Final Muscle info Allied

Lever

A rigid structure (such as a bone) that allows movement to occur around a fixed point.

Fulcrum

The fixed point on which a lever rests and pivots (such as a joint).

Load (Resistance)

The weight or force that a lever system must overcome.

Effort (Applied Force)

The force applied to the lever system to move the load (generated by muscle contraction).

Mechanical Advantage

When the effort arm is longer than the load arm; allows a large load to be moved over a small distance using little effort.

Mechanical Disadvantage

When the load arm is longer than the effort arm; requires more effort than the load weight but allows rapid movement over a large distance.

Class 1 Lever

A lever arrangement where the fulcrum is in the middle (Load-Fulcrum-Effort), similar to a seesaw.

Class 2 Lever

A lever arrangement where the load is in the middle (Fulcrum-Load-Effort), similar to a wheelbarrow.

Class 3 Lever

A lever arrangement where the effort is in the middle (Load-Effort-Fulcrum), similar to tweezers.

Atlanto-occipital joint

The joint between the skull and the neck that acts as the fulcrum for a Class 1 lever when nodding the head.

Skeletal Muscle

The tissue that contracts to apply force/effort to the bones within the body's lever systems.

Bone

The rigid anatomical structure that serves as the actual lever bar in the human body.

Joint

The anatomical structure where two bones meet that serves as the fulcrum in bodily movements.

Parallel muscles

Muscle fibers run parallel to the long axis of the muscle, providing a long range of motion.

Fusiform muscles

A type of parallel muscle that is thick in the middle and tapered at both ends.

Circular muscles

Fibers are arranged in concentric rings around openings, acting as sphincters to close them.

Convergent muscles

Fibers spread over a wide area but come together at a single, central attachment tendon.

Pennate muscles

Fibers run at an angle to the tendon, packed tightly to generate high force.

Unipennate muscles

A pennate type where all muscle fibers are oriented on the same side of the tendon.

Bipennate muscles

A pennate type where muscle fibers are arranged on both sides of a central tendon.

Multipennate muscles

A pennate type where the tendon branches within the muscle, with fibers wrapping around multiple sub-tendons.

Transverse fibers

Muscle fibers that run horizontally across a body region to compress or stabilize an area.

Pectoralis Minor

Depresses, protracts, and rotates the scapula downward; elevates ribs during forced inspiration.

Pectoralis Major

Adducts, medially (internally) rotates, and flexes the humerus at the shoulder joint.

Serratus Anterior

Protracts and rotates the scapula upward; holds the scapula flat against the thoracic wall.

External Intercostals

Elevates the ribs during inhalation to increase thoracic cavity volume.

Rectus Abdominis

Flexes the lumbar spine (trunk) and compresses abdominal viscera.

Internal Obliques

Flexes and laterally flexes the trunk; rotates the trunk to the same side (ipsilateral rotation).

External Obliques

Flexes and laterally flexes the trunk; rotates the trunk to the opposite side (contralateral rotation).

Transverse Abdominis

Compresses abdominal contents; increases intra

Diaphragm

Flattens inferiorly during contraction to expand the thoracic cavity for inhalation

Teres Major

Adducts, extends, and medially (internally) rotates the humerus at the shoulder joint.

Teres Minor

Laterally (externally) rotates the humerus at the shoulder joint; stabilizes the glenohumeral joint.

Trapezius

Elevates, retracts (adducts), and depresses the scapula; rotates the scapula upward.

Subscapularis

Medially (internally) rotates the humerus; stabilizes the glenohumeral joint.

Rhomboid (Major & Minor)

Retracts (adducts), elevates, and rotates the scapula downward; stabilizes the scapula against the thoracic wall.

Levator Scapula

Elevates the scapula and rotates it downward.

Infraspinatus

Laterally (externally) rotates the humerus at the shoulder joint; stabilizes the glenohumeral joint.

Supraspinatus

Initiates abduction of the humerus at the shoulder joint (first 15 degrees); stabilizes the glenohumeral joint.

Latissimus Dorsi

Extends, adducts, and medially (internally) rotates the humerus at the shoulder joint.

Quadratus Lumborum

Laterally flexes the vertebral column; fixes the 12th rib during forced expiration.

