Anatomy: Planes and Location Terms

Anatomy

• Anatomy studies structures seen grossly and microscopically
• Histology (microscopic anatomy) studies cells/tissues using a microscope
• Anatomy helps understand patient diseases

Anatomical Planes

• Coronal (vertical) divides the body into anterior/posterior
• Sagittal (vertical) divides the body into right/left
• Median sagittal plane divides the body into equal right/left halves
• Transverse/horizontal/axial divides the body into superior/inferior

Location Terms

• Anterior (ventral) refers to the front, posterior (dorsal) refers to the back
• Medial: towards the median sagittal plane, lateral: away from the median sagittal plane
• Superior refers to structures closer to the head, inferior refers to structures closer to the feet
  • The head is superior to the shoulders; the knee joint is inferior to the hip joint
• Proximal refers to being closer to a structure's origin, distal refers to being farther
  • The hand is distal to the elbow joint; the glenohumeral joint is proximal to the elbow joint
• Superficial refers to structures closer to the body's surface, deep refers to structures further from the surface
  • The sternum is superficial to the heart, and the stomach is deep to the abdominal wall

Skeletal System

• Divided into axial/appendicular skeletons
• The axial skeleton includes the skull, vertebral column, ribs, and sternum.
• The appendicular skeleton includes upper/lower limb bones
• Consists of cartilage and bone

Cartilage

• Supports soft tissues
• Provides smooth, gliding surfaces for bone articulations
• Enables bone development and growth
• Hyaline cartilage is the most common, i.e. on articular surfaces of bones
• Elastic cartilage is found, i.e. in the external ear
• Fibrocartilage is located, i.e. in the intervertebral discs
• Cartilage lacks blood vessels, lymphatics, or nerves, and is nourished by diffusion

Bones

• Support structures
• Protect vital organs
• Act as calcium/phosphorus reservoirs
• Act as levers for muscles during movement
• Contain blood-producing cells
• Compact bone is dense, forming the outer shell around spongy bone
• Spongy (trabecular/cancellous) bone contains spicules enclosing cavities with marrow (blood-forming cells)
• Long bones are tubular, i.e. humerus/femur
• Short bones are cuboidal, i.e. in wrist/ankle
• Flat bones have two compact bone plates separated by spongy bone, i.e. skull
• Irregular bones have various shapes, i.e. facial bones
• Sesamoid bones are round/oval, developing in tendons, i.e. patella
• Bones are vascular and innervated

Bone Joints

• Skeletal elements meet at joints
• Synovial joints have skeletal elements separated by a cavity
• Solid joints lack a cavity, and skeletal elements are held by connective tissue

Synovial Joints

• Characterized by a cavity, articular cartilage, and a joint capsule
• Hyaline cartilage covers articulating surfaces of skeletal elements
• A joint capsule consist of inner synovial membrane and outer fibrous membrane
• Synovial joint descriptions based on shape and movements
• Articular surface shape produces plane (flat), hinge, pivot, bicondylar, condylar, saddle, and ball and socket
• Movement produces uniaxial, biaxial, and multi-axial types
• Hinge joints uniaxial, ball/socket joints multi-axial
• Plane joints allow sliding/gliding (e.g., acromioclavicular joint)
• Hinge joints allow transverse axis movement, permitting flexion/extension, i.e. elbow [humeroulnar]
• Pivot joints allow longitudinal movement, permitting rotation, i.e. atlanto-axial joint
• Bicondylar joints mostly move around one axis, with limited rotation around a second, i.e. knee joint
• Condylar (ellipsoid) joints allow movement around two axes that are at right angles, i.e, wrist joint
• Saddle joints allow movement around two axes at right angles due to a saddle shape
  • Permits flexion, extension, abduction, adduction, circumduction, i.e. carpometacarpal joint of the thumb
• Ball/socket joints allow movement around multiple axes
  • Permits flexion, extension, abduction, adduction, circumduction, rotation, i.e. hip joint

Solid Joints

• Skeletal elements are connected by fibrous connective tissue or cartilage (fibrocartilage)
• Movements are more restricted than in synovial joints
• Solid joints are divided into fibrous and cartilaginous
• Fibrous joints include sutures, gomphoses, and syndesmoses
  • Sutures only in the skull, linked by a sutural ligament
  • Gomphoses exist between teeth/bone, connected by periodontal ligament
  • Syndesmoses link adjacent bones by ligaments, i.e. interosseous membrane in the forearm
• Cartilaginous joints include synchondroses/symphyses
  • Synchondroses where ossification centers in developing bone are separated by cartilage (growth plate in long bones)
  • Symphyses exist where separate bones are interconnected by cartilage, i.e. pubic symphysis, intervertebral discs.

