Sonya Schuh-Huerta, Ph.D.

Sonya Schuh-Huerta, Ph.D.
MUSCLES OF THE BODY Ch 11 Human Anatomy Sonya Schuh-Huerta, Ph.D. Leonardo Da Vinci

Muscles of the Body Skeletal muscles General principles of leverage
Produce movements General principles of leverage Muscles act with or against each other Criteria used in naming muscles

Naming the Skeletal Muscles
Location Example  the brachialis is located on the arm (brachium) Shape Example  the deltoid is triangular Relative size Maximus, minimus, & longus indicate size Example  gluteus maximus is the large one & gluteus minimus is the small one

Direction of fascicles & muscle fibers Name tells direction in which fibers run Example  rectus abdominis & transversus abdominis (rectus = straight up; transverse  across or at right angle to midline) Location of attachments  name reveals point of origin & insertion Example  brachioradialis

Number of origins 2, 3, or 4 origins Indicated by the words biceps (2), triceps (3), & quadriceps (4) Action Action can be part of the muscle’s name Indicates type of muscle movement Flexor, extensor, adductor, or abductor (ie. extensor digitorum)

Arrangement of Fascicles in Muscles
Skeletal muscles  consist of fascicles Fascicles  arranged in different patterns Fascicle arrangement  tells about action of a muscle

Types of fascicle arrangement Parallel  fascicles run parallel to the long axis of the muscle Strap-like  sternocleidomastoid Fusiform  biceps brachii

Types of fascicle arrangement Convergent Origin of the muscle is broad Fascicles converge toward the tendon of insertion Example  Pectoralis major

Types of fascicle arrangement Pennate Unipennate  fascicles insert into one side of the tendon Bipennate  fascicles insert into the tendon from both sides Multipennate  fascicles insert into one large tendon from all sides

Circular Fascicles are arranged in concentric rings Surround external body openings Sphincter  general name for a circular muscle Examples Orbicularis oris & orbicularis oculi

(b) (a) Circular (orbicularis oris) (c) (b) Convergent (pectoralis major) (d) (f) (g) (c) Fusiform (biceps brachii) (d) Parallel (sartorius) (e) Multipennate (deltoid) (f) Bipennate (rectus femoris) (g) Unipennate (extensor digitorum longus)

Lever Systems: Bone-Muscle Relationships
Movement of skeletal muscles involves leverage Lever  a rigid bar that moves Fulcrum  a fixed point Effort  applied force Load  resistance

Lever Systems Effort x length of effort arm = load x length of load arm (force x distance) = (resistance x distance) Effort 10 kg Effort 0.25 cm 25 cm Fulcrum Load 1000 kg 10 x 25 = 1000 x 0.25 250 = 250 Load Fulcrum (a) Mechanical advantage with a power lever

Bones  act as levers Joints  act as fulcrums Muscle contraction  provides effort Applies force where muscle attaches to bone Load  bone, overlying tissue, & anything being lifted

Levers allow a given effort to Move a heavier load Move a load farther

First-class lever Effort applied at one end Load is at the opposite end Fulcrum is located between load & effort (a) First-class lever Arrangement of the elements is load-fulcrum-effort. L Example: scissors Load Fulcrum Effort In the body: A first-class lever system raises your head off your chest. The posterior neck muscles provide the effort; the atlanto-occipital joint is the fulcrum; and the weight to be lifted is the facial skeleton.

Third-class lever Effort is applied between the load & fulcrum Work speedily Always at a mechanical disadvantage (c) Third-class lever Arrangement of the elements is load-effort-fulcrum. L Example: tweezers or forceps Fulcrum Load Effort In the body: Flexing the forearm by the biceps brachii muscle exemplifies third-class leverage. The effort is exerted on the proximal radius of the forearm; the fulcrum is the elbow joint; and the load is the hand and distal end of the forearm.

