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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 Terms
Origin: 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
Muscles
Location: 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),
Oblique
Number of Origins: Biceps brachii (two
origins) Triceps brachii (three origins).
Locations of the origin and/or
insertion: Sternocleidomastoid
Action 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 hip
Adduction: 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
ankle
Eversion: 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 jaw
Retraction: 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
hip
Medial rotation moves towards the middle of the body,
lateral rotation moves away from the midline
Circumduction: the distal end of a limb
moves in a circle.
The arm and the leg have this action