Skin

• The largest organ in the body
• Consists of the epidermis and dermis
• The epidermis is the outer avascular layer (stratified squamous epithelium) that varies in thickness
• The dermis is a dense bed of vascular connective tissue

Fascia

• Connective tissue with varying fat amounts
• Supports and interconnects organs/structures
• Enables movement of one structure relative to another
• Allows vessel/nerve transit
• Two general categories: superficial and deep
• Superficial (subcutaneous) fascia lies deep to the dermis
• Superficial fascia is loose connective tissue containing fat
• Superficial fascia allows movement of the skin over body areas
• Superficial fascia acts as a conduit for vessels/nerves coursing to/from the skin
• Deep fascia is dense, organized connective tissue
• The outer layer of deep fascia is attached to the deep surface of the superficial fascia
• Deep fascia forms intermuscular septa that compartmentalize muscles of similar function/innervation

Muscular System

• Skeletal muscle forms most of the muscle tissue
• Skeletal muscle has parallel bundles of long, multinucleated fibers
• It's innervated by somatic/branchial motor nerves
• Moves bones/structures, providing support/form
• Cardiac muscle is striated, only in the heart walls (myocardium)
• Cardiac muscle has branching network of cells linked electrically/mechanically
• Its contractions are less powerful than skeletal muscle, but resistant to fatigue
• Cardiac muscle is innervated by visceral motor nerves
• Smooth muscle lacks stripes, consisting of elongated/spindle-shaped fibers
• Smooth muscle can produce slow, sustained contractions
• It's found in blood vessel walls (gastrointestinal/respiratory/genitourinary/urogenital)
• Smooth muscle is innervated by visceral motor nerves

Back

• It is the posterior aspect of the body
• Provides musculoskeletal axis for trunk support
• Bony elements consist mainly of vertebrae
• Proximal ribs, superior pelvic bone aspects, posterior skull contribute to skeletal framework
• Associated muscles interconnect vertebrae/ribs with each other/the pelvis/skull
• Contains the spinal cord and proximal spinal nerve parts which send/receive information

Back Functions

• Skeletal/muscular elements support weight and transmit forces to the lower limbs
• Provides Movement via extrinsic/intrinsic muscles
  • Extrinsic muscles move upper limbs/ribs
  • Intrinsic muscles maintain posture/move the vertebral column; flexion, extension, lateral flexion, rotation
• Protects the nervous system; vertebral column/soft tissues contain the spinal cord and proximal spinal nerve parts

Back Musculature

• Back muscles are organized into superficial, intermediate, and deep groups
• Superficial/intermediate groups are extrinsic muscles from locations other than the back
  • Extrinsic muscles innervated by anterior rami of spinal nerves
• Superficial group muscles are related to/involved in upper limb movements
• Intermediate group muscles are attached to ribs, acting in respiratory function
• Deep group are intrinsic muscles which develop in the back
  • Intrinsic muscles are innervated by posterior rami of spinal nerves, and directly related to vertebral column/head movements
• Superficial muscles are immediately deep to the skin/superficial fascia
  • Connect upper appendicular skeleton (clavicle, scapula, humerus) to axial skeleton (skull, ribs, vertebral column)
  • Include trapezius, latissimus dorsi, rhomboid major/minor, and levator scapulae
  • Rhomboid major/minor and levator scapulae are deep to trapezius in the upper back

Trapezius Muscle

• Flat and triangular
• Base of triangle is along vertebral column (origin)
• Apex points toward the shoulder tip (insertion)
• Trapezius Origin:
  • Medial third of the superior nuchal line
  • External occipital protuberance
  • Ligamentum nuchae
  • The spinous processes/supraspinous ligaments from C7 to T12
• Superior fiber action goes downward
  • Inserts into the lateral third of the clavicle
  • Elevates scapula
• Inferior fiber action goes upward
  • Inserts into medial end of the scapular spine
  • Depresses scapula
• Middle fiber action goes horizontally
  • Inserts into acromial process and superior lip of the scapular spine crest
  • Retracts the scapula
• Superior/inferior fibers together rotate the scapula's lateral aspect upward when raising the upper limb overhead
• Motor innervation is the accessory nerve [XI]
• Blood supply is the superficial branch of the transverse cervical artery

