Muscle Histology Flashcards Preview

SMS Week 4 > Muscle Histology > Flashcards

Flashcards in Muscle Histology Deck (88):

WHat are the two functions of muscle tissue?

contractility and conductivity


WHat are the 3 types of muscle tissue?

smooth (unstriated, involuntary, visceral)

skeletal (striated - voluntary)

Cardiac (striated - involuntary)


What is the embryological origin of muscle tissue?



What is the muscle cytoplasm called?



What is the muscle cell plasma membrane called?



What is the SER called in muscle?

the sarcoplasmic reticulum


What is the term for a linear unit of muscle?

What is an individual muscle cell called?

a linear unit is a sarcomere

an individual muscle cell is a myofiber


What are 5 characteristics of skeletal muscle?

1. straited

2. t-tubule system

3. well developed sarcoplasmic reticulum

4. multinucleated

5. nuclei located at cell periphery


What is responsible for the cross-striations in muscle cells?

the myofibilrs, which are tiny  cylindrical rods within the sarcoplasm of the muscle cell

the banding is due to registry of alternating light and dark portions of myofibrils adjacent to each other


Name the bands/lines/units


The length of a sarcomere is between what?

2 Z lines


What is the A-band?

the anisotropic band

it's the borad, dark-staining band


What is the I-band? Whats inside?

THe I band is the isotropic band, which is narrower than the A band and light-staining

It's bisected by the Z-disc


What is the light-staining area that bissects the A band?

the H band - it's the middle of the sarcomere wher ethe myosin doesn't have any heads


WHat bisects the H band?

the M line


What comprises the myofibrils?

myofilaments: actin and myosin


where are the actin filaments located within the sarcomere?

from the Z-disc strething to the edge of the H band


Where are myosin filaments located in the sarcomere?

from one end of the A-band to the other end of the A-band.

there will be cross-bridges estending from each myosin filament to its neghborin gactin filaments in the A band (the area where they overlap)


What proteins are located in the M-line?

It's at the center of the H band

contains myomesin and C protein that interconnect the thick myosin filaments to maintain teir specific lattice arrangement


What protein in the Z disc is used to anchor the actin filaments?

alpha actinin


In skeletal muscle, where is the sarcoplasmic reticulum located?

It forms a network of cisterns or membranous tubules that run between and around the myofibrils

they tend to form "collars" at each A-I junction-one on each side which are spearated from each other by T-tubules


What does the sarcoplasmic reticulum do?

It binds and releases Ca2+


What are the invaginations of the sarcolemma called? Where are they typically seen in seletal muscle?

They are called T-tubules and they're located at the A-I junctions between the two cisternae "col.ars" of the sarcoplasmic reticulum


The lumen of the T-tubule is continuous with what?

the extracellular space


What is a triad?

the combination of a t-tubule and 2 lateral cisternae collars


What do the T-tubules faciliate?

transmission of electrical impulses from sarcolemma to interior depths of cell


HOw many "triads" are there per sarcomere in skeletal muscle?

2 (one at each A-I junction)


What two forms of actin are located in myofibrils?

G-actin (globular actin) which is the globular monomer that polymerizes to form....

F-actin (fibrous actin), which is two helically wound strands of polymerized G-actin


Myosin is composed of 4 __ and 2 __, which are combined for form ___ meromyosin and ___ meromyosin.

4 light chains and 2 heavy chains

make up heavy meromyosin and light meromyosin.

The light meromyosin is the end that doesn't have the heads (made of the intertwining 2 heavy chains)

the heavy meromyosin is the rod like portion tha tlies parallel to the backgone and then the heads.


WHat are the two components of heavy meromyosin?

1. rod-like portion that lies parallele to the backbone of the filament

2. a globular head which etends laterally as a cross bridge to connect to actin filament - it has to have actin binding sites


What type of enzymatic acitvity can be found near the myosin globular heads?



What does it mean to say that myosin heads are polarized?

they are directed away from the midpoint of myosin filament (which is why there's a bare sonze making the M line)


What are the 3 regulatory molecules involved in skeletal muscle contraction?


troponin complex

calcium ion


What is tropomyosin? What is troponin?

Tropomyosin is the fibrous protein that is helically wound along the groove sof the F-actin helix.

Troponin is the complex that binds the tropomyosin to actin in such a way that the tropomyosin blocks the actin-myosin interactions


What are the three component sof the troponin complex?

