Anatomy Cheat Sheet - Back Muscles

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Questions and Answers

What is the primary function of the external urethral sphincter in males?

To support the pelvic floor

To assist in penile erection

To control ejaculation

To maintain urinary continence (correct)

Which structure is primarily responsible for strengthening the pelvic floor?

Deep transverse perineal muscle

Ischial rami

Superficial transverse perineal muscle

Perineal body (correct)

In females, which of the following structures does the urethrovaginal sphincter encircle?

Vagina and anus

Urethra and vagina (correct)

Vagina and cervix

Urethra and rectum

Which nerve is associated with the deep branch of the penis or clitoris?

Pudendal nerve Signup and view all the answers

What is the origin of the deep transverse perineal muscle?

Inferior pubic rami Signup and view all the answers

Which muscle is described as encircling the membranous urethra in males?

External urethral sphincter Signup and view all the answers

What is the main role of the perineal nerve?

To provide motor innervation to the pelvic floor Signup and view all the answers

What are the ischial rami associated with in the context of pelvic muscles?

Attachment for superficial perineal muscles Signup and view all the answers

What is the primary function of the rectus capitis posterior minor muscle?

Extension of the head at the atlantooccipital joint Signup and view all the answers

Which muscle is responsible for ipsilateral rotation of the head at the atlantoaxial joint?

Obliquus capitis inferior Signup and view all the answers

What does bilateral contraction of the obliquus capitis superior achieve?

Head extension at the atlantooccipital joint Signup and view all the answers

Which nerve is responsible for innervating the rhomboid major muscle?

Dorsal scapular nerve (C5) Signup and view all the answers

Which part of the trapezius muscle is involved in drawing the scapula superomedially?

Descending part Signup and view all the answers

What is the primary function of the latissimus dorsi muscle?

Arm internal rotation and extension Signup and view all the answers

What is the origin of the serratus posterior superior muscle?

Spinous processes of T1-T3 Signup and view all the answers

What role does the levator scapulae muscle play in neck movement?

Lateral flexion of the neck (ipsilateral) Signup and view all the answers

Which muscle aids in the rotation of the glenoid cavity inferiorly?

Rhomboid major Signup and view all the answers

What is the action of the serratus posterior inferior muscle?

Depresses ribs Signup and view all the answers

What is the function of the ascending part of the trapezius?

Scapular depression Signup and view all the answers

Which muscle is innervated by the anterior rami of spinal nerves C3-C4?

Levator scapulae Signup and view all the answers

What distinguishes the function of the obliquus capitis superior muscle from the obliquus capitis inferior?

Obliquus capitis superior also performs lateral flexion Signup and view all the answers

What is the primary function of the Splenius capitis muscle during unilateral contraction?

Lateral flexion and rotation of head (ipsilateral) Signup and view all the answers

Which muscle's bilateral contraction is associated with extension of the cervical and thoracic spine?

Semispinalis thoracis Signup and view all the answers

What is the primary function of the Multifidus lumborum during unilateral contraction?

Lateral flexion of spine (ipsilateral) Signup and view all the answers

Which nerve innervates the Longissimus capitis muscle?

Medial branch of posterior rami of spinal nerves Signup and view all the answers

What structure does the Iliocostalis thoracis muscle primarily insert into?

Angles of ribs 1-6 and transverse process of vertebra C7 Signup and view all the answers

Which muscle assists in rib elevation as well as rotation of the thoracic spine?

Levatores costarum Signup and view all the answers

What is the role of the Interspinales muscles in the spine?

Assisting in the extension of the cervical and lumbar spine Signup and view all the answers

Which muscle is primarily responsible for extending the neck in bilateral contraction?

Longissimus cervicis Signup and view all the answers

What is the primary function of the Pectoralis major muscle at the shoulder joint?

Arm adduction Signup and view all the answers

Which muscle originates from the thoracolumbar fascia?

Longissimus lumborum Signup and view all the answers

What is unique about the Rotatores longi in terms of their function?

They rotate the thoracic spine contralaterally. Signup and view all the answers

Where does the Intertransversarii muscle insert within the lumbar region?

Transverse processes of succeeding vertebrae Signup and view all the answers

What is the function of the Semispinalis cervicis during unilateral contraction?

