Muscle Tissue PPT
Muscle Tissue PPT BIOL 2220
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This 12 page Class Notes was uploaded by Victoria Hills on Monday October 17, 2016. The Class Notes belongs to BIOL 2220 at Clemson University taught by John Cummings in Fall 2016. Since its upload, it has received 5 views. For similar materials see Human Anatomy and Physiology I in Biology at Clemson University.
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Date Created: 10/17/16
Clemson University Fall 2016 Muscle Tissue Slide 2: Classification Criteria Muscle types are classified based on: a) Presence or absence of striations b) Voluntary or involuntary nervous control c) Number of nuclei (Uni or multinucleated) Slides 35: Muscle Types Skeletal muscle tissue: Striated Multinucleated o Nuclei are always pushed to the margins of the cell and not in the middle Voluntary nervous control o Meaning humans determine when and how strong contractions are Cardiac muscle tissue: Striated Uninucleated Involuntary nervous control o Meaning humans do not consciously make it contract Intercalated discs: Communicating junctions Cardiac cells do not run in a parallel structure They are branched instead o Signal is communicated from one cell to another Branching allows the heart to contract as a unit Operates similarly to skeletal muscle Smooth muscle tissue: Nonstriated Uninucleated Nucleus is located in the middle of cells Involuntary nervous control A single smooth muscle cell is a called a spindle because it tapers off at both ends Slide 6: Properties of Muscle Excitability: Muscle tissue is excitable It can respond to a stimulus The response is contraction Contractility: The ability to shorten and thicken No muscle contracts unless it is stimulated Voluntary: o Humans generate messages that cause the muscle to contract Involuntary: o Have to have a signal in order for contraction to occur Extensibility: Muscles can be stretched and is extendable Ex: If the biceps are contracted, the triceps on the other side have to stretch and vice versa Skeletal muscle operates in antagonistic pairs Elasticity: Ability for muscle to return to its original shape Once muscle contracts, and the stimulus is removed, the muscle can go back to the relaxed state Hardest to replicate with artificial muscle Slides 710: Functions of Muscle Motion: Contraction of any type of muscle produces motion/movement Ex: Skeletal muscle specifically functions in locomotion Ex: If the heart contracts, it causes blood to flow through blood vessels Ex: If the lining of the stomach or intestine contract, smooth muscles contracts and creates peristalsis (Special wave of motion) Maintenance of posture: Skeletal muscle opposes gravity and allows humans to maintain posture Through contraction of muscle (Even if it’s partial contraction), humans are able to maintain posture Stabilizing joints: Muscle stabilizes a joint through its ability to contract around the joint Muscle tone: o Maintenance of mild tone in muscle o No muscle is completely relaxed all the time o The greater the muscle tone, the less mobility there will be Even a loose joint such as a synovial joint can be stabilized by having muscles contracting around it Heat production: Contraction of any type of muscle produces heat When cold, shivering first occurs through the contraction of skeletal muscle Chill bumps occur through the contraction of the arrector pili muscles Smooth muscle that contracts and causes hair to stand up in order to generate some heat and help prevent some loss of heat Slide 11: Skeletal Muscle Composition Skeletal muscle tissue is an organ that consists of multiple types of tissue Contains skeletal muscle fibers that have blood vessels that pass through them in order to deliver oxygen Contraction of muscle consumes large amounts of energy Therefore, muscle needs to produce energy for itself Nerve fibers stimulate the muscle to contract Connective tissue provides organization in the muscle Slide 13: Gross Anatomy of Skeletal Muscle Skeletal muscle is an organ that attaches to bone In some cases, the muscle is directly attached to the periosteum of the bone = Direct attachment Extensions of connective tissue that goes all the way to the muscle tissue to attach = Indirect attachment Slide 14/15: Indirect Muscle Attachment Connects muscle to bone Tendon: Ropelike connective tissue attachments Ex: Picture shows how a tendon attaches to the calcaneus Aponeurosis: More sheetlike indirect attachment Connective tissue of the muscle extends beyond the end of the muscle and attaches to bone Therefore, a muscle is going to be attached on both ends Typically, muscle attach across joints to allow the movement of the skeleton 2 attachment points: a) Origin: Attachment on immovable bone b) Insertion: Movable bone Muscles can have 1 or more that 1 origin and insertion Slide 16: Gross Anatomy Epimysium Muscle is directly attached to the periosteum There are no ropelike extensions of connective tissue that function in connecting the muscle to bone Connective tissue surrounds the outer surface of the muscle organ The outer portion of the whole muscle is connected by a sheet of connective tissue that is composed of dense irregular connective tissue called the epimysium This is an extension of the periosteum that is covers up over top the entire muscle Summary: Epimysium covers the outer of portion of the entire muscle Slides 17/18: Gross Anatomy Fascicle and Perimysium Muscle is divided into compartments where each is called a fascicle (Plural is fasciculi), which are further divided into smaller units and made Each bundle of fasciculi is composed of a bundle of muscle fibers that are separated from each other by a wrapper of connective tissue called the perimysium Slide 19/20: Gross Anatomy Muscle Fiber All muscle fibers are considered to be a single muscle cells During embryonic development, there are tiny cells that make up the skeletal muscle These cells fuse together to become a muscle fiber (AKA myofiber) Muscle fibers are contained within the bundle called the fascicle Each muscle fiber is surrounded by a connective tissue sheet/wrapper called the endomysium that is composed of reticular connective tissue Again: Muscle fiber = single muscle cell = myofiber Slide 2123: Microscopic Anatomy Within the fascicle a myofiber (single muscle cell/muscle fiber) is made up of smaller components Sarcolemma: Plasma membrane of a myofiber Called sarcolemma because of the fusing of the tiny cells all together Sarcoplasm: Cytoplasm of muscle cells Contain glycosomes Vesicles that contain granules of glycogen o Glycogen is necessary in order to be broken down to glucose to generate ATP needed for contraction o Glycosomes allow the muscle to not have to receive glycogen from the liver when glucose is needed o Cellular inclusion Contains myoglobin Oxygenbinding pigment o Muscle’s own oxygenstoring pigment o Cellular inclusion Nucleus: Muscles cells are multinucleated due to the fusion of the tiny cells Nuclei are pushed to the margins of the cell Myofibrils: Make up the myofibers Contractile elements of the cell Each muscle cell contains thousands of myofibrils Sarcoplasmic reticulum: Elaborate smooth endoplasmic reticulum in skeletal muscle Surrounds the myofibrils within each muscle fiber Ttubule: Tubules tend to run in a longitudinal fashion along the myofibrils that are interrupted periodically with transverse sections Each muscle cell has a plasma membrane (sarcolemma) that surrounds it Inward extension of the sarcolemma is the Ttubule that runs together with the perpendicular channels called terminal cisternae Picture: Yellow parts are the terminal cisternae + pink parts that are the Ttubules (Transverse tubules) 2 terminal cisternae surround the Ttubule This arrangement is called a triad Picture: Blue parts are the terminal cisternae + yellow parts are the Ttubules Slide 24: Myofibrils Myofibrils are the contractile elements of the muscle that are divided into segments called sarcomeres that are the contractile units of the muscle Ex: Brick wall Whole wall is a myofiber Each layer of bricks is a whole myofibril Each brick is a sarcomere within the myofibril Myofibrils contain protein filaments called myofilaments that function in actually doing the contraction 1 sarcomere meets another sarcomere in terms of structure that have overlapping myofilaments 2 types of myofilaments that make up the myofibril: a) Thin myofilaments: Composed of actin proteins b) Thick myofilaments: Composed of myosin proteins Contraction of muscle is due to the interaction of the thick and thin myofilament proteins (Myosin and actin, respectively) Slide 25: Sarcomere Contractile unit of muscle Picture shows 1 sarcomere of a myofibril Sarcomeres are separated from one another via the Z line (AKA Z disc) Therefore, 2 borders of sarcomeres are the Z lines Sarcomeres run from Z line to Z line A band: Runs the entire length of the thick myofilament (Myosin) Appears darker in picture Includes thin myofilament too Thin and thick myofilaments overlap I band: Area between the Z line and the end of the thick myofilament is only made up of thin myofilaments There is an alteration of light and dark (Thin and thick myofilaments/I bands and A bands) that creates muscle’s striated appearance Organization of the proteins determines the striations H zone: Part in the middle of the sarcomere that is only made up of thick myofilaments (Myosin) M line: Located