The Muscular System Muscles are classified into 4 functional groups:

Transcription

1 The Muscular System Muscles are classified into 4 functional groups: Prime movers (agonists) Antagonists Synergists Fixators 1 muscle can be all four

2 Interactions of Skeletal Muscles Skeletal muscles work together or in opposition Muscles only pull (never push) As muscles shorten, the insertion generally moves toward the origin Whatever a muscle (or group of muscles) does, another muscle (or group) undoes

3 Muscle Classification: Functional Groups Prime movers (agonists) provide the major force for producing a specific movement Antagonists oppose or reverse a particular movement Regulate the motion of prime mover by contracting and providing resistance Agonists & antagonists are located on opposite sides of a joint across which they act Synergists help prime movers by: Adding extra force to a movement Reduce undesirable or unnecessary movement as prime mover contracts E.g. fingers and wrist: can make a fist without bending the wrist Fixators synergists that immobilize a bone or muscle s origin (e.g. scapula)

4 Naming Skeletal Muscles Location of muscle indicate the bone or body region associated with the muscle Shape of muscle e.g., the deltoid muscle (deltoid = triangle; trapezius = trapezoid) Relative size e.g., maximus (largest), minimus (smallest), longus (long) Direction of fibers e.g., rectus (fibers run straight), transversus, and oblique (fibers run at angles to an imaginary defined axis)

5 Naming Skeletal Muscles Number of origins e.g., biceps (two origins), triceps (three origins), quadriceps (four origins) Location of attachments named according to point of origin or insertion Origin is named first Insertion is named second E.g. sternocleidomastoid (sternum, clavicle, mastoid process of the temporal bone) Action e.g., flexor or extensor, as in the names of muscles that flex or extend, respectively

6 Arrangement of Fascicles Parallel fascicles run parallel to the long axis of the muscle (e.g., sartorius) Fusiform spindle-shaped muscles (e.g., biceps brachii) Pennate short fascicles that attach obliquely to a central tendon running the length of the muscle (e.g., rectus femoris) Unipennate: insertion on one side Bipennate: insertion on opposite sides Mulipennate: many insertions into 1 tendon E.g. deltoid muscle

7 Arrangement of Fascicles Convergent fascicles converge from a broad origin to a single tendon insertion Triangular or fan shaped (e.g., pectoralis major of the anterior thorax) Circular fascicles are arranged in concentric rings Surround external body openings (e.g., orbicularis oris, sphincter)

8 Arrangement of Fascicles Arrangement of fascicles determines muscles range of motion and power Muscles with parallel fascicle arrangement shorten the most, but are not powerful Power depends on the total number of muscle cells in the muscle E.g. bipennate and multipennate muscles

9 Arrangement of Fascicles Figure 10.1

10 Bone-Muscle Relationships: Lever Systems Lever a rigid bar that moves on a fulcrum, or fixed point, when a force is applied Used to move a resistance (load) Load resistance moved by the effort Effort force applied to a lever E.g. Joints = fulcrum Bones = levers Muscle contraction = force Load = bone or tissue or objects

11 Bone-Muscle Relationships: Lever Systems Mechanical Advantage (Power lever) Load is close to the fulcrum Effort is applied far from the fulcrum Thus, a small effort over a large distance can move a large load a small distance Mechanical Disadvantage (Speed lever) Load is far from the fulcrum Effort is applied near the fulcrum Thus the force exerted must be greater than the load moved or supported These types of levers provide rapid contraction with a wide range of motion

12 Bone-Muscle Relationships: Lever Systems Figure 10.2a

13 Bone-Muscle Relationships: Lever Systems Figure 10.2b

14 Bone-Muscle Relationships: Lever Systems In summary, small differences in the site of a muscle s insertion (relative to the fulcrum or joint) can translate into large differences in the amount of force a muscle can generate

15 Lever Systems: Classes All levers follow the same principle of: Mechanical advantage: effort farther than load from the fulcrum Mechanical disadvantage: effort closer than load to fulcrum First class the fulcrum is between the load and the effort Second class the load is between the fulcrum and the effort Third class the effort is applied between the fulcrum and the load

