Muscle Tissue (Start of Exam 2)

Question 1

What is muscle? What does it do?

Answer 1

• Muscle tissue makes up 40-50% of total body weight

* All motion of the body is due to contraction and relaxation of muscle

Question 2

3 types of muscle tissue

Answer 2

A. Skeletal = voluntary striated muscle attaches to bone
B. Smooth (visceral) - involuntary muscle
C. Cardiac - also striated but involuntary

Question 3

Layers of Body’s Exterior (Explain, 5)

Answer 3

As one progresses from superficial to deep in most parts of the body, the order of layers of tissue encountered would be the following:

1. epidermis
2. dermis
3. hypodermis = superficial fascia - also sometimes called subcutaneous tissue (contains loose connective tissue and adipose tissue)
4. deep fascia
5. skeletal muscle

Question 4

Layers of Body’s Exterior: superficial fascia (Details/5 functions)

Answer 4

• (What we describe as “fat”)
• immediately deep to the skin
• covers entire body in varying thickness
• loose (areolar) connective tissue
• contains the majority of adipose tissue (fat) in the body
• 5 basic functions
  1. H2O storage
  2. insulation for body
  3. mechanical protection from blows
  4. pathway for nerves and vessels
  5. energy storage (in form of triglycerides in adipose tissue)

Question 5

Layers of Body’s Exterior: deep fascia

Answer 5

• dense connective tissue - contains no fat

- basically tough coat over skeletal muscle

Question 6

Histology of Skeletal Muscle (7 *categories in order)

Answer 6

A. myofilaments (thick and thin) actin and myosin filaments arranged in groups called:
B. myofibrils - multiple myofibrils together form the muscle cell or
C. muscle fiber = muscle cell - this is ensheathed within a deep facial coat called the endomysium - multiple muscle fibers together in fascial sheath will form a:
D. muscle fascicle - groups of muscle fibers forming fascicles are ensheathed within a connective coat called the perimysium. Multiple groups of muscle fascicles together form a:
E. muscle - the muscle itself is ensheathed within a deep fascial sheath called the epimysium. Several muscles together will sometimes form a:
F. muscle group = groups of muscles working together in single action (i.e. quadriceps femoris)
G. continuations of these deep fascial components at the ends of a muscle then compose tendons which are continuous with the periosteum of bone, or form an aponeurosis which is continuous with the aponeurosis of an adjacent muscle.
-note: tendons are sometimes enclosed within sheaths of dense C.T. lined by a synovial membrane called “Tendon Sheaths”

Question 7

Skeletal Muscle Fiber - Cell (5 details)

Answer 7

A. range in size from 1/10 to 1/100 mm (10-100 m) in diameter but may be as long as 30 cm (12 inches)
B. plasma membrane: Sarcolemma
C. cytoplasm: Sarcoplasm
D. smooth endoplasmic reticulum: Sarcoplasmic Reticulum
E. invaginations of the sarcolemma form tubule-like structures which run perpendicular to the muscle fiber. These T-tubules are surrounded on either side by sarcoplasmic reticulum thus forming a triad.

Question 8

Myofilaments (4 big details)

Answer 8

1. both thick and thin myofilaments
2. do not extend length of cell, but rather arranged in compartments called sarcomeres which are separated by “Z-lines” (dense areas seen with light microscope)
3. thin filaments - arranged parallel to thick filaments; but in groups circumferentially around thick filaments.
   * Composed mostly of protein actin but also contain 2 other proteins called:
   a. tropomyosin
   b. troponin
   c. tropomyosin - troponin complex - formed from above 2 proteins
   - this complex inhibits binding to myosin thick filaments to the actin of the thin filaments.
4. thick filaments
   a. composed mostly of protein myosin
   b. myosin molecule is shaped like a rod with a round head
   * many of these arranged together with head projecting outwardly form the thick filaments
   * these heads form “cross bridges” with the actin molecules in contraction

Question 9

Sarcomere (What, 4 details)

Answer 9

• portion between Z lines
  1. actual unit of contraction
  2. A band - stands for anisotropic band - area where one sees thick filaments and thin filaments.
  3. I band - isotropic band - portion where one sees thin myofilaments only (no overlap of thin filaments)
  4. H band - central area of sarcomere which contains thick myofilaments only (no overlap of thin filaments)
• these alternating light and dark bands give skeletal muscle its striated or striped appearance.