at the dead center of the H zone of the sarcomere Muscle contraction is due to the interaction of these thick and thin myofilaments When muscle is excited, the thick myofilaments (Myosin) reach up and grab the thin myofilaments (Actin) Each sarcomere pulls from the M line Slide 26: Thick Myofilaments Composed of myosin protein that has a head and a tail Tails of myosin (~200 myosin proteins) are wrapped around to make the thick myofilament Heads of the myosin protein are oriented towards the Z lines at the ends of the sarcomere Heads are what reach up and grab thin myofilaments (Actin) and pull towards the M line at the middle Each head on myosin has 2 binding sites: a) Actin binding site: When the thick myofilament (myosin) is attached to the thin myofilament (actin), the structure that is created is called a crossbridge b) ATP binding site: In order for muscle to attach to the thin myofilament and pull it towards the center via thick myofilament, energy is required When ATP is bound to the ATP binding site on the head of the myosin protein, the actin binding site is disabled (Blocked) AKA thick myofilament can’t bind to the thin myofilament when ATP is bound This is important since this is what allows the muscle to relax Binding ATP to the ATP binding site causes the thick myofilament to let go of the thin myofilament Splitting ATP allows thick myofilament to grab thin myofilament Slide 27: Thin Myofilaments Composed predominantly of actin that has a myosinbinding site Actin binding site on myosin is what binds to the myosinbinding site on actin Therefore, specific locations on the thin and thick myofilaments interact with each other Tropomyosin: Surrounds the double strand of actin that twists to provide strength and prevent the double strand of actin from breaking apart Dark green “shoe laces” in picture Troponin: Tropomyosin attaches to troponin that is actually attached to the actin Troponin has 3 binding sites: a) Troponin I: o Binding site for actin b) Troponin T: o Binding site for tropomyosin o Binds troponin to tropomyosin to have a troponintropomyosin complex o Review: Troponin I holds the troponintropomyosin complex to actin o Myosin binding site on actin is typically covered up by the troponin tropomyosin complex Therefore the complex needs to be moved out of the way in order for actin and myosin to attach for muscle contraction c) Troponin C: o Binding site for calcium that is not normally present o Only when the muscle is excited is when calcium is released that then binds to troponin C Ultimately makes troponin I disconnect from actin Troponin tropomyosin complex slides out of the way as a result and exposes the myosin binding site so that actin can now bind to myosin Slide 28: Elastic Myofilaments Other myofilaments also exist Elastic myofilaments are composed of titin Typically, when looking at a sarcomere, one can see the thin myofilament and not the thick myofilament is attached to the Z line Titin makes up the elastic myofilament that attaches the thick myofilament to the Z line As muscle contracts, the thick myofilament doesn’t change where it is located (Attached on both ends) The thin myofilament is attached only on one end and is not continuous like the thick myofilaments There is a portion where there is only thick myofilaments present (H zone) Nebulin: Protein on the Z line Attachment where the thin myofilament attaches to the Z line Application: Those with asthma or bronchitis tend to receive nebulizer treatment in order to relax the nebulin protein so that everything constricted will relax Slide 29: Sliding Filament Theory When muscle contracts, it is going to sliding filament theory Thin myofilaments (actin) slide across the thick myofilaments (myosin) The heads of the myosin protein on the thick myofilament can reach up and grab the thin (actin) myofilament *Not all myosin protein heads reach up and pull on the actin at the same time Energy configuration: There is a change from high energy configuration where ATP is bound ATP split, leading to a low energy configuration Myosin heads attach to the myosin binding site on actin and pull actin towards the M line = Power stroke of muscle contraction After this, goes back to high energy As long as calcium is present, shortening and contracting of muscle process can still occur Slide 30: ExcitationContraction Coupling Muscle contraction must start with a nervous impulse (Action potential) Resting membrane potential: When a cell is at rest, it is polarized so that the inside is negative compared to the outside An action potential causes a reversal of this polarity In the picture, the nerve fiber is in yellow that is in close proximity to the muscle As an impulse (Action potential) travels down