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Anatomy & Physiology I
Chapter 10 (Muscular System)
The muscular system is composed of more than 600 muscles.
Muscles are attached to the bones of the skeleton.
40% of total body weight is made up of all body muscles.
Muscles produce movement by shortening in length (contraction).
Muscle functions:
1. Movement – Muscles cause most body movements (walking)
2. Posture – Muscles stabilize joints & maintain position (standing, sitting)
3. Organ volume – Sphincters control flow of organ contents (stomach, urinary bladder)
4. Heat production – 85% body heat produced by muscle contraction (maintains temperature)
5. Movement of substances – (blood in cardiovascular system, food in intestine)
STRUCTURE OF SKELETAL MUSCLE
Muscles are composed of thousands of muscle cells (muscle fibers)
Muscle fibers are surrounded by connective tissue & are supplied by blood vessels & nerves.
Connective tissue covering called endomysium surrounds each muscle fiber.
Perimysium covers muscle fibers bundles (fascicles).
Epimysium covers the whole muscle.
Deep Fascia (dense fibrous connective tissue) covers the epimysium and separates the muscles.
Tendons (extensions of epimysium, perimysium & endomysium), attach to periosteum of bone.
Aponeurosis – broad, sheet-like tendons.
Nerve & Blood Supply:
Nerves provide the electrical stimulus (muscle action potential) that causes muscle contraction.
Blood vessels provide energy (ATP) for muscle contraction & eliminate wastes.
MUSCLE TONE
Tone is a partially contracted state of the muscle, even when the muscles are not in use.
Tone is maintained by alternating contraction and relaxation of various muscle fibers.
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-Muscle tone maintains posture and keeps the muscles in a constant state of readiness for action.
Origin - muscle attachment to a stable bone (does not move).
Insertion - muscle attachment that moves the bone.
GROUP ACTIONS:
Muscles act in groups to effect movements.
They are arranged in opposing pairs (flexors-extensors, abductors-adductors).
Prime mover (agonist) is the main muscle that moves a part
(biceps, triceps)
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Antagonists are muscles that oppose movement by prime movers (triceps, biceps)
For a movement to occur, the antagonist must relax when the prime mover contracts.
If prime mover & antagonist move with equal force, there is no movement (isometric contraction)
Synergists are muscles that aid prime movers.
Fixators stabilize the origin of a prime mover so that it can work efficiently (scapular fixators)
Intrinsic Muscles are inside an organ or region (tongue, iris of eyes)
Extrinsic Muscles are located outside the organ they move (muscles of forearm move hand/fingers,
eye muscles)
NAMING SKELETAL MUSCLES
Some features are used in naming muscles:
*Size:
Maximus, Magnus, Major (Large)
Minimus, Minor (Small)
Vastus (Huge)
Longus, Longissimus (Long)
Brevis (Short)
Latissimus (wide)
*Shape:
Deltoid (triangular)
Trapezius (Trapezoid)
Teres (Round)
Orbicularis (Circular)
Serratus (saw-toothed)
Rhomboideus (Diamond shape)
Platys (Flat)
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Gracilis (Slender)
Quadratus (Square)
Piriformis (Pear-shaped)
Pectinate (Comb-like)
*Direction of fibers:
Rectus (parallel to midline)
Transverse (perpendicular to midline)
Oblique (diagonal)
*Location
Pectoralis (chest)
Brachii (arm)
Gluteus (buttock)
Capitis (head)
Lumborum (lumbar area)
Peroneus (fibula)
Digitorum (digits)
Pollicis (thumb)
Hallucis (great toe)
*Number of origins:
Biceps (two heads)
Triceps (three heads)
Quadriceps (four heads)
*Action
Abductor (moves bone away from midline)
Adductor (moves bone towards midline)
Levator (elevate)
Masseter (chewer)
Sphincter (decreases opening size)
Tensor (makes part rigid)
Pronator (turns palm posteriorly/inferiorly)
*Origin/Insertion
Sternocleidomastoid (sternum/clavicle to mastoid)
Brachioradialis (humerus to radius)
PRINCIPAL SKELETAL MUSCLES: (Refer to: Fig.10.1-10.40 and Table 10.1-10.20)
There are four groups of skeletal muscles in our bodies:
1) Muscles of the head and neck.
2) Muscles of the upper extremities.
3) Muscles of the trunk.
4) Muscles of the lower extremities.
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MUSCLES OF THE HEAD AND NECK
The muscles of facial expression include:
1) Ring-shaped around the lips and the eyes (orbicularis muscles).
2) The muscle surrounding each eye - orbicularis oculi.
3) The muscle surrounding mouth – orbicular oris
a. Zygomaticus – raises angle of mouth
b. Cheek – Buccinator (whistle)
The levator palpebrae superioris lifts the upper eyelid and is the antagonist for the orbicularis oculi.
Muscles of mastication:
There are four pairs of muscles that are responsible for chewing movements or mastication.
[Temporalis, masseter, Medial and Lateral Pterygoids (deep to mandible)].
All of these muscles insert on the mandible.
