Muscles Flashcards
Functions of the muscle
Contraction to cause movement of the skeleton, changing shape of internal organs and rhythmic contractions of the heart
What are the three types of muscle and what to they each control?
Skeletal - Skeleton,eyes,tongue
Smooth - BV,airways, internal
organ shape
Cardiac- Heart
Which muscle types are under voluntary control?
What about involuntary control?
Skeletal
Smooth,Cardiac
Skeletal Muscle Histology
Long cells with multiple nuclei located at the periphery of the cell to make space for contractile system.
Striations (alternating dark and light bands)
Cardiac Muscle Histology
Short cells with centrally located nuclei ( 1 or 2) with branching that allows cells to connect
Striations
Intercalated discs (stain as dark pink lines)
Smooth Muscle Histology
Small tapered cells appearing as sheets of cells.
Myo- means ______.
Sarco- means ________.
Muscle
Flesh
Sarcoplasmic reticulum is ________.
The smoother ER within muscle
Sarcolemma
Muscle cell plasma membrane
Which embryonic layer to muscles come from?
Describe the formation of muscle development from the embryonic stage.
Mesoderm
During gastrulation, the neural tube forms. Somites, blocks of mesoderm, on either side of the neural tube give rise to sclerotomes and dermomyotomes.
What are the embryonic precursors to muscle that arise from somites and what to they form?
- Sclerotomes - Vertebra and Ribs (Bone)
- Dermomyotomes (Dermatome and myotome)
Dermatome- Dermis of Skin
Myotome- Myoblasts; skeletal muscle
What happens to myoblasts in order for them to become ________ muscle?
Skeletal
Myoblasts migrate and fuse to form mature skeletal muscle cells.
What are other names for mature muscle cells?
Myotubes
Myofibers
Muscle Fiber
Extrafusal Fibers
What are satellite cells?
Progenitor stem cells near muscle cells responsible for growth and limited muscle repair.
Skeletal muscle is organized by sheaths of ______ tissue.
Describe the structure of skeletal muscle from the inner most structure.
Connective
Myofiber(muscle cell) is surrounded by endomysium
A bundle of endomysium-surrounded myofibers form a fasicle surrounded by perimysium.
A group of perimysium covered fasicles are surrounded by epimysium which is continuous with tendons.
What do tendons bind?
Muscle to bone
What kind of connective tissue is epimysium?
DRCT
In a skeletal muscle cross section, can you see striations?
What can help us identify if it is a muscle cell?
NO!
Multiple peripherally located nuclei per cell
Abundant Capillaries (space between cells for nutrition)
Describe the internal structure of an individual muscle FIBER.
What does the internal structure allow for?
Muscle cell
MyofibRILS (smaller fibers within the cell) span the length of the cell and are composed of repeating sarcomeres.
Sarcomeres are made of horizontal proteins called myofilaments which appear as dark and light bands.
Striations in muscle cell
What are myofilaments and how do they react to light when staining?
Myofilaments are the thick and thin overlapping horizontal organization of a sarcomere.
These sarcomeres repeat several times to form a myofibril which comprises a myofiber.
The thick (myosin) filaments dye darker.
The thin (actin) filaments dye lighter
What is the contractile unit of the cell?
What is it comprised of?
Sarcomere
Myosin (thick)
Actin (thin)
Describe the structure of a sarcomere
Z-Disc to Z-Disc
In the center of the sarcomere is an A band. The A band is comprised of the myosin and actin filaments in the center.
On either side of the A-band is an I band which hosts the actin filaments. The I band is NOT overlapping with myosin.
The Z-band separate the I-band actin filaments into each “half” of the sarcomere the actin filaments are being shared by. The Z-disc anchors actin filaments in place via proteins
The Sarcomere itself consists of Z-Disc to Z-Disc
A contracted sarcomere will look different than a relaxed sarcomere on an EM. Describe the difference.
The A-band will not change. However, the I-band will shrink in size and become incredibly thin compared to the relaxed sarcomere as the more acting and myosin filaments overlap.
How does contraction occur?
Myosin heads bind to actin filaments to form cross-bridges.
Myosin changes formation and pulls actin towards center of sarcomere causing thick and thin filaments to slide past one another.
Do sarcomeres contract one by one?
No! Sarcomeres contract together.
What starts a contraction?
- A nerve impulse triggers the release of Ach (acetycholine) from at the neuromuscular junction and stimulates receptors in SARCOlemma.