Question 10

Muscle Contraction (How,What’s involved?)

Answer 10

A. A rachet like sliding of thin myofilaments over thick myofilaments with the “cross bridges” of the thick myofilaments establishing new contacts with the thin myofilaments.
B. Thus as muscle contracts one appears to see the I band and the H band decrease in width while the A band remains unchanged and the Z lines move closer together.

Question 11

Arrangement of Muscle Fasciculi (What, 4 details)

Answer 11

A. bundles of muscle fibers within a muscle - fasciculi
B. these can be arranged in 4 basic patterns:
1. parallel - most muscles - fasciculi all run same direction
2. convergent - broad origin, restricted insertion e.g. deltoid
3. pennate (means feather) (unipennate or bipennate)
fasciculi short in relation to whole muscle - directed toward tendon extending length of muscle - oblique arrangement of fascicles
4. circular - circular arrangement enclosing orifice e.g. orbicularis oris
note: pennate is best for strength (power) while parallel allows the greatest range of motion.
note: unipennate - extensor digitorum bipennate - rectus femoris

Question 12

Exercise and Muscle Hypertrophy (3 details)

Answer 12

A. the more a muscle is used the larger it will become.
B. it is unknown if this is due to actual formation of new fibers or due solely to hypertrophy of existing ones. Most people feel it is latter. It is known that the number of myofibrils increases.
C. muscle hypertrophy and increased strength are developed more rapidly with forceful exercise than with prolonged mild exercise.

Question 13

Denervation and Atrophy (What is this)

Answer 13

• disuse of muscle will cause it to become flaccid - continued disuse will result in atrophy (muscle fibers will become replaced by fibrous)
• nerve stimulation is required to maintain muscle tissue

Question 14

Muscular Dystrophy (3 details)

Answer 14

• term that refers to inherited muscle destroying diseases - cause is unknown specifically
• there is no specific drug therapy
• there is a reliable screening test to check for it before symptoms appear - but why?

Question 15

Myasthenia Gravis (6 details)

Answer 15

• abnormality of neuromuscular junction
• neuromuscular junction transmitter substance is acetylcholine which is broken down in the junction by cholinesterase. This disease is caused by under production of acetylcholine or over production of cholinesterase.
• cause is unknown
• symptoms are weakness of muscles
• may progress to death from respiratory paralysis
• treatment is with anticholinesterase drugs

Question 16

Red vs White Muscle (Where,Differences)

Answer 16

A. Skeletal muscles tend to differ in color (e.g. white or dark meat)

B. Red Muscle

1. more and larger mitochondria
2. higher concentration of myoglobin
3. designed for greater metabolic activity
4. contract now "slowly" have greater endurance

C. White muscle

1. fewer and smaller mitochondria
2. little myoglobin
3. designed for faster and less prolonged contraction

D. While in birds white and red muscle fibers are largely segregated (i.e. light and dark meat), in mammals almost all skeletal muscles are a combination of the above two types of fibers (example: you don’t ask for light or dark meat when eating beef)
- however, variable proportions of fibers may differ in different muscles

Question 17

Cardiac Muscle (6 details)

Answer 17

A. striated involuntary muscle
B. found only in the heart
C. behaves similarly to a syncitium
D. cardiac muscle has an inherent beat and if not stimulated will discharge its own membrane potential every time it builds up.
E. cardiac muscle has a much longer period of contraction than skeletal muscle - thus a much longer refractory period. Refractory period lasts until muscle is relaxed - thus tetanus is not possible.
F. Cell
1. each cardiac muscle cell has a centrally located single nucleus
2. rather than being parallel - the fibers freely branch and communicate with each other via intercalated discs.

Question 18

Smooth Muscle (8 details)

Answer 18

A. involuntary muscle
B. within most of the bodies organs
C. not striated
D. spindle shaped
E. a single centrally located nucleus
F. contain actin and myosin - but not arranged in sarcomere
G. under control of ANS
H. two kinds:
1. visceral - forms walls of hollow organs
- fibers bound tightly together
- like cardiac muscle, impulse travels from cell to cell (functional syncitium)
2. multiunit - individual-fibers each with its own motor-nerve junction
- stimulation will cause contraction only of fiber directly stimulated.
- found in walls of blood vessels and arrector pili muscles and iris of the eye.