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Muscle Histology
| Question | Answer |
|---|---|
| muscles form what, in general? | form the flesh of the body |
| "sarco" | "flesh" |
| "flesh" | "sarco" |
| how much of your body weight is muscle? | over 40% of your total body weight = muscle |
| muscle is responsible for what, in general? | responsible for voluntary movements & involuntary activities |
| what regulates muscle function? | nerves |
| how are nerves related to muscle? | they regulate muscle function |
| what are muscles composed of? | composed of muscles cells (i.e. muscle fibers). "myofiber" |
| muscle cell aka? | muscle fiber, or "myofiber" |
| myofiber | is the muscle fiber/i.e. the muscle cell |
| what are myofibers specialized for? | myofibers are specialized for contraction |
| length of cardiac muscle fibers? | 50-100 microns |
| length of smooth muscle fibers? | 30-200 microns |
| length of skeletal muscle fibers? | 100 microns to 30 cm |
| muscle cell = (more specifically? | muscle fiber |
| muscle fiber = (more specifically? | myofiber |
| the plasma membrane of a muscle cell? | sarcolemma |
| sarcolemma | the plasma membrane of a muscle fiber |
| endoplasmic reticulum of a muscle fiber? | sarcoplasmic reticulum |
| sarcoplasmic reticulum | the endoplasmic reticulum of a muscle fiber. a network of membranous channels which surround each myofibril, running parallel to it. |
| myofibril what is it and what does it enable? | makes up the skeletal muscle cel. one of the slender threads of a muscle fiber, composed of numerous myofilaments. It enables the muscle cell to contract |
| myofilament: what is it and what does it contain? | any of the ultramicroscopic threadlike structures of protein composing the myofibrils of striated muscle fibers; thick ones contain myosin, thin ones contain actin |
| cytoplasm of the muscle fiber? | sarcoplasm |
| sarcoplasm: what is it and what does it contain? | cytoplasm of the muscle fiber. contains glycogen & myoglobin |
| myoglobin | red pigment that binds oxygen until it is needed |
| what is the fibrous insulating sheath around the entire skeletal muscle? | epimysium |
| what is the insulating layer around a fascicle of muscle fibers? | perimysium |
| what is the insulating layer around a single muscle fiber? | endomysium |
| epimysium | the fibrous, insulating sheath around an entire skeletal muscle. |
| perimysium | The fibrous sheath enveloping each of the primary bundles or fascicles of skeletal muscle fibers |
| endomysium | The fine connective tissue sheath surrounding each muscle fiber. |
| describe the process of the formation of a skeletal muscle fiber | first the myoblasts fuse to form a multinucleated myoblast (this does not have myofibrils yet). once myofibrils form it becomes the skeletal muscle fiber |
| tendon | a fibrous cord of connective tissue continuous with the fibers of a muscle and attaching the muscle to bone. |
| aponeurosis: what is it, an example? | sheetlike tendinous expansion of connective tissue (dense regular CT). EX: the epicranial aponeurosis or "galea aponeurotica". |
| histologically speaking, when you look at a skeletal muscle, what do you see? what are these? | you see alternating dark and light bands. (striations). these are not surface markings. they involve total fiber thickness. |
| a fibrous cord of connective tissue continuous with the fibers of a muscle and attaching the muscle to bone. | tendon |
| ligament | band of fibrous connective tissue serves to connect bones and strengthen joints |
| break down the muscle cell (what is it made of?) | the myofibers is composed of slender threads i.e. myofibrils. Each myofibril is composed of microscopic threadlike protein filaments, i.e. myofilaments. (actin and myosin) |
| break down the myofilaments? (types and patterns? | there are 2 types of myofilaments (2 protein filaments that overlap eachother in a definitive pattern. |
| actin: what is it, where is it localized | thinner filament of protein in the myofibril. localized in the I band of the myofibrils. |
| myosin: what is it, where is it localized? | thick filament of protein in the myofibril. localized in the A band of the myofibril |
| dark band of myofibril? AKA? what does it contain? | AKA A band. contains actin and myosin protein filaments |
| light band of myofibril? AKA? what does it contain? | I band. contains actin filament only |
| 3D x section of myofibril: what is the pattern of the myofilaments? | six actin surround one myosin. (or in the light band it is just six actin arranged cylindrically with nothing in middle) |
| draw three myofilaments stacked on one another, showing the dark and light bands as well as labeling: A Band, I band, H zone, M line, Z line, sarcomere | draw 3 thick bars stacked (myosin). 2 columns of these w thin lines (actin overlapping). A band corr. to local. of myosin. I band=actin only. the zig zag Z line goes thru I band. lightly curved M line thru myosin. Hzone=center of A band. sarcomere: z to z |