- The sarcoplasmic reticulum (smooth ER) surrounding each myoFIBRIL holds calcium critical for muscle contraction. It is located at the junction of the A and I band of sarcomeres of a myofibril. Terminal cisternae of the SER are here.
- In between 2 of the terminal cisternal, infoldings of the sarcolemma (plasma membrane of myoFIBER) form tubes.
- Stimulation of the T-Tubule membrane by nerve impulse triggers the muscle contraction by allowing the plasma membrane (sarcolemma) to interact with all sarcomeres at once to release Ca2+ Sarcoplasmic Reticulum.
Where is the sarcoplasmic reticulum found?
At the junction of the A and I band in muscle sarcomeres. (Terminal Cisternae are here)
How does the neuromuscular junction look on a histological section?
Dark spots protruding from axons on the periphery of long myofibers
What do actin and myosin sites look like during relaxation?
Actin binding sites are covered by tropomyosin and myosin can’t bind.
What happens to actin and myosin when a contraction signal is sent?
Tropomyosin is covering the binding sites in a relaxed state.
Ca2+ binds to troponin causing it to change shape and allowing tropomyosin to slide away exposing the binding sites on acting. Myosin can now bind to form cross bridges.
Myosin heads pivot to move actin towards center of sarcomere. ATP attaches to myosin heads to allow it to detach and revert to normal position.
This cycle repeats over and over till muscle is fully contracted.
What is required in order to release the skeletal muscle? The lack of this molecule causes what?
ATP
Rigor Mortis
What happens when nerve impulses stop or Ca2+ runs out?
Ca2+ is transported back into the sarcoplasmic reticulum and tropomyosin covers actin sites back to a relaxed state.
What are the three types of myofibers?
Muscle CELL
Type 1 - Slow Oxidative
Type 2 A- Fast oxidative Glycolytic
Type 2 B- Fast glycolytic
Type ___ myofiber is slow oxidative.
What is the rate of contraction?
What is the rate of fatigue?
What kind of respiration is used?
How much force is generated?
Function?
Type 1
- Slow
- Slow
- Aerobic
- Low
- Posture and Distance Running
Type ___ myofiber is fast oxidative and glycolytic.
What is the rate of contraction?
What is the rate of fatigue?
What kind of respiration is used?
How much force is generated?
Function?
Type 2A
- Fast
- Medium
- Aerobic or Anerobic
- Medium
- Jogging
Type ___ myofiber is fast glycolytic.
What is the rate of contraction?
What is the rate of fatigue?
What kind of respiration is used?
How much force is generated?
Function?
Type 2 B
- Fast
- Fast
- Anerobic
- Powerful
- Sprinting, jumping, powerlifting
Which myofiber is the MOST powerful but least efficient?
Type IIb
Can you increase the number of fibers you have? What determines the initial fiber makeup?
Genetics!
Yes you can! Marathoners vs Sprinters.
Marathoners will have more Type I fibers for endurance while sprinters will have more Type II fibers for more power over short distance.
What two things do sensory receptors in our muscles do?
- Proprioception (where are our muscles in space)
- How much force is being placed on the muscle?
What are the two sensory receptors in our muscles?
Muscle Spindles - Detect length
Golgi Tendon Organs - Detect Tension
(Not covering GTO)
Where are muscle spindles located?
Muscle spindles are encapuslated organs located within a muscle along myofibers.
Intrafusal fibers of the spindles are in the capsule while extrafusal fibers help attach spindles to one another and arrange them in parallel.
Intrafusal muscle fibers have _______ fibers that ______.
Nerve fibers that wrap around them.
How do intrafusal muscle fibers interact with nerve impusles/
When the muscle contracts, it pulls the intrafusal fibers which stimulates the nerve to send a message to the brain that the muscle is at Space X when doing Activity X.
Cardiac muscle is made of ________ and found in the __________.
What are they responsible for?
cardiomyocytes and found in the myocardium of the heart wall and are formed there as well.
Involuntary control that is stimulated by the conduction system of the heart by the SA node.
The nervous system directly stimulates cardiac muscle. True or False?
False
The SA node made of cardiac conducting cells does which can fire electrical impulses independently.
____ transmit contractile impulses to some cardiomyocytes and are located ______.
What allows for the impulses to be sent?
Purkinje Fibers , adjacent to the myocardium
Gap Junctions
The LAST STEP
Cardiac and Skeletal Muscle BOTH have ____________.
