Muscle Physiology

Classification

Cillian Scott
Pharma Notes
2 min readApr 26, 2017

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Muscle is classified in three different ways.

Striation

  • Striated — Non-striated

Control

  • Voluntary — Involuntary

Situation

  • Skeletal — Cardiac

Composition

Many levels of sub-division

Muscles are composed of myocytes, myocytes are seperated from each other by fascia.

The entire muscle mass is encompassed in a connective tissue called the epimysium.

Hierarchy of muscle composition

Concise Diagram Illustrating Hierarchy of Muscle Components
  • Muscle mass (epimysium coated)
  • Perimysium
  • Endomysium
  • Myocyte
  • Sarcoplasm
  • Myofibril

Each myofibril consists of two bands, the light band (I — Isotropic), and the dark band (A — Anisotropic)

Myocyte structure

The myocyte is a cylinder with alternating Dark/Light bands, with a nucleus present.

The myofilaments exist in actin and myosin forms.

Muscle Contraction

I-bands move toward the M-Line of the H-Zone

Myosin and actin move closer together and bind.

This process is described by the crossbridge cycle

Crossbridge Cycle

  1. Myosin + Actin Bind
  2. Power-Stroke
  3. Rigor (myosin in low-energy state)
  4. ATP + Myosin head bind
  5. Myosin + Actin Unbind, with the use of ATP.
  6. Step 1 recurs.

Metabolic Classification

Slow oxidative, fast oxidative, and glycolytic skeletal muscle fibres differ in the following with regard to metabolism.

Oxidative Capacity

Both slow oxidative and fast oxidative have the same high oxidative capacity.

Glycolytic fibres have low oxidative capacity

Glycolytic Capacity

Conversely, slow and fast oxidative fibres have low glycolytic capacity, and glycolytic fibres have high glycolytic capacity.

Myosin ATPase Activity

Low in slow oxidative fibres, intermediate in fast oxidative fibres and high in glycolytic

Physiological Classification

Speed of contraction

high in the oxidative fibres and low in glycolytic.

Motor Unit Size

Slow to fast to glycolytic in order of smallest to largest.

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