Physio Ch 07

Question 1

formed by the nerve fiber through invagination into the surface of the muscle fiber present in plasma membrane

Answer 1

branching nerve terminals

Question 2

innervated by large, myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord

Answer 2

skeletal muscle fibers

Question 3

schwann cells insulate this structure from surrounding fluids

Answer 3

motor end plate

Question 4

invaginated membrane between an axon terminal and muscle fiber membrane

Answer 4

synaptic gutter or synaptic trough

Question 5

space between the axon terminal and muscle fiber membrane

Answer 5

synaptic space or synaptic cleft

Question 6

folds at the bottom of synaptic gutter greatly increasing the surface area at which the synaptic transmitter can act

Answer 6

subneural clefts

Question 7

where does acetylcholine get synthesized

Answer 7

cytoplasm of the axon terminal

Question 8

destroys acetylcholine a few milliseconds after it has been released from the synaptic vesicles

Answer 8

acetylcholinesterase

Question 9

neural membrane empty their acetylcholine into the synaptic space by the process of

Answer 9

exocytosis

Question 10

located almost entirely near the mouths of the subneural clefts lying immediately below the dense bar areas

Answer 10

acetylcholine-gated ion channels

Question 11

these positive ions flow through acetylcholine gated channels more than any other ions

Answer 11

sodium ions

Question 12

Why do sodium ions flow through acetylcholine-gated channel more than potassium and calcium?

Answer 12

1. There are only two positive ions in large
   concentration: sodium ions in the extracellular fluid and potassium ions in the intracellular fluid.
2. The negative potential on the inside of the muscle membrane, −80 to −90 millivolts, pulls the positively charged sodium ions to the inside of the fiber, while simultaneously preventing efflux of the positively charged potassium ions
   when they attempt to pass outward

Question 13

this initiates an action potential that spreads along the muscle membrane and causes muscle contraction

Answer 13

end plate potential

Question 14

Mechanisms of destruction of released acetylcholine (2)

Answer 14

(1) Most of the acetylcholine is destroyed by the enzyme acetylcholinesterase,
(2) A small amount of acetylcholine diffuses out of the synaptic space and is then no longer available to act on the muscle fiber membrane

Question 15

a drug that blocks the gating action of acetylcholine on the acetylcholine channels by competing for the acetylcholine receptor sites

Answer 15

curare

Question 16

bacterial poison that decreases the quantity of acetylcholine release by the nerve terminals

Answer 16

botulinum toxin

Question 17

stimulation of the nerve fiber at rates greater than 100 times per second for several minutes often diminishes the number of acetylcholine vesicles so much that impulses fail to pass into the muscle

Answer 17

fatigue

Question 18

enumerate these drugs having the same effect on the muscle fiber as does acetylcholine

Answer 18

methacholine, carbachol, and nicotine

Question 19

enumerate the drugs which inactivate the acetylcholinesterase in the synapses so that it no longer hydrolyzes acetylcholine

Answer 19

neostigmine, physostigmine, and diisopropyl fluorophosphate

Question 20

powerful “nerve” gas poison and inactivates acetylcholinesterase for weeks

Answer 20

diisopropyl fluorophosphate

Question 21

combine with acetylcholinesterase to inactivate the acetylcholinesterase for up to several hours

Answer 21

Neostigmine and physostigmine

Question 22

prevent passage of impulses from the nerve ending into the muscle

Answer 22

curariform drugs

Question 23

a drug that blocks the action of
acetylcholine on the muscle fiber acetylcholine receptors

Answer 23

D-tubocurarine

Question 24

causes muscle paralysis because of inability of the neuromuscular junctions to transmit enough signals from the nerve fibers to the muscle fibers

Answer 24

myasthenia gravis

Question 25

an autoimmune disease in which the patients have developed antibodies that block or destroy their own acetylcholine receptors

Answer 25

Myasthenia gravis

Question 26

nerve ending of skeletal muscle fibers make a junction with muscle fiber near its midpoint

Answer 26

neuromuscular junction

Question 27

When a nerve impulse reaches the neuromuscular junction, how many vesicles of acetylcholine are released
from the terminals into the synaptic space

Answer 27

125 vesicles

Question 28

located near mouths of the subneural clefts lying immediately below the dense bar areas

Answer 28

acetylcholine-gated ion channels

Question 29

protein complex composed of two alpha proteins and one each of beta, delta, and gamma proteins

Answer 29

acetylcholine receptors

Question 30

do not pass through acetylcholine gated channel due to strong negative charges in the mouth of channel

Answer 30

chloride ions

Question 31

Ach is rapidly removed by 2 mechanisms

Answer 31

(1) Most of the acetylcholine is destroyed by the enzyme acetylcholinesterase

(2) A small amount of acetylcholine diffuses out of the synaptic space

Question 32

an increase by millivolt of nerve membrane that is sufficient to initiate more and more sodium channel to open, causing action potential

Answer 32

20 to 30 millivolts

Question 33

increase to about 50-70 millivolts at the local area of the end plate results to

Answer 33

local potential or end plate potential

Question 34

diminishes number of Ach vesicle resulting impulse to fail to pass into the muscle fiber

Answer 34

stimulation of the nerve fiber at rates greater than 100 times per second for several minutes

Question 35

Acetylcholine is synthesized in

Answer 35

cytosol of nerve fiber terminal

Question 36

formed by the Golgi apparatus in the cell body of the motoneuron in the spinal cord

Answer 36

small vesicles

Question 37

occurs in about 1 in every 20,000 characterized by inability of the neuromuscular junctions to transmit enough signals from the nerve fibers to the muscle fibers

Answer 37

myasthenia gravis

Question 38

Resting membrane potential in skeletal fibers

Answer 38

-80 to -90 millivolts

Question 39

Duration of action potential of skeletal muscles

Answer 39

1 to 5 milliseconds

Question 40

velocity of conduction in skeletal muscle

Answer 40

3 to 5 m/sec

Question 41

current penetrate deeply into muscle fiber through this structure, which also transmits the action potential

Answer 41

transverse tubules

Question 42

small and run transverse to the myofibrils

Answer 42

T tubules

Question 43

branch among themselves and form entire planes interlacing among all the separate myofibrils

Answer 43

T tubules

Question 44

communicate with the ECF surrounding the muscle fiber and contain extracellular fluid in their lumen

Answer 44

T tubules

Question 45

internal extension of the cell membrane

Answer 45

T tubules

Question 46

Sarcoplasmic reticulum is composed of?

Answer 46

(1) large chambers called terminal cisternae that abut the T tubules

(2) long longitudinal tubules that surround all surfaces of the actual contracting myofibrils

Question 47

One of the special features of the sarcoplasmic reticulum

Answer 47

excess of calcium ion in high concentrations

Question 48

As action potential reaches the T tubule, the voltage change is sensed by

Answer 48

dihydropyridine receptors

Question 49

dihydropyridine receptors are linked to?

Answer 49

calcium release channels or ryanodine receptor channels

Question 50

Activation of dihydropyridine receptors triggers the opening of

Answer 50

calcium release channels in the cisternae

Question 51

a protein present inside the reticulum that can bind up to 40 times of more calcium

Answer 51

calsequestrin

Question 52

total duration of this calcium “pulse” in the usual skeletal muscle fiber lasts about

Answer 52

1/20 of a second