Chapter 9 - Review Flashcards
describe the general properties of muscle
- Contractility 2. Excitability 3. Extensibility 4. Elasticity
Contractility
The ability of muscle to shorten forcefully
Excitability
The capacity of muscle to respond to a stimulus.
Extensibility
The muscle can be stretched beyond its normal resting length and still be able to contract
Elasticity
The ability of muscle to recoil to its original resting length after it has been stretched.
Whole Muscle
Complete organ consisting of cells, called skeletal muscle fibers, associated with smaller amounts of connective tissue, blood vessels and nerves.
Fasciculi
A bundle of skeletal muscle fibers surrounded by perimisium.
Fiber
Each skeletal fiber is a single long, cylindrical cell containing several nuclei, which are located on the periphery, near the plasma membrane. A single fiber can extend from one end of a muscle to the other.
fascia
Connective tissue sheets within the body
Perimysium
Each fasciculus is surrounded by another, heavier connective tissue layer called the perimyseum.
Epimysium
The entire muscle is surrounded by layer of connective tissue called the epimyseum. It is composed of dense collagenous connective tissue.
Endomysium
a wispy layer of areolar connective tissue that ensheaths each individual muscle fiber. It also contains capillaries and nerves. It overlies the muscle fiber’s cell membrane: the Sarcolemma.
Histology of Muscle Fibers
Skeletal muscle is made up of individual components known as myocytes, or “muscle cells”, sometimes colloquially called “muscle fibers”. They are formed from the fusion of developmental myoblasts (a type of embryonic progenitor cell that gives rise to a muscle cell) in a process known as myogenesis. These long, cylindrical, multinucleated cells are also called myofibers. The myofibers are in turn composed of myofibrils. The myofibrils are composed of actin and myosin filaments repeated in units called a sarcomere, the basic functional unit of the muscle fiber. The sarcomere is responsible for skeletal muscle’s striated appearance and forms the basic machinery necessary for muscle contraction. The term muscle refers to multiple bundles of muscle fibers held together by connective tissue.
Triad
is the structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side
Myofiber
are the functional contractile units of skeletal muscle. Mononuclear satellite cells located between the basal lamina and the plasmalemma of the myofiber are the primary source of myogenic precursor cells in postnatal muscle.
Myofibril
very long chains of sarcomeres, the contractile units of the cell.
Myofilament
are the filaments of myofibrils constructed from proteins.
Describe the sarcomere
It is the basic structural unit and functional unit of skeletal muscle because it is the smallest portion of skeletal muscle capable of contracting. Each Sarcomere extents from one Z disk to an adjacent Z disk
Picture a Sarcomere
Sarcomere and Triad
Image
Titin
It attaches to Z disks and extends along myosin myofiliments to the M line. The myosin mycofilaments are attached to the titin molecules which help hold them in position.
Titin is a giant protein that functions as a molecular spring which is responsible for the passive elasticity of muscle.
troponin
is a complex of three regulatory proteins (troponin C, troponin I, and troponin T) that is integral to muscle contraction[2] in skeletal and cardiac muscle, but not smooth muscle.
Individual subunits serve different functions:
Troponin C binds to calcium ions to produce a conformational change in TnI Troponin T binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex Troponin I binds to actin in thin myofilaments to hold the troponin-tropomyosin complex in place
tropomyosin
Each Actin Myofilament is composed of two strands of fibrous actin (F actin), a series of Tropomyosin molecules and a series of troponin molecules
The two strands of F actin are coiled to form a double helix which extends the length of the actin myofilament.
Troponin and tropomyosin regulate contraction via calcium binding
Simplified schematic of actin backbones, shown as gray chains of actin molecules (balls), covered with smooth tropomyosin filaments. Troponin is shown in red (subunits not distinguished). Upon binding calcium, troponin moves tropomyosin away from the myosin-binding sites on actin (bottom), effectively unblocking it. Modified from Lehman et al. (1994).
What does calcium bind to in regards to Excitation-contraction coupling model of muscle cells?
Calcium binds to troponin.
When does ATP Hydrolysis occur?
After the Cross-bridge, and before the recovery stroke
Sarcomere (Image)
Motor End Plate
What is the role of Ca++ in the presynaptic cell?
It acts as a voltage gate in the presynamptic membrane
What is the function of the synaptic transmitter, ACh?
Acetylcholine is an organic moecule composed of acetic acid and choline.
It is a neurotransmitter, a substance released from a presynaptic membrane that diffuses across the synaptic cleft and alters the activity of the post synaptic cell. Neurotransmitters can stimulate (or inhibit) the production of an action potential in the postsynaptic membrane (the sarcrolemma) by binding to ligand-gated ion channels.
What is the role of Ca++ in the muscle fiber?
