Interactions of Skeletal MusclesInteractions of Skeletal Muscles

Skeletal muscles work together or in Skeletal muscles work together or in oppositionopposition

Muscles only pull (never push)Muscles only pull (never push) As muscles shorten, the insertion generally As muscles shorten, the insertion generally

moves toward the originmoves toward the origin Whatever a muscle (or group of muscles) does, Whatever a muscle (or group of muscles) does,

another muscle (or group) “undoes”another muscle (or group) “undoes”

Muscle Classification: Functional Muscle Classification: Functional GroupsGroups

Prime movers – provide the major force for Prime movers – provide the major force for producing a specific movementproducing a specific movement

Antagonists – oppose or reverse a particular Antagonists – oppose or reverse a particular movementmovement

SynergistsSynergists Add force to a movementAdd force to a movement Reduce undesirable or unnecessary movementReduce undesirable or unnecessary movement

Fixators – synergists that immobilize a bone or Fixators – synergists that immobilize a bone or muscle’s originmuscle’s origin

Naming Skeletal MusclesNaming Skeletal Muscles

Location of muscle – bone or body region Location of muscle – bone or body region associated with the muscleassociated with the muscle

Shape of muscle – e.g., the deltoid muscle Shape of muscle – e.g., the deltoid muscle (deltoid = triangle) (deltoid = triangle)

Relative size – e.g., maximus (largest), Relative size – e.g., maximus (largest), minimus (smallest), longus (long)minimus (smallest), longus (long)

Direction of fibers – e.g., rectus (fibers run Direction of fibers – e.g., rectus (fibers run straight), transversus, and oblique (fibers run straight), transversus, and oblique (fibers run at angles to an imaginary defined axis)at angles to an imaginary defined axis)

Naming Skeletal MusclesNaming Skeletal Muscles

Number of origins – e.g., biceps (two origins) Number of origins – e.g., biceps (two origins) and triceps (three origins)and triceps (three origins)

Location of attachments – named according to Location of attachments – named according to point of origin or insertion point of origin or insertion

Action – e.g., flexor or extensor, as in the Action – e.g., flexor or extensor, as in the names of muscles that flex or extend, names of muscles that flex or extend, respectivelyrespectively

Arrangement of FasciclesArrangement of Fascicles

Parallel – fascicles run parallel to the long axis Parallel – fascicles run parallel to the long axis of the muscle (e.g., sartorius)of the muscle (e.g., sartorius)

Fusiform – spindle-shaped muscles (e.g., Fusiform – spindle-shaped muscles (e.g., biceps brachii)biceps brachii)

Pennate – short fascicles that attach obliquely Pennate – short fascicles that attach obliquely to a central tendon running the length of the to a central tendon running the length of the muscle (e.g., rectus femoris)muscle (e.g., rectus femoris)

Arrangement of FasciclesArrangement of Fascicles

Convergent – fascicles converge from a broad Convergent – fascicles converge from a broad origin to a single tendon insertion (e.g., origin to a single tendon insertion (e.g., pectoralis major)pectoralis major)

Circular – fascicles are arranged in concentric Circular – fascicles are arranged in concentric rings (e.g., orbicularis oris)rings (e.g., orbicularis oris)

Arrangement of FasciclesArrangement of Fascicles

Figure 10.1

Bone-Muscle Relationships: Bone-Muscle Relationships: Lever SystemsLever Systems

Lever – a rigid bar that moves on a fulcrum, or Lever – a rigid bar that moves on a fulcrum, or fixed pointfixed point

Effort – force applied to a leverEffort – force applied to a lever Load – resistance moved by the effortLoad – resistance moved by the effort

Bone-Muscle Relationships: Bone-Muscle Relationships: Lever SystemsLever Systems

Figure 10.2b

Lever Systems: ClassesLever Systems: Classes

First class – the fulcrum is between the load First class – the fulcrum is between the load and the effortand the effort

Second class – the load is between the fulcrum Second class – the load is between the fulcrum and the effortand the effort

Third class – the effort is applied between the Third class – the effort is applied between the fulcrum and the loadfulcrum and the load

Lever Systems: First ClassLever Systems: First Class

Figure 10.3a

Lever Systems: Second ClassLever Systems: Second Class

Figure 10.3b

Lever Systems: Third ClassLever Systems: Third Class

Figure 10.3c

Major Skeletal Muscles: Anterior Major Skeletal Muscles: Anterior ViewView

The 40 superficial The 40 superficial muscles here are muscles here are divided into 10 divided into 10 regional areas of regional areas of the bodythe body

Figure 10.4b

Major Skeletal Muscles: Posterior Major Skeletal Muscles: Posterior ViewView

The 27 superficial The 27 superficial muscles here are muscles here are divided into seven divided into seven regional areas of regional areas of the bodythe body

Figure 10.5b

Muscles: Name, Action, and Muscles: Name, Action, and InnervationInnervation

Name and description of the muscle – be alert Name and description of the muscle – be alert to information given in the name to information given in the name

Origin and insertion – there is always a joint Origin and insertion – there is always a joint between the origin and insertion between the origin and insertion

Action – best learned by acting out a muscle’s Action – best learned by acting out a muscle’s movement on one’s own bodymovement on one’s own body

Nerve supply – name of major nerve that Nerve supply – name of major nerve that innervates the muscleinnervates the muscle

Muscles of the ScalpMuscles of the Scalp

Epicranius (occipitofrontalis) – bipartite Epicranius (occipitofrontalis) – bipartite muscle consisting of the:muscle consisting of the: Frontalis Frontalis Occipitalis Occipitalis Galea aponeurotica – cranial aponeurosis Galea aponeurotica – cranial aponeurosis

connecting above musclesconnecting above muscles These two muscles have alternate actions of These two muscles have alternate actions of

pulling the scalp forward and backwardpulling the scalp forward and backward

Muscles of the FaceMuscles of the Face

11 muscles are involved in lifting the 11 muscles are involved in lifting the eyebrows, flaring the nostrils, opening and eyebrows, flaring the nostrils, opening and closing the eyes and mouth, and smilingclosing the eyes and mouth, and smiling

All are innervated by cranial nerve VII (facial All are innervated by cranial nerve VII (facial nerve)nerve)

Usually insert in skin (rather than bone), and Usually insert in skin (rather than bone), and adjacent muscles often fuseadjacent muscles often fuse

Muscles of the Scalp, Face, and NeckMuscles of the Scalp, Face, and Neck

Figure 10.6

Muscles of MasticationMuscles of Mastication

There are four pairs of muscles involved in There are four pairs of muscles involved in masticationmastication Prime movers – temporalis and masseterPrime movers – temporalis and masseter Grinding movements – pterygoids and buccinatorsGrinding movements – pterygoids and buccinators

All are innervated by cranial nerve V All are innervated by cranial nerve V (trigeminal nerve)(trigeminal nerve)

Muscles of MasticationMuscles of Mastication

Figure 10.7a

Muscles of MasticationMuscles of Mastication

Figure 10.7b

Extrinsic Tongue MusclesExtrinsic Tongue Muscles

Three major muscles that anchor and move the Three major muscles that anchor and move the tonguetongue

All are innervated by cranial nerve XII All are innervated by cranial nerve XII (hypoglossal nerve)(hypoglossal nerve)

Extrinsic Tongue MusclesExtrinsic Tongue Muscles

Figure 10.7c