Gross Anatomy 1 (back muscles, week 1, 2, and 3)

Thoracolumbar fascia

-fascia that encloses deep back muscles in thoracic and lumbar regions -it is thin in thoracic region, but strong and thick in lumbar region -in lumbar region it is divided into 3 layers: • posterior layer: attaches to spinous processes • intermediate (middle) layer: attaches to transverse processes • anterior layer: forms quadratus lumborum fascia and attaches to transverse processes (quadratus lumborum is a muscle of posterior abdominal wall) • deep back muscles are located between posterior and intermediate layers of thoracolumbar fascia

trapezius is innervated by?

Accessory nerve (CN XI), C4 and C4 (pain and proprioception)

Intermediate Back Muscles

two muscles: serratus posterior superior and serratus posterior inferior

suboccipital triangle:

vertebral artery suboccipital nerve greater occipital nerve roof: semispinalis capitus Floor: posterior wall of atlas Muscles: rectus capitus posterior major, obliqqus capitus superior, obliqqus capitus inferior

Axis (C2)

• atypical cervical vertebra • has a bony prominence that projects superiorly from vertebral body -> dens (odontoid process) -> articulates with facet on anterior arch of atlas at median atlanto-axial joint

Vertebra Prominens (C7)

• atypical cervical vertebra • long, non-bifid spinous process (used as landmark to count spinous process) • foramina transversaria are usually smaller than in other cervical vertebrae (usually do not transmit vertebral arteries, but a small accessory vertebral vein)

Suboccipital Triangle

boundaries: • medially: rectus capitis posterior major • laterally: obliquus capitis superior • inferiorly: obliquus capitis inferior covered by semispinalis capitis (roof) floor: posterior arch of atlas and posterior atlanto-occipital membrane contents: vertebral artery (3rd part) and suboccipital nerve (nerve emerges between vertebral artery and posterior arch of atlas)

triangle of auscultation:

bounded inferiorly by latissimus dorsi, medially by trapezius and laterally by medial border of scapula corresponds approximately with 6th intercostal space with no overlying muscles, it is particularly well suited for auscultation (listening to sounds produced by thoracic organs, especially the lungs)

lumbar triangle

bounded medially by latissimus dorsi, laterally by external oblique (abdominal wall muscle) and inferiorly by iliac crest floor: is formed by internal oblique (abdominal wall muscle) on rare occasions, it is the site of a lumbar hernia

Iliocostalis, longissimus, and spinalis are part of?

erector spinae

interspinales:

extend between adjacent spinous processes best developed in cervical and lumbar regions action: extension of spine and stabilization of adjacent vertebrae may also act as proprioceptive organs

intertransversarii:

extend between adjacent transverse processes best developed in cervical and lumbar regions action: lateral flexion of spine and stabilization of adjacent vertebrae -> have 6 times more muscle spindles than other deep back muscles (may function as proprioceptive organs providing sensory information to CNS circuits involved in posture and performance of smooth and accurate movements)

What is the action of Latissimus dorsi

extend, adduct, medially rotate the shoulder

Deep Back Muscles

innervated by dorsal rami of spinal nerves divided into 3 layers: • superficial layer: ---only present in cervical and upper thoracic regions -> consists of spinotransversales muscles (splenius capitis and splenius cervicis) -> fibers run superiorly and laterally • intermediate layer: --- extends whole length of spine -> formed by erector spinae muscle -> fibers are more or less vertically oriented • deep layer: ---extends whole length of spine -> formed by transversospinalis muscle -> fibers run superiorly and medially

Erector Spinae

large muscular mass with an extensive inferior tendinous origin from posterior part of iliac crest, posterior surface of sacrum and spinous processes of lower 2 thoracic and all lumbar vertebrae becomes muscular in lumbar region and divides into 3 columns: • lateral column: iliocostalis • intermediate column: longissimus (largest component) • medial column: spinalis (smallest component) each column has regional subdivisions based on their location and/or superior attachment of muscle fibers: • iliocostalis: lumborum, thoracis and cervicis • longissimus: thoracis, cervicis and capitis

General Features of a Typical Vertebra

vertebral body -> shaped like a short cylinder -> located anteriorly vertebral arch -> bony arch that forms posterior part of vertebra vertebral body and arch enclose an opening -> vertebral foramen in articulated spine, superposition of vertebral foramina creates vertebral canal -> main contents: spinal cord and its surrounding membranes (meninges) and roots of spinal nerves

Transversospinalis

muscle fibers run superiorly and medially from transverse processes to spinous processes depending on length of muscle fibers, it is divided into 3 components (longest muscle fibers are more superficial within transversospinalis, shorter muscle fibers are deeper): • semispinalis: muscle fibers span 6 vertebrae between origin and insertion • multifidus: muscle fibers span 3 to 5 vertebrae between origin and insertion • rotatores: muscle fibers span 1 or 2 vertebrae between origin and insertion Nerve supply: dorsal rami of spinal nerves Arterial Supply: Dorsal branch of Post. Intercostal a. Action: • bilateral contraction -> extension of spine • unilateral contraction: --- lateral flexion of spine to same side of contracting muscle --- rotation of spine to opposite side of contracting muscle • shorter muscles main function is to stabilize vertebral column

