Human Gross Anatomy: Anatomical Concepts, Back Surface Anatomy, & Muscles

Anatomical Concepts

• All anatomical descriptions relate to a consistent anatomical position to avoid ambiguity.

• Terms describing positions are used as if the body is in the anatomical position, even if the donor is horizontal in the lab.

• Anatomical Position

  • Standing

  • Head, palms, and toes facing anteriorly

  • Feet parallel

  Anatomical Planes

• Four imaginary planes intersect the body in the anatomical position:

  • Median

  • Sagittal

  • Frontal (coronal)

  • Transverse

  Median & Sagittal Planes

• Median plane (vertical)

  • Longitudinally through the midline of the body

  • Divides the body into mostly symmetrical right and left halves

• Sagittal planes (vertical)

  • Parallel to the median plane

  • Also known as parasagittal or paramedian

  Frontal (Coronal) Planes

• Vertical planes at right angles to the median plane.

• Divides the body into anterior and posterior portions.

  Transverse (Horizontal) Planes

• At right angles to the median and frontal planes.

• Divides into superior and inferior portions.

• Also known as axial or transaxial planes.

  Summary of Planes

• Median Plane

  • Passes longitudinally through the midline.

  • Divides into symmetrical right and left halves.

• Sagittal Planes

  • Parallel to the median plane.

  • Divides into right and left portions.

• Frontal (Coronal) Planes

  • At right angles to the median plane.

  • Divides into anterior and posterior portions.

• Transverse (Horizontal) Planes

  • Perpendicular to any vertical plane.

  • Divides into superior and inferior portions.

• Clinicians use planar imaging technologies like CT scans to create sections of the body for describing and displaying internal structures.

  Terms of Relationship & Comparison

  Anatomical Relational Terminology

• Superficial: Closer to the body surface (skin) than a deeper structure.

• Intermediate: Between superficial and deep.

• Deep: Farther from the body surface.

• Always relational when comparing one structure to another.

  Examples of Relational Terms:

• Medial: Toward or at the midline of the body; on the inner side of. Example: The heart is medial to the arm.

• Lateral: Away from the midline of the body; on the outer side of. Example: The arms are lateral to the chest.

• Intermediate: Between a more medial and a more lateral structure. Example: The collarbone is intermediate between the breastbone and shoulder.

• Superior/Cranial: Nearer the cranium (head).

• Inferior/Caudal: Nearer the sole of the foot. Caudal refers to the foot or tail region (coccyx in humans).

• Anterior/Ventral: Towards the front surface. Example: The breastbone is anterior to the spine.

• Posterior/Dorsal: Towards the back surface. Example: The heart is posterior to the breastbone.

  • Note: Ventral and anterior are synonymous in humans, but not in four-legged animals. Anterior refers to the leading portion of the body, while ventral specifically refers to the "belly" of a vertebrae animal. Similarly, dorsal and posterior are the same in humans, but dorsal refers specifically to an animal's back.

• Internal - Deep

• External - Superficial

• Proximal: Towards the trunk or point of origin.

• Distal: Away from the trunk or point of origin.

  Combined Terms:

• Combine standard terms for more precise descriptions.

  • Examples: Superolateral, Inferomedial, Anteroinferior, Posterosuperior

  Anatomical Directional Terms - Examples

• The nose is superior to the mouth.

• The elbow is proximal to the wrist.

• The heart is deep to the sternum.

• The ears are lateral to the nose.

• The skin is superficial to the muscles.

  Surface Anatomy

  Skin

• Epidermis (superficial)

  • Mostly dead, flattened cells.

  • Avascular (no blood vessels).

  • Afferent nerve endings (cutaneous sensation).

• Dermis (deep)

  • Highly vascular.

  • Dense layer of interlacing collagen and elastin fibers.

  • Afferent nerve endings.

  • Glands (sweat, oil).

  • Hair follicles.

  Fascia

• Grossly visible connective tissue.

• Superficial fascia

  • aka hypodermis, fatty layer

  • Connects dermis to underlying deep fascia

  • Varies in thickness

• Deep fascia

  • Dense & devoid of adipose tissue

  • Investing fascia

  • Surrounds and supports:

  • Muscles (intermuscular septa)

  • Neurovasculature

  • Organs (viscera)

  Loose Connective Tissue (Areolar)

• Located between muscles and organs.

• Supports and binds muscles, organs, and neurovascular structures.