| draw 3 D x section of myofibrils (showing how corr. myofilaments are arranged) after being cut at 3 places : 1)through the middle I band,2) through the middle A band i.e. H zone (myosin only) and 3)thru sides of A band (actin and myosin overlap) | 1)actin only would be six concentric dots w empty middle. 2)just myosin centers (thick dots) 3)3 concentric actin w thick Myosin in middle |
| sarcomere: what is it and what defines it? | structural and functional unit of the skeletal muscle. it goes from Z line to Zline. |
| Z line | a narrow, darkly staining protein band to which actin filaments are attached. it bisects the I band of skeletal muscles. The distance between Z lines defines the sarcomere length |
| H zone: what does it contain and when is it visible | in the middle of the sarcomere (center of the A band). It contains only myosin and is only visible in relaxed muscle |
| M line | A fine dark band that bisects the H zone in the myofibrils of striated muscle. consists of fine, stabilizing threads that interconnect the myosin filaments. functions to keep myosin in place. |
| a narrow, darkly staining protein band to which actin filaments are attached. it bisects the I band of skeletal muscles. The distance between Z lines defines the sarcomere length | Z line |
| in the middle of the sarcomere (center of the A band). It contains only myosin and is only visible in relaxed muscle | H zone |
| A fine dark band that bisects the H zone in the myofibrils of striated muscle. consists of fine, stabilizing threads that interconnect the myosin filaments. functions to keep myosin in place. | M line |
| terminal cisternae what are they, what do they form, what do they function for | pairs of transversely oriented, bulbous enlargements of sarcoplasmic ret. occurring at regular intervals in skel muscle fibers; together with an intermediate T tubule they constitute a triad. function as the storage area for calcium ions in the myofiber. |
| pairs of transversely oriented tubules of the sarcoplasmic reticulum occurring at regular intervals in skeletal muscle fibers; together with an intermediate T tubule they constitute a triad. function as the storage area for calcium ions in the myofiber. | terminal cisternae |
| triad | constituted by the T-tubule surrounded by a pair of terminal cisternae. |
| T-tubules | "transverse tubules" s a deep invagination of the sarcolemma, which dives down into cell, allowing depolarization of the membrane to quickly penetrate to the interior of the cell. contains ECF. |
| draw the triad | so two "E"s back to back (spine is bulbous, legs are thin). bulbous = terminal cisternae. branching legs are sarc. reticulum. line the tunnel w the "T- tubule" diving down into cell. contains ECF. |
| Neuromuscular junction | connects the nervous system to the muscular system via synapses between efferent nerve fibers and muscle fibers. each muscle fiber is connected to a motor neuron. |
| when does a muscle fiber contract? | the fiber only contracts when stimulated by its motor nerve |
| which neurotransmitter in a neuromuscular junction? | acetylcholine is always the chemical neurotransmitter to skeletal muscle |
| motor end plate: | area of the neuromuscular junction, in which sarcolemma is extensively folded in the area under the end bulb of the neuron. many mitochondria are in this area. |
| 1) As an AP reaches the end of a motor neuron, voltage-dependent ca channels open allowing ca to enter the neuron. Calcium facilitates vesicle binding & subs. neurotransmitter release (ACh) from the motor neuron int0 synaptic clef | 2) ACh diffuses thu synapse and binds to receptors in sarcolemma.The binding of ACh to the receptor can depolarize the muscle fiber, causing cascade that travels along sarcolemma and dives down thru T Tubules. triggers Ca release from terminal cist etc |
| talk about graded responses in terms of muscle contraction | our muscle contractions are relatively smooth and can vary in strength as different different demands are put on them. Variations in the degree of muscle contraction = graded responses |
| motor unit | A motor unit is a contractile unit of a muscle, made up of a motor neuron and the skeletal muscle fibers innervated by that axon. |
| innervation ratio of a motor unit | ratio of motor neuron: muscle fibers innervated |
| groups of motor units do what? | Groups of motor units often work together to coordinate the contractions of a single muscle |
| (motor unit) recruitment | progressive activation of a muscle by successive recruitment of motor units to accomplish increasing gradations of contractile strength. more motor units are "recruited" to contract (and thus more muscle fibers) as more strength is needed. |
| innervation ratio of the motor units controlling the eye? (what are these muscles called?) What is this an example of? | innervation ratio of extra-occular muscles: 1:23. example of "fine control" |
