skeletal muscle

Question 1

muscle fiber

Answer 1

synonym for muscle cell

Question 2

sarcolemma

Answer 2

the plasma membrane of a skeletal muscle fiber that encloses cytoplasm (sarcoplasm)

Question 3

associated with (immediately outside of) the sarcolemma is a coat of polycaccharide material in which are embedded collagen fibrils that at the fiber’s ends, fuse with the ____ of the muscle

Answer 3

tendon

Question 4

a muscle is composed of subunits called

Answer 4

fasciculi

Question 5

each fasciculus is a bundle of

Answer 5

cells

Question 6

each muscle fiber is a bundle of

Answer 6

myofibrils

Question 7

sarcomere

Answer 7

the portion of a myofibril between two adjacent Z-discs

Question 8

thick filament

Answer 8

myosin

Question 9

thin filament

Answer 9

actin

Question 10

each sarcomere is composed of several thousand myofilaments called _____ filaments and _____ filaments

Answer 10

actin

myosin

Question 11

each myosin filament is made of many myosin molecules; each myosin molecule has a tail or body (that includes two arms) and two

Answer 11

heads

Question 12

what three proteins make up actin filaments

Answer 12

F-actin

tropomyosin

troponin complex

Question 13

F-actin:

Answer 13

the helical backbone of the actin filament; contains many “active sites” (binding sites for myosin)

Question 14

tropomyosin

Answer 14

lies atop F-actin and covers up the active sites when contraction is not desired

Question 15

troponin complex (attached intermittently along tropomyosin)

Answer 15

troponin T binds tropomyosin

troponin I binds actins

troponin C binds calcium ions

Question 16

actin filaments attach to

Answer 16

both Z discs of a sarcomere and interdigitate with myosin filaments

Question 17

the sarcomere is made up of a complete

Answer 17

A band and the 2 halves of the I bands adjacent to it

Question 18

I band

Answer 18

all actin (thin filament) in a sarcomere

Question 19

A band

Answer 19

all the myosin (thick filament)

Question 20

titin

Answer 20

a protein that maintains alignment between actin and myosin filaments and also acts like a spring between a Z disc and the end of a myosin filament (may be important in some diseases)

Question 21

stimulus –> CNS –>

Answer 21

movement

Question 22

the synapse between a motor neuron and a skeletal muscle fiber is called a

Answer 22

neuromuscular junction (NMJ)

Question 23

the tiny fluid-filled space between cells at a synapse is the

Answer 23

synaptic cleft

Question 24

molecules of transmitter in the presynaptic axon terminal are contained within

Answer 24

many synaptic vesicles, the walls of which are made of membrane

Question 25

if the synapse is a NMJ, the transmitter is always

Answer 25

acetylcholine (ACh)

Question 26

acetylcholine receptors are embedded in the plasma membrane of the

Answer 26

postsynaptic cell

Question 27

steps of traveling wave of electricity in the motor neuron leading to muscle fiber shortening

Answer 27

EVENTS IN THE NEURON 1. action potential arrives at axon terminal 2. calcium enters terminal 3. acetylcholine is released from terminal EVENTS IN THE SYNAPTIC CLEFT 4. acetylcholine diffuses across synaptic cleft, binds to receptors on sarcolemma, and is broken down by acetylcholinesterase EVENTS IN THE MUSCLE FIBER 5. cation channels open and cations enter 6. fiber produces end plate potential 7. fiber produces action potential 8. action potential travels into interior of the fiber along transverse tubules 9. calcium is released from sarcoplasmic reticulum 10. troponin removes tropomyosin's inhibition of actin-myosin binding 11. myosin pulls on actin, shortening the sarcomere

