Anatomy- Back Muscles

Origin

the fixed attachment site of the muscle to the bone (close to the body PROXIMAL)

Insertion

the attachment site of the muscle to the bone that is movable when the muscle contracts (far from body DISTAL)

When a muscle contracts…

Its insertion is pulled toward the origin

Direct attachment

Short connective tissue fibers

Indirect attachment- 2 methods

connective tissue called a tendon extends beyond the muscle fibers

connective tissue called a aponeurosis sheet extends beyond muscle fibers

What’s more common direct or indirect muscle attachment?

Indirect

Tendon

concentrates force in a limited area

Aponeurosis Sheet

spreads force over a wide area

Isometric contraction

No change in muscle length; no movement = stabilization

Concentric Contraction

muscle length changes and shortens during movement (Concentric climbs)

Eccentric Contraction

muscle length changes and lengthens during movement (Eccentric extends)

Muscles cross… and work in…

one or more joints, groups

Agonist

Primary muscle(s) responsible for a movement

Antagonist

Secondary muscle(s) responsible for opposite movement of the agonist

helps stabilize and control

Synergist

compliments the action of the agonist(s), counteracts unwanted movement

The plasma membrane of a muscle fiber

sarcolemma

The cytoplasm of a muscle fiber

sarcoplasm

Skeletal muscle Fibers

composed of long, cylindrical, multinucleated cells

The sarcoplasm is filled with…

myofibrils

Myofibrils

long rod-like organelles inside muscle cells composed of myofilaments

Myofilaments

the proteins actin and myosin

Repeating segments inside a myofibril

Sarcomeres (muscle segments)

Sarcomeres

The basic unit of muscle contraction

The myofibril protein that resists overstretching

Titin

Thin filaments

composed of actin, extends toward the sarcomere (Light colored bands)

Thick filaments

composed of myosin, at the center of the sarcomere, help split ATP (Dark colored bands)

I Band

thin filaments only

H Zone

thick filaments only

M Line

Thick filaments linked by proteins

Why do muscles appear striated?

Because of the repeating and overlapping Thin and Thick filaments

Epimysium

tough, dense outer layer that surrounds the entire muscle (OUTER)

Perimysium

Thick CT that groups individual muscle fibers (MIDDLE)

Endomysium

Thin inner network of CT that surround individual muscle fibers (INSIDE)

The 3 layers of muscle CT unite at the…

myotendinal junction

Hyaline Cartilage

most common, covers the ends of long bones and joint surfaces; trachea, larynx, nose

Elastic Cartilage

flexible cartilage that easily bend and returns to original shape; ear, epiglottis

Fibrocartilage

toughest and most resilient; intervertebral discs

Trapezius

elevates, retracts, and depresses the scapula

Innervated by spinal accessory nerve (CN11)

Levator Scapulae

elevates the scapula

Innervated by dorsal scapular nerve (C3,4)

Rhomboids

(major and minor) – retract the scapula.

Innervated by dorsal scapular nerve (C4,5)

Latissimus Dorsi

Extends, adducts, and medially rotates the humerus

Innervated by Thoracodorsal nerve (C6,7,8)

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