MUSCULAR NOMENCLATURE

Muscle fiber types

• Slow twitch

• Type 1

• Oxidative

• Fast twitch

• Type 2

• Subtypes -

• Type lla-fast oxidative/glycolytic

• Type llx-fast glycolytic

• Proportions of fast/slow twitch fibers vary

How muscles are named

• Muscles are named based off their location, function, and physical characteristics

• Some are named based on division into functional groups

• Examples :

• Gluteus maximus → size

• Tricep brachial → number of divisions

• Rectus femoris → location

• Hamstrings → group shape

• Abdominals → group location

Muscle shape and fiber arrangement

There are two major categories based on arrangement of muscle fibers

1. Parallel

2. Muscle fibers run along the length of the muscles and are parallel to one another

3. Fiber arrangements →

4. Flat

5. Strap

6. Radiate

7. Fusiform

8. sphincter

9. Pennate

10. Muscle fibers run diagonally in relation to the tendon

11. Tend to be shorter in length

12. Fiber arrangements →

13. Unipennate

14. Bipennate

15. Multipennate

Muscle Terminology

• Action: how the joint moves as a result of the muscle contraction

• Innervation: particular portion of the nervous system that provides a stimulus for muscle actions

• Amplitude: difference in muscle fiber length from minimum to maximum lengthening

• Aponeurosis: connective tissues that connects muscle to muscle

• Fascia: fibrous connective tissue that envelops muscles

• Origin: least moveable point of attachment (most proximal)

• Insertion: most mobile point of attachment (most distal)

Types of muscle contractions

Defining muscle contractions : we tend to think of contractions as shortening of the muscle but not all contractions lead to the muscle shortening.

It is better to think of a contraction as being responsible for joint movement

Types:

• Isometric

• Isotonic

• Isometric

• Isometric contractions mean that tension occurs without change in the length of the joint angle

• Static

• Contractions are occurring in a stable position

• Isotonic

• Isotonic contractions cause the angle of the joint to change

• Dynamic

• Varying levels of tension dictate amount of change in the joint angle

• Concentric - shortening of the muscle

• Eccentric - lengthening of the muscle

Roles of muscles

• Agonist

• Major source of movement

• Antagonist

• Oppose the actions of the antagonist

• Located on the opposite side of the joint

• Relax to allow joint to move

• Stabilizers

• Fixate a joint or area to allow movement of another

• Synergist

• Help prevent unwanted actions by assisting the agonist

Phases of contraction

• Tetanus

• If stimuli occur at a very rapid rate, the muscle doesn't have time to rest

• The result is one long, continual contraction with high tension

• This is referred to as tetanus

• Treppe

• Occurs when a muscle encounters multiple stimuli but at a slow rate

• Allows muscles to completely relax between stimuli

• Each stimuli produces a greater tension than the stimuli before it

• Creates a stair-case effect