Muscles of the back: superficial group?

muscles inserted into bones of upper libs (clavicle, scapula, proximal humerus) Includes: trapezius, latissimus dorsi, levator scapulae, rhomboid minor and major

muscles of the back: deep group

muscles involved with movements of vertebral column and head (proper/intrinsic muscles of back)

Muscles of the back: intermediate group

muscles that insert into ribs (accessory muscles of respiration)

Multifidus

present along whole length of spine in sacral and lumbar regions lies deep to erector spinae (because there is no semispinalis in these areas) in thoracic and cervical regions lies deep to semispinalis fibers insert into spinous processes of all vertebrae from L5 to axis best developed in lumbar region

Semispinalis

present from lower thoracic spine (T10) to skull, but absent in lumbar region has thoracis, cervicis and capitis subdivisions semispinalis capitis • largest muscle mass on back of neck • originates from transverse processes of C7 to T6 or T7 vertebrae and articular processes of C4 to C6 vertebrae • muscle fibers ascend vertically, deep to splenius, and insert into occipital bone, in medial part of area between superior and inferior nuchal lines • usually traversed by a tendinous intersection

Joints Between Vertebral Arches

zygapophysial (facet) joints -> synovial joints between articular processes of adjacent vertebrae • bony articular facets are covered with hyaline cartilage • surrounded by an articular capsule • orientation of articular facets determines type of motion possible between vertebrae • innervated by medial branches of dorsal rami of spinal nerves

Name the Muscles that form the suboccipital triangle

rectus capitus posterior major obliqqus capitus superior obliqqus capitus inferior

Where does the multifidi originate

sacrum and transverse processes of the lumbar through cervical spine

Spinal nerve is a ________ nerve, and contains ___________ and __________ fibers

spinal nerve is a mixed nerve and contains motor and sensory fibers

what are the contents of the suboccipital triangle

suboccipital nerve vertebral artery

muscles of the back: 3 groups

superficial group intermediate group deep group

Ligaments Connecting Axis and Occipital Bone

tectorial membrane: • upward continuation of posterior longitudinal ligament (on anterior wall of vertebral canal) • extends from posterior surface of body of axis to occipital bone (above foramen magnum) • lies posterior to dens, apical ligament, alar ligaments and cruciform ligament

Greater Occipital Nerve

dorsal ramus of C2 spinal nerve curves around inferior border of obliquus capitis inferior -> ascends over suboccipital triangle -> pierces semispinalis capitis and trapezius to reach scalp (does not pierce splenius capitis) it divides into branches that supply skin of posterior part of scalp (run with branches of occipital artery)

suboccipital muscles:

4 short muscles located between occipital bone and axis deepest muscles in upper part of posterior neck (lie deep to trapezius, splenius capitis and semispinalis capitis) components: • rectus capitis posterior major • rectus capitis posterior minor • obliquus capitis inferior • obliquus capitis superior all 4 muscles are supplied by suboccipital nerve (dorsal ramus of C1 spinal nerve)

how many spinal nerves? how many of each type?

8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal

spinalis: thoracis, cervicis and capitis

Nerve supply: dorsal rami of spinal nerves Arterial Supply: Post. br. of internal thoracic a. Action: • bilateral contraction -> extension of spine • unilateral contraction -> lateral flexion of spine to same side of contracting muscle • also contracts during flexion of spine (eccentric contraction) to control movement against gravity

serratus posterior superior origin and insertion?

Origin: SP C7-T3 and ligamentum nuchae Insertion: superior margin of the ribs 2-5

Rhomboid Minor

Origin: lower part of ligamentum nuchae and spinous processes of C7 and T1 vertebrae Insertion: medial border of scapula (at level of root of spine) Nerve supply (both muscles): dorsal scapular nerve (branch of brachial plexus) Arterial Supply: Transverse cervical a., Descending (dorsal) scapular a. Action (both muscles): • help stabilize scapula • retraction of scapula • inferior rotation of scapula

Splenius Capitis

Origin: lower part of ligamentum nuchae and spinous processes of C7 to T3 vertebrae Insertion: fibers run superolaterally and insert into lateral part of superior nuchal line and mastoid process Action (same as Splenius Cervicis) • bilateral contraction: extension of head and neck • unilateral contraction: lateral flexion and rotation of head and neck to same side of contracting muscle

Trapezius:

