Introduction to Muscles

KNR 181 Lab

Skeletal Muscles

Skeletal muscles extend from one bone to another, and cross at least one joint.

Muscle contraction causes movement by pulling one of the bones towards the other. Muscles always pull, never push!

Muscle contraction causes shortening of the muscle.

Muscles are attached to bones via tendons.

Muscle TermsOrigin: the muscles fixed or immovable

point of attachment, also called the head.Insertion: the end of the muscle

attached to the bone undergoing the greatest movement.

Prime Mover: a muscle that provides the major force for producing a specific movement. Also called Agonist.

Muscle Terms:Synergists: muscles that work

together to produce the same movement, and/or reduce undesirable movement.

Antagonists: muscles that oppose, or reverse, a particular movement.

Fixators: muscles that stabilize one or more joints.

Naming of Skeletal MusclesLocation: Pectoralis (chest), intercostal

(ribs), temporalis (temporal bone)Shape: Deltoid (triangular), Trapezius

(trapezoid)Relative size: Gluteus maximus

(largest), gluteus minimus (smallest), Longus and brevis are also used (long and short)

Naming of Skeletal muscles:Direction of muscle fibers: Rectus

(straight), Transverse (right angle), ObliqueNumber of Origins: Biceps brachii (two

origins) Triceps brachii (three origins).Locations of the origin and/or

insertion: SternocleidomastoidAction of the muscle: Adductor longus,

flexor digitorum, supinator

Actions of Skeletal Muscles:Flexion: a bending movement that

decreases the angle of a joint Flexion occurs at the head/neck,

shoulder, elbow, wrist, fingers, hip, waist, hip, knee, and ankle

Extension: a straightening movement that increase the angle of a joint Extension occurs at the same joints as

above, with the exception of the ankle

Actions of skeletal muscles:

Abduction: a lateral movement away from the midline of the body, in the frontal plane. Abduction occurs at the head/neck,

shoulder, and the hipAdduction: a movement towards the

midline of the body, in the frontal plane. Adduction occurs in the same joints as

abduction

Actions of skeletal muscles:

Dorsal Flexion (dorsiflexion): a flexion movement that lifts the foot up, or upwards towards the tibia Dorsiflexion only occurs at the ankle

Plantar flexion: an extension movement that results in the foot/toes moving away from the tibia (pointing the toes, or depressing the foot) Plantar flexion only occurs at the ankle

Actions of skeletal muscles:

Inversion: the sole of the foot turns inward, and the ankle outwards. Inversion only occurs at the ankle joint This is the most common way to sprain

your ankleEversion: the sole of the foot turns

outward, and the ankle inwards. Eversion only occurs at the ankle joint

Actions of skeletal muscles:

Elevation: lifting a body part superiorly Elevation occurs at the jaw and shoulder

Depression: moving a body part inferiorly Depression occurs at the jaw and

shoulder

Actions of skeletal muscles:

Protraction: forward movement in the horizontal plane away from the spine Protraction occurs at the shoulder

(scapula) and the jawRetraction: backward movement in the

horizontal plane towards the spine Retraction occurs at the shoulder

(scapula) and the jaw

Actions of skeletal muscles:

Pronation: forearm rotation where the palm of the hand faces downwards. Pronation occurs only at the elbow and

wrist

Supination: forearm rotation where the palm of the hand faces upwards Supination occurs at the elbow and wrist

Actions of Skeletal muscles:

Rotation: the turning of a bone around its own long axis. Rotation occurs at C1-2 (neck),

shoulder, and hipMedial rotation moves towards the middle of the

body, lateral rotation moves away from the midlineCircumduction: the distal end of a

limb moves in a circle. The arm and the leg have this action