Bio40A ch11text

Page 1:

  • Muscles in the muscular system include both skeletal muscle tissue and connective tissue

    • Function of most muscles is to produce movements of body parts

    • Some muscles stabilize bones for more effective movement

  • Working knowledge of skeletal muscle anatomy is crucial for professionals in allied health and physical rehabilitation fields

  • Muscular system and muscular tissue contribute to homeostasis by stabilizing body position, producing movements, regulating organ volume, moving substances within the body, and producing heat

Page 2:

11.1 How Skeletal Muscles Produce Movements

  • Skeletal muscles exert force on tendons, which pull on bones or other structures

  • Most muscles cross at least one joint and are attached to articulating bones

    • Attachment of muscle's tendon to stationary bone is called origin

    • Attachment of muscle's other tendon to movable bone is called insertion

  • Fleshy portion of muscle between tendons is called belly

  • Actions of a muscle are the main movements that occur when the muscle contracts

  • Certain muscles are capable of reverse muscle action (RMA)

  • Muscles that move a body part often do not cover the moving part

Page 3: Lever Systems and Leverage

  • Bones act as levers and joints function as the fulcrums of these levers

  • A lever is a rigid structure that can move around a fixed point called a fulcrum

  • A lever is acted on by two different forces: the effort (E) and the load (L)

  • Motion occurs when the effort applied to the bone at the insertion exceeds the load

  • The relative distance between the fulcrum, load, and effort determines whether a lever operates at a mechanical advantage or disadvantage

  • Levers are categorized into three types: first-class, second-class, and third-class levers

First-class levers

  • The fulcrum is between the effort and the load

  • Can produce either a mechanical advantage or disadvantage depending on the relative distances of the effort and load from the fulcrum

  • Examples include scissors and seesaws

Second-class levers

  • The load is between the fulcrum and the effort

  • Always produce a mechanical advantage because the load is closer to the fulcrum than the effort

  • Sacrifice speed and range of motion for force

  • Examples include standing up on your toes

Third-class levers

  • The effort is between the fulcrum and the load

  • Always produce a mechanical disadvantage because the effort is closer to the fulcrum than the load

  • Favor speed and range of motion over force

  • Examples include the elbow joint and the biceps brachii muscle

Clinical Connection: Intramuscular Injections

  • Intramuscular injections penetrate the skin and subcutaneous layer to enter the muscle itself

  • Preferred when prompt absorption is desired, larger doses are indicated, or the drug is too irritating to give subcutaneously

  • Common sites for intramuscular injections include the gluteus medius muscle, lateral side of the thigh, and the deltoid muscle of the shoulder

  • Intramuscular injections are given deep within the muscle to avoid injury to major nerves and blood vessels

  • Faster speed of delivery than oral medications but slower than intravenous infusions

Effects of Fascicle Arrangement

  • Skeletal muscle fibers within a muscle are arranged in bundles known as fascicles

  • Fascicles can form different patterns with respect to the tendons: parallel, fusiform, circular, triangular, or pennate

  • Fascicular arrangement affects a muscle's power and range of motion

  • Muscle fibers contract and shorten to about 70% of their original length

Page 4:

  • Skeletal muscles produce movements through opposing pairs of muscles

    • Prime mover (agonist) contracts to cause an action

    • Antagonist stretches and yields to the effects of the prime mover

  • Roles of prime mover and antagonist can switch for different movements

  • If prime mover and antagonist contract with equal force, there will be no movement

  • Prime mover may cross other joints before reaching the joint where its primary action occurs

Page 4 (continued):

  • Lever structure and types of levers

    • Levers divided into three types based on the placement of the fulcrum, effort, and load

    • First-class lever, second-class lever, and third-class lever

  • The type of lever that produces the most force is not specified

Page 4 (continued):

  • Muscle power depends on total cross-sectional area, not length

  • More fibers per unit of cross-sectional area result in more power

  • Fascicular arrangement represents a compromise between power and range of motion

    • Pennate muscles have a large number of short-fibered fascicles, giving them greater power but a smaller range of motion

    • Parallel muscles have fewer fascicles but longer fibers, giving them a greater range of motion but less power

Page 4 (continued):

  • Movements are often the result of several skeletal muscles acting as a group

  • Most skeletal muscles are arranged in opposing pairs at joints

  • Fixators hold the origin of the prime mover steady to allow efficient movement

  • Synergists contract and stabilize intermediate joints to aid the movement of the prime mover

Page 5:

  • Compartments in the limbs consist of skeletal muscles, associated blood vessels, and nerves with a common function

  • Flexor compartment muscles are anterior in the upper limbs, while extensor compartment muscles are posterior

