Muscle

From EvoWiki

Contents 1 Introduction 2 Muscle cells 3 Motor system 4 Types of muscle 4.1 Striated muscle 4.2 Skeletal muscle 4.2.1 Skeletal muscle classes 4.3 Cardiac muscle 4.4 Smooth muscle 5 References 6 External links

Introduction

Muscle is one of the four principle tissue types in animals. Muscle tissue converts chemical energy to mechanical energy and heat. Muscle can contract and is highly excitable (easy to stimulate by nerves).

Muscle cells

Muscle cells are typically elongated and contain fibres which can contract, shortening the cells. The fibres within muscle are called myofibrils (or sarcostyles); these are cylindrical organelles which contain myelin and actin sarcomeres.

Motor system

Main article: motor system Muscles are innervated (they have a nerve supply), and are stimulated either by the nervous system (neurogenic) or neigbouring muscle (myogenic). Vertebrates move muscle due to stimulated from the brain (voluntary) or the autonomic nervous system (involuntary). Different muscles correspond to different regions in the brain and spinal cord.

Types of muscle

Muscle can be classified in different ways. The most common ways of classification are by ther structure and function, whether they are striated, and, for skeletal muscle, how they move.

Striated muscle

Main article: Striated muscle
Striated muscle contains striations visible as light and dark stripes with a light microscope. These striations are caused by the arrangement of actin and myelin in the sarcomere. Skeletal muscle and cardiac muscle are striated muscles; smooth muscle is not striated.

Skeletal muscle

Main article: Skeletal muscle

Skeletal muscle classes

Main article: Muscle Classes
Skeletal muscle can be classified by how they move:

• Adductors - Draw medially, or towards the body midline.
• Abductors - Draw laterally, away from the body midline.
• Pronators - Rotate an appendage (e.g., limb) forward and ventrally.
• Supinators - Rotate an appendage, backward and dorsally.
• Extensors - Extends an appendage, away from the midline.
• Flexors - Flexes an appendage, towards the midline.

Cardiac muscle

Main article: Cardiac muscle

Smooth muscle

Main article: Smooth muscle

References

• Harker, D.W., 2003. Human Physiology & Pharmacology, UWE

External links

• Wikipedia: Muscle

This page is part of the EvoWiki Encyclopedia of Anatomy and Physiology. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z