19 - Physiology of Skeletal Muscles. Functional morphology, mechanism and energetics of contraction. Types of muscle contraction. Types of muscle fibres. Muscle work and muscle fatigue. Electromyography.

sections

physiology of skeletal muscle

morphology og skeletal muscle

types of muscle contractions

types of skeletal muscle fibres

muscle work and fatigue

muscle fatigue

muscle contraction

electromyography

physiology of skeletal muscle

• The skeletal muscles- striated .voluntary muscles.

• Attached to bone and contraction leads to movement of the skeleton

• Under somactic control.

morphology og skeletal muscle

• Made up of myofibrils and connective tissue framework

• Many muscle fibres come together forming bundles called fasiculi.

• Each muscle cell is multinucleated.

• its cytoplasm- sarcoplasm with sarcoplasmic reticulur

  • main intracellular calcium store used for contraction

  • The sarcomere is the structural and functional unit of the muscle fibre.

  • Shortening of the sarcomeres produces the shortening of the myofibril and, in turn, of the muscle fiber of which it is a part.

types of muscle contractions

1. Isotonic contractions- tone stays same, length changes

   • This occurs when muscles maximal force of contraction exceeds the total load on the muscle.

2. Isometric contractions- no change in the length of the muscles during contraction But change in tone,

3. Concentric contractions- muscle fibre shortens when generating force

4. Eccentric contraction- muscle length extends during contraction

5. tonus- state of partial contraction

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types of skeletal muscle fibres

1. Slow contracting muscle fibres type 1

   • Predominant in red muscles

   • Low myosin- ATPase activity

   • High capacity of ATP production via oxidative phosphorylation

   • High level myoglobin- aerobic respiration

2. Fast contracting muscle fibres type 2a

   • red muscle

   • higher myosin ATPase activity compared to type 1

   • high capacity for ATP production via oxidative phosphorylation

   • more capillary network

   • aerobic respiration

3. Fast contracting fibre type 2b

   • White muscle

   • anaerobic

   • Higher myosin ATPase activity has type 1 fires

   • Low capacity for production of ATP via oxidative phosphorylation

   • Sparse capillary network----- main pathway for ATP is glycolysis

muscle work and fatigue

This ability is called gradation of force of contraction.

It is affected by:

• Frequency of nerve impulses

• Synchronisation of impulses

• Recruitment of motor units

muscle fatigue

• reduced ability to contract

• onset of fatigue depends on the duration and intensity of exercise and type of muscle fibres.

• or due to hypoxia and other changes in the muscle

muscle contraction

calcium needed, sliding between actin aand myosin filaments, sarcomere shortens

electromyography

the technique of recording the total electrical activity of the motor nerve and the muscle under study.

• The machine used to record the said electrical activity is called electromyograph and the record obtained is called the electromyogram.

• Electromyography (EMG) system has a recording device connected to electrodes which transmit AP from the tested muscle and a signal amplifier