the nerve, it will cause a release of a neurotransmitter that will diffuse across the synaptic cleft (Space between the nerve and muscle) and bind to receptors on the muscle This next changes the resting membrane potential and allows sodium ions to diffuse into the cell Depolarization If the depolarization is strong enough due a strong enough stimulus, muscle contraction will occur Action potential (impulse) will start by changing the permeability at one spot on the cell at the end of the axon terminal, and once this one spot changes enough (depolarized) The action potential will spread across the entire sarcolemma Neuromuscular junction: Area where the neuron meets the muscle AKA where the neuron comes close to the muscle fiber There is adaptation of the muscle fiber itself Nervous impulses (action potentials) are necessary in order to cause changes to allow calcium to be released to allow muscle contraction of the sarcomere to ultimately occur There is a single attachment of the coupling of the neuron with the muscle fiber (Only a single attachment per muscle fiber) Slide 31: Neuromuscular Junction Have a somatic motor neuron going to voluntary skeletal muscle Humans actively and consciously make a decision to contract the muscle and how strong it is contracted as well Axon portion of the neuron is in close proximity to the muscle cell For each muscle cell (myofiber/muscle fiber), there is only ONE neuromuscular junction This does not create a direct connection There is a space called a synaptic cleft At the end of the axon at the axon terminal, there are a bunch of vesicles called synaptic vesicles that store a neurotransmitter called acetylcholine (Ach) When the impulse (action potential) travels down the nerve, it causes a wave of depolarization down the neuron Opens calcium channels at the axon terminal Calcium flows in and causes the synaptic vesicles to fuse with the plasma membrane of the neuron and release Ach via exocytosis that diffuses across the synaptic cleft Ach receptors located on the muscle fiber The sarcolemma is modified at the neuromuscular junction It has folds that increase the surface area so that it will be able to bind to more Ach and makes the connection more efficient= Region is called the motor end plate and is where the Ach receptors are located The binding of Ach to the Ach receptors Causes membrane permeability changes in muscle Opens ion channels that allow sodium to move in and change the membrane potential Motor end plate also contracts acetylcholinesterase that is an enzyme that breaks down Ach so that the effects of Ach are shortlived and turned off Summary: Nervous impulse (action potential) travels down neuron and creates a wave of depolarization Calcium channels open Calcium flows in Promotes exocytosis of Ach Ach diffuses across the synaptic cleft Ach binds with Ach receptor on motor end plate Opens sodium channels Sodium moves in Action potential continues to depolarize the rest of the sarcolemma Slide 32: ExcitationContraction Coupling Resting muscle gets activated to contract Muscle must be stimulated to contract The stimulation portion of contraction is referred to excitationcontraction coupling Begins with a nervous impulse Excitation part Contraction part belongs to the muscle Ach (Neurotransmitter) triggers the action potential Resting Membrane Potential: There are more potassium ions inside the cell than outside More sodium ions are outside the cell than inside More sodium ions are outside the cell than potassium ions inside the cell More positive charge is therefore outside the cell Creates polarity = Difference in charge Difference in charge between the inside and outside the cell is 80 mv of electricity Because there is more positive charges outside the cell than inside the cell, and the plasma membrane belongs to the cell, the inside is 70 mv = Resting membrane potential When Ach binds to the Ach receptors at the neuromuscular junction on the motor end plate, it causes a change in permeability Sodium ions move into the cell only where these receptors are where the sodium channels are Cell depolarizes and becomes less negative Eventually, the inside of the cell becomes more positive compared to the outside = ~30 mv electricity This is when there is the action potential Instead of just being a localized change in permeability where Ach is located, Ach triggers the generation of an action potential across the entire sarcolemma that experiences a wave of depolarization At an action potential, the whole cell depolarizes Inward hollow tubes called T tubules are extensions of the sarcolemma and the terminal cisternae located on either side of the T tubules (Together make up the triad) have the action potential spread