muscle physiology

Question 1

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

Answer 1

sensory receptors, the afferent leg of the peripheral nervous system

Question 2

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

Answer 2

efferent leg

Question 3

the length of one fibril (approximately)

Answer 3

1 mm

Question 4

the length of one muscle cell (fibre)

Answer 4

100 micrometer

Question 5

the length of myofibril

Answer 5

1 micrometer

Question 6

the length of sarcomere

Answer 6

1.6-3.6 micrometer

Question 7

what structures comprise a triad?

Answer 7

2 terminal cisternae and one T tubule

Question 8

what is the function of T tubule

Answer 8

permit the conduction of electrical impulses

Question 9

the H zone contains

Answer 9

only myosin fibers

Question 10

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

Answer 10

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

Question 11

what is the function of nebulin protein?

Answer 11

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.

Question 12

where can we find the nebulin?

Answer 12

on the actin filament

Question 13

what is the function of the alpha-actinin protein?

Answer 13

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

Question 14

where can we find the alpha-actinin proteins?

Answer 14

on the Z line

Question 15

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

Answer 15

Ca2+ ions enter the presynaptic terminal

Question 16

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

Answer 16

the ACh binding to ACh receptors on the sarcolemma

Question 17

what triggers the SR to release Ca2+?

Answer 17

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

Question 18

what initiates the actin-myosin contraction?

Answer 18

Ca2+

Question 19

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

Answer 19

• 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

Question 20

where is the place for synthesizing empty vesicles?

Answer 20

in the golgi of motoneuron

Question 21

where is the place for synthesizing acetylcholine

Answer 21

in the cytosol

Question 22

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

Answer 22

CLATHRIN

Question 23

Muscle-type nicotinic acetylcholine receptor molecule is composed of

Answer 23

two alpha,

two beta and one delta subunits.

Question 24

what is the role of magnesium in the NMJ?

Answer 24

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

Question 25

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

Answer 25

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

Question 26

what is the affect of cholinesterase inactivator?

Answer 26

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)

Question 27

what is the affect of the acetylcholine esterase enzyme?

Answer 27

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

Question 28

what is the affect of curariform drugs?

Answer 28

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

Question 29

what is the affect of myasthenia gravis?

Answer 29

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

Question 30

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

Answer 30

anaerobic

Question 31

what type of motoneuron involve in the "servo mechanism"

Answer 31

α-motoneurons

Question 32

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

Answer 32

γ-motoneuron +α-motoneurons

Question 33

when a muscle is stretched, which fibers are stimulated?

Answer 33

Ia , II afferent fibers

Question 34

stimulation of Ia afferents stimulates which motoneuron?

Answer 34

alpha motoneuronsin the spinal cord

Question 35

what is the function of γ-motoneuron?

Answer 35

innervate intrafusal muscle fibers adjust the sensitivity of muscle spindle

Question 36

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

Answer 36

contraction in the muscle that was stretched

Question 37

receptors in the golgi tendon causes..

Answer 37

Ib afferent fibers causes relaxation of the muscle

Question 38

extrafusal muscles are innervated by...

Answer 38

α-motoneurons

Question 39

intrafusal muscles are innervated by

Answer 39

γ-motoneuron

Question 40

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

Answer 40

length changes of tension

Question 41

dinamic fibers are sensitive to

Answer 41

length & velocity of tension

Question 42

definition of electro-mechanical coupling

Answer 42

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).