Muscle Physiology

Question 1

describe muscles in a simple manner

Answer 1

excitable tissues (like neurons)

Question 2

how does the action potential affect muscles

Answer 2

induces contractions to generate force for movement

Question 3

what are the types of muscles

Answer 3

• smooth
• cardiac
• skeletal

Question 4

what are the main parts of a skeletal muscle structure

Answer 4

• tendons
• epimysium
• fascicles
• perimysium
• muscle fibres
• endomysium

Question 5

describe tendons

Answer 5

thick connective tissue that connects to bones

Question 6

describe epimysium

Answer 6

• continuation of tendon
• thin outer covering of entire muscle

Question 7

describe fascicles

Answer 7

bundles of muscle fibres

Question 8

describe perimysium

Answer 8

covering of fascicle

Question 9

describe muscle fibres

Answer 9

= muscle cells

Question 10

describe endomysium

Answer 10

covering of muscle fibres

Question 11

what is gross muscle made of

Answer 11

bundles of fascicles

Question 12

what are the main components of a muscle fibre

Answer 12

• sarcolemma
• sarcoplasm
• sarcoplasmic reticulum
• transverse (T) tubules
• (multi)nuclei

Question 13

describe the sarcolemma

Answer 13

muscle plasma membrane

Question 14

describe the sarcoplasm; what does it consist of

Answer 14

muscle cell cytoplasm; consists of mitochondria and myofibrils

Question 15

describe the sarcoplasmic reticulum; what does it consist of

Answer 15

muscle ER; consists of lateral sacs/terminal cisternae

Question 16

what is a triad and what does it do

Answer 16

1 t-tubule in middle and 2 terminal cisternae at ends (swelling), which plays a role with propagating AP leading to muscle contraction

Question 17

draw out the structure of sarcolemma to triad

Answer 17

…..

Question 18

draw out the components of a muscle fibre

Answer 18

…..

Question 19

draw out the skeletal muscle structure

Answer 19

…..

Question 20

how do the SR and terminal cisternae work together

Answer 20

calcium pumps on SR membrane which allows for active transport of calcium ions into SR for storage in TC

Question 21

how do SR and T-tubules work together

Answer 21

activate muscle contractions (propagating AP); transmit signals from sarcolemma to myofibrils

Question 22

describe myofibrils; what protein fibres does it contain

Answer 22

lowest level of bundles (molecular level) and contains actin and myosin protein fibres

Question 23

describe the functional unit of myofibril

Answer 23

sarcomere; has A and I bands, M and Z (start and end) lines, H zone

Question 24

describe the arrangement of muscle that makes it look the way it does

Answer 24

thick and thin filaments arranged in a manner that gives stripey appearance

Question 25

what type of a filament is myosin; actin?

Answer 25

thick; thin

Question 26

draw out a myofibril

Answer 26

....

Question 27

what is the Z-line

Answer 27

the area where thin filaments are held together (edge of sarcomere)

Question 28

what is the M-line

Answer 28

middle of sarcomere where thick filaments are linked together

Question 29

what is the I-band

Answer 29

area of sarcomere with only thin filaments (light in colour)

Question 30

what is the H-zone

Answer 30

area of sarcomere with only thick filaments

Question 31

what is the A-band

Answer 31

area of sarcomere with mainly thick filaments with overlap of thin filaments at edges (dark in colour)

Question 32

what are the main parts of thin filament structure

Answer 32

G-actin with binding site making actin protein making F-actin making thin filament

Question 33

what are the regulatory proteins of the thin filaments

Answer 33

tropomyosin, troponin

Question 34

what is the role of tropomyosin

Answer 34

overlaps myosin binding sites on actin

Question 35

what is the role of troponin

Answer 35

complex of 3 proteins; attaches to actin and tropomyosin which then binds Ca (reversibly) and allows for regulation of skeletal muscle contraction

Question 36

describe the thin filament structure shape

Answer 36

double stranded, helical/twining

Question 37

describe the thick filament structure shape

Answer 37

many hockey stick structures bound together, each end of hockey stick is myosin head binding site (crossbridge)

Question 38

what do the myosin heads bind for

Answer 38

actin and ATPase

Question 39

draw flow of main parts of sarcomere structure at the molecular level

Answer 39

z-line -> titin -> thick and thin filaments overlapped -> z-line

Question 40

what is titin

Answer 40

- elastic and structurally supportive protein - when muscle contracts and expands, titin produces elastic force allowing sarcomere to stretch and return back to shape

Question 41

list the mechanisms of generating force in muscles

Answer 41

- sliding filament model - crossbridge cycle - excitation-contraction coupling

Question 42

describe the sliding filament model

Answer 42

- thin and thick filaments overlap - slide past e/o - individual filaments do not shorten but appearance turns short of muscle

Question 43

how does sliding happen

Answer 43

cyclical formation and breaking of crossbridges

Question 44

describe the steps of crossbridge cycle

Answer 44

- myosin head goes through conformation change due to ATP hydrolysis - cyclic binding/unbinding of crossbridges to thin filaments - results in thin filaments moving toward M line of sarcomere

Question 45

the crossbridge cycle alters the energy content of myosin molecules. describe the energy forms

Answer 45

- high energy: ADP + P bound to myosin so it stores energy (high affinity for actin) - low energy: ATP bound to myosin (low affinity for actin)

Question 46

draw out the crossbridge cycle

Answer 46

.....

Question 47

why are crossbridges out of sync but go through the cycle simultaneously

Answer 47

to allow for gradual movement

Question 48

what would happen if crossbridges were in sync

Answer 48

inefficient use/generation of power

Question 49

describe excitation-contraction coupling

Answer 49

- explains how muscle contractions turn on and off - sequence of events where an AP in the sarcolemma cause contraction - dependent on neural input from motor neuron - requires Ca release from SR

Question 50

describe the role of the neuromuscular junction

Answer 50

- nerves and muscle fibres meet here - essential synapse for muscle contraction and movement - motor neuron innervates several muscle cells which releases acetylcholine - potential generated in end plate to trigger AP in muscle cell

Question 51

motor neuron AP ______ creates muscle cell AP

Answer 51

always

Question 52

what are the roles of Ca, troponin and tropomyosin in excitation-contraction coupling

Answer 52

- low/no Ca: troponin holds tropomyosin over myosin binding sites on actin - Ca present: binds to troponin causing movement of troponin then tropomyosin and exposes binding sites for myosin on actin - cycle occurs and muscle contracts

Question 53

draw a diagram of excitation-contraction coupling

Answer 53

....

Question 54

what are the receptors and releases that cause AP in T-tubule membrane to lead to calcium release from SR membrane

Answer 54

- DHP and ryanodine receptors - calcium-induced calcium release

Question 55

draw gating of SR calcium channels before and after AP

Answer 55

....