Skeletal Muscle Chemical Composition



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Muscular System Notes Continued

Muscles of the Body: Males 42% Body Weight

Females 36% Body Weight

Skeletal Muscle Chemical Composition: 75% Water - 20% Protein – 5% Salts

These Inorganic salts are made up of (Phosphates,

Lactic Acids, Calcium, Magnesium, Sodium, Chloride,

Potassium, Amino Acids, Fats, and Carbohydrates)



Proteins: “Actin” are thin Fibers / “Myosin” are thick Fibers

Actin – Myosin: Protein molecules in muscle fibers that receives energy transfer

Muscle Fiber Types: Type I / Slow Twitch / RED: Long Term, Fatigue

Resistant and well suited for prolonged aerobic use



Type II / Fast Twitch / WHITE: Activated in short

Term. Fatigue quickly



Motor Neuron: “Nerve Cell”

Motor Unit: “Nerve Cell and all the Muscle fibers it stimulates”

Neuromuscular Junction: This is the Gap between the Axon and the Muscle cell

Known as the Synaptic Cleft



Acetylcholine: Chemical neurotransmitter that is released when impulse reaches

the end of the axon diffuses across the synaptic cleft and

attaches to receptors on the sarcolemma. Sarcolemma

becomes temporarily permeable to (Na+) ions which go

rushing into the muscle cell. This gives the muscle cell

excessive positive ions which upsets the cell causing an

action potential (An Electrical Current).

The movement of electrical currents along the sarcolemma causes (Ca++) to be

released from storage areas inside the muscle cell. (Ca++) ions attach to the

action myofilaments and the filaments are triggered and the whole cell

shortens.

Aging causes great atrophy in the muscles. Generally a 70 year old man has 50%

the strength of when he was a 30 year old man.

Muscles of the Head and Neck Head 26 Muscles / Neck 32 Muscles

Name of Muscle Action / Movement of Muscle

Frontalis Draws back scalp, Raises Eyebrows, Wrinkles Forehead

Mentalis Elevates and Protrudes Lower Lip, Used in Pouting

Orbicularis Oculi Closes Eyelids, Used in Blinking, Squinting, & Winking

Orbicularis Oris Closes and Protrudes Lips, Used in Whistling, Forming

many letters during Speech, “Kissing Muscle

Risorius Draws angles of the mouth laterally, Draws lips into

Grinning

Sternocleidomastoid Contraction of one side, Laterally flexes the Neck &

rotates the head to the opposite side,

contraction of both sides together, Flexes Neck

Trapezius Elevates, Depresses, Retracts, and Rotates the Scapula

Rotates the Arm

Temporalis Elevates and Retracts the Mandible, Assists in Side to

Side Movement of the mandible when chewing

Depressor Anguli Oris Draws angles of the Mouth Down & Laterally Opening

Frowning Muscle

Zygomaticus Major Draws angles of the Mouth Upward & Outward, Major

Muscle used in “Smiling and Laughing

Buccinator Draws angles of the Mouth Laterally, Compresses the

Cheek, Used to Create Sucking Action

Masseter Elevates Mandible when chewing, Protracts It

Strongest Muscle in the Body

Occipitalis Draws back scalp, Wrinkles the Forehead

Platysma Draws down the Lower Lip and Angles the Mouth,

Tenses the Skin of the Neck, Helps to Depress

the Mandible

Levator Scapulae Elevates the Scapula

Muscles of the Trunk, Upper & Lower Extremities ------------- 598 Muscles

Root word Meanings of some Muscles

RECT ---------- Straight ---------- (Rectus Femoris)

DELTA ---------- Triangle ---------- (Deltoid)

GASTR ---------- Belly ---------- (Gastrocnemius)

BREVIS ---------- Short ---------- (Peroneus Brevis)

LONGUS ---------- Long ---------- Peroneus Longus)

Muscles of the Pectoral Girdle, Shoulder, Neck, Back and Abdominals

Name of Muscle Action / Movement of Muscle

Pectoralis Major Prime Mover of Arm Flexion

Adducts and Medially Rotates the Arm

Pectoralis Minor Arm Flexion / Adducts & Medially Rotates the Arm

Trapezius Extends the Neck & Shrugs the Shoulders, Elevates

Depresses, Retracts, and Rotates the Scapula

Rotates the Arm

Levator Scapulae Elevates the Scapula

Rhomboids Major & Minor Elevates and Adducts the Scapula

Squares up the Shoulders

Muscles used in “Paddling a Canoe”