  • Synergists contract to stabilize intermediate joints and prevent unwanted movement

  • Some muscles in a group act as fixators to stabilize the origin of the prime mover

  • Arrangement of fascicles in muscles varies

    • Parallel, fusiform, circular, triangular, pennate (unipennate, bipennate, multipennate)

Page 6: Overview of the Principal Skeletal Muscles

  • Organizing muscles into groups is beneficial

    • Muscle groups share common features

    • Grouping muscles simplifies the learning process

  • Sections 11.4-11.23 cover the principal skeletal muscles

  • Each section contains:

    • Objective

    • Overview

    • Muscle names

    • Origins, insertions, and actions

    • Innervation

    • Relating muscles to movements

    • Questions

    • Clinical Connections

    • Figures

Page 6: Clinical Connection Benefits of Stretching

  • Stretching aims to achieve normal range of motion and mobility

  • Best stretching routine involves static stretching

  • Stretching should be done after warming up

  • Benefits of stretching:

    • Improved physical performance

    • Decreased risk of injury

    • Reduced muscle soreness

    • Improved posture

Page 6: Checkpoint

  • Checkpoint questions:

    1. Using the terms origin, insertion, and belly, describe how skeletal muscles produce body movements by pulling on bones.

    2. List the three types of levers and give an example of each.

    3. Define the roles of the prime mover, antagonist, synergist, and fixator in producing various movements of the free upper limb.

    4. What is a muscle compartment?

Page 6: How Skeletal Muscles Are Named

  • Objective: Explain seven features used in naming skeletal muscles

  • Names of skeletal muscles contain combinations of word roots

  • Learning muscle names gives clues about their features

  • Study Table 11.2 to become familiar with muscle name terms

Page 6: Checkpoint

  • Checkpoint question: 5. Select 10 muscles in Figure 11.3 and identify the features on which their names are based.

Page 7:

  • Characteristics used to name muscles:

    • Direction: Rectus (parallel to midline), Transverse (perpendicular to midline), Oblique (diagonal to midline)

    • Size: Maximus (largest), Minimus (smallest), Longus (long), Brevis (short), Latissimus (widest), Longissimus (longest), Magnus (large), Major (larger), Minor (smaller), Vastus (huge)

    • Shape: Deltoid (triangular), Trapezius (trapezoid), Serratus (saw-toothed), Rhomboid (diamond-shaped), Orbicularis (circular), Pectinate (comblike), Piriformis (pear-shaped), Platys (flat), Quadratus (square, four-sided), Gracilis (slender)

    • Action: Flexor (decreases joint angle), Extensor (increases joint angle), Abductor (moves bone away from midline), Adductor (moves bone closer to midline), Levator (raises or elevates body part), Depressor (lowers or depresses body part), Supinator (turns palm anteriorly), Pronator (turns palm posteriorly), Sphincter (decreases size of an opening), Tensor (makes body part rigid), Rotator (rotates bone around longitudinal axis)

    • Number of Origins: Biceps (two origins), Triceps (three origins), Quadriceps (four origins)

    • Location: Temporalis (muscle near temporal bone)

    • Origin and Insertion: Sternocleidomastoid (originating on sternum and clavicle and inserting on mastoid process of temporal bone)

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  • Overview of the Principal Skeletal Muscles:

    • Muscles listed: Orbicularis oris, Depressor anguli oris, Orbicularis oculi, Masseter, Sternocleidomastoid, Trapezius, Scalenes, Deltoid, Pectoralis major, Serratus anterior, Biceps brachii, Brachialis, Triceps brachii, Brachioradialis, Pronator teres, Flexor carpi radialis, Thenar muscles, Hypothenar muscles, Iliotibial tract, Patellar ligament, Tibialis anterior, Fibularis longus, Tibia, Omohyoid, Platysma, Sternohyoid, Latissimus dorsi, External oblique, Rectus abdominis, Brachioradialis, Tensor fasciae latae, Iliacus, Psoas major, Pectineus, Adductor longus, Sartorius, Gracilis, Vastus lateralis, Rectus femoris, Vastus medialis, Tendon of quadriceps femoris, Patella, Gastrocnemius, Soleus

    • Figure 11.3 shows the principal superficial skeletal muscles

Page 9:

  • Example of a muscle named for each characteristic:

    • Direction of fibers: Sternocleidomastoid

    • Shape: Infraspinatus

    • Action: Brachioradialis

    • Size: Gluteus maximus

    • Origin and Insertion: Sternocleidomastoid

    • Location: External oblique

    • Number of tendons of origin: Biceps

Page 10:

  • Muscles of the Head That Produce Facial Expressions:

    • Muscles in this group originate in the fascia or bones of the skull and insert into the skin

    • They move the skin rather than a joint when they contract

    • Functions include closing and opening orifices (eyes, nose, mouth)

    • Examples of muscles in this group: Orbicularis oculi, Levator palpebrae superioris, Occipitofrontalis, Masseter, Platysma, Nasalis, Buccinator, etc.