- The same organization of endomysium, perimysium and epimysium
- Striations
- Multiple Nuclei - Stipulation is that skeletal muscle cells can have hundreds of nuclei while cardiac will have 1-2.
What are key differences between cardiac muscle and skeletal muscle?
- Cell Shape
Skeletal is long, cardiac is short and branched. The branching forms tightly woven bundles that allow cells to withstand contracticle forces
Cardiac cells are irregular in histology.
- Nuclei Location
Skeletal muscle has nuclei on the periphery while cardiac has centrally located ones.
- Intercalated Discs
Junctions between myocytes that mechanically link cells and allow for electrochemical communication and provide an insertion site for actin filaments of firts sarcomere.
What are intercalated discs made of?
Desmosomes - Mechanically link cells to resist strain
Fascia Adherens- Holds cells together at their ends
Forms larger functional muscle fiber
Insertion point for actin filaments of sarcomere
Gap Junctions - Electrochemically couple cells
What junctions of the intercalated discs of ______ muscle allows for an insertion point of actin filaments of the first and last sarcomere?
Cardiac
Fascia Adherens
Describe cardiac muscle contraction.
It is exactly the same as skeletal muscle contraction where an impulse from the heart conduction system releases Ca2+ into the sarcoplasmic reticulum which causes tropomyosin to release allowing for the interaction between actin and myosin.
The difference is that the sarcoplasmic reticulum and the T-tubules of the plasma membrane form DIADS rather than TRIADS at the Z-disc (rather than the A-I Junction). AKA only ONE side of T-tubule is bordered by the Sarcoplasmic ER.
When identifying cardiac muscle what should you look for?
- Striations
- Branching
- Intercalated discs (thin lines)
- 1-2 nuclei
- Irregular Cell Shape
When identifying skeletal muscle what should you look for?
- Striations
- Equal sized cells that are long
- Nuclei at periphery
Smooth muscle is responsible for __________
- Changing the shape and diameter of internal organs tubes. For example, BV, airways, intestines, stomach, uterus.
Walls of some organs or vessels may have smooth muscle in different orientations. The small intestine has one longitudinal and one circular to help propel food.
How is smooth muscle controlled?
Involuntary control via hormones or stimulation via NS.
What are features of smooth muscle on histology?
- Tapered cells (spindle)
- Lack of clear borders between cells
- CT sheaths less prominent
- One nucleus that is flat
- No striations
Why are CT sheaths less prominent in smooth muscle.
They have a thin endomysium but NO epi or perimysium.
Why does smooth muscle lack striations.
Actin and myosin filaments are arranged differently than skeletal muscle which does NOT allow them to form myofibrils arranged in sarcomeres.
How are SM myofilaments organized?
Dense bodies attach to the plasma membrane and serve as insertion site for actin filaments and intermediate filaments of cytoskeleton.
It contains junctions such as desmosomes and gap junctions
How do dense bodies appear on a EM? Which muscle are the associated with?
Smooth
Dark blobs (of proteins)
How does smooth muscle contract?
Smooth muscle is stimulated via NT and hormones BUT it does NOT have T-tubules.
Rather, it has infoldings of the plasma membrane (caveolae) which hold Ca2+.
Ca2+ binds with calponin and uncovers the binding sites on actin which are trapped by caldesmon.
Filaments slide past each other and pull the PLASMA MEMBRANE AND CYTOSKELETAL FILAMENTS.
Smooth muscle contraction occurs as a ______________. However, it can can also contract __________.
Sheet of cells (single-unit)
Individually innervated (Multi-unit)
Instead of neuromuscular junctions, smooth muscle has wider synapses called ________.
What propagates the signal?
Is the associated with single or multi-unit SM?
Varicosities
Stimulates multiple cells at once
Gap Junction
Single-Unit
ex. Stomach
Describe multi-unit muscle cells.
Smooth Muscle
Fewer gap junctions; used for small, individual muscles like erector pili muscle in skin (hair follicle)
How does muscle regenerate?
Hyperplasia- Mitosis
Hypertrophy- Cells that can’t divide grow in size by increasing protein synthesis or adding organelles
Which form of regeneration is better?
Hyperplasia
Smooth Muscle Regeneration
Hyperplasia
Skeletal Muscle Regeneration
Hypertrophy because myofibers cannot undergo mitosis. Satellite cells can fused with damaged myofibers for repair
Cardiac Muscle Regeneration
Hypertrophy or maybe replaced by fibroblasts and connective tissue
Limited evidence of stem cell pop