Rotation of cervical spine (contralateral) Signup and view all the answers

What is the role of the Anterior cervical intertransversarii muscles?

Lateral flexion of the cervical spine Signup and view all the answers

What is the main structural function of the perineal body?

Supports abdominopelvic viscera Signup and view all the answers

Which structure is primarily responsible for maintaining urinary continence in males?

External urethral sphincter Signup and view all the answers

What is the distinguishing feature of the urethrovaginal sphincter in females?

It compresses the urethra and vaginal canal. Signup and view all the answers

Which muscle provides support to the pelvic floor by connecting from the ischial tuberosities?

Superficial transverse perineal muscle Signup and view all the answers

What is the innervation source of the pudendal nerve that affects the perineal region?

Sacral spinal nerves Signup and view all the answers

In males, which area is encompassed by the external urethral sphincter?

Membranous urethra and neck of urinary bladder Signup and view all the answers

Which of the following structures contributes to the maintenance of an erection?

Deep branch of the penis/clitoris Signup and view all the answers

Which anatomical area is associated with the function of the deep transverse perineal muscle?

Stabilizing the pelvic floor Signup and view all the answers

What function does the rectus capitis posterior major muscle primarily perform?

Head extension at the atlantooccipital joint Signup and view all the answers

Which muscle's innervation is provided by the suboccipital nerve?

Obliquus capitis inferior Signup and view all the answers

What is the role of the serratus posterior superior muscle?

Elevating the ribs Signup and view all the answers

Which anatomical location serves as the origin for the latissimus dorsi muscle?

Spinous processes of vertebrae T7-T12 Signup and view all the answers

In which joint does the obliquus capitis superior muscle allow for contralateral head rotation?

Atlantoaxial joint Signup and view all the answers

What is the primary function attributed to the ascending part of the trapezius muscle?

Drawing the scapula inferomedially Signup and view all the answers

Which muscle inserts into the vertebral border of the scapula?

Rhomboid minor Signup and view all the answers

What action is performed by the levator scapulae muscle?

Scapular elevation Signup and view all the answers

Which of the following muscles is involved in head extension at the atlantooccipital joint?

Rectus capitis posterior minor Signup and view all the answers

Which nerve innervates the motor functions associated with the trapezius muscle?

Accessory nerve (CN XI) Signup and view all the answers

What is the primary action of the latissimus dorsi muscle at the shoulder joint?

Shoulder internal rotation Signup and view all the answers

Which type of contraction of the obliquus capitis inferior muscle contributes to head rotation?

Unilateral contraction Signup and view all the answers

What is the role of the rhomboid major muscle in the scapula?

Retracts the scapula Signup and view all the answers

Which of the following describes the innervation of the serratus posterior inferior muscle?

Intercostal nerves T9-T12 Signup and view all the answers

What can be inferred about the function of the Iliocostalis thoracis muscle during unilateral contraction?

It assists in ipsilateral lateral flexion of the spine. Signup and view all the answers

Which muscles have a role in contralateral rotation of the thoracic spine?

Multifidus thoracis Signup and view all the answers

What primary action is facilitated by the Semispinalis capitis during unilateral contraction?

Contralateral rotation of the head Signup and view all the answers

Which of the following best describes the primary function of the Longissimus capitis muscle?

Lateral flexion of the head and neck is achieved unilaterally. Signup and view all the answers

What is the action produced by bilateral contraction of the Spinalis thoracis?

Extension of the thoracic spine Signup and view all the answers

In what scenario is the Intertransversarii muscle primarily active?

In lateral flexion of the spine Signup and view all the answers

Which of the following muscles primarily functions to elevate the ribs?

Levatores costarum Signup and view all the answers

What is the role of the Multifidus muscle group in spinal mechanics?

To assist both in extension and rotation Signup and view all the answers

During unilateral contraction, which muscle primarily allows for lateral flexion of the cervical spine?

Iliocostalis cervicis Signup and view all the answers

Which action is NOT typical of the Pectoralis major at the shoulder joint?

Arm external rotation Signup and view all the answers

Which of the following muscles enables ipsilateral rotation of the head during unilateral contraction?

Splenius capitis Signup and view all the answers

Which statement best describes the function of the Rotatores muscles?

They contribute to the stability of spinal joints. Signup and view all the answers

Which muscle primarily contributes to the rotation of the thoracic spine during unilateral contraction?

