Musculoskeletal System: Muscular System (HY)

Question 1

what are the three types of muscle?

Answer 1

1. skeletal muscle
2. smooth muscle
3. cardiac muscle

Question 2

what is the difference between red/slow-twitch fibers and white/fast-twitch fibers?

1. reasoning for color
2. rate of contraction and fatigue

Answer 2

1. red fibers have high myoglobin content, a red color, and many mitochondria for oxidative phosphorylation for aerobic energy consumption.
   white fibers have lower myoglobin content and a white color.
2. red fibers: slower contraction, sustained activity
   white fibers: faster contraction, faster fatigue

Question 3

what are two types of fibers within skeletal muscle?

Answer 3

1. red/slow-twitch fibers

2. white/fast-twitch fibers

Question 4

what is myogenic activity?

Answer 4

when muscle cells (myocytes) initiate their own contraction without nervous system input or another external signal

Question 5

what types of muscles exhibit myogenic activity?

Answer 5

1. smooth muscle

2. cardiac muscle

Question 6

what is a tonus state of muscle?

Answer 6

constant state of low-level contraction

Question 7

is smooth muscle or skeletal muscle able to undergo more sustained contractions?

Answer 7

smooth muscle

Question 8

what are cardiac muscle cells connected?

Answer 8

connected by intercalated discs that contain gap junctions connecting cytoplasms of adjacent cells for ion flow

Question 9

what does the vagus nerve do to heart rate?

Answer 9

slows heart rate

associated with parasympathetic nervous system

Question 10

what do norepinephrine and epinephrine (aka. adrenaline) do to heart rate?

Answer 10

both increase heart rate by binding to adrenergic receptors
(sympathetic nervous system)

epinephrine increases intracellular calcium levels in cardiac myocytes

Question 11

For the three types of muscles, list the following: striation, in/voluntary, innervation type, # nuclei per cell, Ca2+ req?

Answer 11

skeletal muscle: striated, voluntary, somatic innervation, multiple nuclei, requires Ca2+

smooth muscle: nonstriated, involuntary, autonomic innervation, 1 nucleus, requires Ca2+

cardiac muscle: striated, involuntary, autonomic innervation, 1-2 nuclei, requires Ca2+

Question 12

identify the following lines, bands, and zone of the sarcomere: Z-line, M-line, H-zone, I-band, A-band

Answer 12

Z-line: boundaries of sarcomere
M-line: cuts through middle of sarcomere and myosin filaments
H-zone: contains only thick filaments
I-band: contains only thin filaments
A-band: contains all of the thick filaments even when they overlap with thin filaments

Question 13

during contraction, what happens to the distance between Z-lines and M-lines and the size of the I-band, H-zone, and A-band?

Answer 13

Distance between Z-lines and M-lines decreases
Size of I-band and H-zone deccreases
Size of A-band stays the same

Question 14

what are thick filaments made of?

Answer 14

myosin

Question 15

what are thin filaments made of?

Answer 15

actin, troponin, and tropomyosin

Question 16

what is the function of troponin and tropomyosin?

Answer 16

troponin and tropomyosin are bound to one anotehr and regulate interaction between actin and myosin

Question 17

what is the function of titin in the sarcomere?

Answer 17

prevents excessive stretching by anchoring actin and myosin filaments together

Question 18

what are myofibrils?

Answer 18

sarcomeres attached end-to-end

Question 19

what is the sarcoplasmic reticulum?

Answer 19

a modified endoplasmic reticulum that surrounds myofibrils and contains a high concentration of Ca2+

Question 20

what is the sarcolemma?

Answer 20

cell membrane of a myocyte that can propagate action potentials

Question 21

what are transverse tubules (T-tubules)?

Answer 21

system of tubules perpendicular to myofibrils that can distribution actin potential from sarcolemma to sarcoplasmic reticulum

Question 22

what’s the order of muscle structure starting with sarcomeres?

