Lecture 3: Vertebral Joints + Ligaments, Spinal Cord

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intervertebral joints

• vertebral bones articulate with each other via intervertebral discs

• fibrocartilage joints

zygapophysial joints

• between superior and inferior articular facets of adjacent vertebrae

• orientation of facets determines joint movement

• synovial joints (plane)

costovertebral joints

• thoracic vertebrae articulate with ribs

• synovial joints (plane)

intervertebral discs

fibrocartilage disc between hyaline cartilage covered vertebral bodies

• symphysis joints

• consists of anulus fibrosus and nucleus pulposus

anulus fibrosus

rings of collagen fibers found in intervertebral discs

• weight-bearing resiliency

nucleus pulposus

gel-like cartilage found within intervertebral discs

• adds shock-absorption and height

• becomes thinner and loses water content over time

• accounts of ~25% of vertebral column height

intervertebral disc herniation

nucleus pulpous herniates through anulus fibrosus, impinging on spinal cord or spinal nerve roots leading to back pain and neuropathy

• symptoms = pins and needles, pain, numbness, muscle weakness

vertebral ligaments

1. anterior longitudinal ligament

2. posterior longitudinal ligament

3. ligamentum flavum

4. intertransverse ligaments

5. interspinous ligaments

6. supraspinous ligament

7. nuchal ligament (cervical spine)

anterior longitudinal ligament

broad, flat sheet that covers the anterior and lateral sides of the vertebral bodies

• extends from foramen magnum to the sacrum

• prevents hyperextension of vertebral column

posterior longitudinal ligament

runs within vertebral canal along posterior side of the bodies

• extends from C2 to the sacrum

• prevents hyperflexion of the vertebral column

• reinforces intervertebral discs posteriorly

ligamentum flavum

highly elastic ligament

• extends from lamina of one vertebra to lamina of superior vertebra

• makes up posterior wall of vertebral canal

• resists hyperflexion

intertransverse ligaments

unites transverse processes

• limits lateral flexion

interspinous ligaments

extend between spinous processes of each vertebra

• limits flexion; well developed in Lumbar spine

supraspinous ligament

runs along very posterior surface of spinous processes

• limits flexion; one tough, continuous ligament

• extends from coccyx to C7

• merges with nuchal ligament of cervical spine, extending to occipital protuberance

nuchal ligament

a strong and broad ligament located in the posterior region of the neck (nuchal region); a continuation of the supraspinous ligament in the cervical spine

spinal cord

major conduction pathway between brain and body

• carries motor commands down to muscles

• carries sensory information up from periphery

• executes reflexes independently of the brain

• extends from foramen magnum to L1-L2 and ends in conus medullaris

  • since shorter than vertebral column, inferior nerve roots progressively elongated + exit @ correct vertebral level, forming cauda equina

• protected by vertebrae and vertebral column ligaments, meninges, CSF (cerebrospinal fluid)

conus medullaris

the tapered inferior-most part of the spinal cord that is attached to the filum terminale

• where spinal cord terminates, at L1-L2 vertebral level

• segment of spinal cord from which the sacral and coccygeal nerve roots arise

• after the cord terminates, nerve roots descend within the spinal canal as individual rootlets, collectively referred to as the cauda equina

cauda equina

a bundle of spinal nerve roots at the base of the spinal cord that resemble a horse’s tail

• a collection of peripheral nerve fibers that branch off the lower end of the spinal cord

• contains a bundle of nerves that project distally within the enclosed cavity of the lumbar cistern from the spinal cord and conus medullaris toward the coccyx

lumbar cistern

an enlarged fluid-filled pocket of the subarachnoid space in the lower spine that extends from the end of the spinal cord to the second sacral vertebra

• contains CSF, cauda equina, and filum terminale

• area for spinal tap

spinal cord regions

1. cervical enlargement

2. thoracic

3. lumbar enlargement

4. sacral

cervical enlargement region of spinal cord

C3 to T1/T2

a widened region of the spinal cord that contains an increased volume of neurons to supply the upper limbs

• houses extra motor and sensory neurons to control the upper limbs and form the brachial plexus

thoracic enlargement region of spinal cord

T1-T12

lumbar enlargement region of spinal cord

L1-L5

a widened section of the lower spinal cord that contains a high volume of neurons to supply sensory and motor signals to the lower limbs

sacral region of spinal cord

containins nerve roots (S1–S5) that manage sensation and movement in the lower body and control pelvic organs

s1-co

spinal cord enlargements

more fibers to innervate limbs

gray matter

central part of spinal cord

• consists of dorsal horn, ventral horn, and lateral horn

dorsal horn

sensory information

ventral horn

motor information

ventral roots

the motor root of a spinal nerve, which carries motor information from the spinal cord to the rest of the body and leaves from the anterior side of the cord

ventral rootlets

small bundles of nerve fibers that emerge from the front part of the spinal cord and join together to form the ventral root

