Muscle Tissue

Question 1

4 basic tissues of the body:

Answer 1

Epithelium, connective tissue, muscle tissue, nervous tissue

Question 2

Muscle cells contract to produce movement needed for:

Answer 2

Locomotion, propulsion, and pressure regulation

Question 3

Other names for muscle cells

Answer 3

Myocytes and myofibers (cell and fiber are used interchangeably)

Question 4

What shape are muscle cells and where do they originate?

Answer 4

Spindle-shaped and originate from the mesoderm (myoblasts)

Question 5

Myotubes

Answer 5

Multinucleated tubes of mesenchymal cells that have aligned and fused together

Question 6

Myofilaments

Answer 6

Differentiated myotubes; the nuclei are displaced against the plasma membrane

Question 7

Satellite cells

Answer 7

Undifferentiated mesenchymal cells that function in muscle repair

Question 8

Sarcoplasm

Answer 8

Cytoplasm of muscle cells, contains glycogen and myoglobin

Question 9

Sarcolemma

Answer 9

Plasma membrane of the muscle cell

Question 10

Sarcoplasmic reticulum

Answer 10

The highly specialized smooth ER of a muscle cell (regulates calcium flow)

Question 11

How much of the body weight is made up of skeletal muscle?

Answer 11

50%

Question 12

T/F: Skeletal muscles are involuntary muscles.

Answer 12

False - voluntary

Question 13

Epimysium

Answer 13

The dense irregular connective tissue layer that surrounds muscles

Question 14

Fascicles

Answer 14

Many smaller bundles that make up a whole muscle; composed of myocytes and myofibers

Question 15

Perimysium

Answer 15

Surrounds fascicles; dense connective tissue

Question 16

Myofibrils

Answer 16

Cylindrical bundles contained in myofibers

Question 17

Myofilaments

Answer 17

Smaller bundles found in myofibrils; composed of actin and myosin - contractile proteins and tropomyosin - regulatory proteins

Question 18

Endomysium

Answer 18

Reticular fibers surrounding individual myocytes

Question 19

Describe the components of the I and A bands.

Answer 19

I band - actin only A band - actin and myosin overlap

Question 20

Sarcomere

Answer 20

Contractile or functional unit of the myocyte; includes all elements from Z line to Z line; at full contraction, Z lines (discs) will be drawn closer to each other

Question 21

Z-line

Answer 21

A protein disc that bisects the I band; actin filaments are anchored here

Question 22

Sliding filament model

Answer 22

Each sarcomere shortens –> myofilament length is constant –> I band shortens, almost disappears –>thin filaments slide past thick filaments

Summation of all sarcomere shortening produces contraction of the muscle cell

Question 23

Steps in muscle contraction

Answer 23

1. Binding of calcium to troponin C
2. Conformational change in tropomyosin, exposing the myosin-binding site on actin
3. Myosin head binds to actin; ATP –> ADP moving myosin head
4. Bound thin filaments slide over thick filaments
5. Shortening of entire muscle fiber

Question 24

T-tubules (transverse tubules)

Answer 24

A deep invagination of the sarcolemma (plasma membrane) only found in skeletal and cardiac muscle cells; these invaginations allow depolarizaton of the membrane to quickly penetrate to the interior of the cell allowing calcium release from the sarcoplasmic reticulum

Question 25

Sarcoplasmic reticulum

Answer 25

Equivalent to the endoplasmic reticulum but seen in smooth and striated muscle; stores and releases calcium ions to initiate contractions

Question 26

Identify and describe each numbered structure

Answer 26

1) Myofibrils, made of myosin and thin actin myofilaments 2) Sarcoplasmic reticulum, stores and releases calcium 3) Terminal cisterna, expanded ends of sarcoplasmic reticulum T) Transverse T-tubule, deep tubular finger-like invaginations of sarcolemma (plasma membrane) of skeletal muscle cell create anastomosing network of tubules

Question 27

Describe Type 1 skeletal muscle fibers

Answer 27

* "red muscle" * slow twitch * dark color - rich in myoglobin which accounts for dark color * aerobic metabolism --\> fatigue resistant * high fat, low glycogen content * many mitochondria * myoglobin - to help transfer oxygen

