sTUDY GUIDE MUSCLE
What structures are present in a fascicle?
. Pennate arranged fascicles are short and oblique to central spine looks like a feather 2. Can have Uni-pennate and Bi-pennate 3. Pennate arranged Fascicle has most cells 4. Pennate arranged Fascicle doesn't shorten as much, but has most power.
Describe "refractory period": how does it happen and what is its effect on muscle contraction?
A refractory period follows, during which concentration of K + and Na + are actively restored to their appropriate sides of the sarcolemma by Na +/K + pumps. The muscle cell cannot contract again until Na + and K + are restored to their resting potential states. The refractory period of cardiac muscle is dramatically longer than that of skeletal muscle. This prevents tetanus from occurring and ensures that each contraction is followed by enough time to allow the heart chamber to refill with blood before the next contraction.
Describe the structure of a sarcomere.
A sarcomere is a segment of a myofibril containing thick and thin filaments. Sarcomere is the contractile unit, composed of myofilaments. States that during contraction the thin filaments slide past the thick ones so that actin and myosin filaments overlap to a greater degree.
What is a muscle fiber?
A skeletal muscle fiber is surrounded by a plasma membrane called the sarcolemma, which contains sarcoplasm, the cytoplasm of muscle cells. A muscle fiber is composed of many fibrils, which give the cell its striated appearance.
What is "tetanic contraction" (tetanus)?
A tetanic contraction (also called tetanized state, tetanus, or physiologic tetanus, the latter to differentiate from the disease called tetanus) is a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate.
What is the role and location of the following in a muscle cell:
Ca ion pump- Powered by ATP, it pumps calcium ions back into the sarcoplasmic reticulum, reducing the calcium level around the actin and myosin filaments and allowing the muscle to relax. Calcium ions are also used for signaling inside other cells, and similar pumps are found in the cell membrane of most cells.
neurotransmitter
Chemicals that transmit signals from a neuron to a target cell across a synapse.
Characterize the following zones of the myofibril:
H-zone Narrow region in center of each A band that contains thick filaments but no thin filaments
Explain why skeletal muscles enlarge from exercise - what is "hypertrophy"?
Hypertrophy is a term used to describe one of the ways cells—those tiny units that do important work in our bodies—adapt to environmental changes. Environmental changes can be things like hormonal stimulation, inflammation, or an increased workload.
Characterize the following zones of the myofibril:
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.
Describe possible causes of muscle fatigue.
If muscle weakness is the result of pain, the person may be able to make muscles work, but it will hurt. Fatigue is a feeling of tiredness or exhaustion or a need to rest because of lack of energy or strength. Fatigue may result from overwork, poor sleep, worry, boredom, or lack of exercise.
Explain the function of the following proteins that are components of sarcomeres:
Myosin Myosin is the main component of thick filaments and functions as a motor protein in all three types of muscle tissue. Motor proteins pull various cellular structures to achieve movement by converting the chemical energy in ATP to the mechanical energy of motion, that is, the production of force. In skeletal muscle, about 300 molecules of myosin form a single thick filament.
Characterize the following zones of the myofibril:
Z-disc Narrow, plate-shaped regions of dense material that separate one sarcomere from the next.
List specific muscles that are used for:
kissing Orbicularis Oris
What is "latent period"?
latent period - no change in length; time during which impulse is traveling along sarcolemma & down t-tubules to sarcoplasmic reticulum, calcium is being released, and so on (in other words, muscle cannot contract instantaneously!) contraction period - tension increases (cross-bridges are swiveling)
What is the role and location of the following in a muscle cell:
sarcoplasmic reticulum- The sarcoplasmic reticulum is a specialized type of smooth ER that regulates the calcium ion concentration in the cytoplasm of striated muscle cells.
List specific muscles that are used for:
smiling Smiling and laughing - Zygomaticus Major.
List specific muscles that are used for:
squinting Orbicularis Oculi
If you exercise regularly, and your muscles become larger, do you get many new muscle cells?
the exact mechanism by which exercise enhances strength remains unclear, but its basic principles are understood. Overall, two processes appear to be involved: hypertrophy, or the enlargement of cells, and neural adaptations that enhance nerve-muscle interaction. Muscle cells subjected to regular bouts of exercise followed by periods of rest with sufficient dietary protein undergo hypertrophy as a response to the stress of training.