| innervation ratio of the motor units of the quad? what is this an example of? | innervation ratio of quad = 1: 1,000-2,000. example of "strength" |
| activation of one motor neuron results in: | The activation of one motor neuron will result in a weak but distributed muscle contraction. |
| activation of more than one successively recruited motor unit results in: | The activation of more motor neurons will result in more muscle fibers being activated, and therefore a stronger muscle contraction. |
| explain distribution of the muscle fibers in a single motor unit and the implications when this motor unit is stimulated | muscle fibers of a single motor unit are not clustered all together but are dispersed throughout a whole muscle. so when stimulated, causes a weak contraction over a widely dispersed area (NOT just a localized "twitch" in a small region) |
| advantage of having multiple motor units in a muscle? | they are able to work in "shifts". muscle fibers fatigue when subjected to continual stimulation, so other motor units take over while fatigued ones rest. |
| sliding filament theory | mechanism proposed for muscle contraction where myosin head groups of the thick filaments move along the interdigitated actin of the thin filaments, sliding past them and thereby shortening the sarcomere. |
| crossbridge | myosin has a "head portion that attaches to and detaches from the actin. crossbridge= formed by the globular head of the myosin filament in contact with the active site of the G actin during contraction |
| explain what is actually shortening during contraction | *myofiber shortens, the myofibril shortens, the sarcomere shortens, but the actual myofilaments do NOT shorten: instead they slide past eachother. |
| crossbridging takes place between what? when does it occur and when does it not occur? | crossbridging takes place between actin and myosin. muscles at rest= no crossbridging. muscles at work= crossbridging between actin and myosin |
| what two things are needed to make muscles contract? | ATP and calcium |
| what are the 3 places/times ATP is needed? | 1)for re-concentration of Ca (using active transport) to get Ca back into terminal cisternae (so muscle will stop contracting) 2)to bind myosin head to actin 3)to release myosin head from actin |
| G actin | globular form of actin; bean-shaped polypeptide, has an active site |
| draw G actin | circle with dot in middle |
| F actin | fibrous form of actin; 200 G actin in a line |
| draw F actin | string of circles with dots |
| tropomyosin; definition | two protein strands spiral around the F actin. these are rod-shaped proteins; known as "regulatory" proteins. |
| function of tropomyosin? | inhibits muscle contraction by blocking the interaction of actin and myosin (by blocking the active sites of G actins): except when influenced by troponin. |
| draw tropomyosin? | just draw two cords wrapping around, with very little space. |
| troponin | 3 polypeptide complex attached to tropomyosin strands. "regulatory protein", serves as the attachment site for Calcium. |
| describe journey of calcium to contract. | when stimulated by Action Potential traveling down the sarcolemma, the calcium is released from the terminal cisternae and floods through the muscle, attaching to troponin. |
| what does "regulatory protein" mean? | it regulates whether active sites on the F actin are open or free. |
| what happens when Calcium attaches to troponin? | stimulates the tropomyosin to "squeeze in" or "wring" itself together, moving away from/uncovering the active sites leaving them exposed for the myosin heads. |
| structure of myosin? what do the heads do? | a rod shaped protein filament with 2 heads (heads all stick out all over 3 dimensionally). Heads of the myosin forms a crossbridge with active site of actin. |
| what is contained in the head of the myosin? | contains ATPase and an ATP binding site. |
| where are the heads NOT present in the myosin | not present in the H zone of the myofibril |
| when is myosin head not attached/attached? | when muscle is relaxed, myosin head is not attached. when the head is attached, muscle is moving (goes up, head attaches, makes "power stroke") |
| rigor mortis | stiffening of muscles/body. |
| when does rigor mortis take place? when is its peak? when does decomposing start? | rigor mortis takes place 3-4 hours after death. "peaks" after 12 hours. body is decomposing at 48-60 hours |
| why does rigor mortis take place? | when dead, the body can't reconcentrate Calcium back into terminal cisternae. it is running around in the muscles, stays attached to active sites so body can't detach the myosin head and the muscles can't stop contracting |
| curare | disease: binds to ACh receptors (mimics ACh).ACh is released from neuromuscular junction but cannot bind to receptors of muscle fiber. Causes flaccid paralysis |
| botulism | disease: prevents release of ACh from neuromuscular junction (flaccid paralysis) |
| tetanus | toxin: blocks glycine release, causing over-stimulation of muscles (spastic paralysis) |
