Muscle Tissue

Question 1

General features of muscle tissue

Answer 1

Basic tissue type – the most abundant of the four (~40% body weight)
• Contractile properties - modified/controlled by nervous input.
• Highly vascularized.
• Derived from the embryonic mesoderm

Question 2

Fiber:

Answer 2

individual muscle cell (not to be confused with connective tissue fibers which are extracellular, or nerve fibers which are multiple cellular extensions.)

Question 3

• Sarcolemma:

Answer 3

plasma membrane of muscle cell.

Question 4

• Sarcoplasmic reticulum:

Answer 4

smooth endoplasmic reticulum of muscle cell.

Question 5

• Cardiac muscle

Answer 5

• Located in the heart
• Involuntary control
• Striated
• Mono-nucleated

Question 6

• Smooth muscle

Answer 6

• In hollow organs
• Involuntary control
• Non-striated
• Mono-nucleated

Question 7

Prefixes sarco- or myo - refer to

Answer 7

muscle

Question 8

• Sarcoplasm:

Answer 8

cytoplasm of muscle cell

Question 9

• Skeletal muscle

Answer 9

• Connected to bones
• Voluntary control
• Striated
• Multi-nucleated

Question 10

Muscle tissue develops from

Answer 10

myoblasts

Question 11

What are the characteristics of muscle tissue developing from myoblasts?

Answer 11

• Fusion of mononucleated embryonic myoblasts (multinucleated myotubes)
• Skeletal muscles contract by the 7th week of human development
• The number of fibers does not increase significantly after birth

Question 12

Skeletal muscle has limited regenerative capacity mediated by the mononucleated satellite cells which?

Answer 12

proliferate and fuse after injury

Question 13

What are Satellite cells?

Answer 13

Reserve myoblasts that can form new skeletal muscle fiber

Question 14

What is Plasticity?

Answer 14

ability to change in size (but not number) depending upon use/disease

Question 15

Atrophy

Answer 15

• a decrease in the diameter of individual muscle fibers which occurs when muscles are not used or are denervated.

Question 16

Hypertrophy

Answer 16

• an increase in diameter of fibers after continuous muscle use.

Question 17

Two types of plasticity?

Answer 17

1. Atrophy

2. Hypertrophy

Question 18

perimysium

Answer 18

contains bundles of muscle fibers

Question 19

myofibrils

Answer 19

contraction

Question 20

epimysium

Answer 20

covers the muscle

Question 21

endomysium

Answer 21

seperates muscle fibers

Question 22

Cytoskeletal Elements of Muscle Fibers: Actin and myosin

Answer 22

directly involved with contraction

Question 23

Cytoskeletal Elements of Muscle Fibers: Titins

Answer 23

large proteins that act as microscopic “springs” which allow striated muscle to get back into shape after being stretched

Question 24

Cytoskeletal Elements of Muscle Fibers: Dystrophin

Answer 24

large sub-membrane protein in all types of muscle which cross links with actin (intracellularly) and with trans-membrane glycoproteins (sarcoglycans, dystroglycans) which connect with the laminins (extracellularly); this complex is believed to stabilize the sarcolemma and help transmit the force of contraction[“Trans-membrane Link Proteins”]

Question 25

A nerve induced muscle impulse spreads along T tubules causing Ca++ release from the sarcoplasmic reticulum into the sarcoplasm causing

Answer 25

contraction of the myofilaments

Question 26

Troponin

Answer 26

a globular protein, located at a specific site on each tropomyosin molecule, composed of three subunits: TnT, TnC and TnI

Question 27

TnT

Answer 27

which strongly binds to tropomyosin

Question 28

TnI

Answer 28

which inhibits the actin-myosin interaction

Question 29

TnC

Answer 29

which has the capacity to bind Ca++ and change the conformation (shape) of the complex Myofilaments

Question 30

Innervation: The motor unit consists of

Answer 30

- a single nerve and all the muscle fibers it innervates • A single muscle fiber (cell) is innervated by only one motor neuron, but one neuron may innervate more than one fiber.

