Video Summary - Back Muscles Part 1: Deep Muscles

Main ideas / concepts

Back muscles are numerous, complex, and often neglected in basic anatomy study, but they are crucial for:

Posture stabilization of the vertebral column
Respiration-related movement (via connections to ribs/shoulder girdle mechanics)
Shoulder and trunk motion, especially through stabilization and controlled movement

Anatomically, back muscles are organized into layers:

Deep (intrinsic) layer (focus of this video)
(Mentioned for later) Intermediate and Superficial layers in a second part

Methodology / teaching structure used in the video (step-by-step)

Refresh key bony anatomy needed to understand where deep back muscles attach
- Vertebral column overview
  - 26 bones total
  - 7 cervical, 12 thoracic, 5 lumbar
  - Sacrum = 5 fused vertebrae
  - Coccyx = small triangular fused segment
  - Intervertebral discs (fibrocartilaginous) between vertebrae
- Recognize important vertebral features used for muscle attachment
  - Spinous process (posterior projection)
  - Transverse processes (posterior lateral projections)
  - Superior/inferior articular processes
  - Lamina (broad flat section connecting the processes)
- Additional skeletal landmarks referenced for context:
  - Scapulae (shoulder blades)
  - skull posterior elements (occiput, nuchal lines, mastoid process)
  - Pelvis, proximal humerus, and femur (contextual only)
Describe deep muscles by grouping them into “deep” sublayers Deep muscles are described as three depth sublayers, ordered from deepest to less deep:
1. Transversospinales
2. Erector spinae
3. Spino-transversales (smaller posterior/lateral group)
Give each muscle group’s attachment points and primary actions For each named muscle/group, the video covers:
- Origin/attachment
- Insertion/attachment
- Primary movement functions (e.g., rotation, extension, flexion/rotation, stabilization)
Finish by listing completeness-level “small deep muscles” Mentions additional minor muscles between key processes that stabilize the spine and ribs.

Detailed deep back muscle groups and muscles

1) Deepest layer: Transversospinales (3 muscles)

General role

Associated with transverse and spinous processes along the spine
Contribute to rotation, proprioception, and spinal stabilization

a) Rotatores

Described under transversospinales; “best developed in thoracic region”
Origin: transverse processes of vertebral bodies
Insertion: inferior parts of spinous processes and lamina of the vertebra above
Action: primarily assist trunk rotation
Additional role: small contribution to proprioception and spinal stabilization

b) Multifidus

Name origin: Latin “many/split”
Origin (finger-like slips):
- sacrum
- superior articular processes of lumbar vertebrae
- transverse processes of thoracic vertebrae
- articular processes of cervical vertebrae
Insertion: multiple points into spinous processes of every lumbar, thoracic, and cervical vertebra
Actions:
1. Stabilize the vertebral column
2. Extend neck and trunk when contracting

c) Semispinalis (treated as one muscle though described in parts)

Recognized parts:
- semispinalis capitis (skull-associated)
- semispinalis cervicis (neck-associated)
- semispinalis thoracis (thorax-associated)
Origin:
- superior articular process of C4–C7
- transverse processes of T1–T11
Insertion:
- spinous processes of T6–C2
- occipital bone between the superior and inferior nuchal lines
Actions: assist extension and rotation of head, neck, and trunk

2) Next deep layer: Erector spinae

Overall group function

Performs extension or flexion of the vertebral column depending on:
- Bilateral contraction → flexion
- Unilateral contraction → extension

Common tendinous origin

Connects to parts of:
- lumbar and thoracic vertebrae
- sacrum
- large pelvic ligaments

Subcomponents of erector spinae

a) Spinalis

Often split into:
- spinalis cervicis (collis)
- spinalis thoracis
Thoracic part
- Origin: common tendinous origin + spinous processes T11–L3
- Insertion: spinous processes T2–T8
Collis / neck part
- Origin: spinous processes C2–T10
- Insertion: spinous processes C2–C4 (lateral to spinalis)

b) Longissimus

Divided into:
- capitis, cervicis, thoracis
Origin: common tendinous origin + transverse processes C4–T6
Insertion:
- transverse processes C2–C7
- transverse processes of the thoracic and lumbar spine
- ribs 2nd–12th
- mastoid process (skull)

c) Iliocostalis (lateral iliocostalis)

Divided into:
- iliocostalis thoracis / cholus thoracis and lumborum (as described)
Origin: common tendinous origin + spinous processes L1–L5 and rib angles 3rd–12th
Insertion:
- transverse processes L1–L4
- rib angles 1st–12th
- transverse processes C4–C6

3) Small posterior-lateral neck muscles: Spino-transversales

General function

Extend and rotate head/neck (as described per muscle)

a) Splenius capitis

Origin: nuchal ligament + spinous processes C7–T3
Insertion: mastoid processes + lateral part of superior nuchal line (occipital bone)
Action: extend and rotate the head

b) Splenius cervicis

Origin: spinous processes T3–T6
Insertion: transverse processes C1–C3
Action: extend and rotate the neck

Big-picture takeaway (structure + function)

These deep muscle systems form:

layers (deep → deeper → deepest)
a tube-like band running along the spine

They provide:

stabilization of the vertebral column
most of the extension and rotation movements the body uses routinely

“Completeness” section: additional minor deep muscles (final list)

Interspinalis
- Location: between spinous processes of almost every vertebra
- Best developed: cervical and lumbar regions
- Action: primarily stabilize the vertebral column
Intertransversarii
- Location: between transverse processes, mainly cervical and lumbar
- Action: stabilize the spine
Levatores costarum
- Origin: transverse processes C7–T11
- Insertion: superior borders of ribs
- Action: many small muscles that lift ribs at the costovertebral joints

Speakers / sources featured

Dr. Connor Boylan (speaker; host/instructor)

Back Muscles Part 1: Deep Muscles

Key takeaways