| organophosphates | toxin: inhibits the function of ACh esterase, ACh can't be broken down so you have constant stimulation of muscle fibers (spastic paralysis) |
| myasthenia gravis | auto-immune disease: production of antibodies that bind to ACh receptors, eventually causing destruction of receptors. leads to muscle weakness, flaccid paralysis |
| polio | auto-immune disease: virus that destroys motor neurons in ventral horn. causes muscle pain, weakness,muscle atrophy and eventually flaccid paralysis/respiratory arrest |
| how much of the heat of the body is produced by muscles? | muscles produce 85% of the heat of the body |
| explain shivering | when body temp lowers, your nervous system induces shivering (i.e. rapid skeletal muscle contractions. |
| shivering affect on body temp? | this muscle movement can increase heat production up to 18x that of resting levels. |
| explain the movement of shivering, are they coordinated? | rapid skeletal muscle contractions are NOT coordinated movements, but the body's last ditch effort to warm you up |
| what happens to the H band during contraction? | it disappears |
| what happens to the I band during contraction? | it narrows |
| what happens to the A band during contraction? | it remains the same |
| what does "contraction" imply? | implies internal tension, NOT necessarily the muscle shortening (i.e. holding an anvil) |
| what are the two muscle fiber types? (keep in mind they are MIXED in any muscle) | red fibers (type I) and white fibers (type II) |
| size of red fibers? | smaller |
| size of white fibers? | larger |
| color of red fibers? why? | have a deep red color: have abundant myoglobin & blood capillaries (& mitochondria too) |
| what are red fibers adapted to? (what kind of respiration?) | well adapted to aerobic respiration (does NOT generate lactic acid. (Krebbs) |
| what kind of contraction for red fibers? | slow, powerful contraction |
| red fibers fatigue... | fatigue slowly |
| example of muscles with red fibers? | mastication (chewing) muscles, muscles of respiration, postural muscles |
| who has higher percentage of red fibers? | long distance runners |
| size of white fibers? | larger |
| color of white fibers and why? | they are more pale in color. this is because they have fewer blood capillaries, little myoglobin, fewer mitochondria |
| what are white fibers rich in? | rich in enzymes for converting glycogen to glucose to lactic acid systems (glycolysis) |
| what kind of storage are white fibers high in? | high glycogen storage |
| what are white fibers well adapted to? | well adapted to anaerobic respiration (DOES generate lactic acid). |
| white fibers fatigue... | fatigue more easily. |
| what kind of contraction for white fibers? | have a rapid rate of contraction for a shorter time |
| who has higher percentage of white fibers? | sprinters, or basketball players (stop and go activities, short sprints etc) |
| isotonic contraction | contraction with a change in length but no change in tension (muscle changes length while maintaining constant tension) |
| isometric contraction | contraction (muscle develops tension) without a change in length (muscle develops internal tension but does not shorten) |
| what are the two kinds of contraction? | isotonic and isometric |
| what are the two kinds of isotonic contraction? | concentric and eccentric contraction |
| concentric contraction | a muscle shortens as it maintains tension |
| example of concentric contraction? | lifting up a baby |
| eccentric contraction | a muscle lengthens as it maintains tension |
| example of eccentric contraction? | putting a baby down. acts like a brake to keep you from dropping the baby |
| example of isometric contraction? | holding a baby in the air |
| what keeps you from sinking into a heap on the floor? | the isometric contraction of postural muscles |
| cardiac muscle: is it graded response in contraction? | there is nO recruiting for graded responses: it is an all-or-nothing response (they either fire or they don't) |
| cardiac muscle: is it striated? | yes, striated, with sarcomeres |
| structure of cardiac muscle fibers? what does this allow the myocytes to do? | they have intercalated discs with gap junctions. (allows each myocyte to directly stimulate its neighbors) |
| what is the sarcoplasmic reticulum & T tubules like in cardiac musle? what about calcium? | SR is less developed and T tubules are larger.the myocytes admit supplemental calcium from ECF |
| heart has a pace-maker, what does this mean? | SA node: so "auto-rhythmic" |
| what kind of respiration does cardiac muscle use? | uses aerobic respiration almost exclusively |
| cardiac muscle cells are rich in whatz/ | myoglobin and glycogen (--> glucose --> ATP) |
| what is especially large in a cardiac fiber? | the mitochondria (fill 25% of cell) |
| cardiac muscle and fatigue? | it is highly resistant to fatigue |
Created by:
kalmetina
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