Module 33 - Skeletal Muscle Gross Anatomy Pt.1

Origin/Head

Muscle mend attached to the more stationary bone (of 2)

Insertion

Muscle end attached to the bone with greatest movement

• Ex: in limbs - origin = proximal, insertion = distsal

Belly + features

Largest portion of the muscle between origin and insertion

• Thick, central, contractile portion of muscle

Can muscles have multiple bellies?

Yes

• Bicepes has 2 bellies because it has multiple origins

Tendons

Attaches muscle to bone

Aponeurosis

• Broad tendon

• Flat & sheet-like

Agonist (muscle)

Primary mover that causes the action when the muscle contracts

Antagonist (muscle)

Muscle that opposes the agonist

Example of agonist and antagonist muscles

Movement: Flexing biceps

• Agonist: biceps bc its porducing most of the contraction

• Antagonist: triceps

Synergists + 2 components

Muscles that work together to cause a movement

1. Prime mover

2. Fixator

Prime mover

Muscle that plays major role in accomplishing a movement

Fixator

Stabilizes the joint crosses by the prime mover + prevents movement of the origin of prime mover

Location - Muscle Nomenclature (1/7)

• Named after body regions:

  • Pectoralis (chest)

  • Brachialis (arm)

  • Gluteus

Size - Muscle Nomenclature (2/7)

• Maximus/minimus (largest/smallest),

• Longus/brevis (long/short),

• Major/minor (relative size)

• Vastus (huge muscle)

Shape - Muscle nomenclature (3/7)

• Deltoid > triangle

• Trapezius > Trapezoid

• Teres > Rounded

• Quadratus > Square

Action - Muscle Nomenclature (4/7)

Describes function:

• flexor, extensor, adductor, abductor, or specialized roles (e.g., masseter = chewing)

Fiber Orientation - Muscle Nomenclature (5/7)

• Rectus: fibers are parallel to midline

• Transverse: perpendicular

• Oblique: angled

Origins/Insertions - Muscle nomenclature (6/7)

Names reflect attachment sites

• Sternocleidomastoid → sternum + clavicle + mastoid process

• Brachioradialis → arm + radius

Number of heads - Muscle Nomenclature (7/7)

• Bi- = 2 heads
• Tri- = 3 heads
• OR number of muscles in a group: quad- = 4

Location of Head and Neck muscles

• Anterior > flexion

• Posterior > Extension

• Lateral > Rotation and lateral flexion

Muscles That Cause Flexion of the Neck

• Muscles deep within the neck

• Originate on the anterior side of vertebral bodies + extend to the occipital bone

• AKA anterior muscles

Muscles That Cause Extension of the Neck

• Posterior neck muscles

  • Attach to occipital bone + mastoid process

  • Attach to processes on vertebrae

Muscles That Cause Rotation & Lateral Flexion + Function

• Lateral + posterior muscle groups

• Function: side-to-side movement

What are the 2 prime movers of the head and neck muscles

1. Sternocleidomastoid

2. Trapezius

Sternocleidomastoid — Origins & Insertion

• Origins: manubrium of sternum + clavicle

• Insertion: mastoid process

• 2 heads

• Group: lateral muscle

What actions does the sternocleidomastoid allow?

• Action:

  • forward flexion > contracts both sides

  • Rotation to the opposite side + lateral flexion of the same side > contracts 1 side

Trapezius (Neck Functions) — Origins & Insertions

• Group: posterior muscle

• Origins: broad origin along vertebrae + occipital bone

• Insertions: spine of scapula + clavicle

What actions does the trapezius allow?

• Extension of head

• Lateral flexion of neck

The vertebral column muscles allow what movements?

• Extension

• Lateral flexion

• Rotation

• Maintaining erect posture

What are the 2 muscle groups in the vertebral column?

