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Chapter 7
| Question | Answer |
|---|---|
| What is the bulk of the body's muscle called? | Skeletal muscle because it is attached to the skeleton (or associated CT structures) |
| What does skeletal muscle allow you to do? | influences body contours and shape, allows you to grin and frown, provides a means of locomotion, and enables you to manipulate the environment |
| How is the body muscle balanced | cardiac and smooth muscle- which are major components of the walls of hollow organs and heart |
| what does the heart do? | transport materials within the body |
| What is the primary objective of the muscular system? | investigate the structure and function of the skeletal muscle |
| What is the skeletal muscle? | its voluntary, since it can be consciously controlled and striated |
| What is skeletal muscle composed of? | large, long cylindrical cells, sometimes called fibers, ranging from 10 um to 100 um in diameter and 6 cm in length, but hip is coarse so its 25 cm in length |
| What kind of cells do skeletal muscle have? | multinucleate; multiple oval nuclei can be seen just beneath plasma membrane- called sarcolemma |
| The nuclei are pushed peripherally by the longitudinally arranged____________-- | myofibrils, which nearly fill the sarcoplasm |
| Information about light and dark bands? | light (I) and dark (A) bands along the length of the perfectly aligned myofibrils give the muscle fibers as a whole its stripped appearance |
| Myofibrils are made up of what | smaller threadlike structures called myofilaments |
| Myofilaments have what two contractile proteins | actin and myosin- which slide past each other during muscle activity to bring about shortening or contraction of the muscle cells |
| Who is responsible for the banding pattern in skeletal muscle? | Myofibrils |
| What is the contractile unit of muscle | sacromere- extend from the middle of one I band (its Z disc) to the middle of the next along the length of the myrofibrils. |
| Cross sections of the sarcomere in areas where thin and thick filaments overlap show | each thick filament is surrounded by 6 thin filaments, and each thin filament is enclosed by three thick filaments |
| At each junction of the A and I bands, the sarcolemma indents | into the muscle cell forming a transverse tubule (T-tubule) |
| Terminal Cisternae | These tubules run deep into the muscle cell between cross channels, or terminal cisternae of the smooth endoplasmic reticulum called the sarcoplasmic reticulum (SR) |
| Triads | regions where the SR terminal cisternae about a T tubule on each side are called triads |
| Movable attachment is called | insertion |
| fixed or immovable attachment is called | origin |
| what is the function of tendons | provide durability and to conserve space |
| more info on tendon | tough collagenic CT, they can span round bony prominence that would destroy the more delicate muscle tissues, they can pass over a joint bc their small size |
| CT | provide a route for the entry and exit of nerves and blood vessels that serve the muscle fibers. |
| The larger more powerful muscles have relatively more | CT |
| As we age, the mass of the muscle fibers | decreases and the amount of CT increases |
| The junction between a nerve fiber (axon) and a muscle cell is called- | neuromuscular or myoneural junction |
| Each axon of the motor neuron break into many branches called | axon terminals and each of these branches participates in forming a neuromuscular junction with a single muscle cell |
| Motor unit | together a neuron and all the muscle fibers it stimulates make up the functional structure called this |
| The neuron and muscle fiber are close but they do not | touch |
| What is the neuron and muscle fiber sepearted by | small fluid-filled gap called the synaptic cleft |
| Within the axon terminals there are many | mitochondria and vesicles containing the neurotransmitter (ACh) |
| When a nerve impulse reaches the axon terminal | some of these vesicles release their contents into the synaptic cleft, then ACh rapidly diffuses across the junction and combines with receptors on sarcolemma |
| When receptors bind ACh, a change in the permeability of the sarcolemma occurs: | Channels that allow both NA+ and K+ ions pass breifly- more sodium diffuses into cell than potassium diffuses out, depolarization of the sarcolemma and subsequent contraction of the muscle fiber occurs |
| 3 events in the contraction of skeletal and cardiac muscle fibers | electrical excitation of the muscle cell, excitation-contraction coupling, and shortening of the muscle cell due to the sliding of the myofilaments within it. |
| At rest all cells maintain a potential difference or voltage across their plasma membrane, the inner face of the membrane is approx. | -60 to -90 mV compared with cell exterior |
| What is the potential difference based on? | result of differences in membrane permeability to cations, most importantly sodium (Na+ and K+) ions |
| Intracellular potassium concentration is much _____ than its extracellular concentration | greater |
| intracellular sodium concentration is much _____ than its extracellular concentraion | lesser |
| Steep concentration gradients across the membrane exit for both cations | true |
| What is the plasma membrane more permeable to? | K+, the cells RMP is more negative inside than outside, and the RMP is in particular interest in excitable cells, like muscle cells and neurons |
| When a muscle cell is stimulated the sarcolemma becomes temporarily more permeabile to | Na, which enters the cell, this sudden influx of Na alters the membrane potential, the cell interior becomes less negative which causes depolarization |
| After that the sarcolemma becomes | less permeable to Na and more permeable to K, so they move out of the cell restoring membrane potential called repolarization |
| Action potential | rapid depolariztion and repolarization of the membrane that is propagated along the entire membrane from the point of stimulation is called this |
| Absolute refractory period | period when Na changes permeability and then becomes restricted |
| Relative refractory period | repolarization occurs, and Na is gradually restored, a strong stimulus to the muscle cell provokes another action potential |
| Propogation of the action potential along the sarcolemma causes the release of | calcium ions from storage in the SR within the muscle cell, which bind on regulatory proteins on actin myofilaments, its acts as an ionic trigger & starts contraction, so actin and myosin slide pass each other |
| cont from propogation | once the action potential ends, the calcium ions are almost immediately transported back into the SR-- which causes the muscle cell to relax. |
| The nervous system controls muscle contraction by 2 mechanism | multiple motor unit summation (recruitment)- the gradual activation of more and more motor units & temporal (wave) summation- an increase in the frequency of nerve impulses for each active motor unit |
| Tendons | attach to the periosteum of a bone |
| skeletal muscles are composed of hundreds to thousands of individual cells called muscle fibers, which produce | muscle tension- aka muscle force, can lift 45 kg sack of concrete |
| A motor unit consists of | a motor neuron and all the muscle fibers it innervates. |
| The motor neuron and a muscle fiber intersect at the | NMJ, its the location where the axon terminal of the neuron meets a specialized region of the muscles fibers plasma membrane- called motor end plate |
| Excitation- contraction coupling | entire process where end-plate potential triggers a series of events that results in contraction of muscle cell |
| muscle twitch- | mechanical response to a single action potential. which has three phases latent phase, contraction phase, and relaxation phase |
| latent period | time between generation of ap in a muscle cell and the start of muscle contraction- no force is generated, chemical changes occur like releaseing Ca from SR intracellularly |
| Contraction phase | starts at the end of the latent period and ends when muscle tension peake |
| Relaxation phase | is the period of time from peak tension until the end of the muscle contraction |
| A skeletal muscle produces tension | aka muscle force when nervous or electrical stimulation is applied |
| Motor unit recruitment | increasing number of active motor units, we can produce a steady increase in muscle force |
Created by:
pink23