Lecture 18- Skeletal muscle

Question 1

what is skeletal muscle controlled by?

Answer 1

neurons in the CNS

Question 2

what two neurons in the CNS is skeletal muscle controlled by?

Answer 2

upper motor neurons
lower motor neurons

Question 3

what do upper motor neurons do?

Answer 3

in the motor cortex, synapse on motor neurons in the spinal cord

Question 4

what do lower motor neurons do?

Answer 4

in spinal cord, send axons out the ventral roots and make synapses on muscle cells

Question 5

what is the synapse between the lower motor neurons and muscle cell called?

Answer 5

neuromuscular junction (NMJ)

Question 6

what is the neuromuscular junction synapse like in comparison to a central synapse?

Answer 6

NMJ is a huge synapse (20000 times larger)

Question 7

what is the difference between central synapse postsynaptic membrane and NMJ postsynaptic membrane?

Answer 7

NMJ membrane is highly highly folded and has many nicotinic acetylcholine receptors and Na+ channels. its very folded to increase SA. they also always cause an AP in the postsynaptic muscle cell (because such a large synapse)

Question 8

what is the group of muscle cells controlled by a lower motor neuron called?

Answer 8

motor unit

Question 9

what is a motor unit?

Answer 9

one motor neuron and all of the muscle cells it controls

Question 10

what are the two different ways a motor unit will stimulate other muscle cells?

Answer 10

can stimulate only one muscle cell
can stimulate many (with big muscles)

Question 11

how many synapses does the muscle cell receive?

Answer 11

ONE

Question 12

what is the structure like in skeletal muscles?

Answer 12

consists of a number of muscle fibers lying parallel to one another and held together by connective tissue

Question 13

what is a single skeletal muscle cell known as?

Answer 13

muscle fiber

Question 14

what are 3 descriptors used to describe skeletal muscles structure?

Answer 14

multinucleated
large, elongated and cylindrically shaped
fibers usually extend the entire length of muscle

Question 15

what is a muscle fascicle and what is it surrounded by?

Answer 15

bundle of fibers surrounded by connective tissue (gives the muscle physical strength

Question 16

what is the sarcolemma?

Answer 16

cell membrane of a muscle cell

Question 17

what are T- tubules?

Answer 17

network of tubes that go through muscle cell (continuous with the outside)

Question 18

what is the sarcoplasmic reticulum?

Answer 18

storage bag for calcium

Question 19

what is the myofibril?

Answer 19

basic unit of muscle contraction made of sarcomere

Question 20

what is the sarcomere made of?

Answer 20

Z disks (zig zag)

Question 21

what is the M line?

Answer 21

middle line

Question 22

what are two filaments the myofibril is made of?

Answer 22

thick filaments
thin filaments

Question 23

what are thick filaments made of?

Answer 23

myosin molecule (myosin heads, myosin tail)

Question 24

what are thin filaments made of?

Answer 24

actin chain (troponin, nebulin, tropomyosin, G-actin molecule)

Question 25

describe the structure of thick filaments

Answer 25

shaped like golf club
tail ends are intertwined around each other and oriented toward center
globular heads project out at one end and form cross bridges with actin chain

Question 26

myosin head has two important sites critical to contractile process, what are they?

Answer 26

actin binding site
myosin ATPase (hydrolyses atp to use it for energy)

Question 27

what is G- actin?

Answer 27

globular actin that is spherical but assembles into long chains

Question 28

what does the actin have as apart of its structure to attach to myosin creating cross bridging formation?

Answer 28

binding site to attach to myosin head

Question 29

what kinds of proteins are tropomyosin and troponin?

Answer 29

regulatory proteins

Question 30

what is tropomyosin?

Answer 30

thread like molecules that interact with actin along its spiral groove

Question 31

what is the function of tropomyosin binding sites?

Answer 31

cover myosin binding sites (thus protecting actin)

Question 32

troponin is made of 3 polypeptide units, what are they? what do they bind to?

Answer 32

one binds to tropomyosin
one binds to actin
one can bind with Ca++

Question 33

what does troponin do when not bound to calcium?

Answer 33

stabilizes tropomyosin in blocking position over actins cross bridge binding sites

Question 34

what happens when troponin binds to calcium?

Answer 34

1. tropomyosin moves away from blocking position
2. actin and myosin bind and interact
3. creates cross bridges

Question 35

what connects the thick and thin filaments together?

Answer 35

titin (joins M- lines to Z lines at opposite ends of sarcomere)

Question 36

what are the two important roles of titin?

Answer 36

stabilize position of thick filaments in relation to thin filaments
improves muscles elasticity

Question 37

where is the I band located?

Answer 37

between A bonds

Question 38

function of nebulin

Answer 38

aligns actin filaments

Question 39

function of myomesin

Answer 39

M- line (middle line)

Question 40

what happens when actin and myosin slide past each other?

Answer 40

muscle shortens (contracts), the A band doesnt move but the Z disks slide into A band interconnecting them stronger

Question 41

what is the process of initiating contraction? 5

Answer 41

1. Ca++ levels increase in cytosol
2. Ca++ binds to troponin
3. tropomyosin shits exposing binding site on actin
4. myosin binds strongly to actin and completes power stroke
5. actin filament moves

Question 42

what is a power stroke?

Answer 42

cross bridge bends, pulling thin myofilament inward

Question 43

do actin and myosin contract?

Answer 43

NO

Question 44

myosin is properly called a motor protein, what is that?

Answer 44

a protein that hydrolyzes ATP to convert chemical energy to carry out mechanical work

Question 45

what does the binding of calcium do?

Answer 45

shortens sarcoma