1. Deep group: extends from vertebrae to vertebrae

2. Superficial group: extends from vertebrae to ribs

Prime mover of the superficial group muscles of vertebral column

Erector Spinae

Erector Spinae – Components (3 Subgroups)

• Spinalis: most medial

• Longissumus: intermediate

• Iliocostalis: most lateral

The vertebral column muscles are mostly what kind of fibers?

ST - Type I fibers (60-70%)

• For endurance

Thoracic Muscles are important for…

Breathing

4 Muscle Groups Associated with Rib Cage

1. Scalenes

2. External intercostals

3. Internal intercostals

4. Transversus thoracis

• Diaphragm

Scalene Muscles – Structure + Function

• 3 muscles w/different origins/insertions

• Function: Elevate the first 2 ribs during inspiration

External Intercostals – Structure & Functions

• Located between ribs, superficial → deep

  • Fiber direction = “hands in your pockets”

  • More superficial than internal intercostals

• Function: Elevate ribs → inspiration
  

Internal Intercostals - Strucrue & Functions

• Fibers run opposite to external intercostals

  • Muscle is deeper than external intercostals

• Function: Depress riibs during expiration

  • Pulls inferior ribs back to place

Transversus thoracis - Structure & Function

• Extends from sternum to costal cartilages

• Function: Assist internal intercostals in rib depression during expiration

Diaphragm - Structure & Function

• Major muscle of inspiration

• Dome-shaped, contracts + flattens during inspiration

• Function: increase thoracic cavity volume, separate thoracic and abdominal cavities

Actions of the abodminal wall muscles

• Flexion + rotation of vertebral column

• Decrease volume/compress abdominal + thoracic cavities during:

  • Forced expiration

  • Vomiting

  • Defecation

  • Urination

  • Childbirth

How is the abs structured to add strength?

• Crossing pattern of muscles to support organs

• Multiple layers with different fiber orientation

All layers connect to the

Linea alba

What are the 4 layer of the abdomen wall from superifical to deep?

1. External Abdominal Oblique

2. Rectus Abdominis

3. Internal Abdominal Oblique

4. Transversus Abdominis

Resctus Abdominis - Structure + Functions

• Structure: Most medial ab muscle, fibers run in vertical (rectus) formation

• Function: flexion of vertebral colum + compression

External Oblique - Structure + functions

• Structure: Most superificial layer, fibers run obliquely (hands in your pocket)

• Function: Flexion, rotation, compression of vertebral column

Internal Oblique - Structure + Function

• Structure: deep to external oblique, fibers run perpendicular to external oblique

• Functions: Flexion, rotation, compression

Transverse Abdominis - Structure + Functions

• Structure: Deepest layer, fibers run in a transverse plane (horizontally)

• Function: compression only

What do scapular movement muscles do?

• Attach upper limb to body

• Stabilize + move scapula and clavicle

Where do Scapular muscles originate?

All on the axial skeletion

5 Main scapular muscles

1. Trapezius

2. Levator Scapulae

3. Rhomboid

4. Serratus anterior

5. Pectoralis Minor

Trapezius - Structure + Functions

• Structure: Most superificial muscle in this region, posterior scapular muscle

• Functions: Elevation, depression, rotation of scapula

Levator Scapulae - Structure + Functions

• Structure: Deep to trapezius, extends from cervical vertebrae to top of scapula

• Functions: Elevate + rotate scapula

Rhomboid Minor + Major - Structure + Functions

• Structure: Extends from vertebrae to the medial border of scpula

• Functions: retraction of shoulders + elevation

Which of the rhomboids (minor or major) is the lower one?

Major

Serrus Anterior (Boxer’s muscles) - Strucure + Functions

• Structure: Anterior to scapula

  • Extends from lateral ribs > under the scapula > medial border of scapula

• Functions: hold scapula in place on the thoracic cage, protraction of shoulders, rotation

Pectoralis Major - Structure + Function

• Structure: Extends from 3rd-5th ribs (Origin) to the coracoid process (insertion)

• Function: Depress the scapula