Muscles - Axial and Appendicular

Chapter 11: Muscles (Axial)

Overview of Muscles

Axial Muscles

  • Definition: Muscles that have both origins and insertions on the axial skeleton.

  • Functions:

    • Support and move the head and vertebral column.

    • Involved in facial expression, breathing, chewing, and swallowing.

    • Support and protect abdominal and pelvic organs.

Appendicular Muscles

  • Definition: Muscles that control movements of the upper and lower limbs and the pectoral and pelvic girdles.

  • Organization: Grouped based on locations.

Muscle Groups by Depth

Superficial & Deep Muscles

  • Superficial Muscles:

    • Frontal belly of occipitofrontalis

    • Orbicularis oculi

    • Zygomaticus major

    • Orbicularis oris

    • Platysma

    • Trapezius

    • Deltoid

    • Pectoralis major

    • External oblique

    • Pronator teres

  • Deep Muscles:

    • Temporalis

    • Masseter

    • Sternocleidomastoid

    • Sternohyoid

    • Serratus anterior

    • Teres minor

    • Teres major

Muscle Attachments

Definitions

  • Origin:

    • Less movable attachment of a muscle, typically the more proximal attachment.

    • Example: Origins of biceps brachii are on the scapula.

  • Insertion:

    • More movable attachment of a muscle; pulled toward origin when muscle contracts.

    • Example: Insertion of biceps brachii on radius.

Variations in Designation

  • In cases where it is unclear which attachment is which based on movement or position:

    • Aponeurosis considered as origin and tendon as insertion in muscles where this distinction is common.

    • For muscles with multiple tendons at one end and one at the other end, each tendon at the broad end is considered an origin.

    • Some anatomists refer to attachments as proximal (or superior) and distal (or inferior).

Fascicle Organization

Types of Muscular Organization

  • Circular Muscles:

    • Features concentrically arranged fascicles.

    • Functions as a sphincter to control passage through an opening.

  • Parallel Muscles:

    • Fascicles run parallel to the muscle's long axis.

  • Convergent Muscles:

    • Fascicles merge toward a common attachment site (e.g., tendon or raphe).

    • Capable of pulling in various directions, but less forceful than parallel muscles of the same size.

  • Pennate Muscles:

    • Fascicles organized like a feather.

    • Generate more tension but pull tendons shorter than parallel muscles of the same size.

    • Subtypes: Unipennate, bipennate, multipennate.

Muscle Functions

Organization by Actions

  • Agonist:

    • Prime mover that contracts to produce a movement.

    • Example: Triceps brachii is the agonist for forearm extension.

  • Antagonist:

    • Opposes the action of the agonist, facilitating controlled, smooth movements.

    • Example: Biceps brachii is the antagonist for forearm extension.

  • Synergist:

    • Assists the agonist by contributing tension or stabilizing the point of origin, acting as fixators.

    • Example: Biceps brachii and brachialis work synergistically to flex the elbow joint.

Skeletal Muscle Naming

Naming Conventions

  1. Muscle Action:

    • Describes the primary function of the muscle.

    • Example: flexor digitorum longus flexes digits.

  2. Specific Body Regions:

    • Indicates muscle location.

    • Example: rectus femoris is near the femur.

  3. Muscle Attachments:

    • Describes origins and/or insertions.

    • Example: sternocleidomastoid originates from the sternum and clavicle and inserts on the mastoid process.

  4. Orientation of Muscle Fibers:

    • Indicates organization of muscle fascicles.

    • Example: rectus abdominis has fibers running vertically (rectus).

  5. Muscle Shape:

    • Describes the shape of the muscle.

    • Example: deltoid is shaped like a triangular delta symbol.

  6. Muscle Size:

    • Describes the relative size of the muscle.

    • Example: gluteus maximus is the largest buttock muscle.

  7. Muscle Heads/Tendons of Origin:

    • Indicates how many tendons are present at the less movable attachment.

    • Example: triceps brachii has three heads attaching by tendons to the skeleton.

Muscles of Facial Contraction

General Characteristics

  • Insert into the superficial fascia of skin of the face.

  • Cause movement of skin (facial expressions) during contraction.

  • Most are innervated by the facial nerve (CN VII).

Specific Muscles

  • Occipitofrontalis Muscle:

    • Connects with the epicranial aponeurosis (galea aponeurotica) to form the epicranius.

    • Frontal Belly: Raises eyebrows.

    • Occipital Belly: Retracts the scalp slightly.

Muscles of the Eyelids

  • Orbicularis Oculi:

    • Circular muscle fibers surrounding the orbit.

    • Closes the eye.

Muscles Associated with the Mouth

  • Orbicularis Oris:

    • Closes the mouth and puckers the lips.

