SDL 🧑‍💻

Question 1

what is the definition of motor unit?

Answer 1

Single motor neuron and muscle fibers supplied by it.

Question 2

Does excitation of a single motor neuron cause the contraction of a single muscle fiber?

Answer 2

• No, The smallest possible amount of muscle that can contract in response to the excitation of a single motor neuron is not one muscle fiber but all the fibers supplied by the neuron.

Question 3

compare between muscle fibers of (fine,Precise & graded movements) and (coarse) movements in terms of:

• Number
• Example

Answer 3

Question 4

characters of the muscle fibers that contribute to One motor unit

Answer 4

• The group of muscle fibers that contribute to a motor unit can be intermixed within a muscle.
• Although they contract as a unit, they are not necessarily (neighboring) fibers within the muscle.
• All the muscle fibers in a motor unit are of the same type.

Question 5

what are the types of motor units? and what are their characters?

Answer 5

• On the basis of type of muscle fiber they innervate, and thus on basis of duration of their twitch contraction, motor units are divided into :

Question 6

what is Innervation ratio?

Answer 6

• is the ratio of ms fibers innervated by a single motor neuron
• Lower innervation ratio means fine control of movement.
• Higher innervation ratio means Coarse control of movement.

Question 7

Is Recruitment of motor units during ms contraction random?

Answer 7

No, rather it follows a general scheme, the size principle.

Question 8

what is the general scheme that regulates the recruitment of motor units?

Answer 8

Question 9

Give an example for recruitment of motor units during ms contraction (Leg muscles)

Answer 9

In standing: Small, slow units are first recruited.

In walking: recruitment of FR units increases.

In running or jumping: the FF units are recruited.

• Of course, there is overlap in recruitment, but, in general, this principle holds true.

Question 10

Are differences between types of muscle units inhereted?

Answer 10

• Differences between types of muscle units are not inherent but are determined by, among other things, their activity

Question 11

what happens when the nerve to a slow muscle is cut?

Answer 11

• When the nerve to a slow muscle is cut and the nerve to a fast muscle is spliced to the cut end
• The fast nerve grows and innervates the previously slow muscle which becomes
  a) Fast
  b) Changes in muscle protein isoforms and myosin ATPase activity.

Question 12

what causes the change of a muscle from slow to fast?

Answer 12

Due to changes in the pattern of activity of the muscle as in case of changes in the expression of MHC genes and consequently of MHC isoforms can be produced by changes in the pattern of electrical activity used to stimulate the muscle

Question 13

what is the most common cause of alteration in muscles?

Answer 13

• Change in activity initiated through exercise (or lack)

Question 14

Change in muscle according to activity & exercise

Answer 14

• Increased activity can lead to muscle cell hypertrophy, which allows for increase in contractile strength. Type IIA and IIB fibers are most susceptible to these changes.
• Inactivity can lead to muscle cell atrophy and a loss of contractile strength. Type I fibers (that is, the ones used most often) are most susceptible to these changes.

Question 15

what is the definition of Electro-myography (EMG)?

Answer 15

The process of recording the electrical activity of muscle on an oscilloscope.

Question 16

what does Electro-myography (EMG) study?

Answer 16

motor units activation.

Question 17

Method of using of Electro-myography (EMG)

Answer 17

• Done in un-anaesthetized humans by using :
  a. Small metal disks on skin overlying muscle as the pick-up electrodes or
  b. Hypodermic needle electrodes.
• The record obtained with such electrodes is electromyogram (EMG).
• With needle electrodes, it is usually possible to pick up activity of single muscle fibers.
• The measured EMG depicts the potential difference between ( ) 2 electrodes, which is altered by the activation of muscles in between the electrodes.

Question 18

EMG and recruitment of motor unit

Answer 18

• At rest: little spontaneous activity occurs in the skeletal muscles.
• With minimal voluntary activity a few motor units discharge.
• With increasing voluntary effort, more and more are brought into play to monitor the recruitment of motor units

Question 19

“With increasing voluntary effort, more and more are brought into play to monitor the recruitment of motor units”

• Explain the cause of this phenomenon..

Answer 19

• Number of motor units activated control Gradation of muscle response.
• The frequency of discharge in the individual nerve fibers plays a role
• The tension developed during a tetanic contraction being greater than that during individual twitches.
• The length of the muscle is also a factor.
• The motor units fire asynchronously (out of phase with one another) which cause individual muscle fiber responses to merge into a smooth contraction of the whole muscle.

Question 20

what is the use of EMGs in summary?

Answer 20

• EMGs can be used to quickly (and roughly) monitor abnormal electrical activity associated with muscle responses.