Unit 6 - Ch10 Skeletal Muscle Tissue
What is the neuromuscular junction?
- Muscle receive information to contract from the brain; electricity from the brain travels down nerve cells and transmitted to the muscle cells to contract - The area where the nerve & muscle cells communicate (the junction is a point of contact where things come together) and signal the muscle to contract
Discuss muscle movement around joints.
- Muscles will always move bones around a joint (where bones connect with bones) except the face > therefore skeletal muscles will at least cross over 1 joint, leg muscles cross over more than 1 joint
How are muscles attached to the bone?
- most skeletal muscles run from one bone to another - one bone will move & other bone remains fixed - muscle are attached to bone and the attachments are called origin and insertion
What is hypertrophy, how is it affected?
- myo and sarco mean muscle - muscle cells grow via hypertrophy not division = protein mass increases but you do not gain more muscle cells - muscles grow due the cells getting larger bc of more protein intake (number of muscle cells remain the same)
nerves and blood vessels in skeletal muscle tissue
- nerves and vessels branch repeatedly - smallest nerve branches serve individual muscle fibers
What is the purpose of a z disc?
- serve as the attachment point for the thin filaments - It anchors the actin
How are skeletal muscle fibers categorized?
-how they manufacture energy (ATP) -how quickly they contract oxidative fibers = produce ATP aerobically (w/oxygen) glycolytic fibers = produce ATP anaerobically (w/o oxygen) by glycolysis
List and describe the skeletal muscle functions.
1. Produce skeletal movement - working together with our bones; muscles aid in bone movement = giving us the ability to become mobile (walk, run, swim) 2. Maintain posture and body position -we have postural muscles that aid in this 3. Support soft tissues 4. Guard entrances and exits - -example anal sphincter is a circular muscle that guards the entrance for our exit of our digestive system 5. Maintain body temperature -the integumentary system does this when we get hot...how? We sweat and it evaporates which helps us become cooler. Skeletal muscle is involved when we get cold = shivering
What are the names for the two types of filament in a myofibril? (major proteins)
1. Thin filament = composed of actin proteins 2. Thick filament = composed of myosin proteins
How is the skeletal muscle develop?
1. embryonic mesoderm cells undergo cell division (to increase number) and enlarge 2. several myoblasts fuse together for form a myotube 3. myotube matures into skeletal muscle fiber
What are the stages of neuromuscular junction?
1. nerve impulse (AP) stimulates the release of the neurotransmitter acetylcholine (ACh) into the synaptic cleft 2. ACh stimulates changes in the sarcolemma that excite the muscle fiber. This stimulus is carried down the t tubules to initiate fiber contraction 3. Enzymes on the synaptic cleft break down ACh and thus limit its action to a single muscle twitch
Know the components of sarcomere: A-bands, I-bands, M-line, and Z-disc, H-zone, thick filaments and thin filaments.
A bands: Dark areas that correspond to the areas where thick filaments are present.(thick/thin filament) I bands: Light areas that contain only thin filaments. M line: Protein fibers that connect neighboring thick filaments. (center of sacromere) Z line: A protein disk within the I band that anchors the thin filaments and connects adjacent myofibrils. H zone: Located in the middle of each A band, this lighter stripe appears corresponding to the region between the thin filaments. (Contains thick filaments); thin filament do NOT overlap
Define triad in a skeletal muscle fiber?
A group of one T tubule lying between two adjacent terminal cisternae - 3 structures; one t-tubule and 2 neighboring sarcoplasmic reticulum
whats the difference between A-band & I-band in a sarcomere?
A-band: is the distance from one thick filament across the m-line to the next thick filament within the same sarcomere; the length of one thick filament within the same sarcomere and composed of thick/thin filaments I-band: is the distance from the beginning of one thick filament across the z disc to the beginning of the next thick filament of the neighboring sarcomere; composed of thin filaments
What are muscle fascicles?
Bundles of skeletal muscle cells - when we cut the muscle and look into it the muscle organ is composed of a lot of big round structures
Describe the following types of skeletal muscle fibers: fast fibers (fast glycolytic Type IIx) slow fibers (slow oxidative Type I) intermediate fibers (fast oxidative Type IIa).
Fast glycolytic fiber = w/o oxygen, make very little energy (slow pace). Runs out of energy fast af. Fatigues faster; very strong contractions Slow oxidative fiber = w/oxygen, weak contractions + little energy; can last for many hours; Intermediate Fast oxidative fiber = contracts fast that produces strong contractions (not as strong as glycolytic); contractions can last 30min to 1hr each muscle organ have different ratios of these 3 muscle types
What happens when a muscle contracts?
H zone disappears I band Shrinks; decreases in length A band remains the same M line remains the same Z discs move closer to M line
Describe sarcoplasmic reticulum in a skeletal muscle fiber?