Origin: medial part of superior nuchal line, external occipital protuberance, ligamentum nuchae, spinous process from C7 to T12 vertebrae Insertion: lateral 1/3 of clavicle, acromion and spine of scapula nerve supply: accessory nerve (CN XI ) and vertral rami of C3 and C4 spinal nerves -> latter nerves probably provide sensory (proprioceptive) innervation Innervation: Spinal accessory Nerve (CN XI), Cervical Nerves (C3, C4) Arterial Supply: Transverse Cervical a., Descending scapular a., Post. intercostal a. Action: • helps stabilize scapula • upper fibers elevate scapula • middle fibers pull scapula toward posterior midline (retract) • lower fibers depress scapula • acting together, superior and inferior fibers rotate scapula superiorly (inferior angle moves laterally) -> important movement in order to perform full abduction of arm (bring hand above head)

Rectus Capitis Posterior Major (cadaver)

Origin: spinous process of axis (C2) Insertion: lateral part of inferior nuchal line Nerve supply: suboccipital nerve Arterial Supply: Vertebral a.; Occipital a. Action: extension of head, rotation of head to same side of contracting muscle

Obliquus Capitis Inferior

Origin: spinous process of axis (C2) Insertion: passes superiorly and laterally to insert into transverse process of atlas (C1) Nerve supply: suboccipital nerve Arterial Supply: Vertebral a.; Occipital a. Action: rotation of head to same side of contracting muscle

Rhomboid Major

Origin: spinous processes from T2 to T5 vertebrae Insertion: medial border of scapula (from root of spine to inferior angle) Nerve supply (both muscles): dorsal scapular nerve (branch of brachial plexus) Arterial Supply: Transverse cervical a., Descending (dorsal) scapular a. Action (both muscles): • help stabilize scapula • retraction of scapula • inferior rotation of scapula

Splenius Cervicis

Origin: spinous processes of T3 to T6 vertebrae Insertion: fibers run superolaterally and insert into transverse processes of upper 3 or 4 cervical vertebrae Nerve supply (both muscles): dorsal rami of cervical spinal nerves' Arterial Supply (both muscles): Dorsal branch of Post. intercostal a. Action (same as splenius capitis) • bilateral contraction: extension of head and neck • unilateral contraction: lateral flexion and rotation of head and neck to same side of contracting muscle

Latissimus Dorsi

Origin: spinous processes of lower 6 thoracic, lumbar and sacral vertebrae, posterior part of iliac crest, lower 3 or 4 ribs, and sometimes inferior angle of scapula (attachments to vertebrae and iliac crest are established via thoracolumbar fascia) Insertion: muscles fibers pass superiorly and laterally wrap around inferior border of teres major muscle tendon inserts into floor of intertubercular (bicipital) groove of humerus Nerve supply: thoracodorsal nerve (branch of brachial plexus) Arterial Supply: Thoracodorsal a., Descending scapular a., Trans. Cervical a. Action: extension, adduction and medial rotation of arm at shoulder joint

levatores costarum:

Origin: tips of transverse processes from C7 to T11 vertebrae Insertion: fibers run inferiorly and laterally and insert into rib immediately below (levator costarum brevis) or 2nd rib below (levator costarum longus) Nerve supply: dorsal rami of thoracic spinal nerves Action: elevation of ribs

Obliquus Capitis Superior

Origin: transverse process of atlas (C1) Insertion: lateral part of area between superior and inferior nuchal lines Nerve supply: suboccipital nerve Arterial Supply: Vertebral a.; Occipital a. Action: extension of head, lateral flexion of head to same side of contracting muscle

levator scapulae

Origin: transverse processes of upper 4 cervical vertebrae Insertion: medial border of scapula (from superior angle to root of spine) Nerve supply: ventral rami of C3 and C4 spinal nerves and dorsal scapular nerve (branch of brachial plexus) Arterial Supply: Trans. cervical a., Descending (dorsal) scapular a., Post. intercostal a. Action: • helps stabilize scapula • elevation of scapula • inferior rotation of scapula

Atlanto-axial Joints

ateral atlanto-axial joints: • synovial joints established between inferior articular facets on lateral masses of atlas and superior articular facets of axis median atlanto-axial joint: • pivot synovial joint established between dens of axis and an osteofibrous ring formed by anterior arch of atlas and transverse ligament of atlas • transverse ligament of atlas: attaches to the medial surfaces of the two lateral masses of C1 -> retains dens in position preventing impingement of spinal cord -> thought to be most important ligament of craniovertebral complex of joints • has 2 synovial cavities: anterior and posterior • anterior cavity lies between dens of axis and anterior arch of atlas • posterior cavity lies between dens of axis and transverse ligament of atlas • motion occurs at all 3 atlanto-axial joints simultaneously • main motion is axial rotation • also allow flexion/extension and a small amount of lateral flexion