Muscles of the Neck:
Most important muscles of the neck is the sternocleidomastoid extending from the sternum upward
across either side of the neck to the mastoid process of the temporal bone.
It brings the head forward (flexion) on the chest - when both contract.
Brings head to the opposite side – when one contracts.
Torticollis (wryneck) - Head abnormally fixed due to injury or spasm of the muscle.
Trapezius muscle is located in the back of the neck. It helps hold the head up (extension).
The sternocleidomastoid and trapezius muscles have opposite actions.
The sternocleidomastoid flexes the neck while the trapezius extends the neck.
MUSCLES OF THE TRUNK:
1) Trapezius muscles originate at vertebrae and insert on the clavicle and scapula:
a. To raise the shoulders
b. To pull them back
2) The latissimus dorsi:
a. Originate from the vertebral spine and lower back
3) Muscles of respiration
a. The most important muscle involved in the act of breathing is the diaphragm.
When the diaphragm contracts, the central dome-shaped portion is pulled
downward.
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b. The intercostals muscles are attached between the ribs and fill these spaces
External intercostals - forward and down (Inspiration)
Internal intercostals - backward and up (Expiration)
4) Muscles of the abdomen and pelvis:
The front and side walls of the abdomen have three main muscles in different layers:
1 – The external oblique (outside)
2 – The internal oblique (in the middle)
3 The transverses abdominis (the innermost layer).
Rectus abdominis – Situated in the midline, it flexes vertebral column.
The erector spinae and deep back muscles are responsible for movements of the vertebral column.
Pelvic floor muscles: - Cover the pelvic outlet. Formed of:
1) Pelvic diaphragm (includes Levator Ani)
2) Uro-genital diaphragm
MUSCLES OF THE UPPER EXTREMITIES
The trapezius (shrugging shoulder) and serratus anterior (pulls scapula down & forward) muscles
move the scapula.
The following muscles insert on the humerus and move the arm:
Pectoralis major – adducts, flexes arm
Latissimus dorsi – adducts, medial rotation of arm (swimming)
Deltoid – abducts arm (injection site)
Rotator cuff muscles– rotate arm
Pectoralis Major:
Upper part of the chest in the front
Arises from: sternum, upper ribs, clavicle
Forms the anterior “wall” of the armpit or axilla.
It inserts on the upper part of the humerus.
Serratus Anterior is below the axilla on the side of the chest.
Inserts in the scapula.
Moves the scapula forward.
It also raises the arm above the horizontal level.
Biceps Brachii: (2 heads)
Is located on the front of the arm.
Is often displayed by children as proof of their strength.
It inserts on the radius.
It serves to flex the forearm.
Triceps Brachii: (3 heads)
Located on the back of the arm.
It inserts on the olecranon of the ulna. It is extends arm.
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Most of the muscles that move the hand and fingers originate from the radius and ulna.
1) The flexor carpi (Anterior forearm muscles).
2) The extensor carpi are responsible for many movements of the hand (Post. Forearm
muscles)
3) Flexor digitorum and
4) Extensor digitorum muscles produce finger movements
MUSCLES OF THE LOWER EXTREMITIES
The longest and strongest muscles in the body are specialized for locomotion.
Movement of the thigh and leg:
1) Gluteus maximus:
- Forms part of the buttock.
- This muscle extends and abducts thigh.
- It is very important in walking and running.
2) Gluteus medius:
- Partially covered by the gluteus maximus.
- Serves to abduct the thigh (injection site).
3) Iliopsoas:
Arises from the ilium and the bodies of the lumbar vertebrae.
It crosses the front of the hip joint to insert on the femur.
It is a powerful flexor of the thigh.
It keeps the trunk from falling backward when we are standing erect.
4) Adductor muscles: (longus, brevis, magnus, gracilis)
Located on the medial part of the thigh.
They arise from the pubis and ischium and insert on the femur.
They adduct thigh (horse rider’s muscles).
5) Sartorius:
Long, narrow muscle.
Begins at the iliac spine.
Ends on the upper medial of the tibia.
Used to cross the legs “Tailor’s muscle”
Flexes and medially rotates leg; flexes thigh.
6) Quadriceps femoris: (Rectus femoris Vasus medialis, intermedius & lateralis,)
Covers front and sides of the femur
Has four heads of origin
One from the ilium - Rectus Femoris - also flexes thigh.
Three from femur.
All four insert on the tibia via a common tendon – Patellar ligament
These muscles extend leg.
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7) Hamstring muscles: (biceps femoris, semimembranous, semitendinosus)
Situated on the posterior part of the thigh.
Flex the leg on the thigh (kneeling) and hip extension.
[Originate in ischium, insert in tibia]
Biceps femoris originates in ischium & femur, inserts in fibula
Muscles moving Ankle and Foot:
a) Anterior compartment – Tibialis Anterior. – Dorsi flexes foot.
b) Lateral compartment – Peroneus - Eversion, plantar flexion.
c) Posterior compartment – Gastrocnemius, Soleus, – Plantar flexion (toe dancing)
(end in tendoAchilles)
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