  Neurovascular Bundle

• Typical Contents:

  • Artery: Blood supply.

  • Vein(s): Drainage of low-oxygenated blood.

  • Lymphatics: Drainage of fluids, proteins, and cellular debris.

  • Nerve: Communication with CNS.

  Bones & Bone Cavity

• Deepest structures.

• Attachment sites for muscles.

• Lined by fascia.

  Boney Attachment Sites

• Bone markings indicate:

  • Sites of muscle, ligament, and tendon attachment on external surfaces.

  • Ligaments connect bone to bone.

  • Tendons connect muscle to bone.

  • Areas involved in joint formation or conduits for blood vessels and nerves.

  • Example: Distal attachment site: pectoralis minor m.

  Muscle Attachment Points On Bones

• Tendons attach muscle to bone

• Understanding muscle attachments includes observing

  • What joints are crossed?

  • Look at the muscle

  • Actions of muscles

  • Concentric contraction (shortening of muscle)

  Muscle Attachment Points on Bones - Origin vs Insertion

• Origin:

  • Typically fixed (the bone that does not move during contraction).

• Insertion:

  • Typically kinetic (moves).

  • This attachment moves towards the other attachment (origin).

  Bone & Bone Cavity: Structure of a Typical Long Bone

• All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes

• Diaphysis

  • Tubular shaft that forms long axis of bone

  • Consists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adults

• Epiphyses

  • Ends of long bones that consist of compact bone externally and spongy bone internally

  • Articular cartilage covers articular (joint) surfaces

• Between diaphysis and epiphysis is epiphyseal line

  • Remnant of childhood epiphyseal plate where bone growth occurs

  Muscles of the Back (w/innervation)

• Back muscles are separated into extrinsic and intrinsic components based on their embryological origin and role in movement.

• Extrinsic Muscles:

  • include the trapezius, latissimus dorsi, rhomboid major and minor, levator scapulae, and serratus posterior superior and inferior muscles

• Principal function of the extrinsic muscles of the back is to move the upper extremity by controlling the movement of the scapula and humerus—important bones in the shoulder region

• Extrinsic muscles of the back may also contribute to respiratory movements

• Divided into superficial & deep

  Superficial = Trapezius m. attachments

• Origin

  • Occipital bone

  • Superior nuchal line & external occipital protuberance

  • Origin of trapezius

  • Ligamentum nuchae & spinous processes C7-T12

• Insertion

  • Clavicle

  • Spine of scapula

• Crosses the ‘scapulothoracic’ joint

  • Affects actions of scapula

  Trapezius m. actions – ‘scapulothoracic’ joint

• All fibers contracting:

  • Retraction of scapula

• Ascending fibers contracting:

  • Depression of scapula

• Descending fibers contracting:

  • Elevation of scapula

• Both ascending & descending fibers contracting:

  • Superiorly rotates glenoid cavity

  Trapezius m. innervation

• Innervation

  • Efferent: Accessory n. (CN XI)

  • Afferent C3 & C4

  Trapezius Blood Supply

• Transverse cervical a.

  • Stemming from the thyrocervical trunk of the 1st part of the subclavian artery

  • Transverse cervical a. gives rise to the dorsal scapular a. ~30% of the time

  Superficial = Latissimus dorsi m. attachments

• Origin:

  • Inferior thoracic spinous processes & ribs

  • Thoracolumbar fascia

  • Iliac crest

• Insertion:

  • Floor of intertubercular sulcus (bicipital groove) of humerus

• Crosses the glenohumeral (shoulder) joint

  Latissimus dorsi m. actions - glenohumeral joint

• Of shoulder joint:

  • Medial rotation

  • Extension

  • Adduction

  Latissimus dorsi m. innervation

• Innervation:

  • Thoracodorsal n.

  • Posterior cord of brachial plexus C5-C8

  Latissimus Dorsi – Blood Supply

• Thoracodorsal a.

  • Stemming from the subscapular a.

  • Thoracodorsal a. accompanies the thoracodorsal n.

  Triangle of auscultation

• Optimal location for auscultating lung sounds

• Borders:

  • Lateral: Medial border of scapula (rhomboid major m.)

  • Medial: trapezius m., ascending fibers

  • Inferior: Latissimus dorsi m., superior border

• Lumbar triangle – bounded by latissimus dorsi, external oblique of abdomen & iliac crest. Floor is internal oblique of abdomen. May be a site of “lumbar hernia”.