Embryonic Development of the Muscles
Muscles organized into 4 groups Musculature of the visceral organs Pharyngeal arch muscles Axial muscles Limb muscles

Embryonic Development of the Muscles
Musculature of the visceral organs Includes smooth & cardiac muscle Develops from splanchnic mesoderm Pharyngeal arch muscles Includes Skeletal muscles of the pharynx Muscles of the head & neck Develop from the 4th to 7th somitomeres

Development of the Muscles
First (occipital) myotomes Somitomeres Eye Pharynx Limb bud Myotomes Limb bud (a) 6-week embryo

Pharyngeal Arch Muscles
Pharynx Muscles of facial expression e.g., orbicularis oculi Chewing muscles e.g., temporalis, masseter Suprahyoid muscles (most) Pharyngeal constrictors (key swallowing muscles) Trapezius (c) Pharyngeal arch (branchiomeric) muscles: 4th–7th somitomeres

Axial Muscles Lie anterior & posterior to the body axis
Muscles of the: Thorax, abdomen, & pelvis And many muscles of the: Neck & some of the head Function to move the trunk & maintain posture

Axial Muscles Extrinsic muscles of the eye Deep muscles of the back
e.g., erector spinae Muscles of the anterior & lateral trunk e.g., 1. infrahyoid muscles (neck) 2. intercostal muscles (thorax) 3. external & internal obliques (abdomen) 4. muscles of the pelvic floor Tongue muscles Tongue (d) Axial muscles: 1st–3rd somitomeres and myotomes

Limb Muscles Limb muscles arise from lateral parts of nearby myotomes
Extensors Muscle mass dorsal to limb bones Flexors Muscle mass ventral to limb bones

Limb Muscles Extensors e.g., triceps brachii, extensor digitorum
Flexors e.g., biceps brachii, flexor carpi radialis Extensors Extensors e.g., quadriceps femoris, tibialis anterior Flexors Flexors e.g., hamstrings, gastrocnemius (e) Limb muscles: From myotomes

Muscle Actions & Interactions
A muscle cannot reverse the movement it produces Another muscle must undo the action Muscles with opposite actions lie on opposite sides of a joint

Prime mover (= agonist) Has major responsibility for a certain movement Antagonist Opposes or reverses a movement Synergist  helps the prime mover By adding extra force By reducing undesirable movements

(a) A muscle that crosses on the anterior side of a joint produces flexion* (b) A muscle that crosses on the posterior side of a joint produces extension* Example: Latissimus dorsi (posterior view) Example: Pectoralis major (anterior view) *These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension. *These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.

(c) A muscle that crosses on the lateral side of a joint produces abduction (d) A muscle that crosses on the medial side of a joint produces adduction Example: Medial deltoid (anterolateral view) Example: Teres major (posterolateral view)

Muscle Compartments of the Limbs
Dense fibrous connective tissue divides limb muscles into compartments Muscles in opposing compartments are Agonist & antagonist pairs Each compartment is innervated by one single nerve

Muscle Compartments of Arm & Forearm
The upper limb has anterior & posterior compartments Anterior arm compartment muscles: Flex the shoulder or arm Innervation is the musculocutaneous nerve (we’ll learn later) Anterior forearm compartment muscles: Flex the wrist & digits Innervation is the median or ulnar nerve (..later)

Muscle Compartments of the Arm
Triceps brachii Lateral head Humerus Posterior compartment of arm (extends elbow); innervation: radial nerve Anterior compartment of arm (flexes elbow); innervation: musculocutaneous nerve Long Medial (a) Brachialis Short head Long head Biceps brachii (a) Muscles of the arm Extensors Flexors

Muscle Compartments of the Thigh
Posterior compartment muscles Extend the hip & flex the knee Innervation is the tibial branch of the sciatic nerve (later) Anterior compartment muscles Flex the hip & extend the knee Innervation is the femoral nerve (later) Medial compartment Adduct the thigh Innervation is the obturator nerve (later)

Muscle Compartments of the Thigh
Adductors Vastus lateralis Hamstrings Posterior compartment of thigh (flexes leg and extends thigh); innervation: tibial nerve (portion of sciatic nerve) Medial compartment (adducts thigh); innervation: obturator nerve Anterior compartment (extends leg); innervated by femoral nerve intermedius Rectus femoris Femur Vastus medialis (a) (a) Muscles of the thigh Posterior compartment muscles Anterior compartment muscles of thigh and lateral compartment muscles of leg

Lab Guide for Learning the Muscles

Superficial Muscles of the Body
Head Facial Temporalis Epicranius, frontal belly Masseter Orbicularis oculi Shoulder Zygomaticus Orbicularis oris Trapezius Neck Deltoid Arm Sternohyoid Triceps brachii Sternocleidomastoid Biceps brachii Platysma Thorax Brachialis Forearm Pectoralis minor Serratus anterior Pronator teres Pectoralis major Brachioradialis Intercostals Flexor carpi radialis Abdomen Palmaris longus Pelvis/thigh Rectus abdominis Internal oblique Iliopsoas Transversus abdominis Pectineus External oblique Thigh Thigh Rectus femoris Tensor fasciae latae Vastus lateralis Vastus medialis Sartorius Leg Adductor longus Fibularis longus Gracilis Leg Extensor digitorum longus Gastrocnemius Tibialis anterior Soleus