Question 28

Describe Type 2 skeletal muscle fibers

Answer 28

* "white muscle" * fast twitch * anaerobic metabolism --\> more prone to fatigue * low fat, high glycogen content * less myoglobin and a few mitochondria

Question 29

Describe cardiac muscle

Answer 29

* cardiomyocyte = myocardiocyte = cardiac myocyte * single cell with one central nucleus * cross striated * has intercalated discs * gap junctions * desmosomes * has sarcoplasmic reticulum * has many mitochondria (up to 20% cell volume) - requires a lot of O₂

Question 30

Intercalated discs

Answer 30

Attach cardiac muscle cells to each other, providing strength and the ability to function as a syncytium * a true syncytium is a multinucleated cell (i.e. skeletal muscle cell) * consist of * transverse element * anchor * desmosome - fascia adherens and/or macula adherens * serve for strong attachment * longitudinal element * communication * gap junction (nexus) with ion channels * propagate electric impulse

Question 31

Identify the components of the intercalated disc

Answer 31

1. macula adherens 2. gap junction 3. fascia adherens

Question 32

Atrial myocardium

Answer 32

Atrial muscle cells contain membrane bound granules that are especially numerous at the right atrium; atrial granules have an endocrine function due to the presence of ANF/ANP

Question 33

Name and describe the two types of cardiomyocytes

Answer 33

1. contractile - red 2. conductile - pale pink

Question 34

Purkinje fibers

Answer 34

Modified cardiac muscle cells with 1-2 nuclei, myofibrils are sparse and restricted to periphery of cell; arranged in groups, cells are bigger and paler than contractile cardiac muslce cells

Question 35

Describe smooth muscle cells

Answer 35

* single centrally located nucleus * no striations * no myofibrils! * actin and myosin myofilaments are present but are not ordered * cytoplasmic dense bodies represent anchors for myofilaments (like Z bodies) * desmosomes and gap junctions * no T-tubules and sarcoplasmic reticulum is poorly developed * spindle shaped (fusiform) cells surrounded by a basal lamina and reticular fibers * parasympathetic and sympathetic innervations * contraction involuntary

Question 36

Single unit (unitary) smooth muscle

Answer 36

* found in visceral organs * cells behave like syncytium contracting in a network * sparse nerve innervation but cells communicate via multiple gap junctions

Question 37

Multi-unit smooth muscle

Answer 37

* found in iris of eye * precise contraction * individual innervation of each myocyte * lack of gap junctions, function individually

Question 38

Functions of smooth muscle

Answer 38

* peristalsis - wave-like contractions * vascular dynamics - contraction alters blood flow and important in blood pressure * propulsion * secretion (minor role)

Question 39

Dense bodies

Answer 39

The smooth muscle equivalent of Z discs of skeletal and cardiac muscle; note cigar-shaped nucleus

Question 40

Innervation of smooth muscle

Answer 40

* Innvervated by ANS (sympathetic and parasympathetic system) * allows stimulation (fast & slow) and inhibition of muscle cells * acetylcholine, norepinephrine, epinephrine are common neurotransmitters

Question 41

Myoepithelial cells

Answer 41

* contractile non-muscle cells * ectodermal origin * contain actin/myosin * similar to smooth muscle * can also be stimulated by hormones (mammary gland) * basket-like shape --\> known as basket cells * location: salivary/mammary/lacrimal (crying) glands

Question 42

Satellite cells

Answer 42

Skeletal muscle has limited regeneration capacity, and these cells retain mitotic potential and thus can accomplish some repair; positioned between basal lamina and sarcolemma of muscle cell; fibroblasts also form connective tissue (scar) as part of the repair process

Question 43

Muscle regeneration

Answer 43

* cardiac muscle cells lack the ability to regenerate * smooth muscle regeneration is limited; in addition to some mitotic activity, new smooth muscle cells may be derived from pericapillary mesenchymal cells * in all muscle types, repair is completed by scar tissue formation