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Flashcards in muscle physiology Deck (42)
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1

signals are picked up by [...] receptors and sent to the spinal cord and brain by[...]

sensory receptors, the afferent leg of the peripheral nervous system

2

signals sent back to the spinal cord and then out to motor neurons via the

efferent leg

3

the length of one fibril (approximately)

1 mm

4

the length of one muscle cell (fibre)

100 micrometer

5

the length of myofibril

1 micrometer

6

the length of sarcomere

1.6-3.6 micrometer

7

what structures comprise a triad?

2 terminal cisternae and one T tubule

8

what is the function of T tubule

permit the conduction of electrical impulses

9

the H zone contains

only myosin fibers

10

what is the function of titin protein? where can we find it?

ensures a precise return of actin and myosin
bundles to their original position even after extensive stretch.
can be found between the Z line and the myosin bundles

11

what is the function of nebulin protein?

determine the direction and placement of actin
polymerization during the development of the sarcomere.
Besides, it protects the developed actin fibre from the rearranging effect of other actin-binding proteins.

12

where can we find the nebulin?

on the actin filament

13

what is the function of the alpha-actinin protein?

provides a binding site for the actin molecules at the z line , helps the orientation of actin molecules to the inner part of the sarcomere

14

where can we find the alpha-actinin proteins?

on the Z line

15

what is the trigger to open ACh channels in the nerve terminal at action potential?

Ca2+ ions enter the presynaptic terminal

16

what makes the Na+ ions channels open at the sarcolemma at action potential?

the ACh binding to ACh receptors on the sarcolemma

17

what triggers the SR to release Ca2+?

the action potential caused by Na+ ions entering the muscle cell making the depolarization

18

what initiates the actin-myosin contraction?

Ca2+

19

what happens to the ACh after it flows into the synaptic claft?

• small portion of it disappears by diffusion
• non-receptor-bound ACh is catabolized (Cholin-esterase enzyme cleaves it to
cholin and acetat; Cholin is reabsorbed to the knob – the resynthesis happens in
the cytosol).
• most of the ACh are bound to ACh-Receptor (Ach-R) creating a local EPP

20

where is the place for synthesizing empty vesicles?

in the golgi of motoneuron

21

where is the place for synthesizing acetylcholine

in the cytosol

22

when some ACh molecules do not enter the muscle cell and they return to the neuron by endocytosis, this mechanism is stimulated by

CLATHRIN

23

Muscle-type nicotinic acetylcholine receptor molecule is composed of

two alpha,
two beta and one delta subunits.

24

what is the role of magnesium in the NMJ?

Increases in EC magnesium concentration antagonize acetylcholine receptors and blocks functioning of the sarcomere.
(cattle - muscles will relax: parturient paresis happens.)

25

what is the affect of drugs of action similar to ACh? (for e.g nicotine)

Nicotine (+ methacholine, etc.), Same effect like ACh but it can not be degraded by cholinesterase. Therefore concentration is increased which results in a permanent depolarization - contraction lasts through minutes, hours - intensive spasm

26

what is the affect of cholinesterase inactivator?

ACh is not hydrolyzed, therefore extreme ACh cumulation occurs (neostigmin, ezerin, diisoprop.fluorophosphate (nerve gas)) - repetitively stimulate muscle fibers - spasm (for hours), Laryngeal spasm (lethal)

27

what is the affect of the acetylcholine esterase enzyme?

breaking down ACh into acidic acid and choline in the synaptic claft

28

what is the affect of curariform drugs?

blocking the acetylcholine receptors -> no depolarization -> no contraction-> paresis (loss of voluntary movement)

29

what is the affect of myasthenia gravis?

autoimmune disease AChR blocking auto-antibodies - ACh can not bound to the receptor (or only a small amount can) resulting in the lack of signal transmission - Paresis

30

what type of metabolism will be in the large motor unit?

anaerobic

31

what type of motoneuron involve in the "servo mechanism"

α-motoneurons

32

what type of motoneuron involve in the "co-activation mechanism"

γ-motoneuron +α-motoneurons

33

when a muscle is stretched, which fibers are stimulated?

Ia , II afferent fibers

34

stimulation of Ia afferents stimulates which motoneuron?

alpha motoneuronsin the spinal cord

35

what is the function of γ-motoneuron?

innervate intrafusal muscle fibers adjust the sensitivity of muscle spindle

36

stimulation of α-motoneurons by group Ia causes...

contraction in the muscle that was stretched

37

receptors in the golgi tendon causes..

Ib afferent fibers causes relaxation of the muscle

38

extrafusal muscles are innervated by...

α-motoneurons

39

intrafusal muscles are innervated by

γ-motoneuron

40

the static fibers inside the intrafusal fibers are sensitive to..

length changes of tension

41

dinamic fibers are sensitive to

length & velocity of tension

42

definition of electro-mechanical coupling

The process which starts with the myogenic AP and ends with the contraction of the muscle fibre is usually called electro-mechanical coupling (followed by relaxation).