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A&P Lecture Chap 11
A&P Lecture WK 5 Chap 11 Muscular Tissue
| Term | Definition |
|---|---|
| All muscle cells have the following characteristics: | excitability, conductivity, contractility, extensibility, and elasticity |
| Excitability (responsiveness): | to chemical signals, stretch, and electrical changes across the plasma membrane |
| Conductivity: | local electrical excitation sets off a wave of excitation that travels along with the muscle fiber |
| Contractility: | shorter when stimulated |
| Extensibility: | capable of being stretched between contractions |
| Elasticity: | returns to its original rest length after being stretched |
| Skeletal muscle: | voluntary, stripy/striated muscle usually attached to bones ' - seen throughout the body attached to bone such as the limbs - Average 100 μm in diameter and 3 cm (30,000 μm) long, but can be much thicker - also called muscle fibers or myofibers |
| Striations: | alternating light and dark transverse bands; results from arrangement of internal contractile proteins |
| Voluntary: | usually subject to conscious control (the other muscle types are involuntary) |
| A skeletal muscle also contains fibrous connective tissue which | - gives the muscle more resiliency |
| Skeletal Muscle has the 3 layers of CT which | endomysium surrounds each muscle fiber, perimysium bundles muscle fibers, and epimysium surrounds the entire muscle |
| Endomysium surrounds | each muscle fiber - around the single cell - the singular spaghetti noodle |
| Perimysium bundles | muscle fibers into fascicles - surrounds bundles of cells - connective tissue cover as a singular box of spaghetti noodles |
| Epimysium surrounds | the entire muscle - brown box that contains multiple boxes of spaghetti |
| Collagen is somewhat | extensible and elastic - Stretches slightly under tension and recoils when released - Resist excessive stretching, protects muscle from injury - Returns muscle to its resting length - Contributes to power output and muscle efficiency |
| In summary connective tissue is | embedded within muscular tissue and becomes the tendon within the bone |
| Components of a muscle fiber: | sarcolemma, sarcoplasm, myofibrils, glycogen, myoglobin, mitochondria, multiple nuclei |
| Sarcolemma: | plasma membrane of a muscle fiber |
| Sarcoplasm: | cytoplasm of a muscle fiber |
| Myofibrils: | long protein cords occupying most of sarcoplasm |
| Glycogen: | carbohydrate stored to provide energy for exercise |
| Myoglobin: | red pigment; provides some oxygen needed for muscle activity |
| Muscle fibers have many mitochondria; | bean-shaped near sarcolemma, and deeper ones are tubular and dynamic in shape |
| muscle fiber has Multiple nuclei, averaging | 30 to 80 per millimeter; serve role in fiber repair |
| Sarco: means | the muscle cell |
| Sarcoplasmic reticulum SR: | smooth ER that forms a network around each myofibril - has tons of calcium, which it holds |
| Terminal cisterns: | dilated end-sacs of SR which cross the muscle fiber from one side to the other - Acts as a calcium reservoir; it releases calcium through channels to activate contraction - Within cisterns, calcium is bound to a protein called calsequestrin |
| Transverse (T) tubules: | tubular infoldings of the sarcolemma which penetrate through the cell and emerge on the other side Each T tubule has two terminal cisterns associated with it on either side |
| Myofibrils are composed of | muscle filaments, or myofilaments |
| Three kinds of myofilaments: | thick filament (myosin), thin filament (actin), |
| Thick filament (myosin) is made of | several hundred myosin molecules (myosin is a motor protein) Each molecule shaped like a golf club: two chains intertwined to form a shaft-like tail and a double globular head |
| Thin filament (actin): | composed of three different protein types: fibrous actin, tropomyosin, and troponin |
| Fibrous (F) actin: | two intertwined strands of globular (G) actin subunits, each with an active site that can bind to head of myosin molecule |
| Tropomyosin: | each blocks six or seven active sites on G actin subunits - long stringy protein that physically blocks the active sites - string of lights that hangs |
| Troponin: | small, calcium binding protein on each tropomyosin molecule - tac that hangs the string of lights |
| in thick filament myosin heads | Heads directed outward in a helical array around the bundle Heads on one half of the thick filament angle to the left, while heads on other half angle to the right Bare zone with no heads in the middle |
| Of the myofilaments, | myosin and actin are the contractile proteins - they do the work of contraction |
| Tropomyosin and troponin act as regulatory proteins - they regulate whether or not | actin and myosin can be together, - if not they actin and myosin would forever be contracted - only occurs when SR releases calcium stores - will only release if cell is excited in plasma membrane |
| When muscle is stimulated/excited it | When muscle is stimulated/excited it contracts |