  • Buccinator:

    • Compresses the cheek against the teeth during chewing.

Muscles of Mastication (Chewing)

Main Muscles

  • Masseter:

    • Action: Elevates and protracts the mandible.

    • Origin: Zygomatic arch.

    • Insertion: Coronoid process and angle of the mandible.

  • Temporalis:

    • Action: Elevates and retracts the mandible.

    • Origin: Temporal fossa.

    • Insertion: Coronoid process of the mandible.

  • Pterygoid Muscles:

    • Lateral Pterygoid: Opens and protrudes the jaw.

    • Medial Pterygoid: Elevates the jaw.

Muscles of Facial Expression

Superficial Muscles

  • Epicranius (front & occipital bellies)

  • Procerus

  • Orbicularis oculi

  • Corrugator supercilii

  • Levator palpebrae superioris

  • Levator labii superioris

  • Zygomaticus minor

  • Zygomaticus major

  • Risorius

  • Depressor anguli oris

  • Depressor labii inferioris

  • Platysma

Deep Muscles

  • Masseter

  • Buccinator

  • Orbicularis oris

  • Mentalis

  • Sternocleidomastoid

Extrinsic Eye Muscles

Functions

  • Insert onto the outer surface of the eye to facilitate movement.

Rectus Eye Muscles

  • Medial Rectus: Pulls the eye medially.

  • Lateral Rectus: Pulls the eye laterally.

  • Inferior Rectus: Pulls the eye inferiorly and medially.

  • Superior Rectus: Pulls the eye superiorly and medially.

Oblique Eye Muscles

  • Inferior Oblique: Elevates and turns the eye laterally.

  • Superior Oblique: Depresses and turns the eye laterally.

Sternocleidomastoid Muscle Description

  • Action: Ipsilateral lateral flexion and contralateral rotation of the head.

  • Origin: Manubrium and sternal end of the clavicle.

  • Insertion: Mastoid process.

Muscles of Respiration

Major Muscles

  • External Intercostals:

    • Elevate ribs during inspiration, increasing thoracic cavity volume.

  • Internal Intercostals:

    • Located deep to external intercostals, depress ribs during forced expiration.

  • Diaphragm:

    • Dome-shaped muscle partitioning thoracic and abdominal cavities; most crucial muscle for breathing.

Muscles of the Abdominal Wall

Functions

  • Compression of Organs: Holds abdominal organs in place.

  • Vertebral Column Stabilization: Flexes and stabilizes the vertebral column.

Main Muscles

  • External Oblique: Located superficially.

  • Internal Oblique: Located deep to the external oblique.

  • Transversus Abdominis: The deepest abdominal muscle.

  • Rectus Abdominis:

    • Segmentation: Partitioned into four segments by fibrous tendinous intersections.

    • Action: Flexes the vertebral column and compresses the abdomen.

    • Origin: Pubic symphysis.

    • Insertion: Xiphoid process and cartilage of ribs 5, 6, 7.

Muscles of the Pectoral Girdle

Overview

  • Origin: Muscles that originate on the axial skeleton.

  • Insertion: Insert on scapula and clavicle.

  • Function: Can stabilize or move the scapula.

  • Classification: Can be further categorized into anterior or posterior thoracic muscles.

Examples of Muscles
Superficial Muscles

  • Rhomboid Major

  • Rhomboid Minor

  • Deltoid

  • Latissimus Dorsi

  • Trapezius

Deep Muscles

  • Levator Scapulae

  • Supraspinatus

  • Infraspinatus

  • Teres Minor

  • Teres Major

Specific Functions and Actions

  • Pectoralis Minor: Helps to depress and protract the scapula, essentially hunching the shoulders.

  • Serratus Anterior: A fan-shaped muscle located between the ribs and the scapula, which protracts and stabilizes the scapula.

  • Pectoralis Major:

    • Action: Adducts and medially rotates the arm.

    • Origin: Clavicle, cartilage of ribs 2-6, sternum.

    • Insertion: Intertubercular groove of the humerus.

  • Trapezius:

    • Action: Elevates, adducts, depresses, and rotates the scapula.

    • Origin: Occiput, spinous process of C7-T12.

    • Insertion: Clavicle, acromion, and spine of the scapula.

  • Latissimus Dorsi:

    • Action: Prime arm extensor; adducts and medially rotates the arm.

    • Origin: Spinous processes of T7-S5, iliac crest.

    • Insertion: Intertubercular groove of the humerus.

  • Deltoid:

    • Action: Abducts, extends, and rotates the arm (both medial and lateral rotation).

    • Origin: Acromial end of the clavicle, acromion and spine of the scapula.

    • Insertion: Deltoid tuberosity of the humerus.