ANATOMY & PHYSIOLOGY

THE MUSCULAR SYSTEM

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Skeletal Muscles Work Together• Since muscles can only contract and shorten, to produce

opposing motions it takes at least two different muscles.• Muscle classifications:

• Agonist: muscle that causes an action• Antagonist: a muscle working in opposition to agonist

• Example: the biceps brachii is the agonist when flexing the elbow to lift weights, but is the antagonist when the triceps brachii is extending the elbow to move a bowling ball back to prepare to bowl

• Synergists: muscles that work together to cause a movement

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� Skeletal Muscle Actions

� Muscles are connected to bones at origins and insertions

� Origins are ends that do not involve movement

� insertions usually span a joint that moves

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Information Revealed By the Names of Skeletal Muscles

• The naming of muscles usually follows one of 7 criteria:– Location of the muscle – frontalis, temporalis– Relative size of the muscle – maximus, minimus– Shape of the muscle – deltoid, trapezius, rhomboid– Direction of muscle fibers – rectus, oblique, transversus– Direction of muscle fibers – rectus, oblique, transversus– Location of attachments – sternocleidomastoid– Number of origins – biceps, triceps, quadriceps– Action of the muscle – adductor, flexor

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Figure 11.1

Lever Systems

• Lever systems help move a load more efficiently or with greater speed.

• Quickly show lever types next

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Types of Lever Systems: First Class

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Types of Lever Systems: Second Class

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Types of Lever Systems: Third Class

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Major Skeletal Muscles, Anterior View

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Major Skeletal Muscles, Posterior View

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Muscles of the Scalp and Face• Epicranius consists of:

– frontalis (or frontal belly of epicranius)– occipitalis (or occipital belly of epicranius)– These two muscles pull the scalp forward and backward

• Various muscles are involved in opening and closing the eyes and mouth, and smilingand mouth, and smiling– Ex: orbicularis oculi, orbicularis oris, zygomaticus, etc.

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

• There are multiple muscles involved in mastication (chewing)– Prime movers – temporalis and masseter– Synergists – buccinator and orbicularis oris

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Muscles of Facial Expression

Figure 11.4a

Muscles of Facial Expression

Figure 11.4b

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• Inferior and superior rectus muscles• Lateral and medial rectus muscles

Extrinsic eye muscles (oculomotor or extra-ocular muscles)

• Lateral and medial rectus muscles• Inferior and superior oblique muscles

Extrinsic Eye Muscles

Figure 11.5

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Muscles of Mastication

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Muscles of the Neck: Head Movements• Sternocleidomastoid muscles flex the head/neck if they are

both contracted or rotate the head if only one is contracted• The trapezius muscle works with the deeper splenius

muscles to extend and hyperextend the head/neck

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Muscles of the Deep Back: Trunk Movements

Erector spinae is the prime mover of back extension

Erector spinae muscles consist of three columns on each side of the vertebrae vertebrae (iliocostalis, longissimus,

and spinalis)Lateral bending of the back

is accomplished by unilateral contraction of these muscles

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Muscles of Respiration: Inspiration• 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 inspirationvolume to allow inspiration

• Diaphragm – most important muscle in inspiration

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Muscles of Respiration: Expiration

• Internal intercostals – deeper layer that aids in forced expiration

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Muscles of the Abdominal Wall• The abdominal wall is composed of 4 paired muscles

1. external obliques2. internal obliques3. rectus abdominis4. transversus abdominis

• Their fascicles run at right and oblique angles to one • Their fascicles run at right and oblique angles to one another, giving the abdominal wall added strength

• They are involved with lateral flexion & rotation of the trunk• They help promote urination, defecation, childbirth,

vomiting, coughing, and screaming (and laughing)

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Muscles of the Abdominal Wall

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Muscles of the Abdominal Wall

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An Overview of the Appendicular Muscles of the Trunk

Figure 11.13b

Muscles that Position the Pectoral Girdle

Figure 11.14a

Muscles that Position the Pectoral Girdle

Figure 11.14b

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Shoulder Muscles Found on Thorax

• Some of the muscles that control the shoulder (humerus or scapula) are found on the thorax– Anterior Thorax:

• pectoralis major, • pectoralis minor, and • serratus anterior• serratus anterior

– Posterior Thorax: • latissimus dorsi, • trapezius, • levator scapulae, and • rhomboids

