Muscle physiology 2

Question 1

What are the two main factors influencing the gradation (tension developed by skeletal muscle) ?

Answer 1

1. The number of muscle fibres contracting
2. The tension developed by each muscle fibre

Question 2

Explain how frequency of stimulation & summation of contractions brings about increased tension in skeletal muscle?

Answer 2

Because the duration of AP is much shorter the the twitch produced as a result of the AP therefore making it possible to summate twitches to bring about a stronger contraction through repetitive fast stimulation of skeletal muscle

Question 3

What is tenatus described as ? (hint occurs when too much stimulation of the muscle)

Answer 3

It is when muscle is stimulated so rapidly it doesn’t have time to relax which results in a maximal sustained contraction known as tenatus

Question 4

Why can cardiac muscle not be tenatised ?

Answer 4

Due to its long refractory period

Question 5

Describe the idea of optimum muscle tension development

Answer 5

Maximal tetanic contraction can be achieved when the muscle is at its optimal length (lo)

Question 6

What are the two different types of muscle contraction ?

Answer 6

Isotonic and Isometric muscle contraction

Question 7

Describe what movements Isotonic muscle contraction is used for

Answer 7

Used for:

• Body movements and moving objects.
• Muscle tension remains constant as the muscle length changes

Question 8

Describe the movements Isometric muscle contractions are used for

Answer 8

Used for:

• Supporting objects in fixed positions and maintaining body posture.
• Muscle tension develops at constant muscle length

Question 9

How is muscle tension transmitted to the bone in both isotonic and isometric muscle contractions ?

Answer 9

Transmitted to the bone via there elastic components (tendons)

Question 10

Appreciate that skeletal muscles are not all the same (there is 3 main types) what are the main differences in general between these 3 types of skeletal muscles ?

Answer 10

• The enzymatic pathways for ATP synthesis
• The resistance to fatigue - the greater the capacity to synthesie ATP the greater the resistance to fatigue
• The activity of myosin ATPase - this determines the speed at which energy is made available for cross bridge cycling i.e. the speed of contraction

Question 11

What are the 3 main metabolic pathways which supply ATP to muscle fibres ?

Answer 11

• Transfer of high energy phosphate from creatine Phosphate to ADP - immediate source for ATP
• Oxidative phosphorylation: main source when O2 is present
• Glycolysis: main source when O2 is not present

Question 12

What are the 3 main types of muscle fibres ?

Answer 12

• Slow oxidative Type I
• Fast oxidative Type IIa
• Fast glycotic Type IIx

Question 13

Match the type of muscle fibre to the description of it:

1. (also known as slow-twitch fibres) are used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
2. (also known as intermediate-twitch fibres) use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging
3. (also known as fast-twitch fibers) use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping

Answer 13

1. Slow oxidative type I fibres (also known as slow-twitch fibres) are used mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking
2. Fast oxidative (Type IIa) fibres (also known as intermediate-twitch fibres) use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging
3. Fast glycolytic (Type IIx) fibres (also known as fast-twitch fibers) use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping

Question 14

What is the activity of motor units influenced by ?

Answer 14

Input from the brain and a variety of receptors

Question 15

Define the term reflex action

Answer 15

Reflex action is a stereotyped response to a specific stimulus, they are the simplest form of co-ordinated movement

Question 16

Describe what stretch reflex is

Answer 16

It is a negative feedback reflex that resists change in muscle length to maintain optimal resting length of muscle

• Sensory receptor is the muscle spindle and is activated by muscle stretch (e.g. by tendon hammer shown in pic)
• This rapidly stretches the muscle resulting in its contraction

Question 17

How are different stretch reflexs good at localising lesions ?

Answer 17

Because different stretch relfex tests, test specific nerves and spinal segments

Question 18

What are the sensory receptors for stretch reflexes and describe there action

Answer 18

Muscle spindles - which are a collection of specialised muscle fibres known as intrafusal fibres which have sensory nerve endings known as annulospiral fibres.

When the fibres are stretched there firing increases bringing about muscle contraction (i believe)

Question 19

What are the 4 main causes of impairment of skeletal muscle function ?

Answer 19

1. Intrinsic disease of muscle
2. Disease of NMJ
3. Disease of lower motor neurons which supply the muscle
4. Disruption of input to motor nerves (e.g. upper motor neuron disease)

Question 20

What are the symptoms of muscle disease?

Answer 20

• Muscle weakness / tiredness
• Delayed relaxation after voluntary contraction (myotonia)
• Muscle pain (myalgia)
• Muscle stiffness