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  • Muscles of facial expression cause frowning, smiling, pouting, and squinting

    • Occipitofrontalis (frontal belly)

    • Orbicularis oculi

    • Nasalis

    • Levator labii superioris

    • Zygomaticus minor

    • Zygomaticus major

    • Levator anguli oris

    • Buccinator

    • Risorius

    • Orbicularis oris

    • Depressor anguli oris

    • Depressor labii inferioris

    • Mentalis

    • Platysma

    • Epicranial aponeurosis

    • Temporalis

    • Occipitofrontalis (occipital belly)

    • Posterior auricular

    • Zygomatic arch

    • Sternocleidomastoid

    • Splenius capitis

    • Trapezius

    • Levator scapulae

    • Middle scalene

    • Mandible

    • Masseter

    • Splenius cervicis

  • The buccinator muscle forms the major muscular portion of the cheek

    • It compresses the cheeks during blowing, whistling, and sucking

    • It assists in chewing

  • Bell's Palsy is a unilateral paralysis of the muscles of facial expression

    • It is due to damage or disease of the facial nerve (VII)

    • Possible causes include inflammation of the facial nerve, ear surgery, or infection by the herpes simplex virus

    • Symptoms include drooping of the face, inability to wrinkle the forehead, close the eye, or pucker the lips on the affected side

    • 80% of patients recover completely within a few weeks to a few months

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  • Muscles of the head that produce facial expressions can be grouped into those that act on the mouth and those that act on the eyes

  • Muscles that act on the mouth:

    • Orbicularis oris: Closes and protrudes lips, compresses lips against teeth, and shapes lips during speech

    • Zygomaticus major: Draws angle of mouth superiorly and laterally, as in smiling

    • Zygomaticus minor: Raises upper lip, exposing upper teeth

    • Levator labii superioris: Raises upper lip

    • Depressor labii inferioris: Depresses lower lip

    • Depressor anguli oris: Draws angle of mouth laterally and inferiorly, as in opening mouth

    • Buccinator: Presses cheeks against teeth and lips, assists in mastication

    • Risorius: Draws angle of mouth laterally, as in grimacing

    • Mentalis: Elevates and protrudes lower lip, pulls skin of chin up, as in pouting

  • Muscles that act on the eyes:

    • Occipitofrontalis (frontal belly): Draws scalp anteriorly, raises eyebrows, and wrinkles skin of forehead horizontally

    • Orbicularis oculi: Closes eyelids

    • Nasalis: Widens nostrils

    • Levator labii superioris: Raises upper lip

    • Zygomaticus minor: Raises upper lip

    • Zygomaticus major: Raises angle of mouth

    • Levator anguli oris: Draws angle of mouth laterally and superiorly

    • Risorius: Draws angle of mouth laterally

    • Orbicularis oris: Closes and protrudes lips

    • Depressor anguli oris: Draws angle of mouth laterally and inferiorly

  • The platysma muscle in the neck draws the outer part of the lower lip inferiorly and posteriorly, as in pouting, and depresses the mandible.

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  • Muscles of the head that move the eyeballs (extrinsic eye muscles) and upper eyelid

    • Extrinsic muscles of the eyeball are fast contracting and precisely controlled skeletal muscles

  • Muscles that move the eyeballs are called extrinsic eye muscles

    • Origin outside the eyeballs (in the orbit) and insert on the outer surface of the sclera

  • Three pairs of extrinsic eye muscles control movements of the eyeballs:

    • Superior and inferior recti

    • Lateral and medial recti

    • Superior and inferior obliques

  • Actions of the oblique muscles cannot be deduced from their names

    • Superior oblique muscle moves the eyeballs inferiorly and laterally

    • Inferior oblique muscle moves the eyeballs superiorly and laterally

  • Levator palpebrae superioris does not move the eyeballs, it raises the upper eyelid

Page 14:

  • Strabismus is a condition where the two eyeballs are not properly aligned

    • Can be hereditary or due to birth injuries, muscle problems, brain control center issues, or localized disease

  • Strabismus can be constant or intermittent

  • Treatment options for strabismus include surgery, visual therapy, and orthoptics

  • Origin, insertion, action, and innervation of the extrinsic eye muscles:

    • Superior rectus: Moves eyeballs superiorly and medially, innervated by oculomotor (III) nerve

