Muscles Part 1

Question 1

sarcolemma

Answer 1

similar to cell membrane

Question 2

sarcoplasm

Answer 2

similar to cytoplasm

Question 3

sarcoplasmic reticulum

Answer 3

similar to smooth ER; stores calcium and regulates its release

Question 4

4 features of sarcolemma

Answer 4

1. phospholipid bilayer with proteins and carbs
2. semi-permeable
3. resting membrane potential
4. invaginations called t-tubules

Question 5

function of t-tubules

Answer 5

delivers the signal for the muscle contraction into the interior of the muscle fiber

Question 6

resting membrane potential

Answer 6

at rest the outside of the sarcolemma has a net positive charge and the inside has a net negative charge (-95 mV)

Question 7

what are the 2 reasons for the RMP

Answer 7

1. sodium-potassium pump

2. potassium leak channels

Question 8

how does the Na+/K+ pump contribute to the cell’s RMP

Answer 8

it uses ATP to pump 3 Na+ out and 2 K+ in which puts more positive ions outside the cell

Question 9

how does the K+ leak channel contribute to the cell’s RMP

Answer 9

a lot of K+ ions leak through to the outside of the cell increasing the positive charge outside

Question 10

what ions contribute to the negative charge inside the sarcolemma

Answer 10

proteins and Cl-

Question 11

terminal cisternae

Answer 11

sacks formed on both sides of t-tubules out of SR that store Ca^2+

Question 12

myofibril

Answer 12

cylindrical organelles that extend the entire length of the muscle fiber;
a bundle of thick and thin filaments arranged in a way to be able to form a contraction

Question 13

basic components of thick myosin

Answer 13

2 intertwined strands with a globular head and elongated tail; heads have actin and ATP binding sites

Question 14

what is thin actin composed of

Answer 14

2 strands of globular subunits (G-actin), each with a myosin binding site

Question 15

troponin

Answer 15

a regulatory protein attached to tropomyosin which contains a binding site for Ca^2+

Question 16

tropomyosin

Answer 16

a twisted regulatory protein that covers myosin binding sites in resting muscles

Question 17

I bands

Answer 17

extends from both directions of Z disc; contains only thin filaments

Question 18

A band

Answer 18

central region of sarcomere containing thick and thin filaments

Question 19

H zone

Answer 19

central portion of A band containing only thick filaments

Question 20

M line

Answer 20

protein disk in middle of H zone, connects thick filaments

Question 21

Z disc

Answer 21

z line to z line is one sarcomere

Question 22

which bands/zones disappear during max contraction

Answer 22

I band and H zone

Question 23

motor unit

Answer 23

single motor neuron and the fibers it controls

Question 24

neuromuscular junction

Answer 24

location where motor neuron innervates a cell

Question 25

synapse

Answer 25

place of contact of a neuron with another cell

Question 26

how does an electrical impulse travel through a cell

Answer 26

turns electrical signal into a chemical signal into the cell then turned back into electrical signal throughout the cell

Question 27

motor neuron

Answer 27

sends the signal to initiate a contraction of skeletal muscle

Question 28

3 components of neuromuscular junction

Answer 28

1. synaptic knob
2. motor end plate
3. synaptic cleft

Question 29

synaptic knob

Answer 29

the expanded tip of the neuron which houses synaptic vesicles filled with neurotransmitter ACh

Question 30

motor end plate

Answer 30

specialized region of sarcolemma with lots of folds and lots of ACh receptors

Question 31

synaptic cleft

Answer 31

separates synaptic knob and motor end plate

Question 32

what are the 3 steps of muscle contraction

Answer 32

1. excitation of skeletal muscle fiber
2. excitation-contraction coupling
3. crossbridge cycling

Question 33

basic steps of excitation

Answer 33

1. nerve signal triggers entry of Ca^2+ into synaptic knob through voltage-gated channels
2. Ca^2+ triggers release of ACh vesicles into synaptic cleft
3. ACh diffuses across cleft and binds with ACh receptors at motor end plate

Question 34

basic steps of coupling

Answer 34

1. binding of ACh opens chemically-gated Na+ channels
2. inflow of Na+ causes reversal of charges across sarcolemma
3. altered MP triggers opening of voltage-gated Na+ channels
4. inflow of Na+ causes reversal of charges across sarcolemma which opens the next channel and so on along the sarcolemma into t-tubules
5. when ATP enters t-tubules it triggers opening of voltage-gated Ca^2+ channels in the terminal cisternae
6. Ca^2+ diffuses into sarcoplasm and reaches sarcomeres

Question 35

what is the threshold to open the voltage gated channels

Answer 35

-55 mV

Question 36

what is a muscle impulse

Answer 36

the consecutive opening of voltage-gated Na+ channels along the sarcolemma and into t-tubules

Question 37

basic steps of contraction

Answer 37

1. Ca^2+ binds to troponin which shifts tropomyosin and exposes the myosin binding site
2. myosin is preset with an ATP that is has already cleaved, so it binds to actin molecule creating a cross-bridge
3. actin binding causes Pi to be released and a conformational change in myosin leads to a power stroke
4. the ADP is released and a new ATP comes which releases the crossbridge and resets myosin

Question 38

power stroke

Answer 38

sliding of thin filament toward center of A band