across them too Slide 3337: Sarcoplasmic Reticulum Review: Triad is made up of T tubule + terminal cisternae located on either side of the T tubule Calcium is stored in the sarcoplasmic reticulum As the action potential passes by the triad, the muscle cell’s permeability changes (depolarization) Causes the terminal cisternae, which are enlarged areas of the sarcoplasmic reticulum, to release stored calcium into the sarcoplasm Calcium then binds to troponin C that causes troponin I (Holds the troponintropomyosin complex in place) to let go of the troponintropomyosin complex and expose the myosin binding site (active site) on actin Myosin head can then attach to actin and start the sliding filament theory/power stroke— Pull thin myofilaments toward the center of the sarcomere Technically: As soon as a muscle fiber is activated by an action potential, excitation coupling is over Overall summary: a) Ach triggers generation of action potential across sarcolemma and down T tubules b) Action potential passes triads c) Terminal cisternae release calcium into the sarcoplasm d) Some calcium binds to troponin (TnC) e) Removes tropomyosin from active sites on actin f) Myosin heads attach to actin and pull thin myofilaments toward center of sarcomere Slide 38: Power Stroke Steps: Thick myofilament (Myosin) binds to thin myofilament (Actin) via the myosin head that creates an attachment called the crossbridge Next, there is a change from a high energy configuration to a low energy configuration so that the actin is pulled towards the H zone and ultimately the M line When ATP binds with the myosin head, myosin lets go of actin ATPase splits ATP and the released energy returns the myosin head to higher energy configuration Cycle is able to repeat as long as calcium and ATP are present Power stroke of the sarcomere can occur about 5 times per second if these are present Once the action potential is achieved, the contraction of the individual muscle fiber is an allornothing phenomenon Contraction will shorten or thicken the sarcomere to the same degree each time it is activated Difference between a weak contraction and a large contraction is due to the number of muscle fibers: o Each muscle fiber, when contracted, contracts to its greatest ability o Therefore, in order to achieve stronger muscle contraction, it is necessary to activate more muscle fibers Review: 2 Roles of Calcium a) Binds to troponin C to expose the myosin binding site b) Release Ach neurotransmitter Bone is a reservoir for calcium If not enough calcium is being obtained in the diet that is needed to run these processes, calcium stored in bone will be released Cardiac muscle works similarly to skeletal muscle calcium will also be needed here to make this happen Slide 39: Recovery Refers to allowing a contracted muscle go back to its relaxed state Calcium is actively pumped back into the sarcoplasmic reticulum Reduced calcium levels frees tropomyosin to create the troponintropomyosin complex and block the myosin binding site on actin Crossbridge between the thick and thin myofilaments disconnects due to the addition of ATP to make them let go of each other High energy configuration state Muscle relaxes ultimately Slide 41: Motor Unit There is only 1 attachment between a neuron and 1 muscle fiber In the picture, a somatic neuron and many muscle fibers are shown Each muscle fiber has a single connection to a neuron BUT one neuron is capable of attaching to many different muscle fibers Based on the picture, the blue fibers synapse with 2 different muscle fibers and the red fibers synapse with 3 muscle fibers Motor unit: The motor neuron + all of the fibers it stimulates Not all motor units in a muscle fire at the same time: Ex: Blue fibers send a signal to the muscle and achieve a certain contraction strength Ex: Red fibers send a signal and achieve a slightly stronger contraction strength due to there being 3 instead of 2 like blue Ex: If both blue and red fibers send signals, a very strong contraction strength is achieved This means that power or strength of contraction is dependent on the number of motor units involved The more motor units, the stronger the contraction Different motor neurons connected to different muscle fibers prevent fatigue of muscle and sustain contraction When ATP splits, lactic acid builds up Muscle fiber is not able to hold the contraction as a result Signal then passes down to another set of fibers (Ex: Red instead of blue) that allows the first set to rest Key point: It is possible to change what fibers are contracting in order to extend the duration of contracting Specifically do this through alternating which motor units are being used
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