Rotatores longi Signup and view all the answers

What action is primarily performed by the Interspinales muscles?

Extension of the cervical spine Signup and view all the answers

Study Notes

Superficial (Extrinsic) Muscles of the Back

Suboccipital Muscles

Rectus Capitis Posterior Minor
- Origin: Posterior tubercle of atlas
- Insertion: Medial part of inferior nuchal line
- Innervation: Atlantooccipital joint
- Function: Head extension
Rectus Capitis Posterior Major
- Origin: Spinous process of axis
- Insertion: Lateral part of inferior nuchal line
- Innervation: Atlantooccipital joint
- Function: Head extension (bilateral contraction)
Obliquus Capitis Inferior
- Origin: Spinous process of axis
- Insertion: Transverse process of atlas
- Innervation: Posterior ramus of spinal nerve C1 (suboccipital nerve)
- Function: Head rotation (ipsilateral) and head extension (bilateral contraction)
Obliquus Capitis Superior
- Origin: Transverse process of atlas
- Insertion: Occipital bone (between superior and inferior nuchal lines)
- Innervation: Posterior ramus of spinal nerve C1 (suboccipital nerve)
- Function: Head rotation (contralateral), head lateral flexion (ipsilateral)

Superficial Layer Muscles

Trapezius
- Parts: Descending, Transverse, Ascending
- Descending: Origin at medial third of superior nuchal line; Insertion at lateral third of clavicle
  - Function: Draws scapula superomedially
- Transverse: Origin at broad aponeurosis from spinous processes T1-T4; Insertion at acromion, spine of scapula
  - Function: Supports scapula
- Ascending: Origin at spinous processes T5-T12; Insertion at medial end of spine of scapula
  - Function: Draws scapula inferomedially
Levator Scapulae
- Origin: Transverse processes of C1-C4
- Insertion: Medial border of scapula (from superior angle to root of spine)
- Innervation: Anterior rami of C3-C4, Dorsal scapular nerve (C5)
- Function: Draws scapula superomedially and lateral flexion of neck (ipsilateral)
Rhomboid Major
- Origin: Spinous processes of T2-T5
- Insertion: Medial border of scapula (from inferior angle to root)
- Innervation: Dorsal scapular nerve (C5)
- Function: Draws scapula superomedially, rotates glenoid cavity inferiorly
Rhomboid Minor
- Origin: Nuchal ligament, spinous processes of C7-T1
- Insertion: Root of spine of scapula
- Innervation: Dorsal scapular nerve (C5)
- Function: Supports position of scapula
Latissimus Dorsi
- Origins: Spinous processes T7-T12, thoracolumbar fascia, and posterior third of iliac crest
- Insertion: Intertubercular sulcus of humerus
- Innervation: Thoracodorsal nerve (C6-C8)
- Functions: Arm internal rotation, adduction, extension, assists in respiration

Intermediate Layer Muscles

Serratus Posterior Superior
- Origin: Nuchal ligament, spinous processes C7-T3
- Insertion: Superior borders of ribs 2-5
- Innervation: 2nd-5th intercostal nerves
- Function: Elevates ribs
Serratus Posterior Inferior
- Origin: Spinous processes of T11-L2
- Insertion: Inferior borders of ribs 9-12
- Innervation: Anterior rami of spinal nerves T9-T12
- Function: Depresses ribs### Muscles of the Posterior Thorax
Depresses and draws ribs posteroinferiorly.
Innervated by 9th-11th intercostal nerves and subcostal nerve.

Deep Muscles of the Back: Superficial Layer

Splenius Capitis: Origin at spinous processes C7-T3, nuchal ligament; inserts at mastoid process and occipital bone; extends and laterally rotates head.
Splenius Cervicis: Origin at spinous processes T3-T6; inserts at transverse processes C1-C3; extends and laterally rotates neck.

Deep Muscles of the Back: Intermediate Layer (Erector Spinae Group)

Iliocostalis: Comprised of cervicis, thoracis, and lumborum; functions in spine extension.
- Cervicis: Origin at angles of ribs 3-6; inserts at transverse processes C4-C6.
- Thoracis: Extends and laterally flexes spine.
- Lumborum: Origin from sacrum; inserts at angles of ribs 5-12 and transverse processes L1-L4.
Longissimus: Comprised of capitis, cervicis, and thoracis; extends and laterally flexes spine.
- Capitis: Inserts at mastoid process.
- Thoracis: Extends spine from L1-L5 and T1-T12.
Spinalis: Comprised of cervicis and thoracis; extends cervical and thoracic spine.