Explain the function of the following proteins that are components of sarcomeres:
titin Titin is the third most plentiful protein in skeletal muscle (after actin and myosin). This molecule's name reflects its huge size. With a molecular mass of about 3 million daltons, titin is 50 times larger than an average-sized protein. Each titin molecule spans half a sarcomere, from a Z disc to an M line, a distance of 1 to 1.2 μm in relaxed muscle. Each titin molecule connects a Z disc to the M line of the sarcomere, thereby helping stabilize the position of the thick filament. The part of the titin molecule that extends from the Z disc is very elastic.
Compare epimysium, perimysium and endomysium - where is each located in a muscle?
Endomysium- The delicate connective tissue that surrounds the skeletal muscle fibers and ties adjacent muscle fibers together
Explain the function of the following proteins that are components of sarcomeres:
Molecules of the protein myomesin form the M line. The M line proteins bind to titin and connect adjacent thick filaments to one another. Myomesin holds the thick filaments in alignment at the M line.
What structure is pictured in this diagram?
Myofilaments
What is the function of myoglobin and where is it found?
Myoglobin (symbol Mb or MB) is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells.
What is the role and location of the following in a muscle cell:
Sarcoplasm- Sarcoplasm is the cytoplasm of muscle cells (which are also known as muscle fibers). Sarcoplasm is also sometimes referred to as myoplasm.
Explain what contributes to skeletal muscle having perpendicular lines (striations).
Striated Muscle. In contrast to smooth muscle, cardiac and skeletal muscle types possess an internal ultrastructure of highly organized contractile myofilaments. Actin and myosin myofilaments are stacked and overlapped in regular repeating arrays to form sarcomeres.
What role does creatine phosphate play in muscle energetics?
A decrease in intracellular concentrations of creatine (Cr) and CrP results in a hypo dynamic state of cardiac and skeletal muscle pathology. Furthermore, many experimental studies have shown that CrP may play two important roles in the regulation of muscle energetics and work. People have two general types of skeletal muscle fibers: slow-twitch (type I) and fast-twitch (type II). Slow-twitch muscles help enable long-endurance feats such as distance running, while fast-twitch muscles fatigue faster but are used in powerful bursts of movements like sprinting.
What is "motor unit"?
A motor unit is made up of a motor neuron and the skeletal muscle fibers innervated by that motor neuron's axonal terminals. Groups of motor units often work together to coordinate the contractions of a single muscle; all the motor units within a muscle are considered a motor pool.
neurotransmitter receptors
A neurotransmitter receptor (also known as a neuroreceptor) is a membrane receptor protein that is activated by a neurotransmitter. ... The influx of ions through ion channels opened due to the binding of neurotransmitters to specific receptors can change the membrane potential of a neuron.
Characterize the following zones of the myofibril:
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.
What is the role of Ach and enzyme acetylcholinesterase and where can you find them?
Acetylcholinesterase is involved in the termination of impulse transmission by rapid hydrolysis of the neurotransmitter acetylcholine in numerous cholinergic pathways in the central and peripheral nervous systems. The enzyme inactivation, induced by various inhibitors, leads to acetylcholine accumulation, hyperstimulation of nicotinic and muscarinic receptors, and disrupted neurotransmission.
Explain the function of the following proteins that are components of sarcomeres:
Actin The main component of the thin filament is the protein actin. Individual actin molecules join to form an actin filament that is twisted into a helix. On each actin molecule is a myosin-binding site, where a myosin head can attach.
Describe how excitation-contraction coupling works in a skeletal muscle.
An action potential in the skeletal muscle cell is what triggers muscle cell contraction. We have seen that calcium ions regulate whether contraction can occur. Thus, what is needed is a way to link muscle excitation (the depolarization of the action potential) to Ca++ release from the sarcoplasmic reticulum
Why is action potential important for muscle contraction and how is it generated?
An action potential is part of the process that occurs during the firing of a neuron. During the action potential, part of the neural membrane opens to allow positively charged ions inside the cell and negatively charged ions out. This process causes a rapid increase in the positive charge of the nerve fiber. Action potentials are caused when different ions cross the neuron membrane. A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron.