    • Inferior rectus: Moves eyeballs inferiorly and medially, innervated by oculomotor (III) nerve

    • Lateral rectus: Moves eyeballs laterally, innervated by abducens (VI) nerve

    • Medial rectus: Moves eyeballs medially, innervated by oculomotor (III) nerve

    • Superior oblique: Moves eyeballs inferiorly and laterally, innervated by trochlear (IV) nerve

    • Inferior oblique: Moves eyeballs superiorly and laterally, innervated by oculomotor (III) nerve

    • Levator palpebrae superioris: Elevates upper eyelids, innervated by oculomotor (III) nerve

Page 15:

  • Muscles that move the mandible and assist in mastication and speech

    • Masseter muscle

      • Origin: Maxilla and zygomatic arch

      • Insertion: Angle and ramus of mandible

      • Action: Elevates mandible, as in closing mouth

      • Innervation: Mandibular division of trigeminal (V) nerve

    • Temporalis muscle

      • Origin: Temporal bone

      • Insertion: Coronoid process and ramus of mandible

      • Action: Elevates and retracts mandible

      • Innervation: Mandibular division of trigeminal (V) nerve

    • Medial pterygoid muscle

      • Origin: Medial surface of lateral portion of pterygoid process of sphenoid bone; maxilla

      • Insertion: Angle and ramus of mandible

      • Action: Elevates and protracts (protrudes) mandible and moves mandible from side to side

      • Innervation: Mandibular division of trigeminal (V) nerve

    • Lateral pterygoid muscle

      • Origin: Greater wing and lateral surface of lateral portion of pterygoid process of sphenoid bone

      • Insertion: Condyle of mandible; temporomandibular joint (TMJ)

      • Action: Protracts mandible, depresses mandible as in opening mouth, and moves mandible from side to side

      • Innervation: Mandibular division of trigeminal (V) nerve

  • Muscles that move the eyeballs

    • Eyelids open the eyes

    • Antagonist to the orbicularis oculi, which closes the eyes

  • Arranging muscles according to their actions on the eyeballs

    • Elevation, depression, abduction, adduction

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  • Muscles of the head that move the tongue and assist in mastication and speech

    • Tongue is vital to digestive functions, taste detection, deglutition, and speech

    • Tongue's mobility aided by attachment to mandible, styloid process of temporal bone, and hyoid bone

    • Tongue divided into lateral halves by a median fibrous septum

    • Extrinsic tongue muscles originate outside the tongue and insert into it

    • Intrinsic tongue muscles originate and insert within the tongue

  • Extrinsic tongue muscles

    • Genioglossus muscle

      • Origin: Mandible

      • Action: Pulls the tongue downward and forward

    • Styloglossus muscle

      • Origin: Styloid process

      • Action: Pulls the tongue upward and backward

    • Hyoglossus muscle

      • Origin: Hyoid bone

      • Action: Pulls the tongue downward and backward

Page 17:

  • Functions of the tongue:

    • Extrinsic and intrinsic muscles of the tongue are arranged in both lateral halves of the tongue.

  • Muscles that move the tongue and assist in mastication and speech:

    • Genioglossus muscle: Originates from the mandible and undersurface of the tongue and hyoid bone. Depresses tongue and thrusts it anteriorly.

    • Styloglossus muscle: Originates from the styloid process of the temporal bone. Elevates tongue and draws it posteriorly.

    • Hyoglossus muscle: Originates from the greater horn and body of the hyoid bone. Depresses tongue and draws down its sides.

    • Palatoglossus muscle: Originates from the anterior surface of the soft palate. Elevates posterior portion of tongue and draws soft palate down on tongue.

  • Clinical Connection: Intubation during Anesthesia:

    • General anesthesia causes total relaxation of muscles.

    • Paralysis of the genioglossus muscle can obstruct the airway to the lungs.

    • Mandible is manually thrust forward or a tube is inserted to protect the airway.

Page 18:

  • Muscles of the anterior neck that assist in deglutition and speech:

    • Digastric muscle: Elevates the hyoid bone and larynx during swallowing and speech. Depresses the mandible in reverse muscle action.

    • Stylohyoid muscle: Elevates and draws the hyoid bone posteriorly, elongating the floor of the oral cavity during swallowing.

    • Mylohyoid muscle: Elevates the hyoid bone and helps press the tongue against the roof of the oral cavity during swallowing.

    • Geniohyoid muscle: Elevates and draws the hyoid bone anteriorly, shortening the floor of the oral cavity and widening the throat.

    • Infrahyoid muscles: Depress the hyoid bone and move the larynx during swallowing and speech.

    • Omohyoid muscle: Composed of superior and inferior bellies, depresses the hyoid bone.