When an action potential reaches the presynaptic terminal, it causes voltage-gated calcium ion (Ca++) channels in the plasma membrane of the axon to open; as a result, Ca++ diffuses into the cell. Once inside the cell, the Ca++ causes the contents of a few synaptic vesicles to be secreted by exocytosis from the presynaptic terminal into the synaptic cleft.
What is the role of the sarcoplasmic reticulum in contraction?
The sarcoplasmic reticulum releases calcium ions during muscle contraction and absorb them during relaxation.
What are the differences between red and white muscle regarding: function?
Red (Slow Twitch)- has a high fatigue resistance, maintains posture and performance of endurance activities
White (IIA Fast Twitch)- endurance activites in endurance trained muscles
White (IIb Fast Twitch)-Rapid, intense movements of short duration
What are the differences between red and white muscle regarding: Perfered source of energy?
Red (slow twitch)-low Glycogen concentration, high Aerobic capacity, low anaerobic capacity.
White (IIa)-High Glycogen Concentration, Intermediate aerobic capacity, high anaerobic capacity
White(IIb)-high glycogen concentration, low aerobic capacity, highest anaerobic capacity.
What are the differences between red and white muscle regarding: Speed of contraction
Red-Slow twitch-Cantract more slowly
White- Fast twitch-respond rapidly
What are the differences between red and white muscle regarding: Glycogen content?
Red (Slow-twitch)-low glycogen concentration
White (Fast twitch)- High glycogen concentration
What are the differences between red and white muscle regarding: Myoglobin content
Red (Slow twitch)-High Myoglobin Content
White (IIA Fast twitch)- high myoglobin content
White (IIB Fast Twitch)- Low myoglobin content
What are the differences between Type IIa and Type IIb muscle fibers?
Fast-twitch muscle fibers come in two forms, Type IIA or Fast-twitch glycolytic (FOG) fibers, or and type IIb fast-twitch glycolitic (FG) fibers.
Type IIa fibers rely on both anaerobic and aerobic ATP production, whereas type IIb fibers rely almost exclusively on anaerobic glycolysis for ATP production. In Men, type IIa are the largest diameter fibers.
Does exercise increase muscle cell mass? muscle cell number? What kind of exercise is involved with your answer?
Intense exerciss that requires anaerobic respiration such as weight lifting, increases muscular strength muscular strength and mass and causes fast-twitch muscle fibers to enlarge more than slow-twitch fibers,
Conversely, aerobic exercise increases the vasularity of muscle and causes slow-twitch muscle to enlarge more.
What are the sources of ATP for contraction?
Chreatine phosphate, Glycogen, ATP Generated directly from Cellular Respiration
What is the difference between aerobic and anaerobic respiration? In what part of the cell is each performed?
Aerobic respiration is the type of respiration that occurs in the presence of oxygen whereas anaerobic respiration is the type of respiration that occurs in the absence of oxygen. During aerobic respiration high level of energy of 38 ATP molecules is produced contrary to anaerobic respiration where only 2 ATP molecules of energy are produces hence low energy levels.
Aerobic accurs in the mitochondria
What is oxygen debt?
a cumulative deficit of oxygen resulting from intense exercise; the deficit must be made up when the body returns to rest
Describe a motor unit.
Differentiate between isotonic and isometric exercise.
Isometric
The easiest way to understand what isometric exercises are is to just think of them static, or still, exercises, because that’s exactly what they are. When you perform an isometric exercise, you don’t move or put your muscle(s) through any range of motion. You simply hold a pose for as long as you can. Examples would include: holding a static pushup position; holding a dumbbell in one hand mid bicep curl; or even pushing against an immovable object, such as a wall.
Isotonic
Isotonic exercises are the exact opposite of isometric exercises: You are moving and you are working your muscle(s) through a range of motion. Isometric exercises are actually the most common type of strength training exercises people do. For example, lifting weights, calisthenics, swimming, rock climbing, cycling: they’re all isotonic movements.
Function of the Neuromuscular junction
What are cross-bridges in a fiber?
Myosin
Differentiate between the power stroke and the recovery stroke in contraction?
ATP is consumed as an energy source for the power-stroke, pulling the thin filaments toward the H-zone. When the power-stroke occurs, ADP is released.
Describe the sliding filament model of contraction.
ATP activates myosin, bringing it to a higher energy state, ready to form cross-bridges with the thin actin filament.
Myosin acts as a molecular ratchet by binding to an actin filament and changing shape, thereby pulling the actin filament toward the A-band.
ATP binds again, destabilizing the myosin filament and enabling it to bind to another site along the actin filament, increasing the strength of contraction.
All the myosin heads contract simultaneously, shortening all the sarcomeres, causing the muscle to contract.
The myosin heads pull the A-band toward the Z-lines at the end of each sarcomere, shortening the length of the I-band.
