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Physi 2
Muscle Contraction
| Question | Answer |
|---|---|
| What is the sarcolemma? | Muscle cell membrane. Each muscle cell/fiber is innervated by its own single nerve ending. |
| What is a motor unit? | All the muscle fibers that are innervated by a single motor neuron. |
| Hundreds to thousands of these are in each muscle fiber and are composed of even smaller structures called myofilaments. | Myofibrils |
| What is the thin filament in which attach to the Z-discs (lines) and have about 3000 per myofibril? | Actin |
| What is the thick filament and has cross bridges that protrude to interact with actin filaments? There are about 1500 per myofibril. | Myosin |
| What is the sarcomere? | The distance between two Z-discs that connects muscle. Each sarcomere can shorten it's width therefor shortening the entire muscle. |
| What makes up a muscle fiber? | A muscle fiber is composed of hundreds to thousands myofibrils that are made up of smaller structures called myofilaments. The myofilaments are actin and myosin, and sarcomere. |
| What does actin connect to? | Actin connects to Z-discs. The distance between the two Z-discs is one sarcomere. |
| What is the sarcoplasm and where is it located? | The sarcoplasm is the cytoplasm of muscle cells and is located between the myofibrils. |
| The sarcoplasm has a high concentration of what ions and enzymes? | K, Mg, PO4, and protein enzymes. |
| Where are mitochondria located in the muscle cell, and what is their purpose? | Mitochondria are located in the sarcoplasm around the myofibrils and produce ATP. |
| Sarcoplasmic Reticulum (SR) stores what ion, and where in the SR is it mostly stored? | Ca++ and it is mostly stored in the terminal cisternae which is the wide ending of the SR that is located my the Z-discs. |
| The sarcoplamic reticulum is more extensive in which type of muscle? | Skeletal muscle |
| Events leading up to muscle contraction are first initiated by an AP conduction in a motor neuron in which does what to the terminal? | The AP causes depolarization of the terminal. |
| Where is ACh released before crossing into the cleft? | ACh is released from the neuromuscular junction before crossing into the cleft. |
| After ACh binds to ACh-gated ion channels what ion is responsible for depolarization of the muscle? | An influx of Na+ is responsible for depolarization of the muscle. |
| Describe the end plate potential EPP? | The EPP is an AP that is conducted all over the muscle surface depolarizing entire muscle membrane including T-tubules. |
| What are T-tubules and what is their purpose? | T-Tubules are extensions of the sarcolemma into the heart of the cell located near the Z-disc, that increase surface area of the muscle membrane. AP depolarizes the tubules and what is near them, which is the SR. |
| What happens when the SR is depolarized? | Releases Ca++ ions onto myofibrils. |
| What does the release of Ca++ ions onto the myofibrils cause? | Ca++ ions triggers the filament interaction, sliding of actin and myosin. |
| What ends the muscle contraction? | Ca++ ions pumped back into the SR |
| In a relaxed muscle would the filaments be overlapped with Z discs close together or barely overlapping? | relaxed muscle |
| If the Z-discs are close together and the filaments are overlapped, is the muscle contracted or relaxed? | The muscles are contracted. |
| Myosin complex is made up of what? | Globular protein heads, cross bridges or flexible hinges where the heads join into myosin. The head contains the molecule of ATPase enzyme. |
| What are the three components of the actin complex? | F-actin, Tropomyosin, and Troponin. |
| In the actin complex what is a double stranded protein molecule that attaches to the Z discs? | F-actin |
| What is tropomyosin and what does it do? | Tropomyosin is a protein that wraps around F-actin. It blocks the active sites if the muscle is relaxed. It has ADP molecules (active sites) for myosin interaction. |
| Troponin is a system that helps bind tropomyosin to actin and is composed of three units. What are those units and how do they contribute to the binding? | 1)troponin i-has affinity for actin 2)troponin t-has affinity for tropomyosin 3)troponin c-has affinity for calcium |
| How does Troponin-Tropomyosin complex inhibit Actin Mysosin binding? | It blocks the active sites on F-actin by lying on top of it. |
| How does Ca++ unblock the Troponin-Tropomyosin complex and expose the active sites for actin myosin bonding? | Ca++ binds to troponin c, and pulls the tropomyosin into the groove, unblocking the actin filament and exposes the active sites. |