    • Sternohyoid muscle: Depresses the hyoid bone.

    • Thyrohyoid muscle: Elevates the thyroid cartilage to produce high sounds.

  • Checkpoint 10: Muscles contracted when examining the inside of the mouth:

    • Genioglossus muscle

    • Styloglossus muscle

    • Mylohyoid muscle

    • Digastric muscle

Page 18 (Continued):

  • Muscles of the anterior neck that assist in deglutition and speech:

    • Suprahyoid muscles: Located superior to the hyoid bone, elevate the hyoid bone, floor of the oral cavity, and tongue during swallowing.

    • Infrahyoid muscles: Located inferior to the hyoid bone, stabilize the hyoid bone and move the larynx during swallowing and speech.

Page 19:

Suprahyoid Muscles

  • Digastric muscle:

    • Anterior belly from inner side of inferior border of mandible

    • Posterior belly from temporal bone

    • Action: Elevates hyoid bone

    • Innervation: Anterior belly - mandibular division of trigeminal (V) nerve, Posterior belly - facial (VII) nerve

  • Stylohyoid muscle:

    • Origin: Styloid process of temporal bone

    • Insertion: Body of hyoid bone

    • Action: Elevates hyoid bone and draws it posteriorly

    • Innervation: Facial (VII) nerve

  • Mylohyoid muscle:

    • Origin: Inner surface of mandible

    • Insertion: Body of hyoid bone

    • Action: Elevates hyoid bone and floor of mouth, depresses mandible

    • Innervation: Mandibular division of trigeminal (V) nerve

  • Geniohyoid muscle:

    • Origin: Inner surface of mandible

    • Insertion: Body of hyoid bone

    • Action: Elevates hyoid bone, draws hyoid bone and tongue anteriorly, depresses mandible

    • Innervation: First cervical spinal nerve (C1)

Infrahyoid Muscles

  • Omohyoid muscle:

    • Origin: Superior border of scapula and superior transverse ligament

    • Insertion: Body of hyoid bone

    • Action: Depresses hyoid bone

    • Innervation: Branches of spinal nerves C1-C3

Q: What is the combined action of the suprahyoid and infrahyoid muscles?

Clinical Connection: Dysphagia

  • Dysphagia is a clinical term for difficulty in swallowing.

  • Causes of dysphagia include:

    • Nervous system disorders that weaken or damage muscles of deglutition (stroke, Parkinson's disease, cerebral palsy)

    • Infections

    • Cancer of the head, neck, or esophagus

    • Injuries to the head, neck, or chest.

Page 20:

  • Muscles of the neck are involved in moving the head and flexing the cervical portion of the vertebral column.

  • The sternocleidomastoid (SCM) muscles flex the cervical portion of the vertebral column and flex the head when contracted together.

  • The SCM muscles laterally flex and rotate the head when contracted individually.

  • The SCM muscle consists of two bellies, with variable separation.

  • Bilateral contraction of certain neck muscles extends the head, while unilateral contraction primarily involves rotation of the head.

  • The sternocleidomastoid muscle divides the neck into two major triangles: anterior and posterior.

  • The anterior triangle is bordered by the mandible, cervical midline, and anterior border of the sternocleidomastoid muscle.

  • The anterior triangle is subdivided into three paired triangles.

Page 21:

  • The sternocleidomastoid muscle divides the neck into two principal triangles: anterior and posterior.

  • The triangles of the neck are important anatomically and surgically because of the structures within their boundaries.

Note: The main ideas and supporting details have been summarized in bullet points.

Page 22: Muscles of the Abdomen That Protect Abdominal Viscera and Move the Vertebral Column

  • Objective: Describe the origin, insertion, action, and innervation of the muscles that protect the abdominal viscera and move the vertebral column.

  • Anterolateral abdominal wall composed of skin, fascia, and four pairs of muscles: external oblique, internal oblique, transversus abdominis, and rectus abdominis.

    • External oblique: superficial muscle with fascicles extending inferiorly and medially.

    • Internal oblique: intermediate flat muscle with fascicles extending at right angles to those of the external oblique.

    • Transversus abdominis: deep muscle with fascicles directed transversely around the abdominal wall.

  • External oblique, internal oblique, and transversus abdominis form three layers of muscle around the abdomen.

  • Structural arrangement provides protection to the abdominal viscera when muscles have good tone.

Page 23: Muscles of the Abdomen That Protect Abdominal Viscera and Move the Vertebral Column (Figure 11.10)

  • Anterolateral abdominal muscles protect the abdominal viscera, move the vertebral column, and assist in forced exhalation, defecation, urination, and childbirth.