| tropomyosin and troponin act like a | switch that determines when fiber can (and cannot) contract - Contraction activated by release of calcium into sarcoplasm and its binding to troponin - troponin changes shape and moves tropomyosin off the active sites on actin |
| Excitable parts: | T-tubules, sarcoplasmic reticulum, and plasma membrane |
| Contractile proteins: | myosin and actin |
| Regulatory proteins: | troponin and tropomyosin |
| Sliding filament theory: steps to show contraction steps | 1. Signal from motor neuron causes plasma membrane to depolarize - signal (neurotransmitter) acetylcholine is released into neuromuscular junction (NMJ) 2. Signal conducts across plasma membrane & down T-tubules |
| Sliding filament theory: steps to show contraction steps after 2. Signal conducts across plasma membrane & down T-tubules | 3. Sarcoplasmic reticulum releases calcium (Ca2+) 4. Calcium binds to Troponin - changes shape 5. Troponin releases tropomyosin 6. Tropomyosin uncovers Actin (falls off it) 7. Myosin binds to Actin and pulls Actin towards the M-Line |
| Protein does not shorten just | the sarcomere |
| Skeletal muscle cannot contract unless, | stimulated by a nerve - If nerve connections are severed or poisoned, a muscle is paralyzed (denervation atrophy) |
| Denervation atrophy: | shrinkage of paralyzed muscle when nerve remains disconnected |
| Skeletal muscle cells are served by somatic motor neurons | nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles - Their axons, called somatic motor fibers, lead to the skeletal muscle Neurons are unidirectional - can only go one way |
| somatic motor neurons has | - Each nerve fiber branches out to a number of muscle fibers - Each muscle fiber is supplied by only one motor neuron |
| 1 muscle cell gets one neuron: | One neuron can innervate more than one cell - Innervates: powering |
| Motor unit: | one nerve fiber and all the muscle fibers innervated by it; they behave as a functional unit |
| Motor unit = | one motor neuron + all the muscle cells it innervates |
| Muscle fibers of one motor unit: | - dispersed throughout muscle - Contract in unison - Produce weak contraction over wide area - Ability to sustain long-term contraction - take turns contracting - Effective contraction usually requires contraction of several motor units at once |
| Average motor unit contains | 200 muscle fibers distributed across as many as 100 fascicles Motor units can vary in size |
| Small motor units | : provide a fine degree of control |
| Large motor units: | provide more strength than control Powerful contractions supplied by large motor units with hundreds of fibers |
| Sarcomere: | segment from Z disc to Z disc; functional contractile unit of muscle fiber - Muscle cells shorten because their individual sarcomeres shorten - Z disc (Z lines) are pulled closer together as thick and thin |
| filaments slide past each other - Neither thick nor thin filaments change | length during shortening, only the amount of overlap changes - During shortening, dystrophin and linking proteins also pull on extracellular proteins - Transfers pull to extracellular tissue |
| Sliding filament theory to make | the muscles contract - In the neuron it releases acetylcholine cells to have the muscles contract |
| Motor unit: | one nerve cell/motor neuron and how many muscle cells that it has terminal - causes it to start the sliding filament theory - sliding filament theory uses the specific synapse called the neuromuscular junction (NMJ) |
| One signal muscle cell is only touched by one signal neuron - | the three branches are the muscle cells in the drawing |
| In the drawing if all neurons are connected to the muscle cell then | it is all stimulated |
| The motor unit means the | whole drawing with the neuron and the muscle cells (branches) |
| The difference in strength in muscle contraction depends on | the amount of motor units - if want a stronger muscle contraction needs more motor units than a weaker muscle contraction like kicking your feet which requires less |
| Synapse: | point where a nerve fiber meets its target cell When target cell is a muscle fiber, the synapse is also called a neuromuscular junction (NMJ) or motor end plate - Synapse is where they meet in the drawing (neuromuscular junction) |
| Each terminal branch of the nerve fiber within the NMJ forms a separate synapse with the muscle fiber consisting of: | Axon terminal Contains synaptic vesicles with neurotransmitter called acetylcholine (ACh) Nerve impulse causes synaptic vesicles to undergo exocytosis releasing ACh into synaptic cleft |
| Axon terminal: | swollen end of nerve fiber |
| Synaptic cleft: | narrow gap between axon terminal and sarcolemma |
| muscle cell sarcolemma has millions of ACh receptors: | proteins that respond to ACh |
| Muscle fibers and nerve cells are | electrically excitable cells Their membranes exhibit voltage changes in response to stimulation |
| Electrophysiology: | the study of electrical activity of cells |