Rotatores

deepest muscles located in groove between spinous and transverse processes best developed in thoracic region extend from a transverse process to the spinous process of vertebra located immediately above (rotator brevis) or to spinous process of 2nd vertebra above (rotator longus)

borders of the triangle of auscultation are:

latissimus dorsi rhomboid major trapezius

serratus posterior inferior:

lies deep to latissimus dorsi Origin: spinous processes from T11 to L2 or L3 vertebrae Insertion: fibers run superolaterally -> insert into lower 4 ribs Nerve supply: 9th, 10th, 11th intercostal nerves and subcostal nerve (ventral rami of T9 to T12 spinal nerves) Arterial Supply: Post. intercostal a. Action: depression of ribs

serratus posterior superior:

lies deep to rhomboid muscles Origin: lower part of ligamentum nuchae and spinous process of C7 to T2 or T3 vertebrae Insertion: fibers run inferolaterally -> insert into 2nd to 5th ribs Nerve supply: 2nd to 5th intercostal nerves (ventral rami of T2 to T5 spinal nerves) Action: elevation of ribs Arterial Supply: Post. intercostal a.

Rectus Capitis Posterior Minor

located medial and partly under rectus capitis posterior major Origin: posterior tubercle of atlas (C1) Insertion: medial part of inferior nuchal line Nerve supply: suboccipital nerve Arterial Supply: Vertebral a.; Occipital a. Action: extension of head

vertebral arch consists of:

• 2 pedicles -> form sides of vertebral arch -> fuse anteriorly with vertebral body • 2 laminae -> complete arch posteriorly, and meet each other in posterior midline • vertebral arch gives rise to 7 processes: • 1 spinous process -> projects posteriorly in midline from junction of 2 laminae • 2 transverse processes -> project laterally from junction of laminae and pedicles • spinous and transverse processes serve as levers and receive attachments of muscles and ligaments • 4 articular processes (2 superior and 2 inferior) -> project superiorly and inferiorly from junction of laminae and pedicles -> articulate with articular processes of vertebrae above and below • superior and inferior margins of pedicle are known as superior and inferior vertebral notches, respectively • superposition of vertebrae in articulated spine creates intervertebral foramina • intervertebral foramina transmit spinal nerves out of vertebral canal (spinal nerves can be compressed at intervertebral foramina causing peripheral motor and/or sensory problems) also transmit blood vessels in and out vertebral canal • boundaries of intervertebral foramen: • superior: pedicle of vertebra above • inferior: pedicle of vertebra below • anterior: intervertebral disc and small parts of bodies of both vertebrae • posterior: inferior articular process of vertebra above and superior articular process of vertebra below (together form a zygapophysial/facet joint)

cervical spinal nerves (except C8) are named according to vertebra located below nerve, as nerve exits vertebral canal → examples:

• C1 spinal nerve exits vertebral canal between occipital bone and atlas • C5 spinal nerve exits vertebral canal between C4 and C5 vertebrae C8 spinal nerve exits vertebral canal between C7 and T1 vertebrae

from T1 down, spinal nerves are named according to vertebra located above nerve, as nerve exits vertebral canal → examples:

• T6 spinal nerve exits vertebral canal between T6 and T7 vertebrae

Intervertebral Discs

• account for 20-25% of length of vertebral column • thinnest in upper thoracic region and thickest in lumbar region • parts: --- peripheral part -> anulus fibrosus --- central part -> nucleus pulposus • allow movement between adjacent vertebrae and serve as shock absorbers when load on vertebral column is increased

nervous system: (two classifications)

• anatomical classification: • central nervous system (CNS): brain and spinal cord • peripheral nervous system (PNS): spinal nerves, cranial nerves and associated ganglia • ganglion (pl. ganglia): collection of neuronal cell bodies (neurons) in PNS • functional classification: • somatic nervous system: controls skeletal muscle • autonomic nervous system: controls smooth muscle, cardiac muscle and glands

Ligaments Connecting Axis and Occipital Bone

• apical ligament of dens: extends from tip of dens to anterior margin of foramen magnum • alar ligament (one on each side): extends from side of dens to medial surface of occipital condyle (primarily involved in limiting contralateral rotation of head) cruciform ligament: transverse ligament of atlas + superior and inferior longitudinal bands • superior longitudinal band: extends from superior margin of transverse ligament to occipital bone • inferior longitudinal band: extends from inferior margin of transverse ligament to posterior surface of body of axis • longitudinal bands are mostly involved in holding transverse ligament in position

Dermatome

• area of skin innervated by sensory fibers of a single spinal nerve • sensory fibers from a single spinal nerve usually reach skin in more than one cutaneous nerve • cutaneous nerves usually contain sensory fibers from more than one spinal nerve

Atlas (C1)

• atypical cervical vertebra with no body and no spinous process • consists of anterior and posterior arches and 2 lateral masses • anterior arch is shorter -> has a tubercle in midline of its anterior surface (anterior tubercle) and an articular facet for dens (of C2) in midline of its posterior surface (takes part in median atlanto-axial joint) • posterior arch is longer -> has a tubercle in midline of its posterior surface (posterior tubercle) and a groove for vertebral artery immediately posterior to each lateral mass • each lateral mass has 2 articular facets -> superior articular facet articulates with occipital condyle (takes part in atlanto-occipital joint) -> inferior articular facet articulates with superior articular facet of C2 (takes part in lateral atlanto-axial joint)

Anulus Fibrosus

• composed of fibrocartilage with collagen fibers arranged in 10 to 20 concentric layers or sheets (lamellae) • in each lamella, bundles of collagen fibers have same orientation (65º with respect to vertical) • in consecutive lamellae, collagen fibers are oriented perpendicular to each other

Costal Elements

• costal elements develop in all regions of vertebral column, but only in thoracic region they give rise to separate bones (ribs) • in all other regions of vertebral column, costal elements are smaller and fuse with corresponding vertebrae • in cervical region, costal elements form anterior parts of transverse processes, which end in anterior tubercles • in lumbar region, costal elements form what we call "transverse processes" -> that's why transverse processes of lumbar vertebrae are sometimes referred to as "costal processes" -> true transverse processes of lumbar vertebrae are represented by mammillary and accessory processes • in sacrum, costal elements form anterior portions of lateral parts of sacrum

arachnoid:

• delicate membrane applied to internal surface of dura mater → continuous superiorly with arachnoid around brain → inferiorly extends to lower end of dural sac (S2) • subdural space → potential space between dura mater and arachnoid (normally they are in contact with each other) • subarachnoid space → wide, real space between arachnoid and pia mater → filled with cerebrospinal fluid (CSF) → continuous superiorly with subarachnoid space around brain → inferiorly it terminates at level of S2 • subarachnoid space inferior to conus medullaris is known as lumbar cistern → contains CSF, ventral and dorsal roots of cauda equina and filum terminale internum (no spinal cord) • lumbar puncture (spinal tap) → introduction of needle into lumbar cistern through L3/L4 or L4/L5 interspaces in order to collect a CSF sample or administer a drug • arachnoid also lines inside of dural sleeves around roots of spinal nerves → creates small lateral extensions of subarachnoid space

adult → L1/L2 intervertebral disc

• different growth rate of spinal cord and vertebral column causes spinal nerve roots (mainly lumbar and sacral) to elongate considerably → distance between their origin from spinal cord and corresponding intervertebral foramen increases • nerve roots inferior to conus medullaris hang like a horse's tail from lower part of spinal cord → cauda equina (filum terminale is found in center of cauda equina) • because of difference in length between spinal cord and vertebral column, spinal cord segments do not correspond with vertebral levels

as the spinal nerves exit vertebral canal, they divide into 3 branches, what are they

• dorsal (posterior) ramus → supplies skin of back and deep back muscles → it usually divides into medial and lateral branches • ventral (anterior) ramus → usually largest of 3 branches → supplies skin and muscles of limbs, skin and muscles of anterolateral trunk, skin and muscles of anterolateral neck and superficial and intermediate back muscles • recurrent meningeal (sinuvertebral) branch → goes back into vertebral canal → supplies meninges, blood vessels, ligaments, periosteum and intervertebral discs

Craniovertebral Joints

• established between occipital bone, atlas and axis • specially adapted for head movements • there are no intervertebral discs between occipital bone and atlas or atlas and axis • includes: --- 2 atlanto-occipital joints --- 3 atlanto-axial joints (1 median and 2 lateral)

Uncovertebral Joints (of Luschka)

• established between uncinate processes of a cervical vertebra and edges of lower surface of vertebral body immediately above • appear after 10 years of age • located at lateral margins of intervertebral discs • considered to be synovial joints by some authors, others consider them to result from degeneration of intervertebral discs • common site of osteophyte (spur) formation that may cause neck pain

Posterior Longitudinal Ligament

• extends along posterior aspects of vertebral bodies and intervertebral discs (anterior wall of vertebral canal) from C2 to sacrum • limits flexion of vertebral column • in lower thoracic and lumbar regions, posterior longitudinal ligament is denticulated -> it is narrower over vertebral bodies and wider over intervertebral discs

Sacrum

• formed by fusion of 5 sacral vertebrae • forms most of posterior wall of pelvic cavity • wedge-shaped -> upper end is wider (base) -> lower end is narrower (apex) -> base articulates with L5, and apex articulates with coccyx • anterior border of base projects forward in midline -> promontory • ala of sacrum -> lateral part of base (one on each side of S1 body) • anterior (pelvic) surface is concave and has 4 pairs of anterior sacral foramina (transmit ventral rami of S1-S4 spinal nerves) • posterior (dorsal) surface is rough and convex -> has 4 pairs of posterior sacral foramina (transmit dorsal rami of S1-S4 spinal nerves) posterior surface has 5 ridges: • 1 median sacral crest -> represents tips of spinous processes • 2 intermediate sacral crests -> represent articular processes • 2 lateral sacral crests -> represent tips of transverse processes posterior sacral foramina are located between intermediate and lateral sacral crests on each side • lateral surface of sacrum has an articular facet for hip bone (1 on each side) -> auricular surface -> takes part in sacroiliac joint • sacral tuberosity -> irregular area posterior to auricular surface (gives attachment to interosseous sacroiliac ligament) • sacrum encloses sacral canal, which ends inferiorly in sacral hiatus -> sacral cornua (horns): 2 bony prominences located one on each side of sacral hiatus

Plexuses

• plexuses give rise to multi-segmental nerves → most nerves that originate from plexuses contain fibers from ventral rami of more than one spinal nerve • conversely, ventral rami of spinal nerves participating in plexuses contribute fibers to multiple nerves

Nucleus Pulposus

• gelatinous material containing large amount of water (70-90%), small number of collagen fibers with no uniform orientation and a few cells (notochordal cells early in life, fibroblasts, chondrocytes) -> water content decreases with age • remnant of notochord of embryo -> located slightly closer to posterior margin than to anterior margin of disc • semi-fluid nature of nucleus pulposus allows it to change its shape • a sudden increase in compression load of vertebral column causes nucleus pulposus to become flattened -> outward pressure of nucleus pulposus is accommodated by anulus fibrosus • sometimes outward pressure of nucleus pulposus is too great -> anulus fibrosus ruptures -> nucleus pulposus herniates (most commonly posterolaterally into vertebral canal or intervertebral foramen)

Ligamentum Nuchae (Nuchal Ligament)

• homologous to supraspinous ligament in cervical region • midsagittal membrane that separates right and left muscles of posterior neck and provides attachment for them • its posterior border is free and superficial -> extends from external occipital protuberance to tip of spinous process of C7 • its superior border attaches to external occipital crest (midline bony ridge extending from external occipital protuberance to posterior margin of foramen magnum) • its anterior border attaches to posterior tubercle of atlas and spinous processes of remaining cervical vertebrae • it helps to support weight of head when inclined forward (writing, reading)

spinal cord development

• in embryo (up to 8th week of development), spinal cord extends entire length of vertebral canal → spinal cord segments are aligned with corresponding vertebrae → there is a short distance between origin of a spinal nerve from spinal cord and its corresponding intervertebral foramen • thereafter, vertebral column grows faster than spinal cord → inferior end of spinal cord comes to lie at progressively higher levels: • 6th month of pregnancy → level of S1 • newborn → level of L3

Lumbar Vertebrae

• large vertebral body with a kidney-shaped outline • large and triangular vertebral foramen • large, rectangular spinous process that projects straight posteriorly • no foramen transversarium or costal facets • mammillary process -> small bony prominence located on posterior aspect of superior articular process • accessory process -> small bony prominence located on posterior aspect of transverse process, near its origin from vertebral arch • articular facets are almost sagittally oriented • superior articular facets are concave and face medially and slightly posteriorly • inferior articular facets are convex and face laterally and slightly anteriorly • orientation of articular facets facilitates flexion/extension, allows some lateral flexion, but limits axial rotation • superior articular facets are located on each side of base of dens -> articulate with inferior articular facets of atlas at lateral atlanto-axial joints

ligaments

• ligamentum flavum: connects laminae of adjacent vertebrae -> composed almost entirely of elastic tissue (yellowish color when fresh) -> limits separation of laminae during flexion and helps to restore erect posture • interspinous ligament: fills space between two adjacent spinous processes -> limits flexion • supraspinous ligament: fibrous cord running along midline of back connecting tips of spinous processes from C7 to sacrum limits flexion • some authors describe intertransverse ligaments connecting adjacent transverse processes (functionally not very important)

Pia Mater

• membrane that adheres intimately to surface of spinal cord and roots of spinal nerves as far as intervertebral foramina • continues beyond conus medullaris as a thin thread → filum terminale • denticulate ligament → extension of pia mater in coronal plane that helps stabilize spinal cord within dural sac → attaches medially to side of spinal cord, between ventral and dorsal roots of spinal nerves → extends across subarachnoid space → attaches laterally to dura mater via 20-21 "tooth-like" projections (denticulations) that penetrate arachnoid

Joints of the Vertebral Column

• movement between 2 adjacent vertebrae is limited, but summation of movements among all vertebrae results in a large range of motion for the whole vertebral column • movements of vertebral column include flexion, extension, lateral flexion, rotation (axial rotation) and circumduction

cells of the nervous tissue

• neurons: responsible for reception, integration and transmission of nerve impulses • supporting cells: • CNS: neuroglial (glial) cells → astrocytes, oligodendrocytes, microglia, ependyma • PNS: Schwann cells and satellite cells • parts of a neuron: • cell body (perikaryon/soma): central part of cell where nucleus and most organelles are located • dendrites: usually multiple and short cell processes → carry impulses toward cell body • axon: single cell process (usually long) → carries impulses away from cell body

Curvatures of the Vertebral Column

• on a side view, vertebral column has 4 curvatures • primary curvatures (kyphoses) -> develop during fetal period due to flexed fetal position -> convex posteriorly -> located in thoracic and sacral regions -> maintained throughout life as a result of differences in height between anterior and posterior parts of vertebrae • secondary curvatures (lordoses) -> begin to appear during fetal period, but do not become obvious until infancy -> concave posteriorly -> located in cervical and lumbar regions -> maintained primarily by differences in thickness between anterior and posterior parts of intervertebral discs • cervical curvature (lordosis) becomes fully evident when an infant begins to raise (extend) head while prone or to hold head erect while sitting • lumbar curvature (lordosis) becomes apparent when an infant begins to assume upright posture, standing and walking • excess thoracic kyphosis (clinically shortened to "kyphosis") -> abnormal exaggeration of primary curvature in thoracic region (humpback or hunchback) • excess lumbar lordosis (clinically shortened to "lordosis") -> abnormal exaggeration of secondary curvature in lumbar region (hollow back or sway back) • scoliosis -> abnormal curvature of vertebral column in coronal (frontal) plane (to right or left)

Spinal Cord (definition and parts)

• part of CNS located within vertebral canal • begins superiorly at foramen magnum, where it becomes continuous with medulla oblongata (part of brainstem) • ends inferiorly at L1/L2 intervertebral disc (adult) • roughly cylindrical in shape with no uniform diameter • cervical enlargement: extends approximately from C5 to T1 spinal cord segments (not vertebrae) → gives rise to brachial plexus (nerves that supply upper limb) • lumbosacral (lumbar) enlargement: extends approximately from L1 to S3 spinal cord segments (not vertebrae) → gives rise to lumbar and sacral plexuses (nerves that mostly supply lower limb) • inferiorly, spinal cord tapers off into conus medullaris • conus medullaris gives rise to a connective tissue filament derived from pia mater → filum terminale → attaches inferiorly to coccyx

Cervical Vertebrae

• small vertebral body (compared to thoracic and lumbar vertebrae) • uncinate processes -> elevated lateral margins of superior surface of vertebral body • large and triangular vertebral foramen • foramen transversarium -> opening in transverse process that transmits vertebral artery and accompanying veins and nerve plexus • transverse processes end in anterior and posterior tubercles • spinous process is short and usually bifid • superior articular facets face superiorly and posteriorly -> inferior articular facets face inferiorly and anteriorly • orientation of articular facets allows for flexion/extension, lateral flexion and axial rotation (cervical region is more mobile than thoracic and lumbar regions)

Coccyx

• small, wedge-shaped bone formed by fusion of usually 4 rudimentary coccygeal vertebrae • forms, with sacrum, posterior wall of pelvic cavity • base -> upper end that articulates with apex of sacrum • apex-> lower end • 1st coccygeal vertebra has rudimentary transverse and superior articular processes (latter ones are known as coccygeal cornua/horns)

Meninges of the spinal cord:

• spinal cord is surrounded by 3 connective tissue membranes: dura mater, arachnoid and pia mater dura mater: • dense, strong, fibrous sheet that forms a loose sac around spinal cord and cauda equina • continuous above (at foramen magnum) with dura mater of brain • inferiorly, dural sac terminates blindly at lower border of S2 • filum terminale internum: upper part of filum terminale (within dural sac) • filum terminale externum (coccygeal ligament): lower part of filum terminale (from end of dural sac [S2] to coccyx) • dura mater is separated from walls of vertebral canal by epidural (extradural) space → contains loose connective tissue with fat and internal vertebral venous plexus (space where anesthetic agent is injected for epidural anesthesia/block) • dura mater forms a sleeve around roots of each spinal nerve → at intervertebral foramen dura mater becomes continuous with epineurium of spinal nerve (connective tissue that surrounds a nerve)

Identification of Specific Vertebral Spinous Processes

• spinous process of C7 is usually visible as prominent eminence in midline at base of neck (spinous process of T1 is often more prominent than spinous process of C7) • root of spine of scapula is at level of spinous process of T3 • inferior angle of scapula is at level of spinous process of T7 • horizontal line connecting highest points of right and left iliac crests crosses spinous process of L4 • sacral dimples (mark location of posterior superior iliac spines) are at level of spinous process of S2

Overview of the Vertebral Column

• strong and flexible bony column that extends from base of skull, superiorly, to pelvis, inferiorly • it is composed of approximately 33 bones (vertebrae) • it is divided into 5 regions -> in upper 3 regions there is movement between adjacent vertebrae -> in lower 2 regions there is no movement between adjacent vertebrae: --- cervical -> consists of 7 vertebrae (C1-C7) --- thoracic -> consists of 12 vertebrae (T1-T12) --- lumbar -> consists of 5 vertebrae (L1-L5) --- sacral -> consists of 5 vertebrae (S1-S5), which fuse with each other to form a single bone (sacrum) --- coccygeal -> usually consists of 4 rudimentary vertebrae (Co1-Co4), which fuse with each other to form a single bone (coccyx)

Anterior Longitudinal Ligament

• strong ligament extending along anterior aspects of vertebral bodies and intervertebral discs from occipital bone to upper sacrum • limits extension of vertebral column

Atlanto-occipital Joints

• synovial joints established between occipital condyles (convex) and superior articular facets on lateral masses of atlas (concave) • each joint has its own articular capsule, but right and left joints work in unison (bicondylar synovial joints) • allow mostly flexion/extension with small amounts of lateral flexion and axial rotation • occipital bone and atlas are also connected by anterior and posterior atlanto-occipital membranes -> extend from anterior and posterior arches of atlas to anterior and posterior margins of foramen magnum, respectively (posterior atlanto-occipital membrane arches over vertebral artery)

Joints Between Vertebral Bodies

• upper and lower surfaces of vertebral bodies are covered by a layer of hyaline cartilage (vertebral or cartilaginous end-plate) -> sandwiched between vertebral end-plates of adjacent vertebrae are intervertebral discs (symphysis or secondary cartilaginous joint) • intervertebral discs provide strong attachments between vertebral bodies, uniting them into a continuous semi-rigid column -> also form part of anterior border of intervertebral foramina • intervertebral discs are reinforced by anterior and posterior longitudinal ligaments

L4 spinal nerve exits vertebral canal between L4 and L5 vertebrae formed by union of two roots:

• ventral (anterior) root: consists of nerve fibers (axons) carrying impulses away from CNS (motor or efferent fibers) → neuronal cell bodies giving rise to these fibers are located in spinal cord • dorsal (posterior) root: consists of nerve fibers (axons) carrying impulses toward CNS (sensory or afferent fibers) • dorsal root has a swelling (dorsal or posterior root ganglion) → contains cell bodies of sensory neurons → pseudounipolar (unipolar) neurons → cell body gives rise to a single process that shortly after divides into peripheral and central processes (branches)

Spinal nerves: 3 branches are mixed nerves (contain motor and sensory fibers)

• ventral rami of thoracic spinal nerves (except T1) have a segmental distribution (innervate skin and muscles in a band pattern) → do not share fibers with nerves located above or below them → constitute 2nd to 11th intercostal nerves and subcostal nerve • ventral rami of cervical, T1, lumbar and sacral spinal nerves share fibers with nerves located above or below them and form complicated networks of nerves (plexuses) • cervical plexus → formed by ventral rami of C1-C4 → supplies neck • brachial plexus → formed by ventral rami of C5-T1 → supplies upper limb • lumbar plexus → formed by ventral rami of L1-L4 → supplies anterior abdominal wall and lower limb • sacral plexus → formed by ventral rami of L4-S4 → supplies lower limb and perineum

Ossification of the Vertebrae

• vertebrae develop by endochondral ossification • each vertebra is ossified from 3 primary and 5 secondary ossification centers • primary centers: one in body and one in each half of vertebral arch -> centers for arch give rise to pedicles, laminae and articular, transverse and spinous processes • secondary centers give rise to tips of spinous and transverse processes -> also appear on superior and inferior surfaces of vertebral body where they are referred to as annular/ring epiphyses and form peripheral, smooth parts of superior and inferior surfaces of vertebral body

Thoracic Vertebrae

• vertebral body is larger than that of cervical vertebrae and it has a heart-shaped outline • vertebral foramen is smaller than that of cervical vertebrae and it is circular in shape • vertebral bodies of most thoracic vertebrae have 4 costal facets (2 superior and 2 inferior) for articulation with heads of ribs (head of a typical rib articulates with bodies of 2 adjacent thoracic vertebrae -> body of numerically corresponding vertebra and body of vertebra above) • most thoracic vertebrae (except last 2) also have costal facets on transverse processes (transverse costal facets) -> articulate with tubercles of numerically corresponding ribs • long, overlapping spinous process that projects posteriorly and inferiorly • articular facets are almost coronally oriented -> plane of facets lies on an arc centered about vertebral body • superior articular facets face posteriorly, and slightly superiorly and laterally • inferior articular facets face anteriorly, and slightly inferiorly and medially • axial rotation is favored by orientation of articular facets • attachment of ribs, vertical orientation of articular facets and overlapping spinous processes limit flexion/extension, and to some degree, lateral flexion • atypical thoracic vertebrae will be discussed with thoracic cage