Give examples of how muscles are named based on their shape or location.
An even smaller number of muscles are named after the parts of the body where they start and end -- their origin and insertion. The sternocleidomastoid muscle, for example, originates from both the sternum and clavicle (breastbone and collarbone) and inserts into the mastoid bone (just below the ear).
List distinctive features of skeletal, cardiac and smooth muscle cells.
Both skeletal and cardiac muscles appear striated, or striped, because their cells are arranged in bundles. Smooth muscles are not striated because their cells are arranged in sheets instead of bundles
BOTOX blocks Ach release in neuromuscular junction. What would you expect as a result?
Botulinum toxin causes muscle paralysis because no acetylcholine enters the synaptic cleft
Compare epimysium, perimysium and endomysium - where is each located in a muscle?
Epimysium- The dense layer of collagen fibers that surround an entire skeletal muscle.
postsynaptic cell
In a chemical synapse, the postsynaptic membrane is the membrane that receives a signal (binds neurotransmitter) from the presynaptic cell and responds via depolarization or hyperpolarization. The postsynaptic membrane is separated from the presynaptic membrane by the synaptic cleft.
presynaptic cell
In a chemical synapse, the presynaptic membrane is the cell membrane of an axon terminal that faces the receiving cell. The postsynaptic membrane is separated from the presynaptic membrane by the synaptic cleft.
What is the role of Ca ions in skeletal muscle contraction?
In turn this trigger the sarcoplasmic reticulum to release calcium ions into the muscle interior where they bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction.
Characterize the following zones of the myofibril:
M-line Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.
If a muscle is used for very fine movements like the movement of an eyeball, do you expect it to have large or small motor units?
It depends on the number of branches in the motor neurons. A lesser number of branches (collateral) results in the activation in only a few motor neurons. A motor unit with 1000 fibers would be involved in powerful, gross movements. The greater the number of fibers in a motor unit, the more powerful the contraction, and the less fine control exhibited by the motor unit
Skeletal muscles contract when stimulated by a nerve impulse. List 2 other things that can initiate the contraction of a smooth muscle cell.
It is energized by ATP and is activated by a calcium pulse, however, calcium binds to calmodulin rather than to troponin (which is not present in smooth muscle fibers) and myosin must be phosphorylated to become active in contraction
Explain the sliding filament theory - what is sliding and where?
It is the process of muscle contraction involving the sliding of actin & myosin myofilaments past each other to shorten the length of each sarcomere. According to the sliding filament theory, the myosin (thick) filaments of muscle fibers slide past the actin (thin)filaments during muscle contraction, while the two groups of filaments remain at relatively constant length.
What would happen to muscle contraction if you block acetylcholinesterase?
It will interfere with cross-bridge formation and prevent muscle contraction
ligand-gated channels
Ligand-gated ion channels are membrane proteins that are fundamental signaling molecules in neurons. These molecules are localized in the plasmalemma and on intracellular organelles and can be gated by both intracellular and extracellular ligands.
Describe ligand-gated, voltage-gated and non-gated (leak) ion channels: what opens each one and what is the function of each?
Ligand-gated ion channels- Activated by binding of ligands to the channel receptor mediated Voltage gated sodium channels transmit fast action potential from cell body to axon terminal(in the neurons) Sodium Channels( fastest), Potassium Channels and Calcium Channels. Ion Channels are pore-forming membrane proteins that establish and control the voltage gradient across the membrane by allowing the flow of ions down their electrochemical gradient regulated by ligand binding diffusion, Responsible for processes such as: Heart beat (cardiac conduction) Muscle contraction (neurotransmission) Hormone secretion Vision and olfaction Pain Cognition And pretty much everything else
Define the term "excitable cell".
Nerve cells and muscle cells are excitable. Their cell membrane can produce electrochemical impulses and conduct them along the membrane. In muscle cells, this electric phenomenon is also associated with the contraction of the cell.
List the steps and key components of the mechanism pictured below. In which types of cells does it happen?