  • Muscles depicted in the figure:

    • External oblique

    • Internal oblique

    • Transversus abdominis

    • Rectus abdominis

  • Other anatomical features shown in the figure:

    • Tendinous intersections

    • Inguinal ligament

    • Serratus anterior

    • Scapula

    • Clavicle

    • Aponeurosis of internal oblique

    • Aponeurosis of external oblique

    • Cremaster muscle around spermatic cord

    • Linea alba

    • Anterior superior iliac spine

    • Superficial inguinal ring

    • Pubic tubercle of pubis

    • Anterior layer of rectus sheath

    • Pectoralis major

    • Biceps brachii

    • Latissimus dorsi

    • Deltoid

    • Posterior layer of rectus sheath

    • Subcutaneous layer

    • Skin

    • Superior view of transverse section of anterior abdominal wall superior to umbilicus (navel)

Page 24: Abdominal Muscles and Inguinal Hernia

  • Body builders focus on developing the "six-pack" effect of the abdomen

  • Some individuals have a variant and can develop an "eight-pack"

  • Muscles of the anterolateral abdominal wall have multiple functions:

    • Contain and protect abdominal viscera

    • Flex, laterally flex, and rotate the vertebral column

    • Compress the abdomen during forced exhalation

    • Produce force for defecation, urination, and childbirth

  • Aponeuroses of external oblique, internal oblique, and transversus abdominis muscles form rectus sheaths

  • Rectus sheaths meet at the midline to form the linea alba

  • Linea alba stretches during pregnancy

  • External oblique aponeurosis forms the inguinal ligament

  • Superficial inguinal ring is the outer opening of the inguinal canal

  • Inguinal canal contains different structures depending on gender

  • Rectus abdominis muscle extends the entire length of the anterior abdominal wall

  • Muscle is interrupted by tendinous intersections

  • Tendinous intersections are fused with the anterior wall of the rectus sheath

  • Hypertrophy of the rectus muscle can result in easily demonstrated intersections

  • Inguinal hernia is a protrusion of an organ through the weak area in the abdominal wall

  • Inguinal hernia is more common in males due to larger inguinal canals

  • Treatment of hernias usually involves surgery

  • Sports hernia is a painful strain in the lower abdomen or groin

  • Sports hernia does not cause a visible lump

  • Sports hernia occurs more frequently in males and is due to simultaneous contraction of abdominal and adductor muscles

  • Treatment of sports hernia includes rest, ice, anti-inflammatory

Page 25:

  • The diaphragm is the most important muscle for breathing

    • It separates the thoracic and abdominal cavities

    • It has a convex superior surface and a concave inferior surface

  • The diaphragm originates from the xiphoid process of the sternum, the inferior six ribs and their costal cartilages, the lumbar vertebrae and their intervertebral discs, and the twelfth rib

  • The fibers of the muscular portion converge and insert into the central tendon

  • The central tendon fuses with the inferior surface of the pericardium and the pleurae

  • The diaphragm has three major openings through which various structures pass between the thorax and abdomen

  • Movements of the diaphragm help return venous blood passing through abdominal veins to the heart

  • The diaphragm, along with the anterolateral abdominal muscles, helps increase intra-abdominal pressure to evacuate the pelvic contents during defecation, urination, and childbirth

  • The diaphragm also helps support the vertebral column and prevent flexion during weight lifting

  • Other muscles involved in breathing are the intercostals, which span the intercostal spaces

    • The external intercostals elevate the ribs during inhalation to help expand the thoracic cavity

    • The internal intercostals draw adjacent ribs together during forced exhalation to help decrease the size of the thoracic cavity

  • The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles, and quadratus lumborum muscle

Page 26:

  • The muscles of the thorax alter the size of the thoracic cavity for breathing

  • The diaphragm and external intercostal muscles are used during quiet inhalation and exhalation

  • During deep, forceful inhalation, the sternocleidomastoid, scalene, and pectoralis minor muscles are also used

  • During deep, forceful exhalation, the external oblique, internal oblique, transversus abdominis, rectus abdominis, and internal intercostals are also used

Page 27:

  • The diaphragm is the muscle associated with breathing

  • It is innervated by the phrenic nerve

Page 28:

Muscles of the Pelvic Floor That Support the Pelvic Viscera and Function as Sphincters

  • The levator ani muscle is an important muscle of the pelvic floor

  • It supports the pelvic viscera and resists the inferior thrust during functions such as forced exhalation, coughing, vomiting, urination, and defecation

  • The levator ani muscle also functions as a sphincter at the anorectal junction, urethra, and vagina

  • The ischiococcygeus muscle pulls the coccyx anteriorly after it has been pushed posteriorly during defecation or childbirth