Interconnecting tubules of the endoplasmic reticulum that surround each myofibril - recall rough and smooth ER; in skeletal & cardiac muscle cell we have a modified smooth ER - it wraps around each myofibril - is very important for muscle; involved in contractions - all about calcium; stores/releases/absorb it when needed (relax = absorb) > once it releases it floods the skeletal muscle cell and the calcium gets resorbed back
What is cytosol?
Intracellular fluid
Describe t-tubules in a skeletal muscle fiber? (transverse tubules)
Invaginations of the sarcolemma that project deep into the cell. - surrounded by sarcoplasmic reticulum on either side (making an area w/ 3 structures = triad) - each tubule makes it the outside of the cell
Describe the microscopic anatomy of a muscle fiber. Include the sarcolemma, T-tubules, sarcoplasmic reticulum.
Muscle Cell is surrounded by a connective tissue sheath called the endomysium. The "membrane" of the muscle cell is known as the sarcolemma. At the motor end plates of neuromuscular junctions, action potentials continue from the axon terminal to the sarcolemma via acetylcholine. The action potential continues down sarcolemma and into T (transverse) tubules. Due to a mechanical link between the t tubules and the sarcoplasmic reticulum, action potentials traveling down the T tubules cause Voltage-gated Calcium channels in the sarcoplasmic reticulum. are opening calcium channels allowing Ca2+ ions to diffuse into sarcolemma.
What is the function of the neurotransmitter (acetylcholine) within the neuromuscular junction?
Neurotransmitter responsible for stimulating muscle contractions > diffuses across the synaptic cleft and binds to receptor molecules on the sarcolemma, where it induces an impulse that initiates fiber contraction
When a muscle is contracted is it at FULL force?
No, because the amount of force that is generated by the muscle always depends on the weight of the object that we are going to move
What is the gross anatomy of skeletal muscle. Include the epimysium, perimysium, endomysium, fascicles, and myofilaments (actin and myosin).
SM consists of a muscle organ, which contains a collection of fascicles. The outermost CT that extends around and into SM is called Epimysium. Each fascicle contains bundles of SM cells and each fascicle is surrounded by Perimysium. Inside Fascicles, are muscle cells, wrapped by thin CT called endomysium. Inside the SM are proteins called myofilaments.
Define terminal cisternae
Sac-like regions of the sarcoplasmic reticulum that contain calcium ions
Name the 3 groups of skeletal muscle fibers?
Slow oxidative fibers (red slow oxidative) Fast glycolytic fibers (white fast glycolytic) Fast oxidative fibers (intermediate) MUSCLE CELL CONTAINS ALL THREE
What is the function of epimysium?
The connective tissues surrounding the entire muscle
What is the function of perimysium?
The connective tissues surrounding the fascicle - we wrap it with CT bc each fascicle contains many skeletal muscle fiber cells
What is the function of the axon terminal within the neuromuscular junction?
The nerve part of the junction is a cluster of enlargements at the end of the axonal process that stores chemical messenger molecules, neurotransmitters > separated from the sarcolemma of the muscle fiber by a space called the synaptic cleft
What is a sacromere composed of?
The region of the myofibril between two Z lines that is the contractile unit of a muscle cell > unit of organization of the thick and thin filaments > so everything in between neighboring z discs is a sarcomere
how do muscles cells relax?
When sarcoplasmic reticulum goes into calcium reabsorption the inside of the skeletal muscle cell no longer has calcium
Whats the issue with synaptic cleft?
When the nerve impulse reaches the nerve ending; it reaches a dead end and the nerve impulse cannot jump across the synaptic cleft to tell the skeletal muscle cell to contract so it is done by releasing a chemical messenger aka neurotransmitters
Why is some muscle pale, what is dark muscle?
White/pale muscle contains fast glycolytic fibers bc they make their energy w/o oxygen so they don't have a lot of blood going here > the diameter of these cells tend to be big bc a lot of protein Red/dark muscle contains slow oxidative fibers bc they make their energy using oxygen so a lot of blood vessels; tend be red and dark > diameter of these cells are small bc less protein
What is skeletal muscle composed of?
connective tissue and contractile cells
What does a myofibril contain & structure?
contains = the contractile filaments within the skeletal muscle cell structure = contractile units within muscle cells; contain round structures made of myofilaments called thin filaments and thick filaments. > thick and thin filaments organized into sarcomeres; basically many sarcomeres organized one after the next (back to back)
What are the three connective tissue layers of the muscle? and purpose.
endomysium, perimysium, and epimysium - Bind the muscle cells together. - Provide strength and support to the entire muscle. - Are continuous with the tendons at the ends of the muscle.