Nerve impulse arrives at axon terminal od motor neuron and triggers release of acetylcholine (ach). Ach diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP). Acetylcholinesterase in synaptic cleft destroys Ach so another potential does not arise unless more Ach is released from motor neuron. Muscle AP traveling along transverse tubule opens Ca2+ releases channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm. Ca2+ binds troponin on the thin filament, exposing the binding sites for myosin. Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere. Ca2+ releases channels in SR close and Ca2+ active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm. Troponin- Tropomyosin complex slides back into position where it blocks the myosin binding sites on actin. Muscles relaxes.
List the part of muscle cell contraction starting from action potential in the motor neuron and ending with relaxation of the myofibrils.
Nerve impulses that originate in the central nervous system cause muscles to contract. Both neurons and muscle tissue conduct electrical current by moving ions across cellular membranes. A motor neuron ends in a synapse with a muscle fiber. The interior of the muscle cell near the ends of the sarcoplasmic reticulum. The interface between a motor neuron and muscle fiber is a specialized synapse called the neuromuscular junction. Upon adequate stimulation, the motor neuron releases a flood of neurotransmitters that bind to postsynaptic receptors and triggers a response in the muscle fiber which leads to muscle movement.
Compare epimysium, perimysium and endomysium - where is each located in a muscle?
Perimysium- Nerves and blood vessels that service the muscle fibers are in the connective tissue
Define RMP. What is the magnitude of RMP in a typical skeletal muscle cell?
RMP is the voltage that exists across a cell membrane when the cell is not transmitting electrical signals; polarity is such that the inside of the cell is negative with respect to the outside. RMP of neurons is -70 mV. - Exists because more negative charges inside cell and more positive charges outside cell -All cells in the body have a negative RMP range of (-5mV to -100mV)
neurotransmitter reuptake
Reuptake, or re-uptake, is the reabsorption of a neurotransmitter by a neurotransmitter transporter of a pre-synaptic neuron after it has performed its function of transmitting a neural impulse.
What is the role and location of the following in a muscle cell:
Sarcolemma- the plasma membrane of a muscle cell, the sarcolemma generally maintains the same function in muscle cells as the plasma membrane does in other eukaryote cells. It acts as a barrier between the extracellular and intracellular compartments, defining the individual muscle fiber from its surroundings.
synaptic vesicles
Small membranous sacs filled with molecules of acetylcholine (ACh)
Explain the phases of action potential: depolarization, repolarization and hyperpolarization - which channels open and which ions flow though membrane during each phase?
Step 1 - Resting Potential. Sodium and potassium channels are closed. Sodium and potassium channels are closed. Na+ rush into the cell; K+ are concentrated inside the cell. Potential difference: -85 mV. Step 2 - Depolarization. Sodium channels open in response to a stimulus. Sodium channels open in response to a stimulus. Na+ rush into the cell according to the dictates of diffusion. Final potential difference +30 mV Step 3 - Repolarization. Na+ channels close and K+ channels open. Na+ channels close and K+ channels open. K+ rush out of the cell according to the dictates of diffusion. Potential difference: slightly below -85 mV. Step 4 - Resting Conditions Re-established. Na+ and K+ channels are closed. Na+ and K+ channels are closed. Sodium-potassium exchange pump moves Na+ out and K+ in. Resting potential difference: -85 mV.
What is the role and location of the following in a muscle cell:
T-tubules- Transverse tubules (T-tubules) are extensions of the sarcolemma (muscle cell membrane) that penetrate the center of skeletal and cardiac muscle cells.
Distinguish between a ligament and a tendon.
Tendons usually connect muscles to bones. ... Tendons may also attach muscles to structures such as the eyeball. A tendon serves to move the bone or structure. A ligament is a fibrous connective tissue which attaches bone to bone, and usually serves to hold structures together and keep them stable.
What is "all-or-none principle" for action potential?
The all-or-none law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus. If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response.
If you prevented Na voltage-gated channels from closing what would be the effect on the membrane potential? What would be the effect on the muscle cell or neuron?
The cell will be very positive, the membrane will not repolarize, and the Voltage-gated K channels will open, but not close. Remember that voltage-gated K channels open in response to depolarization. They do not close until the cell is repolarized. The cell will be more positive.
Which proteins are present in thick filament and in thin filament?
