Human Anatomy
General Features of Muscle
General myology for MBBS: muscle types, fibre arrangement, actions and supporting structures, mapped to NMC codes AN3.1 to AN3.3.
MedNext Academy | 3 min read
General Features of Muscle
General myology for MBBS: muscle types, fibre arrangement, actions and supporting structures, mapped to NMC codes AN3.1 to AN3.3.
This chapter covers the basic structure, classification and actions of muscle, the tissue that moves the body. It introduces fibre arrangement, the vocabulary of muscle action, and supporting structures such as tendons, aponeuroses, retinacula and bursae.
High-yield: General Features of Muscle
- Muscle tissue is of three types: skeletal, cardiac and smooth.
- Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and striated, and smooth muscle is involuntary and non-striated.
- A muscle is attached at its origin, usually the more fixed proximal end, and its insertion, usually the more mobile distal end.
- By fibre arrangement muscles are described as parallel, pennate, fusiform, convergent or circular.
- Pennate muscles, in which fibres run oblique to the tendon, generate more force but over a shorter range.
- The prime mover, or agonist, produces the intended movement while the antagonist opposes it.
- Synergists assist the prime mover and fixators steady the proximal attachment.
- The tendon of insertion is largely aponeurotic in flat muscles such as the external oblique.
- A sesamoid bone in a tendon, such as the patella, alters the angle of pull and improves leverage.
- Muscle is supplied by a neurovascular hilum, and its nerve carries motor, sensory and autonomic fibres.
- About half of the fibres in a motor nerve to muscle are sensory, carrying proprioception.
- The strength of a muscle is proportional to its physiological cross-sectional area, not its length.
- A retinaculum is a thickened band of deep fascia that holds tendons close to a joint.
- A bursa is a fluid-filled sac that reduces friction where a tendon or muscle crosses bone.
Types of muscle tissue
- **Skeletal:** Voluntary, striated, multinucleate; moves the skeleton and is under conscious control.
- **Cardiac:** Involuntary, striated, branching fibres joined by intercalated discs; found only in the heart.
- **Smooth:** Involuntary, non-striated, spindle-shaped cells; in walls of viscera and vessels.
- **Action terms:** Agonist produces the movement, antagonist opposes, synergist assists, fixator steadies the origin.
NMC competencies in this chapter
- **AN3.1:** Types of muscle tissue and their features
- **AN3.2:** Classification of muscles by fibre arrangement and action
- **AN3.3:** Structure of muscle, tendons and related structures
Frequently Asked Questions
What are the three types of muscle?
Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and striated, and smooth muscle is involuntary and non-striated. Each has a distinct location and control mechanism.
What is the difference between agonist and antagonist?
The agonist, or prime mover, produces the intended movement, while the antagonist opposes it and controls the movement. Synergists assist and fixators steady the origin.
Why are pennate muscles stronger?
In pennate muscles the fibres run obliquely into the tendon, so more fibres fit into a given volume and the physiological cross-section is larger, generating greater force over a shorter range.
What is a retinaculum?
A retinaculum is a thickened band of deep fascia that binds tendons close to a joint, preventing them from bowstringing when the muscle contracts, as at the wrist and ankle.
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