Muscular System

THE MUSCULAR SYSTEM

Skeletal Muscle • Found associated to bones • multinucleated • striated / banded appearance • striated voluntary muscle • voluntary control via nervous system • Contraction could be slow to fast

Smooth Muscle • Found in walls of blood vessels and hollow organs • Single nucleus • small spindle shaped cells • tapering ends / single oval nucleus • no striations • Contraction is very slow and is due to autonomic nervous system

Cardiac Muscle • Found in the heart • Usually single nucleus • prominent striations and branchings and single nucleus • muscles are connected to each other via junctions called intercalated discs • pacemaker cells control their contraction which is involuntary • Contraction is slow

GROSS ANATOMY OF SKELETAL MUSCLE

1. Sarcoplasmic reticulum •

Provides the calcium which acts as the GO signal for contraction

Neuromuscular Junction • This is the junction between the sarcolemma of a muscle cell and the axonal terminal of a neuron • Synaptic cleft – The space between the end of the axonal terminal and the sarcolemma

GROSS ANATOMY OF SKELETAL MUSCLES

Head Muscles Facial

Frontalis • Covers frontal bone • Raises your eyebrows • Wrinkles your forehead

Orbicularis oculi • Encircles the eyes • allows one to wink and close his eyes

Buccinator • Runs horizontally across the cheek • For whistling

Zygomaticus • Smiling muscle

Head Muscles Chewing

Masseter • Closes the jaw by elevating the mandible

Temporalis • Overlies the temporal bone • Acts as the synergist of masseter in closing the jaw

Neck and Trunk Muscles Anterior

Platysma • Very superficial • Sheetlike muscle from the neck to the mouth • Pulls the mouth downward into a sag

Sternocleidomastoid • “prayer muscle” • Contraction of both sides flexes neck as if bowing in prayer • Contraction of one side would turn the head

Pectoralis Major • Forms anterior wall of axilla and upper part of the chest • Adducts and flexes the arm

Intercostal Muscle • Found between the ribs • External intercostal – Raises the ribs outward in breathing

• Internal intercostal – Depresses the ribcage upon exhalation

Abdominal Girdle Muscles • Rectus abdominis – Flexion of vertebral column

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• External Oblique – Rotates and bends the trunk

• Internal Oblique – Rotates and bends the trunks

• Transversus abdominis – Compresses abdominal contents

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Neck and Trunk Muscles Posterior

Trapezius • Kite-like shape • Extends the head • Elevates, depress, adduct and stabilize the scapula

Latissimus Dorsi • Covers the lower back • Extends and adducts the humerus • Used when arms are brought down in swimming or striking a downward blow

Erector Spinae • Prime mover of back extension • Composed of longissimus, iliocostalis and spinalis • Controls the act of bending over at the waist

Deltoid • Forms the rounded shape of the shoulder • Prime movers of arm abduction

Muscles of the Upper Limb

Biceps Brachii • Bulges upon flexion of the elbow • Acts to flex and supinate the forearm

Triceps Brachii • Antagonist of the biceps • Prime mover of elbow extension • Used in delivering a straight punch

Muscles of the Lower Limb

Gluteus Maximus • Forms most of buttock flesh • Powerful hip extensor when walking, jumping and climbing the stairs

Gluteus Medius • Used mainly for giving intramuscular injections • It is a hip abductor and important in steadying the pelvis when walking

Iliopsoas • Prime mover of hip flexion

Sartorius • Thin and strap like • used when crossing the legs • runs obliquely across the anterior aspect of the thigh

Quadriceps Group • Found at the anterior thigh • Acts to extend the knee and flex the hip • Parts: – Rectus femoris – Vastus medialis – Vastus lateralis

Hamstring Group • Found at the posterior thigh • For knee flexion • Formed by the: – Biceps femoris – Semi-membranosus – Semi-tendinosus

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Tibialis Anterior • Found on the anterior leg • Acts on dorsiflexion and inverts the foot

Peroneus Muscle • Found at the lateral area of the leg • Group helps the gastrocnemius in plantar flexion • Everts the foot

Gastrocnemius • Curved over the posterior leg forming the “calves” • Prime mover for plantar flexion (lifts the heels)