| What is happening during the power stroke? | After the active sites are exposed, the myosin head binds to actin and pulls inward. Cleavage of ATP on myosin head, provides the energy for the power stroke. The new ATP allows release of actin and myosin. |
| When does maximum tension develop in the sarcomere? | When the overlap between actin and myosin are at their maximum. |
| When the Z-discs start to run into myosin heads what happens to the tension? | It starts to decrease. |
| Will tension develop if the actin and myosin are too far apart? | Nope! |
| Is AP in muscle longer or shorter than in nerves and what is it's resting potential? | AP is of a longer duration than in nerves, and is slower than the nerves. Its resting membrane potential is (-70)-(-90)mV. |
| When the SR is depolarized what happens that is important for muscle contraction? | It releases Ca++ into the cytoplasm which then binds to troponin c & pulls tropomyosin off actin's active site and allows for A-M binding & contraction can occur. |
| Where is the most Ca++ released in the SR? | Terminal cisternae, located at the end of the SR, has the greatest Ca++ concentration. |
| Where is the Ca++ pump? | The SR is filled with Ca++ pumps. ATPase pump is in the walls of SR and constantly pumps so that Ca++ can be resequestered into SR. |
| What is the EPP safety factor? | The impulse that arrives at the neuroomuscular junction causes about 3-4 times greater as much EPP that is required to stimulate the muscle fiber (15-30mV) so that muscle contractions are not firing constantly. |
| Stimulation of a nerve fiber at rates >100Hz for several minutes depletes ACh vesicles and the # of ACh released with each stimulus gradually decreases is known as what? | Junctional Fatigue |
| Do whole muscle contractions need many motor units or just a single motor unit? | Many motor units are needed for these. |
| Isometric contraction is what? | Muscle contracting w/o shortening. Sarcomere remains the same length during the contraction. |
| What type of contraction is needed for forces to oppose gravity such as keeping your head up, or sitting upright? | Isometric |
| Type of muscle contraction that that does not change the tension, fixed load? | Isotonic |
| The type of muscle contraction that occurs while I life an object off of a desk or that occurs while I am walking is what? | Isotonic, because the load is the same, therefor the tension is not changing with muscle contraction. |
| How is summation accomplished? | By recruitment of additional motor units, multiple fiber summation. Stronger signal will recruit larger motor units. |
| Frequency Summation requires what? | An increase in the frequency of stimulation increases the strength of contraction. Does not allow complete relaxation between contractions. |
| What happens with Tetanization summation? | When a muscle fiber is stimulated so rapidly that it does not relax between stimuli and a smooth, sustained contraction occurs. |
| What type of fatigue results from a depletion in muscle glycogen? | Metabolic Fatigue (no fuel) |
| What is depleted in neuromuscular fatigue? | ACh loss or depletion. |
| What is lost and results in fatigue when there is an interruption of blood flow? | O2 is lost. |
| How does atrophy develop? | When muscle is unused, and the rate of decay of contractile protein exceeds rate of replacement. |
| What can happen almost immediately upon denervation? | Atrophy can happen in the absence of nerve signals. Contracture can also happen which replaces fibrous tissue with muscle tissue. Fibrous tissue shortens permanently with time. |
| Type of smooth muscle that is mainly controlled by nervous stimuli? | Multiunit smooth muscle. |
| Describe the muscle fibers in multiunit smooth muscle. | In multiunit smooth muscle each fiber is innervated separately and controlled by a single nerve ending. It contracts independently, insulated by a separate basement membrane, seldom contract spontaneoulsy. |
| Where is multiunit smooth muscle found? | In the eye, iris, ciliary muscles, pilorector muscle ( hairs erect by sympathetic NS) |
| Describe single unit smooth muscle fibers. | They are represented by a large number of fibers that act (contract) together as a single unit. Usually controlled by non-nervous stimuli. They are arranged in sheets or bundles, have gap junctions for sites of electrical connections. |
| Where are single unit smooth muscle located? | In the visceral smooth muscle, all hollow organs, gut, ureters, blood vessels, bile ducts, uterus. |
| Do smooth muscle cells contain actin, myosin, and troponin complex as in skeletal muscle? | No, smooth muscle contains actin and myosin, but NO troponin complex. |
| Is Ca++ needed for contraction in smooth muscle? | Yes, Ca++ is needed for contraction and ATP for energy. |
