Anatomy Study Guide 5-The Muscles PDF

STUDY GUIDE Faculty of Medicine Lecture 5 Muscles ILOs: Student will be able to 1. Differentiate between the 3 main types of muscles...

STUDY GUIDE Faculty of Medicine Lecture 5 Muscles ILOs: Student will be able to 1. Differentiate between the 3 main types of muscles 2. Classify skeletal muscles according to line of pull and action 3. List modes and sites of muscle attachment. 4. Define: prime mover, agonist, synergist, antagonist & fixator ------------------------------------------------------------------------------------------------------------------------------- Muscles are formed of muscle fibers (= muscle cells = myocytes) which contain myofibrils. Types of Muscles: Smooth muscles (plain, involuntary, unstriated, visceral): These are the muscles of the respiratory, alimentary and vascular systems. Cardiac muscles (involuntary but striated): The muscles of the heart. They are called striated because microscopically they show alternating light and dark bands due to the arrangement of the myofibrils inside the muscle fibers. The former 2 types are controlled by the autonomic nervous system. Skeletal muscles (striated, voluntary): They form the main bulk of our bodies, about half of the body weight is skeletal muscles (the red meat). They are called skeletal as they are attached mainly to the skeleton (bone and cartilage). Skeletal muscles are controlled by the somatic nervous system Arrangement of Muscle Fibers in Skeletal Muscles: 1. Parallel (strap) type: The muscle fibers are parallel to each other, e.g., sartorius muscle. 2. Fusiform type: Similar to the parallel type but the middle of the muscle is wider than the ends (spindle-like) e.g., biceps brachii. 3. Circular type: Surrounds an opening e.g., orbicularis oris. 4. Triangular type: The muscle fibers converge into a narrow terminal tendon, e.g., temporalis muscle. 5. Pennate (feather-like) type: The muscle fibers run obliquely to become attached to the sides of the tendon: a- Unipennate: The muscle fibers lie on one side of the tendon, e.g., flexor pollicis longus muscle. b- Bipennate: The muscle fibers lie on both sides of the tendon, e.g., dorsal interossei muscles. c- Multipennate: The muscle contains a series of tendinous intersections. The muscle fibers are attached to the sides of the intersections in a bipennate arrangement, e.g., deltoid muscle. d- Circumpennate: The muscle fibers are arranged radially around a central tendon, e.g., tibialis anterior muscle. 1 Attachments of Skeletal Muscles: Each muscle has at least 2 attachments: a- The less mobile attachment is called the origin. It is usually the proximal attachment. b- The more mobile attachment is called the insertion It is usually the distal attachment. Origins and insertions are attached mainly to the periosteum of bones. This attachment may take the form of: 1- Fleshy broad area attached directly to the periosteum as most of the origins. 2- Tendon: Cord or band of dense bundles of fibrous tissue as most of the insertions. 3- Aponeurosis: Flat sheet of densely arranged fibrous tissue e.g., aponeurosis of external oblique muscle of the abdomen. N.B.: a- Identical muscles of both sides may meet in the middle line and become inserted into each other forming a thin fibrous line called a raphe. b- On some occasions, the origin may be the movable end to do the needed movement i.e. reversed movement. c- Sesamoid bones may develop in muscles at the sites of friction. Functions of Skeletal Muscles: 1. By shortening, the muscle produces movement in one or both bones to which it is attached. 2. They keep the balance of the body. 3. They are responsible for heat production. 4. They act as pumps for venous blood. Skeletal Muscle Action and Power: A skeletal muscle contracts according to orders from motor nerves. The muscle may contract as a whole or partially. The prime mover (agonist) is the muscle initiating the action. Some other muscles assist the prime mover, and they are called the synergists and usually they are innervated by the same source. The group of muscle which act together to oppose the action of the synergists are called antagonists. According to the number of joints crossed, muscles are classified into: 1. Uni-articular muscles: Cross only one joint. 2. Bi-articular muscles: Cross 2 joints. 3. Multi-articular muscles: Cross more than 2 joints. 2