Erector Spinae (Iliocostalis, Longissimus, Spinalis)

Extends the vertebral column and head when contracting bilaterally; laterally flexes the vertebral column when contracting unilaterally

Epicranius (Occipitofrontalis)

Moves the scalp, wrinkles the forehead, and elevates the eyebrows

Frontalis

Elevates the eyebrows and wrinkles the skin of the forehead horizontally

Occipitalis

Retracts the scalp posteriorly

Corrugator Supercilii

Draws the eyebrows medially and inferiorly, creating vertical wrinkles above the nose

Orbicularis Oculi

Closes the eyelids (palpebral part blinks gently; orbital part tightly squints)

Zygomaticus Major

Elevates and draws the corners of the mouth laterally (smiling)

Risorius

Draws the corners of the mouth directly laterally

Levator Labii Superioris

Elevates and everts the upper lip

Depressor Labii Inferioris

Depresses and draws the lower lip laterally

Depressor Anguli Oris

Depresses the corners of the mouth inferiorly and laterally (grimacing)

Orbicularis Oris

Closes, compresses, puckers, and protrudes the lips (kissing and whistling)

Mentalis

Elevates and protrudes the lower lip while wrinkling the skin of the chin

Buccinator

Compresses the cheeks against the teeth, keeps food between teeth, and aids in blowing/sucking

Nasalis

Flares the nostrils (alar part) and compresses the nasal cartilages (transverse part)

Masseter

Elevates and protrudes the mandible to close the jaw firmly

Temporalis

Elevates the mandible to close the jaw; retracts the mandible with its posterior fibers

Medial Pterygoid

Elevates, protrudes, and produces side-to-side grinding movements of the mandible

Lateral Pterygoid

Depresses and protrudes the mandible to open the jaw; guides side-to-side grinding

Platysma

Depresses the mandible and corners of the mouth; tenses the skin of the lower face and neck

Splenius Capitis

Bilaterally extends the head/neck; unilaterally rotates and laterally flexes the head to the same side

Sternocleidomastoid

Bilaterally flexes the neck and elevates the sternum; unilaterally rotates face to the opposite side

medial head of the triceps brachii

Forearm extension at the elbow joint

brachialis

Forearm flexion at the elbow joint

lateral head of the triceps brachii

Forearm extension at the elbow joint

long head of the triceps brachii

Forearm extension at the elbow joint; arm extension and adduction at the shoulder joint

biceps brachii

Forearm flexion and supination at the elbow joint; weak arm flexion at the shoulder joint

brachioradialis

Forearm flexion at the elbow joint (when semi-pronation)

extensor carpi ulnaris

Wrist extension and adduction (ulnar deviation)

deltoid

Arm abduction (middle part); arm flexion and internal rotation (anterior part); arm extension and lateral rotation (posterior part)

vastus intermedius

Leg extension at the knee joint

piriformis

Thigh external rotation, abduction (when flexed); stabilizes the hip joint

gluteus minimus

Thigh abduction and internal rotation; stabilizes the pelvis

psoas major

Thigh flexion at the hip joint; lateral flexion of the trunk

adductor magnus

Thigh adduction, flexion (adductor part), extension (hamstring part), and internal rotation

vastus lateralis

Leg extension at the knee joint

vastus medialis

Leg extension at the knee joint

semimembranosus

Leg flexion and internal rotation at the knee joint; thigh extension and internal rotation at the hip joint

gluteus medius

Thigh abduction and internal rotation; stabilizes the pelvis

soleus

Foot plantarflexion at the ankle joint

rectus femoris

Leg extension at the knee joint; thigh flexion at the hip joint

biceps femoris (long head)

Leg flexion and external rotation at the knee joint; thigh extension and external rotation at the hip joint

semitendinosus

Leg flexion and internal rotation at the knee joint; thigh extension and internal rotation at the hip joint

gastrocnemius

Foot plantarflexion at the ankle joint; leg flexion at the knee joint

sartorius

Thigh flexion, abduction, and external rotation at the hip joint; leg flexion and internal rotation at the knee joint

gluteus maximus

Thigh extension, external rotation, abduction (upper fibers), and adduction (lower fibers) at the hip joint; stabilizes pelvis