The contractile nature of this protein complex is based on the structure of the thick and thin filaments. The thick filament, myosin, has a double-headed structure, with the heads positioned at opposite ends of the molecule. Troponin is associated with the thin filaments and can bind to the actin molecules. There is usually one troponin per 6-8 actin molecules. Tropomyosin is a long thin protein that extends between, and binds to, the troponin molecules.
Explain the mechanism of impulse transmission in a chemical synapse.
The electrical signals cannot travel from one neuron to the next directly. The signal crosses the gap, called a synapse, between cells in chemical form. One neuron releases chemicals in response to an action potential (nerve impulse). They then bind to receptors on the surface of the post-synaptic neuron.
What is the role of Na/K-pump (also known as Na/K-ATPase) in maintaining the RPM?
The leak channels allow Na+ and K+ to move across the cell membrane down their gradients (from a high concentration toward a lower concentration). With the combined ion pumping and leakage of ions, the cell can maintain a stable resting membrane potential.
What is the role of the following membrane proteins in action potential in muscle cells: Ligand-gated Na-channels (Ach receptors)
The nicotinic acetylcholine receptor and other neurotransmitter receptors that are ligand-gated ion channels contain five subunits. Each subunit contains a transmembrane α helix (M2) that lines the channel. The resulting influx of K+ ions hyperpolarizes the cell membrane, slowing heart contraction.
Distinguish between fast glycolytic and slow oxidative muscle fibers. What would be the useful function of each in the body? Give examples where you would find muscles of each type.
The rate of fatigue. Fast glycolytic fibers fatigue rapidly, while slow oxidative fibers are highly resistant to fatigue. Muscles that need to be active continuously, such as weight-supporting postural muscles, contain a higher percentage of fatigue-resistant slow oxidative muscle fibers.
synaptic end bulb
The rounded tips of the terminal branches are called synaptic knobs, (end bulbs, axon terminals, synaptic terminals, terminal boutons or buttons). Inside the synaptic knobs are vesicles (synaptic vesicles) that contain neurotransmitter molecules. A synaptic knob usually lies adjacent to another cell.
What is "threshold voltage" and how does it work?
The threshold voltage, commonly abbreviated as Vth or VGS (th), of a field-effect transistor (FET) is the minimum gate-to-source voltage differential that is needed to create a conducting path between the source and drain terminals.
Explain the function of the following proteins that are components of sarcomeres:
Tropomyosin and Troponin Smaller amounts of two regulatory proteins—tropomyosin and troponin are also part of the thin filament. In relaxed muscle, myosin is blocked from binding to actin because strands of tropomyosin cover the myosin-binding sites on actin. The tropomyosin strands in turn are held in place by troponin molecules. You will soon learn that when calcium ions (Ca2+) bind to troponin, troponin undergoes a conformational change (change in shape); this change moves tropomyosin away from myosin-binding sites on actin, and muscle contraction subsequently begins as myosin binds to actin.
Voltage gated K-channels
Voltage-gated K+ channels (Kv) play an important role in regulating contraction of vascular smooth muscle cells (VSMC) through their effects on membrane potential and on voltage-gated Ca2+ channel activity.
Voltage-gated Na-channels
Voltage-gated sodium channels are responsible for action potential initiation and propagation in excitable cells, including nerve, muscle, and neuroendocrine cell types
List specific muscles that are used for:
chewing food The Muscles of Mastication more commonly known as the muscles of the jaw consist of three muscles the Temporalis, Masseter and Pterygoid Muscles which work together to move the mandible at the Temporomandibular Joint. These three muscles are solely responsible for the chewing action, grinding the teeth, moving our mandible from side to side and assisting us to speak.
What is the role and location of the following in a muscle cell:
voltage-gated Ca-channels- Voltage-dependent calcium channels (VDCCs), also known as voltage-gated calcium channels (VGCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (e.g., muscle, glial cells, neurons, etc.) with a permeability to the calcium ion Ca2+.
Explain the function of the following proteins that are components of sarcomeres:
α-actinin The dense material of the Z discs contains molecules of α-actinin, which bind to actin molecules of the thin filament and to titin. Molecules of the protein myomesin form the M line. The M line proteins bind to titin and connect adjacent thick filaments to one another. Myomesin holds the thick filaments in alignment at the M line.