  • Injury to the levator ani muscle during childbirth or episiotomy can lead to urinary stress incontinence

  • Kegel exercises can be used to strengthen and tighten the muscles that support the pelvic viscera

  • Kegel exercises involve the alternate contraction and relaxation of the muscles of the pelvic floor

  • The levator ani muscle is composed of three parts: pubococcygeus muscle, puborectalis muscle, and iliococcygeus muscle

  • The pubococcygeus muscle originates from the pubis and ischial spine and inserts into the coccyx, urethra, anal canal, perineal body, and anococcygeal ligament

  • The puborectalis muscle originates from the posterior surface of the pubic body and forms a sling posterior to the anorectal junction

  • The iliococcygeus muscle originates from the ischial spine and inserts into the coccyx

  • The ischiococcygeus muscle supports the pelvic viscera, resists increase in intra-abdominal pressure, and pulls the coccyx anteriorly following defecation or childbirth

Page 29:

  • The perineum is the region of the trunk inferior to the pelvic diaphragm

  • It extends from the pubic symphysis anteriorly to the coccyx posteriorly and to the ischial tuberosities laterally

  • The perineum is divided into an anterior urogenital triangle and a posterior anal triangle

  • The perineal body is a muscular intersection anterior to the anus where several perineal muscles insert

  • The muscles of the perineum are arranged in two layers: superficial and deep

  • The superficial layer includes the superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles

  • The deep muscles of the male perineum are the deep transverse perineal and external urethral sphincter muscles

  • The deep muscles of the female perineum are the compressor urethrae, sphincter urethrovaginalis, and external urethral sphincter muscles

  • The external anal sphincter keeps the anal canal and anus closed except during defecation

Relating Muscles to Movements

  • The muscles of the perineum can be categorized based on their actions:

    • Supporting and maintaining the position of the pelvic viscera

    • Resisting an increase in intra-abdominal pressure

    • Constriction of the anus, urethra, and vagina

Checkpoint 15

  • Kegel exercises strengthen the muscles of the perineum

Page 30:

  • The perineum is bordered by the pubic symphysis anteriorly, the coccyx posteriorly, and the ischial tuberosities laterally

Muscles of the Perineum

  • The urogenital diaphragm assists in urination in both males and females, ejaculation in males, and strengthens the pelvic floor

  • The muscles of the perineum include the superficial transverse perineal, bulbospongiosus, ischiocavernosus, deep transverse perineal, and external urethral sphincter muscles

  • Each muscle is described in terms of its origin, insertion, action, and innervation

Page 31: Muscles of the Deep Perineal Region

  • Deep transverse perineal muscle

    • Location: Ischial ramus, perineal body of perineum

    • Function: Helps expel last drops of urine and semen in males

    • Innervation: Perineal branch of pudendal nerve of sacral plexus

  • External urethral sphincter

    • Location: Ischial and pubic rami, median raphe in males and vaginal wall in females

    • Function: Helps expel last drops of urine and semen in males, urine in females

    • Innervation: Sacral spinal nerve S4 and inferior rectal branch of pudendal nerve

  • Compressor urethrae

    • Location: Ischiopubic ramus, blends with same muscle of opposite side anterior to urethra

    • Function: Serves as accessory sphincter of urethra

    • Innervation: Perineal branch of pudendal nerve of sacral plexus

  • Sphincter urethrovaginalis

    • Location: Perineal body, blends with same muscle of opposite side anterior to urethra

    • Function: Serves as accessory sphincter of urethra and facilitates closing of vagina

    • Innervation: Perineal branch of pudendal nerve of sacral plexus

  • External anal sphincter

    • Location: Anococcygeal ligament, perineal body of perineum

    • Function: Keeps anal canal and anus closed

    • Innervation: Sacral spinal nerve S4 and inferior rectal branch of pudendal nerve

Muscles that move the pectoral girdle (Page 31)

  • Anterior thoracic muscles

    • Subclavius muscle

      • Location: Under the clavicle, extends from clavicle to first rib

      • Function: Steadies the clavicle during movements of the pectoral girdle

    • Pectoralis minor muscle

      • Location: Deep to the pectoralis major muscle

      • Function: Assists in movements of the scapula, assists in forced inhalation

    • Serratus anterior muscle

      • Location: Between the ribs and scapula

      • Function: Moves the scapula, saw-toothed appearance of origins on the ribs

  • Posterior thoracic muscles

    • Trapezius muscle

      • Location: Extends from the skull and vertebral column to the pectoral girdle

      • Function: Covers the posterior neck region and superior portion of the trunk, forms a trapezoid shape