  Superficial = Rhomboid Major & Minor Muscle Attachments

• Origin:

  • Spinous processes of C7 and T1 (minor) and spinous processes of T2-T5 (major)

• Insertion:

  • Medial border of scapula

  Rhomboids – Joint movements

• Stabilizes scapula

• Act together (and with middle trapezius fibers) to retract (adduct) scapula - “squaring shoulders”

• Downward rotation of scapula - glenoid cavity is downward

  Rhomboids - Innervation

• Dorsal Scapular Nerve (C4&C5) (From the brachial plexus C5 ventral primary ramus)

  Rhomboids – Blood Supply

• Dorsal Scapular Artery

• DSA comes from the third part of the subclavian a.

• DSA anastomoses with suprascapular a. and subscapular a. to form the scapular anastomosis;

• DSA is a branch of the transverse cervical a. in ~30%

  Superficial – Levator Scapula – m. attachments

• Origin:

  • Transverse processes of C1-C4

• Insertion:

  • Medial border of scapula, superior to spine

  Levator Scapula – Joint movements

• Elevates/adducts scapula in synergy with superior fibers of trapezius;

• Tilts glenoid cavity downward when scapula is fixed,

• Laterally flexes neck to the same side

  Levator Scapula - Innervation

• Cervical spinal nerves and dorsal scapular nerve (C4-C5)

• Same nerve innervation as rhomboids

  Levator Scapula – Blood Supply

• Dorsal Scapular Artery

• DSA comes from the third part of the subclavian a.

• DSA anatstomoses with suprascapular a. and subscapular a. to form the scapular anastomosis;

• DSA is a branch of the transverse cervical a. in ~30% of people

  Intermediate Serratus Posterior Superior M. Attachments

• Origin:

  • Nuchal ligament, spinous processes of C7 to T3

• Insertion:

  • Superior borders of ribs 2-4

  Serratus Posterior Superior- Joint movements

• Elevates ribs

  Serratus Posterior Superior - innervation

• 2nd to 5th intercostal nerves branches of the ventral primary rami of spinal nerves T1-T4

  Serratus Posterior Superior - Blood Supply

• Posterior intercostal aa. 1-4

  Intermediate Serratus Posterior Inferior M Attachments

• Origin:

  • Thoracolumbar fascia, spines of vertebrae T11-T12 and L1-L2

• Insertion:

  • ribs 9-12, lateral to the angles

  Serratus Posterior Inferior - Joint movements

• Pulls down lower ribs

  Serratus Posterior Inferior - Innervation

• Branches of the ventral primary rami of spinal nerves T9-T12

  Serratus Posterior Inferior - Blood Supply

• Lowest posterior intercostal a.,

• Subcostal a.,

• first two lumbar aa.

  Intrinsic (Deep) Back Muscles

  Intrinsic = Splenius Capitis & Cervicis

  Splenius Capitis & Cervicis – M. Attachments

• Origin:

  • Ligamentum nuchae*, spinous processes of vertebrae C7-T6

• Insertion:

  • mastoid process of temporal bone and occipital bone (capitis); transverse processes of C2-C4 vertebrae (cervicis)

  • *ligamentum nuchae is a strong, elastic ligament extending from the occipital bone of the skull along the tips of the spinous processes of the cervical vertebrae. It binds the cervical vertebrae together and inhibits excessive head and neck flexion, thus preventing damage to the spinal cord in the vertebral canal.

  Splenius Capitus & Cervicis – Joint Movements

• Extend or hyperextend head; when splenius muscles on one side are activated, head rotates and bends laterally toward the same side

  Splenius Capitus & Cervicis - Innervation

• Dorsal Rami of Cervical Spinal Nerves

  Splenius Capitus & Cervicis – Blood Supply

• Occipital a. that arises from the external carotid a.

• Cervicis also receives blood from Dorsal branches of the posterior intercostal arteries from the thoracic aorta.