TnT - binds entire trponin molecule to propomyosin

TnC - binds Ca++

TNI - binds to actin preventing actin myosin interactions


What does calcium ion do?

It binds to TnC and causes a conformation shift in the complex so that tropomyosin shifts over exposing previously blocked active sites on the actin filament


What does the protein titin do?

it's a large, linear, elastic protein that helps position the myosin filaments precisely within the sarcomere

It extends from the z-disc to half of the myosin filament - so there are two per sarcomere


What does the protein nebulin do?

It's a long non-elastic protein  - two molecules of which wrap around each actin filament to help anchor it to the z-disc (in accition to alpha actinin)

it probably also regulates the length of the actin - otherwise it might unwrap and become too long


What hypothesis is generally accepted about the contraction mechanism of skeletal muscle?

the sliding filament hypothesis


What happens to the following during contraction?

a band




The A band remains constant

The I band becomes smaller and may even disapear (because the actin filaments are now overlapping with the myosin filaments completely)

The Z discs will get closer together as the sarcomere shortens

The H band narrows and is eventually obliterated


What are the 3 connective tissue coats around muscle tissue?

endomysium - surrounds each individual muscle fiber (made of fine reticular fibers)

Perimysium - connective tissue sheath around groups of muscle fibers (fasicles)

Epimysium - the outermost sheath of CT that surroudns the entire muscle


The connective tissue sheaths extend from the end of the muscles to form what?

the muscle tendons


True or false, the length of indvidual muscle cells within a muscle fascicle can vary.

True - they can extend from one end oall the way to the other, from one end to the middle, or just located in the middle


What are the 3 general types of skeletal muscle fibers?





Describe how blood reaches the muscle fibers.

There is a very rich blood supply to muscles for obvious reasons

the larger arteries follow the perimysium

artieroles penetrate the fasicles

capillaries run parallele to individual myofibers


In what connective tissue layer is the lymphatics system located?

In the perimysium


Describe the motor end plate.

It's the myo-neural junction

- the myelina sheath of the axon is lost as the nerve fibers approach the surface of muscle cell

- the axon bbranches close to the surface of the muscle cells so branches occupy the recesses in the surface of the muscle fiber (the primary synaptic clefts)

- subneural apparatu (seconday synaptic clefts formed by infolding of sarcolemma) contain acetylcholinersterases

- Synaptic vesicles are located in the axon terminals and contain acetylcholine


What does a motor nunit consist of?

a motor neurn and the muscle fibers innervated by it

there can be lots of fibers innervated by one motor neuron


The closer the radio o motor neurons to the number of muscle fibers innervated, the ____ the control

the greater (or finer) the control


What are the two muscle sensory structures we discussed?

. muscle spindles

golgi tendon organs


What are muscle spindles comprised of?

a group of small specialized muscle fibers called intrafusal fibers enclosed in a CT capsule


The central region of the intrafusal fibers will have many nuclei in what two different arragnemets?q

1. nuclear bag fibers

2. nuclear chain fibers


How many CT capsules are there in a muscle spindle?


an internal capsule immediately surrounding the intrafusal fibers and an external capusule surrounding the internal capsule


Describe the sensory innervation of the muscle spindles.

Describe the motor innervation of muscle spindles.

1. large diameter fibers forming annulospiral or primary endings around the nuclear bag or chain fibers
2. smaller diameter fibers forming flower spray endings on the intrafusal fibers outside the mid-region

efferent fibers form motor end plates on either side of the mid-region of intrafusal fibers


What are golgi tendon organs comprised of?

spindle-shaped bodies comprised of collagen and enclosed by a thin capsule


What are golgi tendon organs sensitive to?

stretching forces on the tendon


True or false: hypertrophy of muscle tissue is due to the increase in the number of muscle fibers.

False - it is due to the increase in size of the fibers already present


How does cardiac muscle differ from skeletal muscle. What is the main diagnostic feature?

1. the sarcoplasmic reticulum is less well developed than in skeletal muscle

2. just one nucleus per cell

3. The nucleus is located at the center of the cell (not periphery)

4. Intercalated disks are the diagnostic feature (although sometimes hard to see under staining)

5. The cells are elongated and branching (unlike skeletal which are just tubes)


True or false: skeletal muscle myofibrils are more distinct than in cardiac muscle.

True - in cardiac muscle the myofibrils branch and blend with adjacent myofibrils so they are less distinct.