Question 31

What is a Neurotransmitter Vesicles?

Answer 31

found within terminal axonal bulbs; contain the neurotransmitter acetylcholine

Question 32

What is a Synaptic Cleft?

Answer 32

synaptic space between motor axon and skeletal muscle.

Question 33

What is the junctional folds?

Answer 33

area of the sarcolemma which contains acetylcholine receptors and cholinesterase which breaks down the neurotransmitter

Question 34

What is the end plate nuclei?

Answer 34

Stimulated by neuregulins (secreted by motor neurons) to transcribe AChR genes

Question 35

ATP is replenished by a variety of means:

Answer 35

- creatine phosphate - stored glycogen - aerobic metabolism of glucose, fatty acids and other high-energy molecules

Question 36

Ia neuron

Answer 36

sends signals to spinal cord

Question 37

Gamma neurons

Answer 37

maintain degree of contraction in Intrafusal fibers

Question 38

Muscle Spindles

Answer 38

encapsulated structures that contain intrafusal fibers; dispersed among the extrafusal fibers of the muscle.

Question 39

Main functions of muscle spindles

Answer 39

proprioception, muscle tone, and reflexes.

Question 40

Extrafusal Fibers - majority, provides force

Answer 40

* Red Fibers (Type I, Slow-Twitch) * White Fibers (Type II, Fast-Twitch) * Intermediate Fibers

Question 41

• Intrafusal Fibers - sensory feedback

Answer 41

Nuclear Chain Fibers | Nuclear Bag Fibers

Question 42

Extrafusal: Red Fibers (Type I, slow-twitch)

Answer 42

+ Contain large amounts of myoglobin (similar to hemoglobin; binds oxygen) which gives them a red color + Abundant mitochondria + Oxidative respiration - energy derived from oxidative phosphorylation of fatty acids + Relatively small diameter + Contract slowly, but continue to function over long periods of time (e.g. in maintaining posture)

Question 43

Extrafusal: White Fibers (Type II, fast-twitch, fatigue-prone)

Answer 43

``` + Contain little myoglobin + Glycolytic respiration + Abundant glycogen + Relatively large caliber packed with myofibrils + Contract quickly but fatigue easily ```

Question 44

Growth in cardiac muscle

Answer 44

arises from differentiation and growth of single cells which do not fuse - beyond early childhood, cardiac cells do not have the ability to regenerate after injury (e.g. heart attack) - however, hypertrophy can occur (i.e. individual cells grow in size but not number).

Question 45

The cardiac muscle cells are located in the

Answer 45

myocardium (middle layer of the heart) which is bounded by the endocardium on the inside and the epicardium on the outside.

Question 46

The vagus nerves (parasympathetic) ____ the heart rate

Answer 46

decrease

Question 47

Natriuretic Peptides are produced by:

Answer 47

atrial (ANP) or ventricular (BNP)

Question 48

Function of Natriuretic peptides

Answer 48

Function: decrease blood pressure, acting to: 1) Promote kidney diuresis and natriuresis (loss of water and Na+). 2) Cause vasodilatation. 3) Inhibit central sympathetic outflow

Question 49

Structure of smooth muscle: spindle shaped -

Answer 49

each cell surrounded by basal lamina and reticular fibers that physically couple the cells together.

Question 50

Mononucleated - structure of smooth muscle

Answer 50

- nucleus centrally located and elongated

Question 51

Most sarcoplasmic organelles are confined to a

Answer 51

conical region at each pole of the nuleus

Question 52

Dense Bodies distributed along the

Answer 52

sarcolemma - contain actinin (similar to Z-lines of striated muscle); they are anchoring sites for actin filaments and intermediate filaments (desmin, vimentin).

Question 53

Gap junctions between individual fibers make them

Answer 53

electrically coupled - the number of these junctions depend upon the type of smooth muscle.

Question 54

No T tubules -

Answer 54

numerous caveolae (“tiny caves”) on the cell surface that may be involved in sequestering Ca++.

Question 55

Characteristic presence of neurotransmitter-carrying vesicles termed

Answer 55

Varicosities