcolemma and through the T tubules in order to quickly spreading throughout the muscle fiber.
Myofibrils
Threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments.
Sarcoplasm
The cytoplasm of a muscle fiber; inside the sarcolemma; contains myoglobin (a red-colored protein found only in muscles; binds to oxygen molecules that diffuse into muscles fibers from interstitial fluid, and releases oxygen when it is needed by the mitochondria for ATP production).
Sarcoplasmic reticulum (SR)
A fluid-filled system of membranous sacs that encircle myofibril.
Terminal cisterns
Dilated ends sacs of the sarcoplasmic reticulum (SR) that butt against the T tubule from both sides; release calcium ions to trigger muscle contraction.
Triad
Formed by a T tubule and two terminal cisterns on either side of it.
Filaments (myofilaments)
Contractile proteins within myofibrils that are two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin, and troponin; sliding of thin filaments past thick filaments produces muscle shortening.
Thin filament
Are 8 nm in diameter and 1-2 um long and are composed of the protein actin.
Thick filament
Are 16 nm in diameter and 1-2 um long and are composed of the protein myosin.
Sarcomeres
Compartments of filaments inside a myofibril; are the basic functional units of a myofibril.
Z discs
Narrow, plate-shaped regions of dense material that separate one sarcomere from the next.
A band
Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments called the zone of overlap.
I band
Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments. A Z disc passes through center of each I band A mnemonic that will help you to remember the composition of the I and H bands is as follows: the letter I is thin (contains thin filaments), while the letter H is thick (contains thick filaments).
H zone
Narrow region in center of each A band that contains thick filaments but no thin filaments A mnemonic that will help you to remember the composition of the I and H bands is as follows: the letter I is thin (contains thin filaments), while the letter H is thick (contains thick filaments).
M line
Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.
Contractile proteins
Myosin and actin; proteins that generate force during muscle contractions.
Myosin
Contractile protein that makes up thick filament; molecule consists of a myosin tail and two myosin heads, which bind to myosin binding sites on actin molecules of thin filament during muscle contraction.
What two binding sites does each myosin head have?
- An actin-binding site.
- An ATP-binding site.
Motor proteins
Pull various cellular structures to achieve movement by converting the chemical energy ATP to the mechanical energy of motion, that is, the production of force.
Actin
Contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.
Regulatory proteins
Tropomyosin and troponin; proteins that help switch muscle contraction process on and off.
Tropomyosin
Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin.
Troponin
Regulatory protein that is a component of thin filament; when calcium ions bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
Structural proteins
Titin, α-Actinin, myomesin, nebulin, and dystrophin; proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix.
Titin
Structural protein that connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.
Dystrophin
Structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons.
The sliding filament mechanism
As the thin filaments slide inward, the I band and H zone narrow and eventually disappear altogether when the muscle is maximally contracted.
What are the four steps of the contraction cycle?
- ATP hydrolysis: myosin head hydrolyzes ATP and becomes energized and oriented.
- Attachment of myosin to actin: myosin head binds to actin, forming a cross-bridge.
- Power stroke: myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere (power stroke).
- Detachment of myosin from actin: as myosin head binds ATP, the cross-bridge detaches from actin.
Voltage-gated Ca2+ channels
Located in the T tubule membrane; the main role of these channels in excitation-contraction coupling is to serve as voltage sensors that trigger the opening of the Ca2+ release channels.
Ca2+ release channels
Are present in the terminal cisternal membrane of the sarcoplasmic reticulum (SR). When a skeletal muscle fiber is at rest, the part of the Ca2+ release channel that extends into the sarcoplasm is blocked by a given cluster of voltage-gated Ca2+ channels, preventing Ca2+ from leaving the SR. When a skeletal muscle fiber is excited and an action potential travels along the T tubule, the voltage-gated Ca2+ channels detect the change in voltage and undergo a conformational change that ultimately causes the Ca2+ release channels to open. Once these channels open, large amounts of Ca2+ flow out of the SR into the sarcoplasm around the thick and thin filaments.
Ca2+ -ATPase pumps
Use ATP to constantly transport Ca2+ from the sarcoplasm into the sarcoplasmic reticulum (SR).
Neuromuscular junction (NMJ)
The synapse between a somatic motor neuron and a skeletal muscle fiber; where muscle action potentials arise from.
Synaptic cleft
Small gap that separates two cells; cells don’t physically touch so the action potential can’t “jump the gap” from one cell to another.