16 Lever Systems: First Class Figure 10.3a

17 Lever Systems: Second Class Effort applied at one end, fulcrum at the other end, with the load in between. Second Class lever systems are rare in the body, but when they occur they are always working at a mechanical advantage e.g. muscle insertion is always farther from the fulcrum than the load to be moved Figure 10.3b

18 Lever Systems: Third Class Effort is applied between the load and the fulcrum Third class levers operate at great speed and always at a Mechanical disadvantage e.g. forceps e.g. most skeletal muscles e.g. biceps Figure 10.3c

19 Lever Systems In summary, differences in positioning of the effort, load, and fulcrum modify muscle activity with respect to: 1) speed of contraction 2) range of motion 3) the weight of the load that can be moved

20 Lever Systems Mechanical disadvantage levers (speed levers) Force is lost (not strong) Speed, range of motion is gained Mechanical Advantage levers (power levers) Force is gained (strong) Speed, ranged of motion is lost but stability is gained

21 Major Skeletal Muscles: Anterior View Over 600 muscles in the body We will consider the 125 principal pairs The 40 superficial muscles here are divided into 10 regional areas of the body Figure 10.4b

22 Major Skeletal Muscles: Posterior View The 27 superficial muscles here are divided into seven regional areas of the body Figure 10.5b

23 Muscles: Name, Action, and Innervation Name and description of the muscle be alert to information given in the name Origin and insertion there is always a joint between the origin and insertion Action best learned by acting out a muscle s movement on one s own body Nerve supply name of major nerve that innervates the muscle

24 Muscles of the Scalp Epicranius (occipitofrontalis) bipartite muscle consisting of the: Frontalis: w/ the aponeurosis fixed; raises the eyebrows, wrinkles forehead skin Occipitalis: fixes aponeurosis and pulls scalp posteriorly Galea aponeurotica cranial aponeurosis connecting above muscles These two muscles have alternate actions of pulling the scalp forward and backward

25 Muscles of the Face 11 muscles are involved in lifting the eyebrows, flaring the nostrils, opening and closing the eyes and mouth, and smiling All are innervated by cranial nerve VII (facial nerve) Usually insert in skin (rather than bone), and adjacent muscles often fuse

26 Muscles of the Face Corrugator supercilii: draws eyebrows together & inferiorly Orbicularis oculi: blinking Zygomaticus: smile muscle Risorius: draws corner of lips laterally Levator labii superioris: raises upper lip Depressor labii inferioris: pout muscle Depressor anguli oris: draws corners of mouth downward and laterally Orbicularis oris: kissing and whistling muscle Mentalis: protrudes lower lip & wrinkles chin Buccinator: compresses cheek Platysma: helps depress mandible

27 Muscles of the Scalp, Face, and Neck Figure 10.6

28 Muscles of Mastication There are four pairs of muscles involved in mastication (chewing and biting) Prime movers temporalis and masseter Grinding movements pterygoids and buccinators All are innervated by cranial nerve V (trigeminal nerve) Gravity can depress the jaw. When it can not, the digastric and mylohyoid of the neck contract Intrinsic tongue muscles are arranged in several planes to change the shape of the tongue. But they do not move the tongue Extrinsic tongue muscles anchor and move the tongue.

29 Muscles of Mastication Masseter: prime mover of jaw closure Temporalis: closes jaw, synergist of pterygoids Medial pterygoid: elevates jaw, synergist of temporalis & masseter muscles Lateral pterygoid: pulls mandible aneriorly & helps move mandible side to side Buccinator: keeps food between teeth

30 Muscles of Mastication Figure 10.7a

31 Muscles of Mastication Figure 10.7b

32 Extrinsic Tongue Muscles Three major muscles that anchor and move the tongue All are innervated by cranial nerve XII (hypoglossal nerve) Genioglossus: protrudes tongue Hyoglossus: depresses tongue and draws its sides downward Styloglossus: retracts tongue

33 Extrinsic Tongue Muscles Figure 10.7c