Where is sarcoplasm typically seen in cardiac muscle cells?

at each pole of the nucleus


Where are intercalated disks located in cardiac muscle? What do they ook like?

they occur wher eyou'd expect to see a Z disc - it marks the spot of a cell-cell attachment

they look like dark step-like cross bands


How does the T-tubule system differ from skeletal muscle to cardial muscle?

in cardiac muscle the t-tubule system is larger (wider) and located at the Z lines instead of at the A-I junction


How does the sarcoplasmic reticulum differn from skeletal muscle to cardiac muscle?

In cardiac muscle it ia less developed and only forms a simple plexiform arrangement of the tubular elements without ternimal disternae


Skeletal muscle has triads, cardiac muscle has ____.

diads - a T-tubule and a terminal portion of adjacent sarcoplasmic reticulum


What are the three cell-to-cell junction types found in an intercalated disc of cardiac muscle?

1. gap junctions = nexuses

2. desmosome

3. fascia adherens (anchoring points for actin filaments)


what are atrial granules? Where are they located? WHat do they contain?

They are unique to atrial cardiac muscle cells

they contain atrial natriuretic peptide

this serves to lower blood pressure by decreasing the renal tubules capability to resorb sodium and water


What types of connective tissue fibers occur around the cardiac muscle cells? How about in between bundles of cardiac muscle cells?

reticular and collagenous fibers around each cardiac muscle cell

collagenous and elastic fibers between bundles of cells


the vascular supply for the cardiac muscle is derived from what?

the coronary arteries


Branches from what nervous system terminate on cardiac muscle?

autonomic - sympathetic and parasympathetic


The conduction system of cardiac muscle is comprised of what fibers?

purkinje fibers - specialized muscle cells


How are purkinje fibers different from other cardiac muscle cells?

the myofibrils are reduced in number

they contain more sarcoplasm

the nucleia re more rounded

they are larger in idamter

they lack T-tubules

they have more glycogen


How does cardiac muscle differ from skeletal muscle in terms of emryological origin?

they are both from mesoderm, but the myoblasts fuse in skeletal muscle and not in cardiac muscle


Does smooth muscle have striations? T-tubules?

no for both


In addition to contractility and conductivity, what is another function of smooth muscle?

it can produce extreacellular products like colagen, elastin, glycosaminoglycans, proteoglycans and growth factors

(not always)


What does smoothe muscle look lik eunder a microscope?

They are fusiformly shaped (ends tapered, oval mucleus in center, corkscrew shape when contracted, cluster in sheeths)

cytoplasm is eosinophilic



each smooth muscle cells is surrounded by what type of connective tissue?

reticular fibers


Mitochondria and other organelles tend to cluster where in smooth muscle cells?

at the poles of the nuclei


FOr the actin in smooth muscle cells, is there also tropomyosin? Troponin?

there is tropomyosin, but not troponin


How are the actin and myosin filaments arranged in smooth muscle?

not in a precise manner like in skeletal and cardiac

more like bundles that run obliquely through cytoplasm


What are the dense bodies of smooth muscle comparable to in skeletal muscle?

the z-discs, because the dense bodies contain alpha actinin to achnor actin myosin filament bundles


Where are the dense bodies located? (2)

1. located along the inner aspects of the sarcolemma

2. scattered throughout the cytoplasm


What are caveolae?

they are pinocytotic-like invaginations of the sarcoplasmic reticulum

may function as the equivalent of the T-tubules

may also work in concert with the sarcoplasmic reticulum to modulate Ca+ availability


What are the steps in the mechanism for smooth muscle contraction?

1. Ca++ binds to calmodulin

2. complex activates myosin light chain kinase

3. myosin light  chain kinase phosphorylates one of the two light chains of the myosin molecule head

4. this exposes an actin binding site on myosin head

5. myosin head binds to actin and contraction occurs


Why does smooth muscle contraction take longer (and is more prolonged) than skeletal muscle?

the phosphorylation process is slower, so it takes longer for the myosin heads to be able to bind to actin and longer to let go


Why doe smooth muscle contraction require less energy than skeletal muscle?

ATP hydrolysis takes longer than in skeletal muscle


How are impulses transmitted from muscle cell to muscle cell in smooth muscle?

through gap junctions


Do smooth muscle cells retain mitotic capability?

yes - think about the pregnant uterus