11.7 muscular system

Question 1

protozoa and amoeba

Answer 1

move via power stroke, recovery stroke and amoeba move via pseudopodia

Question 2

flatworms

Answer 2

hydrostatic skeleton. with longitude and circle muscles. contraction moves it

Question 3

annelids

Answer 3

hydro skeleton but also setae, and peristalsis

Question 4

Skeletal muscle structure

Answer 4

(striated muscle) – voluntary movement, fibers are multinucleated cells
- made of myofibrils, sarcomeres, sarcoplasmic reticulum, etc.

Question 5

Myofibrils

Answer 5

filaments divided into sarcomeres

Question 6

Sarcomeres

Answer 6

– individual contractile units separated by a border (Z-line)

Question 7

Sarcoplasmic reticulum

Answer 7

– stores Ca2+; surrounds myofibrils

Question 8

Sarcoplasm

Answer 8

cytoplasm

Question 9

Sarcolemma

Answer 9

– plasma membrane of muscle cells; can propagate action potential

i. Invaginated by T-tubules- channels for ion flow
ii. Wraps several myofibrils together to form a muscle cell/muscle fiber

Question 10

Mitochondria

Answer 10

present in large amounts in myofibrils

Question 11

sarcomere structure

Answer 11

actin thin filaments, myosin thick filaments
- Z line – boundary of a single sarcomere; anchor thin filaments
- M line – center of sarcomere
- I band – region containing thin filaments (actin) only (on ends, only purple above)
- H zone – region containing thick filaments (myosin) only (in middle, only green above)
- A band – actin and myosin overlapping (one end of overlap to the other end of overlap)
o H and I reduce during contraction, while A does NOT
- Note: striations are the result of alternating thin actin + thick myosin (I bands and A bands)

Question 12

contraction

Answer 12

1. Action potential of neuron releases acetylcholine when meets neuromuscular jxn
2. Action potential then generated on sarcolemma and throughout T-tubules
3. Sarcoplasmic reticulum releases Ca2+
4. Myosin cross bridges form – result of Ca2+ binding to troponin on actin helix
   Note: at the end of each contraction cycle, Ca2+ is actively pumped back into the sarcoplasmic reticulum

Question 13

sliding filament model of contraction

Answer 13

ATP binds to myosin head. myosin and actin unbind, then mysin head is cocked back.

2. Ca+ exposes binding sites on actin. binds troponin and pulls back tropomyosin
3. cross bridges between myosin and actin forms
4. ADP is released, sliding motion of actin brings z lines together
5. new ATp attaches, and myosin bridges unbind

Question 14

strength of muscle contraction

Answer 14

single muscle fiber cannot be increase, but strength of overall contraction
can be increased by recruiting more muscle fibres

Question 15

Motor unit:

Answer 15

the neuron + muscle fibers it innervates. Each muscle fiber (cell) forms synapses with only
one motor neuron, but each motor neuron typically synapses with many muscle fibers.

Question 16

recruitment

Answer 16

when a greater quantity of muscle fibers are activated by the
brain rather than an increase in frequency of action potentials that stimulate muscle fiber contraction. used for slow to fast twitch

Question 17

small vs large motor units

Answer 17

Intricate movements tend to use smaller motor units (e.g. finger), whereas muscles requiring greater
force (e.g. back) have larger motor units.

Question 18

simple twitch

Answer 18

response of a single muscle fiber to brief stimulus; latent, contraction, relax
1. Latent period – time between stimulation and onset of contraction; lag
o Action potential spreads on sarcolemma and Ca2+ ions released
2. Contraction
3. Relaxation (absolute refractory period) – unresponsive to stimulus

Question 19

summation

Answer 19

– contractions combine and become stronger and more prolonged
(repeated APs summate)

Question 20

tetanus

Answer 20

continuous sustained contraction; muscle cannot relax; will release if maintained (in tetanus, rate of muscle stimulation so fast that twitches blur into one
smooth constant)

Question 21

tonus

Answer 21

state of partial contraction; muscle never completely relaxed

Question 22

Subthreshold:

Answer 22

no motor units respond

Question 23

Threshold:

Answer 23

one motor unit responds.

Question 24

Submaximal:

Answer 24

increasing #’s of motor units respond.

Question 25

Maximal:

Answer 25

all motor units respond.

Question 26

Supramaximal:

Answer 26

all motor units respond.
- Speed and amplitude remain constant during an action potential. As stimulus intensity increases, the # of AP’s goes up.

Question 27

Type I: Skeletal muscle

Answer 27

slow-twitch, lots of myoglobin, lots of mitochondria, aerobic endurance [they split ATP at a slow
rate, result: slow to fatigue but slow contraction velocity. Appear red, small in diameter.

Question 28

Type IIA: skeletal muscle

Answer 28

IIA: fast-twitch, endurance by not as much as type 1 (can use aerobic + anaerobic equally) [split
ATP at high rate: contract rapidly]. Lots of myoglobin. Resistant to fatigue but not as much as Type 1.
Appear red to pink, intermediate in diameter.

Question 29

Type IIB: skeletal muscle

Answer 29

IIB: fast-twitch, low myoglobin, lots of glycogen, generate power. Few myoglobin, use glycolysis
(anaerobic primarily). Split ATP at a fast rate. Appear white, large in diameter.

Question 30

(hyperplasia)

Answer 30

increase in size adult muscle

Question 31

(hypertrophy)

Answer 31

which sees an increase in: diameter of muscle

fibers, # of sarcomeres and mitochondria, sarcomere length adult muscle

Question 32

smooth muscle

Answer 32

involuntary. one nucleus no striation, autonomic NS. slow to contract.

Thick & thin filaments attached to IFs, contract
IF’s pull dense bodies together. smooth muscle length shrinks.
* no sarcomere org

Question 33

Single-unit: Smooth Muscle

Answer 33

visceral, connected by gap jxns, contract as single unit (stomach uterus,
urinary bladder)

Question 34

Multiunit: Smooth Muscle

Answer 34

each fiber directly attached to neuron; can contract independently (iris, bronchioles, etc)

Question 35

Note: smooth muscle does not have

Answer 35

T-tubules, striations, troponin, or tropomyosin. It instead

uses myosin light change kinase to overcome lack of troponin.

Question 36

Cardiac Muscle

Answer 36

striated, one or two central nuclei; cells separated by
intercalated discs that have gap jxn to allow AP’s to chain flow via electrical synapse; involuntary; lots of
mitochondria. Grows by hypertrophy.

Question 37

Both smooth and cardiac muscle are ____

Answer 37

myogenic – capable of contracting without stimuli from nerve cells