| Electrical activity depends on concentration differences in ions in | the intracellular fluid ICF vs extracellular fluid ECF |
| intracellular fluid ICF contains | greater concentrations of negative anions (negatively charged proteins, nucleic acids, phosphates) than ECF; trapped within cell - Membrane is polarized: contains a net negative charge - has more potassium ions (K+) than ECF, |
| extracellular fluid ECF contains | ECF has more sodium ions (Na+) than the ICF has a positive charge |
| Any difference in charge between two points is called an | electrical potential or voltage |
| In an unstimulated (resting) cell: | The plasma membrane is electrically polarized (charged) with a negative resting membrane potential (RMP) |
| In a stimulated cell: | Ion channels in membrane open, allowing Na+ to flow into cell (down its electrochemical gradient); causes depolarization of the membrane - Then, additional ion channels allow K+ to flow out of cell; causes repolarization of the membrane |
| The up-and-down voltage shift is called an | action potential |
| Threshold: | the minimum power it takes to reach depolarization - minimum voltage that causes a muscle twitch |
| Even if the same voltage is delivered, different stimuli cause twitches varying in strength, because: | muscle’s starting length -> tension generation Muscles fatigue after continual use Warmer muscles’ enzymes work faster Muscle cell’s hydration level -> cross-bridge formation Increasing frequency of stimulus delivery increases tension output |
| how a stimulus is processed steps (action potential) | 1. depolarization (sodium inward) 2. repolarization (potassium outward) 3. hyperpolization (potassium gates close) |
| Depolarization: | sodium from extracellular fluid creates a channel/gate in the resting membrane to go inside to make an equilibrium - Na+ goes in |
| Repolarization: | potassium opens a slower gate in the resting membrane from the intracellular fluid to make an equilibrium as it exits to the ECF - K+ goes out |
| Hyperpolization | : when the potassium gates are closing |
| Action potential shows that the inside ICF has | more potassium outside has more sodium |
| If a stimulus occurs from the motor neuron/nervous system to change the membrane potential | Stimulus from neuron causes some sodium gates to open and as long as the stimulus is strong enough the gates open and causes depolarization and it changes from negative to positive |
| After depolarization | potassium gates open up and potassium moves out of the cell and repolarizes the inside back to negative Afterwards, it dips into hyperpolarization as the potassium gates close - creating equilibrium And it goes back to resting membrane potential |
| Sustained contraction has | the muscle cell continuously stimulated |
| Four major phases of contraction | excitation, Excitation–contraction coupling, contraction, relaxation |
| Excitation | : action potentials in motor nerve fiber lead to action potentials in the muscle fiber |
| Excitation–contraction coupling: | events that link the action potentials on the sarcolemma to activation of the myofilaments, thereby preparing them to contract |
| Contraction: | the step in which the muscle fiber develops tension and may shorten |
| Relaxation: | when stimulation ends, a muscle fiber relaxes and returns to its resting length potassium is picked up again and actin is covered up again |
| Excitation of a muscle fiber: simpler steps | A. Arrival of a nerve signal: B. Acetylcholine (ACh) is released C. Binding of acetylcholine to receptor D. Acetylcholine causes depolarization |
| Excitation of a muscle fiber: The first thing that opens up is | E. sodium channels - because neuron told it to - sodium goes into cell causes depolarization F. depolarization causes positive charge reached, potassium gates open and goes outward causing repolarization - travels across the plasma membrane |
| Excitation of a muscle fiber: after depolarization across plasma membrane | G. signal travels across T-tubule H. sarcoplasmic reticulum dumps calcium inside cell - calcium binds to troponin (yellow blobs) |
| Excitation of a muscle fiber: tropomyosin filaments | I. Tropomyosin filaments gets out of way - myosin grabs onto actin to get into the middle/center - myosin is using tons of ATP to let go of actin |
| Excitation of a muscle fiber: relaxation | after dumping acetylcholine there is acetylcholinesterase which breaks down and leans it up Dumping calcium is also put back into the organelle, and actin is covered by tropomyosin |
| Rigor mortis: | hardening of muscles/ stiffening of body beginning 3-4 hours after death Deteriorating sarcoplasmic reticulum releases Ca2+ & sarcolemma allows Ca2+ to enter cytosol Ca2+ activates myosin-actin cross-bridge formation & muscle-contraction |
| rigor mortis muscle relaxation | requires ATP, and ATP production is no longer produced after death Fibers remains contracted until myofilaments begin to decay Rigor mortis peaks about 12 hours after death, then diminishes over the next 48-60 hours |
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Katepop10