    • Levator scapulae muscle

      • Location: Posterior portion of the neck, deep to sternocleidomastoid and trapezius muscles

      • Function: Elevates the scapula

    • Rhomboid major and rhomboid minor muscles

      • Location: Deep to the trapezius muscle

      • Function: Pass inferiorly and laterally from the vertebrae to the scapula, used when forcibly lowering the raised upper limbs

Relating Muscles to Movements (Page 31)

  • Expulsion of urine and semen: Deep transverse perineal muscle, external urethral sphincter

  • Erection of the clitoris and penis: None mentioned in this section

  • Closure of the anal orifice: External anal sphincter

  • Constriction of the vaginal orifice: Sphincter urethrovaginalis

Checkpoint 16: Borders and contents of the urogenital triangle and anal triangle

  • Urogenital triangle

    • Borders: Pubic symphysis, ischial tuberosities, imaginary line connecting the ischial tuberosities

    • Contents: External genitalia, urethra, vagina

  • Anal triangle

    • Borders: Coccyx, ischial tuberosities, imaginary line connecting the ischial tuberosities

    • Contents: Anal canal, anus

Muscles of the Thorax That Move the Pectoral Girdle (Page 31)


  • Main action of the muscles: Stabilize the scapula as a steady origin for most of the muscles that move the humerus, move the scapula to increase the range of motion of the humerus

Page 32: Muscles of the Thorax That Move the Pectoral Girdle

Relating Muscles to Movements

  • Arrange the muscles in this section according to the following actions on the scapula: (1) depression, (2) elevation, (3) abduction, (4) adduction, (5) upward rotation, and (6) downward rotation.

  • The same muscle may be mentioned more than once.

Actions of muscles that move the scapula

  • Elevation: superior movement of the scapula, such as shrugging the shoulders or lifting a weight over the head.

  • Depression: inferior movement of the scapula, as in pulling down on a rope attached to a pulley.

  • Abduction (protraction): movement of the scapula laterally and anteriorly, as in doing a "push-up" or punching.

  • Adduction (retraction): movement of the scapula medially and posteriorly, as in pulling the oars in a rowboat.

  • Upward rotation: movement of the inferior angle of the scapula laterally so that the glenoid cavity is moved upward. This movement is required to move the humerus past the horizontal, as in raising the arms in a "jumping jack."

  • Downward rotation: movement of the inferior angle of the scapula medially so that the glenoid cavity is moved downward.

ANTERIOR THORACIC MUSCLES

  • Subclavius

    • Origin: Rib 1

    • Insertion: Clavicle

    • Action: Depresses and moves clavicle anteriorly and helps stabilize pectoral girdle

    • Innervation: Subclavian nerve

  • Pectoralis minor

    • Origin: Ribs 2–5, 3–5, or 2–4

    • Insertion: Coracoid process of scapula

    • Action: Abducts scapula and rotates it downward. RMA: Elevates ribs 3–5 during forced inhalation when scapula is fixed.

    • Innervation: Medial pectoral nerve

  • Serratus anterior

    • Origin: Ribs 1–8 or 1–9

    • Insertion: Vertebral border and inferior angle of scapula

    • Action: Abducts scapula and rotates it upward. RMA: Elevates ribs when scapula is stabilized. Known as "boxer's muscle" because it is important in horizontal arm movements such as punching and pushing.

    • Innervation: Long thoracic nerve

POSTERIOR THORACIC MUSCLES

  • Trapezius

    • Origin: Superior nuchal line of occipital bone, ligamentum nuchae, and spines of C7–T12

    • Insertion: Clavicle and acromion and spine of scapula

    • Action: Superior fibers upward rotate scapula; middle fibers adduct scapula; inferior fibers depress and upward rotate scapula; superior and inferior fibers together rotate scapula upward; stabilizes scapula. RMA: Superior fibers can help extend head.

    • Innervation: Accessory (XI) nerve and cervical spinal nerves C3–C5

  • Levator scapulae

    • Origin: Transverse processes of C1–C4

    • Insertion: Superior vertebral border of scapula

    • Action: Elevates scapula and rotates it downward

    • Innervation: Dorsal scapular nerve and cervical spinal nerves C3–C5

  • Rhomboid major

    • Origin: Spines of T2–T5

    • Insertion: Vertebral border of scapula inferior to spine

    • Action: Elevates and adducts scapula and rotates it downward; stabilizes scapula

    • Innervation: Dorsal scapular nerve

  • Rhomboid minor

    • Origin: Spines of C7–T1

    • Insertion: Vertebral border of scapula superior to spine

    • Action: Elevates and adducts scapula and rotates it downward; stabilizes scapula

    • Innervation: Dorsal