Superficial Muscles of the Body
Neck Epicranius, occipital belly Arm Sternocleidomastoid Triceps brachii Trapezius Brachialis Shoulder Deltoid Forearm Infraspinatus Brachioradialis Teres major Extensor carpi radialis longus Rhomboid major Triangle of auscultation Flexor carpi ulnaris Latissimus dorsi Extensor carpi ulnaris Hip Extensor digitorum Gluteus medius Gluteus maximus Iliotibial tract Thigh Adductor magnus Gracilis Hamstrings: Biceps femoris Leg Semitendinosus Gastrocnemius Semimembranosus Soleus Fibularis longus Calcaneal (Achilles) tendon

Muscles of the Head – Facial Expression
Muscles of facial expression Lie in the face & scalp Thin & variable in shape Often insert in the skin  not on bones (Innervated by cranial nerve VII  the facial nerve)

Muscles of the Face & Head
Corrugator supercilii Orbicularis oculi Levator labii superioris Zygomaticus minor and major Buccinator Risorius Orbicularis oris Mentalis Depressor labii inferioris Depressor anguli oris Platysma Galea aponeurotica Frontal belly Occipital Temporalis Masseter Sternocleidomastoid Trapezius Splenius capitis Epicranius

Muscles of Mastication & Tongue Movement
4 main pairs of muscles involved in mastication Innervated by mandibular division of the trigeminal nerve (cranial nerve V) Prime movers of jaw closure Masseter & temporalis Side-to-side movement Pterygoid muscles Compression of cheeks Buccinator muscles PLAY PLAY PLAY A&P Flix: Buccinator A&P Flix: Masseter A&P Flix: Temporalis

Muscles of Mastication & Tongue Movement
Lateral pterygoid Medial Masseter pulled away (b) Orbicularis oris Temporalis Masseter Buccinator (a)

Muscles of the Anterior Neck & Throat – Swallowing
The neck is divided into anterior & posterior triangles Anterior triangle Divided into suprahyoid & infrahyoid muscles Participate in swallowing Pharyngeal constrictors Swallowing muscles  squeeze food into esophagus

Muscles of the Anterior Neck & Throat
Tensor veli palatini Levator veli palatini Styloid process Superior pharyngeal constrictor Buccinator Mandible Middle pharyngeal constrictor Mylohyoid (cut) Hyoid bone Thyrohyoid membrane Geniohyoid Hyoglossus Inferior pharyngeal constrictor Thyroid cartilage of larynx Esophagus Trachea

Muscles of the Neck & Vertebral Column
Head movement: Sternocleidomastoid Splenius muscles Neck movement – scalenes Base of occipital bone 1st cervical vertebra Mastoid process Middle scalene Sternocleido- mastoid Anterior scalene Posterior scalene (a) Anterior

Mastoid process Splenius capitis Spinous processes of the vertebrae Splenius cervicis (b) Posterior

Trunk extension Deep muscles of the back Maintain normal curvatures of the spine Form a column from sacrum to the skull Erector spinae group Largest of the deep back muscles

Ligamentum nuchae Mastoid process of temporal bone Semispinalis capitis Longissimus capitis Iliocostalis cervicis Semispinalis cervicis Longissimus cervicis Semispinalis thoracis Iliocostalis thoracis Longissimus thoracis Spinalis thoracis Iliocostalis Erector spinae Longissimus Spinalis Multifidus Iliocostalis lumborum Quadratus lumborum External oblique

PLAY PLAY PLAY A&P Flix: Iliocostalis A&P Flix: Spinalis
A&P Flix: Longissimus

Deep Muscles of the Thorax –Breathing
Deep muscles provide movements for breathing External intercostal muscles Lift the rib cage during inhalation Internal intercostal muscles Aid expiration during heavy breathing

Deep Muscles of the Thorax—Breathing
External intercostal Internal intercostal PLAY PLAY A&P Flix: External intercostal muscles A&P Flix: Internal intercostal muscles