Deep Muscles of the Back: Deep Layer

Semispinalis Group: Extends head and neck.
- Capitis: From articular processes C4-C7; inserts at nuchal lines of occipital bone.
- Cervicis: From transverse processes T1-T6; inserts at spinous processes C2-C5.
- Thoracis: Similar function with different origins and insertions.
Multifidus: Provides stability; supports spine extension and rotation.
Rotatores: Rotates thoracic spine; categorized into breves and longi based on levels.

Deepest Layer: Interspinales and Intertransversarii

Interspinales: Connect spinous processes; aid in spine extension.
- Cervicis, thoracis, and lumborum regions present.
Intertransversarii: Stabilizes spine; aids lateral flexion.

Levatores Costarum

Elevates ribs; innervated by posterior rami of spinal nerves T1-T12.

Anterolateral Muscles of the Trunk: Muscles of the Thoracic Cage

Pectoralis Major: Adducts and rotates arm; innervated by lateral and medial pectoral nerves.
Pectoralis Minor: Stabilizes scapula; innervated by medial pectoral nerve.
Serratus Anterior: Draws scapula forward; innervated by long thoracic nerve.
Subclavius: Anchors and depresses clavicle; innervated by nerve to subclavius.
Intercostals: External intercostals elevate ribs; internal intercostals depress ribs; innervated by intercostal nerves.
Respiratory Diaphragm: Main muscle of breathing; innervated by phrenic nerves.

Muscles of the Abdominal Wall

External Abdominal Oblique: Flexes and rotates trunk; innervated by intercostal and subcostal nerves.
Internal Abdominal Oblique: Similar functions with a different fiber orientation; innervated by intercostal nerves.
Transversus Abdominis: Compresses abdominal viscera; innervated by intercostal nerves.
Rectus Abdominis: Flexes trunk; innervated by intercostal nerves.
Pyramidalis: Tenses linea alba, innervated by subcostal nerve.

Muscles of the Pelvic Floor

Levator Ani: Supports pelvic viscera and increases intraabdominal pressure; includes puborectalis, pubococcygeus, and iliococcygeus.
Coccygeus: Flexes coccyx; innervated by spinal nerves S4 and S5.
Obturator Internus: Externally rotates thigh; stabilizes hip joint.

Perineal Muscles

External Anal Sphincter: Supports pelvic floor; innervated by pudendal nerve.
Bulbospongiosus: Assists in erection and supports perineal body; function differs in males and females.
Ischiocavernosus: Facilitates erection; attaches to crus of clitoris or penis.### Muscles and Nerves of the Pelvic Floor
Deep Branch Function: Maintains erection in both males (penis) and females (clitoris).
Innervation: Supplied by the perineal nerve (of pudendal nerve).
Walls of Vagina: Provides support and maintains structural integrity of the pelvic region.

Deep Transverse Perineal Muscle

Origin: Inferior pubic rami and ischial rami.
Insertion: Perineal body, which assists in maintaining pelvic floor integrity.
Function: Strengthens pelvic floor to support abdominal and pelvic organs.

Superficial Transverse Perineal Muscle

Origin: Ischial tuberosities.
Insertion: Connects at the perineal body, aiding in pelvic stability.

External Urethral Sphincter

Male Anatomical Features: Encircles membranous urethra and extends anteriorly to the prostatic urethra, neck of the urinary bladder, and to ischial rami (compressor urethrae).
Function in Males: Maintains urinary continence by compressing the urethra.
Female Anatomical Features: Encircles the urethra and neck of the bladder, extending to ischial rami (compressor urethrae), and encircles the vagina (urethrovaginal sphincter).
Function in Females: Maintains urinary continence and constricts the vaginal canal.

Completion of Muscle Charts

Progress Acknowledged: Mastery of trunk muscle origins, insertions, innervations, and functions.
Next Steps for Study: Focus on learning muscles of the lower limb, upper limb, and head & neck.
Resources Available: Detailed muscle charts on every region of the body are accessible for further learning.