Skeletal Muscle and Smooth Muscle Flashcards Preview

Histology Exam 2 > Skeletal Muscle and Smooth Muscle > Flashcards

Flashcards in Skeletal Muscle and Smooth Muscle Deck (40):

Identify the structure that the arrows are pointing to

Arrows are pointing to Z-lines in skeletal muscle.  Also visible are the I-bands (lighter) and A-bands (darker)


What are the two types of filaments that make up muscle and how do they contribute the the appearance of muscle?

Thick myofilaments-Myosin (heavy and light chains)

Thin myofilaments-G-actin which is compacted together to form f-actin

The regular alignment of the thick and thin filaments within the myofilbril within the myofiber produces a characteristic banding pattern


Define the following terms:







Sarcomere-the basic structureal and functional unit of striated muscle.

A-bands-fixed in width by the length of the thick myosin filaments (appear dark)

I-bands-change in width as the muscle contracts and relaxes

Z-line-bisects the I-band and is attachment point for actin thin filaments

M-lines-Cross link the centers of the thick filament

H-zones-in the central part of the A-bands defining an area where thick and thin filaments do not overlap.




Describe the process of muscle contraction in relation to actin and myosin.

Actin (thin) and myosin (thick) filaments interact so that the thin filaments are pulled into the A-band.  This causes the width of the , H-zone, and entire sarcomere to decrease.


What are the components of thick and thin myofilaments?

Thick-Myosin, heavy and light

Thin-Actin, Filamentous and globular proteins. troponin and tropomyosin.


What two functional properties make muscles capable of integrated movement?

1. Contractility-individual muscle fibers can contract 2. Conductivity-muscle fibers are capable of conducting an electrical potential along their membrane


What are two types of striated muscle?

1. Cardiac muscle - involuntary 2. Skeletal muscle - voluntary, somatic muscles of the body


What type of cell are skeletal muscles derived from?

mesenchymal cells


Give the muscle specific term for the following cell components: 1. Cytoplasm 2. Smooth endoplasmic reticulum 3. Plasmalemma 4. Fiber/filament

1. Sarcoplasm 2. Sarcoplasmic reticulum 3. Sarcolemma 4. Myofiber/myofibril/myofilament


What is the relationship of filaments, fibers, and fibrils in muscle cells?

Myosin and actin filaments make up a myofibril. Many myofibrils make up a muscle fiber.


Define myofibril

Composed of two types of overlapping protein structures (myofilaments) and combine to make a muscle fiber.


When is a muscle strongest?

When fully contracted.


The outer membrane of the skeletal muscle fiber and has numerous invaginations into the interior of the fiber called T-tubules



What is a T-tubule?

Transverse tubules surround myofibrils and contain extra cellular fluid and bring the action potential depolarization to the interior of the muscle fiber


Where is the intracellular site for storage, uptake, and release of calcium?

Sarcoplasmic reticulum


What are the expanded portions of the SR that flank the T-tubules?

Terminal cisternae flank T-tubules at the A-I junctions in skeletal muscle


What does the triad in skeletal muscle refer to?

Structure formed by a T-tubule flanked on either side by sarcoplasmic reticulum (terminal cisternae). They are located at the level of Z-lines.


How many triads per sarcomere?



Discuss the location of cytoplasmic organelles?

Mitochondria and glycogen granules are located btwn myofibrils and other cytoplasmic organelles (RER, Golgi...) are clustered at the ends of elongated peripheral nuclei.


What are the 3 types of connective tissue in muscle and what do they surround?

1. Epimysium-surrounds whole skeletal muscle 2. Perimysium-Encompasses muscle fascicles/group of muscle fibers 3.Endomysium-Surrounds each single muscle fiber/muscle cell


Discuss the steps in muscle contraction

1. Nerve impulse is generated and action potential is transmitted along sarcolemma and along T-tubules 2. Depolarization of T-tubules at triad triggers release of calcium from the cisternae 3. Calcium binds thin filaments initiating actin-myosin interaction and pulling of the thin filaments toward the center of the A-band and the sarcomeres become shorter 4. The SR re-accumulates calcium and muscle relaxes passively


True or False: the thin filaments shorten during muscle contraction?

False Sarcomeres become shorter but thick and thin filaments stay same length


What are the three muscle fiber types?

1. Red fibers (type1) 2. White fibs (type 2) 3. Intermediate fibers


Why do red fibers appear red?

The many mitochondria and high concentrations of myoglobin and glycogen


Define type 1 and type 2 fibers as pertaining to contraction and fatigue

1. Red fibers (T1) are fatigue resistant and slow contracting 2. White fibers (T2) are more quickly fatigued but contract faster. Also have 3 subtypes related to ATPase properties.


Define motor unit

A motor unit is a motor neuron and all of the muscle fibers innervated by it


In order for precise muscle control would you expect more or fewer fibers within the motor unit?



How many motor neurons innervate 1 muscle fiber?

Only one


What is the specialized area where the neurons make synaptic contact with muscle fibers?

Motor end plates


What functional purpose do junctional folds serve? Where will they be found?

Increase area of the synaptic cleft and are located in the motor end plates


What type of nerve is associated with muscle fibers?

Somatic efferent


What are muscle spindles?

Muscle spindles are specialized receptors located within the belly of a muscle which provide information about changes in muscle tension to the CNS.


Muscle spindles are a type of what?

Proprioceptor (gives sense of self)


Discuss differences in intrafusal and extrafusal muscle fibers.

Intrafusal fibers are located within the muscle spindle and are innervated by gamma motor neurons. They are responsible for conveying information about changes in length. Extrafusal fibers are muscle fibers not in the spindle, are innervated by alpha motor neurons and responsible for muscle contraction.


What are 3 main features of smooth muscle and where is it usually found?

1. Involuntary 2. No transverse bands (striations) 3. Contraction usually changes the size or shape of the organ with which it is associated -Smooth muscle is located in arteries, GI tract, reproductive tract, and iris of the eye


Describe the appearance of smooth muscle as seen under the light microscope.

1. Long spindle shaped cells 2. Leptochromatic nucleus that is centrally located 3. Cytoplasm stains acidophilically 4. Small amount of connective tissue surrounding each cell ( Endomysium)


Where would you find calveolae?

Calveolae are found as small invaginations in the sarcolemma (plasma membrane) of smooth muscle cells.


What special role do Calveolae have?

These initiate smooth muscle contraction by releasing calcium ions that in turn activate a kinase that phosphorylates myosin and allows myosin to interact with actin. Go second messengers!


What are dense bodies?

In smooth muscle they are dark staining patches that serve as attachment sites for intermediate and myosin filaments.


What are gap junctions?

Space between adjacent cells that is used for communication (ionic coupling) between cells