Deep Muscles of the Thorax –Breathing
Diaphragm Most important muscle of respiration! Flattens as it contracts Increases the volume of the thoracic cavity How does this aid in breathing? Innervated by phrenic nerve (your brain controls)

Deep Muscles of the Thorax—Breathing
Xiphoid process of sternum Foramen for inferior vena cava Foramen for esophagus Costal cartilage Central tendon of diaphragm Diaphragm Foramen for aorta Lumbar vertebra 12th rib Quadratus lumborum Psoas major

Muscles of the Abdominal Wall
Lateral & anterior abdominal wall Formed from 3 flat muscle sheets External oblique Internal oblique Transversus abdominis Fourth muscle pair Rectus abdominis Inserts at the linea alba

Pectoralis major Serratus anterior Linea alba Tendinous intersection Transversus abdominis Rectus abdominis Internal oblique External oblique Inguinal ligament (formed by free inferior border of the external oblique aponeurosis) Aponeurosis of the external oblique (a) PLAY PLAY A&P Flix: Internal obliques A&P Flix: External obliques

External oblique Rectus abdominis Internal oblique Transversus abdominis PLAY PLAY A&P Flix: Transverse abdominis A&P Flix: Rectus abdominis

Muscles of the Pelvic Floor
Pelvic floor (pelvic diaphragm) Sheet of 2 muscles Both support pelvic organs Levator ani Formed from iliococcygeus, puborectalis, & pubococcygeus Coccygeus

Muscles of the Pelvic Floor
Anterior Pubococcygeus Symphysis pubis Levator ani IIiococcygeus Urogenital diaphragm Urethra Vagina Anal canal Obturator internus Coccyx Piriformis Levator ani Pelvic diaphragm Coccygeus Posterior

Muscles of the Perineum
Midline raphe Bulbospongiosus Ischiocavernosus Penis Clitoris Superficial transverse perineal muscle Urethral opening Vaginal opening Levator ani Anus Gluteus maximus Male Female

Superficial Muscles of the Anterior Thorax
Movements of the scapula Pectoralis major Pectoralis minor Serratus anterior Subclavius PLAY PLAY A&P Flix: Pectoralis major A&P Flix: Serratus anterior PLAY A&P Flix: Pectoralis minor

Superficial Muscles of Anterior Thorax
Sternocleidomastoid Subclavius Clavicle Subscapularis Deltoid Pectoralis minor Pectoralis major Coracobrachialis Sternum Serratus anterior Biceps brachii Humerus

Superficial Muscles of the Posterior Thorax
Movements of the scapula Trapezius Levator scapulae Rhomboid major Rhomboid minor PLAY PLAY A&P Flix: Trapezius A&P Flix: Levator scapulae PLAY PLAY A&P Flix: Rhomboid major A&P Flix: Rhomboid minor

Superficial Muscles of the Posterior Thorax
Levator scapulae Trapezius Supraspinatus Clavicle Deltoid Spine of scapula Rhomboid minor Infraspinatus Rhomboid major Teres minor Teres major Humerus Latissimus dorsi

Muscles Crossing the Shoulder Joint
Movements of the arm Deltoid Pectoralis major Clavicle Deltoid Sternum Pectoralis major Coracobrachialis Triceps brachii Lateral head Long head Medial head Biceps brachii PLAY A&P Flix: Deltoid Brachialis Brachio- radialis (a) Anterior view

Movements of the arm A&P Flix: Latissimus dorsi A&P Flix: Supraspinatus A&P Flix: Infraspinatus Supraspinatus Spine of scapula Deltoid (cut) PLAY Greater tubercle of humerus Infraspinatus PLAY Teres minor Teres major PLAY Triceps brachii Lateral head Long head Latissimus dorsi Humerus Olecranon process of ulna Anconeus (b) Posterior view

Supraspinatus Movements of arm A&P Flix: Teres minor A&P Flix: Teres major A&P Flix: Subscapularis Spine of scapula Deltoid (cut) Greater tubercle of humerus PLAY Infraspinatus Teres minor PLAY Teres major PLAY Triceps brachii Lateral head Long head Latissimus dorsi Humerus Olecranon process of ulna Anconeus (b) Posterior view

Questions…. What’s Next
Questions…? What’s Next? Lab: Muscles Next Lecture: Muscles cont… Wed Lab: Finish Muscles & Review

Sonya Schuh-Huerta, Ph.D.

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Sonya Schuh-Huerta, Ph.D.

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