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• Adductors– Deltoid muscles– Supraspinatus muscles

• Medial rotators– Subscapularis muscles

Shoulder muscles

– Subscapularis muscles– Teres major muscles

• Lateral rotation– Infraspinatus muscles– Teres minor muscles

• Flexion and adduction– Coracobrachialis

• Flexion of the shoulder joint– Pectoralis major muscles

More shoulder movements

– Pectoralis major muscles

• Extension of the shoulder joint– Latissimus dorsi muscles

Muscles that Move the Arm

Figure 11.15a

Muscles that Move the Arm

Figure 11.15b

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Muscles Inserting On and Moving the Humerus

– Flexion at shoulder (humerus moves anteriorly)• Pectoralis major • Anterior fibers of deltoid

– Abduction at shoulder (humerus moves laterally)• Lateral fibers of deltoid

– Extention at shoulder (humerus moves posteriorly)– Extention at shoulder (humerus moves posteriorly)• Latissimus dorsi • Posterior fibers of deltoid

– Stability and rotation at the shoulder (4 rotator cuff muscles)• Supraspinatus• Infraspinatus• Teres minor • Subscapularis

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Rotator Cuff, Anterior View)

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Muscles Moving the Antebrachium

• Elbow flexion– Biceps brachii and – Brachialis

• Elbow extension– Triceps brachii– Triceps brachii

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Muscles Moving the Antebrachium

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Movements at the Hip Joint• Flexion of the Hip (femur moves anteriorly)

• Anterior compartment muscles – Rectus femoris, tensor fascia latae and iliopsoas

• Extension of the hip (femur moves posteriorly)• Posterior compartment muscles

– Gluteus maximus and – 3 Hamstring muscles– 3 Hamstring muscles

» Biceps femoris, Semitendinosus, Semimebranosus• Adduction of the hip (femur moves toward midline)

• Medial compartment muscles– Adductors (5 of them)

• Abduction and Rotation of the Hip– Gluteus medius, gluteus minimus, and sartorius

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Movements at the Knee Joint: Some of the Same Muscles (+hip)

• Extension of the knee (tibia and fibula move anteriorly)– The Quadriceps:

• Rectus femoris+hip

• Vastus lateralis• Vastus medialis• Vastus intermedialis (deep to rectus femoris)

• Flexion of the knee (tibia and fibula move posteriorly): • Flexion of the knee (tibia and fibula move posteriorly): – The Hamstrings:

• Biceps femoris+hip

• Semitendinosus+hip

• Semimembranosus+hip

• Because the knee is “backwards” compared to the hip and most other joints, a muscle that flexes the hip would extend the knee.

• And a muscle that extends the hip, would flex the knee. 47

Movements at the Hip: Flexors, Adductors and Rotators

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Movements at the Hip: Extensors

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Movements at the Knee: Extensors

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• Quadriceps femoris– Three vastus muscles– Rectus femoris muscle

Extensors of the knee

Animation: Muscles of the lower limbsPLAY

Movements at the Knee: Flexors

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• The hamstrings– Biceps femoris muscles– Semimembranosus muscles– Semitendinosis muscles

Flexors of the knee

– Semitendinosis muscles

• Popliteus muscle unlocks the knee joint

Movements at the Ankle

– Plantar Flexion (toes point downward)• Posterior compartment muscles

– Gastocnemius– Soleus

– Dorsiflexion (toes point upward)• Anterior compartment muscles• Anterior compartment muscles

– Tibialis anterior

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Movement at the Ankle: Plantar Flexors

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• Plantar flexion– Gastrocnemius muscle– Soleus muscle

• Eversion and plantar flexion

Movements at the ankle

• Eversion and plantar flexion– Fibularis muscle

• Foot position and toe movement is accomplished by muscles originating on the talus and metatarsal bones

Movement at the Ankle: Dorsiflexors

• Muscles of the anterior compartment are the primary toe extensors and ankle dorsiflexors

• They include the tibialis • They include the tibialis anterior

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• Plantar flexion– Gastrocnemius muscle– Soleus muscle

• Eversion and plantar flexion

Movements at the ankle

• Eversion and plantar flexion– Fibularis muscle

• Foot position and toe movement is accomplished by muscles originating on the talus and metatarsal bones

Extrinsic Muscles That Move the Foot and Toes

Figure 11.21c, d

Intrinsic Muscles of the Foot

Figure 11.22b