Answer 22

sarcomeres –> myofibrils –> myocytes/muscle cell/muscle fiber –> muscle

Question 23

What are the three stages of muscle contraction?

Answer 23

1. initiation
2. shortening of the sarcomere
3. relaxation

Question 24

what occurs during initiation of muscle contraction?

Answer 24

1. motor/efferent neuron sends a signal to the neuromuscular junction
2. acetylcholine is released from the nerve terminal and binds to receptors on sarcolemma, causing depolarization
3. depolarization triggers action potential through sarcolemma, through T-tubules, and then sarcoplasmic reticulum
4. Ca2+ release upon action potential reaching sarcoplasmic reticulum
5. Ca2+ binds to troponin –> conformational change of tropomyosin
6. myosin-binding sites on actin thin filament become exposed

Question 25

what is the motor end plate?

Answer 25

another name for the nerve/axon terminal specifically in the neuromuscular junction

Question 26

what is a motor unit?

Answer 26

a nerve terminal + the group of myocytes that the nerve terminal controls

Question 27

what are the four steps of the actin-myosin cross-bridge cycle that allows for shortening of the sarcomere?

Answer 27

1. Resting stage: ADP+Pi bound to myosin 2. Ca2+ binding: Ca2+ binds to troponin, myosin binds to actin 3. Powerstroke: ADP+Pi dissociation from myosin provides energy for powerstroke/sarcomere contraction/actin filament sliding over myosin filament 4. ATP stage: ATP binding to myosin leads to myosin dissociation from actin; ATP hydrolysis leads to recocking of myosin head

Question 28

what is the sliding filament model?

Answer 28

sequential shortening of the sarcomere due to repetitive binding and release of myosin head this is what actually occurs in muscle contraction

Question 29

what enzyme degrades acetylcholine in the neuromuscular junction during muscle relaxation?

Answer 29

acetylcholinesterase

Question 30

what happens during muscle relaxation?

Answer 30

1. signal termination due to acetylcholine degradation by aceylcholinesterase 2. sarcolemma repolarizes 3. calcium release stops 4. sarcoplasmic reticulusm takes up calcium from sarcoplasm, controlling intracellular calcium contraction and preventing excessive contraction 5. ATP binds to myosin heads, dissociating myosin from actin and allowing sarcomere to return to original width

Question 31

what is simple twitch? what are its three periods?

Answer 31

response of a single muscle fiber to a brief stimulus at/above threshold 1. latent period 2. contraction period 3. relaxation period

Question 32

what is the latent period of simple twitch?

Answer 32

time between stimuli reaching threshold value and muscle contraction during this time, action potential goes through muscle and calcium is released from sarcoplasmic reticulum

Question 33

what happens during (frequency) summation?

Answer 33

frequent and prolonged stimulation --> insufficient time to relax --> contractions combine, becoming stronger and more prolonged

Question 34

what is tetanus, the physiological phenomenon?

Answer 34

when contractions become so frequent that muscles cannot relax

Question 35

what is oxygen debt?

Answer 35

= the difference between amount of oxygen needed by muscles and the amount of oxygen available = the amount of oxygen needed to convert lactic acid back into pyruvate

Question 36

what are two supplemental energy reserves in muscles in addition to oxidative phosphorylation in mitochondria of red/slow-twich fibers?

Answer 36

1. creatine phosphate + ADP --> ATP + creatine | 2. glycolysis + fermentation to make ATP

Question 37

How does creatine phosphate help with energy production in muscles?

Answer 37

during rest, ATP transfers a phosphate group to creatine to produce creatine phosphate and ADP. when needed, this reaction is reversed to generate ATP from ADP.

Question 38

when does muscle fatigue occur?

Answer 38

insuffient oxygen supply --> anaerobic metabolism: glycolysis+fermentation --> lactic acid this occurs during times of high exercise or prolonged tetanus