| What is the difference in the actin and myosin in smooth muscle from skeletal muscle? | Actin is bound together by dense bodies, and some inside cell that form intracellular bridges. These protein bridges transmit the force of contraction to adjacent cells. The myosin is interspersed randomly b/t actin filament and the ratio is M:A 1:15. |
| Is muscle contraction slower in smooth muscle or faster? | Muscle contraction occurs at a much slower frequency in smooth muscle,(skeletal 10-300x faster) Cross bridge interaction b/t actin and myosin in smooth is much longer bc they have less ATPase activity. |
| Speed of contraction/relaxation cycle in smooth muscle is.... | 1-3 sec; excite-->contracts-->relax about 30x longer than skeletal. |
| Why is smooth muscle able to generate a greater force then skeletal with a slower and longer contraction? | B/c the longer interaction b/t actin and myosin causes a greater force than a shorter actin and myosin interaction. |
| Skeletal muscle can shorten 1/4-1/3 of it's total length compared to smooth muscle which can shorten to how much of it's length? | Can shorten 2/3 of it's entire length due to it's random arrangement of filament not in a synchronized order. |
| What are some of the factors that increase Ca++ in smooth muscle? | nerve stimulation, hormones, and stretch. |
| Since smooth muscle lacks a troponin complex how is there actin-myosin interaction? | A regulatory protein calcium calmodulin binds 4 Ca++ ions and the Ca/CM complex binds to enzyme and activates, myosin kinase (phosphorylating enzyme) which phohsphorolates myosin head, allowing Myosin-actin interaction. |
| What causes relaxation in smooth muscle? | Myosin phosphatase removes the PO4 from myosin, allowing the filaments to separate thus stopping the contraction. |
| What type of muscle receives it's AP from nerve branches over a sheet of muscle whose inner layers are excited by the upper layers? | Smooth muscle. Not a specialized NMJ. |
| Smooth muscle has varicosities instead of EPP. What is varicosity? | Multiple sites of neurotransmitter release. Schwann cell insulates b/t the varicosities and the gaps in the schwann cells are localized at the varicosities. |
| Which type of smooth muscle uses both ACh and NE as transmitters that can be both excitatory and inhibitory? | Smooth muscle |
| In smooth muscle, if ACh excites what does NE do? | NE would inhibit and vice versa. |
| What type of smooth muscle is contact junction prevalent in and what does contact junction mean? | Contact junction is more prevalent in multiunit smooth muscle. It is short latency signals that act quickly bc the varicosities containing neurotransmitters sit directly on muscle. How the eye muscles work very fast. |
| What is the resting membrane potential in smooth muscle? Is is lower or higher than skeletal? | RMP is (-50)-(-60)mV. It is about 30mV or so less than skeletal muscle. |
| Do action potentials occur in single unit, multiunit or both? | Only in single unit. |
| In smooth muscle the spike potential is how much longer in duration than skeletal muscle? | 10-50msec longer. |
| Describe what an AP with a plateau is in smooth muscle. | AP with a plateau are the result of delayed repolarizing, causes a prolonged contraction or plateau. As seen in a uterus. |
| Smooth muscle has more voltage gated Ca++ channels & less voltage Na+ channels than skeletal muscle, why is this important for smooth muscle? | Ca++ influx is responsible for + feedback cycle in smooth muscle; where as Na+ is for skeletal. Ca++ channels are slower than Na+ but remain open for longer (plateau). |
| What is a slow wave potential and in what muscle does this occur? | Smooth muscle. Causes spontaneous AP in some smooth muscle, but is not a full contraction but a slow wave rhythm. By itself won't trigger a contraction but it is possible for it to depolarize itself to threshold. (Peristalsis.) |
| Where does stretch activation occur and what is it? | Stretch activation occurs in single unit visceral smooth muscle. Food in gut causes a stretch that contributes to peristaltic activity by inherent slow wave activity plus depolarization by stretch. |
| Local tissue factors that cause vasodialation, control local blood flow in smooth muscle by non-nervous stimulation consist of what? | Ions-lack of O2, excess CO2, Excess H+, excess K+ or decrease Ca++. Adenosine-direct vasodilaroty effects, and lactic acid buildup. Mild to moderate temp decrease. |
| Hormonal factors that affect contraction in smooth muscle are? | ACh, NE, Epinephrine, Angiotensin, vasopressin, oxytocin, Histamines and serotonin, hormone gated receptors can be inhibitory or excitatory. |
Created by:
ngawlik
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