Skeletal Muscle Contractions – Characteristics

SKELETAL MUSCLE CONTRACTIONS – CHARACTERISTICS

Q. 1

Many different types of muscle contractions exist. In which type of contraction is muscle tension is generated, but the length of the muscle does not change?

 A

Concentric

 B

Eccentric

 C

Isokinetic

 D

Isometric

Q. 1

Many different types of muscle contractions exist. In which type of contraction is muscle tension is generated, but the length of the muscle does not change?

 A

Concentric

 B

Eccentric

 C

Isokinetic

 D

Isometric

Ans. D

Explanation:

In isometric contractions, muscle tension is generated but the length of the muscle does not change.

  • Concentric contractions are a type of isotonic contraction in which the muscle shortens during the contraction.
  • Eccentric contractions are also a type of isotonic contraction in which the muscle lengthens during the contraction.
  • In isokinetic contractions, muscle tension is generated as the muscle contracts at a constant velocity over a full range of motion.

 

Ref: Medical Physiology: Principles for Clinical Medicine Page 249.

 


Q. 2

The force of muscle contraction can be increased by all of the following except:

 A

Increasing the frequency of activation of motor units

 B

Increasing the number of motor units activated

 C

Increasing the amplitude of action potentials in the motor neurons

 D

Recruiting larger motor units

Q. 2

The force of muscle contraction can be increased by all of the following except:

 A

Increasing the frequency of activation of motor units

 B

Increasing the number of motor units activated

 C

Increasing the amplitude of action potentials in the motor neurons

 D

Recruiting larger motor units

Ans. C

Explanation:

Action potential follows an all or none law. When sufficient amplitude is reached to produce a motor response, increasing the amplitude further will not have any effect on the motor response. 

Ref: Review of Medical Physiology by William F Ganong, 19th Edition Page 70 ; Biomechanics and Biology of Movement By Benno Maurus Nig, Page 275.

 


Q. 3

When measuring skeletal muscle tension that develops during isometric contractions, it is observed that:

 A

Total tension is inversely proportional to the length of the fiber

 B

Total tension increases monotonically with the length of the fiber

 C

Active tension increases monotonically with the length of the fiber

 D

Active tension first increases then decreases with the length of the fiber

Q. 3

When measuring skeletal muscle tension that develops during isometric contractions, it is observed that:

 A

Total tension is inversely proportional to the length of the fiber

 B

Total tension increases monotonically with the length of the fiber

 C

Active tension increases monotonically with the length of the fiber

 D

Active tension first increases then decreases with the length of the fiber

Ans. D

Explanation:

The total tension that is developed on stimulating a muscle isometrically is the sum of the passive tension of the unstimulated muscle and the active tension exerted by stimulation. The passive tension increases monotonically with the length of the fiber. Active tension, however, increases up to the resting length of the fiber and then declines as the length is increased further. The total tension therefore also shows first an increase and then a decrease as a fiber is lengthened.


Q. 4

The force of muscle contraction can be increased by all of the following except :

 A

Increasing the frequency of activation of motor units

 B

Increasing the number of motor units activated

 C

Increasing the amplitude of action potentials in the motor neurons

 D

Recruiting larger motor units

Q. 4

The force of muscle contraction can be increased by all of the following except :

 A

Increasing the frequency of activation of motor units

 B

Increasing the number of motor units activated

 C

Increasing the amplitude of action potentials in the motor neurons

 D

Recruiting larger motor units

Ans. C

Explanation:

C i.e. Increasing the amplitude of action potential in the motor neurons.

Action potential follows an all or none law. If sufficient amplitude is reached to produces a response, increasing the amplitude further will not have any effect on the function to follow.

Factors res onsible for gradingof muscular activity

Number of motor units

With minimal voluntary activity only a few motor units discharge. With increasing voluntary

(Recruitment)

effect more and more units are brought into play – ‘Recruitment phenomenon’.

 

With increasing motor units, force of muscle contraction increases

Frequency of Contraction

Frequency of discharge in the individual fibre play a role. Tension developed during a tetanic

(Summation)

contraction (with rapidly repeated stimulation) is greater than during individual twitches

Large motor units

Force of contraction depends on length of muscle – starling’s law


Q. 5

Twitch of a single motor unit is called :

 A

Myoclonic-jerk

 B

Fasciculation

 C

Tremor

 D

Chorea

Q. 5

Twitch of a single motor unit is called :

 A

Myoclonic-jerk

 B

Fasciculation

 C

Tremor

 D

Chorea

Ans. B

Explanation:

B i.e. Fasciculation

Fasciculation

is visible or palpable twitch within a single muscle due to spontaneous discharge of one motor unit.Q

[Each single motor neuron & the muscle fibres it innervates constitute a motor unit]

Fibrillation

Fine, irregular contraction of individual fibers, they are not visible grossly.

Tremor

Rhythmic abnormal involuntary movement.

Chorea

Rapid, jerky, semipurposive irregular movement more commonly occurring in the distal part.



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