• carry motor info OUT (autonomic and sensory)

lateral horn

autonomic information (thoracic)

white matter

peripheral part of spinal cord

• consists of dorsal columns and laterocorticospinal tract

dorsal columns

sensory information

laterocorticospinal tract

the largest descending motor pathway in the central nervous system, responsible for controlling fine, voluntary movements of the contralateral (opposite side) limbs

spinal nerve

formed by dorsal and ventral roots of spinal cord

• dorsal root and dorsal rootlets = sensory

• dorsal root ganglion

• ventral rootlets and ventral root = motor

  • therefore, this structure has mixed function

dorsal root ganglion

sensory cell bodies

• emerges from the dorsal root of the spinal nerves

dorsal roots

carry sensory neural signals to CNS from PNS

• carry sensory messages from various receptors (ie, pain and temperature) at the periphery toward the central nervous system for a response

dorsal rootlets

a small bundle of nerve fibers that emerges from the back of the spinal cord and joins other rootlets to form the sensory dorsal root of spinal nerve

meninges

1. dura mater

2. arachnoid mater

3. pia mater

dura mater

“tough mother”: outer covering of spinal cord inside vertebral canal

• fibrous tissue (some elastic)

• adheres to foramen magnum superiorly

• anchored to coccyx via filum terminale

• ensheathes dorsal and ventral roots and dorsal root ganglion, forming dural root sheaths

dural root sheaths

tubular extensions of the tough outer membrane surrounding the spinal cord, the dura mater, that covers a spinal nerve root as it exits the spinal canal

filum terminale

a delicate strand of fibrous connective tissue that anchors the bottom of the spinal cord to the tailbone

epidural space

between vertebral column and spinal cord dura mater

arachnoid mater

“spider mother”: lies against inner surface of dura

• fibrous and elastic tissue

• connected to pia mater via arachnoid trabeculae

arachnoid trabeculae

delicate connective tissue strands that connect arachnoid mater to pia mater

subarachnoid space

formed between arachnoid and pia, filled with CSF

• forms lumbar cistern around cauda equina nerves

pia mater

“soft mother”: innermost covering of spinal cord and spinal roots

• thin fibrous and elastic tissue

• forms filum terminale

denticulate ligaments

fibrous ligaments that laterally attch pia to arachnoid/dura

• protects cord from damage during movement

spinal nerves

31 pairs branch from the spinal cord

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral

• 1 coccygeal

where C1 spinal nerve emerges

between occipital bone and atlas

where C1-7 spinal nerves exit

above same-named vertebrae, through intervertebral foramina

• ie: C2 nerve emerges between C1 and C2 vertebrae

• C8 nerve exits between C7 and T1 vertebrae (no C8 vertebrae)

how thoracic and coccygeal nerves exit

• through intervertebral foramina or sacral foramina (angled inferiorly and posteriorly)

• exit below same-named vertebrae

  • ie: T2 nerve emerges between T2 and T3 vertebrae

spinal nerve development

1. early in development, spinal cord fills vertebral canal → nerve roots exit horizontally at their own levels

2. spinal cord completes growth at birth long before vertebral column

• lumber cistern forms as potential space

3. since each nerve’s exit is fixed at its segment of origin, elongating vertebral column stretches lower roots into progressively longer, more steeply inferiorly and posteriorly angled courses forming cauda equina below cord’s end

somatic innervation

consists of

1. dorsal ramus

2. ventral ramus

the nervous system network that supplies sensory input from the skin, joints, and limbs and controls voluntary contractions of skeletal muscles

dorsal ramus

mixed nerve fibers that go to deep back muscles and overlying skin

ventral ramus

mixed nerve fibers that go to remaining trunk and limbs

dermatome

band of skin supplied by sensory fibers of a single dorsal spinal nerve root

• adjacent dermatomes overlap

• nerve root injury → dermatome-patterned sensory loss

cervical dermatome

C2-C8 skin regions

thoracic dermatome

T1-T12 skin regions

lumbar dermatome

L1-L5 skin regions

sacral dermatome

S1-S5 skin regions

myotome

the muscle(s) supplied by a single ventral spinal nerve roots

• muscles supplied by multiple segments → single-root injury weakens, rarely paralyzes

• tested clinically as movements

• root injury → movement-pattern weakness; peripheral nerve injury→complete paralysis of its muscle

nerve plexus

nerve network where ventral rami of several spinal nerves merge and redistribute fibers into named peripheral nerves