Axon terminal
End of the motor neuron at the neuromuscular junction (NMJ).
Synaptic end bulbs
Neural part of the neuromuscular junction (NMJ).
Synaptic vesicles
Membrane-enclosed sacs that are suspended in the cytosol within the synaptic end bulbs.
Motor end plate
Region of the sarcolemma opposite the synaptic end bulbs.
Acetylcholine receptors
Integral transmembrane proteins that ACh specifically binds to; these receptors are found in junctional folds.
Junctional folds
Deep grooves in the motor end plates that provide a large surface area for ACh.
What are the four steps in a muscle action potential?
- Release of acetylcholine.
- Activation of ACh receptors.
- Production of muscle action potential.
- Termination of ACh activity.
How does creatine phosphate produce ATP?
Creatine phosphate is formed from ATP while muscle is relaxed, and transfers a high-energy phosphate group to ADP, forming ATP during muscle contraction. Provides about 15 seconds of energy.
How does anaerobic glycolysis produce ATP?
The entire process of the breakdown of muscle glycogen into glucose and production of pyruvic acid from glucose via glycolysis both produce ATP and lactic acid. Because no oxygen is needed, this is an anaerobic pathway. Provides about 2 minutes of energy.
How does aerobic respiration produce ATP?
Within mitochondria, pyruvic acid, fatty acids, and amino acids are used to produce ATP via aerobic respiration, an oxygen-requiring set of reactions (the Krebs cycle and the electron transport chain). Provides several minutes to hours of energy.
Motor unit
Consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates. A single somatic motor neuron makes contact with an average of 150 skeletal muscle fibers, and all of the muscle fibers in one motor unit contract in unison. Typically, the muscle fibers of a motor unit are dispersed throughout a muscle rather than clustered together. Whole muscles that control precise movements consist of many small motor units.
Myogram
A record of a muscle contraction.
Latent period
Delay, lasting about 2 milliseconds. During this period, the muscle action potential sweeps over the sarcolemma and calcium ions are released from the sarcoplasmic reticulum (SR).
Contraction period
Lasts about 10-100 milliseconds. During this period, calcium binds to troponin, myosin-binding sites on actin are exposed, and cross-bridges form. Peak tension develops in the muscle fiber.
Relaxation period
Lasts 10-100 milliseconds. During this period, calcium is actively transported back into the sarcoplasmic reticulum (SR), myosin-binding sites are covered by tropomyosin, myosin heads detach from actin, and tension in the muscle fiber decreases.
Refractory period
Period of lost excitability; when a muscle fiber receives enough stimulation to contract, it temporarily loses its excitability and cannot respond for a time; characteristic of all muscle and nerve cells; duration of the period varies.
Wave summation
The phenomenon in which stimuli arriving at different times causes larger contractions; when a second stimulus occurs after the refractory period of the first stimulus is over, but before the skeletal muscle fiber has relaxed, the second contraction will be stronger than the first.
Unfused (incomplete) tetanus
When a skeletal muscle fiber is stimulated at a rate of 20 to 30 times per second, it can only partially relax between stimuli. The result is a sustained but wavering contraction.
Fused (complete) tetanus
When a skeletal muscle fiber is stimulated at a higher rate of 80 to 100 times per second, it does not relax at all. The result is a sustained contraction in which individual twitches cannot be detected.
Concentric isotonic contraction
When the muscle shortens and pulls on another structure, such as a tendon, to produce movement and to reduce the angle at a joint. (Eg. Picking up a book from a table).
Eccentric isotonic contraction
When the muscle lengthens. During an eccentric isotonic contraction, the tension exerted by the myosin cross-bridges resists movement of a load and slows the lengthening process (Eg. Putting a book down onto a table).
Isometric contraction
The tension generated is not enough to exceed the resistance of the object to be moved, and the muscle does not change its length (Eg. Holding a book steady using an outstretched arm).
Slow oxidative (SO) fibers
Fast oxidative-glycolytic (FOG) fibers
Fast glycolytic (FG) fibers
Visceral (single-unit) smooth muscle tissue
Connect to one another by gap junctions and contract as a single unit.
Multi-unit smooth muscle tissue
Lack gap junctions and contract independently.
Dense bodies
Functionally similar to Z-discs in striated muscle fibers. Some dense bodies are dispersed throughout the sarcoplasm, while others are attached to the sarcolemma; thin filaments and bundles of intermediate filaments attach to these.
