Week 27

Clinical Anatomy of the Vertebral Canal, Spinal cord and Spinal nerves

Understand the concepts & associated principles, functional and clinical applications of the topographical anatomy of the vertebral canal, spinal cord and spinal nerves

Vertebral Column

extends from the skull to the apex (tip) of coccyx and forms the skeleton of the neck, back and the main part of the axial skeleton (the articulated bones of the skull, vertebral column, ribs and sternum)

72-15cm long in adults and ¼ is formed by the fibrocartilaginous intervertebral (IV) discs that separate and bind the vertebra

functions:o protects the spinal cord and spinal nerveso supports the weight of the bodyo provides partly rigid and flexible axis for the body and a pivot for the heado plays an important role in posture and locomotion

consists of 33 vertebrae in 5 regions:o 7 cervicalo 12 thoracico 5 lumbaro 5 sacralo 4 coccygeal

motion only occurs between the 24 cervical, thoracic and lumbar vertebrae the 5 sacral vertebrae are fused to form the sacrum and the 4 coccygeal are fused to

form the coccyx flexible because consists of many small bones separated by resilient IV discs

Curvatures 1° = thoracic and sacral curvatures develop during foetal period 2° = cervical and lumbar curvatures begin developing in foetal period but do not become

obvious until infancy (with holdingthe head up and walking)

Abnormal curvatures Kyphosis – (hunchback/humpback) abnormal ↑ of thoracic curvature Lordosis – (hollow back/sway back) anterior rotation of the pelvisat hip joint

producing ↑lumbar curvature Scoliosis – (crooked or curved back) abnormal lateral curvature

Vertebrae

vary in size from one region of the vertebral column to another a typical vertebra consists of a:

o vertebral bodyo vertebral (neural) archo seven processes

the vertebral body o anterior, gives strength to the vertebral column and supports the body weight

the vertebral arch o posterior to bodyo formed by right and left pedicles and laminae

pedicles o short, stout processes that join vertebral arch to vertebral bodyo project posteriorly to meet two broad, flat plates of bone – laminae

vertebral foramen o formed by vertebral arch and posterior wall of vertebral body

vertebral canal o succession of vertebral foramina in the articulated columno contains spinal cord, meninges, fat, spinal nerve roots and vessels

vertebral notches o indentations formed by the projection of the body and articular processes

above and below the pedicleo superior an inferior notches of adjacent vertebrae contribute to the IV foramina

IV Foramina o passage for spinal nerves roots and accompanying vessels and contain dorsal

root ganglia 7 processes:

o spinous process – projects posteriorly from vertebral arch at junction of laminae– overlaps vertebra below

o 2x transverse processes – project posterolaterally from junctions of pedicles and laminae

o 4x articulate processes – 2x superior and 2x inferior– also arise from junctions of pedicles and laminae– are in apposition with the corresponding vertebrae superior and inferior

to them and restrict movement in certain directions

Regional Characteristics of the Vertebrae

Cervical– distinctive feature is oval foramen of transverse process (for passage of the vertebral artery)– C3-C7 – large vertebral foramina due to cervical enlargement of the spinal cord– C3-C6 – short spinous processes– C7 – long spinous processes, therefore this vertebra is called the vertebra prominens– C1 and C2 are atypical

Atlas (C1)– widest of the cervical vertebrae and supports the skull– kidney-shaped, concave superior articular surfaces receive the two large protuberances at

the sides of the foramen magnum, the occipital condyles– no spinous process or bodyAxis (C2)– strongest of the cervical vertebrae because C1 rotates on it– has two large superior articular surfaces on which the atlas rotates– dens (odontoid process) is distinguishing feature which projects superiorly– dens is held in place by the transverse ligament of the atlas which prevents horizontal

displacement of the atlas– has large bifid spinous process that can be felt deep in the nuchal groove

Thoracic– characteristic features are costal facets for articulation with ribs– one facet on each side of the vertebral body (articulation with head of rib) and one on each

transverse process of T1-T10 (for tubercle of rib)– spinous processes are long and slender and middle ones are directed inferiorly over

vertebral arch of vertebra below– T1 is atypical in that it has an entire costal facet for the 1st rib superiorly and a demifacet

that contributes to the articular surface for the 2nd rib inferiorly; and has a long, almost horizontal spinous process

Lumbar massive kidney-shaped body when viewed anteriorly triangular vertebral foramen long and slender transverse processes with accessory process on posterior surface of

base of each process short, sturdy and thick spinous processes L5 is largest of all movable vertebrae and carries the weight of the whole upper body transverse processes project posterosuperiorly as well as laterally – on the posterior

surface of the base of each one is an accessory process (attachment for medial intertransverse lumborum muscle)

on the posterior surface of the superior articular process is the mamillary process (attachment for multifidus and medial intertransverse muscles)

Sacrum Consists of five fused vertebrae (fuse shortly after puberty) curved with a convex posterior surface. narrow inferior portion is called the apex and the broad superior region is called the

base

Coccyx small most inferior vertebrae consisting of 3-4 fused vertebrae acts as a site of muscle and ligament attachment

Spinal Cord and meninges located in the vertebral canal formed by successive vertebral foramina

Spinal cord:o cylindrical and slightly flattened anteriorly and posteriorlyo protected by spinal cord and its ligaments and muscles, the meninges and CSFo begins as continuation of the medulla oblongata, the caudal part of the

brainstemo adults: extends from foramen magnum to tapering end (medullary cone) at L2

(usually)o enlarged in 2 regions for innervation of the limbs:

Cervical enlargement (C4-T1): most ventral rami of the spinal nerves arising from it form the brachial plexus of nerves that innervates the upper limbs

Lumbosacral enlargement (T11-L1): ventral rami make up the lumbar and sacral plexuses that innervate the lower limbs

o cauda equina – the bundle of spinal nerve roots running through the lumbar cistern (subarachnoid space) and consists of spinal nerve roots arising from the lumbosacral enlargement and the medullary cone

Spinal Meninges: Dura Mater:

o outermost, tough fibrous and elastico separated from the vertebrae by the extradural or epidural space that contains

adipose tissue and a venous plexuso forms the dural sac – long tubular sheath within the vertebral canal that

adheres to margin of foramen magnum of skull where it is continuous with te dura mater of the brain

o pierced by spinal nerves and anchored inferiorly to the coccy by the terminal filum

Arachnoid mater:o delicate, avascular membrane of fibrous and elastic tissueo lines dural sac and encloses CSF-filled subarachnoid space containing spinal

cord, spinal nerve roots and spinal gangliao not attached to dura but held against it by pressure of CSF

Pia mater:o innermost covering membrane of the spinal cord and also coverso consists of flattened cellso separated from arachnoid by subarachnoid space containing CSF

Spinal Nerves 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

several rootlets emerge from the dorsal and ventral surfaces of the spinal cord and converge to form the dorsal and ventral roots of the spinal nerves

Dorsal roots of spinal nerves contain sensory afferent fibres from skin, subcutaneous and deep tissues and viscera

Ventral Roots of spinal nerves contain motor/efferent fibres to skeletal muscle and may contain presynaptic autonomic fibres

Ventral Gray horns of spinal cord – made up of the cell bodies of axons of ventral roots Spinal/Dorsal root ganglia – cell bodies of axons making up the dorsal roots (outside the

spinal cord) dorsal and ventral nerve roots unite at their points of exit from the vertebral canal to

form a spinal nerve each spinal nerve then divides almost immediately to form a dorsal 1° ramus (supply

skin and muscle of the back)and a ventral 1° ramus (supply limbs and rest of trunk)