Latissimus Dorsi

• Large, flat, triangular
• Origin:
  • T7-L5, sacrum, iliac crest, ribs 10-12
• Inserts into the floor of the intertubercular groove of the humerus
• Action:
  • Extends, adducts, medially rotates the upper limb
  • Depresses shoulder
• Nerve supply: thoracodorsal nerve of the brachial plexus

Levator Scapulae

• Slender
• Origin: transverse C1-C4 vertebral processes
• Inserts into the upper portion of the scapula's medial border
• Action: elevates the scapula, assists in rotating the scapula inferiorly
• Nerve supply: Spinal nerves C3/C4 and dorsal scapular nerve

Rhomboids

• Rhomboid minor is superior to rhomboid major
• Rhomboid minor is a small, cylindrical muscle
  • Originates from ligamentum nuchae and spinous processes of CVII/TI
  • Attaches to the medial scapular border opposite the scapular spine root
• Rhomboid major: from the spinous processes of TII and TV
  • Attaches to media scapular border inferior to rhomboid minor (between scapular spine and inferior angle)
• Rhomboid action; retracts/pulls the scapula toward the vertebral column
  • Rotates the scapula's lateral aspect inferiorly

Intermediate Group of Back Muscles

• Serratus posterior superior/inferior
• Consists of thin muscular sheets in the superior/inferior back regions
• Located deep to the superficial group, fibers attach ribs after passing obliquely outward
• Helps in respiration
• Serratus posterior superior lies deep to the rhomboid muscles
  • Originates from lower ligamentum nuchae, spinous processes of CVII to TIII and supraspinous ligaments
  • Inserts on the upper rib borders II to V, just lateral to angles
  • Elevates ribs II to V
  • Anterior rami of T2 to T5 thoracic nerves innervate
• Serratus posterior inferior lies deep to latissimus dorsi muscle
  • Originates from spinous processes of TXI to LIII and supraspinous ligaments
  • Inserts on the lower rib borders IX to XII, just lateral to angles
  • Depresses ribs IX to XII
  • Anterior rami of T9 to T12 lower thoracic nerves innervate

Deep Group of Back Muscles

• Intrinsic muscles extend from the pelvis to the skull
• Innervated by posterior rami of spinal nerves
• Inclues extensors/rotators:
  • Head/neck- splenius capitis/cervicis (capitis/cervicis spinotransversales muscles)
  • Vertebral column- erector spinae and transversospinales
  • Short segmental muscles- interspinales and intertransversarii

Clinical Anatomy

• Nerve injuries affecting superficial back muscles
• Paralysis of Trapezius caused by injury to the accessory nerve [XI]
  • Patient has shoulder drooping and inability to raise arm/shrug shoulder
• Paralysis of Latissimus dorsi is a result from injury to the thoracodorsal nerve
  • Patients have diminished ability to do pull-up exercises
• Paralysis of Rhomboid, results from an injury to the dorsal scapular nerve
  • Patients will experience displacement of the scapula laterally, on the affected side

Spinal Cord

• Extends from foramen magnum disk between LI and LII vertebrae
• In neonates, the spinal cord extends to vertebra LIII, but can reach as low as vertebra LIV
• Distal end is cone shaped (conus medullaris)
• Fine connective tissue filament (filum terminale) continues inferiorly from the conus medullaris

Spinal Nerves

• Each spinal nerve connects to the spinal cord by posterior/anterior roots
• The dorsal root contains sensory neuron processes to the CNS
• The ventral root contains motor nerve fibers from the CNS
• Medially, posterior/anterior roots divide into rootlets that attach to the spinal cord
• Spinal Segment – Area of the spinal cord that gives rise to the posterior and anterior rootlets, that will form a single pair of spinal nerves
• As each spinal nerve emerges from an intervertebral foramen, it divides into two major branches:
  • Small posterior ramus
  • Larger anterior ramus
• Posterior rami supply intrinsic back muscles/skin
• Anterior rami supply skeletal muscles including trunk and limbs, except certain head regions
• All major somatic plexuses (cervical, brachial, lumbar, sacral) are formed by anterior rami

Spinal Nerve Nomenclature

• There are roughly 31 pairs
• Named by position relative to vertebrae
  • 8 cervical nerves (C1-C8)
  • 12 thoracic nerves (T1-T12)
  • 5 lumbar nerves (L1-L5)
  • 5 sacral nerves (S1-S5)
  • 1 coccygeal nerve (Co)
• C1 emerges between the skull/CI
• C2 to C7 emerge above respective vertebrae
• C8 emerges between CVII/TI
• Remaining spinal nerves, starting with T1, emerge below respective vertebrae