  Intrinsic = Errector Spinae – M. Attachments

• Iliocostalis

  • Origin:

  • Iliac crests (lumborum); inferior 6 ribs (thoracic); ribs 3-6 (cervicis

• Insertion:

  • angles of ribs (L&T); transverse processes of C4-C6

  Intrinsic = Errector Spinae – M. Attachments

• Longissimus

  • : Origin:

  • Transverse processes of lumbar through cervical vertebrae

• Insertion:

  • transverse processes of thoracic or cervical vertebrae and to ribs superior to origin as indicated by name; capitis inserts into mastoid process of temporal bone

  Intrinsic = Errector Spinae – M. Attachments

• Spinalis

  • Origin:

  • Spinous process of upper lumbar and lower thoracic vertebrae

• Insertion:

  • Spinous process of upper thoracic and cervical vertebrae

  Intrinsic = Errector Spinae – Joint Movements

• Iliocostalis:

  • Extends and laterally flex the vertebral column, maintain erect posture

• Longissimus:

  • T&C extend and laterally flex vertebral column; Capitis extends head and turns the face toward the same side

• Spinalis:

  • Extends vertebral column

  Intrinsic = Errector Spinae – Innervation

• Dorsal Rami of Spinal Nerves

  Intrinsic = Errector Spinae – Blood Supply

• Supplied segmentally by:

  • Deep cervical a.

  • Posterior intercostal aa.

  • Subcostal aa.

  • Lumbar aa.

  Transversospinalis – M. Attachments

• Semispinalis

  • Origin:

  • transverse processes of C7-T12

• Insertion:

  • Occipital bone (capitis); Spinous processes of cervical (cervicis); Thoracic vertebrae T1-T4 (thoracis)

  Transversospinalis – Joint Movements

• Extends vertebral column and head

• Rotates vertebral column & head to the opposite side

  Transversospinalis - Innervation

• Spinal nerves (Dorsal rami)

  Transversospinalis – Blood Supply

• Semispinalis capitis receives blood from the occipital artery

• Semispinalis cervicis receives its blood from the occipital, vertebral and deep cervical arteries

• Semispinalis thoracic receives its blood from the dorsal branches of the posterior intercostal arteries

  Transversospinalis: Multifidus & Rotatores - M. Attachments

• Origin:

  • transverse processes

• Insertion:

  • spinous processes above

  Transversospinalis: Multifidus & Rotatores - Joint Movements

• Stabilize the spine

• Rotation

  Transversospinalis: Multifidus & Rotatores - Innervation

• Dorsal primary rami

  Transversospinalis: Multifidus & Rotatores – Blood Supply

• Supplied by multiple arteries localized to region along the vertebral column:

  • Cervical region: vertebral, deep cervical, and occipital arteries

  • Thoracic region: dorsal branches of posterior intercostal and subcostal arteries

  • Lumbar region: Dorsal branch of lumbar a., lateral iliac a.

  Suboccipital Muscles – M. Attachments

• Rectus Capitus Posterior Major

  • Origin: Spinous process C2

  • Insertion: occipital bone

• Rectus Capitus Posterior Minor

  • Origin: Posterior tubercle C1

  • Insertion: occipital bone

• Obliquus Capitus Superior

  • Origin: TP C1

  • Insertion: occipital bone

• Obliquus Capitus Inferior

  • Origin: Spinous process C2

  • Insertion: TP C1

  Suboccipital Muscles – Joint Movements

• Postural support of the head and neck, allow extension and rotation movements of the neck.

  Suboccipital Muscles - Innervation

• Suboccipital nerve, which is formed by the dorsal ramus of C1

  Suboccipital Muscles - Blood Supply

• Branches from vertebral a.

  Suboccipital Triangle

• Three of the four muscles form the suboccipital triangle, a common anatomic landmark that localizes the vertebral artery and suboccipital nerve

• This landmark is particularly important to surgeons operating in the posterior cervical region to avoid life-threatening bleeding.

  SUBOCCIPITAL TRIANGLE

• Boundaries:

  • Superior oblique, inferior oblique & rectus capitis posterior major

• Floor:

  • Posterior atlanto-occipital membrane, posterior arch of atlas

• Contains:

  • Vertebral artery & suboccipital nerve

• In roof:

  • Greater occipital nerve & occipital artery

  SUBOCCIPITAL NERVE

• Posterior ramus of C1

• No skin distribution

• Rectus capitis posterior major/minor

• Superior/inferior obliques

• Semispinalis capitis

  GREATER OCCIPITAL NERVE

• Posterior ramus of C2

• Semispinalis capitis

• Splenius capitis

• Inferior oblique via connection to C1

• Skin of posterior scalp

  Lumbar Triangle

• May be a site of lumbar hernia

• Borders:

  • Posteriorly: Latissimus dorsi

  • Anteriorly: External oblique of abdomen

  • Inferiorly: iliac crest

• Floor is internal oblique of abdomen