Question 28

synaptic transmission

Answer 28

the process whereby a signal is passed between neurons or other excitable cells

Question 29

events in the neuron

Answer 29

1. an action potential arrives at the axon terminal of the motor neuron 2. the segment of axon terminal membrane in which the action potential is occurring is electrically positive on the inside with respect to the outside 3. each synaptic vesicle contains about 5000 ACh molecules 4. the arriving action potential will function to cause the release of ACh into the synaptic cleft from synaptic vesicles 5. the depolarization of the axon terminal, that is the action potential, opens voltage-gated calcium channels and thus increases the permeability of the axon terminal membrane to Ca++ 6. calcium ions enter the axon terminal, where they allow synaptic vesicles to move to and fuse with the inside surface of the axon terminal plasma membrane; this allows the vesicle contents to be released via exocytosis

Question 30

events in the synaptic cleft

Answer 30

1. each arriving action potential causes the discharge of about 300 vesicles (300 * 5000 = 1,500,000) 2. the ACh binds to ACh receptors embedded in the muscle fiber sarcolemma 3. most of the ACh is quickly removed from the synaptic cleft by being broken down by the enzyme acetylcholinesterase

Question 31

events in the muscle fiber

Answer 31

1. the binding of 2 ACh molecules to a single ACh receptor opens an ion channel specific for cations 2. the influx of Na+ makes the cell less negative on the inside (depolarizes the cell), thus producing a graded potential in the muscle fiber 3. the graded potential is called an excitatory postsynaptic potential (EPSP), aka an end plate potential (EPP) 4. the action potential travels along the sarcolemma in both directions 5. when an action potential gets to a T tubule, it travels inward into the fiber in addition to moving along the sarcolemma; thus T tubules carry the electrical signal into the interior of the fiber 6. T-tubule protien (dihydropyridine receptor) senses the voltage change due to the action potential and interacts with nearby sarcoplasmic reticulum protein (ryanodine receptor/calcium release channel) 7. opening of the calcium release channels allows many calcium ions to move out of the sarcoplasmic reticulum and into the sarcoplasm surrounding the myofibrils

Question 32

bernard katz recorded miniature end plate potential (mEPPs) from the muscle fiber in the

Answer 32

absence of stimulation of the motor neuron

Question 33

each miniature end plate potential (mEPP) is caused by

Answer 33

the spontaneous discharge of 1 synaptic vesicle

Question 34

virtually every end plate potential is large enough to elicit an

Answer 34

action potential in the sarcolemma

Question 35

transverse (T) tubules

Answer 35

invaginations of the sarcolemma into the interior of the muscle fiber that lie at right angles to the myofibrils; they are made of membrane and filled with ECF

Question 36

sarcoplasmic reticulum (SR)

Answer 36

membranous structure that is adjacent and mostly parallel to the myofibrils, in contact with the T tubules, and a storage depot for calcium

Question 37

a T tubule protein called a dihydropyridine receptor "senses"

Answer 37

the voltage change due to the action potential, becomes activated, and interacts with a protein in the nearby sarcoplasmic reticulum called a ryanodine receptor/calcium release channel, which is also an ion channel specific for calcium

Question 38

excitation-contraction (EC) coupling- the traid

Answer 38

the junction between two terminal cisternae and a T-tubule

Question 39

sliding filament theory of contraction

Answer 39

1. ADP is released from the myosin head, which clears the way for another ATP to bind 2. ATP binds to the myosin head, which causes actin and myosin to dissociate; myosin head is "sprung" or "uncocked" 3. ATP is hydrolyzed to ADP plus P (both remain attached to the myosin head); this causes a conformational change in myosin that "cocks" the head 4. If and only if calcium ions are present, calcium binds to troponin C, causing troponin to "tug on" tropomyosin, which moves tropomyosin away from the active sites on myosoin 5. the myosin head binds to actin; the head when attached to myosin is called a "cross bridge" 6. the phosphate group is released from the myosin head, causing pivoting (that is "springing" or "uncocking" of the myosin head 7. because myosin is attached to actin, it pulls on actin as it changes shape, and the Z disc attached to the actin myofilament is pulled along the actin 8. this happens at both ends of the sarcomere, and thus the two Z discs are pulled toward each other, and the sarcomere shortens (ADP remains attached to myosin) 9. myosin and actin remain attached to each other until the ADP is released from myosin and ATP binds 10. many cycles of myosin head springing occur, ratcheting the "right" and "left" actin filaments closer and closer together