What are the functions & location of smooth muscle?
function = nonstarited, involuntary, fusiform in shape (spindle) cells = fusiform shape, uninucleate (1); Single Central Nucleus location = lines hollow organs
What are the functions & location of skeletal muscle?
function = striated, voluntary, myofibers, cells = elongated cells, long cylindrical shape, many nuclei = multinucleate (more than 2), Multiple Peripheral Nuclei location = attached to bones or (some facial muscles) to skin > we have the ability to contract and move our bodies
What are the functions & location of cardiac muscle?
function =striated, involuntary, branches, cardiocytes cells = short & branched, uni or binucleate (1 or 2); be intercalated discs is where we can identify a muscle cell; Single Central Nucleus location = found in the heart
What is the function of the acetylcholine receptor within the neuromuscular junction?
integral transmembrane proteins to which ACh specifically binds > the binding regenerates the nerve impulse, and that AP travels along the sarcolemma to the entrance of the t tubule to the triad where it reaches sarcoplasmic reticulum and causes it to release its calcium stores; calcium causes the sliding filament theory = muscles contract
What is a Motor unit and how does the size of the motor unit affect muscle contraction?
is a nerve cell + all muscle cells that it innervates - the size depends on the # of muscle cells that the nerve cell innervates > motor unit 1 connects to 2 muscle cells (picking up a pencil we activate unit 1) > motor unit 2 connects to 3 muscle cells (bigger & strong) we only activate this one when picking up something like a stapler BUT picking up a car? we need to activate both motor unit 1 & 2
Explain slow vs fast in regards to skeletal muscle fiber? (contractions)
is all about contraction speed > slow means the muscle contract slowly and it does not contract strong > fast means the muscle contract fast and can produce a lot of power
Where does muscle tissue develop from?
myoblasts; it fuses to form skeletal muscle fibers many myoblasts cells = mature skeletal muscle cell - muscle cells that begin to fuse with each other and as they do that the nuclei's get together = helps grow the cell - lots of myoblast cells coming together each donating a nucleus = skeletal muscles cells are multinuclei
What is the function of motor neurons within the neuromuscular junction?
nerve cells that innervate muscle fibers Recall: A neuron has cell processes that extend from the cell body: Dendrites are receptive regions of the neuron; an axon is a long, singular cell process that initiates and transmits nerve impulses
What is each skeletal muscle supplied?
one nerve, one artery, and one or more veins - nerves and blood vessels - one nerve = does not mean one nerve cell; each nerve contains a lot of nerve cells - Each muscle organ is innervated (the nervous system is connected to it) by many nerve cells
what is the origin, what is the insertion and how do they relate to each other when a muscle contracts?
origin = less movable attachment insertion = more movable attachment - When a muscle contracts the origin is the attachment that moves the least and insertion is the attachment that moves the most - when a muscle contracts the insertion moves whatever it's attached to towards the origin ex) Brachialis attaches to both bones the humerus and the radius; when this muscle contract it causes the radius and ulna to move up towards the arm (💪 bicep curls) so it's called the insertion bc it causes the most movement
What is the sarcolemma of a muscle fiber called?
plasma membrane of the muscle cell - the nuclei is pressed by the sarcolemma because inside of the cell we have lots of myofibrils (proteins)
what causes a muscle cell to contract more strongly than another?
protein > the more protein a muscle has the more powerful the contraction produces > more protein = stronger contraction but also more energy is needed
What is the function of neuromuscular junction?
signals the muscle to contract - the area where the nerve & muscle cells communicate (junction is a point of contact where things come together) and signals the muscle to contract
What is another alternative name for muscle fibers?
skeletal muscle cells
What is the skeletal muscle composed of?
skeletal muscle tissue connective tissue blood vessels nerves
What is a characteristic that is found in both skeletal and cardiac muscle?
striations; however cardiac muscle have dark lines = intercalated discs —> boundary between neighboring cardiac muscle cells
What is the function of the synaptic cleft within the neuromuscular junction?
terminal boutons are separated from the sarco- lemma of the muscle fiber by a space - the gap in between the nerve cell and skeletal muscle cell
What is motor unit recruitment?
the ability for the nervous system to activate different # of motor units depending on the weight; alter how strong a muscle contracts based on the weight
What is the function of the acetylcholinesterase within the neuromuscular junction?
the enzyme that breaks down acetylcholine (in the synaptic cleft) immediately after the neurotransmitter signals a contraction
What is the function of endomysium?
the innermost layer of connective tissue that wraps around individual muscle fibers - made of connective tissue, surrounds individual muscle cells - Functions to electrically insulates muscle cells from one another
If we shined light 💡 through a myofibril, will it light through the A band or I band? why?
the light would have a hard time going thru the a band bc of the density of the thick filaments and thru the i band the light will shine thru bc there are no thick filaments
what gives rise to striations?
the myofibril is organized by a band and i band
What is the sliding filament theory?
theory that actin (thin) filaments slide toward each other during muscle contraction, while the myosin (thick) filaments are still - Each of these myosin proteins contain a round myosin head that is playing tug a war and when a muscle cell receives the signal to contract all of these myosin heads grab the thin actin filament and it pulls it towards the end lines of both sides; each thin filament is attached to a z disc - thick filaments are pulling on the thin filaments towards the end lines; the z disc gets closer to the m line and overall length of the sacromere becomes smaller when contracted
True or False? Each muscle is an organ.
true
