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The muscular system I
“Muscles of the head neck
and trunk”
Dr. Nabil Khouri
Dr. Nabil Khouri MD MSc, PhD
Interactions of Skeletal Muscles
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Skeletal muscles work together or in
opposition
Muscles only pull (never push)
All muscles have an Origin and Insertion
Origin of a muscle is close to body center
Insertion is far from body center.
As muscles shorten, the insertion generally
moves toward the origin
Whatever a muscle (or group of muscles)
does, another muscle (or group) “undoes”
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Muscle Classification: Functional Groups
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Prime movers – provide the major force for producing
a specific movement
Antagonists – oppose or reverse a particular
movement
Synergists
 Add
force to a movement
 Reduce undesirable or unnecessary movement
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Fixators – synergists that immobilize a bone or
muscle’s origin
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Naming Skeletal Muscles
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Location of muscle – bone or body region associated
with the muscle
Shape of muscle – e.g., the deltoid muscle
(deltoid = triangle)
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)
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Naming Skeletal Muscles
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Number of origins – e.g., biceps (two origins) and
triceps (three origins)
Location of attachments – named according to point
of origin or insertion
Action – e.g., flexor or extensor, as in the names of
muscles that flex or extend, respectively
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Arrangement of Fascicles
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Parallel – fascicles
run parallel to the
long axis of the
muscle (e.g.,
sartorius)
Fusiform – spindleshaped muscles
(e.g., biceps
brachii)
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Arrangement of Fascicles
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Pennate – short
fascicles that attach
obliquely to a central
tendon running the
length of the muscle
(e.g., rectus femoris)
Convergent – fascicles
converge from a
broad origin to a
single tendon
insertion (e.g.,
pectoralis major)
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Arrangement of Fascicles
Circular – fascicles
are arranged in
concentric rings
(e.g., orbicularis oris)
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Bone-Muscle Relationships:
The Lever Systems
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Lever – a rigid bar that moves on a fulcrum, or fixed
point
Effort – force applied to a lever
Load – resistance moved by the effort
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Lever Systems: Classes
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First class – the fulcrum is between the load and the effort
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Lever Systems: Second class lever
Figure 10.3b
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Third class lever
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Third class lever:
the effort is applied between the fulcrum and the load
Figure 10.3c
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Axial Muscles
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Muscles of the head and Neck
Thoracic wall
Abdominal wall
Diaphragm
Muscles of the trunk:
Back
Appendicular muscles
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Muscles of the upper limb
Muscles of the lower limb
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Muscles of the head and
neck
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Dr. Nabil Khouri MD MSc, PhD
Muscles of the Scalp
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Occipito-frontalis
Epicranius (occipitofrontalis) – this muscle consists of two:
 The
Frontalis
 The Occipitalis
 Galea aponeurotica – cranial aponeurosis connecting the
two muscles
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These two muscles have alternate actions of pulling the
scalp forward and backward
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MsC, PhD
Muscles of the Face
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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
Dr. Nabil Khouri MD MsC, PhD
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Muscles of facial expression:
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Change shape of eyes and mouth
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Innervated by the 7th cranial nerve (facial nerve)
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Bell,s palsy
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Examples: Orbicularis oris muscle
Orbicularis oculi muscle
Frontalis muscle
Zygomatic muscle
Buccinator muscle
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MsC, PhD
Muscles of mastication:
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Move the mandible (insertion): open and close
(chewing)
Innervation by the 5th cranial nerve (trigeminal
nerve)
Masseter muscle: closes
Temporalis muscle: closes
Lateral Pterygoid muscle: opens
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Muscles of Mastication
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Muscles Of mastication
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Platysma muscle
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Origin : from deep fascia
of pect. Major M
Insertion
 lower
mandible margin
 Muscles of mouth angle
 Anterior fibers cross to the
opposite side
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Muscles of the neck
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Sternocleidomastoid muscle
Suprahyoid muscles
Infrahyoid muscles
Scalene muscles
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Muscles of the Neck
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Dr. Nabil Khouri MD MSc, PhD
Muscles of the Anterior Neck :
Supra-hyoid
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These deep throat muscles form the floor of the
oral cavity, anchor the tongue, elevate the hyoid,
and move the larynx superiorly during swallowing
For full discribtion regarding the origin and insetion and action of this
groups of muscle:
http://www.docstoc.com/docs/108855590/Muscles-of-MasticationMuscles-of-the-Neck-Muscles-of-the-Thoracic
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MsC, PhD
Muscles of the Anterior Neck:
Supra-hyoid
Supra-hyoid
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Muscles of the Anterior Neck :
infra-hyoid
infra-hyoid
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MSc, PhD
Muscles of the Neck: Head Movements
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Major head flexor is the sternocleidomastoid muscle
Synergists to head flexion are the suprahyoid and
infrahyoid
Lateral head movements are accomplished by the
sternocleidomastoid and the scalene muscles
Head extension is accomplished by the deep splenius
muscles and aided by the superficial trapezius
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MsC, PhD
Muscles of the Neck: Head Movements
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Dr. Nabil Khouri MD MsC, PhD
Muscles of the Trunk
Thoracic wall Muscles: Intercostal muscles
 Diaphragm
 Abdominal wall muscles
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Muscles of the Thorax: Respiratory muscles
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Internal intercostals – deeper
layer that aids in forced expiration
The primary function of deep thoracic muscles is to promote movement for
breathing
External intercostals – more superficial layer that lifts the rib cage and
increases thoracic volume to allow inspiration
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Muscles of the Thorax: Resp. Muscles
•Diaphragm – most important muscle in inspiration
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Muscles of the Abdominal Wall
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Muscles of the Abdominal Wall
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Muscles of the back
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Stabilization of the Scapulae
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Elevators
Trapezius (upper)
 Levator scapulae
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Rotators
Rhomboid minor
 Rhomboid major
 Serratus anterior
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Depressors
Trapezius (lower)
 Pectoralis minor
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(next slide)
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Latissimus dorsi
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Teres major
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Trunk Movements: Deep Back
Muscles
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The prime mover of back extension is the erector
spinae
Erector spinae, or sacrospinalis, muscles consist of
three columns on each side of the vertebrae –
iliocostalis, longissimus, and spinalis
Lateral bending of the back is accomplished by
unilateral contraction of these muscles
Other deep back extensors include the semispinalis
muscles and the quadratus lumborum
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Trunk Movements: Deep Back Muscles
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings