Skeletal Muscle and Smooth Muscle

Question 1

Identify the structure that the arrows are pointing to

Answer 1

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

Question 2

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

Answer 2

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

Question 3

Define the following terms:

Sarcomere

A-bands

I-bands

Z-line

M-lines

H-zones

Answer 3

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.

Question 4

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

Answer 4

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.

Question 5

What are the components of thick and thin myofilaments?

Answer 5

Thick-Myosin, heavy and light

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

Question 6

What two functional properties make muscles capable of integrated movement?

Answer 6

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

Question 7

What are two types of striated muscle?

Answer 7

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

Question 8

What type of cell are skeletal muscles derived from?

Answer 8

mesenchymal cells

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

Define myofibril

Answer 11

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

Question 12

When is a muscle strongest?

Answer 12

When fully contracted.

Question 13

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

Answer 13

Sarcolemma

Question 14

What is a T-tubule?

Answer 14

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

Question 15

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

Answer 15

Sarcoplasmic reticulum

Question 16

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

Answer 16

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

Question 17

What does the triad in skeletal muscle refer to?

Answer 17

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

Question 18

How many triads per sarcomere?

Answer 18

2

Question 19

Discuss the location of cytoplasmic organelles?

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Discuss the steps in muscle contraction

Answer 21

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

Question 22

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

Answer 22

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

Question 23

What are the three muscle fiber types?

Answer 23

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

Question 24

Why do red fibers appear red?

Answer 24

The many mitochondria and high concentrations of myoglobin and glycogen

Question 25

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

Answer 25

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.

Question 26

Define motor unit

Answer 26

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

Question 27

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

Answer 27

Fewer

Question 28

How many motor neurons innervate 1 muscle fiber?

Answer 28

Only one

Question 29

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

Answer 29

Motor end plates

Question 30

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

Answer 30

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

Question 31

What type of nerve is associated with muscle fibers?

Answer 31

Somatic efferent

Question 32

What are muscle spindles?

Answer 32

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

Question 33

Muscle spindles are a type of what?

Answer 33

Proprioceptor (gives sense of self)

Question 34

Discuss differences in intrafusal and extrafusal muscle fibers.

Answer 34

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.

Question 35

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

Answer 35

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

Question 36

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

Answer 36

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)

Question 37

Where would you find calveolae?

Answer 37

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

Question 38

What special role do Calveolae have?

Answer 38

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!

Question 39

What are dense bodies?

Answer 39

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

Question 40

What are gap junctions?

Answer 40

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