MIDTERM 2

Question 1

what is the primary function of muscle tissue and what are the 3 types of muscle tissue?

Answer 1

primary function: generation of force - creates movement, maintains posture, stabilizes joints, etc…
3 types of muscle tissue:
1. skeletal muscle
2. cardiac muscle
3. smooth muscle

Question 2

Describe Skeletal Muscle Tissue

Answer 2

• made up of long, multi-nucleated cells arranged parallel to one another
• extend nearly the entire length of the muscle
• contractions are voluntary (conscious thought)
• most are attached by connective tissue to skeleton - contraction can produce movement of a body part

Question 3

describe cardiac muscle tissue

Answer 3

• short and highly branched with one nucleus
• intercalated discs join adjacent cells together
  
  • contain gap junctions and desmosomes (modified tight junctions)
  • unite cells and permit coordination of contraction
• contraction is involuntary (unconscious)
• synchronous contraction of many fibers produces the force for the heart pump

Question 4

describe smooth muscle tissue

Answer 4

• no striations
• long and flat with pointed ends - spindle shaped
• single centrally located nucleus
• line most hollow organs - also eye, skin, and some glandular ducts
• involuntary contractions
• many linked to one another by gap junctions - allows for synchronized contraction

Question 5

what is a fascicle and what does its arrangement influence

Answer 5

a bundle of muscle fibers within a skeletal muscle - the arrangement of muscle fascicles impacts the function of the muscle

Question 6

describe the structure of the skeletal muscle fiber

Answer 6

fibers are thin cylinders
- lengths up to 30 centimeters
- thickness up to 100 micrometers

Question 7

define myofibrils

Answer 7

the most abundant organelle of muscle fibers - made up of mostly contractile proteins

Question 8

define the sarcoplasmic reticulum (SR)

Answer 8

surrounds myofibrils - stores and releases calcium ions (required for contraction)

Question 9

define transverse tubules (T-tubules)

Answer 9

deep inward extensions of sarcolemma - surround each myofibril
- form tunnel-like network within muscle fibers
- continuous with exterior of cell - filled with extracellular fluid

Question 10

define terminal cisternae

Answer 10

enlarged sections of SR - flank each T-tubule
two terminal cisternae plus corresponding t-tubule form a triad mitochondria

Question 11

name the three types of myofilaments

Answer 11

thick filaments
thin filaments
elastic filaments

Answer 12

thick filaments: composed of bundles of contractile protein myosin
- globular heads at each end linked by intertwining tails
- heads are connected to tails by a hinge-like neck
- each head has an active site that binds with actin
- myosin tails from opposite sides are anchored together at the M-line

Question 13

Thin filaments – Composed of actin, tropomyosin, and troponin
Define Actin

Answer 13

• multiple actin subunits string together and form two intertwining strands in a functional thin filament
• each bead-shaped actin has an active site - binds with myosin heads

Question 14

Define tropomyosin

Answer 14

long, rope-like regulatory protein; twists around actin, covering up active sites

Question 15

define troponin

Answer 15

small globular regulatory protein; holds tropomyosin in place; assists with turning contractions on and off.

Question 16

define the sarcomere

Answer 16

the smallest functional unit of a skeletal muscle fiber

Question 17

I band

Answer 17

only thin filaments

Question 18

z disc

Answer 18

in the middle of the I band - composed of structural proteins that:
- anchor thin filaments in place and to one another
- serve as attachment points for elastic filaments
- attach sarcomeres to one another across entire diameter of muscle fiber

Question 19

A band

Answer 19

contains a zone of overlap, with both thick and thin filaments - generates tension during contraction

Question 20

H zone

Answer 20

middle of A band where only thick filaments exist

Question 21

M line

Answer 21

dark line in middle of A band - structural proteins hold thick filaments in place - serve as an anchoring point for elastic filaments

Question 22

How does a sarcomere extend

Answer 22

from one z-disc to the next and it is the functional unit of contraction

Question 23

describe the sliding filament mechanism

Answer 23

it reflects the tension generation during muscle contraction
- myosin heads attach to actin -> pull thin filaments towards the M line -> brings the z-discs closer together (shorten sarcomere)
- both I band and H zone narrow
- A band remains unchanged

sarcomeres are arranged end to end within each myofibril - during contraction, they shorten whole muscle fiber

Question 24

define crossbridge formation

Answer 24

when myosin and actin are bound to each other

Question 25

define crossbridge cycling

Answer 25

the on and off interaction between myosin and actin that pulls thin filaments towards the M line

Question 26

list the steps with descriptions of the cross-bridge cycle

Answer 26

ATP Hydrolysis: myosin head becomes cocked once ATP is bound and energy is gathered through ATP hydrolysis
Crossbridge formation: myosin binds to actin at a 90° angle relative to the thick filament
Power stroke: ADP and Pi are released from myosin. This causes myosin to pull actin toward the M line as it pivots to a relaxed position. Crossbridge is at a 45° angle relative to thick filament
Detachment: another ATP binds to myosin, breaking the attachment to actin.

Question 27

Describe the contraction cycle

Answer 27

may repeat as long as a stimulus to contract continues and ATP is available
- myosin head re-cocked, binds to first actin molecule, and power stroke repeats
- myosin binds to second actin, and so on, over and over
- for average contraction, process will repeat about 20-40 times for each myosin head in each sarcomere