Latissimus Dorsi Arm Extensions “Swimmers Muscles

Supraspinatus Arm Abduction

Inferaspinatus Arm Adduction & Lateral Rotation

Rotator Cuff Muscles Subscapularis, Infraspinatus, Supraspinatus,

Teres Minor, Subscapularis

These Muscles Stabilize the Shoulder Joint

Prevent downward dislocation of humerus

Serratus Anterior Protraction of the Scapula

Teres Major Adducts and Medially rotates the Arm

Deltoid Flexion and Medially Rotation of the Humerus

Rectus Abdominus Flexes the Vertebral Column

Increases Abdominal Pressure

“Most Superficial” of All Abdominals



6 Pack Abdominal Look

External Oblique Rotates and Laterally Flexes the Trunk

Located on the Sides of the Torso

Helps with Posture but less

Internal Oblique Rotates and Laterally Flexes the Trunk

2nd Deepest Group / Helps with Posture as well

Transversus Abdominus Compresses Abdominal Contents / Stability to Trunk

“Deepest” of all the Abdominal Muscles

Helps in Breathing & Posture of the Body

External Intercostals Pulls Ribs toward one another, Elevates Ribs

Helps in Breathing – Inspiration

Internal Intercostals Depresses the Ribs

Helps in Breathing – Expiration

Diaphragm Prime Mover of Inspiration



Muscles of the Buttocks, Upper and Lower Extremities

Name of Muscle Action / Movement of Muscle

Buttocks Muscles

Gluteus Maximus Powerful Extension of the Hips

Allows for Running with Power

Allows for Standing up from a Seated Position

Anchors Lower Limbs to the Trunk

Gluteus Medius Abducts the Femur and Medially Rotates the Femur

Gluteus Minimus “Smallest” of the Gluteus Muscles

Abducts the Femur and Medially Rotates the Femur

Tensor Faciae Latae Most Anterior of Muscles on the Lateral surface of the

Ilium


Deep Rotator Muscles

Piriformis Laterally Rotates the Hips

“Sciatic Nerve” Exits the Hips Inferiorly to this Muscle

Obturator Internus Laterally Rotates the Hips

Obturator Externus Laterally Rotates the Hips

Superior Gemellus Laterally Rotates the Hips

Inferior Gemellus Laterally Rotates the Hips

Quadratus Femoris Laterally Rotates the Hips



Hips and Thigh Muscles

Quadriceps Muscles Rectus Femoris, Vastus Lateralis, Vastus Medialis,

Vastus Intermedius

Rectus Femoris Flexes the thigh and Extends the Knee

Vastus Lateralis Extends the knee

Vastus Medialis Extends the knee

Vastus Intermedius Extends the knee

Sartorius “Longest Muscle” in the Body

Flexes the thigh, Rotates the Thigh Laterally

Allows for Sitting Cross – Legged

Comes from Latin word meaning “Tailor”, because

of tailor’s habit of sitting cross legged.

Femoral Triangle Iliopsoas, Pectineus, Adductor Longus

Iliopsoas Flexes the trunk at the thigh “Hip Flexors”

Strongest of the Hip Flexors

Helps with Standing and Walking

Pectineus Flexes the trunk at the thigh “Hip Flexors”

Adductor Longus Flexes the hip and lateral rotates the thigh “Hip Flexors”

Tensor Facia Latae Most Anterior of Muscles on the Lateral surface of the

Ilium


Hamstring Muscles Biceps Femoris, Semitendinosus, Semimbranosus

Biceps Femoris Extends the thigh and Laterally Flexes the Knee

Semitendinosus Extends the thigh, Flexes the Knee and Medially

Rotates the Leg

Semimembranosus Extends the thigh, Flexes the Knee and Medially

Rotates the Leg

Adductor Magnus Adducts and Laterally Rotates the Thigh

A Synergist muscles in Thigh Extension

Adductor Brevis Flexes the Hip and Laterally Rotates the Thigh

Gracilis 2nd Longest Muscle in the Body. Goes from the Hip

To below the Knee

Lower Legs

Tibialis Anterior Dorsiflexion of the Ankle, Inversion of the Foot

Tibialis Posterior Plantar Flexes the Foot and Inverts the Foot

Supports the Arches of the Foot

Extensor Hallucis Longus Extends the Big Toe and Dorsiflexion of the Foot

Extensor Digitorum Longus Extends the Digits II – V & Dorsiflexes the foot

Peroneus Tertius Dorsiflexes the Foot and Everts the Foot

Peroneus Longus Dorsiflexes the Foot and Everts the Foot

Peroneus Brevis Plantar Flexes the Foot and Everts the Foot

“Peroneus” comes from the Latin Word for Fibula

Gastrocnemius Plantar Flexes the Foot and Flexes the Knee

Soleus Plantar Flexes the Foot

Plantaris Plantar Flexes the Foot

Flexor Hallucis Longus Flexes the Big Toe

Flexor Digitorum Longus Flexes Distal Phalanges II – V



Arms , Forearms, and Hands

Triceps Brachii Prime Mover of the Forearm Extension

Adducts and Stabilizes the Shoulder

Biceps Brachii Flexes the Elbow Joint, Supinates the Forearm

Brachialis Major Forearm Flexor

Pronator Teres Pronates the Forearm

Flexor Carpi Radialis Flexor or the Wrist and Abducts the Hand

Flexor Carpi Ulnaris Flexor of the Wrist and Adducts the Hand

Stabilizes the Wrist

Flexor Digitorum Profundus Finger Flexor

Pronator Quadratus Promotes the Forearm

Extensor Carpi Radials Extends and Abducts the Wrist

Longus & Brevis

Extensor Digitorum Prime Mover of the Finger Extension



Abductor Pollicis Longus Abducts and Extends the Thumb

Extensor Pollicis Longus Extends the Thumb


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